Resonance assessment in power systems with DFIG-based wind parks: Análise de ressonancia em sistemas de potencia com parques eólicos baseados em GIDA

Abstract

The increase of the penetration of wind parks (WP) based on doubly-fed induction genera- tors (DFIG) in electric power systems may bring problems associated with high-frequency resonances in the range between 180 Hz and 1500 Hz. There are two main phenomena to be analyzed: unstable resonances, when a resonance occurs in frequencies where the DFIG voltage source converters (VSC) have negative damping characteristic; and weakly damped resonances close to frequencies such as 5𝑡ℎ, 7𝑡ℎ, 11𝑡ℎ and 13𝑡ℎ harmonics, which are typically present as background grid distortions. Traditionally, these resonances are studied with electromagnetic transient (EMT) simulations as they are able to account for all dynamic characteristics of the circuit. However, numerous EMT simulations are generally required in the studies, which leads to high computational costs. This dissertation develops simplified approaches to address these resonances. Prior to developing these methods, it is first confirmed that, at frequencies between 180 Hz and 1500 Hz, the DFIG can be modeled as a linear impedance using the average model of the VSCs. Then, a chart is developed to quickly identify if a WP can become unstable. This chart establishes a risk region: if WP and grid characteristics (short-circuit level to wind park size ratio and reactive compensation to wind park size ratio) lay inside this region, the WP can become unstable. It is found that this risk region can be significantly reduced by properly designing the control parameters of the converters. Therefore, high-frequency instabilities are unlikely to become a general concern for utilities. Nevertheless, weakly damped harmonic resonances can still occur and must be considered when operating and designing DFIG-based WPs. Two additional charts are proposed to analyze the risk of weakly damped harmonic res- onances in the system. The charts establish a risk region by correlating the short-circuit level of the grid...