Virtual Synchronous Generator Design Based Modular Multilevel Converter for Microgrid Frequency Regulation

Renewable energy sources (RESs) have been widely incorporated into modern power systems to accommodate the growing global demand for electricity and decrease greenhouse gas emissions. As a consequence, fast-response power converter, which serve as the interface between large-scale renewable generation and microgrids, gradually take over the function of frequency regulation earlier supplied by synchronous generators (SG). Therefore, this paper proposes a comprehensive design of Virtual Synchronous Generator (VSG) on the basis of Modular Multilevel Converter (MMC) with the aim of microgrids frequency regulation. The proposed control strategy predicated on the well-known swing equation (i.e., inertia and damping properties), in addition to the droop characteristics of conventional SG, which provides the required phase angle and frequency to control the MMC to behave as a VSG. Furthermore, proportional-integral-resonant controller is adopted to properly control the circulating currents of the MMC, in order to allow the energy transfer between submodule capacitors during frequency transient occurrences to promote the system frequency regulation. The proposed design technique provides an easy way to achieve and estimate multiple frequency control objectives such as primary frequency regulation, secondary frequency regulation, and virtual inertia. Eventually, simulation results were conducted to verify the efficacy of the proposed design scheme.