三电平中点箝位型逆变器中点电压平衡和控制方法研究

Research on neutral-point potential balancing and control method for three-level NPC inverter

建立了三电平中点箝位型逆变器中点电压的数学模型;分析了在不同的负载条件下,传统的最近三矢量合成方法中点电压存在不能平衡的区域;利用合成空间矢量的调制方法,实现了对中点电压的有效控制。为了在扇区切换时输出矢量平稳过渡,提出了在每个大区内全部采用相同首发小矢量的方法。用MATLAB/Simulink仿真研究了中点电压平衡控制的效果,并用MOSFET搭建了三电平逆变器实验电路模型,对中点电压平衡控制效果进行了验证。实验结果证明了基于合成空间矢量的三电平NPC逆变器中点电压平衡控制方法的有效性。

A significant problem with neutral-point-clamped three-level inverters is the fluctuation in the neutral-point voltage. The mathematics model of neutral-point potential is developed while the neutral-point potential is unbalanced. In this paper the limitations of neutral-point potential balancing problem for different loading conditions of three-level neutral-point-clamped inverters is explored. And a novel modulation approach for the complete control of the neutral-point potential is introduced. The new modulation approach, which bases on the virtual space vector concept, guarantees the balancing of the neutral-point potential for any load over the full range of converter output voltage and for all load power factors. In order to avoid the abrupt change of output voltage vectors during the process of desired vector changing from one section to another, a novel space vector modulation algorithm is proposed, in which the same small vectors are adopted as first active Vector. Some simulation and experiment results are given to validate the method.