Research And Development Of A Digital Sensorless Control System Based On DSP

In modern industrial field ,CNC machines have become the main part of the equipments. Generally speaking, The CNC machine is a mechanical motion equipment constituted by of X-Y stage and Z- axis device, meanwhile each axis is derived by a actuator such as direct current motor(DC motor) or alternating current motor(AC motor). Owing to its inherent properties such as high power density, low power factor, high efficiency and torque to inertia, Permanent magnetic synchronous motors(PMSMs) are widely used in various fields which need high control precision and perfect reliability characteristic, for example, aeronautic and astronautic field,CNC machine, following system of radar and various military weapon, robot etc.Speed sensor with high resolution such as encoder, velocity-measure motor is necessary in high performance loop-closed control system.The cost of the sensor is about one third of the total servo system, in addition the length is about one third of the motor, what's worst, according to the statistical data from Fujimotor more than 60% of the faults occurred on the sensor. Obviously a speed/position sensor increases the cost and volume of the system, decreases the reliability and in some conditions it doesn't work or can't be installed. The scheme that estimating the rotor position by measuring the phase voltage or current based on some advanced algorithms is receiving more and more attentions. In recent years sensorless control technique becomes one of the most active techniques for PMSM and will be the trend in the future.It is known that PMSM is a nonlinear, coupled and high-order system, the result is not satisfied using traditional linear control method. With the development of the digital signal processor non-linear control technique is gradually applied into PMSM. The sliding-mode variable structure theory is applied to the FOC for PMSM in the paper and as a result the the motor can be controlled without mechanical sensor.The main works and contributions include:(1) The full digital sensorless control scheme based on DSP is proposed after giving a serious research on the domestic and overseas actuality of the field,especially the key techniques,the speed estimation based on sliding-mode variable structure and space vector Pulse-Width Modulation,are studied detailedly.(2) The mathematical model of the permanent magnet synchronous motor and the algorithms is set up based on the television and magnetics,the strategy is verified and improved during the simulation study.(3) The hardware and software are designed and implemented based on digital signal processor (DSP) TMS320F2812 for its excellent computational capability and rich peripheral resource.Finally some experiments are implemented under different conditions such as start-up, speed variety and torque variety. The results shows that the speed estimation follows the actual value commendably. The overshoot of the speed estimation is about 1.414%,the steady state error is about 4r/ min when the speed reference is 500r / min without load. The experience results verify the control algorithm under different conditions, and also demonstrate the proposed algorithm has not only good dynamic/steady-state performance but also perfect robustness and reliability.It can be seen that the structure of the control system is very simple; the cost is greatly reduced while the robustness is increased. The system can be applied on electrical driving system such as CNC machine, robot, packaging and printing fields.