No description available.

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.

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

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

Conventionally, system simulations of induction motor drives use lumped parameters model of the motor. This approach assumes motor parameters to be constant during the entire operation of the drive. Unfortunately, these are known to vary significantly over the operating range of the motor due to factors such as magnetic saturation, skin effects, and operating temperature. The variations in motor parameters affect motor output and control parameters resulting in degraded drive performance. One way of overcoming this problem is by coupling the field model of the induction motor with the drive simulation. By replacing the lumped parameters model with the field model, the influence of different operating conditions on motor parameters can be taken into account dynamically. In this thesis such an approach is investigated by coupling the finite element analysis of an induction motor with the system simulation of the field oriented controlled drive. The results obtained for the coupled simulation are promising and possible future works to make this method of simulation more accurate and reliable are recommended.

No description available.

Induction motors are reliable and widely used in industrialised nations. However induction motors, like any other machine, will eventually fail. If the failure is not anticipated, it can result in a significant revenue loss. Therefore, there is a strong need to develop an efficient maintenance program. The most cost-effective solution is condition-based maintenance. An effective condition-based maintenance program requires an on-line condition monitoring system that can diagnose the condition of an induction motor in order to determine the types of faults and their severity while the motor is under a normal operating condition. The work in this thesis investigates the detection of stator and rotor faults (i.e. shorted turn faults, eccentricity faults, and broken rotor bar faults) using three types of sensor signals (i.e. current, leakage flux, and vibration) under different loading conditions. The work is based on an extensive series of sensor measurements taken using a number of nominally identical healthy machines (2.2 kW) and custom-modified machines (2.2 kW) with configurable stator and rotor fault settings. The thesis starts by investigating the estimation of rotor speed and rotor slot number. These two parameters are important in determining the fault frequency components that are used for detecting the stator and rotor faults. The rotor speed investigation compares four different estimation methods from the three different sensor signal types. It is found that the speed estimation techniques based on the eccentricity harmonics and the rotor frequency in the stator current, the axial leakage flux, and the motor vibration sensor signals can detect the rotor speed very accurately even when the load is as low as 2%. Similarly, this thesis proposes three different rotor slot number estimation techniques from the three different types of sensors and demonstrates that all three techniques can estimate the rotor slot number accurately. In addition, it is shown that the reliability of the estimation techniques can be increased significantly when the three techniques are combined. The shorted turn investigation in this thesis examines and compares potential shorted turn features in the three sensor signal types under five different fault severities and ten different loading conditions. The useful shorted turn features are identified in the thesis, and then examined against variations between the healthy machines in order to determine the loads and the fault severities in which the feature can reliably detect the faults. The results show that the feature based on the EPVA (extended Park’s vector approach) is the best method. This feature can detect turn to turn faults with a severity of 3.5% or greater at loads greater than 20% and phase to phase turn faults with a severity of 1.7% or greater under all loading conditions. However, estimating the fault severity is generally found to be difficult. The thesis also examines the feasibility of detecting static eccentricity faults using the different types of sensor signals under ten different loading conditions. The thesis compares potential eccentricity features under nine different fault severities. The useful features are identified and then combined through weighted linear combination (WLC) in order to produce a better eccentricity fault indicator. The indicator begins to show significant magnitude variation when the fault severity is greater than or equal to 25% and the load is greater than or equal to 25%. The experimental results show that detecting the static eccentricity faults is possible but estimating the fault severity may be difficult. Furthermore, the effects of misalignment faults on the useful eccentricity features are investigated. In this thesis, the analysis of broken rotor bar faults is performed under motor starting and rundown operation. The starting analysis introduces a new approach to detect broken rotor bar faults that utilises the wavelet transform of the envelope of the starting current waveform. The results of the wavelet transform are then processed in order to develop a normalised parameter, called the wavelet indicator. It is found that the wavelet indicator can detect a single broken bar under all loading conditions during motor starting operation. The indicator also increases its magnitude as the severity of the fault increases. On the other hand, the rundown analysis proposes several broken rotor bar fault detection techniques which utilise the induced voltage in the stator windings and the stator magnetic flux linkage after supply disconnection. The experimental results show that detecting the faults during rundown is generally difficult. However, the wavelet approach, which is based on monitoring changes in the motor torque for a given slip, seems to give the best result. / Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2008

Call number: LD2668 .T4 1960 C42

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy