考虑三电平中点钳位型变换器中点电压波动抑制的混合调制方法

三电平中点钳位型变换器存在中点电压不平衡的固有问题。零序电压注入法可以很好地控制三电平变换器的中点平衡,而且具有原理简单、计算简便等优点,但是在调制系数比较大或者功率因数较低的情况下存在不可消除的低频波动。双调制波方法可以在全范围内消除中点波动,但其会造成开关频率的增大和谐波性能恶化。本文结合零序电压注入和双调制波混合调制方法的优点,达到了在消除低频波动的同时又能最大程度上降低开关频率和保持谐波性能的目的。仿真和实验结果证明了所提出的混合调制方法的正确性和可行性。

Hybrid PWM Strategy for Neutral Point Voltage Fluctuation Suppression of Three Level Neutral Point Clamped Converter

The essential problem of the neutral point voltage converters is that how to keep voltage balance of the dc-link capacitors. Zero sequence voltage can be injected to control the neutral point voltage balance of the three-level converter, but low frequency fluctuations cannot be eliminated when the modulation index is high or power factor is low. The double signal PWM method can eliminate the neutral point fluctuation in the whole range, but will increase the switching frequency and deteriorate the output waveforms of the inverter. In this paper, a hybrid modulation scheme is adopted to achieve the goal of eliminating the low frequency fluctuation and reducing the switching frequency. The above advantages of the hybrid modulation scheme are verified by simulation and experimental results.