负载不平衡条件下双PWM换流器控制策略

Control Strategy for Dual PWM Converter under Unbalanced Load

为解决低压配电网因负载不对称引起的输出电压不平衡问题,本文在传统的双脉宽调制PWM换流器基础上,设计了一种逆变侧四桥臂的换流器结构。该结构保留了整流侧的基本控制方法;逆变侧在对比传统电压电流双环控制的基础上,研究了一种改进双环控制策略,首先采用复系数滤波器实现对正、负序分量的分离和提取,然后通过设计正、负序电压同步控制取代传统的电压外环单独控制。通过改进的双PWM换流器,不仅能实现网侧背景谐波的有效隔离,更能消除逆变侧因负载不对称而引起的电压不平衡问题。通过PSCAD/EMTDC进行仿真验证,仿真结果表明所提控制策略行之有效。

To solve the problem of unbalanced output voltage caused by asymmetric load in low-voltage distribution net?work,a four-leg converter structure on the inverter side was designed in this paper based on a traditional dual pulse width modulation(PWM)converter.This structure retained the basic control method on the rectifier side.On the in?verter side,an improved double-loop control strategy was studied based on the comparison of traditional current and voltage double-loop control.First,a complex coefficient filter was used for achieving the separation and extraction of positive-and negative-sequence components.Then,the design of positive-and negative-sequence voltage synchroniza?tion control replaced the traditional outer voltage control.The improved dual PWM converter can not only isolate the background harmonics on the grid side effectively,but also solve the problem of unbalanced voltage caused by the asym?metric load on the inverter side.Finally,simulation experiments were carried out using PSCAD/EMTDC,and simula?tion results indicated the effectiveness of the proposed control strategy.