Variable speed operation of permanent magnet alternator wind turbines using a single switch power converter

Advantages of operating wind turbine generators at variable speed are well known. Various approaches have been proposed to extract maximum power from the turbines by operating them at the optimum tip-speed ratio. Often, they feature a three-phase controlled rectifier d-c link followed by a three-phase inverter type of power converter topology to deliver constant frequency a-c output power from a variable speed generator coupled to the turbine. However, in stand-alone power supply applications for remote sites, where the power level is a few kW or less, this approach is economically unjustifiable. This paper presents a single switch power electronic converter to regulate the power output of a permanent magnet alternator driven turbine feeding a battery, featuring minimal additional costs suitable for low power applications. Power converter operation and a control strategy to maintain optimum tip-speed ratio are discussed in the paper. Computer simulations of the complete system verifying the proposed concepts are presented.