不平衡电网下PWM整流器功率补偿预测优化控制

Predictive Optimal Control of PWM Rectifiers With Power Compensation in Unbalanced Grids

PWM整流器广泛应用于并网电力转换系统,然而电网电压不平衡可能导致电能质量下降,影响变换器的正常运行。为了改善电网电压不平衡情况下的电能质量,针对PWM整流器提出了带功率补偿的模型预测功率控制(MPPC)策略。该方法通过使用电网电压、电流及其90°滞后信号在αβ静止坐标系中的分量计算功率补偿值,而无需复杂的正负序分量提取。此外,针对有限控制集模型预测功率控制(FCS-MPPC)由于开关频率可变而导致控制变量高波动的问题,提出了一种优化开关序列的模型预测功率控制策略(OSS-MPPC)。该方法基于多矢量合成,并通过对开关序列优化实现了固定开关频率控制,在消除有功功率脉动的同时显著改善了网侧电流质量。当电网处于不平衡状态时,通过与传统FCS-MPPC的仿真和实验结果进行对比,验证了PWM整流器可在所提OSS-MPPC控制策略作用下连续可靠运行。

PWM rectifiers are widely used in grid-connected power conversion systems,however,grid voltage imbalances can impair the power quality and the performance of the converter.To this end,The model predictive power control(MPPC)strategies with power compensation are proposed for PWM rectifiers to improve the power quality in case of imbalanced grid voltage.In the strategies,the power compensation value is calculated by using the grid voltage,current and their 90°lag signals in theαβstationary coordinate system;meanwhile,the complex component extraction can be avoided.In addition,an optimized switching sequence MPPC(OSS-MPPC)strategy is proposed in this paper to address the problem of high fluctuation in controlled volumes of finite control set MPPC(FCS-MPPC),which is caused by irregular switching frequency.The method is based on multi-vector synthesis and through optimization of the switching sequence to achieve fixed switching frequency control,which significantly improves net-side current while eliminating active power pulsations.When the grid is unbalanced,comparison by simulation and laboratory results with conventional FCS-MPPC verify that the OSS-MPPC strategy with power compensation in this paper can ensure the continuous and reliable operation of PWM rectifiers.