| Over the years, dc motors have been widely used for variable speed drives for numerous industrial applications despite the fact that ac machines are robust, less expensive, and have low inertia rotors. The main disadvantage of the ac machines is the complexity in control and the cost of the related circuitry. With the advent of vector control, ac machines have overcome this disadvantage and are being employed in different applications where dc motors were traditionally used. The d-q modeling, simulation and analysis of the different vector control strategies are presented with the results for different configurations of the drive system. A Computer Aided Engineering (CAE) package has been developed to serve as a modeling tool for the entire drive system including the motor, converter, controller and the load. This package provides a user friendly environment to perform an interactive dynamic simulation to assess the torque ripple, losses, efficiency, torque, speed, and position responses and their bandwidth and evaluates the suitability of the drive system for a particular application. By utilizing the similarity between the vector controlled induction motor drive and the separately excited dc motor, a method for the design and study of the speed controller for the speed/position drive is formulated. This results in the simplicity of the design approach and helps in improving the performance of the drive system. Finally, a novel sensorless vector control scheme which eliminates the position transducer is formulated. The only input for this control scheme is the stator current measured by current transducers. The modeling, simulation and analysis for the different schemes is performed using the CAE package and experimental verification is performed with the aid of a DSP based drive system. |
