基于下垂控制的并联逆变器间环流控制策略

Circulating Current Control Strategy Between Parallel Inverters Based on Droop Control

针对线路阻抗差异导致微网在孤岛运行时存在功率耦合问题,传统下垂控制策略难以实现精确的功率均分,从而导致并联系统间存在较大环流。为此,首先建立了并联逆变器数学模型,在分析并联系统功率传输特性和环流特性的基础上,提出一种容性条件下的下垂控制策略。在传统下垂控制中加入虚拟电容,保证等效连线阻抗主要呈容性的同时,解决输出功率耦合以及引入虚拟阻抗导致的电压跌落问题;然后对无功环节进行改进,通过将固定不变的下垂系数改为变系数来改善功率均分精度,从而实现更好的环流抑制效果;最后,进行了仿真分析。结果表明,所提控制策略可以提高功率的均分精度,极大减小了环流,验证了控制策略的正确性和有效性。

In view of the power coupling problem of microgrid in island operation due to the difference of line impedance,the traditional droop control strategy is difficult to achieve accurate power sharing,which results in a large circulating current between parallel systems.To this end,a mathematical model of parallel inverters is first established,and a droop control strategy under capacitive conditions is proposed on the basis of analyzing the power transmission characteristics and circulating current characteristics of the parallel system.The virtual capacitor is added to the traditional droop control to ensure that the equivalent wiring impedance is mainly capacitive,and at the same time solve the output power coupling and the voltage drop caused by the introduction of virtual impedance;then the reactive power link is improved,by fixing the constant the droop coefficient is changed to a variable coefficient to improve the accuracy of power sharing,so as to achieve a better circulation suppression effect;Finally,a simulation analysis is carried out,and the results show that the proposed control strategy can improve the accuracy of power sharing,greatly reduce the circulating current,and verify the correctness and effectiveness of the control strategy.