A Sophisticated Grid-forming Dispatchable-Virtual Oscillator Control with Robust Inner Current Control for Improving Transient Stability

Dispatchable-virtual oscillator control (D-VOC) is a promising time-domain grid-forming (GFM) technology designed to emulate the dynamic behavior of physical oscillators. Large-signal stability (LSS) is a crucial aspect of power system planning, mainly concerning the ability of power sources to synchronize with each other following a disturbance. However, GFM transient stability analysis typically omits the influence of inner current control (ICC) and voltage control (VC), potentially resulting in inaccurate assessments. Indeed, this paper analyzes the impact of ICC, VC, and current reference angle on the LSS of D-VOC, determining that incorporating ICC, though improving the precision of stability evaluations, simultaneously constrains the region of attraction (RoA). Moreover, the RoA is characterized using both the general quadratic and polynomial Lyapunov functions. In order to address these challenges, this study proposes a sophisticated framework, namely adaptive D-VOC (AD-VOC), an enhancement of standard D-VOC that introduces an additional degree of freedom through outer loop feedback and ICC feedforward to support fault ride-through. The proposed control is compared with the D-VOC and virtual synchronous generator (VSG) GFMs and numerical simulations show that the AD-VOC performs better than the traditional D-VOC and VSG in terms of adaptability, stability, and flexibility during short-circuit and load variation disturbances, marked by a substantial improvement in the RoA and accelerated dynamic response. Consequently, the proposed method not only reduces the overall cost associated with power electronics converters but also extends their operational lifespan. The proposed approach is further validated by implementing the AD-VOC in a lab-scale microgrid running in real-time.