Grid Fault Current Injection using Virtual Synchronous Machines featuring Active Junction Temperature Limitation of Power Devices

The recent years have seen an exponential growth in the electric generation from renewable energy sources, such as wind and sun. This scenario represents an opportunity to decarbonize part of the energy sector and phase out fossil fuels. However, particular care must be taken to ensure the correct operation of the electric grid. With a large penetration of power electronics based generation, special care must be taken in case of grid faults, due to limited short circuit current capabilities of static converters, supporting the grid in case of faults. For this reason, static converters have to be transiently overloaded to inject fault currents larger than their nominal limit, mimicking the behavior of synchronous generators. Therefore, this paper proposes the combined solution of a transiently overloadable virtual synchronous machine (VSM) converter equipped with real-time semiconductor junction temperature limitation. The VSM provides the necessary short circuit current references and the inverter can be overloaded with an active thermal control strategy, avoiding the oversizing of the power semiconductors, by properly exploiting their thermal limits. This represents a possible path for further power electronics integration into the grid.