具备零电流开关与谐波抑制的电流源型变换器新拓扑

Novel Current Source Converter Topology with ZCS and Harmonic Suppression

为了克服传统电流源型变换器(current source converter,CSC)交流侧需要加装大容量交流电容器作为缓冲装置的缺点,将直流电流分配电路与传统并联式12脉波CSC相结合,研究了一种可以省去交流电容器并能有效抑制谐波的并联式7电平电流注入式电流源型变换器拓扑。该拓扑具有以下特点:通过开闭直流电流分配电路中的开关元件,将直流电流变换成2路幅值相同、相位互差30°、6倍于基波频率、7电平阶梯形周期变化且具有零值区间的三角波注入电流,两主桥开关元件在注入电流的零值区间内进行切换,实现了零电流开关(zero current switching,ZCS);变换器交流侧不需要配置大容量交流电容器,降低了设计成本,提高了系统的可靠性;主桥开关频率为50Hz的前提下,利用7电平阶梯形三角波注入电流可增加交流输出电流的电平数,改善了电流波形的谐波特性,使交流输出电流近似正弦波。另外还详细分析了新拓扑的工作机理,在PSCAD/EMTDC平台进行了仿真研究,搭建了实验平台,通过实验验证了理论分析的正确性和可行性。结果表明,所提出的新拓扑性能优良,结构简单,具有实用价值。

For a traditional current source converter （CSC）, a large capacity AC capacitor is required to be a buffer device on the AC side. To overcome this shortage, combining a DC current distribution circuit with the traditional parallel 12-pluse CSC, we figure out a seven-level current-reinjection CSC topology, which needs no AC capacitor but can effectively restrain harmonics. By switching the switches in the DC current distribution circuit, a DC current is distributed into two triangle-waveform reinjection currents, which have the same magnitude and the same frequency （six times the fundamental frequency） but a phase difference of 30°with each other. Moreover, the distributed currents have the same step case of 7-levels with zero periods, and the switches in the two main bridges commutate in the zero periods, i.e. the zero current switching （ZCS） is achieved. Furthermore, in this case, the large capacity AC capacitor is not necessary on the AC side of the converter, reducing the design cost and improving the system in reliability. Meanwhile, under the premise that the switch frequency of the main bridge is 50 Hz, making use of the 7-level-stepped triangular-waveform reinjection currents can increase the level number of the AC output current, so as to improve the output＇s harmonic characteristics and make it close to sinusoidal waveforms. The operation of the proposed topology is analyzed in detail, and is studied through simulations in the software PSCAD/EMTDC. All the simulative and theoretical results are finally verified by experiments on a newly-built experimental platform, and it is proved that the proposed topology performs well with its simple and feasible structure.