阅读说明：本技术 一种直流配电网改进主从控制方法 (Improved master-slave control method for direct-current power distribution network ) 是由 霍现旭 徐科 李树鹏 尚学军 李国栋 张剑 杨卫东 吴东 谢兴峰 吴在军 曹骁勇 于 2019-11-29 设计创作，主要内容包括：本发明涉及一种直流配电网改进主从控制方法,其技术特点在于：包括以下步骤：步骤1、设计带死区的自适应下垂控制器；步骤2、设定其中一个MMC换流站为主站,工作模式为恒压控制模式,设定其他MMC换流站为从站,工作模式采用步骤1的带死区的自适应下垂控制器的控制模式。本发明能够在通信故障时实现运行模式的无缝切换和确保直流电压的稳定。(The invention relates to an improved master-slave control method for a direct-current power distribution network, which is technically characterized by comprising the following steps of: the method comprises the following steps: step 1, designing a self-adaptive droop controller with a dead zone; and 2, setting one of the MMC converter stations as a master station, setting the working mode as a constant voltage control mode, setting other MMC converter stations as slave stations, and adopting the control mode of the self-adaptive droop controller with the dead zone in the step 1 in the working mode. The invention can realize seamless switching of the operation mode and ensure the stability of the direct current voltage when the communication fails.)

1. A master-slave control method for improving a direct current distribution network is characterized by comprising the following steps: the method comprises the following steps:

step 1, designing a self-adaptive droop controller with a dead zone;

and 2, setting one of the MMC converter stations as a master station, setting the working mode as a constant voltage control mode, setting other MMC converter stations as slave stations, and adopting the control mode of the self-adaptive droop controller with the dead zone in the step 1 in the working mode.

2. The improved master-slave control method for the direct current distribution network according to claim 1, wherein the method comprises the following steps: the specific steps of the step 1 comprise:

(1) measuring three-phase voltage and current of the MMC network side, and measuring voltage and current of the MMC direct current side;

(2) obtaining a reference phase theta and an angular frequency omega of an alternating current power grid through phase locking according to the three-phase alternating current voltage obtained through measurement in the step (1);

(3) d, carrying out dq conversion on the three-phase alternating-current voltage and current at the MMC network side according to the reference phase theta of the alternating-current power grid obtained in the step (2) to obtain a d-axis component u of the voltage_dAnd q-axis component u_qObtaining d-axis component i of current_dAnd q-axis component i_q；

(4) U obtained according to step (3)_d、u_q，、i_d、i_qCalculating the active power P_gAnd reactive power Q_g；

(5) Designing an MMC AC side outer ring controller as constant reactive power control, and controlling a reactive power reference value Q^*And MMC actual output reactive power Q_gCalculating q-axis reference value i of current inner loop through PI_q ^*；

Designing MMC direct current side outer ring control as self-adaptive droop control with dead zones, and calculating d-axis reference value i of current inner ring_d ^*；

(6) And designing a decoupled current inner loop controller under a dq coordinate system, and calculating to obtain an output voltage reference value required by MMC modulation through a PI controller, voltage feedforward and coupling compensation.

3. The improved master-slave control method for the direct current distribution network according to claim 2, wherein the method comprises the following steps: step 1, step 5, designing MMC direct current side outer ring control to be self-adaptive droop control with dead zones, and calculating d-axis reference value i of current inner ring_d ^*The method comprises the following specific steps:

(1) according to the extreme operation condition of the power distribution network, calculating the maximum value U which can be reached by the voltage on the direct current side of the direct current power distribution network from the MMC2 when the direct current power distribution network is in stable operation_dc2maxAnd minimum value U_dc2min；

(2) According to U_ddc2maxAnd U_dc2minDetermining a dead band upper bound value for an adaptive droop controllerAnd lower bound value

(3) According to the measured direct current voltage of the slave station MMC

let Delta U_dc2＝U_dc ^*-U_dc2，

(4) Designing the inverse of the adaptive droop coefficient

In the formula, P_2maxFor the maximum active power, P, that the MMC2 converter station can output₂ ^*The method comprises the steps that delta is a set value of active power of an MMC2 converter station, and is a maximum deviation range allowed by direct-current voltage;

(5) calculating the active power regulating quantity delta P of the slave converter station according to the direct current voltage_dc2 ^*＝sng*β₂*|ΔU_dc2|；

(6) Will be delta P_dc2 ^*With given value of active power P₂ ^*And a measured value P_g2The deviation is superposed and sent to a PI controller to form self-adaptation with dead zoneDroop control to calculate the current inner loop d-axis reference i_d ^*。

Technical Field

The invention belongs to the technical field of direct current power distribution networks, relates to a control method of a converter station, and particularly relates to an improved master-slave control method of a direct current power distribution network.

Background

With the rapid development of renewable energy, more and more new energy sources are connected to a power distribution network in a large quantity for power generation and energy storage, and the trend of the power distribution network becomes bidirectional flow, which puts higher requirements on the capacity, reliability, electric energy quality and the like of the power distribution network. In addition, with the great progress of the power electronic technology and the direct current load technology, the direct current distribution network has received wide attention of domestic and foreign scholars. Compared with a traditional power grid commutation type Converter (Line commanded Converter, LCC), the Modular Multilevel Converter (MMC) has the advantages of no commutation failure, good output characteristic, Modular structure, capability of realizing rapid decoupling control and the like, and is widely applied to a direct-current power distribution network Converter station in recent years.

At present, most documents of voltage control of the direct current power distribution network still concentrate on research and analysis of a converter or a microgrid control technology, a mature direct current power distribution network control strategy does not exist, and a related voltage cooperative control method of the flexible direct current power distribution network mainly refers to a voltage control method in flexible direct current power transmission, wherein the voltage control methods suitable for the flexible direct current power distribution network mainly comprise three methods: Master-Slave Control (Master/Slave Control), voltage droop Control (DroopControl), and voltage Margin Control (Margin Control). The master-slave control is to use one converter station as a relaxation node to control the direct-current voltage of the system, other converter stations adopt constant-power control, the control mode depends on the rapid communication among the converters, and the regulation pressure of the master station is higher. The direct current voltage droop control means that all converter stations with power regulation capability share direct current voltage control by utilizing a given slope relation between each direct current power (or current) and direct current voltage, the control mode does not need an upper-layer controller and communication, has good modularity and expansibility, but has deviation in steady-state operation, the load change of a direct current distribution network is complex, frequent large load change can cause voltage fluctuation, even the voltage deviation exceeds a rated range in steady operation, and the selection of the slope of the control method is difficult. The voltage margin control is that when the main converter station has a fault or the power is out of limit and the direct current voltage cannot be continuously maintained to be constant, the other converter station is switched to a fixed direct current voltage control mode and operates in a new direct current voltage reference value. Therefore, compared with a flexible direct-current transmission system, the direct-current power distribution network has more nodes and more complex power flow, and the stable operation of the direct-current power distribution network is easier to realize by adopting a master-slave control mode than other modes.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides an improved master-slave control method for a direct current power distribution network, which can realize the switching of an operation mode and the stable control of direct current voltage when the master-slave control fails in communication and improve the rapidity and the reliability of the control of the direct current voltage when the direct current power distribution network is disturbed.

The invention solves the practical problem by adopting the following technical scheme:

a master-slave control method for improving a direct current distribution network comprises the following steps:

step 1, designing a self-adaptive droop controller with a dead zone;

and 2, setting one of the MMC converter stations as a master station, setting the working mode as a constant voltage control mode, setting other MMC converter stations as slave stations, and adopting the control mode of the self-adaptive droop controller with the dead zone in the step 1 in the working mode.

Further, the specific steps of step 1 include:

(1) measuring three-phase voltage and current of the MMC network side, and measuring voltage and current of the MMC direct current side;

(2) obtaining a reference phase theta and an angular frequency omega of an alternating current power grid through phase locking according to the three-phase alternating current voltage obtained through measurement in the step (1);

(3) d, carrying out dq conversion on the three-phase alternating-current voltage and current at the MMC network side according to the reference phase theta of the alternating-current power grid obtained in the step (2) to obtain a d-axis component u of the voltage_dAnd q-axis component u_qObtaining d-axis component i of current_dAnd q-axis component i_q；

(4) U obtained according to step (3)_d、u_q，、i_d、i_qCalculating the active power P_gAnd reactive power Q_g；

(5) Designing an MMC AC side outer ring controller as constant reactive power control, and controlling a reactive power reference value Q^*And MMC actual output reactive power Q_gCalculating q-axis reference value i of current inner loop through PI_q ^*(ii) a Design MMC direct current side outer loop control to take dead zone self-adaptation to hang downControl to calculate the d-axis reference value i of the current inner loop_d ^*；

(6) And designing a decoupled current inner loop controller under a dq coordinate system, and calculating to obtain an output voltage reference value required by MMC modulation through a PI controller, voltage feedforward and coupling compensation.

And in the step 1, the MMC direct-current side outer ring control is designed to be self-adaptive droop control with a dead zone in the step (5), so that a d-axis reference value i of the current inner ring is calculated_d ^*The method specifically comprises the following steps:

(1) according to the extreme operation condition of the power distribution network, calculating the maximum value U which can be reached by the voltage on the direct current side of the direct current power distribution network from the MMC2 when the direct current power distribution network is in stable operation_dc2maxAnd minimum value U_dc2min；

(2) According to U_dc2maxAnd U_dc2minDetermining a dead band upper bound value for an adaptive droop controllerAnd lower bound value

(3) According to the measured direct current voltage of the slave station MMC

And

determining a value of the sign function;

is provided with

(4) Designing the inverse of the adaptive droop coefficient

In the formula, P_2maxFor the maximum active power, P, that the MMC2 converter station can output₂ ^*The method comprises the steps that delta is a set value of active power of an MMC2 converter station, and is a maximum deviation range allowed by direct-current voltage;

(5) calculating the active power regulating quantity delta P of the slave converter station according to the direct current voltage_dc2 ^*＝sng^*β₂ ^*|ΔU_dc2|；

(6) Will be delta P_dc2 ^*With given value of active power P₂ ^*And a measured value P_g2The deviation is superposed and sent to a PI controller to form a self-adaptive droop controller with a dead zone, so that a d-axis reference value i of the current inner ring is calculated_d ^*。

The invention has the advantages and beneficial effects that:

1. the invention improves the control method of the slave converter station on the basis of master-slave control of a direct current power distribution network, designs a self-adaptive droop control method with a dead zone from the power outer ring of the slave converter station, realizes that the slave converter station works in a constant power mode when the direct current power distribution network is in a steady state, can accurately control active power output, and can quickly switch the running state to the self-adaptive droop control without depending on communication if the direct current voltage deviation is overlarge, for example, a master station is fully loaded and has sudden load change, the master station quits running due to faults, a direct current bus is broken, and the like, when the direct current power distribution network has disturbance such as running state conversion and N-1 faults, and the like. Therefore, the invention not only overcomes the defects that the master-slave control can not realize the switching of the operation mode and the stable control of the direct current voltage when the communication is in fault, but also improves the rapidity and the reliability of the direct current voltage control when the direct current distribution network is disturbed.

2. The invention provides an improved master-slave control method of a direct current power distribution network aiming at the defect that master-slave control cannot realize switching of operation modes and stable direct current voltage control in case of communication faults.

3. The invention is suitable for both-end direct-current power distribution networks and multi-end and annular direct-current power distribution networks, and realizes that the output of active power can be accurately controlled from the converter station when the direct-current power distribution network operates in a steady state.

Drawings

FIG. 1 is a diagram of a double-ended hand-in-hand DC power distribution system according to the present invention;

FIG. 2 is a schematic diagram of a decoupled current inner loop controller in dq coordinate system according to the present invention;

FIG. 3 is a schematic diagram of a d-axis band dead zone adaptive droop controller of the present invention;

FIG. 4 is a schematic diagram of a q-axis reactive power controller of the present invention;

FIG. 5 is a diagram of simulation results of Simulink according to the present invention.

Detailed Description

The embodiments of the invention will be described in further detail below with reference to the accompanying drawings:

the medium-voltage direct-current power distribution system comprises two MMC converter stations, namely a main converter station and a slave converter station, as shown in fig. 1, the two converter stations form a double-end direct-current power distribution network structure in a hand-in-hand mode, wherein one converter station MMC1 is set as a main station, and the other converter station MMC2 is set as a slave station.

A master-slave control method for improving a direct current distribution network comprises the following steps:

step 1, designing a self-adaptive droop controller with a dead zone;

the specific steps of the step 1 comprise:

(1) measuring three-phase voltage and current of an MMC2 network side, and measuring voltage and current of an MMC2 direct current side;

(2) obtaining a reference phase theta and an angular frequency omega of an alternating current power grid through phase locking according to the three-phase alternating current voltage obtained through measurement in the step (1);

(3) d, carrying out dq conversion on the three-phase alternating-current voltage and current at the network side of the MMC2 according to the reference phase theta of the alternating-current power network obtained in the step (2) to obtain a d-axis component u of the voltage_dAnd q-axis component u_qObtaining d-axis component i of current_dAnd q-axis component i_q；

(4) U obtained according to step (3)_d、u_q，、i_d、i_qCalculating the active power P_gAnd reactive power Q_g；

(5) Designing the MMC2 AC-side outer-loop controller as constant-reactive power control, as shown in FIG. 4, and setting the reactive power reference value Q^*And MMC actual output reactive power Q_gCalculating q-axis reference value i of current inner loop through PI_q ^*(ii) a Designing the MMC direct current side outer ring control as the self-adaptive droop control with the dead zone, as shown in FIG. 3, thereby calculating the d-axis reference value i of the current inner ring_d ^*；

(6) Designing a decoupled current inner loop controller under a dq coordinate system, and calculating and obtaining an output voltage reference value required by MMC modulation through a PI controller, voltage feedforward and coupling compensation as shown in figure 2.

And 2, setting the MMC1 of the main converter station to be in a constant voltage control mode, and taking charge of controlling the direct-current voltage, and taking charge of active power regulation by adopting self-adaptive droop control with a dead zone for the MMC2 of the slave converter station.

In this embodiment, the MMC2 direct-current side outer loop design control in step (5) in step 1 is a dead-zone adaptive droop control, so as to calculate a d-axis reference value i of the current inner loop_d ^*The method comprises the following specific steps:

(1) according to the extreme operation condition of the power distribution network, calculating the maximum value U which can be reached by the voltage on the direct current side of the direct current power distribution network from the MMC2 when the direct current power distribution network is in stable operation_dc2maxAnd minimum value U_dc2min；

(2) According to U_dc2maxAnd U_dc2minDetermining a dead band upper bound value for an adaptive droop controller

And lower bound value

(3) According to the measured direct current voltage of the slave station MMC

And

determining a value of the sign function;

is provided with

(4) Designing the inverse of the adaptive droop coefficient

In the formula, P_2maxFor the maximum active power, P, that the MMC2 converter station can output₂ ^*The method comprises the steps that delta is a set value of active power of an MMC2 converter station, and is a maximum deviation range allowed by direct-current voltage;

(5) calculating the active power regulating quantity delta P of the slave converter station according to the direct current voltage_dc2 ^*＝sng^*β₂ ^*|ΔU_dc2|；

(6) Will be delta P_dc2 ^*With given value of active power P₂ ^*And a measured value P_g2The deviation is superposed and sent to a PI controller to form a self-adaptive droop controller with a dead zone, so that a d-axis reference value i of the current inner ring is calculated_d ^*。

In order to verify the effectiveness and superiority of the voltage control strategy, a double-end hand-in-hand direct-current power distribution network simulation system shown in the figure 1 is built through an MATLAB/Simulink toolbox. The main simulation parameters of the system are shown in table 1:

TABLE 1 Main simulation parameters of the System

Starting the direct-current power distribution network, when the direct-current power distribution network reaches a steady state in 1s, the load of the 1.2s direct-current power distribution network suddenly changes, the load suddenly changes from 0MW to 7MW, the 1.5s main station MMC2 suddenly quits operation due to faults, the 1.55s converter station is switched into a constant-voltage control mode, the system is simulated by respectively adopting a traditional master-slave control method and the improved master-slave control method, and the simulation result is shown in figure 5. As can be seen from fig. 5, when the conventional master-slave control is adopted, when a disturbance occurs to the dc power distribution system, the fluctuation range of the dc voltage is greater than that of the improved master-slave control strategy, after the 1.5s master station MMC2 suddenly quits operation due to a fault, the dc voltage deviation of the conventional master-slave control strategy exceeds 5% of the rated dc voltage value, and the improved master-slave control strategy always ensures that the dc voltage deviation range is within 5% of the rated dc voltage value. The effectiveness and superiority of the method are verified.

It should be emphasized that the examples described herein are illustrative and not restrictive, and thus the present invention includes, but is not limited to, those examples described in this detailed description, as well as other embodiments that can be derived from the teachings of the present invention by those skilled in the art and that are within the scope of the present invention.