模块化多电平换流器的直流侧主动充电策略

A DC-side Active Charging Strategy for Modular Multilevel Converters

柔性直流输电工程中,无源端的换流阀通过有源端进行预充电,子模块电压最多只能充到额定电压的一半。如果按照正常解锁逻辑,会产生非常大的直流过电流,因此必须通过主动充电策略将子模块的电压充到额定值。文中结合模块化多电平换流器直流侧不控充电及正常运行的特点,设计了通过逐步递减投入子模块个数的直流侧主动充电策略,可以实现无源端换流阀从直流侧不控充电状态至正常解锁运行状态的平滑过渡。同时,分析了直流侧主动充电过程的桥臂电流特性。最后,通过仿真和实际工程应用验证了设计的直流侧主动充电策略的可行性。

In the voltage source converter based high voltage direct current （VSC-I-tVDC） transmission project, the converter valve of the passive terminal must be pre-charged via the active terminal, while the sub-modules can only be charged to half the rated voltage at most. A very large DC current will be generated if the converter is deblocked in normal logic. So the submodules must be charged to the rated voltage by an active charging strategy. According to the characteristics of DC-side uncontrolled charge and normal operations of the modular multilevel converter （MMC）, a DC side active charging strategy for progressively decreasing the operated sub-modules is designed. The strategy makes possible the smooth transition of the converter valve of the passive terminal from the uncontrolled charging state to the normal deblocked operation state. Besides, the characteristics of the bridge arm current in the DC-side active charging process are analyzed. Finally, simulation results and the project application have verified the strategy designed.