MMC-HVDC系统的低频模型预测控制方法

Research on Model Predictive Control for MMC-HVDC with Low Switching Frequency

由于模型预测控制(model predictive control,MPC)具有原理简单、可同时实现多目标控制等优点,在模块化多电平换流器(modular multilevel converter,MMC)中应用越来越多,但传统模型预测控制存在计算量大、换流器开关频率高等问题。提出一种改进的模型预测控制方法,首先利用交流电流指标函数寻找最优开关状态组合,其次根据相邻时刻上子桥臂投入模块数目的变化,对开关状态组合进行优化,最后设计一个综合指标函数同时完成子模块电容电压平衡控制与环流抑制。该方法大幅减少了寻优过程的计算量,且降低了换流器的平均开关频率,减小了系统损耗,适合应用于MMC系统。基于MATLAB平台搭建了11电平三相MMC-HVDC仿真系统,仿真结果验证了所提方法的有效性和正确性。

Being simple in principle and capable of controlling multiple objectives, the model predictive control （MPC） is more andmore widely used in modular multilevel converter （MMC）. However, the traditional MPC strategy has the problems of largecomputation and high switching frequency. An improved MPC method is thus proposed in this paper. Firstly, the current costfunction is used to find the optimal combination of switch states; and then, the combination of switch states is optimized according tothe input modular number on each sub-bridge arm at the adjacent time; finally, an integrated cost function is designed to control thecapacitor voltage balance and eliminate the circulating current. The proposed method not only substantially reduces the calculationburden, but also reduces the average switching frequency of MMC and the power system＇s energy consumption, and is thusapplicable to MMC system. An 11-level three-phase MMC-HVDC simulation system is established based on Matlab, and thesimulation results have verified the effectiveness and feasibility of the proposed method.