Research on Compound Pitch Control Technology of Direct-drive Permanent Magnet Wind Turbine

The conventional PID pitch controller was usually used in direct-drive permanent magnet wind turbine in order to maintain the output power unchanged above the rated wind speed. However, due to the complex structure of wind tur- bine as well as high nonlinearity of wind speed, the effect of PID control method is often less than ideal. A new pitch con- trol method combined with fuzzy adaptive PID and fuzzy feed forward controller is proposed in this paper. The fuzzy adaptive PID controller is able to ensure the unit having a better control result than PID controller at various wind speeds. The fuzzy feed forward controller has improved the responsiveness of pitch control system. With the simulation of a 1.5MW wind turbine, the responsiveness and stability of wind turbine can be effectively proved by the new pitch control method above the rated wind speed, the system's overshoot is also reduced, which satisfies the demand of power control. At present, the pitch control method is usually adopted above the rated wind speed by large wind turbines. The aer- odynamic torque of wind turbine is changed by adjusting the pitch angle to achieve constant power. The PID controller is mostly used to achieve the pitch control in wind turbines. However, due to the randomness of the wind speed varia- tions and the strong nonlinearity of the wind turbines, PID control cannot achieve satisfactory results. In recent years, many researchers try to design pitch controllers by using intelligent methods, such as reference (1), variable universe adaptive fuzzy control strategy is used to control the pitch angle above the rated power, which effectively reduces the fluctuation effect of high frequency component of wind speed data on power regulation. It shows that the system has good dynamic performance. In reference (2), the control strategy combining predictive control based on neural net- works with feed-forward control is presented, which realized the control of the wind turbine, but it is difficult to establish the optimal reference model. In reference (3), the compound pitch control strategy combining fuzzy feed-forward control- ler with fuzzy PID controller is presented. The fuzzy PID controller used the switching rule of the fuzzy controller and the PID controller in different working condition. Although to some extent, the controller improved the control effect, but the PID control parameters could not be properly adjust- ed with the working conditions. So when the wind speed changes, its control effect may be worse. Based on the above studies, the new compound pitch controller combining fuzzy adaptive PID controller with fuzzy feed-forward controller is proposed. The PID control parameters are adaptive adjusted according to the system error and the rate of error changes by the fuzzy rules. Using fuzzy feed-forward control changes the influence of inertial and delay of pitch-regulated system on dynamic performance. Above rated wind speed, the input pitch angle of wind turbine is gotten by combining the dif- ferent output values of the fuzzy adaptive PID controller and the feed-forward controller. The simulation results show that the new method can effectively ensure the rapid response and stability of wind turbine, reduce the overshoot of system, and the effect of the control is better.