The Research On Current Sensorless AC-servo Drives In Lockstitch Sewing Machine

High performance PMSM drive system needs high-performance current, speed and position feedback, which not only makes the system more complex but also increases the cost of production and maintenance. Therefore, nowadays researches on reducing and even eliminating sensors becomes very hot, among which eliminating position and speed sensor is more popular. However, in such systems having high requirement of position as sewing machine drive system, the position and speed sensor is necessary. So current sensorless drive system of PMSM is introduced in this thesis. Based on a DSP TMS320LF2407A controller specially designed for motor control, PMSM is studied in this thesis, which is used to drive automatic high-performance sewing machine. And the current sensorless drive system of PMSM is designed. Firstly, the system structure, production technics and design requirements of sewing machines are introduced briefly. Then the math model of PMSM, theory of field-oriented control of PMSM and space vector PWM are described particularly, and the implementation diagram and coordinate conversion of FOC vector control are also provided here. Secondly, after analyzing the control strategy of PMSM control system without current sensor, a novel estimation approach for current estimation is proposed. According to the voltage equations deduced from the math model of PMSM, the implantation diagram is modified, and the current module is constructed in which current control is realized by reference current and simulation current. And the estimation error caused by dead time of PWM is compensated by the average-based method. Moreover, the model of the proposed system is builded and simulated on MATLAB platform, and simulation results show that the method is simple, feasible, and the system added the compensation has good performance. Finally, based on this, the processor TMS320LF2407A is selected as the core part of hardware control circuit, and software is designed in combination with the control of sewing machine. Then, experiments based on this platform are made on the sewing machine drive system with current sensor, and the results show that the system can fulfill the work prearranged well, and achieve design goals. Consequently, the current sensorless servo system can be obtained by modifying the system mentioned above. Experiment results show that this system also can finish the production work well, and further prove that the control method of current sensorless system has some practical values.