Research On Doubly Fed Electric Machine Drive System Of Distributed Drive Electric Vehicle

With the continuous development of new energy electric vehicle technology,the types of drive machines used in electric vehicles are gradually increasing.Because the driving machine characteristic will directly affect the vehicle dynamic performance and fuel economy,so the choice of driving machine and corresponding driving system with its excellent performance is crucial to the development of electric vehicle industry.Based on the international cooperation program(2010DFB83650)of the Ministry of science and technology,this paper takes a compact distributed drive electric vehicle as the research object and focus on the following points: research on the key technologies such as theory analysis,configuration design and control strategy of doubly fed electric machine drive system;build a double fed electric machine test with double converters;test and verify the excellent performance of the doubly fed electric machine drive system.First of all,according to the characteristic of doubly fed machine controlled by double converter in driving system,the basic principle and speed regulation method are analyzed.The steady state equivalent circuit of doubly fed electric machine is established and then the energy conversion relation of stator and rotor and the expression of active and reactive power are also deduced.In combination with the driving and braking conditions of electric vehicles,the power transfer of doubly fed electric machines under different running conditions is analyzed and summarized,which provides a theoretical guidance for the design of electric machine control strategies.The dynamic mathematical model of doubly fed electric machine is established,and the transformation method of stator and rotor three-phase coordinate system to stationary two phase coordinate system,rotor two phase coordinate system and synchronous rotating two phase coordinate system are given,which lays a foundation for subsequent research.The expressions of current,voltage,flux linkage space vector synthesis are given by the synthesis calculation of space vectors.Through the analysis of the active power of the rotor and stator compound vector,the consistency between the analysis of the space vector model and the analysis of the equivalent circuit model is pointed out.Then,space vector method is adopted to establish the steady state equation of a double fed machine used for electric vehicle,so that the steady state analysis results are more closely connected with the dynamic analysis results and the dynamic control of the electric machine can be guided by the analysis of the steady-state model.The steady-state performance of the doubly fed machine is simulated and analyzed by using the vector control method based on stator magnetic field orientation.In order to make full use of the characteristics of the double converter control and to prevent the failure of the automobile drive system,two alternate operation modes are proposed and the steady expression of correlation model is derived respectively.In addition,for the sake of embodying the advantages of doubly fed electric machine,the speed range and influencing factors of vehicle doubly fed electric machine and asynchronous motor are analyzed with the same parameter.Thirdly,according to the different working states of the driving and braking energy feedback of the electric vehicle,the topology and working principle of the three-phase PWM converter are analyzed.With the consideration of the doubly fed electric machine drive system of distributed drive electric vehicle,a layout scheme with the least number of converters is proposed and according to this configuration,a variable flux linkage stator voltage control method is proposed to adapt to the normal operation of the electric machine drive system.Based on the analysis of the factors affecting the capacity of the stator and rotor side converter,a control strategy for minimizing the converter capacity is proposed to reduce the required bus voltage and the production cost and to facilitate the arrangement.Finally,in order to reduce the voltage harmonics of the converter on the stator side,the switching angle of the converter is optimized by genetic algorithm.The results show that the selected harmonic is eliminated effectively after the optimization of the method,thus reducing the torque ripple due to voltage harmonics.Fourthly,According to the model reference adaptive principle,the MRAS speed identification based on stator flux linkage is analyzed and studied,and the initial position and the angle of rotor are determined and analyzed.The state equation of the dynamic model of doubly fed electric machine in two phase stationary coordinate system and synchronous rotating coordinate system is analyzed,and the state equation of the dynamic model of the alternative operation mode of the doubly fed electric machine is given.A speed control system based on stator flux oriented PI vector control is designed,and the MRAS speed identification method based on stator flux linkage is used for simulation analysis and verification.The results show that the speed observation performance is good and it is concluded that the stator variable frequency acceleration will be beneficial to reduce the torque ripple of the process.When the inductance and resistance parameters are changed by the external influence,the PI parameters of torque regulator are adjusted on-line by the fuzzy control method and the simulation results show that the dynamic torque ripple of motor has been improved greatly.Fifthly,the longitudinal dynamic analysis of the driving and braking conditions of the distributed drive electric vehicle under longitudinal driving is carried out.According to the characteristics of distributed drive electric vehicle,the balanced torque distribution control strategy of two modes,power and braking,is proposed.This strategy will effectively reduce the load difference of each drive motor,which is conducive to the unified cooling of the motor and prolong its service life.Based on two different cycle conditions of NEDC and US06,the longitudinal dynamics of vehicle is simulated and analyzed whose results verify the effectiveness of the proposed strategy.Finally,d SPACE-1103 is selected as the rapid prototyping controller and test platform was built to control the doubly fed electric machine with double converters.Then,The performance of doubly fed electric machine based on rotor reactive power full compensation is tested and analyzed.The test results show that the drive system of the doubly fed electric machine can run at an extremely high power factor,which reflects the superiority of the drive system.