Design Of Doubly Fed Wind Turbine Based On Double-mode Operation

With the development of wind power generation technology and the decreasing cost of the wind farm,the wind fields with good wind conditions have been fully developed.Doublyfed wind turbines are the mainstream models in the world now,but due to the low power coefficient and high iron lost out of its VSCF operation range,especially in the low speed wind area,it is very significant to do research on improving power generation efficiency of double-fed wind turbine in low wind speed conditions.Firstly,the connection and difference between the doubly-fed wind power generation technology and the direct-driven permanent magnet power generation technology are analyzed.Some disadvantages of the doubly-fed generator compared to the direct-driven permanent magnet generator at low wind speed are described.At the same time,the operation principle and control strategy of the traditional doubly-fed generator are expounded in details.Secondly,based on the operation principle of the traditional doubly-fed generator and combined with the characteristics of the direct-driven generator,the topology of a new double-mode of doubly-fed generator is proposed.And the new generator has two operation modes,low-speed and super-synchronous operation mode and traditional doubly-fed operation mode.In the meantime,the operation principle and control strategy of the lowspeed and super-synchronous operation mode are analyzed in depth,the minimum iron loss model is proposed to calculate the stator reference power.Then,a simulation model of 2MW traditional doubly-fed generation system is established on the PSCAD / EMTDC platform.Based on the simulation model of 2MW traditional doubly-fed generation system,this thesis sets a switching converter between stator and power network,and then verifies the control strategy of low-speed and super-synchronous operation mode in double-mode generator.Thirdly,according to operation data which got in the low-speed and super-synchronous operation mode and the limit of the capacity due to the rotor-side converter,the switching wind speed of the two modes and the required capacity of stator-side converter is solved.Then the process of mutual switching between the two modes is analyzed by block diagram,and the simulation curves of the wind turbines in the switching process are simulated by MATLAB.Finally,comparing the characteristics of the traditional doubly-fed generator,the traditional doubly-mode generator and the new double-mode generator proposed in this paper,the new one has the advantages of improving the capacity of the energy captured at low wind speed and reducing the iron loss.Based on the wind-speed data of a low-wind-speed field in the north field of China,the analysis of examples of the new double-mode generator is completed,and the economic practicality of double-mode generator mentioned in this paper is verified.