用于光伏并网变换器的MMC控制策略研究

Research on MMC-Based Control Strategy of Grid-Connected PV Converter

为了解决模块化多电平变换器(modular multilevel converter,MMC)应用于大型光伏并网系统的电压不平衡以及环流过大等问题,本文提出将PIR控制器与电容电压排序法结合的控制策略。该方法可有效抑制环流电流中的直流和交流谐波成分,减小电容电压波动;结合排序法对直流电容充放电进行选择,减少控制系统中的PI调节参数,实现电容电压平衡。最后,基于Simulink构建了仿真模型,仿真结果表明,该控制策略不仅可实现模块化多电平变换器在并网过程中的均压和环流控制,还能有效改善电能质量。

In order to solve the problems,such as voltage unbalance and circulating current when applying modular multilevel converter (MMC)to large scale photovoltaic (PV)grid-connected system,a control strategy,which combines PIR controller and capacitance voltage sorting method,was proposed in this paper.By restraining the DC and AC harmonic components of circulating current,this strategy can reduce the capacitance voltage fluctuation.Moreover,the voltage balance was accomplished by using the sorting method to select the mode of charge or discharge of the DC capacitor which can reduce the parameters of PI control system at the same time.Finally,a model was designed based on Simulink,and the simulation results testify that the method can not only help modular multilevel in- verters realize voltage balance and circulating current control in syehronization,but also effectively improve the power Quality.