Application of imitated frequency droop technique and predictive control for power sharing in DC microgrid comprising SMES and PV systems

Abstract

This paper represents an efficient decentralized control approach for standalone ring-bus low-voltage direct current (DC) microgrids comprising photovoltaic (PV) and superconducting magnetic energy storage (SMES) systems. The proposed method addresses three challenging issues; effects of inner control loop on transient and steady-state performance, power sharing, and operating mode selection. Since the conventional proportional-integral (PI) controllers as internal control loop of DC-DC converters provide slow and unstable response, finite control set-model predictive control (FCS-MPC) schemes with exact discretization method are designed for PV boost and SMES D-class converters. Furthermore, by modifying the classic droop control method in alternating current (AC) microgrids, an imitated angular frequency droop method is presented for power sharing and voltage stabilization in ring-bus low-voltage DC microgrid. The proposed proficient state selection (PS2) strategy effectively determines PV-SMES operating modes by utilizing the SoC of local SMES and the output voltage of corresponding DG. Simulation studies performed in MATLAB/SIMULINK under load change, irradiance variation of PV system, operating mode transition, topology change, and DG outage conditions confirm the effectiveness of the proposed MPC-based approach in accurate voltage regulation, power sharing among distributed generations (DGs), as well as minimizing the effects of these disturbances and uncertainties compared to conventional PI controllers with pulse-width modulation (PWM) method.