Off-grid Microgrid Adaptive Switching Control Method under Topology-changing Scenarios

The off-grid microgrid adaptive switching control method generates control instructions based on preset rules and algorithms, and uniformly deploys key equipment to achieve the switching of on-grid and off-grid modes. However, the switching control efficiency of specific working conditions is low. Therefore, the off-grid microgrid adaptive switching control method under the scenario of variable topology is studied. The microgrid adaptive switching controller is designed and subdivided into a grid-connected PQ controller and an island U/f controller. When switching from grid-connected to off-grid, the grid-connected PQ controller relies on the PQ control mode of active current and reactive current to avoid voltage and current fluctuations by adjusting the power reference value. When switching from off-grid to grid-connected, the island U/f controller uses the main control inverter to adjust the voltage and frequency, and adjusts the voltage and frequency errors through PI control to ensure stable off-grid operation. In view of the phase and frequency differences between the microgrid and the main grid during switching, the phase pre-synchronization compensation technology is adopted, and the compensation method based on the phase-locked loop (PLL) is used to dynamically adjust the relevant values to optimize the compensation effect, so as to achieve safe and stable on-grid and off-grid switching. The simulation results show that after applying the off-grid microgrid adaptive switching control method under the topology-changing scenario, the voltage and current waveforms fluctuate briefly during the switching, but can quickly stabilize, which verifies the good regulation ability of the method on voltage and current; in the passive off-grid switching control response evaluation simulating the main grid fault, the method has obvious advantages in frequency adjustment, stabilizing to $50 \mathrm{~Hz} \pm 0.05 \mathrm{~Hz}$ at $\mathrm{t}=500 \mathrm{~ms}$, and then continuing to be stable, which can stabilize the frequency more quickly, reduce fluctuations and recovery time, and has high practical application value.