Circulating Current Mitigation Among Sources in DC Microgrid Using Distributed Secondary Controllers

In general droop controllers are utilized in microgrids to ensure fair power sharing between similar sources when feeding different loads. Nevertheless, due to the difference in feeding line impedances, the supplied power from different sources varies from its expected values. To mitigate this problem a modified method of droop controller that utilizes the shift and/or adjustment in the droop gain is proposed in this literature. The current used techniques give an improved performance as it allows a higher degree of freedom to the controller. Nevertheless, these techniques use distributed proportional-integral control, that can cause a winding-up phenomenon. Further, the dynamic response of the secondary controller is poor while taking the action to improve the current sharing accuracy among the source current converters. To alleviate the issue, a modified secondary controller with the employment of full communication system has been proposed in the paper. The information of each source current is shared among the sources by low bandwidth communication. The suggested secondary controller ensures proportional sharing of current among the sources and improves the dynamic response of dc microgrid. To improve the dynamic response of the microgrid, the step size by which the secondary controller modifies the droop gain of the sources is adaptively changed so as to damp out the oscillations occurring in the microgrid during step variation in load demand. The proposed controller enhances the effective damping of dc source converter and suppressing unwanted oscillations occurring in dc microgrid. The performance of the suggested modified secondary controller is validated from the simulation studies taken place under MATLAB/Simulink environment.