CONTROL OF IMPROVED FULL BRIDGE THREE LEVEL DC/DC CONVERTER FOR PMSG BASED WIND TURBINES IN A DC GRID

Abstract

The systematic procedure leading to the improved three level dc/dc converter for wind energy conversion systems is discussed. A feed forward control scheme that ensures the proper functioning of this converter is proposed. Moreover, the merits and demerits of this converter as compared to conventional converters is highlighted. In particular, the advantages of TL converter includes reduced voltage stress of the switches, reduced filter size, and improved dynamic response. It is shown that TL converters are highly suitable for high input/output voltage and medium-to-high-power dc—dc power conversions. A full-bridge three level dc/dc converter for a wind turbine in a dc grid is improved by inserting a passive filter into the dc/dc converter to improve the performance of the converter. The passive filter can effectively reduce the voltage stress of the medium frequency transformer in the improved full-bridge three level (IFBTL) dc/dc converter. A modulation strategy, including two operation modes, is proposed for the IFBTL dc/dc converter. Then, a voltage balancing control strategy is proposed for the IFBTL dc/dc converter. Furthermore, the control of the wind turbine based on the IFBTL dc/dc converter in a dc-grid system is presented.