Improvements of Droop Control Strategy for Grid-Connected Inverters of Micro-Sources

Big droop coefficients tend to reduce stability of microgrid, while small droop coefficients result in slow responding of inverter. In order to overcome the disadvantage, we propose a kind of droop control strategy based on nonlinear droop characteristic which is similar to that of magnetic hysteresis. Through real-time changing droop gains appropriately, the proposed strategy is to improve load power distribution accuracy, effectively suppress the wide fluctuations of frequency and voltage, and improve the stability of the system. At the same time, adding a feed forward path on the power droop block further improves the stability. Then the reduced small-signal mathematical model of microgrid is developed, confirming the small disturbance stability. The time domain simulation is conducted in the power systems computer aided design. The results verify the effectiveness of the control strategy.