基于MMC的内环优化控制策略研究

Research on Optimal Control Strategy of Inner Loop Based on MMC

当MMC系统与弱电网相连时,弱电网中存在含量较高的除基波外的其他低频的谐波,由于PI控制器对低频直流分量抑制作用较差,交流侧的低频谐波将会耦合到直流侧,导致直流电压的低频纹波干扰,甚至可能会降低并网电能质量。基于此,针对电流内环提出一种复合控制器,该控制器由PI环节与准比例-谐振控制器级联组成,用于改进传统内环控制器,从而实现直流分量的准确跟踪与抑制谐波干扰,提高电流内环控制器的鲁棒性与准确性。最后通过在MATLAB/SIMULINK上搭建仿真平台,验证了所提优化策略的有效性。

Modular Multilevel Converter(MMC)is currently one of the most commonly used topologies in the field of HVDC transmission,and the inner loop current controller in its control strategy generally uses PI controllers.When the MMC system is connected to the weak power grid,there are high content of lowfrequency harmonics other than the fundamental wave in the weak power grid.Because the PI controller has poor suppression of low-frequency DC components,the low-frequency harmonics on the AC side will be coupled to the DC side,causing low-frequency ripple interference of the DC voltage,and may even reduce the quality of grid-connected power.Based on the above issues,this article proposes a composite controller for the current inner loop.The controller is composed of a PI link and a quasi-proportional-resonant controller cascaded to improve the traditional inner loop controller to achieve accurate tracking and suppression of the DC component.Harmonic interference improves the robustness and accuracy of the current inner loop controller.Finally,by building a simulation platform on MATLAB/SIMULINK,the simulation verifies the effectiveness of the proposed optimization strategy.