飞跨电容型MMC状态误差反馈控制策略及稳定性分析

State Error Feedback Control Strategy and Stability Analysis of Flying-capacitor Modular Multilevel Converter

模块化多电平变换器(modular multilevel converter,MMC)在电机低速大转矩负载下运行时存在电容电压波动较大的问题,限制了其在中压传动领域中的应用。高频注入法可解决该问题,但会在电机侧引入高幅值的共模电压,因此提出飞跨电容型模块化多电平变换器(flying-capacitor modular multilevel converter,FC-MMC)。在子模块电容电压均衡基础上,FC-MMC采用多环反馈控制对各半桥臂平均电容电压、环流和输出电流进行控制,每个相单元需要3个电容电压外环,2个电流内环,共需8个PI(proportion integral,PI)参数,且多环控制系统的全局渐近稳定性无法证明。为此,文中建立三相FC-MMC的状态空间模型,提出状态误差反馈控制策略,对控制器的增益系数进行优化设计,并运用Lyapunov理论对闭环控制系统的稳定性进行分析。提出的方法与传统的多环PI控制相比,由于每个相单元只需要1个调节系数,避免了复杂的参数整定过程。仿真和实验结果表明,提出的控制策略具有良好的动静态响应性能。

Modular multilevel converter(MMC)have the technical challenges of large capacitance voltage fluctuation when the motor runs under constant-torque low-speed operation,which limits its application of medium-voltage variable-speed drive system.High frequency injection method can solve this problem,but high amplitude common mode voltage will be introduced into the motor side,so the flying-capacitor modular multilevel converter(FC-MMC)was proposed.On the basis of submodule capacitor voltage has been balanced,FC-MMC uses multi-loop feedback control to control the SM average capacitor voltage,circulating current and output current of each half-arm,each phase unit requires three capacitor voltage outer loops,two current inner loops,needs eight PI parameters,and the global asymptotic stability of the multi-loop control system cannot be proved.For these reasons,this paper established the state space model of three-phase FC-MMC for the first time,proposed a state error feedback control strategy and optimized the tuning gain,and proved the stability of the proposed control strategy based on Lyapunov theory.Compared with the traditional multi-loop PI control,the method proposed in this paper only needs one tuning gain for each phase unit,which avoids the complex parameter tuning process.The simulation and experiment results show that the proposed control strategy has good dynamic and static response performance.