SIMULATION OF Y SVM BASED VSI FED INDUCTION MOTOR DRIVE

Abstract

Space Vector Modulation (SVM) Technique has become the most popular and important PWM technique for three phase Voltage Source Inverters for the control of AC Induction, Brushless DC, Switched Reluctance and Permanent Magnet Synchronous Motors. The Space vector modulation technique is an advanced, computation intensive PWM technique and is possibly the best among all the PWM techniques for drives applications. The space vector modulation (SVM) technique is more popular than any other conventional technique because of its excellent features such as wide linear modulation range, lower base band harmonics, better dc link utilization, lower THD, less commutation losses, higher efficiency etc. In the recent years, many studies have been developed to find out different solutions for the induction motor control having the features of precise and quick torque response, and reduction of the complexity of field oriented algorithms. The Direct Torque Control (DTC) technique has been recognised as the most viable solution to achieve these requirements. The conventional DTC drive contains a pair of hysteresis comparators, a flux and torque estimator and a voltage vector selection table. The torque and flux are controlled simultaneously by applying suitable voltage vectors, and by limiting these quantities within their hysteresis bands, de-coupled control of torque and flux can be achieved. However, as with other hysteresis-bases systems, DTC drives utilizing hysteresis comparators suffer from high torque ripple and variable switching frequency. These disadvantages of the conventional DTC can be overcome by combining DTC with space vector modulation (SVM) technique. In this control technique, flux and torque PI controllers will correspondingly generate d and q components of the reference voltage space vector. This space vector is then realized by means of a SVM pulse width modulator, which generates firing command to the inverter, there by dramatically reducing the torque ripple. In the present dissertation work, simulation study of the Direct Torque Control with space vector modulation (DTC SVM) has been carried out in the MATLAB/SIMULINK environment. A comparative study of DTC SVM technique with classical DTC has been performed in SIMULINK, which shows that, with DTC SVM technique, the torque ripple and current distortion are drastically reduced, while maintaining the dynamic performance levels as good as classical DTC. iv