低压微电网下垂控制策略研究

Research on drooping control strategy of low-voltage micro-grid

在孤岛模式时通过把逆变器等效输出阻抗设计成近似感性的前期条件下采用频率/有功、电压/无功的传统下垂控制法,但由于输出的无功与线路阻抗有关而各逆变器位置分散使连接线路阻抗存在差异,故难以实现无功功率的合理分配。本文分析传统下垂控制原理,并通过虚拟电抗法把逆变器的等效输出阻抗设计成近似感性,在此基础上采用一种改进下垂控制策略。该策略通过调节下垂控制中的参考电压来大致补偿线路阻抗差异上的电压降落,同时配合一个动态下垂系数来代替传统的固定下垂系数动态调节输出的无功功率,从而改善微电网无功功率输出的分配精度抑制系统环流。最后通过MATLAB/Simulink搭建两台逆变器并联运行模型并采用传统下垂控制与改进下垂控制相比较的方法验证改进控制策略的可行性。

In the island mode,The conventional droop control method of frequency/active power,voltage/reactive power is adopted when the equivalent output impedance of the inverter is designed to approximate the precondition of sensibility.However,due to the output reactive power is related to the impedance of the line,and the positions of the inverters are dispersed to make the impedance of the connection line different,it is difficult to achieve a reasonable distribution of reactive power.In this paper,the traditional droop control principle is analyzed,and the equivalent output impedance of the inverter is designed to be approximated inductive by the virtual reactance method.Thus,an improved droop control strategy is adopted to solve it.This strategy roughly compensates for the voltage drop on the line impedance difference by adjusting the reference voltage in the droop control.At the same time,a dynamic droop coefficient is used in place of the traditional fixed droop coefficient to dynamically adjust the output reactive power,Thus,the distribution accuracy of reactive power output of microgrid can be improved and the system circulation can be suppressed.Finally,a parallel operation model of two inverters is built by MATLAB/Simulink,and the feasibility of the improved control strategy is verified by comparing traditional droop control with improved droop control.