Direct torque control (DTC) is a suitable control method for electric drives which are supplied by inverters, specially voltage source inverters (VSI). This method has some advantages compared with other methods such as field oriented control (FOC) with some drawbacks like switching frequency variation, that leads to introduce DTC improvement methods. Using space vector modulator (SVM) in DTC structure is the most important method that is referred to as space vector modulator for direct torque control (SVM-DTC). Utilizing regenerative braking method in electrical transportation makes it necessary to analyze the traction motor behavior in regenerative braking mode. In this paper three major types of SVM-DTC are mentioned and SVM-DTC method with Closed Loop Torque and Flux Control in the Stator flux coordinates is used for simulation of traction motor driver of Ghatar Shahri Esfahan Organization. Moreover, traction motor behavior in regenerative braking mode using SVM-DTC driver is simulated.The simulation results are analyzed in the paper
1.Direct Torque Control (DTC)
2. Space Vector Modulation (SVM)
3. Traction Motor Drive
4. Speed Control of Induction Motors
5. Regenerative Braking.
Fig. 1. Block diagram of DTC
Fig. 2. Block diagram of SVM-DTC based on closed loop flux and torque control in stator flux coordinates
Fig. 3. Applied load torque at speed 0[201.4 rad/s.
Fig. 4. Simulation results of SVM-DTC with reference speed of 201.4 rad/
Fig. 5. Applied load torque at speed of 170 rad/s
Fig. 6.simulation results of SVM-DTC with reference speed of 170 rad/s.
Fig. 7 DC-link behavior during regenerative braking with and without regenerated energy absorption.
Fig. 8. Traction motor and DC-link behavior during regenerative braking with regenerated energy absorption.
In the case of induction traction motor control methods ,DTC has better performance. DTC has some shortcoming such as varying switching frequency proportional to motor speed variation. Therefore, it is necessary to use maximum sampling frequency in DTC. These issues result in increasing flux ripple in lower speed and increasing torque ripple in higher speed in addition to increasing switching loss. SVM-DTC with fixed switching frequency solves these problems significantly. Among different methods of electrical braking, regenerative braking has special advantages such as reduction in energy consumption and improvement in power quality of DC link. SVM-DTC operation is also appropriate and acceptable in regenerative braking. Therefore, it is suggested to utilize SVM-DTC in electric rail transportation applications
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