Study On The Control Strategy Of Sensorless Brushless DC Motor

Compared with sensor brushless DC motors, sensorless DC motors have the merits of simple structure, high efficiency, reliable performance and easy maintenance. They have better application in the fields of national defense, aerospace, robots and automotive electronics. However, there are some deficiencies in the control strategies of rotation rate which greatly limit its further application. Hence, the study on rotation rate control strategies of sensorless brushless DC Motors has very great significance. This essay has a deep research on the rotation rate control system of sensorless brushless DC Motors.1. On the basis of the speed regulation theory of sensorless brushless DC Motors and the analysis of its structure and basic working theories, the conceptual design on sensorless brushless DC Motors regulating system of double closed loop has been established. For electric current loop, the adaptive current adjuster is designed; for the speed loop, based on fuzzy PID controller, the rotating speed adjuster is designed. The results of experiments show that the controlling strategies adopted in this essay can effectively achieve the stable speed regulation of sensorless brushless DC Motors.2. So far as the difficulties of sensorless brushless DC Motors in detecting rotor position, the essay has proposed the method of rotor position detection based on back EMF Third Harmonics, and designed back EMF detection circuits and low-pass filter circuit. After low-pass filter circuit filter out high frequency harmonic signals, the accurate rotor position can be obtained.3. As to the torque ripple suppression of sensorless brushless DC motors, PID torque ripple suppression method on the basis of BP neutral network parameter self-study has been adopted. The experimental results show the pulse suppression method applied in this essay can effectively suppress the torque ripple.4. Digital rotation rate control system of sensorless brushless DC motors has been designed through utilizing digital signal processor TMS320LF2812. The essay mainly accomplished the design of PWM control, DC sequential sampling model, signal acquisition unit and I/O control; furthermore designed current detection circuit, motor driving circuit, voltage detection circuit, low-pass filter circuit and power supply circuit, etc.