Small-Signal Stability Analysis for Grid-Connected VSG with Lyapunov's Second Method

Due to the access of a large amount of renewable energy, the stability feature of the power system has changed dramatically. Especially the introduction of power electronic devices, weakening the system inertia and bringing new stability problems such as power oscillation, voltage and frequency stability risks. VSG control is a good way to improve the system's dynamic response as a kind of power electronic. Since the VSG's operation is mimic the dynamic process of a synchronous generator, it increases the inertia by reducing parts of the electronics' flexibility. However, the control interaction of the VSG control loop is complex and sensitive, and different operating conditions appreciable impact on the system stability. This paper pointed out that by using the Lyapunov second method, the stability degree of the power system operating point can be expressed intuitively. By calculating the energy function, the stability of different stable operating points of a system can be quantified. Through the visualized expression of the system operating point's stability, we can directly compare the stability degree with different operating points and provide a regulation reference for the selection of operating points. Study cases are also given out in this paper.