Enhanced Grid-Forming Operation of Virtual Synchronous Generator Units

Virtual synchronous generator (VSG) control, incorporating frequency and voltage droop mechanisms, is a promising grid-forming (GFM) technology that emulates conventional generators by providing virtual inertia, frequency regulation, and damping. However, transient stability analysis typically omits the influence of inner current control (ICC) and voltage control (VC), potentially resulting in an inaccurate assessment. This paper investigates the influence of considering the VC and ICC and the current reference angle on VSG transient stability. Integrating VC and ICC into VSG stability studies yields more accurate results but reduces the VSG domain of stability (DoS). In order to address these aspects, this paper proposes a sophisticated approach, namely combined feedback feedforward-VSG (FB-FF-VSG) control, which incorporates the standard VSG with additional feedback into the outer loop and feedforward in the ICC in order to enhance transient stability and allow fault ride-through (FRT) by expanding the DoS. Additionally, an enlarged DoS promotes stability across a broader range of initial conditions. Numerical simulations show that the proposed control has better performance with respect to traditional VSG and virtual oscillator control (VOC) in terms of adaptability, stability, and flexibility across a spectrum of disturbances, including three-phase faults and load variations, marked by a substantial improvement in the DoS and accelerated dynamic response. The proposed approach is further validated by implementing the controller in a lab-scale microgrid.