Fixed Frequency Sliding Mode Control for Parallel Linked Distributed Generators in the Isolated AC Microgrid

Parallel linked inverter-interfaced distributed generators (DGs) have been utilized to increase the power capacity and system reliability and maintain the power supply at the critical load end. However, the control methods are crucial for ensuring a stable output voltage from the DGs. In this paper, the authors have proposed parallel linked inverter-interface DGs based on a voltage control strategy in an isolated AC microgrid (MG). Each three-phase parallel DG consists of an inductor-capacitor (LC) filter at the output and is connected to the AC distribution bus (DB) to meet the critical load demand. Fixed frequency sliding mode control (FFSMC) regulates the voltage at the output under steady-state, linear, nonlinear, and unbalanced load conditions. The constant switching frequency-based control design is employed, and the chattering phenomenon is diminished by smoothing the control law in a boundary layer. The proposed FFSMC provides stability against severe variations of load as well. The droop control method and virtual output impedance (VOI) loop are examined to ensure active and reactive power sharing between the parallel-linked DGs. The implementation of the FFSMC has been evaluated in a MATLAB/Simulink environment through simulations. The simulation outcomes reveal the efficiency of FFSMC in terms of quick response time, superior robustness, stable performance, and a low total harmonic distortion (THD).