Adaptive-SMC Based Output Impedance Shaping in DC Microgrids Affected by Inverter Loads

Inverter connected single-phase AC loads cause second-order oscillations in source currents and DC bus voltage. These oscillations degrade the efficiency and reliability of the DC microgrid. In this paper, an adaptive sliding mode control based output impedance shaping (ASMC-OIS) methodology is proposed for voltage regulation, proportional load sharing, and second-order ripple management in a DC microgrid. By using the proposed control method, the magnitude of the output impedance of the source interfacing converter is increased at 2f_ac programmably, which results in the reduction of second-order ripple currents propagating through the converter. Instead, it is propagated to the DC-link capacitor or towards the nodes which consists of some ripple absorption active or passive filter. This leads to an increase in the energy density of the ripple filters. The dynamic consensus-based secondary control is incorporated to ensure proportional load current sharing. A graph theoretical analysis is presented to analyze per unit load sharing among all the nodes. Stability of the proposed controller is analyzed considering multiple source nodes using Lyapunov's approach. A DC microgrid consisting of parallel-connected DC-DC boost converters, DC load, and inverter load is simulated to verify the proposed control strategy. The proposed ASMC-OIS methodology is validated through experimentation.