Direct torque control (DTC) is one of the most excellent control strategies of torque control in induction machine. It is considered as an alternative to the field oriented control (FOC) or vector control technique. These two control strategies are different on the operation principle but their objectives are the same. They aim to control effectively the torque and flux. Torque control of an induction machine based on DTC strategy has been developed and a comprehensive study is present in this research. The performance of this control method has been demonstrated by simulations performed using a versatile simulation package, Matlab/Simulink. Several numerical simulations have been carried out in a steady state and transient operation on a speed control mode.
1. Direct torque control
2. Induction machine
3. Vector control
Fig.1 Direct torque control of induction machine
Fig. 2: Developed model of direct torque control of induction machine
EXPECTED SIMULATION RESULTS:
(a)Estimated torque (b) Rotor speed
(c) Stator flux magnitude (d) Stator flux magnitude constrained in hysteresis band
(e) Locus of the stator flux (f) D-axis and q-axis stator current
(G) Stator current
Fig. 3: a-g: DTC behaviour during start-up with no load
Fig. 4: Steady state response of rotor speed with no load
Fig. 5: Dynamic behaviour of DTC during a load Torque step command from +20 Nm to -20 Nm
Fig. 6: The effect of flux hysteresis band on the DTC performance
The work carried out in this paper is aimed and focused to develop a direct torque control simulink model. The DTC architecture allows the independent and decoupled control of torque and stator flux. The implementation of the DTC model has been deeply described and justified its realization. In order to show the effectiveness of the model, a numerical simulation has been performed on a 7.5 kW induction machine fed by an IGBT PWM inverter. The feasibility and the validity of the developed DTC model, based on switching table technique, have been proved by simulation results obtained in the torque control mode.
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