Frequency-Selective Impedance Control for DC Microgrids

In this paper a novel impedance control technique is developed. The technique is aimed to suppress the steady-state ripples of a micro grid's DC-bus voltage, caused by load's current harmonics. The effect is achieved by lowering the bus impedance at the selected frequencies, that correspond to the frequency spectrum of the loads. The frequency-selective impedance control (FSIC) is implemented by increase of the voltage-loop gain at the specified frequencies using the cascade of the resonance-type controllers (R-controllers). The R-controllers are tuned to the parameters of the distortion. Since the oscillation frequency of the R-controller isn't restricted by the voltage-loop's bandwidth, the control capabilities of a power converter are extended up to its Nyquist frequency. An approach to configure the R-controllers is developed. The effectiveness of the technique is proved by the experiments at the DC micro grid prototype. The experiments demonstrate a significant reduction of the bus voltage ripples under the FSIC.