MATLAB / SIMULINK implementation of the Direct Torque Control Scheme for induction motors is presented in this paper. Direct Torque Control (DTC) is an advanced control technique with fast and dynamic torque response. The scheme is intuitive and easy to understand as a modular approach is followed. A comparison between the computed and the reference values of the stator flux and electromagnetic torque is performed. The digital outputs of the comparators are fed to hysteresis type controllers. To limit the flux and torque within a predefined band, the hysteresis controllers generate the necessary control signals. The knowledge about the two hysteresis controller outputs along with the location of the stator flux space vector in a two dimensional complex plane determines the state of the Voltage Source Inverter (VSI). The output of the VSI is fed to the induction motor model. A flux optimization algorithm is added to the scheme to achieve maximum efficiency. The output torque and flux of the machine in the two schemes are presented and compared.
- Direct Torque Control
- Induction Motor
- Flux Optimzation
Figure 1: Block Diagram of Conventional DTC Scheme
Figure 2: Block Diagram of the Flux Optimized DTC Scheme
EXPECTED SIMULATION RESULTS
Figure 3: Stator d-q flux space vector without flux optimization
Figure 4: Stator d-q flux space vector with flux optimization
Figure 5: Variation of Stator Flux – Conventional DTC Scheme
Figure 6: Variation of Stator Flux – Optimized DTC Scheme
Figure 7: Variation of Mechanical Speed – Conventional DTC Scheme
Figure 8: Variation of Mechanical Speed – Optimized DTC Scheme
Figure 9: Electromagnetic Torque – Conventional DTC
Figure 10: Electromagnetic Torque – Optimized DTC
Figure 11: Percentage Efficiency of Flux Optimized DTC
In this paper, DTC for an induction motor drive has been shown along with flux optimization algorithm. DTC is a high performance, robust control structure. A comparative analysis of the two DTC schemes, with and without flux optimization algorithm has been presented. With flux optimization implementation, it is observed that the efficiency of the about 87% has been obtained. MATLAB simulation of a 15 Hp IM drive has been presented to confirm the results.
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