Study on Power Smoothing Control Strategy and Control System Design of Direct-driven Permanent Magnet Synchronous Generator for Wind Turbine

Study on Power Smoothing Control Strategy and Control System Design of Direct-driven Permanent Magnet Synchronous Generator for Wind Turbine
　　With the deteriorating environment and the growing energy crisis around the world,the full development and utilization of renewable energy has become the consensus of the world countries. As one of the most common renewable clean energy sources,wind energy has been made widely attention, and wind power technologies have made a rapid development in the past two decades.In all kinds of wind power generation systems, a wind energy generation system(WEGS) with direct-driven permanent magnet synchronous generators (DDPMSG) has been widely applied due to Magnet lifter its simple drive train system, high operational reliability, and high power generation efficiency and so on. To improve its performance, some appropriate control strategies have to be used. As for the WEGS with DDPMSG using the dual PWM AC/DC/AC voltage source converter, both the machine-side converter and the grid-side converter have to be controlled.The purposes of controlling the machine-side converter is to control the active power of wind turbines and wind energy availability, at the same time, the torque ripple can be also limited. In addition, the purposes of controlling grid-side converter is to control the active and reactive power delivered to the grid.Due to the uncertainty, uncontrollablety and stochasticly of wind energy, the output electric power of a WEGS has usually large fluctuation.
　　If the grid-connected system is unrestricted, the power fluctuation not only will affect the economics of the grid operation, but also may even threaten the safe operation of the whole electrical power. Especially,with the increaseing total installed capacity of wind turbine systems, this problem may become more and more obvious. Therefore, it is an urgent task to improve the output power quality of grid-connected WEGS by introducting advanced control strategies .In this thesis , the control strategies of damping the active power output fluctuations of a WEGS with DDPMSG are deeply researched. Firstly, as for the base of simulation and analysis, the mathematical models in the components of the WEGS with DDPMSG are established, respectively. The vector control mathematical model of the machine-side converter is also established by the coordinate transformation. Based on the analysis on the mathematical model of the grid-side converter, a voltage orienting vector http://www.999magnet.com/products/131-magnetic-lifter control model of grid-side converter is proposed. Taking into account the highly nonlinear of the wind turbine due to the effect of aerodynamic performance and the great inertia of the blade, it is difficult to obtain good performance by using the conventional PID pitch control strategy.
　　Thus, a fuzzy variable pitch controller is designed, and the simulation results have shown that the fuzzy variable pitch control has better performance by comparing with the traditionall PID pitch control. In addition, considering the WEGS is the strongly coupled, nonlinear, parameter variable system, a sliding mode control is introduced in the power control loop. The simulation results have shown that the sliding mode control system not only has better dynamic performance, but also eliminate the effects on the machine parameters variations and external disturbances, and has good robustness. Also, the main shortcoming of the WEGS with the conventional power control strategy is analyzed, and a new control strategy which do not require auxiliary equipment is proposed. That is , within the effective range of the wind speed, the fuzzy control is used to regulate the operation speed of the wind turbine , and torque dynamical sliding mode control is used to regulate the active power, the simulation results have shown that the control strategy can effectively control the output active power fluctuations due to the wind speed fluctuations and so on. At the same time, a flywheel energy storage system in the http://www.999magnet.com/products/131-magnetic-lifter DC-link is studied without changing the control strategies on the grid-side and the machine-side converter. The smooth control of the output active power is achieved based on the energy control strategy of the flywheel energy storage system; Finally, an experimental platform applied to WEGS with DDPMSG is set up by using the high-speed digital signal processor(DSP) and integrated intelligent power modules (IPM). A series of experiments have been performed in this platform, such as the independent control of active power, the independent regulation of the reactive power, variable-speed constant-frequency operation, the largest wind power tracking control and so on. And the experimental results verify the correctness of the foregoing analysis.From the viewpoint of electrical power, this thesis seeks to improve the control strategy of a WEGS with DDPMSG. The related work maybe provide a theory basis for the engineering design and lay the foundation for the practical application.