基于微分平坦理论的模块化多电平换流器控制器设计

Differential Flatness Based Design of Controller for Modular Multilevel Converter

简述了微分平坦理论的基本概念,根据其定义选取2组系统输出量,并证明了选取的2组输出量能使模块化多电平换流器满足微分平坦条件,因此,可采用微分平坦理论指导换流器控制器设计。根据微分平坦理论设计了相应控制器,其过程包括平坦输出参考轨迹生成和控制器实现。参考轨迹生成是根据系统期望输出在空间规划状态变量参考轨迹,控制器实现则根据系统输入方程产生期望前馈输入控制量。为消除换流器模型不确定性和内外部扰动等因素的影响,使用误差反馈补偿校正系统平坦输出,快速地跟踪参考轨迹。仿真结果验证了该控制系统设计的有效性。

After the brief description of differential flatness, according to its basic definition two sets of system output variables are chosen to certify that the two chosen output variables can make the modular multilevel converter （MMC） controller satisfying the condition of differential flatness, thus the differential flatness theory （DFT） can be applied to guide the design of MMC controller. A DFT based MMC controller is designed, and two aspects are involved in the design process： the generation of reference trajectories of flatness output and the implementation of the controller. The generation of reference trajectory is that the reference trajectories of state variables are planned in space according to the desired system output, and the implementation of the controller means to generate the desired feed-forward input controller variable according to system input equations. To eliminate the impacts of uncertainty of the converter model and such factors as internal and external disturbances, the error feedback compensation is used to calibrate system flatness output and to track the reference trajectories rapidly. Simulation results show that the design of the control system is effective.