Improving the Transient Stability of the Virtual Synchronous Generator
Abstract
The majority of the Distributed Energy Resources (DERs), i.e., Energy Storage Systems (ESSs) and Renewable Energy Systems (RESs), utilize inverters to convert the Direct Current (DC) power to the Alternating Current (AC) power needed by the majority of the consumers. Proliferation of the inverter-based DERs has caused significant changes in the operation of the modern electric power systems. Inverters lack the mechanical inertia that is inherent in the traditional power generators, i.e., rotating electrical machines. As a result, the emerging inverter-dominated power systems suffer from lower stability margins, excessive frequency deviations, and poor dynamic response to disturbances. This issue has adversely affected the integration of the highly advantageous inverter-based renewable energy systems in microgrids and active distribution systems. Appropriate inverter control can be used to emulate virtual inertia by imitating the behavior of traditional generation units. Based on this idea, the concept of virtual synchronous generator (VSG) has been proposed.
VSGs suffer from the transient stability issues that affect the operation of the Synchronous Generators (SGs). They can become unstable due to prolonged faults. Unlike the SGs that can handle significant over-current stress, VSGs have limited overcurrent capacity. The studies conducted in this research indicate that the current limiting strategy of the VSG significantly impacts its transient stability. The impacts of different inverter current limiting strategies on the performance of the VSG are investigated and the one that leads to the largest transient stability margin is identified.