三电平牵引变流器改进同步空间矢量调制策略

An Improve Synchronized Space Vector Modulation Strategy for Three-Level Inverter

高铁及城市轨道交通三电平牵引变流器由于受变流器开关损耗的限制,开关频率通常较低(≤1kHz)。当变流器运行于中、高频区域时,载波比的下降会导致变流器输出电压中含有大量的低次谐波,所以需要采用同步调制策略加以抑制,而传统同步空间矢量调制策略仅能保证变流器输出波形的同步性与对称性,并未对输出波形质量进行进一步的优化,导致变流器输出波形依然含有幅值较高的低次谐波。针对这一问题,该文以变流器输出波形同步性、三相对称性、半波对称性为条件,推导得到同步空间矢量调制开关序列设计规则。在此基础上,形成备选开关序列集,并以输出线电压加权总谐波畸变率(WTHD)为评价指标,得到了不同脉冲数下的最优开关序列并形成改进多模式同步空间矢量调制策略。通过仿真与实验分析,验证了所提策略可以有效提升牵引变流器中、高频区输出波形质量。

Due to the limitation of switching loss,the switching frequency of three-level traction inverter for high-speed railway and urban railway is usually low than 1kHz.If the inverter is operated in the medium and high frequency regions,the decrease of carrier ratio will lead to the increase of low-order harmonics in the output voltage,so synchronous modulation strategy should be adopted.The conventional strategy can only guarantee the synchronization and symmetry of the output waveform,and fails to further optimize the quality of the output waveform.As a result,the amplitudes of low-order harmonics in the output waveform are still high.The design rules of switching sequence for the synchronous space vector modulation(SVM)were deduced according to the restriction of synchronization,three-phase symmetry,half-wave symmetry and quarter-cycle symmetry.Then an alternative switching sequence set was established,and the optimal switching sequence was obtained by evaluating the weighted total harmonic distortion.Simulation and experimental results show that the proposed strategy can effectively improve the output waveform quality of traction inverter.