T型三电平光伏逆变器适应低电压穿越的调制策略探讨

Modulation Scheme for Low Voltage Ride Through of T-type Three-level PV Inverter

针对T型三电平逆变器在低电压穿越时存在的损耗分布不均,从而影响逆变器的可靠运行的问题,首先在T型三电平逆变器的损耗模型和热传递模型基础上,分析并比较了三电平逆变器在正常运行与低电压穿越时损耗分布和热应力,提出了一种适应低电压穿越的调制策略,通过合理分配冗余矢量,转移中间管的损耗,从而避免中间管过温而导致失效;然后,针对低电压故障和电压恢复过程中的存在三电平逆变器中点电压不均问题,改进了调制方式,通过在三电平逆变器低电压穿越的全过程,既实现了逆变器的损耗均匀分布,又减小中点电压的不平衡。最后,在250 k W的T型三电平光伏逆变器上进行了低电压穿越的实验验证。

Unbalance loss distribution may occur during low voltage ride through （LVRT） of three-level inverter. Based on the loss model and thermal model, the loss distribution of inverter was analyzed. An advanced modulation method was proposed. The loss of devices was redistributed by rearrange redundant vectors in space vector modulation （SVM）. Then, the dynamic neutral voltage balance was considered by eliminating average neutral current every frequency cycle. Both proper loss distribution and the NP voltage balance are obtained. At last, experiment in 500 kW T-type three-level inverter is implemented to verify this method.