Converter-Dominated Grids: Control and Protection Concepts for Ancillary Services of the Future

Abstract

Because of the change in the future energy system to a more decentralised bidirectional power flow, the power system gets more complex. To ensure a reliable and safe electrical grid in future power systems, ancillary services (AS) have to be provided by decentralized distributed energy resources. Current controls and protection systems have to be adjusted. The first focus is on the provision of AS in the future energy system. Two Services will be specified, the voltage and the frequency stability. Different algorithms will be presented and validated. In the low voltage level a reinforcement learning controller is developed to provide voltage stability from the grid connection point of the inverter. For the frequency stability different controllers are developed. For the control power a two staged controller will provide active power to ensure a stable frequency. Due to the decreasing inertia caused by the reduction of synchronous generators, a grid-forming inverter was developed. This control concepts, based on a virtual synchronous generator, enables the inverter to provide inertia. The various controllers were tested in both software and hardware. After that, the second focus lies on analysing the performance of conventional protection systems in converter�dominated grids. It will be shown that especially distance protection systems are negatively influenced by intermediate infeed. Then, it will be evaluated how the converters contribute to AS provision during faults. Next, new developments of both protection systems and converter controls will be shown. It will be stated that the converter can play an active role in the protection system environment to support the functionality of conventional protection systems. Finally, a methodology together with a testbed will be presented for experimental validation of both the findings and developed concepts with a simplified and laboratory-scale testbed of a medium-voltage grid.