This paper describes a combination of direct torque control (DTC) and space vector modulation (SVM) for an adjustable speed sensorless induction motor (IM) drive. The motor drive is supplied by a two-level SVPWM inverter. The inverter reference voltage is obtained based on input-output feedback linearization control, using the IM model in the stator – axes reference frame with stator current and flux vectors components as state variables. Moreover, a robust full order adaptive stator flux observer is designed for a speed sensorless DTC-SVM system and a new speed-adaptive law is given. By designing the observer gain matrix based on state feedback control theory, the stability and robustness of the observer systems is ensured. Finally, the effectiveness and validity of the proposed control approach is verified by simulation results.
1. Adaptive stator flux observer
2. Direct torque control
3. Feedback linearization
5. Space vector modulation
Fig. 1.The block diagram of the DTC-SVM system
Fig. 2. Speed and torque response curve of conventional DTC. Fig. 3. Speed and torque response curve of proposed DTC-SVM.
Fig. 4. D-Q axes stator flux curve. Fig. 5. Stator flux trajectory curve.
A novel DTC-SVM scheme has been developed for the IM drive system, which is on the basis of input-output linearization control. In this control method, a SVPWM inverter is used to feed the motor, the stator voltage vector is obtained to fully compensate the stator flux and torque errors. Furthermore, a robust full-order adaptive flux observer is designed for a speed sensorless DTCSVM system. The stator flux and speed are estimated synchronously. By designing the constant observer gain matrix based on state feedback H∞ control theory, the robustness and stability of the observer systems is ensured. Therefore, the proposed sensorless drive system is capable of steadily working in very low speed, has much smaller torque ripple and exhibits good dynamic and steady-state performance.
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