考虑中点电压不平衡的中点箝位型三电平逆变器空间矢量调制方法

论述了中点电压偏移时，中点箝位型(neutral point clamped, NPC)三电平逆变器的空间矢量调制方法(space vector pulse-width modulation，SVPWM)。当中点电压偏移时，电压矢量本身的变化和平衡算法所带来的冗余矢量作用时间所引起的合成误差。经计算得到不同调制度时的合成误差曲线。将中点电压的不平衡因子引入矢量的选择和作用时间的计算中，利用不平衡因子调整矢量作用时间。比较了当逆变器带有异步电机负载时，传统矢量调制方法和改进的调制方法在电机启动过程系统的响应特性。表明改进的算法不仅能使三电平逆变器的输出电压谐波含量大幅减少，并且中点电压不平衡、电机转矩脉动、电流畸变也大幅度减小。

SVPWM Algorithm for NPC Three-level VSI Considering Unbalance Neutral Point Voltage

When unbalanced neutral point voltage occurring, a novel space vector PWM (SVPWM) for three-level neutral-point-clamped (NPC) voltage source inerter is discussed. There are two causes that make for the output vector synthesis error, one is the voltage vector variation due to neutral point voltage unbalance, the other is dwell time distribution of redundancy small voltage vector aiming to control voltage of neutral point. Based on analysis of the two causes, the angle and magnitude error curves are acquired by computing in different modulation index. Aimed at defaults above, an improved SVPWM control strategy is proposed based neutral point voltage distortion factor feed-forward. The comparison between traditional SVPWM and the improved SVPWM is verified by prototype in laboratory when inverter driving an induction motor. The results indicate that the output voltage waveform is improved not only，but also the distortion of neutral point voltage, torque ripple of induction motor and is decreased.