降低模块化多电平换流器子模块电容值的控制方法

模块化多电平换流器(MMC)因必须对子模块电容电压波动范围进行限制,导致所需的子模块电容值较大,带来较大的成本和体积问题。提出了一种降低MMC所需电容容量的运行方式和参数设计方法。所提方法将子模块电容电压直流分量的实际运行值适当降低一定的比例,使电容电压波动的最大允许幅度增大,使选择较小的电容值成为可能。详细分析了所提方法的运行方式。为使所提出的降低电容容量的运行方式能够更好地实现,还提出了一种可以实现交流端口电流、直流端口电流和内部环流解耦控制的桥臂瞬时电流直接控制方法。通过这一方法可以直接控制换流器的内部环流分量,并能够动态调节各桥臂子模块电容电压。通过RT-LAB平台对所提出的运行方式进行了详细的仿真研究,验证了其可行性和有效性。

A Control Strategy for Reducing Submodule Capacitance Value of Modular Multilevel Converter

For modular multilevel converters (MMCs), a quite large capacitor is required to limit the ripple component of the capacitor voltage, which causes size and cost problems. A new operation mode and control strategy is proposed to reduce the capacitor requirements of MMC. In the proposed operation mode, the DC voltage of the submodule is appropriately decreased to make the maximum permissible ripple voltage increased and the choice of a smaller capacitor possible. The required capacitance in the proposed operation mode is analyzed at length. To implement the proposed operation mode, an instantaneous current control strategy is proposed to directly control the MMC arm currents. In the proposed control strategy, the AC-side current, the circulating current, and the DC-side current can be controlled, respectively. The simulation results using RT-LAB have verified the feasibility and effectiveness of the proposed operation mode and control strategy. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2011AA05A102).