一种T型NPC三电平三相四桥臂中点电位控制策略

A Novel Strategy of Neutral Point Potential Balancing for T-NPC Three-level Three-phase Four-leg Inverters

T型中点箝位三电平(TNPC)逆变器因其损耗低、效率高已被广泛应用,但中点电位平衡是关键问题之一。针对中点电位偏移,采用直流侧并联半桥模块并且中线串接电感构成第四桥臂的结构,分析了第4桥臂数学模型及在三相负载平衡和不平衡工况下中点偏移电压谐波次含量,根据中点偏移电压谐波次含量不同提出基于PIR比例积分谐振的电压电流双环控制。该方法能够实现第4桥臂与TNPC独立控制,仿真和实验结果表明该方法能够保证直流侧中点电位平衡。

T-type neutral point clamped（TNPC） grid-connected inverter has been widely used for its low loss and high efficiency, but the neutral-point potential balancing is one of the key issues. In view of neutral-point potential deviating,this paper adopts the DC side shunt half-bridge-module and the midline concatenated inductance, which constitute the structure of fourth leg. This paper analyzed the mathematical model of the fourth leg and harmonic contents of the neutral-point potential under balanced and unbalanced load. Considering of the harmonic times of neutral-point potential,double loop control based on PIR（proportional integral resonant） controller was introduced. This algorithm can realize independent control of fourth leg and TNPC. Simulation and experimental results verify the validity of the neutral-point potential balancing in DC side.