基于SHEPWM电压矢量寻优的中点电位平衡控制算法

Neutral Point Potential Balance Control Algorithm Based on Voltage Vector Optimization of SHEPWM

随着中高压大功率逆变器的快速发展,降低开关损耗、提高系统效率越来越受到重视,而降低开关损耗最常见的方法就是降低开关频率。降低功率器件的开关频率会导致输出电能的谐波特性变差,应用特定谐波消除脉宽调制(specific harmonic elimination pulse width modulation,SHEPWM)在低开关频率下能够保证良好的谐波性能,但中点钳位型(neutral point clamped,NPC)三电平逆变器在SHEPWM应用下存在固有的中点电位不平衡问题,需要进行中点电位主动平衡控制。为了保持SHEPWM良好的谐波特性和低开关频率特点,现有的开关角修正法和冗余小矢量法的中点电位控制能力较弱。针对两种传统中点电位控制算法的不足,提出了一种基于SHEPWM电压矢量寻优的中点电位平衡控制算法。通过建立中点电位代价函数,遍历电压矢量,同时实现了开关状态和作用时间的在线修正,加快了中点电位平衡速度。实验结果表明,在相同的冗余小矢量切换限制次数和开关角修正值下,电压矢量寻优法的中点电位平衡时间最短。所提出的算法兼顾了开关频率和平衡时间等因素,相较于两种传统平衡算法的单独应用具有更快的平衡速度。

With the rapid development of medium and high voltage high-power inverters,more and more attention has been paid to reducing switching loss and improving system efficiency.The most common way is lowering switching fre-quency,which can lead to a deterioration of the harmonic performance of the output voltage.Applying specific harmonic elimination pulse width modulation(SHEPWM)can achieve a good harmonic performance at low switching frequencies.However,there is an inherent problem of neutral point potential imbalance when SHEPWM is applied to neutral point clamped(NPC)three-level inverters,which asks for an active balance control.To keep the good harmonic performance of SHEPWM at low switching frequencies,the existing methods of switch angle correction and redundant small vectors have to live with a weak ability on neutral point potential control.To overcome these shortcomings,an algorithm of neu-tral point potential balancing is presented in this paper,based on optimization of SHEPWM voltage vectors.By establishing the cost function of neutral point potential and traversing the voltage vectors,the switching state and action time are both corrected online,and the process of neutral point potential balancing is sped up.Experimental results show that,under a limited number of switching redundant small vectors and a fixed value of correcting switching angles,the proposed algorithm holds a shorter balancing time compared with the two existing methods above,and balances the switching frequency and balancing time at the same time.