Model reduction strategy of doubly-fed induction generator-based wind farms for power system small-signal rotor angle stability analysis

Following the decarbonisation and decentralisation of energy industry, wind energy is becoming a promising generation source to reduce greenhouse emission, and meet future energy demand. Unlike traditional generation using synchronous generators, many wind turbines use induction generators, e.g., doubly-fed induction generators, due to the cost effective design of adjustable-speed operation and flexibility in reactive power control. However, a growing number of doubly-fed induction generator-based wind farms has significantly increased the complexity of system dynamic model, and hence increased the computational burden of power system dynamic study. This becomes a serious concern in the electricity system operation, where a fast power system stability assessment is required to assure the real-time system security during high levels of wind power penetration. In this paper, a novel model reduction strategy of doubly-fed induction generators is derived to improve the efficiency of power system dynamic study, while the study accuracy is still maintained to an acceptable level. To achieve this, a method to assess the modeling adequacy of doubly-fed induction generators for small-signal rotor angle stability analysis is firstly introduced. By evaluating the damping torque contribution to stability margin from different dynamic model components of doubly-fed induction generators, the proposed method provides a quantitative index (i.e., participation level) to show the involvement of each dynamic model component of doubly-fed induction generators in affecting power system damping, and thus can instruct how to reduce the model of doubly-fed induction generators in an efficient and accurate manner. On this basis, five model reduction plans and a model reduction strategy have been proposed according to the previously defined participation levels. The effectiveness of the proposed strategy is demonstrated in the New England test system and a real large power grid in Eastern China respectively. It has been proved that the proposed the model reduction strategy of doubly-fed induction generators for power system dynamic study is undoubtedly useful to the electricity system operator, with a key benefit in reducing model complexity and improving computational efficiency of a large-scale power system with an increasing number of wind power generation.