Using Virtual Synchronous Generators to Resolve Microgrid Protection Challenges

Microgrids and related microgrid technologies enable networks to keep power on when the normal supply is unavailable as well as provide the ability to support high penetrations of renewable and distributed generation. Microgrids, particularly those that operate with significant penetrations of renewable generation, present unique protection challenges. One challenge is a shortage or absence of inertia that can leak to system stability issues and, from a protections standpoint, rapid protection operation. Another challenge is that the fault current characteristics of inverter-based generation in the microgrid are very different from synchronous generators and can vary by vendor, product, and settings. A Virtual Synchronous Generator (VSG) in a Battery Energy Storage System (BESS) can address these two challenges. A VSG consists of an inverter with intelligent controls and automation. As the name implies, a VSG has characteristics that are like a synchronous generator. The short circuit capabilities and ability to supply virtual inertia provide a solution to these two challenges. In addition, because it is based on inverter-based power electronics, the VSG provides fast responses that can be tuned to suit the needs of the application. The combination of a VSG in a BESS with smart automation also enables distributed black start support, including from 100% renewable generation. A BESS with VSG was demonstrated in a large renewable microgrid in South Australia. The ESCRI-SA Dalrymple project went into operation in 2018, and supports a 91 MW wind farm, more than 3 MW of distributed rooftop solar interconnected with hundreds of kilometers of transmission and distribution lines. This project is characterized by high reliability and is a critical component of the protection schemes the transmission system operator (TSO) uses for customer reliability in a network with high renewable share, both outside and within the microgrid. providing support across the TSO’s network and within the microgrid through seamless islanding capabilities. This work describes the protection used, characterizes it in the framework of common North American protection schemes, and provides insight on adapting the grid-forming technology and approaches from South Australia to North American utility networks.