网压不平衡下环流注入对模块化多电平换流器的影响分析

Analysis of the Impact on Modular Multilevel Converter with Circulating Current Injection under Unbalanced Grid Voltage

在网压不平衡工况下,采用开关函数、三维图分析及函数拟合的方法,给出合理的环流注入策略,实现模块化多电平换流器(MMC)桥臂电流峰值、模块电压波动的降低。分析环流注入对桥臂电流峰值、有效值以及模块电压波动的影响,得出环流注入降低桥臂电流峰值的最佳相位与不同工况下注入环流幅值的限定公式,以及环流注入降低模块电压波动的最佳相位及其注入幅值的限定公式。综合考虑桥臂模块电流、电压耐受能力后,提出一种可以实现桥臂电流峰值限定及模块电压波动限幅的环流注入控制方法。最后通过Matlab/Simulink仿真与实验平台验证了理论分析的正确性以及提出方法的有效性。

Based on the switching function,the 3D-graph analysis and the fitting method,this paper proposes a reasonable circulating current injection method to reduce the peak value of arm current and the capacitor voltage ripple of the module under unbalanced grid voltage.The impacts of circulating current injection on the peak value and root mean square value of the arm current as well as the capacitor voltage ripple are analyzed.The best angle to minimize the peak value of arm current and the formula to limit circulation injection amplitude under different conditions are obtained,and the best angle to minimize the capacitor voltage ripple and its limited formula of amplitude are further obtained.Considering the tolerance of current and voltage in sub module,a circulating current injection method is proposed,which can limit peak value of arm current as well as the capacitor voltage ripple.Finally,the correctness of the analysis and the effectiveness of the proposed method are verified in Matlab/Simulink simulation and the experimental platform.