Online grid impedance estimation for enhancing the stability of type IV wind turbines connected to weak networks [articol]

Abstract

Large scale integration of wind power is one of the main challenges in today power systems. Large off -shore wind farms are usually connected to grids through long transmission lines or cables. These weak grid conditions have great influence on the stability of wind power plant’s operation. This paper analyses the stability issues raised by integrating wind farms into ac network with very weak conditions .The paper also proposes a gain schedule based adaptive controller for the grid side converter to enhance the power system stability at the point of connection. In order to identify the weakness level of the grid to generate the appropriate stabilizing control action an online grid impedance estimation scheme is introduced. The scheme depends on the Extended Kalman-Filter (EKF) to estimate the equivalent grid impedance without the need of active disturbance injection. Using the proposed control scheme the system can operate under very weak grid conditions with higher wind power penetration levels. Simulations under low short circuit ratios are conducted to show the enhanced system stability using the proposed approach.