PSCAD (power system computer aided design) -based hybrid micro-grid system, controller and method

文档序号：1819187 发布日期：2021-11-09 浏览：32次中文

阅读说明：本技术 一种基于pscad的混合微电网系统、控制器及方法 (PSCAD (power system computer aided design) -based hybrid micro-grid system, controller and method ) 是由娄彦涛程晓绚任军辉李嘉丰李天泽熊显智党瑞李智轩于 2021-08-23 设计创作，主要内容包括：本发明公开了一种基于PSCAD的混合微电网系统、控制器及方法,其中该系统包括：交流母线、直流母线及配电网；交流母线和直流母线连接至配电网；直流微电网,包括：直流微电网超级电容,直流微电网光伏,直流微电网蓄电池,直流负载及直流充电桩；交流微电网包括：微型燃机,交流微电网超级电容,交流微电网光伏,风机,电能质量管理装置,柴油发电机,交流微电网蓄电池及交流负载；直流微电网和交流微电网与交流母线连接；控制器,用于根据微电网的当前运行情况及预设底层控制策略和上层能量管理策略,控制直流微电网和交流微电网运行。本发明提供了一种基于PSCAD的分布式交直流混合微电网方案,保证了供电可靠性和电能质量。(The invention discloses a PSCAD-based hybrid micro-grid system, a controller and a method, wherein the system comprises: the system comprises an alternating current bus, a direct current bus and a power distribution network; the alternating current bus and the direct current bus are connected to a power distribution network; a direct current microgrid comprising: the system comprises a direct-current micro-grid super capacitor, a direct-current micro-grid photovoltaic, a direct-current micro-grid storage battery, a direct-current load and a direct-current charging pile; the AC microgrid includes: the system comprises a micro gas turbine, an alternating current micro-grid super capacitor, an alternating current micro-grid photovoltaic, a fan, an electric energy quality management device, a diesel generator, an alternating current micro-grid storage battery and an alternating current load; the direct-current micro-grid and the alternating-current micro-grid are connected with the alternating-current bus; and the controller is used for controlling the operation of the direct current micro-grid and the alternating current micro-grid according to the current operation condition of the micro-grid, a preset bottom layer control strategy and an upper layer energy management strategy. The invention provides a distributed alternating current-direct current hybrid micro-grid scheme based on PSCAD, which ensures the power supply reliability and the electric energy quality.)

1. A control method of a hybrid microgrid based on PSCAD is characterized by comprising the following steps:

monitoring the current operation conditions of the direct current micro-grid and the alternating current micro-grid;

according to the monitored current running conditions of the direct current micro-grid and the alternating current micro-grid, a preset bottom layer control strategy is used for carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro-grid storage battery to realize power sharing and simultaneously connecting a fan and an alternating current micro-grid photovoltaic power source, the diesel generator and the micro gas turbine are discharged while the alternating current micro-grid storage battery is charged by adjusting a positive droop coefficient and/or a negative droop coefficient, and the preset upper layer energy management strategy is used for controlling the direct current micro-grid and the alternating current micro-grid to run; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

2. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method of claim 1 when executing the computer program.

3. A computer-readable storage medium storing a computer program for performing the method of claim 1.

4. A controller for a PSCAD-based hybrid microgrid, comprising:

the monitoring unit is used for monitoring the current running conditions of the direct current micro-grid and the alternating current micro-grid;

the control unit is used for presetting a bottom layer control strategy according to the monitored current running conditions of the direct current micro-grid and the alternating current micro-grid, carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro-grid storage battery to realize power sharing and simultaneously connecting a fan and an alternating current micro-grid photovoltaic power source, realizing that the diesel generator and the micro gas turbine discharge while the alternating current micro-grid storage battery is charged by adjusting a positive droop coefficient and/or a negative droop coefficient, and controlling the direct current micro-grid and the alternating current micro-grid to run by the preset upper layer energy management strategy; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

5. A hybrid microgrid system based on a PSCAD, comprising:

the system comprises an alternating current bus, a direct current bus and a power distribution network; the alternating current bus and the direct current bus are connected to the power distribution network through an interface converter and a transformer;

a direct current microgrid comprising: the system comprises a direct-current micro-grid super capacitor, a direct-current micro-grid photovoltaic, a direct-current micro-grid storage battery, a direct-current load and a direct-current charging pile; the direct-current micro-grid is connected with the direct-current bus;

the AC microgrid includes: the system comprises a micro gas turbine, an alternating current micro-grid super capacitor, an alternating current micro-grid photovoltaic, a fan, an electric energy quality management device, a diesel generator, an alternating current micro-grid storage battery and an alternating current load; the alternating-current microgrid is connected with the alternating-current bus;

the controller of claim 4.

6. The PSCAD-based hybrid microgrid system of claim 5, wherein said micro-combustion engine, diesel generator and AC microgrid battery are controlled using a back-to-back voltage transformation and frequency conversion architecture.

7. The PSCAD-based hybrid microgrid system of claim 5, wherein said controller is specifically configured to control the operation of the DC microgrid according to a DC microgrid energy management strategy:

when wind and light are insufficient and the state of charge value of the direct-current micro-grid storage battery is greater than or equal to 80, if the photovoltaic value of the direct-current micro-grid is smaller than the direct-current load value and the direct-current load value is smaller than the sum of the photovoltaic value of the direct-current micro-grid and the value of the direct-current micro-grid storage battery, controlling the direct-current micro-grid photovoltaic to operate in a Maximum Power Point Tracking (MPPT) mode, discharging the direct-current micro-grid storage battery to compensate the direct-current load, and returning when the discharge reaches below 20;

when wind and light are insufficient and the state of charge value of the storage battery of the direct-current microgrid is greater than or equal to 80, if the photovoltaic value of the direct-current microgrid is not less than the direct-current load value and the direct-current load value is not less than the sum of the photovoltaic value of the direct-current microgrid and the storage battery value of the direct-current microgrid, the photovoltaic of the direct-current microgrid is controlled to operate in an MPPT mode, the storage battery of the direct-current microgrid discharges at the maximum power, the alternating-current microgrid with insufficient power is compensated, and the direct-current microgrid returns when the discharge reaches below 20.

8. The PSCAD-based hybrid microgrid system of claim 5, wherein said controller is specifically configured to control the operation of an AC microgrid according to an AC microgrid energy management strategy:

the method comprises the following steps that a micro gas turbine and a diesel generator are used as a black start standby power supply, and meanwhile, when the load of an alternating current micro-grid is higher than a preset value, the standby power supply is used as a distributed power supply to be connected into the alternating current micro-grid; the alternating current micro-grid photovoltaic and the fan preferentially supply power to the alternating current load, and the alternating current micro-grid storage battery and the alternating current micro-grid super capacitor provide power support for the alternating current load under normal work and a mode higher than a preset electric quantity.

9. The PSCAD-based hybrid microgrid system of claim 8, wherein the controller is specifically configured for, in grid-connected microgrid energy management of alternating current:

when the sum of the value of the fan and the photovoltaic value of the alternating-current microgrid is detected to be greater than or equal to the alternating-current load value and the wind and light are sufficient, if the charge state value of the storage battery of the alternating-current microgrid is greater than or equal to 80, the wind and light are sufficient, the fan and the photovoltaic of the alternating-current microgrid are controlled to operate in an MPPT mode, the electric quantity of the storage battery of the alternating-current microgrid is full, and the charging and discharging power of the storage battery of the alternating-current microgrid is zero;

when the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is detected to be larger than or equal to the alternating-current load value and sufficient wind and light are detected, and the state of charge value of the storage battery of the alternating-current micro-grid is larger than 20 and smaller than 80, if the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is larger than the alternating-current load value, the wind and light are sufficient, the fan and the photovoltaic of the alternating-current micro-grid are controlled to operate in an MPPT mode, redundant power is used for charging the storage battery of the alternating-current micro-grid, and the wind and light are returned when the charging is more than eighty percent;

the controller is specifically used for the following steps during the energy management of the alternating-current off-grid microgrid:

when the state of charge value of the storage battery of the alternating-current microgrid is greater than or equal to 80, if the sum of the value of the fan and the photovoltaic value of the alternating-current microgrid is greater than or equal to the alternating-current load value, controlling the fan and the alternating-current microgrid to operate at constant photovoltaic power, setting the power as alternating-current load power, and setting the charging and discharging power of the storage battery of the alternating-current microgrid to be zero;

when the state of charge value of the alternating current micro-grid storage battery is greater than or equal to 80, if the alternating current load value is greater than the sum of the fan value and the alternating current micro-grid photovoltaic value, and the load value is less than or equal to the sum of the fan value, the alternating current micro-grid photovoltaic value and the alternating current micro-grid storage battery value, the fan and the alternating current micro-grid photovoltaic are controlled to operate in an MPPT mode, the alternating current micro-grid storage battery discharges, and the discharging power is obtained by subtracting the fan value from the alternating current load value and then subtracting the alternating current micro-grid photovoltaic value.

10. The PSCAD-based hybrid microgrid system of claim 5, wherein said controller is specifically configured for black start operation of the microgrid overall structure according to a black start energy management strategy as follows:

when detecting that the storage battery of the alternating current micro-grid can be normally started, the diesel generator can be normally started or the micro gas turbine can be normally started, parallel droop control is carried out to establish alternating current bus voltage;

when the voltage of the alternating current bus reaches a preset alternating current standard value, controlling the fan and the alternating current micro-grid photovoltaic to send power to the alternating current bus at a preset rate, and recovering the power supply of the load;

when the state of charge of the storage battery of the direct-current microgrid is monitored to be below a preset normal level value, controlling the alternating-current microgrid to feed energy to the direct-current microgrid, and operating the storage battery of the direct-current microgrid in a PQ mode;

when the direct-current bus voltage is detected to be lower than a preset direct-current standard value, controlling the direct-current micro-grid storage battery to operate in a VF mode, and establishing the direct-current bus voltage;

when the voltage of the direct current bus reaches a preset direct current standard value, controlling the fan and the photovoltaic of the alternating current micro-grid to send power to the alternating current bus at a preset rate, and recovering load power supply;

the black start operation ends.

Technical Field

The invention relates to the technical field of alternating current and direct current hybrid micro-grids, in particular to a hybrid micro-grid system based on PSCAD (power system computer aided design), a controller and a method.

Background

This section is intended to provide a background or context to the embodiments of the invention that are recited in the claims. The description herein is not admitted to be prior art by inclusion in this section.

As the installed capacity of the distributed power supply is continuously improved, the occupation ratio and the permeability of the distributed power supply in the medium-low voltage distribution network are also continuously increased, and the distributed power supply has the characteristics of randomness and intermittence when outputting power, so that the problem of generating various influences on the voltage, frequency and power balance of a power system is also highlighted. The micro-grid is a small power generation and distribution system integrating devices such as a distributed power supply, a load and an energy storage device, and a more flexible operation mode provides an effective solution for accessing a large-scale distributed power supply into a power system.

In order to more efficiently consume the distributed power supply and ensure the power supply reliability and the power quality, the research on the micro-grid and the key technology thereof is particularly important. The existing design method of the alternating current-direct current hybrid micro-grid mainly comprises the following steps:

the design method of the alternating current-direct current hybrid micro-grid based on the energy router comprises a plurality of alternating current-direct current sub-micro-grids, and can directionally simulate various existing and future micro-grid structures.

The design method of the alternating current-direct current hybrid micro-grid system based on the Monte Carlo random algorithm utilizes the Monte Carlo algorithm to randomly generate simulated operation data in different connecting seasons, and combines constraints of economic optimization, reliability and the like to design the alternating current-direct current hybrid micro-grid system.

The existing design method of the alternating current-direct current hybrid micro-grid mostly comprises a fan, a photovoltaic part, an energy storage part and other distributed power supply parts, the control design mode of the whole system is mostly master-slave control, and the operation working condition of the whole system is single, so that the power supply reliability and the electric energy quality cannot be guaranteed.

Disclosure of Invention

The embodiment of the invention provides a distributed alternating current-direct current hybrid micro-grid system based on PSCAD (power system computer aided design) for ensuring power supply reliability and electric energy quality, which comprises the following components:

the controller is used for carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro grid storage battery according to the monitored current running conditions of the direct current micro grid and the alternating current micro grid and a preset bottom layer control strategy, realizing power sharing and simultaneously accessing a fan and an alternating current micro grid photovoltaic power source, realizing that the diesel generator and the micro gas turbine discharge while the alternating current micro grid storage battery is charged by adjusting a positive droop coefficient and/or a negative droop coefficient, and controlling the direct current micro grid and the alternating current micro grid to run by the preset upper layer energy management strategy; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

The embodiment of the invention also provides a controller of a distributed AC/DC hybrid micro-grid based on PSCAD, which is used for ensuring the power supply reliability and the power quality, and comprises:

the monitoring unit is used for monitoring the current running conditions of the direct current micro-grid and the alternating current micro-grid;

the control unit is used for carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro grid storage battery according to the monitored current running conditions of the direct current micro grid and the alternating current micro grid and a preset bottom layer control strategy, realizing power sharing and simultaneously accessing a fan and an alternating current micro grid photovoltaic power source, realizing that the diesel generator and the micro gas turbine discharge while the alternating current micro grid storage battery is charged by adjusting a positive droop coefficient and/or a negative droop coefficient, and controlling the direct current micro grid and the alternating current micro grid to run by the preset upper layer energy management strategy; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

The embodiment of the invention also provides a control method of the distributed alternating current-direct current hybrid micro-grid based on PSCAD, which is used for ensuring the power supply reliability and the power quality, and the control method comprises the following steps:

monitoring the current operation conditions of the direct current micro-grid and the alternating current micro-grid;

The embodiment of the invention also provides computer equipment which comprises a memory, a processor and a computer program which is stored on the memory and can run on the processor, wherein the processor executes the computer program to realize the control method of the PSCAD-based hybrid microgrid.

An embodiment of the present invention further provides a computer-readable storage medium storing a computer program for executing the above-mentioned control method for a hybrid microgrid based on a PSCAD.

In the embodiment of the invention, compared with the technical scheme of designing the alternating current-direct current hybrid microgrid based on an energy router and the alternating current-direct current hybrid microgrid based on a Monte Carlo random algorithm in the prior art, the distributed alternating current-direct current hybrid microgrid scheme based on the PSCAD comprises the following steps: the system comprises an alternating current bus, a direct current bus and a power distribution network; the alternating current bus and the direct current bus are connected to the power distribution network through an interface converter and a transformer; a direct current microgrid comprising: the system comprises a direct-current micro-grid super capacitor, a direct-current micro-grid photovoltaic, a direct-current micro-grid storage battery, a direct-current load and a direct-current charging pile; the direct-current micro-grid is connected with the direct-current bus; the AC microgrid includes: the system comprises a micro gas turbine, an alternating current micro-grid super capacitor, an alternating current micro-grid photovoltaic, a fan, an electric energy quality management device, a diesel generator, an alternating current micro-grid storage battery and an alternating current load; the alternating-current microgrid is connected with the alternating-current bus; the controller is used for carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro grid storage battery according to the monitored current running conditions of the direct current micro grid and the alternating current micro grid and a preset bottom layer control strategy, realizing power sharing and simultaneously accessing a fan and an alternating current micro grid photovoltaic power source, realizing that the diesel generator and the micro gas turbine discharge while the alternating current micro grid storage battery is charged by adjusting a positive droop coefficient and/or a negative droop coefficient, and controlling the direct current micro grid and the alternating current micro grid to run by the preset upper layer energy management strategy; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive shaft of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the cross shaft of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative shaft of the coordinate system.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts. In the drawings:

FIG. 1 is a schematic structural diagram of a PSCAD-based hybrid microgrid system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an inverter LC filter circuit according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of inductor current in bidirectional DC-DC boost mode according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of the inductor current in the bidirectional DC-DC buck mode according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a droop control circuit according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of the relationship between transmission line power and line in an embodiment of the present invention;

FIG. 7 is a graph illustrating negative and normal droop coefficients in an embodiment of the present invention;

FIG. 8 is a diagram illustrating a pre-synchronization structure according to an embodiment of the present invention;

FIG. 9 is a diagram illustrating the generation of a reset signal according to an embodiment of the present invention;

FIG. 10a is a flow chart of wind-solar energy shortage management in a grid-connected mode according to an embodiment of the present invention;

FIG. 10b is a flow chart of wind-solar sufficient energy management in a grid-connected mode according to an embodiment of the present invention;

FIG. 10c is a flow chart of the off-grid mode battery power sufficiency energy management in an embodiment of the present invention;

FIG. 10d is a flowchart illustrating the off-grid mode battery moderate energy management process according to an embodiment of the present invention;

FIG. 10e is a flowchart illustrating an off-grid mode battery low-battery energy management process according to an embodiment of the present invention;

FIG. 11a is a schematic diagram of a battery SOC switching hysteresis design according to an embodiment of the present invention;

fig. 11b is an overall flow chart of energy management of the alternating-current grid-connected microgrid in the embodiment of the present invention;

fig. 12a is a flowchart of an off-grid microgrid energy management state 1 of an alternating current in an embodiment of the present invention;

fig. 12b is a flowchart of an off-grid microgrid energy management state 2 of an alternating current in an embodiment of the present invention;

fig. 12c is a flowchart of an off-grid microgrid energy management state 3 of an alternating current in an embodiment of the present invention;

FIG. 13 is a flowchart illustrating black start energy management according to an embodiment of the present invention;

FIG. 14 is a circuit diagram of a test load circuit according to an embodiment of the present invention;

FIG. 15 is a schematic diagram of a PSCAD-based controller for a hybrid microgrid according to an embodiment of the present invention;

fig. 16 is a flowchart illustrating a method for controlling a PSCAD-based hybrid microgrid according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.

Before describing the embodiments of the present invention, first, terms related to the present invention will be described.

1. PSCAD: power Systems Computer aid Design Power system electromagnetic transient simulation software.

2. APF: active Power Filter Active Filter.

3. MPPT: maximum Power Point Tracking of Maximum Power Point.

4. SOC: state of Charge State of Charge.

For deeper analysis and research, the embodiment of the invention provides a distributed alternating current and direct current hybrid microgrid scheme based on PSCAD, and theoretical guidance is provided for electrical design, controller and energy management system configuration of a real microgrid system. The scheme comprises a design method of a comprehensive alternating current-direct current hybrid micro-grid system of a diesel generator, a micro gas turbine, an electric energy quality control device and the like, and a comprehensive energy coordination control strategy on the upper layer is considered by combining a control design method of a multi-converter parallel system under the normal operation condition and the fault operation condition.

The method aims to research the system design problem of the comprehensive alternating current-direct current hybrid micro-grid comprising a diesel generator, a micro gas turbine, an electric energy quality control device and the like, the multi-converter parallel system control design problem under the condition of combining normal operation and fault operation and the energy optimization scheduling problem. According to the national specification requirements on the design specification of a distributed power supply access power distribution network, the operation control specification of a micro power grid access power distribution network and the like, the research and the complete set of design capability of the micro power system are further improved, and the final purpose is to provide a PSCAD-based distributed AC/DC hybrid micro power system design method, design the integral system structure and the control method of the AC/DC hybrid micro power system, and test is performed by utilizing a PSCAD software environment to form a set of design specification of the micro power system.

The invention provides a distributed alternating current and direct current hybrid micro-grid system design method based on PSCAD, which forms a set of design specifications:

(1) the direct-current micro-grid system comprising a direct-current super capacitor, a photovoltaic panel, a storage battery, a direct-current load and a charging pile and the alternating-current system comprising a micro-combustion engine, the super capacitor, a photovoltaic system, a direct-drive fan, an APF device, a diesel generator, the storage battery and an alternating-current load are designed, the combined control of a bottom-layer control strategy and an upper-layer energy management strategy is completed, and the integral coordinated operation of the micro-grid is realized.

(2) According to the capacity and the requirement of the micro-grid system, parameters of filter inductors and capacitors for droop control, rectification control and inversion control are designed, and parameters of the LLC are designed.

(3) A micro-grid comprehensive control strategy and a grid-connected and off-grid pre-synchronization control strategy and logic are designed, and seamless grid connection and fault grid disconnection can be achieved.

(4) Negative sequence low voltage ride through control is designed, including control structures, control parameters and control ideas.

(5) And designing an upper-layer energy management strategy of the microgrid, wherein the strategy comprises functions of power scheduling, fault detection, droop coefficient adjustment, mode switching and the like.

The PSCAD-based distributed ac/dc hybrid microgrid scheme is described in detail below.

Fig. 1 is a schematic structural diagram of a hybrid microgrid system based on PSCAD according to an embodiment of the present invention, and as shown in fig. 1, the hybrid microgrid system based on PSCAD includes:

In particular implementation, the controller is not shown in fig. 1.

The distributed AC/DC hybrid micro-grid system based on the PSCAD is a distributed AC/DC hybrid micro-grid system based on the PSCAD, a set of micro-grid system design specifications are formed, and power supply reliability and power quality are guaranteed. The following detailed description is made with reference to the accompanying drawings.

1. Micro-grid overall topology structure and function building

The alternating current-direct current hybrid microgrid designed in the embodiment of the invention integrally comprises a 400V/50Hz alternating current bus, a 660V adjustable direct current bus and a 10KV power distribution network, and the overall topological structure of the microgrid is shown in figure 1.

1.1: building a direct-current microgrid based on PSCAD: the system comprises a super capacitor model, a photovoltaic panel model, a storage battery model, a direct current load model and a charging pile model. Wherein:

the super capacitor is connected with the direct current bus through a bidirectional DC-DC circuit and is controlled by adopting a power current double closed loop.

The photovoltaic panel is connected with the bus through the Boost circuit, and maximum power output of the photovoltaic panel under different environments and energy demand environments can be guaranteed by adopting a control mode of MPPT and constant power switching.

The storage battery is connected with the bus through the bidirectional DC-DC, and the control mode of voltage and power switching is adopted, so that the storage battery can stabilize the bus voltage under the off-grid condition, and the power balance of the direct-current micro-grid can be ensured under the grid-connected condition.

1.2: building an alternating current microgrid based on PSCAD: the system comprises a micro-gas turbine model, a super capacitor model, a photovoltaic model, a direct-drive fan model, an APF (active power quality management) device (the power quality management device in figure 1), a diesel generator model, a storage battery model and an alternating-current load model. Wherein:

the output characteristics of the micro gas turbine are simulated by adopting an equivalent mathematical model of the micro gas turbine, and the micro gas turbine is connected to an alternating current bus through an AC-DC-AC structure.

The super capacitor adopts a two-stage structure, the front stage is a bidirectional DC-DC circuit, the rear stage is an inverter circuit, and a simulation model is as follows:

the photovoltaic adopts a two-stage structure, the front stage is a Boost circuit, the rear stage is an inverter circuit, and the Vdc-Q is adopted to control the voltage of a direct current capacitor so as to ensure the power output.

The direct-drive fan is connected to the alternating current bus through an AC-DC-AC structure.

The design of the APF device considers unbalanced voltage drop, improves a phase-locked loop, and detects fundamental wave positive sequence active current by adopting a d-p method.

The diesel generator adopts a mathematical equivalent model to simulate the output characteristic of the diesel generator and is connected to an alternating current bus through an AC-DC-AC structure.

The storage battery adopts a two-stage structure, the front stage is a bidirectional DC-DC circuit, the rear stage is an inverter circuit, and droop control is adopted; the alternating load model is divided into three stages.

1.3: the capacity of the wind power generation system is not less than 2.1MW, the wind power generation system comprises an external wind power generator characteristic model, a wind power converter model and a wind power generation system control strategy, all control characteristics of wind power generation and a wind power generation front-stage power generation mode can be simulated, the front stage adopts torque control, and the rear stage adopts Vdc-Q control. The photovoltaic power generation system capacity is no less than 1.75MW, and the photovoltaic power generation system capacity contains a photovoltaic cell model, a photovoltaic inverter model and a photovoltaic system control strategy, can simulate the photovoltaic front-stage power generation mode, and the control strategy comprises an MPPT mode and a constant power mode, can realize switching between the MPPT mode and the constant power mode, and can simulate the influence of illumination intensity and temperature on the emitted power. An external characteristic model is built for the diesel generator according to the operation principle of the diesel generator, and the capacity is not less than 500 kW. The micro gas turbine builds an external characteristic model according to the operation principle of the micro gas turbine, and the capacity is not less than 500 kW. The diesel generator and the micro-combustion engine can be used as a backup of the energy storage battery to operate in power control from a micro source, and can also work in a droop control mode with the energy storage battery. The parameters of the super capacitor monomer are 515V, 2600F and 100kW 20s, the super capacitor monomer comprises 2 sets of super capacitor control strategies, the voltage of the direct current capacitor is controlled by adopting Vdc-Q, the power output is ensured, and the input and output power regulation function can be realized. The battery voltage of the energy storage battery system is 600V-800V, the capacity is 500kWh, and the energy storage battery system comprises 2 sets of battery pack models, energy storage converter models and energy storage system control strategies. The energy storage system at least comprises two control strategies of a V/F mode and a P/Q mode, the V/F control strategy is adopted when the energy storage inverter operates in an off-grid mode, and the P/Q control strategy is adopted when the inverter operates in a grid-connected mode. The electric energy quality treatment device meets the requirements of GB/T14549 and other related standards; the load system comprises an electric automobile charging pile and other alternating/direct current loads, the loads are divided into three levels (a first level load, a second level load and a third level load), and the first level load, the second level load and the third level load are respectively connected into the micro-grid through the controllable circuit breaker.

1.4: the control system model comprises a micro-grid independent operation simulation model, a grid-connected to independent switching simulation model and an independent to grid-connected simulation model; under the normal operation condition, the control strategies of micro-grid black start control, off-grid operation control, grid-connected to off-grid operation control, off-grid to grid-connected operation control, power factor control, tie line active power control, tie line reactive voltage control and the like are included.

2. Microgrid converter parameter design

2.1: inverter LC parametric design, as shown in fig. 2.

The inverter bridge is used for realizing alternating current-direct current electric energy conversion. Ui is the inverter bridge output voltage, I_iFor the inverter bridge outputting a current, V_dcFor the inverter bridge input voltage, Z (load) is the AC load, L_f、C_fIs an ideal device including a filter inductor and a filter capacitor, U_oFor the load terminal voltage output after filtering, I_oIs the load current output after filtering. The specific parameter design is shown in formula (1).

U_o1Is U_oA corresponding nominal value; omega₁＝100π，ω_n＝ω_s/50，ω_sIs the switching frequency.

2.2: bi-directional DC-DC parametric design

The bidirectional DC-DC circuit and the step-up and step-down operation modes are shown in fig. 3 and 4.

In the present invention, V_BThe input side direct current voltage is in the range of 600-800V; the capacity P of the DC-DC converter is 50kW, so the corresponding output current is 62.5-83.3A. The bus voltage 660V is selected, the current pulse rate is selected to be 20%, and according to the above analysis, the minimum value of the corresponding inductance is as follows:

to simplify the calculation, consideration is made from the power and energy point of view. For the DC/DC power P, when the current generates +/-ripple, the energy of the ripple in a half switching period is multiplied by P multiplied by Tc/4. Assuming that the energy fluctuations are all embodied in the form of variations in the voltage of the capacitor C1 and the desired amount of voltage fluctuation is not greater than σ, then

The substitution value P is 50kW, Δ is 20%, fc is 6kHz, σ is 5%, uc is 600V, and C can be obtained₁＝2.2584e-05F

Set the rated voltage of the output side as U_NThe maximum allowable voltage duration is U_L. Setting the minimum time interval of DSP detection and control as Ts, when the DC/DC works at rated power P and the load is cut off suddenly, the capacitor C₂It should be ensured that its output voltage does not exceed the maximum voltage U within 2Ts_HI.e. by

Carry in numerical value, get P50 kW, U_N＝700V，U_L＝700V，U_HWhen Ts is 200 μ s at 750V, C can be obtained₂≥5.5172e-04F。

3. Microgrid underlying control strategy

3.1 droop control Structure

The micro-grid adopts a comprehensive control strategy, and the relation between the traditional droop control voltage and the frequency is shown as the following formula:

three micro-sources (a micro gas turbine, a diesel generator and an alternating current micro-grid storage battery) adopt droop control to perform power equalization, and are simultaneously connected with power sources such as fan photovoltaic and the like, and the structure of the micro-source is shown in figure 5.

Because the output of power on the line is related to the current angle and the voltage angle, when the impedance is inductive, the output active power is in direct proportion to the impedance angle, and therefore, the effect of power uniform division can be achieved by changing the given output voltage and frequency of the inverter.

According to the micro gas turbine, the diesel generator and the alternating-current micro-grid storage battery are subjected to power equalization under the droop control of the controller according to the bottom layer control strategy, and are simultaneously connected to the fan and the alternating-current micro-grid photovoltaic power source.

3.2 droop control derivation

The relationship between voltage transmission and wiring is shown in fig. 6. Fig. 6 shows the relationship between the output line and the voltage when two voltage source converters are connected in parallel. V₁∠θ_1L、V₂∠θ_2LRespectively representing the voltages at the output points of the two converters, Z₁、Z₂Representing the impedance values, phi, of the two output lines, respectively_Z1、Φ_Z2Respectively representing the angle, V, of the line impedance_LRepresenting the voltage of the grid-connected point, I₁、I₂Respectively representing the converter output current.

The converter output power satisfies the defined formula:

in the formula (I), the compound is shown in the specification,representing the angle between voltage and current, i.e. the impedance angle. The relationship between active and reactive power and voltage and impedance can thus be obtained:

when the transmission line is inductive, the impedance angle approaches 90 degrees, and the impedance angle can be converted into:

from circuit knowledge, all circuit frequencies in the system are equal in steady state, with:

therefore, when the droop coefficients of the two micro sources are in inverse proportion to the given power proportion, the active power sharing can be met, and the active power sharing condition is shown as the formula (10):

reactive power is related to system voltage, and the relation among reactive droop coefficient, impedance and reactive power is obtained through the joint type (7) and (8):

the droop reactive power distribution mode is not unique, and a droop coefficient condition of the reactive power sharing condition is given by imitating an active power sharing condition:

the droop coefficient condition does not guarantee the reactive power distribution, therefore, the targets of (11), (12) and reactive power sharing are combined, and another condition of reactive power sharing is solved:

3.3 establishing a two-stage control architecture

The double-stage control is superior to the single-stage control in all aspects, and theoretically, the double-stage control can have wider upper limit and lower limit of output power than the single-stage control. The design adopts a drooping form of three micro sources (a micro gas turbine, a diesel generator and an alternating-current micro-grid storage battery) in an alternating-current micro-grid, controls according to a drooping characteristic curve, and controls the micro sources by adopting a back-to-back voltage transformation and frequency conversion structure in order to ensure the controllability of the diesel generator and a micro gas turbine system. That is, in one embodiment, the back-to-back voltage and frequency conversion structure is adopted in the embodiment of the present invention to control the micro gas turbine, the diesel generator and the ac microgrid battery.

3.4 design of negative sag factor

When the droop control is in stable operation, the output power and the droop coefficient are related to the droop rated power. The micro gas turbine and the diesel generator are in one-way power transmission, and the storage battery can be charged and discharged. In consideration of the characteristic difference between the micro sources, the patent proposes a concept and an implementation method of the negative droop coefficient. The negative droop coefficient, like the positive droop coefficient, is a differential adjustment, and the concept of negative droop coefficient is shown in fig. 7.

In FIG. 7, f₀Is a frequency (AC bus frequency) reference value, P₁、P₂The intercept of the cross shaft of the grid-connected inverter is respectively two different micro sources (a diesel engine and a micro combustion engine). By adjusting the slope of the droop coefficient, the diesel engine and the micro-combustion engine can discharge while the storage battery is charged, the power proportion is flexible and adjustable, and the flexibility of the system is greatly improved by the method.

According to the above, the controller is specifically used for realizing the discharge of the diesel generator and the micro gas turbine while the charging of the alternating current micro grid storage battery is realized by adjusting the positive droop coefficient and/or the negative droop coefficient; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

4. Low voltage ride through control under microgrid fault conditions

4.1: and simulating single-phase, two-phase and three-phase faults and detecting the low-voltage ride-through effect. According to the control target: the method comprises the steps of suppressing double-frequency fluctuation of power, and detecting whether the double-frequency fluctuation of active power and reactive power is effectively suppressed or not under the condition of single-phase and two-phase faults of the photovoltaic fan. And (3) suppressing the negative sequence current, and detecting whether the photovoltaic fan effectively suppresses the negative sequence current under the condition of a one-way two-phase fault. And establishing an energy consumption resistance circuit, and detecting whether the direct current capacitor impact is effectively reduced or not and whether the grid-connected fault current is effectively reduced or not.

4.2: and building a phase-locked loop model under the fault based on PSCAD.

4.3: and (4) extracting and simulating positive and negative sequence components by using a wave trap based on PSCAD construction.

4.4: considering that the grid voltage and the grid side current do not contain negative sequence components when the grid voltage is balanced, the control scheme which is also suitable for the grid voltage balance is adopted, and the control algorithm does not need to be switched when the grid is normal and the grid voltage is unbalanced.

5. On-grid and off-grid pre-synchronization control strategy

5.1: presynchronization control

In the presynchronization process, the phase angle voltage needs to be consistent with a large power grid, and a presynchronization control link is designed by considering the integral relation between an angle and a frequency difference, so that the angle difference can realize no-static-error control in the presynchronization process. The control structure is shown in fig. 8.

If three synchronous signal values are given in the presynchronization process, a circulation phenomenon can be generated, one presynchronization compensation signal is given to a single converter, and the state of the other two converters follows the first converter by utilizing the characteristics of droop power equalization and the characteristic of difference adjustment. The method is essentially realized by utilizing the circulation phenomenon between the converters, and the converters are indirectly regulated by utilizing the circulation.

5.2: on-grid and off-grid control

Designing the grid-connected and off-grid logic, wherein the logic is as follows:

(1) and judging the voltage fault condition of the power grid, and if the voltage fault condition of the power grid is judged, not connecting the power grid.

(2) And switching the grid-connected and off-grid states by receiving an active grid-connected and off-grid instruction, wherein 1 is grid-connected and 0 is off-grid. And comparing the amplitude value and the frequency value of the detected voltage with the set value, and outputting a signal of 1 when the frequency or the voltage exceeds the set threshold value for a certain time, namely the voltage or the frequency is abnormal. And outputting a signal 1 when the voltage and the frequency are abnormal, and obtaining a passive grid connection and disconnection instruction through OR operation, wherein 1 is a grid disconnection instruction, and 0 is a grid connection instruction.

(3) And performing AND operation on the active grid-connected and off-grid instruction and the system passive grid-connected and off-grid instruction to obtain a grid-connected and off-grid execution instruction.

(4) And adding integral reset, and generating a reset pulse by adopting an exclusive-or delay method, wherein the structure is shown in fig. 9.

(5) After the presynchronization is completed, the control strategy is not changed, and the presynchronization value is cleared at the same time of grid connection. The method can realize seamless conversion of droop control into constant power control, has no switching of control strategies, and realizes seamless grid connection. The droop control method is characterized in that the droop control difference adjusting characteristic and the voltage stability of a large power grid are essentially utilized, when the voltage of the large power grid is constant, the droop converter performs difference adjustment according to the rated power given by the droop control ring, when the output power is not matched with the rated power, the voltage and the frequency are changed, and the phase angle difference is increased until the power meets the requirement.

6. Embedded PSCAD micro-grid energy management program based on C language

Step 6.1: DC microgrid energy management

The direct-current micro-grid comprises a super capacitor of 100kW, a photovoltaic of 500kW, a storage battery of 500kWh, a direct-current load of 100kW +50kW and a charging pile of 60 kW. The direct-current micro-grid is connected to a 10kV power distribution network bus through an interface converter and a transformer.

The energy management target of the direct-current microgrid is as follows: whether bus voltage is stable in an integral micro-grid island operation mode is detected, a storage battery is used as a starting power supply, after the bus voltage is established, the bus voltage is merged into an ultra-low capacitor, a photovoltaic and a charging pile, the bus voltage change and the power change are detected, and the power compensation effect of a super capacitor is verified. The dc energy management flow chart is shown in fig. 10a to 10 e.

As shown in fig. 10a to 10e, in one embodiment, the controller is specifically configured to control the operation of the dc microgrid according to a dc microgrid energy management policy.

As shown in fig. 10a, in an embodiment, the controller is specifically configured to:

when wind and light are insufficient and the state of charge value of the direct-current microgrid storage battery is greater than or equal to 80, if the direct-current microgrid photovoltaic value is not less than the direct-current load value and the direct-current load value is not less than the sum of the direct-current microgrid photovoltaic value and the direct-current microgrid storage battery value, controlling the direct-current microgrid photovoltaic to operate in an MPPT mode, discharging the direct-current microgrid storage battery at the maximum power, supplementing the direct-current microgrid with insufficient power, and returning when the direct-current microgrid storage battery is discharged to below 20;

when wind and light are insufficient and the state of charge value of the storage battery of the direct-current micro-grid is smaller than 80, the photovoltaic of the direct-current micro-grid is controlled to operate in an MPPT mode, and the storage battery of the direct-current micro-grid is charged at the maximum power.

As shown in fig. 10b, in an embodiment, the controller is specifically configured to:

when wind and light are insufficient, if the charge state value of the storage battery of the direct current micro-grid is greater than or equal to 80, controlling the photovoltaic constant-power operation of the direct current micro-grid, and the charge and discharge power of the storage battery of the direct current micro-grid is zero;

when wind and light are insufficient, if the state of charge value of the direct-current micro-grid storage battery is not larger than 20, controlling the direct-current micro-grid photovoltaic to operate in an MPPT mode, and charging the direct-current micro-grid storage battery at the maximum power;

when wind and light are insufficient, if the state of charge value of the storage battery of the direct current micro-grid is larger than 20 and smaller than 80, the photovoltaic of the direct current micro-grid is controlled to operate in an MPPT mode, the storage battery of the direct current micro-grid is charged, and the charging power is obtained by subtracting the direct current load value from the photovoltaic value of the direct current micro-grid.

As shown in fig. 10c, in an embodiment, the controller is specifically configured to:

when the state of charge value of the storage battery of the direct current microgrid is greater than or equal to 80, if the photovoltaic value of the direct current microgrid is greater than or equal to the direct current load value and the wind and light are sufficient, controlling the photovoltaic constant power operation of the direct current microgrid, and the charging and discharging power of the storage battery of the direct current microgrid is zero;

when the state of charge value of the direct-current microgrid storage battery is greater than or equal to 80, if the direct-current microgrid photovoltaic value is smaller than the direct-current load value, the wind and light are insufficient, and the direct-current load value is smaller than the sum of the direct-current microgrid photovoltaic value and the direct-current microgrid storage battery value, controlling the direct-current microgrid photovoltaic to operate in an MPPT mode, automatically discharging the direct-current microgrid storage battery to complement power, and returning when the discharge reaches 20 ℃;

and when the state of charge value of the storage battery of the direct current micro-grid is greater than or equal to 80, if the direct current load value is not less than the sum of the photovoltaic value of the direct current micro-grid and the storage battery value of the direct current micro-grid and the wind and light are insufficient, controlling to switch the direct current load.

As shown in fig. 10d, in an embodiment, the controller is specifically configured to:

when the state of charge value of the storage battery of the direct current microgrid is greater than 20 and less than 80, if the photovoltaic value of the direct current microgrid is greater than the direct current load value and the wind and light are sufficient, controlling the photovoltaic of the direct current microgrid to operate in an MPPT mode, and enabling the charging power of the storage battery of the direct current microgrid to be the value obtained by subtracting the direct current load value from the photovoltaic value of the direct current microgrid;

when the state of charge value of the storage battery of the direct current microgrid is greater than 20 and less than 80, if the photovoltaic value of the direct current microgrid is not greater than the direct current load value, the wind and light are insufficient, and the direct current load value is less than or equal to the sum of the photovoltaic value of the direct current microgrid and the storage battery value of the direct current microgrid, controlling the photovoltaic of the direct current microgrid to operate in an MPPT mode, automatically discharging the storage battery of the direct current microgrid to complement power, and returning when the power is discharged to 20;

and when the state of charge value of the storage battery of the direct current micro-grid is more than 20 and less than 80, if the direct current load value is more than the sum of the photovoltaic value of the direct current micro-grid and the value of the storage battery of the direct current micro-grid, and the wind and light are insufficient, controlling to switch the direct current load.

As shown in fig. 10e, in an embodiment, the controller is specifically configured to:

when the state of charge value of the storage battery of the direct current microgrid is less than or equal to 20, if the photovoltaic value of the direct current microgrid is greater than the direct current load value and the wind and light are sufficient, controlling the photovoltaic of the direct current microgrid to operate in an MPPT mode, and enabling the charging power of the storage battery of the direct current microgrid to be the value of the photovoltaic value of the direct current microgrid minus the direct current load value;

and when the state of charge value of the storage battery of the direct current micro-grid is less than or equal to 20, if the photovoltaic value of the direct current micro-grid is less than or equal to the direct current load value and the wind and light are insufficient, controlling to switch the direct current load.

6.2: AC microgrid energy management

The alternating-current microgrid considers the direct-current microgrid as an uncontrollable load, an energy management strategy similar to that of the direct-current microgrid is adopted, and the electric quantity of the storage battery and the power of the load are considered as strategy switching conditions. In consideration of the cost problem, the micro-gas turbine and the diesel generator are used as a black-start standby power supply, and are used as a distributed power supply to be connected into the micro-grid when the load of the micro-grid is high. Clean energy such as photovoltaic and fan preferentially supplies power for the load, and the battery provides power support for the load with super capacitor under normal work and high electric quantity mode. The flow is shown in fig. 11a to 11 b.

Under the grid-connected mode, the large power grid plays a role in voltage support and power support for the micro-grid, and the large power grid can provide power for the micro-grid or absorb extra power of the micro-grid. The condition of power exchange between the large power grid and the micro power grid is determined by load power.

In the off-grid mode, the charging and discharging conditions of the wind and the light are jointly determined by the SOC of the storage battery and the load power. When the battery electric quantity is insufficient, the wind and light MPPT operates, and when the battery electric quantity is sufficient, the wind and light operate according to the load limit power.

That is, in one embodiment, the controller is specifically configured to control the ac microgrid operation according to an ac microgrid energy management strategy.

That is, in one embodiment, the controller is specifically configured to: the method comprises the following steps that a micro gas turbine and a diesel generator are used as a black start standby power supply, and meanwhile, when the load of an alternating current micro-grid is higher than a preset value, the standby power supply is used as a distributed power supply to be connected into the alternating current micro-grid; the alternating current micro-grid photovoltaic and the fan preferentially supply power to the alternating current load, and the alternating current micro-grid storage battery and the alternating current micro-grid super capacitor provide power support for the alternating current load under normal work and a mode higher than a preset electric quantity.

That is, in one embodiment, as shown in fig. 11b, the controller is specifically configured to, during grid-connected microgrid energy management for alternating current:

when the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is detected to be larger than or equal to the alternating-current load value and sufficient wind and light are detected, and the state of charge value of the storage battery of the alternating-current micro-grid is larger than 20 and smaller than 80, if the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is not larger than the alternating-current load value, the wind and light are sufficient, the storage battery of the alternating-current micro-grid is directly charged with the maximum power, and the charging returns when the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is larger than eighty percent;

when the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is detected to be larger than or equal to the alternating-current load value and sufficient wind and light, and the state of charge value of the storage battery of the alternating-current micro-grid is not larger than 20, the fan and the photovoltaic of the alternating-current micro-grid are controlled to operate in an MPPT mode, the storage battery of the alternating-current micro-grid is insufficient, and the storage battery of the alternating-current micro-grid is charged with the maximum power.

That is, in one embodiment, as shown in fig. 11b, the controller is specifically configured to, during grid-connected microgrid energy management for alternating current:

when the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is detected to be smaller than the alternating-current load value and wind and light are insufficient, if the charge state value of the storage battery of the alternating-current micro-grid is larger than or equal to 80, the sum of the fan value and the photovoltaic value of the alternating-current micro-grid is smaller than the sum of the fan value and the photovoltaic value of the alternating-current micro-grid, the fan and the photovoltaic of the alternating-current micro-grid are controlled to operate in an MPPT mode, power is insufficient to support the alternating-current load, and the photovoltaic value of the alternating-current micro-grid is subtracted from the discharge power of the storage battery after the fan value is given as the alternating-current load value;

when the sum of the fan value and the photovoltaic value of the alternating-current microgrid is detected to be smaller than the alternating-current load value and wind and light are insufficient, if the charge state value of the storage battery of the alternating-current microgrid is greater than or equal to 80, the sum of the fan value and the photovoltaic value of the alternating-current microgrid is not smaller than the alternating-current load value, and the alternating-current load value is not smaller than the sum of the fan value, the storage battery value of the alternating-current microgrid and the photovoltaic value of the alternating-current microgrid, the fan and the photovoltaic of the alternating-current microgrid are controlled to operate in an MPPT mode, the storage battery of the alternating-current microgrid discharges at the maximum power, and the large power grid is complemented with power shortage;

That is, in one embodiment, as shown in fig. 12a, the controller is specifically configured to, during off-grid microgrid energy management for ac:

when the state of charge value of the storage battery of the alternating-current microgrid is greater than or equal to 80, and if the sum of the value of the fan and the photovoltaic value of the alternating-current microgrid is greater than or equal to the alternating-current load value, the fan and the alternating-current microgrid are controlled to operate at constant photovoltaic power, the power is given as alternating-current load power, and the charging and discharging power of the storage battery of the alternating-current microgrid is zero.

That is, in one embodiment, as shown in fig. 12a, the controller is specifically configured to, during off-grid microgrid energy management for ac:

when the state of charge value of the alternating current micro-grid storage battery is greater than or equal to 80, if the alternating current load value is greater than the sum of the fan value and the alternating current micro-grid photovoltaic value, and the load value is less than or equal to the sum of the fan value, the alternating current micro-grid photovoltaic value and the alternating current micro-grid storage battery value, controlling the fan and the alternating current micro-grid photovoltaic to operate in an MPPT mode, discharging the alternating current micro-grid storage battery, and subtracting the alternating current micro-grid photovoltaic value after the discharging power is obtained by subtracting the fan value from the alternating current load value;

when the state of charge value of the alternating current micro-grid storage battery is greater than or equal to 80, if the alternating current load value is greater than the sum of the fan value, the alternating current micro-grid storage battery value and the alternating current micro-grid photovoltaic value, and the load value is less than or equal to the sum of the fan value, the alternating current micro-grid storage battery value, the diesel generator value and the alternating current micro-grid photovoltaic value, controlling the fan and the alternating current micro-grid photovoltaic to operate in an MPPT mode, operating the diesel generator at the maximum power, discharging the storage battery, and subtracting the alternating current micro-grid photovoltaic value and the diesel generator value from the discharging power after subtracting the fan value from the alternating current load value;

when the state of charge value of the alternating current micro-grid storage battery is greater than or equal to 80, if the alternating current load value is greater than the sum of the fan value, the alternating current micro-grid storage battery value, the diesel generator value and the alternating current micro-grid photovoltaic value, and the load value is less than or equal to the sum of the fan value, the alternating current micro-grid storage battery value, the diesel generator value, the alternating current micro-grid photovoltaic value and the micro gas turbine value, controlling the fan and the alternating current micro-grid photovoltaic to operate in an MPPT mode, operating the maximum power of the diesel generator and the maximum power of the micro gas turbine, discharging the alternating current micro-grid storage battery, and subtracting the alternating current micro-grid photovoltaic value, the diesel generator value and the micro gas turbine value after the discharging power is that the alternating current load value subtracts the fan value;

and when the state of charge value of the storage battery of the alternating current microgrid is greater than or equal to 80, controlling the switching load if the alternating current load value is greater than the sum of the fan value, the storage battery value of the alternating current microgrid, the diesel generator value, the photovoltaic value of the alternating current microgrid and the micro gas turbine value.

That is, in one embodiment, as shown in fig. 12b, the controller is specifically configured to, during off-grid microgrid energy management for ac:

when the state of charge value of the storage battery of the alternating-current microgrid is more than 20 and less than 80 and the sum of the value of the fan and the photovoltaic value of the alternating-current microgrid is more than the alternating-current load value, if the redundant power is more than the charging power of the storage battery of the alternating-current microgrid, controlling the maximum power charging of the storage battery of the alternating-current microgrid and controlling the photovoltaic limit power of the fan and the alternating-current microgrid at the same time;

when the state of charge value of the storage battery of the alternating-current microgrid is more than 20 and less than 80 and the sum of the fan value and the photovoltaic value of the alternating-current microgrid is more than the alternating-current load value, if the redundant power is less than or equal to the charging power value of the storage battery of the alternating-current microgrid, the storage battery of the alternating-current microgrid is controlled to be charged;

when the state of charge value of the storage battery of the alternating-current microgrid is more than 20 and less than 80 and the sum of the fan value and the photovoltaic value of the alternating-current microgrid is less than the alternating-current load value, if the power exceeds the power and is less than or equal to the discharge power of the storage battery, the storage battery of the alternating-current microgrid is controlled to discharge;

when the state of charge value of the storage battery of the alternating-current microgrid is more than 20 and less than 80, and the sum of the fan value and the photovoltaic value of the alternating-current microgrid is less than the alternating-current load value, if the power exceeds the discharge power of the storage battery, eighty percent of rated power of the diesel generator is started, the power of the diesel generator, the micro gas turbine or the storage battery of the alternating-current microgrid is less than or equal to the load power, and the control is finished;

when the state of charge value of the storage battery of the alternating-current microgrid is more than 20 and less than 80, the sum of the fan value and the photovoltaic value of the alternating-current microgrid is less than the alternating-current load value, if the power exceeds the discharge power of the storage battery, eighty percent of rated power of the diesel generator is started, the power of the diesel generator, the micro gas turbine or the storage battery of the alternating-current microgrid is more than the load power, the micro gas turbine is started, and the power of the diesel generator, the micro gas turbine or the storage battery of the alternating-current microgrid is less than or equal to the load power, the control is finished;

when the state of charge value of the storage battery of the alternating-current microgrid is more than 20 and less than 80, the sum of the fan value and the photovoltaic value of the alternating-current microgrid is less than the alternating-current load value, if the power exceeds the discharge power of the storage battery, eighty percent of rated power of the diesel generator is started, the power of the diesel generator, the micro gas turbine or the storage battery of the alternating-current microgrid is more than the load power, the micro gas turbine is started, when the power of the diesel generator, the micro gas turbine or the storage battery of the alternating-current microgrid is more than the load power, the load is cut off, and when the preset condition is reached, the primary load is ensured.

In addition, in fig. 12b, the excess power refers to wind power generation power + photovoltaic power generation power-load, and the micro-source refers to all distributed power sources existing in the microgrid.

That is, in one embodiment, as shown in fig. 12c, the controller is specifically configured to, during off-grid microgrid energy management for ac:

when the state of charge value of the storage battery of the alternating-current microgrid is less than or equal to 20, controlling the fan and the photovoltaic of the alternating-current microgrid to operate in an MPPT mode, setting the maximum power of the storage battery for charging when the electric quantity of the storage battery is insufficient, and returning when the state of charge value of the storage battery of the alternating-current microgrid is greater than or equal to 80; and if the state of charge value of the storage battery of the alternating-current microgrid is less than 80, repeatedly controlling the fan and the photovoltaic of the alternating-current microgrid to operate in an MPPT mode, and giving the maximum power of the storage battery for charging when the electric quantity of the storage battery is insufficient, and returning until the state of charge of the storage battery of the alternating-current microgrid is more than or equal to 80.

6.3: black start of micro-grid overall structure

A diesel generator, a micro gas turbine and a storage battery in the alternating-current micro grid are subjected to droop control, bus voltage is established, and the bus voltage is gradually merged into a fan, a photovoltaic micro source and the like under the control of the maximum power after being stabilized. The flow is shown in fig. 13.

In one embodiment, as shown in fig. 13, the controller is specifically configured to perform the following operations of the microgrid overall structure black start according to a black start energy management policy:

the black start operation ends.

In one embodiment, as shown in fig. 13, the controller is further configured to: and when the direct-current bus voltage is detected to be lower than a preset direct-current standard value, controlling the direct-current micro-grid storage battery to operate in a VF mode, and establishing the direct-current bus voltage.

6.4: photovoltaic active anti-islanding test

The test load parameters were inductance 1e-4H, capacitance 2.9e-3F, and resistance 2.25 ohms, as shown in FIG. 14.

The load quality factor is calculated to be 2.04, and when the grid of the photovoltaic inverter is disconnected, the converter adopting an active anti-islanding strategy actively raises the frequency, so that a passive anti-islanding detection device is triggered to perform islanding protection.

In conclusion, the technical scheme of the invention has the following beneficial effects: the invention provides a distributed AC/DC hybrid micro-grid system design method based on PSCAD according to the requirements of the state on the design specification of a distributed power supply access power distribution network, the operation control specification of a micro-grid access power distribution network and the like, wherein the designed AC/DC hybrid micro-grid system comprises a diesel generator, a micro gas turbine, a photovoltaic, a storage battery, a super capacitor, a fan, a DC charging pile, an electric energy quality control device and the like. The invention provides control methods such as droop control, low-voltage ride through control and the like for the whole system. The invention provides a relatively complete PSCAD simulation implementation method, and on the basis, a bottom layer control idea and an upper layer control idea are completely designed by using an embedded C language. The three droop controls are adopted on the bottom control, so that the robustness of the system is improved; the micro-sources are all controlled in two stages, so that the controllability of the system is improved, and the bottom layer is closely connected with the upper layer; the concept of negative droop coefficient is provided, so that the energy management strategy is more flexible to realize; the on-grid and off-grid presynchronization control strategy realizes seamless grid connection, indirectly adjusts the state of the whole microgrid by utilizing circulation, and has stronger robustness compared with common presynchronization. Technical guidance is provided for the research and the complete set design of the system related to the microgrid.

The embodiment of the invention also provides a controller of the distributed alternating current and direct current hybrid micro-grid system based on PSCAD, which is described in the following embodiment. Because the principle of solving the problems of the controller is similar to that of the distributed AC/DC hybrid micro-grid system based on the PSCAD, the implementation of the controller can refer to the implementation of the distributed AC/DC hybrid micro-grid system based on the PSCAD, and repeated parts are not described again.

Fig. 15 is a schematic structural diagram of a controller of a PSCAD-based hybrid microgrid according to an embodiment of the present invention, where as shown in fig. 15, the controller includes:

the monitoring unit 01 is used for monitoring the current operation conditions of the direct current micro-grid and the alternating current micro-grid;

the control unit 02 is used for carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro grid storage battery according to the monitored current running conditions of the direct current micro grid and the alternating current micro grid and a preset bottom layer control strategy so as to realize power sharing and simultaneously connect a fan and an alternating current micro grid photovoltaic power source, realizing the charging of the alternating current micro grid storage battery and simultaneously discharging the diesel generator and the micro gas turbine by adjusting a positive droop coefficient and/or a negative droop coefficient, and controlling the running of the direct current micro grid and the alternating current micro grid by a preset upper layer energy management strategy; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

The embodiment of the invention also provides a control method of the distributed alternating current and direct current hybrid micro-grid system based on PSCAD, which is described in the following embodiment. Because the principle of solving the problems of the method is similar to that of the distributed AC/DC hybrid micro-grid system based on PSCAD, the implementation of the method can refer to the implementation of the distributed AC/DC hybrid micro-grid system based on PSCAD, and repeated parts are not described again.

Fig. 16 is a schematic flow chart of a control method of a hybrid microgrid based on a PSCAD according to an embodiment of the present invention, as shown in fig. 16, the method includes the following steps:

step 101: monitoring the current operation conditions of the direct current micro-grid and the alternating current micro-grid;

step 102: according to the monitored current running conditions of the direct current micro-grid and the alternating current micro-grid, a preset bottom layer control strategy is used for carrying out droop control on the micro gas turbine, the diesel generator and the alternating current micro-grid storage battery to realize power sharing and simultaneously connecting a fan and an alternating current micro-grid photovoltaic power source, the diesel generator and the micro gas turbine are discharged while the alternating current micro-grid storage battery is charged by adjusting a positive droop coefficient and/or a negative droop coefficient, and the preset upper layer energy management strategy is used for controlling the direct current micro-grid and the alternating current micro-grid to run; the droop coefficient is obtained according to the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the diesel generator and the relation between the frequency and the intercept of the cross shaft of the grid-connected inverter of the micro-combustion engine; the positive droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator and the micro gas turbine is positioned on the positive axis of the coordinate system, and the negative droop coefficient is a droop coefficient corresponding to the condition that the intercept of the transverse axis of the grid-connected inverter of the diesel generator or the micro gas turbine is positioned on the negative axis of the coordinate system.

The distributed alternating current-direct current hybrid micro-grid scheme based on PSCAD provided by the embodiment of the invention realizes that:

1. the built complete simulation model comprises an alternating current-direct current hybrid micro-grid, and the idea that three different micro-sources of a micro-gas turbine, a diesel engine and a storage battery jointly adopt droop control is provided. In order to improve the controllability of the system, a back-to-back two-stage pressure and frequency regulating structure is provided on a micro gas turbine and a diesel generator. Under the working condition that the charging and discharging requirements are not uniform, the droop coefficient is adjusted through an upper-layer control strategy, and the simultaneous existence of the positive droop coefficient and the negative droop coefficient is realized.

2. By adopting a comprehensive control idea combining droop control and constant power output control, the method can ensure the stability of the system while ensuring the stability of the output power of the main micro source, and the multiple converters perform peak clipping and valley filling on the micro grid, thereby improving the robustness of the whole structure of the micro grid.

3. Droop control is adopted as a control strategy of a bottom layer main micro source in the whole process of the presynchronization process, the presynchronization signal is cleared while the grid connection is successful, and the output power of the droop converter is equal to the rated power after the grid connection under the method. And no control strategy is switched in the grid connection process, and no voltage and current impact exists at the moment of grid connection, so that seamless grid connection is realized.

4. The method can sacrifice the power sharing effect in the process of partial grid connection and disconnection, indirectly modulate and regulate the frequency of the other two converters by using the circulating current between the converters, and improve the stability in the pre-synchronization process.

5. An energy management strategy is designed in the embedded C language, the operation mode and the operation state of the micro-grid are adjusted, the plug-and-play performance of droop control and the micro-source characteristics of a micro gas turbine and a diesel engine are utilized, the micro-grid is used as a standby power supply after being stabilized, and the micro-grid is connected to the micro-grid when in need.

In the embodiment of the invention, the distributed AC/DC hybrid microgrid scheme based on the PSCAD can realize the distributed AC/DC hybrid microgrid based on the PSCAD, form a set of microgrid system design specifications and ensure power supply reliability and electric energy quality.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

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