Optimal design method for operation interval of modular multilevel flexible HVDC transmission power

The invention relates to an optimal design method for the operation interval of the modular multilevel flexible HVDC transmission power and belongs to the technical field of flexible HVDC transmission. According to the method, firstly, the sub-module capacitance voltage fluctuation, the voltage modulation ratio, the energy storage requirement, and the functional relationship between the valve flowcapacity and the power operating point are analyzed and deduced. Secondly, the running boundary of each power is drawn from the constraints of the energy storage requirement, the modulation ratio, and the valve flow capacity. An intersection is taken and then an optimized MMC-HVDC power operation interval is obtained. Based on the method, a running point, which might cause the DC bus voltage overvoltage or the bridge arm output voltage distortion in the power operation range defined by the submodule capacitance voltage fluctuation constraint, can be removed. Therefore, the smooth and safe operation of the MMC-HVDC tr