Bidirectional speed range extension of DFIG‐based WECS with dynamic minimum dc‐bus voltage

Abstract

Enlarging the speed range of wind turbines is an effective way to increase power production in low-frequency band wind which contains more energy and is very challenging for DFIG-based wind energy conversion system (WECS). The analysis shows that current controllability of the converter is the main factor limiting bidirectional speed range extension (BSRE). This problem can be solved by increasing dc-bus voltage, but a constant and high dc-bus voltage will increase the electrical stress and switching losses of the converter. This paper proposed a dynamic minimum dc-bus voltage (DMDCV) technique in which the dc-bus voltage can automatically adjust to enable the back-to-back voltage source converter to work in linear modulation mode at its minimum value, thus supporting BSRE while also achieving multiple goals including low electrical stress and low switching losses. Two implementation methods of DMDCV with and without modulation depth loop are proposed and discussed. The co-simulation results verified the feasibility of DMDCV and the advantages of BSRE in improving power generation.