Design and performance evaluation of a unity power factor converter for wind energy conversion systems

Abstract

Wind turbine driven Permanent Magnet Synchronous Generators (PMSG) find increasing applications due to their numerous advantages. Small scale stand-alone wind energy systems are receiving considerable attention due to their importance in locations that are far flung and where conventional generation and grid interface may not be possible.In this work, a front-end diode bridge rectifier employing three current control methods- Average Current Control (ACC), Hysteresis Current Control (HCC) and Equal Distance Current Control (EDCC) - has been incorporated in a wind turbine- generator driven stand-alone system. These are implemented by controlling the switching periods of three bidirectional switches in the Unity Power Factor (UPF) front-end rectifier. The objective is to justify the relevance of this topology in a Wind Energy Conversion System (WECS) to achieve high input power factor, low Total Harmonic Distortion (THD) in the input line currents and extraction of maximum possible real power from the generator. From the studies conducted, it is concluded that the ACC consistently achieves an input power factor higher than 0.995, while the HCC achieves an input power factor of 0.994. This high input power factor is achieved during the constant wind speed as well as the variable wind speed conditions. The THD of the line currents is 6%- 7% for the ACC depending on the wind speed while it is 6%- 8% for the HCC. These values are acceptable for stand-alone systems. The efficiency of mechanical power to electrical power conversion is also high at 97% - 99%. The AC power available at the input of the UPF rectifier is transferred without significant losses to the DC bus link output. The system is simple in its topological construction and proves to be highly reliable and is appropriate for implementation in low to medium power stand-alone systems.