一种用于平衡三电平逆变器中点电位的滞环控制+精确控制策略研究

Research on one hysteresis control + precise control strategy of three-level inverter for neutral-point potential balance

中点电位不平衡是二极管中点箝位(NPC)型三电平逆变器存在的固有问题,在学术及工程实践中受到了广泛关注。中点电位平衡控制方法可以分为两大类,硬件和软件方法,基于硬件的控制方法主要是依靠外部电路调整,一般通过Boost和Buck等电路对电容进行充放电来调节中点电位以达到平衡,因而增加了整个逆变器的成本。在深入分析引起中点电位不平衡因素的基础上介绍了一种提高中点电位鲁棒性的滞环控制+精确控制策略。该控制策略将滞环控制与精确控制方法相结合,设置一定的环宽作为两种算法的切换条件,超出设定环宽使用滞环控制,在环宽内使用精确控制方法。进行了仿真和实验验证,结果证明该方法解决了滞环控制粗略、存在控制盲区并且控制效果受功率因数影响大的问题,同时弥补了精确控制中当中点电压发生偏移以后不具备将中点电位拉回平衡点的能力。有效地抑制中点电位波动,提高中点电位控制的鲁棒性。

The unbalance of neutral-point potential is an inherent problem of three-level neutral point clamped（ NPC） inverter,it is paid wide range attention in academic research and engineering practice.This NPC method is divided into two types： hardware and software method. The hardware method mainly depends on external circuit to adjust,in with Boost and Buck circuit are used to control the capacitor charge and discharge and implement the balance of neutral point voltage. This method increases the cost of whole inverter. The factors were analyzed which cause the unbalance of neutral-point voltage,and one hysteresis and precise control strategy of improving the robustness of neutral-point voltage was introduced.This control strategy combines hysteresis control with precise control,and a certain band width is set as the two different control methods switching condition. If the neutral-point voltage exceeds the band width,the hysteresis control strategy was employed,and the precise control strategy was employed vice verse.The method was validated through simulation and experiment. The results of simulation and experiment show that the method solve the hysteresis control problem of rough control,existing blind area and influencing by power factor,at the same time,make up for the ability which balance the neutral point when the neutral voltage is one-sided during adopting the precise control. This method is effective to control fluctuation and deviation of neutral point voltage and improve robustness of neutral point control.