Virtual Inertia-based Control Strategy for Stable Operation of a Weak Grid Using Modular Multilevel Converter

When power electronic converters are employed to integrate renewable energy sources into a power grid, it can result in reduced system inertia, potentially leading to the creation of a weak grid. This reduction in inertia may cause significant frequency fluctuations within the grid. This paper introduces the utilization of a virtual synchronous generator as a control mechanism for a three-phase modular multilevel converter. The primary objective is to ensure stable frequency responses in a weak grid, especially when faced with abrupt power variations at the Point of Common Coupling. The suggested control strategy comprises four control loops, with the VSG-dependent output current control enhancing the system’s ability to accurately track the output current of the modular multilevel converter (MMC). Two other control loops are allocated to the voltage balancing control for submodules (SM) and to the mitigation of circulating current. Results of the simulations in MATLAB/Simulink validate the accuracy and performance of the proposed VSG-based method of control in weak grid-connected MMCs.