Torque ripple analysis and reduction for wind energy conversion systems using uncontrolled rectifier and boost converter

A conventional topology for a small-scale wind energy conversion system consists of a permanent magnet synchronous generator, a diode bridge rectifier, a boost converter and a grid-side inverter. Since generator phase currents contain low-order harmonics and cannot be controlled independently using a diode bridge rectifier, electromagnetic torque ripple is relatively large and may have a detrimental effect on the life of the turbine through fatigue induced by shaft torque ripple. This study investigates methods to reduce this electromagnetic torque ripple, from both the viewpoints of the circuit topology and the control strategy. The effect of the DC-side capacitor on torque ripple is investigated and different control strategies and their effect on torque ripple are compared and analysed. This shows that the torque ripple can be reduced by removing the DC-side capacitor and can be further reduced by controlling DC-side current to a constant value. These methods have been investigated theoretically and the validity of the results confirmed by both simulation and experiment.