Research On Power Optimization Sliding Mode Control Of Direct-driven Permanent Magnet Synchronous Wind Generator System

With the world environmental pollution and energy crisis are getting serious, wind power as a clean, renewable energy has made rapid development. The direct drive permanent magnet(D-PMSG) wind power system has become the focus in wind power system as for the features of smaller size, lower cost, higher generation efficiency, simpler structure and good operation reliability. The main content of the paper is power optimization control strategy under full wind speed and sensorless control method of the D-PMSG wind power generator side.Firstly, the mathematical model of various parts in D-PMSG system are established. Considering the maximum power point tracking(MPPT) mechanism, a MPPT control strategy based on the tip speed ratio control and fixed pitch control for below-rated wind speed is adopted. A double-loop chatting free full order sliding mode controller is designed. According to the current wind speed, get the reference rotor speed by the tip speed ratio method. Under the control of rotor speed and current by the chatting free full order sliding mode controller, the rotor speed can track the reference speed quickly and the chattering can be eliminated effectively. The MPPT control target for below-rated wind speed can be realized by the proposed method.Secondly, this paper designed the robust adaptive pitch controller in order to inhibit the fluctuations in rotor speed and output power under the above-rated wind speed condition. Even if the system parameters are completely unknown or uncertain, by introducing a comprehensive error variable, the robust adaptive pitch controller is designed and the adaptive parameter update algorithm can be gotten. Robust adaptive pitch controller can guarantee the performance of the control system with appropriate parameters, the rotor speed can be kept at its rated value and realize the constant power output. Compared with the fuzzy control and traditional PID control, the simulation verified the proposed method is effective.Thirdly, in order to eliminate the fluctation in the output power, power smoothing control scheme which combine pitch control with generator torque control is proposed to the above the rated wind speed condition. Pitch controller is designed to regulate the mechanical power of the turbine. Torque control method is used to inhibit power fluctuations quickly. So the control method can guarantee system of constant power operation. By utilizing the characteristics of quick response of torque control, the output power characteristic can be optimized further. Additionally, power optimization control strategy for the full wind speed is also proposed. When wind speed is under the rated value, chattering free full order sliding mode control based on tip speed ratio control method is adopted, while for the above rated value, the power smoothing control strategy which combined pitch control with generator torque control is used. So system can achieve power optimization control under full wind speed.Finally, the paper studies on the sensorless control methods to reduce the cost and increase the reliability of the wind power system. An adaptive full-order sliding mode observer is proposed, combined with chattering free full order sliding mode control and adaptive control. A full-order sliding mode manifold is designed based on voltage-equilibrium equation of PMSG. The designe of the Control law can eliminate the chattering and singularity problems effectively. An adaptive observer is proposed to estimate the back EMF. After the above steps, the rotor speed can be estimated from the adaptive law. So that the extracted speed and rotor position signal are more smoothly.