Circulating current suppression of converter excited wind power generation system with DC output

Recently, the research on HVdc transmission from offshore windfarm is attracting many researchers. Additionally, dc output from the wind power generator is expected to have some merits when it is connected to the HVdc transmission system. This paper shows new induction generation system for wind power generation with dc output. The authors propose the system which has the voltage source converter (VSC) exciting induction generator and the PFC converter to absorb the real power in parallel. In this scheme, the circulating current flows between two converters, since the DC side of VSC and PFC converter are connected commonly. The circulating current causes three phase imbalance in ac output and the rating and the cost of VSC increase. Decreasing the circulating current is necessary to have better performance of proposed system. This paper investigated the method of the circulating current reduction by the simulation, analysis and experiment. Then it is shown that shifting the phase of the switching signal of PFC converter. The VSC current is also decreased at the same time and enables cost reduction of the whole system.