大功率并联电流源变流器五电平特定谐波消除法

随着电压和功率等级的不断提高,并联电流源拓扑被广泛应用于中压大功率电流源系统的扩容.为解决并联电流源系统中直流桥臂电流不均衡和共模电压过高这2个问题,提出了一种应用于大功率并联电流源的五电平特定谐波消除(5L-SHE)调制方法,同时实现了直流桥臂电流的均衡控制和共模电压的抑制,并且保证了在较低开关频率下并网电流的电能质量.首先,按照脉宽调制(PWM)电流模长的不同将开关状态进行分类,并计算每个开关状态所对应的共模电压大小;其次,在分析冗余开关状态对直流桥臂电流均流影响的基础上建立了均流控制策略;再次,以共模电压较低的开关状态构建5L-SHE波形,并依据均流策略对冗余开关状态进行合理挑选.最后,通过仿真和实验验证了所提方法的有效性.

Five-level Selective Harmonic Elimination Method for High-power Parallel Current Source Converter

With the increase of voltage and power levels, parallel current source converters (CSCs) are widely used in the expansion of medium-voltage high-power current source systems. In order to solve the two problems of unbalanced DC bridge arm current and high common mode voltage in parallel current source systems, a five-level selective harmonic elimination (5L-SHE) modulation method for high-power parallel current source converters is proposed,which simultaneously achieves DC bridge arm current balancing and common mode voltage reduction, and ensures the power quality of grid current at low switching frequency. Firstly, the switching states of parallel CSCs are classified according to the norm of pulse width modulation (PWM) current, and the common mode voltage corresponding to each switching state is calculated. Secondly, the current balancing control strategy is established based on the influence analysis of the redundant switching states on DC bridge arm current. Thirdly, the switching state with lower common-mode voltage is selected to construct the 5L-SHE waveform, and the corresponding redundant switching state is reasonably selected according to the current balancing strategy. Finally, the effectiveness of the proposed method is investigated through simulation and experiment.