Current equalizing for a multi-modular current source converter

Phase-shifted SPWM technique is adopted to control a directly-paralleled multi-modular current source converter for super-conducting magnetic energy storage system (SMES) to reach high power and low harmonics. The phase-shifting of the carriers results a serious current unbalance between each converter modules when the high power switch devices work on low switch rate. This paper analyses the problems of the classic current balancing methods and introduces the carrier-swapping method into phase-shifted SPWM technique, to eliminate such current unbalance in a multi-modular current source converter without adjusting the amplitude and phase angle of the modulation waveforms of each module respectively. Experimental results are given to prove the effectiveness of current equalization provided by the carrier-swapping method.