Research On Design Methods And Related Problems Of Permanent Magnet Synchronous Motor For Electric Vehicles Application

Due to the energy and environment issues, the conventional automobile industry is changing to"electric". Most countries and automobile companies have invested a lot of money to do the research on electric vehicles. Electric machine dirve system is the core component of the electric vehicle and it is the research focus of the area. However, many current designs are limited to conventional design method of the electric machine supplied by industrial frequency electricity and it is based on the fact that electric machine often operates under rated speed. The electric machine applied in electric vehicle is very different. It should cooperate with the operation of the electric vehicle like frequently start, stop, accelerate and decelerate. Its operation status is very complex and conventional design method can not satisfied the requirements of the electric vehicle. Thus, in this paper, it is tried to study associated problems of permanent maget synchoronous motor (PMSM) from the requirements of the electric vehicle and provide new design method for the electric machine applied in electric vehicles.The drive machine for electric vehicle application not only focus on rated speed and rated power, but also regard maximum speed, maximum power and high efficiency region. A design methd of permanent magnet synchronous motor for electric vehicles was presented based on the specifications'analysis. The method included six parts. (1) Sizing procedure. (2) Design of magnetic circuit, winding and electric circuit. (3) Design of rated performance. (4) Caculation of speed ratio under flux weakening control and overoload ratio. (5) Design of region performance. (6) Performance design based on the driving cycle of electric vehicle. The design method combined the control strategy all the time. It realized the calculation of speed ratio under flux weakening control, overoload ratio and Map diagram. The calculation results had higher accuracy and more accord to the practical. The performance design based on the driving cycle of electric vehicle made the design of electric machine considered the driving condition of the electric vehicle and made the electric machine more fulfill the requirements of the vehicle.The dimension of electric machine is very important for the vehicle arrangement and it is very meanful to get the diemension calculation results fast and accurate on the vehicle design stage. Thus, the sizing method was studied in this paper. The relation between stator inner diameter and outer diameter was derived from the basic relation of motor dimesion and it combined the parameters like electric loading. It solved the problem that it is difficult to calculate power using conventional sizing equation when dimension is known.Calculation of armature reaction reactance is the necessary procedure of the permanent magnet motor design for electric vehicles application. The calculation usually needs a lot of finite element computation. To change this situation, conventional analytical calculation method of direct axis and quadrature axis armature reaction reactance was improved in this paper. It improved the accuracy compared with conventional analytical method and reduced the calculation time compared with finite element method. Based on it, the comparison method of rotor configuration based on armature reaction reactance conversion coefficient was presented. It helped the comparison of different projects in the initial design procedure.Temperature rise, especially for the dynamic temperature rise is the fundation of complex operation analysis for the electric mahchine used in electric vehicles. For the steady state temperature rise calcution, the end winding part was added to determine the highest temperature spot in the electric machine. For dynamic temperature rise, the error of lumped heat capacity method was analized and an approximate calculation equation is presented based on it. Then, the dynamic temperature rise calculation was equavilate to the model of one dimensional composite medium heat conduction. The approximate solution of patical differencial equations within solution area was obtained by Green's function. The solution could not only describe the temperature variation principle with time, but also reflect the the dimentional distribution of temperature. The solution accuracy was verified by test and the error was within 10%.The type of electric driven machine is determined by the configuration of electric vehicle. Using the above method, the design features of low-speed high-torque type, high-speed low-torque type and high-speed high-torque type electric driven machine were discussed and corresponding design suggestions were given. These three types were corresponded to the real drive system of electric vehicle: double-motor plus AMT hybrid system, single shaft torque hybrid system, double electric machine plus planet gear hybrid system and wheel drive system respectively.The design method of permanent magnet synchronous motor for electric vehicles has considered the features of electric vehicle. It has verified by several real engineering practices and formed some foundations for the research on the electric driven machine used in electric vehicles. The research was supported by National 863 electric vehicle programe"drive motor and its control system of Hongqi hybrid electric car","drive motor and its control system of Jiefang hybrid electric bus", transverse programe"research on high power density permanent magnet synchoronous motor"and civil programe"research and develop of electric wheel". The permanent magnet synchronous motor for the hybrid electriv car of First Automobile Works designed by the method presented in this paper has passed the National 863 test. The test results verified the effectiveness of the design method.