Compressor Using A Permanent Magnet Motor Control Systems Development

Reciprocating compressor plays an important role in the national economy for it's advantages like wide-range use and so on. In our country, reciprocating compressor is mainly droved by asynchronous induction machine, which leads the fact that the efficiency is very low. At present ordinary Permanent Magnet Control system usually accept PI control arithmetic with the velocity and torque feedback equipment as its controller. However the price of this controller is still high comparing with the low-cost compressor, meanwhile air force in the compressor is varying according to the motor's rotation, which means the load of the motor has periodical ripple. In this situation, the character that stability is in contradiction with response velocity of PI parameter integration method is obvious. In some critical situation where sophisticated control is needed, the Permanent Magnet Synchronous Motor is usually used as the air compressor driver. However, the control is quite complicated and expensive. In order to solve this contradiction, a low-cost control especially for reciprocating compressor was proposed.In the dissertation, reciprocating compressor's torque characteristics on the condition of single compression, double compression in the same pressure rate and double compression in different pressure rate were analyzed in detail from the viewpoint of compressor design. Research on optimizing the resistance characteristic of the compressor was done to facilitate the control development.Theories for Brushless DC Motor and the direct torque control of the Permanent Magnet Motor were presented. On the basis of the idea of direct torque control as reference, and took the reciprocating compressor's torque into consideration, varying duty-cycle control method was put forward. Simulink toolbox and simulation programs written in MATLAB were used to verify the feasibility of this method.Torque ripple due to untimely phase conversion was analyzed in detail. Mathematical models for back-EMF current and torque ripple in untimely phase conversion were developed. An experimental circuit board was built for the proposed control system, including the rectification circuit, power driver circuit, back EMF detection circuit and so on. PIC programs were written to implement functions like phase conversion jump-start, back EMF detection and so on.A proper curve obtained through experiment, which represents the relation between voltage and frequency, was presented to guarantee that the motor could jump-start steadily. Experiment verified that capacitance, duty-cycle and frequency would affect the detection of back EMF; and that the varying duty-cycle control method is necessary and feasible, which provides a novel design way for the Brushless DC Motor used as compressor driver.