Abstract:
The inverter-based distributed generation (DG) units in Microgrid calls for robust control techniques that attain high performance not only during normal operating conditions but also under unbalanced conditions. Microgrid contains a cluster of loads along with distributed generators operating as a unified controlled system. Interconnecting DGs with a grid using power electronic converters has enhanced concerns regarding safe operation and protection of the equipment. Many control strategies have been proposed for enhancing the stability of microgrid for proper load sharing. This work proposes two separate controllers based on the sliding mode control for an autonomous mode and grid-tied mode of operation. Frictional-Order Sliding Mode Voltage Control (FOSMVC) technique is developed for single and parallel voltage source inverter (VSI) in autonomous mode maintains the quality of the output voltage of the DG system despite unbalanced and/or non-linear load currents. Also, this controller improves the steady state and dynamic response under sudden load fluctuation. Droop control approach and virtual output impedance (VOI) loop are investigated to guarantee the accurate power-sharing among DG units in parallel operation. Sliding Mode Current Control (SMCC) approach is adopted for the grid-tied mode where the controller works as a current controller. The proposed controller effectively abandons the grid voltage disturbances and the parameter uncertainties. Furthermore, PQ sharing control is designed for the parallel operating of DG units by delivering available power to the grid side in order to ensure power-sharing requirements. The stability of the proposed controllers is proven by applying the Lyapunov stability theorem. Both controllers have been simulated in the real-time domain of Simulink/MATLAB environment. Finally, the performance of the proposed FOSMVC is compared with the conventional proportional integral (PI) controller. The simulation results show the THD of the output voltage of 0.40% and 1.53% for FOSMVC, and 1.82% and 6.84% for PI controller under linear and nonlinear load, respectively. The results also validate that the proposed control technique is quite effective due to its robust response and less sensitive to external disturbances.
