Rotating Speed Control Of Variable Speed Constant Frequency Wind Turbines Using Double-Fed Induction Generator

Variable speed constant frequency (VSCF) wind turbine using Double-fed induction generator (DFIG) can run in a bigger working wind speed. Because it can offer many advantages, such as a high efficiency of wind energy extraction, the capability of decoupling control of active and reactive power and reduction of inverter cost, VSCF wind turbine has been applied widely.This paper concentrates on pitch control and rotating speed control of VSCF wind turbines using DFIG. The mathematical models of DFIG and wind turbine are built, and the capability of decoupling control of active and reactive power by vector control is studied. Based on these, a fuzzyPID-PID dual-mode variable pitch control scheme of VSCF wind turbine is proposed. With this control scheme, the rotation speed can keep around the rated value while the wind speed changing random above the rated value. High reliability, good dynamic response, strong adaptability and high precision are demonstrated by simulations. Strong nonlinear, big moment of inertia and mechanical damping changes according to rotating speed are the characters of VSCF wind turbines. A new Nonlinear-PID (NLPID) controller for rotating control is proposed. Fast response, small overshoot, high precision, strong adaptability and high robustness are obtained by this strategy.Besides, the control strategies of VSCF wind turbines during different running areas are described in detail. Based on this, VSCF wind turbines using DFIG running in the whole working wind speed range is studied by simulations. The system can keep the rated output power above rated wind speed; when wind speed is under the rated value, system can estimate the optimal rotating speed without test of wind speed and reach the maximum wind energy capturing or keep the rotating speed constant. The rotating speed can track the optimal value quickly.