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

With numerous advantages, the direct drive, grid-connected permanent magnet synchronous generation system represents one important trend of wind power applications nowadays. With active controls, parallel operation is becoming a promising solution in three-phase power conversion. In order to solve the zero-sequence circulating current problem, a novel converter topology with isolated DC link dual back-to-back PWM parallel converter has been proposed for the application of PMSG to the VSCF power conversion. A carrier phase shifted (CPS-SPWM) technique is used in parallel converter systems in order to reduce current ripples. Carrier phase shifted technique based on paralleling back to back PWM converter was applied on direct drive wind power system. Good performance is attained even if the switching frequency is only 1 k Hz as shown in the experimental results, which means that high equivalent switch frequency and current waveform under low switch frequency condition are realized. At the same time, avoid a zero-sequence circulating problem.