Advanced Control Strategies to Enhance Stability of DC Microgrids Islanded under Dynamic Conditions

Islanding of microgrids leads to unwanted fluctuations in power, voltage, current, and frequency parameters. In this paper, a comprehensive three-level control strategy is proposed to stabilize an islanded microgrid by sending control commands to the distributed generation (DG) units based on inverters. The first level of control involves droop control, which manages the power control. The second control level ensures the stability of the voltage and frequency of the network. To implement this control level, the Maximum Power Point Tracking (MPPT) method is used for the DC converter connected to the DG unit, and the Virtual Oscillator Control (VOC) method is employed to control parallel inverters. Finally, the third control level, located at the load side, is responsible for stabilizing the power of the islanded microgrid under varying load conditions, which is implemented using a Shunt Active Power Filter (SAPF) controlled by Model Predictive Control (MPC). Sensitivity analysis of the proposed control model is carried out under transient conditions caused by load variations, environmental changes (changes in irradiance levels), and consequently, changes in the output power of the DG units. Simulation results in the MATLAB/Simulink environment show that the proposed control strategy can stabilize the microgrid and minimize the fluctuations of power, voltage, and frequency under various operating conditions.