Small Signal Equivalent Modeling for Large ES-Embedded DFIG Wind Farm with Dynamic Frequency Response

A simplified equivalent model that replaces detailed large-scale wind farms is an effective method for conducting complex simulation analyses and avoiding the dimensional catastrophe problem in power systems. In recent years, wind farms are equipped with the energy storage (ES) for improved primary frequency support action to react to low inertial power systems. Nonetheless, the existing equivalent models disregard the function of the ES, thus failing to capture the frequency response characteristics under the synergistic action of every doubly-fed induction generator (DFIG) and ES. This paper proposes a frequency response equivalent method for ES-embedded DFIG that takes into account coordinated control between ES and DFIG to accurately represent the primary frequency regulation capability. Based on a small signal model analysis, the general equivalent frequency response formula of ES-embedded DFIG system is derived. A multi-machine equivalent model is developed with variable operating states and the power response mutation resulting from ES intervention. To acquire the equivalent parameters of the preceding model, an improved two-stage parameter identification model is proposed to capture the accurate frequency response curve prior to and following ES action. Multiple large-scale wind farms are included in the two-area, four-generator system that validates the proposed method.