Application of parallel back-to-back PWM converter on the direct-drive wind power system

Direct-drive wind power system needs full-scale power converters. To overcome the limits in the capacity and switching frequency, converters are connected in parallel which is simple, modular designed and easy to extend. The paper presents an effective control method to enable the parallel operation meet the demand of large current input. The carrier phase shift technique based parallel back-to-back PWM converter is used on the direct-drive wind power system, with a switching frequency as low as 1 kHz. Experimental results demonstrate the method achieve an equivalent high switching frequency, improve the waveforms of output currents while avoid internal circular currents. This is very important for full-scale power converters used in the wind power system.