Study on multi-loop overcurrent suppression control method for grid forming inverter

Renewable energy sources have been widely installed as a countermeasure to global warming. However, a significant increase in their capacity will reduce power system inertia and stability. Grid forming (GFM) inverters have been researched and developed worldwide to maintain power system inertia and stability. The GFM inverter supports power system stability even during power system disturbances, using virtual inertia functions in the GFM controller. Besides single-loop GFM controllers for frequency and voltage control, multi-loop type GFM controllers have been proposed to suppress overcurrents; since the GFM inverter operates as a voltage-controlled voltage source, overcurrents may occur in the event of power grid disturbances such as power line faults. However, the multi-loop GFM controller may lose phase synchronisation with the grid voltage and fall into unstable operation due to a phase shift in the grid voltage when the power line fault is cleared, and the grid voltage is recovered. This paper proposes a new GFM control method for keeping the phase synchronization with the grid voltage by adding a limiter to the frequency controller. MATLAB/Simulink simulation studies validated the proposed control method.