Third harmonic injection by MMC-swiss rectifier for offshore HVDC wind turbine applications

Abstract

In this paper, Modular Multilevel Converter MMC-Swiss rectifier for harmonic mitigation is presented and simulated by PLECS software package. The mathematical calculations and system simulation are performed for a converter with nominal power of 400 MW and 400KV DC. The characteristic of Swiss rectifier including the operation principle, modulation strategy and relevant equations are described in detail. The MMC is used as a combination with Swiss rectifier because of its simplicity to be integrated for applications that required different level of voltages and currents, such as offshore wind turbine. Where, there is a trend to generate the electricity and transmit it in DC form due to its economic reasons. Therefore, the usage of MMC-Swiss rectifier is viable for High Voltage Direct Current HVDC applications. The contribution of Swiss rectifier is to make the current drawn from the supply by a converter, pure sinusoidal and this achieved by injecting third harmonic current in the circulating current from the DC side. Thus, this would reduce the THD and improve the power quality of the AC side currents.