模块化多电平变流器内部动态的阻尼控制方法

Damping Control Method of Internal Dynamics for Modular Multi-level Converter

建立模块化多电平变流器(modular multilevel converter,MMC)内部动态数学模型,模型以上下桥臂储能和环流电流为状态变量,分析直接调制和间接调制方式下桥臂电容电压储能的稳定性,考虑数学模型中存在的时变参数均为工频周期变量,采用线性周期时变(linear time periodic,LTP)系统分析方法,通过计算庞加莱(poincare)算子判断系统稳定性。进一步推导MMC内动态误差状态方程,基于此判断出系统阻尼完全由桥臂损耗和等效电阻提供,属于弱阻尼特性,对此,提出基于直流电流反馈的阻尼控制方法,经PSCAD仿真验证所设计控制方法正确,有效。

An internal dynamic mathematical model of a modular multi-level converter （MMC） was established. Energy stored in upper and lower arms and circulation current were chosen as state variables. Stability of energy stored in arms was analyzed under both direct and indirect modulation methods. Linear time periodic （LTP） method and Poincare operator were used to adapt to periodic time-varying parameters in mathematical models and to determine system stability. Furthermore, error dynamic equation of MMC was deduced. Based on this, it is known that the damping of the system is completely caused by the arm loss and an equivalent resistance. Since the equivalent resistance is relatively small, the MMC becomes a weak damping system. The damping control strategy based on DC current feedback was proposed. The feasibility and performance of the designed control method were verified by PSCAD simulation.