直接并联模块化逆变器零序环流抑制

Restraining Zero-Sequence Circulating Current of Directly Parallel Modular Inverters

新型FREEDM微网中,采用逆变器直接并联技术可提高固态变压器的并网容量,但受到运算放大器零点漂移、谐波扰动以及信号延迟等因素的影响,该技术存在严重的零序环流问题。在并联逆变器间零序环流的平均模型和同步旋转坐标模型基础上,分析dq0坐标轴参考信号与输出电压的关系,提出理想机模型对PWM调制波参考信号进行误差反馈调节,实现各逆变器之间互不干扰地进行零序环流抑制,采用顺序控制方案,增加了控制器的调节效率和准确度。在PSCAD/EMTDC环境下仿真结果表明,所采用控制策略对零序环流具有有效的抑制作用,同时提高了功率均分的准确度。

In the FREEDM microgrid, direct parallel inverter technology can improve the capacity of solid state transformers. However, there will be large zero-sequence circulating currents, due to the impacts of the zero drift of operational amplifiers, harmonic disturbances and signal delay. Based on the average model and synchronous rotating coordinate model of zero-sequence circulating currents among direct parallel inverters, this article analyses the relationship between dq0 reference signal and the output voltage. Then an ideal machine model is proposed, to regulate the reference voltage of PWM carriers with error feedback according to a certain order, and to realize the zero-sequence circulating currents restraining and power sharing. The case study in PSCAD/EMTDC shows that the control strategy can restrain the zero-sequence circulating currents effectively, and improve the accuracy of power sharing.