Control of back-to-back-connected neutral-point-clamped converters in wind mill applications

This paper analyzes back-to-back-connected neutral-point-clamped converters in wind turbine applications. A control strategy for the grid-connected converter is proposed that is able to operate under unfavorable voltage conditions. The positive-sequence voltage detector is able to provide an accurate position of the grid voltage vector so that the controller is always synchronized. The wind generator, which is a permanent magnet machine with an external rotor, operates properly throughout a voltage-dip process. The task of balancing voltages on the dc-link capacitors of the back-to-back connection is performed by the modulation strategies. Simulation and experimental results are provided.