Control of Parallel Multirectifiers for a Direct-Drive Permanent-Magnet Wind Power Generator

This paper presents control strategies for a multi-megawatt direct-drive permanent-magnet wind power generator with parallel-operating rectifiers linked by common dc bus. A model of a number of n rectifiers in parallel with a common dc link and zero-sequence current dynamics are derived and analyzed. The parallel-operating control is designed to restrain currents that flow between the power modules caused by power-device discrepancy and asynchronous operation of the parallel units. The multiple sets of pulse width modulation driving signals are generated by individual current control and produced by carrier phase-shifting synchronously. Each converter module is independent of each other identifying the rotor position by using an observer. The currents of each module are balanced and synchronized with respect to each other producing the optimal total generator torque. The experimental results that were obtained on a 1.5-MW platform proved the effectiveness of the control strategies.