Circulating Current Elimination in Parallel Operation of non-isolated AC-DC 4-leg Converters

Due to current limitations of semiconductor modules there is necessity of paralleling for higher power achievement. On the one hand particular transistors in one converter can be paralleled providing one of the simplest and cheapest approach. On the other hand, numbers of converters can be paralleled giving an opportunity for diversification power, improved reliability and converter maintenance [1], [2]. In other words, the power can be increased by adding another device to a system. Additionally, for low load, some of the converters can be switched off from a grid to achieve higher efficiency. For AC-DC converters zero-sequence voltage component of $3^{\text{r}\text{d}}$ harmonic is often applied due to increase power capability. However, for non-isolated parallel converters, this approach causes additional equalizing current flow that circulate between converters. A compensation technique for that issue is proposed by adding additional neutral current controller as well as common zero-sequence voltage factor for all parallelly connected converters.