三电平动态电压恢复器的中点电位平衡问题

Neutral Point Voltage Balancing of Three-level Dynamic Voltage Restorer

此处针对不平衡电压暂降补偿工况下,中点箝位型(NPC)三电平动态电压恢复器(DVR)中点电位不平衡问题展开研究,分析表明此工况下的中点电位不仅存在3倍于输出频率的波动,而且存在更大成分的输出频率的波动。传统的双调制波方法仅适用于平衡补偿工况,此处对电压不平衡补偿工况下的双调制波算法的通用理论公式进行推导,证明双调制波方法可以在全范围内消除中点电位波动,同时平衡补偿工况仅是双调制波方法通用理论公式的一个特定工况。同时针对电压不平衡补偿工况下中点电位直流不平衡问题,提出一种适用于任意补偿工况的通用补偿量计算方法,并对边界值进行有效限制,中点电位直流平衡过程快速、有效。仿真和实验结果证明了所提方法的正确性和可行性。

The neutral point clamped(NPC)three-level dynamic voltage restorer(DVR)is studied.The analysis shows that the neutral point potential under the condition of voltage unbalance compensation not only Has a fluctuation of 3 times the output frequency,but also has a larger fluctuation of the output frequency.The traditional dual modulation wave method is only applicable to the balanced compensation condition.The general theoretical formula of the double modulation wave algorithm is deduced,and that the double modulation method is proved under this condition can eliminate the neutral point potential fluctuation in the whole range,and the balance compensation condition is only a specific condition of the general theoretical formula of the double modulation wave method.At the same time,aiming at the DC unbalance problem of neutral point potential,a general compensation calculation method suitable for any compensation condition is proposed,which makes the balancing process fast and accurate.This method takes into account the load current,switching frequency,capacitance value and voltage difference between upper and lower buses,and effectively limits the boundary value.Simulation and experimental results show the correctness and feasibility of the proposed method.