基于占空比调制的模块化多电平换流器模型预测控制

近年来,模型预测控制因其原理简单、控制方式直接、多目标控制容易实现等优点被广泛应用于模块化多电平换流器(MMC).但当前的模型预测控制方法主要存在开关频率不固定、各模块功率损耗不均衡、平均开关频率较高等问题.文中提出一种基于占空比调制的模型预测控制方法.首先,根据交流输出电流和环流的控制目标,利用MMC离散数学模型,逆向推导得到桥臂电压差与电压和的参考值,并将其直接换算为上下桥臂投入模块数的占空比.然后,利用载波进行调制并结合所提子模块电容电压平衡方法,实现了MMC定频控制.所提方法无须对目标函数进行遍历寻优和权重系数调节,计算量低且与子模块数量无关,容易实现子模块故障容错.最后,仿真和基于StarSim软件的实验验证了所提方法的有效性和正确性.

Duty-cycle Modulation Based Model Predictive Control of Modular Multilevel Converter

In recent years, model predictive control (MPC) has been widely used in modular multilevel converters (MMCs) because of its advantages such as simple principle, direct control pattern, and easy realization of multi-objective control. However, the existing MPC methods mainly have the problems such as inconstant switching frequency, unbalanced power loss of each module, and high average switching frequency. This paper proposes a duty-cycle modulation based MPC method. First, according to the control objectives of AC output current and circulating current, the discrete mathematical model of MMC is used to reversely derive reference values of difference and the sum values for the bridge arm voltage, and the reference values are directly converted to the duty cycle of the number of modules in the upper and lower bridge arms. Then, the carrier is used for modulation and combined with the proposed voltage balance method of the sub-module capacitor to achieve the constant frequency control of MMCs. The proposed method does not need to traverse the objective function and adjust the weight coefficient, the calculation amount is low and has nothing to do with the number of sub-modules, and it is easy for the method to achieve the fault tolerance of sub-modules. Finally, simulations and StarSim software-based experiments verify the effectiveness and correctness of the proposed method.