Low-Voltage Survivability of Islanded Microgrids With Mixture of Single-Phase and Three-Phase DGs under Harmonic Conditions

Unbalanced low-voltage survivability of islanded microgrids under three-phase nonlinear load conditions in terms of primary control of distributed generations (DGs) is a research gap. This paper bridges the gap by proposing dynamic-sliding mode controller (SMC) for the voltage control loop and a novel current limiting strategy (CLS) based on the sliding-discrete Fourier transform (DFT) algorithm. The proposed sliding-DFT-based CLS separates fundamental and harmonic components of the reference value of inverter current and only restricts its fundamental component to a value less than the threshold value. The proposed dynamic-SMC, which presents robust performance with low chattering phenomenon, in combination with the sliding-DFT-based CLS prevents DG's output voltage distortion. This feature is favorable for supplying local and sensitive loads. Moreover, single-phase washout filter-based power sharing method has been implemented to ensure precise active power sharing and frequency regulation of the microgrid with mixture of single-phase and three-phase DGs during asymmetrical short-circuit faults as well as better fault clearance dynamics than the conventional three-phase droop control method. The offline and hardware-in-the-loop (HIL) simulation results also confirm the effectiveness of the proposed CLS and voltage controller applied to the control structure of DGs operating in the grid-forming mode in comparison with existing methods.