Indirect vector controlled induction motor drives are gaining acceptance because they allow the induction motor to be controlled like a separately excited dc motor, i.e. they achieve decoupling of torque and flux producing currents. But, the effectiveness of these drives is lost as they are highly parameter sensitive. Studies have indicated that the decoupling of the torque and the flux channels is lost when machine parameters change with temperature, saturation, etc. Many schemes have been proposed to overcome these parameter sensitivity effects. But most of these schemes themselves are parameter-dependent and hence inapplicable to high precision control applications. A new parameter compensation scheme which uses air gap power equivalence for sensing parameter changes is developed in this thesis. It is shown that this scheme is independent of key motor parameters and requires no additional transducers for implementation. / M.S.

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. / Ph. D.

This research investigates the modeling and simulation, using the state transition approach to nonlinear system simulation, of a DC drive system. The drive system that was modeled is a closed loop system composed of a velocity loop with an inner current loop. The power stage is composed of a pulse generator module and a scr bridge, while the motor is a permanent magnet DC motor. A detailed development of each module model is included to reveal the open loop characteristics of the system. A total system state model was developed from each of the modules and closed loop simulations were run. The results show that the system may be modeled and simulated using this technique. However, the exactness of the simulation is heavily dependent on the DC motor parameters selected for the model. / Master of Science

Vector control technique is being widely used in ac motors drives for precise dynamic control of torque, speed and position. The application of vector control scheme to the induction motor drive and the complete modeling, analysis and simulation of the drive system are presented in this thesis. State space models of the motor and the speed controller and the real time models of the inverter switches and the vector controller are integrated to model the drive. Performance differences due to the use of PWM and hysteresis current controllers are examined. Simulation results of the torque and speed drive systems are given. The drive system is linearised around an operating point and the small signal response is evaluated. / Master of Science

A microprocessor control scheme for variable speed switched reluctance motor(SRM) drives is discussed. A particular implementation derived from first principles of the SRM is presented. The Intel 8088 microprocessor is used for the design implementation. It is shown that given the control requirements of the SRM like firing different phases according to rotor position and phase currents, a microprocessor controller is a good choice. The controller is economical since it uses standard TTL chips. The slow response at low speeds is also discussed. Experimental results performed on a static inductive load using a simulated position feedback are presented, showing how the current control available at lower speeds is lost at higher speeds, due to limited dc bus voltage. A listing of the controller software with adequate comments and the circuit diagrams are appended. / Master of Science

The blood pumping chambers and drive pump for a totally implantable artificial heart have been developed at the biomedical engineering laboratory. The drive pump is driven by an electric motor and provides alternate pumping of the blood pumping chambers. The blood pumping chambers are diaphragm pumps and have uniquely captured valves. The pressure waveforms produced by the blood pumping chambers were measured at 26, 52 and 78 beats per minute and the hemolysis caused by the blood pumps was measured under pressures likely to be encountered in the body. The average hemolytic index over the three trials was 0.041 for the right blood pumping chamber and 0.040 for the left blood pumping chamber. / M.S.

The thesis shows a simplified representation for an armature rectifier driving a DC motor load. This representation was obtained from the nonlinear equations relating the output current of the armature rectifier into the DC motor as a function of the input control variable for continuous and discontinuous current conduction. Using this simplified representation, a velocity regulator with gears connecting the DC motor to an inertia load was examined by the Bode diagram method to observe the effects of twist in the load shaft and backlash in the gears on the stability of the velocity regulator. Velocity damping and friction were neglected in the analysis. It was discovered that the armature rectifier operating in discontinuous current presented stability problems which are not encountered in a velocity regulator using a conventional rotating armature supply to drive a DC motor. Linear stabilization techniques were used to stabilize the control system to overcome the effects of twist in the load shaft and backlash in the gears for both continuous and discontinuous conduction of the armature rectifier. / M.S.

This thesis provides a comparison of three different power circuit arrangements of thyristors for controlling the speed of an induction motor through control of the stator voltage. The output voltage harmonic structure is provided for each circuit along with a comparison of the motor torque-speed characteristics. Means for coping with the motor heating problem, which results from adjustable voltage control, are discussed and curves are provided to evaluate the additional heating which results from the non-sinusoidal stator voltage. The principles of phase control are developed for single phase circuits and expressions are developed for calculating the input power factor which can be less than unity, even when the load is a resistance. These principles are then extended to three phase circuits where expressions for determining the phase sequence of the harmonics are developed. The applicability of superposition to the qualitative analysis of the effect of stator voltage harmonics upon motor performance is demonstrated, and the problems encountered in the quantitative application of superposition is discussed. / Master of Science

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