Low-Voltage Ride-Through Algorithm for Grid-Forming Converters

In recent years, the increasing integration of renewable energy sources into power systems has led to significant changes in grid operation. Power electronic converters are primarily used to connect this power plants to the electrical system and, as key components in modern power systems, grid-forming (GFM) converters have emerged to provide the ability to autonomously establish and maintain system stability without the need for synchronous generators (SGs). The current contribution during faults is one of the main differences between SGs and power converters, which can affect protective systems. The most recent grid codes require a fast current injection in the event of a fault. This paper presents a low-voltage ride-through (LVRT) control strategy for grid-forming converters based on virtual-flux orientation according to the European Commission Regulation (EU) 2016/631 and the Spanish Technical Supervision Standard (NTS) requirements. For the validation of this control algorithm, a hardware test bed has been implemented consisting of two DC voltage sources emulating a photovoltaic (PV) plant feeding the DC bus of a voltage source converter (VSC) and, finally, a grid emulator where the different voltage faults have been programmed.