A novel grid-forming technology for transient stability enhancement of power system with high penetration of renewable energy

Abstract

Owing to the limited inertia and voltage support of traditional grid-following inverters, grid-forming (GFM) technologies with voltage source characteristics, such as droop and virtual synchronous generator (VSG) control, have been proposed recently. However, it is difficult to achieve the same transient performance as that of traditional synchronous generators (SGs) because of the inherent current tolerance of power electronic devices. In this paper, a novel GFM technology with improved speed-power feedback control, defined as a motor-generator pair (MGP), is proposed. In addition, a state-space model is established to illustrate the control stability of the proposed GFM technology. The models and power angle characteristics of four GFM methods, namely droop, VSG, SG, and MGP, are first compared theoretically. Then, considering the current limitations and control delays, the transient response and interactions of the above GFM technologies are simulated in an IEEE 3-generator 9-bus system. The results show that the current saturations may limit the transient support of GFM inverters significantly and may also result in forced overcurrent and imbalanced power in the transient process, because of the slow response of SG governor in the system. Furthermore, compared with GFM inverters, MGP has more satisfactory transient stability because of its spontaneous inertia and faster response in primary frequency regulation than SGs owing to its similar response speed to inverters. Finally, an experimental platform including a 5 kW MGP prototype is established, and the transient performance of the proposed GFM is verified and compared.