NPC三电平逆变器最优化虚拟电压矢量控制

摘要

The unbalanced neutral point voltage of three-level inverter can not only cause increased voltage stress on the switching device,but also increase the total harmonic distortion (THD) of the output current.So,the control of the unbalanced neutral point voltage of threelevel inverter is always the research focus for scholars.A control strategy that balances the neutral point voltage for three-level neutral clamped inverter systems is proposed.The proposed control strategy makes continual virtual voltage vectors with finite discrete voltage vectors of three-level inverter.Then,the cost function,which can flexibly control the comprehensive performance of the inverter,is defined according to the control goals including reference voltage and balance of neutral point voltage.The virtual voltage vectors,which track reference voltage and balance neutral point voltage,as well as minimize cost function,can be gotten with the optimization method.This method can not only guarantee good tracking effect of output voltage,but also has strong neutral point voltage balancing and anti-interference ability.Effective verification has been made by simulation and experiment.%三电平逆变器的中点电位不平衡不仅使开关管的电压应力增加,还会导致输出电流的谐波畸变率增高.因此,三电平逆变器的中点电位平衡控制一直是国内外学者的研究热点.以中点钳位型(NPC)三电平逆变器作为研究对象,提出了一种最优化虚拟电压矢量中点电位平衡控制方法.该方法首先以三电平逆变器固有的有限个离散电压矢量为基础,构造出连续的虚拟电压矢量.然后以参考电压和中点电位平衡为控制目标定义代价函数,此代价函数可以灵活方便地控制逆变器的综合性能.由最优化方法求解出使代价函数值最小的虚拟电压矢量,即为控制参考电压和中点电位平衡的全局最优解,此方法不仅可以保证输出电压有较好的跟踪效果,还具有较强的中点电位平衡能力和抗干扰能力.仿真和实验都对此进行了有效的证明.