Various aspects related to controlling induction motor are investigated. Direct torque control is an original high performance control strategy in the field of AC drive. In this proposed method, the control system is based on Space Vector Modulation (SVM), amplitude of voltage in direct quadrature reference frame (d-q reference) and angle of stator flux. Amplitude of stator voltage is controlled by PI torque and PI flux controller. The stator flux angle is adjusted by rotor angular frequency and slip angular frequency. Then, the reference torque and the estimated torque is applied to the input of PI torque controller and the control quadrature axis voltage is determined.The control d-axis voltage is determined from the flux calculator. These q and d axis voltage are converted into amplitude voltage. By applying polar to Cartesian on amplitude voltage and stator flux angle, direct voltage and quadratures voltage are generated. The reference stator voltages in d-q are calculated based on forcing the stator voltage error to zero at next sampling period. By applying inverse park transformation on d-q voltages, the stator voltages in α and β frame are generated and apply to SVM. From the output of SVM, the motor control signal is generated and the speed of the induction motor regulated toward the rated speed. The simulation Results have demonstrated exceptional performance in steady and transient states and shows that decrease of torque and flux ripples is achieved in a complete speed range.
1. Amplitude voltage
2. Direct Torque Control (DTC)
3. Space Vector Modulation (SVM)
4. Stator flux angle
Fig. 1: DTC-SVM scheme
Fig. 2: Simulation of proposed SVM-DTC
EXPECTED SIMULATION RESULTS:
Fig. 3: Electromagnetic torque in Classical DTC Fig. 4: Electromagnetic torque in SVM-DTC
Fig. 5: Stator flux in classical DTC Fig. 6: Stator flux in SVM-DTC
Fig. 7: Rotor speed in Classical DTC Fig. 8: Rotor speed in SVM-DTC
Fig. 9: Stator current in Classical DTC Fig.10: Stator current in SVM-DTC
This proposed method describes the performance of Direct Torque Control (DTC) based on space vector modulation, amplitude voltage and stator flux angle. In this system, hysteresis controller is substituted with PI torque controller and PI flux controller while switching table is replaced by SVM in order to improve the performance of this system especially at low speed, SVM is based on amplitude voltage and stator flux angle. The stator flux angle is controlled by PI torque controller and stator angular frequency and this gives a high accuracy for the value of the angle due to presence of PI torque controller. The amplitude voltage is controlled by PI torque and PI flux controller. This proposed method shows a reduction ability of flux and torque ripple with constant switching frequency and fast response of speed .This control technique can be done practically by using Digital Signal Processing (DSP) board.
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