不平衡工况下基于虚拟阻抗法的并联三相四桥臂逆变器的桥臂控制

摘要

Under unbalanced conditions,the three-phase four-leg inverter parallel system not only can output balanced three-phase voltage waveforms,but also can expand the capacity of the system.Compared with the traditional three-leg inverter parallel system,the three-phase four-leg inverter parallel system need to control the positive,negative and zero sequence current,so the control of three-phase four-leg inverter parallel system is more complex.In this paper,the distribution of the sequence current in parallel operation of three-phase four-leg inverter is analyzed.In order to make the inverter output of positive,negative and zero sequence current to distribute according to the parallel inverter capacity.This paper puts forward a new control method that the positive sequence current uses a droop control,negative sequence current and the fourth leg current use virtual impedance method respectively control the positive sequence current,negative sequence current and zero sequence current distribution of the inverter output,and the front three leg and the fourth leg of the three-phase four-leg inverter control independently.Finally,the output voltage is balanced at the same time the output current and the output power of the parallel system are distributed according to the capacity of the parallel inverter under unbalanced conditions,and the circulation of the system is reduced.The correctness of the method is verified by simulation and experiment.%不平衡工况下,三相四桥臂逆变器并联系统不仅可以输出平衡的三相电压波形,而且还可以拓展系统的容量.与传统的三桥臂逆变器并联系统相比,三相四桥臂逆变器并联系统需要对正序、负序和零序电流进行控制,因此三相四桥臂逆变器的并联控制系统更为复杂.该文对三相四桥臂逆变器并联运行时,各序电流的分配进行了分析.为了使逆变器输出的正序、负序和零序电流能够按并联逆变器的容量分配,提出了正序电流使用下垂控制、负序电流与第四桥臂电流使用虚拟阻抗法分别控制正序、负序和零序电流的分配,并且对三相四桥臂逆变器的前三桥臂与第四桥臂分别进行控制,最终在不平衡工况下使并联三相四桥臂逆变器系统输出电压平衡且输出电流和输出功率按并联逆变器的容量分配,减小系统的环流.仿真和实验验证了该方法的有效性.