柔性直流输电系统换流器损耗与电压等级的关系研究

柔性直流输电一般采用模块化多电平换流器（MMC），换流器损耗是衡量柔性直流输电系统的重要指标之一。推导了MMC子模块的通态损耗解析表达式、开关损耗解析表达式。从表达式可以看出，换流器损耗不仅与MMC子模块数量有关，还与柔性直流输电系统的容量、电压等级有关。详细分析了柔性直流输电系统容量与电压等级对换流器损耗的影响规律，得出了保证损耗最低的换流器输电电压等级的选取方式。仿真算例表明，采用所提方法确定的电压等级可以保证MMC换流器具有更低的损耗。

Relationship between the Power Loss of Modular Multilevel Converter and Transmission Voltage Level

Normally MMC (modular multi-level converter) is adopted in the flexible HVDC transmission system. The power loss of converter is one of the most important indexes to evaluate the performance of flexible HVDC system. In this paper, an analytical expression for the on-state and switching loss of MMC is derived. As can be seen from the expression, the power loss of converter is not only related to the number of MMC sub modules, but also the capacity and voltage level of the flexible HVDC transmission system. In this paper, a detailed investigation of the influence of the capacity and voltage level of HVDC system on the power loss of converter is carried out, so as to identify the optimal voltage class that reduces the power loss to a minimum. Simulation results show that the proposed method can be used to find out the voltage level that helps lower the power loss.