开关损耗优化的级联型逆变器全区域空间矢量调制策略

Switching Loss Optimized SVPWM Algorithm for Cascade Multilevel Inverters in all Region

利用错时采样技术将级联型逆变器的多电平空间矢量脉宽调制(SVPWM)简化为逆变器各层采样点相互错开,每个采样点仅需控制某层3个功率单元的分解三电平SVPWM调制;通过分析功率单元H桥电路的内在关系,本文从三电平短矢量的6种冗余开关形式中选出一种开关损耗最优的开关动作序列;推导出逆变器正常运行状况下的线性调制策略,以及故障运行状况下维持输出基波电压不变的三电平过调制策略;最后利用傅里叶级数推算出线性调制和过调制区域内输出基波和谐波电压幅值的计算公式。通过样机实验表明,本文提出的调制策略在保证开关损耗最优的前提下,不仅可以应用于线性调制区域,而且也可以应用于过调制区域,同时两个区域内都能保证基波电压的幅值随调制比成线性输出关系。在功率单元直流电压下降或部分功率单元故障旁路时,使用过调制策略可以使系统从线性工作状态平稳过渡到六阶梯波状态,直至六阶梯波时输出最大值;同时,相应过调制算法易于软件实现,是一种适用于级联型逆变器的全区域调制方法。

This paper applies sample time staggered technique to make the sample time stagger happened between the layers of the cascade multilevel inverters.However it could not only control three power cells of any certain layer,but also the multilevel SVPWM problem is simplified,and becomes a decomposition three-level SVPWM.Secondly,by analyzing the relation among the power cells of cascaded multilevel inverters.This paper proposes a novel optimal switching loss action sequence picked from six redundancy short vectors of three levels of H-bridge.Thirdly,it derives a linear modulation algorithm under normal condition,and an over-modulation algorithm under fault condition.In the last,the equation of the fundamental and harmonic voltage amplitude is derived by fourier series in linear modulation and over-modulation regions.The experimental result demonstrates that the linear and over-modulation methods mentioned by this paper could be applied in each region and could keep fundamental component amplitude with the modulation ratio in a linear relationship,meanwhile the switching losses are optimized.The over-modulation method could smoothly transform the inverter from linear condition to six pulse condition,when the DC voltage of power cell dropping and any power cell bypassed.Of course,it could be easy to develop the over-modulation software,so it may be a simple elegant solution for space vector pulse width modulation in cascaded multilevel converter.