Scalable State-Space Model of Voltage Source Converter for Low-Frequency Stability Analysis

Low frequency instability phenomena in power electronic based power systems can originate both at converter and at power system level. At the converter level, the interaction between PLL, dc-link and ac voltage control in voltage source converters (VSCs) connected to a weak grid can lead to instability. At the power system level, the interactions among different parallel VSCs can produce oscillatory phenomena, and even result in instability. However, a model to study the instability phenomena at both levels is still under development. In this paper, a scalable VSC state space model, which captures the interactions among PLL, dc-link and ac voltage control is proposed. The proposed model is suitable for interconnection, and an example of power system modeling is shown. The model is then validated through simulations and experimental tests. Eigenvalue analysis is carried out to investigate the influence of the control parameters on the stability.