The Research On Key Control Techniques Of High Speed Drive System For Ac Machines

The high speed drive system for ac machines has been widely applied in various industrial applications such as main spindle drives, traction and electric vehicle drives, and plays a significant role in automation equipment. Based on the relevant documented literatures, this dissertation focuses on the key control techniques of high speed drives for ac machines. The profound theoretic analysis and study have been made for the purpose of developing the high-performance high speed spindle drive system.Induction machine (IM) and permanent magnet synchronous machine (PMSM) have been widely used in spindle driving for CNC machine tools because they are well suited to high-speed operation by means of flux-weakening. The rotor flux-oriented vector control method is a desirable candidate for wide speed range control because decoupling control between torque and flux can be realized easily. Firstly, indirect rotor flux-oriented control method for IM and direct rotor flux-oriented control method for PMSM are analyzed in detail, an unified control platform for ac machines is constructed. Based on this platform, the key problems of high speed drive system are presented as the current allocation strategy, the voltage optimize control scheme and the wide range accurate flux-oriented method.The most important one of these key problems is the allocation of the current references, which is how to control the flux current and the torque current respectively to produce maximum torque under operation constraints. Therefore, the machine operating constraints and the optimal current trajectory for maximum torque operation have been investigated in detail, and the guidelines for the implementation of the current assignment strategy is summarized. Following the guidelines, a novel solution for current allocation that effectively considered compensation for load variations and voltage coordinate control is proposed to realize the optimal current control.In the flux-weakening region, the back-EMF of the machine is approaching the maximum output voltage of the inverter, and few voltage margins can be supplied to regulate the dynamic current, so overmodulation technique for space-vector pulsewidth modulation (SVPWM) inverter is significant to enhance the utilization ration of dc-link voltage and load capacity in high speed region. Due to the modification of the reference voltage vector in the general overmodulation method, the flux-orientation can't be guaranteed and torque ripple is also introduced into the flux-oriented control system. An improved PWM modulation strategy for smooth output of full range voltage was proposed to expand the operating speed range of the motor and achieve fast dynamic response.By vector rotation transformation, decoupling control between torque and flux can be obtained, at the same time, a coupling effect generates between flux current loop and torque current loop, which brings unfavorable influence on the current regulation as the synchronous frequency approaches the current regulator bandwidth. In this dissertation, limitations in the performance of the classical synchronous proportional and integral (PI) current regulator are outlined, and another PI current regulator with anti-windup control is implemented by complex vector method, by which the transient performance of the current loop is improved signicantly in the high frequency region.In the indirect rotor flux-oriented control system of induction machine, the rotor flux position is calculated by current model. Because of neglecting iron losses and environment temperature, an inaccurate rotor time constant may result in an incorrect flux-oriented operation. The compensation issue for rotor flux phase position is investigated comprehensively, and a novel on-line optimizing algorithm for tracking the rotor time constant variation based on observing the reactive power error is proposed to guarantee accurate rotor flux orientation.At last, the whole high speed drive system for ac machines based on rotor flux orientation has been fully implemented and the validities of the proposed key control algorithms have been verified. Experimental investigations show that the proposed strategies provide a substantial improvement of the performance for IM and PMSM over a wide speed range.