An Improved Droop-Control Strategy to Provide Flat Output Impedance of Power Converters in DC Microgrids

In this paper, an improved control strategy is proposed for droop-controlled dc power converters to ensure maximally flat magnitude response of the converter's output impedance within the voltage loop bandwidth with no impedance peaking at the cut-off frequency, resulting in the non-overshooting voltage transients under step-load change and minimizing the risk of source-to-load interactions. The first-order dynamics is provided by the proposed control strategy incorporating two independent load current feed-forward paths into the proportional and integral parts of the voltage loop PI-compensator in combination with the output capacitor's current control. The adaptive current gain approach is developed to ensure low sensitivity of the control performance to the converter's input and output voltage variations. The single-pole small-signal model of the power converter's output impedance under the proposed droop-control strategy is developed. Simulations and experiments were conducted to validate the effectiveness of the proposed control strategy.