Modelling of Wind Power under Stressed Voltage Conditions

Abstract

With high share of wind power and other renewable energy sources, conventional synchronous generators are being replaced by converter connected non-synchronous generators. Large share of renewable energy source based generations poses various challenges towards secure and stable operation of power systems, one of which is voltage stability. Suitable wind power models are required for long-term voltage stability assessment of power systems with large share of wind power. The objective of this PhD project “Modelling of Wind Power under Stressed Voltage Conditions” is to develop wind power models for long-term voltage stability assessment during stressed voltage conditions. A methodology is developed to estimate voltage and active power dependent reactive power capability of wind power plants based on an aggregated wind power collection system. Results show that the reactive power capability estimation using the proposed method is sufficiently precise compared to the value computed using detailed wind power collection system. This estimated reactive power capability is utilised to develop wind power plant support strategies during stressed voltage conditions. A novel reactive power control strategy of wind power plant is developed to provide maximum reactive power support during stressed conditions. This control strategy performs better than the other conventional control strategies, consequently improving voltage stability of the power system. Impact of wind power fluctuation and uncertainty on voltage stability assessment is also studied in this PhD work. A novel methodology is developed to quantify the impact of active power fluctuation on reactive power capability of wind power plant. Findings indicate that the robustness of wind power plants as reactive power source decreases with increase in time period of voltage stability assessment study. The study underlines thus the importance of selection of appropriate time period in order to yield higher confidence in wind power plants as reactive power source. The results have shown that reactive power support from wind power plant even with low robustness index can considerably improve voltage stability of the power system. Neglecting wind power fluctuations can have substantial error in voltage stability assessment. A novel probabilistic voltage stability assessment methodology with reactive power support from wind power plant is developed which reduces the error in voltage stability assessment significantly. This is especially valuable during stressed voltage conditions, when errors in voltage stability assessment can lead to voltage instability in voking potential blackout. Results have shown that the proposed probabilistic assessment methodology gives significantly higher confidence in the predicted bounds of voltage stability assessment when compared to the deterministic voltage stability assessment based on persistence. This PhD research work is carried out at the Department of Wind Energy in Technical University of Denmark. This work is done as a part of Security Assessment of Renewable Power Systems (SARP) project funded by Energinet under Public Service Obligation scheme (Forskel 12427).