Research On Design Technology And Application Of Direct-drive Permanent Magnet Generator With Wind Turbine

The wind power is not only the fastest development but also with the most scales using and commercialization prospects of the renewable energy. And the wind power generation is the most effective way to using this energy. Cancelling the gearbox and using the permanent magnetic synchronous motor as the main generator, the direct drive permanent magnet wind generation system is attractive because of its simple construct. So the simply construct, high efficiency and low faults become the characteristics of this system. Because of having the able of working on severe environment, this system is suitable for large capacity offshore wind power.In this paper, the direct drive permanent magnet generator is taken as the main researching object. The main research of this paper as follow:(1)The basic structure of the direct drive permanent magnet(DDPM) wind turbine is introduced.The principle and power characteristic of the wind turbine is elaborated.And then the main work is on the mathematical model of the DDPM wind generator and inverter,the control strategy,the model of the DC bus and the theory of the maximum wind energy capture.All of these is the foundations for later research.(2)Since the DDPM wind generator is connect into grid by a full power inverter,the current and the output power is controlled by the inverter of the motor.Thus the design method of the DDPM wind generator is different from the previous generator.In order to analysing the operator characteristic of the DDPM wind generator accurately,the key problem is setting up a new model which is based on the control strategy of the inverter. In this paper,the stator voltage equation and the relationship between the stator voltage and the DC bus with the vector control motor inverter id=0are derived by analysing the operator characteristic on the condition of controlling of the inverter.The laws of the stator voltage and the power factor varies with the variation of the electromagnetic power are studied.The important operator features of the DDPM wind generetor with the vector control id=0are obtained.All of these research work are crucial to establish the new model in next chapter.(3)The limitations of the design method of the tradition sychronous generator which is connected into the grid directly is analysed.In this paper,combining the theory of the vector control and the classical "Calculation of magnetic circuit" and "Parameter calculation",the new design model based on the inverter vector control is proposed.Considering the influence of the inverter control strategy,this design model can reflect the practical opertation more accuracy. The correctness of the proposed model is approved by the simulation and the comparative analysis.(4)As the DDPM wind generator process low speed and big size,the chosen of its slot/poles combination and size of the permanent magnet have a lot of space.How to analysing the influence of the design parameters to the performance and the weight of the motor is the critical condition for optimal design.Accordingly in this chapter,this problem is analysied on the condition of the control of inverter.The analytic model of the parameter analysis of the DDPM wind generator is established.Taking use of this analytic model the follow relationships(pole number and the size, the inductance parameter and the iron-core loss,the slot/pole combination and the winding coefficient,the waveform of the electromotance,the thichness and width of the permanent magnet and the no-load flux density,electromotance,inductance parameter and the the iron-core,number of conductors and the performance of the motor) are discussed.Some valuable conclusions are gained.And all conclusions are approved by parameters of electromagnetic design of the DDPM wind generator.(5)The cogging torque is inherent in permanent motor.And it effects the cut-in speed and the energy captruce directly. So how to decreasing cogging torque is also a key problem in the design system.Firstly,the mechanism of the generation of the is analyzed. The relationship between the design parameter and the cogging torque is considered.The method that reasonable slot/pole combination,changing the amature parameters and changing the permanent magnet parameters are reviewed.The novel concept elementary cogging unit is proposed by analysing the relationship betweent the single permanent magnet and the general cogging torque of the motro on the different slot/pole combination.The permanent magnet can be divided into many elementary cogging unit.And the cogging torque generated by the each unit process the same amplitude and phase.A new method based on the elementary cogging unit is presented to reduce the cogging torque.This method is not only simple but also effective.And more,no additional cogging torque harmonic is bringed.(6)A2MW DDPM wind generator is designed by using the proposed model and methods.The simulation of finite element and the performance of the system are carried out by Ansoft and Matlab software. Manufacturing and test of the generator are finished in Xiangtan Machine Group Co., Ltd. The test results show that the performance of the motor can meet the design requirement perfectly. And the test data fit well with the design data. All of those indicate that the design model and the analysis methods proposed in this paper are effective and correct.