Transient synchronous stability analysis and enhancement control strategy of a PLL-based VSC system during asymmetric grid faults

• Published in: Protection and control of modern power systems Vol. 8; no. 1; pp. 35 - 17
• Main Authors: Luo, Yi, Yao, Jun, Chen, Zhaoyang, Huang, Sen, Chen, Shiyue, Zhang, Qi, Qin, Zhentao
• Format: Journal Article
• Language: English
• Published: Singapore Springer Nature Singapore 01.12.2023; Springer Nature B.V; SpringerOpen
• Subjects: Alternative energy sources; Assessment criterion; Asymmetric grid faults; Asymmetry; Dual-sequence PLL; Electrical Machines and Networks; Energy; Energy Systems; Enhancement control strategy; Equal area criterion; Equilibrium; Faults; Influence; Integrating centralized and distributed renewables in future power system; Low voltage; Original Research; Phase locked loops; Power Electronics; Renewable and Green Energy; Renewable resources; Stability analysis; Stability criteria; Synchronism; Synchronous machines; Transient stability; Transient synchronous stability; Voltage source converters (VSC); Wind power; Dual-sequence PLL; Enhancement control strategy; Voltage source converters (VSC); Asymmetric grid faults; Transient synchronous stability; Assessment criterion
• ISSN: 2367-2617; 2367-0983
• DOI: 10.1186/s41601-023-00302-0

The stability of a voltage source converters (VSC) system based on phase-locked loop (PLL) is very important issue during asymmetric grid faults. This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of synchronous generators. Based on the model, the synchronization characteristics of the VSC system under asymmetric grid faults are described, and the interaction mechanisms, as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained. Using the equal area criterion, the influences of sequence control switching action, detection delay, and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed, respectively. In addition, a transient stability assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed. Finally, the analytical results are validated through simulation and experiments.