Research And Design On Flux Linkage Self-Control Based Direct Torque Control System Of Permanent Magnet BLDCM

The research and development of electric vehicles has become a global consensus,it s very important for energy conservation and emissions reduction,the protection of the ecological environment and the reduction of urban haze.The driving force of electric car comes only from electric motor,hence the car performance is mostly determined by its motor performance.Permanent magnet brushless DC motor is such a new energy saving electrical machine,which has the merits of small volume,light weight,high efficiency,low rotary inertia,highly control precision and so on.It also has good mechanical character as common DC motors.So the permanent magnet brushless DC motor is chosen as the power system for electric vehicle.In this dissertation the direct torque control and commutation torque ripple suppression of the BLDC are respectively studied.Firstly,this paper analyzes the basic structure and working principle of brushless DC motor,and the mathematic model of it is deduced,which provides a theoretical basis for direct torque control strategy and the construction of the simulation model.Through the analysis of the traditional direct torque control principle of brushless DC motor,it has the difficulties of flux linkage estimation and reference.Based on analysis of the characteristics of brushless DC motor(BLDCM)and the trajectory of the flux linkage after applying the space voltage vector according to the position signal,a novel BLDCM flux linkage self-control based direct torque control(DTC)scheme is proposed.In this scheme,only single hysteresis-controlled torque loop is adopted.The voltage vectors is decided by both the torque loop output and position of magnetic poles.not only the torque control of the motor is well realized and flux linkage self-control is achieved.The control system is simplified by the presented scheme through eliminating the flux linkage loop.Additionally,the reason of commutation torque ripple is stated in detail in this paper,and the commutation torque ripple suppression strategy is put forward.The simulation model according to the control strategy is built in the environment of PLECS,through analyzing the simulation results,this control strategy is effective and feasible.According to the simulation model,The Permanent Magnet BLDCM controller for pure electric vehicle is designed and made.The hardware circuit based on DSP and CPLD is designed and the software program is programmed.Based on the analysis of the experimental current waveforms,the square wave control can be realized by this designed controller.The whole drive system has been installed on the pure electric car,the electric car is on the actual road and achieves good test results.