基于电力电子变压器的优化级联多电平变换器矢量均压算法

Optimized Vector and Voltage Balancing Algorithm for Cascaded Multilevel Converter Based on Power Electronics Transformer

级联多电平变换器由于具有较好的灵活性与易模块化使得其在电力电子牵引变压器(power electronic traction transformer,PETT)系统中得到了广泛应用。而该变换器功率单元间电压不平衡是其亟待解决的问题。针对该问题,提出一种适应于多电平变换器的空间矢量(space vector pulse width modulation,SVPWM)脉宽调制均压算法。算法以三功率单元级联变换器为例,首先构造级联变换器的矢量分布三维图并确定系统冗余矢量;其次,利用能量守恒原则以系统平均电压为基准,通过在每一时刻实时对比各个功率单元与平均电压的差异来决定下一时刻各功率单元输出电平变化趋势,且确保所变化数值最小。相比于传统矢量均压算法,所提算法不仅能均住各功率单元带不同工况负载时的直流电压,且确保功率单元的开关管动作次数与电压应力达到最小,使得开关损耗减少、系统效率与器件运行寿命提升,此外算法可计算且便于扩展。最后,通过Matlab/Simulink软件与小功率实验平台共同验证所提均压算法的正确性与可行性。

The cascade multilevel converter has been widely used in power electronic traction transformer(PETT)system because of its good flexibility and modularity.However,the unbalanced voltages between different power cells is an inherent issue to be urgently solved.In order to solve this problem,an optimized space vector pulse width modulation(SVPWM)voltage balancing algorithm is proposed in this paper.A three-power-cell cascaded multilevel converter is taken as an example to construct three-dimensional(3-D)space vector distribution space and then the redundant space vectors are generated along with.In addition,based on the average voltage,the variation tendency of output voltages at next dwelling time can be determined by the comparison between the dc-link voltages in all power cells and the average voltage.Also the minimum number of switching transition can be guaranteed simultaneously.Compared with the generalized algorithms,the proposed algorithm can not only balance the unbalanced voltages under the conditions of different unbalanced voltages,but also achieve the minimum voltage stress,which can reduce the switching loss,improve the system efficiency and increase its service life.The proposed algorithm is calculable and extensible and is finally verified by simulation and experimental results.