Stability of Small-Gain Closed-Loop System and Its Applications in VSC-Based DC/AC Power Systems

Abstract

In a VSC-based HVDC/AC power system, dynamic interactions introduced by the HVDC system are usually weak. Hence, the small-signal stability of the HVDC/AC system is not affected significantly by the HVDC system. This paper presents a description of a weakly coupled VSC-based HVDC/AC power system by a small-gain closed-loop model that consists of two open-loop subsystems interconnected by a small gain. A special condition of open-loop modal proximity of the HVDC/AC system is examined, i.e., in the small-gain closed-loop model, an oscillation mode of one open-loop subsystem is close to an oscillation mode of the other open-loop subsystem on the complex plane. Our analysis indicates that when the open-loop modal proximity occurs, the corresponding closed-loop oscillation modes repulse each other. The closed-loop modal repulsion results in strong dynamic interconnection of the open-loop subsystems, thereby degrading the closed-loop system stability. Two examples are presented to demonstrate the applications of the proposed small-gain closed-loop model. Finally, the utility and accuracy of the closed-loop modal repulsion are evaluated from the viewpoint of the stability of HVDC/AC power systems.

Keywords:

• stability of closed-loop system
• power system oscillation modes
• voltage source converter (VSC)
• phase-locked loop (PLL)
• VSC-based HVDC line

Additional information

Funding

Project supported by the Fundamental Research Funds for the Central Universities (YJ201654).

Notes on contributors

Wenjuan Du

Wenjuan Du received the Ph.D. degree from the University of Bath, Bath, U.K., in 2009. She is currently a Full Professor in the School of Electrical Engineering, Sichuan University, Chengdu, China. Her main research interests include power system stability analysis and control, including energy storage systems, FACTS, EV, and renewable power generations.

Qiang Fu

Qiang Fu is working toward the Ph.D. degree in the School of Electrical and Electronic Engineering, North China Electric Power University, Beijing, China. His main research interests include power system stability analysis and control considering wind power integration.

Haifeng Wang

Haifeng Wang is a Full Professor in the School of Electrical Engineering, Sichuan University, Chengdu, China. He had worked in the U.K., for years and was the Chair in Electrical Engineering and a Full Professor with the Queen’s University Belfast, Belfast, U.K., before he moved to China. His main research interests include power system stability analysis and control.