Power electronics systems used in wind energy conversion systems (WECS) are very important in modern variable speed large wind turbines and have become a focal point in the research of devices and their control mechanism. Most modern wind turbines operate at variable speed. This paper provides an in-depth review of power electronics systems used to interface variable speed wind turbine to the electric grid. The different variable speed induction generator-converter combinations are compared on the basis of topology, efficiency, cost and control techniques. Comparisons of the variable-speed and fixed-speed wind turbines (WT) are discussed. Moreover, attempts are made to highlight future trends and future challenges in power electronic systems in wind power generation.