Research On Control System Of Electric Vehicle Motor

Motor vehicles are modern societies'important means of transportation. The rapidly increasing number of cars brought rapid growth to serious environmental problems. Automobile gas emission have become one of the main air pollution, and oil crisis of recent years also makes an urgent task to develop low emission, low fuel consumption of new vehicles in the worldwide automobile industry. Electric car becomes the ultimate solution of vehicle development because of its zero pollution and zero emission.Permanent magnet synchronous motor (PMSM) is a new type of synchronous motor whose material is made up by rare earth permanent magnets instead of field windings, and it has the speed-control characteristic of general DC motor. It has simple structure, small size, light weight, high efficiency, high power factor, little heating of the rotor body, a large overload capacity, the smaller moment of inertia and torque ripple. Compared with traditional electromagnetic synchronous motor, permanent magnet synchronous motor doesn't require current excitation, has no electrical excitation and rotor excitation heating problems which are the attribute of electrically excited motor. So it has simple structure, high reliability and is easy to use; Contrary to the induction motor, permanent magnet synchronous motor has no slip loss, and its motor speed is strictly proportional to frequency, which is good for improving the motor efficiency and power factor. Because of small volume and light weight, permanent magnet synchronous motor can achieve the requirement of accurate and rapid control.The mathematical model of permanent magnet synchronous motor shaft in the stationary phase is a nonlinear, multivariable, strong coupling of complex systems, in which condition it is very difficult to analyze and solve the equation of this coordinates. So we need to use space vector control technique. By using space vector control technology and making transformation from the stationary coordinate to the rotating coordinate, we can achieve the decoupling of excitation component, and torque component from the stator currents, the permanent magnet synchronous motor can control magnetic communication and torque separately just like the DC.Permanent magnet synchronous motor control strategy is the development of induction motor control strategy, because the permanent magnet rotor flux is almost constant and does not require observations on controlling the rotor flux. So, the induction motor based on vector control strategy is more suitable in the control of permanent magnet synchronous motor.The vector control of Permanent magnet synchronous motor with position sensor is a control method with high performance and variable frequency, it is based on the mathematical model of the permanent magnet synchronous motor and use coordinates transform to decompose magnetic flux currents and torque current which has coupled together in the stator windings. By fulfill the purpose of respective magnetic flux control and torque control, we can make Permanent magnet synchronous motor to achieve control characteristics of the DC permanent magnet synchronous motor. Vector control not only control the frequency and amplitude of the motor voltage, but also control the phase of motor drive voltage, thus it has the virtue of high precision control, good low-frequency characteristics, and fast torque dynamic response.The design of our whole control system is based on DSP series TMS320LF2406A chip of TI Company, which is composed by the main control unit, drive unit, rotary variable drive unit, communications memory cell, pre-charge control elements. Based on the hardware platform, we have programmed control procedures to achieve the control of rotation speed and current dual-loop vector, and have completed software design of vector-control algorithm with position sensor.