Modelling and analysis of grid forming control with cascaded current and voltage loop

The paradigm shift from synchronous machine-based power systems to renewable-based power systems has made it necessary to develop grid-forming control methods that enhance stability, particularly under weak grid conditions. This paper focuses on the modelling and analysis of a voltage source converter (VSC) based Static Synchronous Compensator (STATCOM) employing cascaded grid-forming (GFM) controls. The outer loop regulates voltage, while the inner loop is a fast current control that can also assist with current limitation during grid events. A customizable current limiting logic has been developed as a part of this control, which helps to ride through overcurrent events without compromising the device limits. Phasor analysis is provided for GFM control responses under phase jump event. Simulation results under various grid stress events demonstrate the performance of the proposed controls, followed by hardware validation results in RTDS environment. The proposed control strategy provides a robust response under various grid conditions, thereby enhancing system stability.