Control of Parallel Multiple Converters for Direct-Drive Permanent-Magnet Wind Power Generation Systems

This paper proposes control strategies for megawatt-level direct-drive wind generation systems based on permanent magnet synchronous generators. In the paper, a circulating current model is derived and analyzed. The parallel-operation controllers are designed to restrain reactive power circulation and beat-frequency circulation currents caused by discontinuous space-vector modulation. The control schemes do not change the configurations of the system consisting of parallel multiple converters. They are easy to implement for modular designs and large impedance required to equalize the current sharing is not needed. To increase the system reliability, a robust adaptive sliding observer is designed to sense the rotor position of the wind power generator. The experimental results proved the effectiveness of the control strategies.