A nonlinear droop method to improve voltage regulation and load sharing in DC systems

It is well-known that load sharing among paralleled sources in dc grid can be achieved by droop control. However, practical factors that influence the load sharing and voltage regulation are seldom discussed, like the sensor discrepancy and cable resistance. In this paper, the impact from cable resistance is analyzed and verified by experiment. To suppress the impact from practical factors, instead of using constant droop resistance, a nonlinear droop method is proposed. In the proposed method, the value of droop resistance is a function of output current. Its value increases when the converter's output current increases. The proposed method needs only the local output current information so the advantage of traditional droop control is preserved. Different second-order droop functions are evaluated and compared. The effectiveness of proposed droop method is verified by simulation and experiment. The experimental result proves the proposed nonlinear droop method has better load sharing at heavy load and tighter bus voltage regulation at light load. The necessary droop voltage range to fully utilize the capacity of paralleled sources is also reduced.