Feed-forward active attenuation of low frequency common-mode voltages in DC microgrids

DC microgrids are regarded as a pathway to substantially enhance buildings energy efficiency and improve integration with distributed generation and storage devices. In low power DC power systems, the lack of galvanic isolation at the utility grid interface will generate a common-mode (CM) path that will provide a low impedance circuit for DC bus ground faults and electric shock currents. Therefore the mitigation of CM voltages in the microgrid DC bus is important to contribute to a safer environment for users. In this paper, the CM voltage spectrum of DC microgrids with single-phase grid interface will be analysed and solutions to attenuate it will be discussed. A feed-forward active compensation technique is proposed to reduce the magnitude of low frequency components in the CM voltage spectrum. Experimental results show that this technique can attenuate the CM voltage to non-dangerous magnitudes without interfering with the microgrid differential mode behaviour.