Loss calculation method and loss characteristic analysis of MMC based VSC-HVDC system

Modular Multilevel Converter (MMC) has been accepted as the most competitive alternative for Voltage Source Converter (VSC) HVDC application. It is a very important issue to evaluate the converter losses and efficiency for a VSC-HVDC installation. A method is proposed to calculate the losses of a MMC using a digital calculation way. The switching waveforms are simulated in the digital calculation and the voltage and current waveforms of a line-frequency period are thereby obtained. Then using the parameters provided in the device datasheet, the switching losses and conduction losses can be obtained. A digital calculation program was developed and the converter losses of a MMC are calculated for various operating conditions. The losses of various devices in a submodule are calculated. The impacts of the switching frequency and circulating current are also comprehensively analyzed.