Adaptive virtual admittance control of bidirectional DC/DC converters for DC bus voltage ripple suppression in DC microgrids

DC microgrids have the risk of wideband DC bus voltage ripples. The ripple frequency may vary with system operating conditions, increasing the difficulty in voltage ripple suppression. To this end, an adaptive virtual admittance control strategy of the existing bidirectional DC/DC converter (BDC) with active power filtering capability is proposed. A ripple detection method based on the windowed-interpolated discrete Fourier transform is integrated, which allows the working frequency band of virtual ripple admittance to be automatically tuned. The proposed strategy reduces the impedance of BDC at the ripple frequency, allowing it to provide the ripple compensation current. To achieve synergistic suppression of multiple BDCs considering compensation capabilities and avoid overcurrent, the adaptive virtual ripple admittance based on the remaining deliverable current is designed. According to the difference of voltage ripple distribution due to line impedances, the virtual ripple admittance can be further adjusted by the secondary adjustment of management system to enhance the ripple suppression effect. Further, the stability analysis of the proposed strategy and comparison with fixed virtual admittance control are conducted. Finally, the effectiveness of the proposed strategy in the DC bus voltage ripple suppression and ripple compensation current distribution is verified by experiments.