阅读说明：本技术 一种模块化储能变流器并联控制方法和系统 (Parallel control method and system for modular energy storage converters ) 是由 郭勇 丁勇 詹小海 石祥建 刘为群 金建新 支秉忠 李健 李海郁 于 2020-05-11 设计创作，主要内容包括：本发明公开一种模块化储能变流器并联控制方法和系统。控制环路通过模拟同步发电机的外特性来实现储能变流器各模块的并联,设置并联的储能变流器的DCAC模块在并网和离网状态下的有功功率控制和无功功率控制控制模式；在储能变流器离网模式下上层控制器通过对DCAC模块控制器实际输出电压和角速度进行修正,使得模块化储能变流器各DCAC模块均流。本发明通过合理设计有功功率控制环及数字惯性调节器,可以同时在并网以及离网运行时取得较好的控制效果,使系统稳定性大大提高：在并网时功率震荡及超调小,动态特性较快,有利于跟踪功率指令,在离网时,可以提供较大的转动惯量,提高系统的频率稳定性。(The invention discloses a parallel control method and a parallel control system for modular energy storage converters. The control loop realizes the parallel connection of all modules of the energy storage converter by simulating the external characteristics of the synchronous generator, and sets active power control and reactive power control modes of DCAC modules of the energy storage converters connected in parallel in grid-connected and off-grid states; and in the off-grid mode of the energy storage converter, the upper layer controller corrects the actual output voltage and the angular speed of the DCAC module controller, so that each DCAC module of the modular energy storage converter has current sharing. By reasonably designing the active power control loop and the digital inertia regulator, the invention can obtain better control effect during grid-connected operation and off-grid operation at the same time, thereby greatly improving the system stability: when the grid is connected, the power oscillation and the overshoot are small, the dynamic characteristic is fast, the power instruction can be tracked, and when the grid is disconnected, the larger rotational inertia can be provided, and the frequency stability of the system is improved.)

1. A parallel control method for a modular energy storage converter is disclosed, wherein the energy storage converter comprises a DCAC module and an upper controller connected with the DCAC module, and is characterized by comprising the following steps:

obtaining active power control output according to the actual output active power of the energy storage converter and the active power reference value of the energy storage converter, obtaining the actual output angular velocity omega of the virtual synchronous generator according to the active power control output, and integrating the actual output angular velocity omega of the virtual synchronous generator to output a voltage phase theta;

according to the actual output reactive power of the energy storage converter and the reactive power reference value of the energy storage converter, reactive power control output is obtained, and according to the reactive power control output, an output voltage instruction u of a q-axis controller of the energy storage converter is obtained_q ^*And d-axis controller output voltage command u_d ^*；

According to the output voltage phase theta and the q-axis controller output voltage instruction u of the virtual synchronous generator_q ^*And d-axis controller output voltage command u_d ^*Obtaining an output voltage reference of the energy storage converter, and outputting a PWM (pulse width modulation) switching signal to control the energy storage converter according to the output voltage reference of the energy storage converter;

setting active power control and reactive power control modes of DCAC modules of all energy storage converters connected in parallel in grid-connected and off-grid states;

the upper layer controller stores energy and converts current by the DCAC module in the off-grid mode of the energy storage converterQ-axis controller output voltage command u_q ^*D-axis controller output voltage command u_d ^*And correcting the signal of the angular speed omega of the virtual synchronous generator to make the DCAC modules of the modular energy storage converters flow uniformly.

2. The parallel control method for the modular energy storage converters as claimed in claim 1, wherein the method for obtaining the virtual synchronous generator actual output angular speed ω according to the actual output active power of the energy storage converters and the active power reference value of the energy storage converters comprises the following steps of:

actual output active power P of input energy storage converter_oAnd the active power reference value P of the energy storage converter_refAnd obtaining active power control output, inputting the active power control output to a rotor motion equation module, outputting the actual output angular speed omega of the virtual synchronous generator by the rotor motion equation module, and outputting a voltage phase theta after integrating the actual output angular speed omega.

3. The parallel control method for the modular energy storage converters as claimed in claim 1, wherein the output voltage command u of the q-axis controller of the energy storage converter is obtained according to the actual output reactive power of the energy storage converter and the reference value of the reactive power of the energy storage converter_q ^*And d-axis controller output voltage command u_d ^*The specific method comprises the following steps:

actual output reactive power Q of input energy storage converter_oAnd the reactive power reference value Q of the energy storage converter_refObtaining reactive power control output, inputting the reactive power control output to a rotor flux linkage equation module, and outputting a voltage instruction u output by a q-axis controller of the energy storage converter through droop control by the rotor flux linkage equation module_q ^*And d-axis controller output voltage command u_d ^*。

4. The parallel control method of modular energy storage converters as claimed in claim 1, wherein the parallel control method comprises the steps ofAccording to the output voltage phase theta and q axis controller output voltage instruction u_q ^*And d-axis controller output voltage command u_d ^*Obtaining an output voltage reference of the energy storage converter, wherein the output voltage reference of the energy storage converter outputs a PWM (pulse width modulation) switching signal to control the energy storage converter specifically comprises the following steps:

outputting a voltage command u to an output voltage phase theta and q axis controller_q ^*And d-axis controller output voltage command u_d ^*The output voltage reference of the energy storage converter output by the stator voltage model is input to the voltage and current closed-loop module, the voltage and current closed-loop module controls the output modulation wave voltage, and the PWM switching signal is output according to the modulation wave voltage to control the energy storage converter.

5. The parallel control method for the modular energy storage converters as claimed in claim 1, wherein in a grid-connected state, the active frequency control and the reactive power control of the DCAC module of the energy storage converter adopt proportional integral control, and in an off-grid state, the active frequency control and the reactive power control of the DCAC module of the energy storage converter adopt proportional control.

6. The parallel control method for the modular energy storage converters as claimed in claim 2, wherein the rotor motion equation module adopts a digital inertia element to simulate the rotor characteristics of the synchronous generator, and the expression of the digital inertia element is as follows:

wherein (1-k)_c) Is the inertia time constant, z is the sampling Laplace transform operator, k_cIs an intermediate parameter.

7. The parallel control method for the modular energy storage converters as claimed in claim 1, wherein: the DCAC module sends the actual active power output signal and the actual reactive power output signal to an upper layer controller through a digital communication bus, and receives an active power reference value and a reactive power reference value from the upper layer controller.

8. The parallel control system of the modularized energy storage converter is characterized in that the energy storage converter comprises DCAC modules and an upper layer controller connected with the DCAC modules, and the control system comprises: an active frequency control loop, a reactive voltage control loop, a rotor motion equation simulation, a rotor flux equation simulation, a stator voltage model and a voltage and current closed loop,

the active frequency control loop is used for obtaining active power control output according to the actual output active power of the energy storage converter and the active power reference value of the energy storage converter;

the rotor motion equation simulation is used for controlling output according to active power to obtain an actual output angular velocity omega of the virtual synchronous generator, and integrating the actual output angular velocity omega of the virtual synchronous generator to output a voltage phase theta;

the reactive voltage control loop is used for obtaining reactive power control output according to the actual output reactive power of the energy storage converter and the reactive power reference value of the energy storage converter;

the rotor flux linkage equation simulation is used for obtaining an output voltage instruction u of the q-axis controller of the virtual synchronous generator according to the reactive power control output_q ^*And d-axis controller output voltage command u_d ^*；

The stator voltage model is used for outputting a voltage command u according to the output voltage phase theta and the q-axis controller_q ^*And d-axis controller output voltage command u_d ^*Obtaining an output voltage reference of the energy storage converter;

the voltage and current closed loop is used for outputting a PWM (pulse width modulation) switching signal to control the energy storage converter through a closed loop regulator according to the obtained output voltage reference, the actual output voltage and the actual output current of the energy storage converter;

the active frequency control loop and the reactive frequency control loop both comprise analog selection switches, and the analog selection switches are used for setting control modes of DCAC modules of all energy storage converters connected in parallel in grid-connected and off-grid states;

the upper layer controller is used for outputting a voltage instruction u to the DCAC module virtual synchronous generator q-axis controller in the off-grid mode of the energy storage converter_q ^*D-axis controller output voltage command u_d ^*And correcting the signals of the angular speed omega to equalize the current of each modular energy storage converter DCAC module.

9. The parallel control system of modular energy storage converters as claimed in claim 8, wherein the active frequency control loop is configured to use proportional integral control for the active frequency control and reactive power control of the DCAC module of the energy storage converter in the grid-connected state, and to use proportional integral control for the active frequency control and reactive power control of the DCAC module of the energy storage converter in the off-grid state.

10. The parallel control system of the modular energy storage converters as claimed in claim 8, wherein the rotor motion equation module simulates the rotor characteristics of the synchronous generator with a digital inertia element, and the expression of the digital inertia element is:

wherein (1-k)_c) Is the inertia time constant, z is the sampling Laplace transform operator, k_cIs an intermediate parameter.

Technical Field

The invention belongs to the technical field of energy storage, and particularly relates to a parallel control method for a modular energy storage converter.

Background

The bidirectional energy storage DCAC converter is used as an interface between an energy storage element in an energy storage system and an alternating current power grid, and plays an important role in the whole energy storage system. In the application occasions with high power and high reliability, the energy storage converter mostly adopts the redundant parallel connection and hot plug technology of a plurality of modules of the converter. In actual use, a corresponding number of converter modules can be put into the system according to the actual requirements of the system, and different modules are combined to run in a parallel connection mode so as to meet the requirements of different power grades and hot standby. The main problems of the parallel connection of the DCAC inversion modules are as follows: when the inversion modules work in parallel, the inversion modules have amplitude difference and phase difference, and if the outputs of the inversion modules are connected in parallel without measures, circulation current is formed.

The existing literature has made many researches on the parallel control strategy of multiple converters, and the method is mainly divided into an external characteristic droop method of a master-slave mode, a distributed mode and no communication connection line. The master-slave control method has the advantages of simple current-sharing control circuit and high current-sharing precision, but because the slave module must depend on the master module to work, the parallel system does not realize redundancy and has low reliability. The distributed mode adopts a main controller voltage loop and each module receives a current loop instruction, and has the defects that the modules have stronger coupling relation and the main controller needs redundancy backup. The disadvantage of the droop method of the frequency voltage external characteristic of the wireless communication connection is that: the droop control of the external characteristic is artificially introduced, and the external characteristic of the system output is poor. Moreover, the current technical scheme is developed for a unidirectional converter or an off-grid inverter, and a parallel control strategy of the bidirectional converter and the parallel off-grid energy storage converter is not shown.

Disclosure of Invention

The invention aims to provide a parallel control method of a modular energy storage converter, which realizes parallel control of a bidirectional grid-connected and grid-disconnected modular energy storage converter and ensures stable operation of a system.

On one hand, the invention discloses a parallel control method for a modular energy storage converter, wherein the energy storage converter comprises a DCAC module and an upper layer controller connected with the DCAC module, and the control method comprises the following steps: obtaining an active power control output according to the actual output active power of the energy storage converter and an active power reference value of the energy storage converter, obtaining an actual output angular velocity omega of the virtual synchronous generator according to the active power control output, and integrating the actual output angular velocity omega of the virtual synchronous generator to output a voltage phase theta;

according to the actual output reactive power of the energy storage converter and the reactive power reference value of the energy storage converter, reactive power control output is obtained, and according to the reactive power control output, an output voltage instruction u of a q-axis controller of the virtual synchronous generator is obtained_q ^*And d-axis controller output voltage command u_d ^*；

According to the output voltage phase theta and q axis controller output voltage instruction u of the energy storage converter_q ^*And d-axis controller output voltage command u_d ^*Obtaining an output voltage reference of the energy storage converter, and outputting a PWM (pulse width modulation) switching signal to control the energy storage converter according to the obtained output voltage reference of the energy storage converter;

setting active power control and reactive power control modes of DCAC modules of all energy storage converters connected in parallel in grid-connected and off-grid states;

the upper-layer controller outputs a voltage instruction u to the DCAC module virtual synchronous generator q-axis controller in the off-grid mode of the energy storage converter_q ^*D-axis controller output voltage command u_d ^*And correcting the signals of the angular speed omega to equalize the current of each modular energy storage converter DCAC module.

In a second aspect, the invention discloses a parallel control system for a modular energy storage converter, wherein the energy storage converter comprises DCAC modules and an upper controller connected with the DCAC modules, and the control system comprises: an active frequency control loop, a reactive voltage control loop, a rotor motion equation simulation, a rotor flux equation simulation, a stator voltage model and a voltage and current closed loop,

the active frequency control loop is used for obtaining active power control output according to the actual output active power of the energy storage converter and the active power reference value of the converter;

the rotor motion equation simulation is used for controlling output according to active power to obtain an actual output angular velocity omega of the virtual synchronous generator, and integrating the actual output angular velocity omega to output a voltage phase theta;

the reactive voltage control loop is used for obtaining reactive power control output according to the actual output reactive power of the converter and a reactive power reference value of the converter;

the rotor flux linkage equation simulation is used for obtaining an output voltage instruction u of a q-axis controller of the converter virtual synchronous generator according to the reactive power control output_q ^*And d-axis controller output voltage command u_d ^*；

The stator voltage model is used for outputting a voltage instruction u according to the converter output voltage phase theta and q-axis controller output voltage_q ^*And d-axis controller output voltage command u_d ^*Obtaining output voltage reference u of energy storage converter_a ^*、u_b ^*、u_c ^*；

The voltage and current closed loop is used for outputting a voltage reference u according to the energy storage converter_a ^*、u_b ^*、u_c ^*And the actual output voltage u_a、u_b、u_cThe actual output current outputs a PWM switching signal through a closed-loop regulator to control the energy storage converter;

the active frequency control loop and the reactive frequency control loop both comprise analog selection switches, and the analog selection switches are used for setting control modes of DCAC modules of all energy storage converters connected in parallel in grid-connected and off-grid states;

the upper layer controller is used for outputting a voltage instruction u to the DCAC module virtual synchronous generator q-axis controller in the energy storage off-grid mode_q ^*D-axis controller output voltage command u_d ^*And correcting the signals of the angular speed omega to equalize the current of each modular energy storage converter DCAC module.

Adopt the beneficial effect that above-mentioned scheme brought:

the converter module combination mode of the invention is flexible, the direct current side of the converter can work in parallel or independently, the alternating current output side can work in parallel and independently, the converter can run in a grid-connected mode or an off-grid mode, and better control effect can be obtained during the grid-connected operation and the off-grid operation by reasonably designing an active power control ring and a digital inertia regulator, so that the system stability is greatly improved: when the grid is connected, the power oscillation and the overshoot are small, the dynamic characteristic is fast, the power instruction can be tracked, and when the grid is disconnected, the larger rotational inertia can be provided, and the frequency stability of the system is improved. And the modularized energy storage system operates stably, and the modules are in digital communication, so that the realization is simple and the anti-interference capability is strong.

Drawings

FIG. 1 is a prior art energy storage converter single module circuit diagram;

FIG. 2 is a schematic diagram of converter module connections in an embodiment of the present invention;

FIG. 3 is a block diagram of a single module control of a converter in an embodiment of the present invention;

FIG. 4 is a block diagram of a converter multi-module parallel control according to an embodiment of the present invention;

FIG. 5 is a block diagram of active frequency (current sharing) control in an embodiment of the present invention;

fig. 6 is a reactive voltage (voltage sharing) control block diagram in an embodiment of the present invention.

Detailed Description

The technical scheme of the invention is explained in detail in the following with the accompanying drawings.

As shown in fig. 1, a topology of a prior art energy storage converter module, fig. 1 shows that a modular energy storage converter comprises: DCAC module and upper controller. The DCAC module comprises a hot plug terminal, a direct current side EMI filter, a direct current contactor, a storage battery side decoupling capacitor, a three-phase I-type three-level inverter bridge, a three-phase alternating current inverter side inductor, a three-phase alternating current filter capacitor, a grid-connected relay, a three-phase alternating current grid side inductor, an alternating current side EMI filter, a fuse and an alternating current/direct current pre-charging loop. The hot plug terminal is an interface between the storage battery and the alternating current bus.