Research On Sensorless Control Strategy Of Doubly-fed Induction Generaor

With the development of global economy and human society, the energy sources and the environmental protection become two important issues of the world. The development of renewable energy sources has become a social consensus. As a clean renewable energy source, wind power generation is becoming more and more important and attractive. Based on the project as Supported program of Anhui Province during the10th Five-year Plan Period and the project as Supported program of the Ministry of Science and Technology during the11th Five-year Plan Period, this dissertation choses the doubly-fed induction generator (DFIG) as the research subject and makes a deep study on both the theory and practice, aided by simulations and experiments. The control system of DFIG requires accurate information of the rotor speed and rotor position, while the present control systems of DFIG use speed sensors to get information, but the sensors themselves bring a lot of problems, such as the cost increase and low reliability. That is why this dissertation focuses on the sensorless control of DFIGWith an analysis of the DFIG’s structure and operation theory, this dissertation makes an introduction of present DFIG’s sensorless control strategies and points out their respective merits and drawbacks. The DFIG must possess the capability to operate in both of the motor and generator mode while set in the real wind farm, but most sensorless control strategies can only be applied to generator mode. This paper proposes a new model reference adaptive control (MRAC) strategy that can solve this problem. The main research content included in this paper can be listed as follows:(1) Brief introduction of China’s wind energy distribution, the development of wind power system, the installed capacity of wind power generation in the world, the main types of wind power generators, as well as the trend of wind power generation in the future. Some hot engineering topics of the wind farm, such as the yawing, pitch control and low voltage ride through (LVRT) were also introduced..(2) The wind power generation system is been introduced and the operation theory with equivalent circuit of DFIG are analyzed following the discusion of the DFIG’s merits. On the control strategy of MW level DFIG, four operation modes such as start mode, MPPT mode, constant power control mode and stop mode are taken into study according to their sequence being put into operation.(3) The mathematic model of MW level DFIG is established respectively in the three phase A-B-C still frame, two phase α-β still frame and two phase synchronously rotating d-q frame. The energy flow within DFIG system is analyzed in four operation mode. Main types of wind power converter are introduced and the vector control strategies based on stator voltage and stator current are also proposed.(4) An110KW DFIG experimental prototype that integrates DFIG, back-to-back converters, controllers and monitor is built up in the laboratory to meet the requirements of theory verification, and the experiments demonstrate the feasibility of proposed methods.(5) With a study on the merits and drawbacks of various sensorless control strategy of DFIG, a new model reference adaptive control strategy is proposed in the dissertation, that can acquire correct rotor speed and better system performance compared to those previous strategy and is easy to be implemented.