Enhancing Security in Microgrids via Grid-Forming Converter Control by Contingency Mitigation, Overload Protection, and Voltage Balancing

Abstract

System-critical applications in microgrids call for the continuation of power supply, even under failure, in order to provide high levels of power quality and security. This is supported by the proposed method of comprehensive converter control for counteracting contingencies ($\text{C}^{5}$) in four-wire electrical networks. The method detects and addresses unbalanced short-circuit faults and line overloading by means of algorithm-based mitigation functions to protect converter hardware and continue operation of grid-forming voltage sourced converters. The combination of three mitigation functions is devised for the grid-forming converter control: the maximum sinusoidal current utilizer, the overload phase balancer, and the fast virtual impedance-based current limiter. Through this complementary set of functions, it becomes possible to achieve a continued converter operation at nominal phase voltages in non-faulty phases and to provide full current utilization in faulty phases under short-circuit scenarios. The method provides a fast and accurate current limitation without distorting fault currents, as well as the ability to transition smoothly between overload conditions, contingencies, and normal operation. In this way, the method contributes to maintaining power quality. Simulations and laboratory experiments demonstrate the method's effectiveness and confirm its added value in enhancing modern power supply.