A Novel Autonomous Current-Sharing Control Strategy for Multiple Paralleled DC–DC Converters in Islanded DC Microgrid

Due to the existence of line impedances and low-bandwidth communication, the traditional peer-to-peer control method based on droop control has difficult meeting the requirements of current sharing and voltage stability in islanded DC microgrids at the same time. In this paper, a novel current-sharing control strategy based on injected small ac voltage with low frequency and low amplitude is proposed for multiple paralleled DC−DC converters. The small ac voltage is superimposed onto the output voltage of each converter. Then, the reactive circulating power is generated and used to regulate the output DC voltage of each converter. Under the droop characteristic between the injected frequency and output DC current, a feedback mechanism is generated to realize the accurate current sharing. On this basis, a reactive power-voltage limiter link and virtual negative impedance are added. Under the interaction of the two links, the bus voltage drop caused by line impedances can be almost completely eliminated. This method does not need any communication or to change the hardware structure. The controller design process is presented in detail along with a system stability analysis. Finally, the feasibility and effectiveness of the proposed control strategy are validated by the results obtained from simulations and experiments.