不平衡电网下双dq坐标变换的M3C微分平坦控制策略

Differential flatness control strategy of modular multilevel matrix converter based on double dq coordinate transformation under unbalanced grid conditions

针对目前模块化多电平矩阵变换器(M3C)研究中常用的双αβ坐标变换解耦不彻底、传统PID控制方法效果差、不平衡工况研究少等问题,在分析拓扑结构和数学模型的基础上,采用双dq坐标变换对电气量进行解耦,建立了M3C的输入输出侧数学模型,分别对电压、电流进行正负序分离,并结合微分平坦理论,推导了输入侧、输出侧的微分平坦控制(DFC),最后模拟了两种不平衡工况下的运行情况。仿真结果表明,与线性PID控制相比,非线性的微分平坦控制提高了内环电流的跟踪速度和精度,更适用于非线性的M3C系统。在电网平衡或电网出现不对称故障时,微分平坦控制下M3C系统的动态稳定性与快速性更好,电能质量更高,电流谐波含量最多可以降低1.42%,能够更有效地抑制负序电流。

Aiming at the problems of incomplete decoupling of doubleαβcoordinate transformation commonly used in modular multilevel matrix converter(M3C)research,on the basis of the analysis of topological structure and mathematical model,poor effect of traditional PID control method,and little research on unbalanced working conditions,etc.,double dq coordinate transformation was adopted to decouple the electrical quantity.The mathematical model of M3C’s input and output side was established,the voltage and current were separated in positive and negative order,and the differential flatness control(DFC)of the input side and the output side was derived by combining the differential flatness theory.Finally,the operation under two unbalanced conditions was simulated.Compared with linear PID control,the simulation results show that nonlinear differential flat control improves the tracking speed and accuracy of inner loop current,and is more suitable for nonlinear M3C system.When the power grid balance or asymmetric fault occurs,M3C system under differential flat control has better dynamic stability and rapidity,higher power quality,and can suppress negative sequence current more effectively.The current THD can be reduced by up to 1.42%.