三电平变流器中点电位平衡及低开关损耗SVPWM策略

SVPWM Scheme for Three-Level Converters with Neutral-Point Potential Balancing and Switching Loss Reduction

分析二极管钳位型三电平变流器主电路原理。在此基础上,结合大功率变流器自身控制的要求与特点,基于不连续空间矢量脉宽调制(SVPWM)方法,提出一种能够同时降低开关损耗和控制中点电位平衡的混合调制策略。该策略包含通过检测变流器交流侧三相瞬时电流的方向以及直流侧两个电容的电压差值来切换矢量序列方式,实现中点电位平衡控制和选择电流最大相或较大相不动作来降低开关损耗两个部分,这两个部分之间采用滞环控制方式进行切换。最后,通过仿真和实验验证了所提混合调制策略不仅能够实现中点电位平衡控制,而且还能有效地减小开关损耗,实现算法简单,在工程实践上具有一定的实用性。

In this paper,working principle of three-level neutral point clamped(NPC)converter is analyzed.On this basis,combined with high power NPC control requirements and characteristics,a hybrid modulation strategy based on discontinuous space vector pulse width modulation(SVPWM)is proposed to reduce switching loss and keep neutral-point voltage balancing.The strategy consists of two parts.One is switching vector sequence to achieve neutral-point voltage balancing by detecting the direction of the three-phase instantaneous current at AC side and dc-link voltage difference,the other is applying no action principle of maximum or larger current phase to reduce switching loss.The switching between the two parts is controlled by hysteresis.Finally,the simulation and experimental results verify that the proposed strategy can effectively balance neutral-point potential and reduce switching loss.The algorithm is simple and has a certain practicality in engineering practice.