Design And Research On Stator Flux Oriented Vector Control System Of Asynchronous Motor

Research on the control scheme of AC induction motor speed system has been always a hot issue in the field of AC drive control. The scheme can be divided into two kinds of vector control based on rotor flux oriented RFO (Rotor Flux Orientation, RFO) and direct torque control DTC (Direct Torque Control, DTC) based on stator flux in general.The effect of vector control based on rotor flux relies heavily on the rotor parameters of AC motor, especially the rotor resistance Rr which varies seriously as the increasing motor winding’s temperature during the running progress of the motor. The accuracy of the rotor flux orientation can be affected greatly, which can lead to the failure of the whole algorithm finally; The control effect of this algorithm with poor commonality varies greatly in a variety of different motors. Inverters can’t achieve good control performance on motors with different parameter and capacity. Although DTC overcomes the effect of the rotor side parameters, its torque ripple is significantly larger than vector control, poor low speed performance, and the accuracy of the stator flux oriented depends on stator resistance Rs. It also exists the problem of the rising temperature of the motor wedding. This paper introduces a stator flux oriented SFO (Stator Flux Orientation, SFO) vector control scheme which has combined with the advantage of RFO’s continuous and smooth speed control, overcomed the problem ofDTC’s large torque ripple based on the two methods and provided a powerful guarantee of continuity and rapidity for the control system. Through large simulation experiments under all condition on small, medium and large capacity motor with low and high speed, no load and full load by Matlab/Simulink, results show that this algorithm is suitable for a variety of capacity AC motors under appropriate controller parameter with good static and dynamic performance.In addition, this paper has also made its corresponding improvements for the problems existed in DTC. This paper uses SVPWM (Space Vector Pluse Width Modulation, SVPWM) algorithm instead of traditional three phase current hysteresis comparator in RFO and some voltage vectors’combination in DTC to realize PWM (Pluse Width Modulation, PWM) wave modulation; It discusses the cumulative error and the error to amplitude and phase while computing the stator flux by traditional integrator. It utilizes double integrator based on coordinate transformation with fixed threshold to observe the stator flux Ψs and gives the corresponding simulation results; It has made some useful explorations on the aspect combined the speed sensorless control technology with this algorithm. The model reference adaptive strategy MRAS (Model Reference Adaptive System, MRAS) has been taken to replace the traditional computing method using the slip angular frequency ωst and synchronous angular frequency ωe. This method estimates the motor speed by two rotor flux observer model error adjusted by PI controller. The character of this control scheme has been analyzed by low and high speed simulation. At last, this paper makes a further look at this control scheme, it can get a better suitability with the stator resistance online identification.