基于SHEPWM的三电平NPC逆变器中点电位平衡控制算法

摘要

以三电平中性点钳位型(NPC)逆变器为对象,提出基于特定次谐波消除脉宽调制(SHEPWM)的中点电位平衡控制算法.首先介绍空间矢量脉宽调制中点电位平衡原理与SHEPWM开关角求解模型,然后分析三相SHEPWM波形在不同调制度下对应的开关矢量序列和作用角度,基于此设计了三种冗余矢量调整方案,最后通过检测负载电流与中点电位,由中点电位滞环控制器和控制逻辑组合作用,直接对三相脉宽调制信号进行在线调整,实现中点电位平衡.实验结果表明:不同的矢量调整方案具有不同的中点电位平衡速度、平均开关频率等,但均不影响线电压的谐波消除能力;采用中点电位三级滞环控制器可兼顾中点电位平衡、波形对称、共模电压幅值,且不增加器件开关次数.%A balancing control algorithm of neutral point potential for three-level neutral-point-clamped (NPC) inverter based on selective harmonics elimination pulse-width modulation (SHEPWM) is proposed.Firstly,the principle of neutral point potential balance for space-vector pulse-width modulation (PWM) and the mathematical model of SHEPWM are described.Then,the switching vector sequence and the switching angle corresponding to the three phase SHEPWM waveforms at different modulation indices are analyzed,with three kinds of redundant vector adjustment schemes designed.Finally,in order to realize neutral point potential balance,the load current and the neutral point potential are detected,and the three-phase PWM signal can be directly adjusted on-line by the hysteresis controller and the control logic.Experimental resnlts show that different vector adjustment schemes have different neutral point potential balancing speeds and average switching frequencies,none of which affects the harmonic elimination ability of line voltage.And the neutral point potential three-stage hysteresis controller can counterpoise the performance of the neutral potential balance,symmetrical waveform,amplitude of commonmode voltage,without increasing the nurnber of times of switching.