Research On Speed Sensorless Field-Oriented Control Strategy Of Induction Motor

Research of high-performance speed sensorless vector control technology is coincident with the development trend of national industrial modernization. And the research also has important practical significance for the improvement of electrical automation of our country. Nowadays, the national vector-controlled inverter products are still left behind at the high-performance import ones. In this dissertation, researches are focused on high-performance speed sensorless vector controlled induction motor drives. Theory analysis, simulations and experiments are performed concerning rotor flux observer, field-oriented robust control and dead-time compensation.Based on the analysis of limitation of conventional rotor flux observer, two different kinds of improved flux observer are proposed. The first one is based on voltage model method. An improved voltage model flux observer with the programmable low-pass filter (LPF) is proposed. LPF is normally used to replace the pure integrator of back electromotive force to avoid dc drift and saturation problems. However, the LPF estimator introduces magnitude and phase observed errors, results in degraded estimation performance at low frequency. In addition, the LPF with fixed cutoff frequency is difficult to provide good estimation for wide speed range. To solve the problems, an improved programmable LPF rotor flux observer with an error-decaying mechanism is introduced. The other one is the improved full-order flux observer. The observer error system is transformed into synchronous rotation frame to avoid nonlinear and complicated dynamics of the observer. And stability conditions can be achieved through the single-input and single-output error system. To improved parameter robustness of the observer, stator resistance is identified synchronously based on an improved adaptive mechanism. The feasibility of the two proposed observers are verified through the experimental results.The speed sensorless field-oriented control for induction motor may be detuned due to load torque disturbance and rotor time constant variation. Based on the analysis of dynamic model of field-oriented controlled induction motor considering the load torque disturbance, a novel adaptive disturbance observer is proposed. And disturbance torque feedforward control for speed regulator is designed to obtain satisfactory dynamic response by realizing the compensation for external load disturbance. Then a practical rotor time constant estimation method based on model reference adaptive system with reactive power model is presented. Convergence of the estimator is proved using the Popov's super-stability theory. And the sensitivity of motor parameters to the model is analyzed. The experimental results verify the validity of the proposed robust control schemes for speed sensorless field-oriented controlled induction motor drives.Since dead-time effect of the inverter has great influence on phase voltage reconstruction and current controller for speed sensorless vector control system. A novel dead-time compensation strategy is presented to compensate dead-time error voltage and eliminate zero-current clamping effect. The factors influencing dead-time effect are analyzed, and the expression of equivalent dead time is deduced. The average dead-time compensation technique is adopted to compensate error voltage at the stationary frame. To improve the accuracy of current polarity detection, magnetizing and torque current components are transformed into the synchronous rotation frame. Therefore, compensating voltage vector can be determined according to the sector which the current vector locates according to the filtered current components. In addition, a zero-current clamping phenomenon eliminating scheme is adopted to improve the compensation performance. The proposed compensation method was implemented in the vector controlled induction motor. Experimental results demonstrate the feasibility of the dead-time compensation strategy.Based on the above works, a vector-control driver for series induction motors with TMS320F2812 DSP has been developed. The key parts of hardware and software structures have been designed. Experimental results show that the inverter prototype achieves satisfactory performance. And the research has built stable base for the industrialization of the high-performance speed sensorless vector control inverter.