An improved droop control strategy for accurate current sharing and DC-BUS voltage compensation in DC microgrid

This paper addresses load current sharing among parallel-connected DC-DC converters and bus voltage drop issues caused by traditional droop method in low-voltage DC microgrid. Conventionally, I-V droop control is an effective way to parallel converter modules due to its high reliability, extendibility and economy. However, when the effect of mismatching line resistances is considered, the traditional droop control has limitations on the voltage regulation while the load current sharing accuracy is maintained. In this paper, an improved nonlinear droop control method is adopted to realize both accurate load current sharing and local output voltage improvement, which is achieved by adaptively adjusting nonlinear I-V droop curve with the information of DC bus voltage. Meanwhile, a secondary controller of DC bus voltage restoration is introduced to realize voltage drop compensation through the secondary regulation of I-V curve. The simulation model with two source converters and a single Constant Power Load (CPL) was built in Matlab-Simulink, which can be extended to multiple sources and multiple loads connected to the DC bus. Compared with the simulation results of the traditional droop control method and another improved droop control method, the better performance of the adopted control strategy is validated.