Analysis of a High-Power, Resonant DC-DC converter for DC Wind Turbines

This paper is introducing a new method of operation for a series resonant converter, with intended application in megawatt high-voltage DC wind turbines. Compared to a frequency controlled series resonant converter operated in sub resonant mode, the method (entitled pulse removal technique) allows the design of the medium frequency transformer for highest switching frequency, while being operated at lower frequency without saturation. The main focus of this paper is to identify and analyse the operating modes of the converter with pulse removal technique. With the use of variable frequency and variable phase displacement in sub resonant mode, the new method of operation promises transformer size reduction and facilitates soft-switching transition of the IGBTs and line frequency diodes on rectifier side. Four modes of operation are identified, while equations for output power, voltage and current stress are identified. Experimental results are concluded on a 1 kW, 250V / 500V prototype.