Development Of Electric Special Vehicle Drive And Automatic Transmission System

With serious air pollution and environmental awareness enhanced,to develop energy-powered electric vehicles can ease the pressure on environmental governance to some extent.The project was commissioned by the enterprise to develop electric vehicles controller.Brushless DC motor is selected as the drive motor because it has characteristics of high efficiency,large torque and good speed performance,what's more,it avoids the problem of brush motor that is brush easily be worn.Two issues need to be addressed: 1.There is a large torque ripple when brushless DC motor is running,resulting in big noise and vibration in vehicles going forward.2.With a fixed reduction ratio mode,the electric vehicle can not meet the performance requirements of load starting,climbing and high-speed running.A controller is designed based on continuous current control method to reduce commutation torque ripple and the system has function of automatic transmission.Finally,practicality of continuous current control method on electric vehicles controller was verified through experimental platform debugging and loading test.Combined with the development goals,the main contents of this paper are as follows:(1)Composition and basic working principle of brushless DC motor control system are described.Mathematical model and work process are analyzed.Detailed analyses of reasons for commutation torque ripple and continuous current control method have been given.This method can effectively avoid current fluctuations in non-commutated windings,thereby reducing the commutation torque ripple.(2)Automatic transmission method using in the controller operation and brush DC motor control method are narrated.Control circuit has been improved to reduce the number of MOSFET in the transmission device.The working principle of the transmission,Hall signal and Law of automatic transmission are presented and speed matching method is introduced to improve the stability of the shifting process.(3)Hardware circuit of the controller was designed,mainly including: the master chip dsPIC30F4011 peripheral circuit,power supply circuit,main circuit and driver circuit of three-phase inverter,various signal detection and protection circuit,etc.(4)Software programs of various functions for the controller were completed and debugged combined with hardware circuit.After loading test of three months,the controller is still in stable operating condition.Control precision and effect both meet the business requirements,thus,the controller is reliable.