Modified droop controller for paralleling of dc-dc converters in standalone dc system

Dc systems are gaining popularity because of its high efficiency, high reliability and easy interconnection of renewable sources as compared to ac systems. In standalone dc system, parallel dc-dc converters are used to interconnect storage element and loads. Use of master-slave controller for paralleling is limited because of its high cost, low reliability and complexity. Although conventional droop controllers overcome these limitations, they cannot simultaneously ensure equal current sharing (in per unit) and low-voltage regulation. This is due to the error in measurement of voltage feedback signal. To address this limitation, modified droop controller is proposed in this study. Circulating current between converters is used to modify nominal voltages such that error between them is reduced. This improves current sharing among converters. The advantage of the proposed method is that, equal current sharing is achieved along with low-voltage regulation. The effectiveness of the proposed scheme is verified through detailed simulation study. To confirm the viability of the scheme, experimental studies are carried out on a scaled-down laboratory prototype developed for the purpose and results are included in this study.