Research On The Key Techniques For High-speed Control Of Induction Motor

With the development and application of AC drive system, Speed range,steady-state accuracy and dynamic response are demanded better. The capacity offield weakening operation has been widely applied in various industrial fields such asmain spindle drives, traction and electric vehicle drives. As a representative ofhigh-performance AC motor control, Flux-oriented vector control achieves adecoupling of the stator current excitation component and torque component, it hasunique advantages and convenience in adjusting the flux and becomes one of the mainmethods to study induction motor high speed operation. This paper systematicallyanalyzes the key technology for induction motor high speed operation based on vectorcontrol. The field weakening control, PWM technology and current regulator design isstudied. The main contents of this paper are as follows:Induction motor high speed operation based on field weakening control will leadto the decay of system output torque and dynamic performance inevitably. Accordingto the limits of voltage and current, this paper analyzes the maximum torque operatingpoint of motor in the whole speed range deeply, Torque-maximizing field-weakeningcontrol is provided. The principle of control is clear and simple. By the feedback ofreference voltage, it can adjust the magnetizing current optimally in the whole rangeand independent from motor parameters. Simulation results show that the fieldweakening control is stable, has a good dynamic characteristic. The ability ofmaximum torque operation over the entire speed range is ensured.Voltage source PWM inverter is commonly used as a drive unit with fastdynamic response. Although its output current has little harmonic waves by SpaceVector PWM control，Bus voltage utilization is not the maximum. Based on thefundamental phase voltage equivalence, this paper analyzes the trajectory of outputvoltage vector in over-modulation region emphatically. Inverter can transfer tosix-step mode with trajectory control, while output voltage reaches the maximum. Through the combination of over-modulation and the field weakening control, thevoltage limit boundary is increased and the output torque of the motor running at highspeed is further improved.In addition, when the vector control system is running at high speed, theperformance of current regulator is deteriorated by the dq-axis coupling voltage andthe digital control delay, Stability of system is affected. This paper builds the discretedomain model of induction motor, system features using different current regulators iscompared. Based on the discrete domain pole-zero cancellation method, a new currentregulator design is presented. It can decouple the dq-axis voltage and compensatecontrol delay in whole range. The ability of high-frequency signal regulation isimproved. Simulation and experiment results show that the precision and stability ofsystem is improved in wide speed range by using the presented current regulator.Finally, Referring to reciprocal power-fed coaxial connected AC drive, this paperestablishes the dual induction motor vector control system simulation model. Directflux oriented control based on full-order flux observer is used. By modeling thecoupling, torque transmission between two motors is achieved, simulating the actualrigid connection. Compared with experimental results, the simulation has a goodreferential.