No description available.

M.Ing. (Mechanical Engineering) / A hydromechanical traction system for a wheeled vehicle is being examined in order to generate information that will be applicable to the design of the drive system controller. The functional analysis of the drive system leads to the description of the system and component properties. A design methodology is proposed by which the system components could be dimensioned and the system layout constructed by taking into account the specified functional requirements concerning the system performance. An explicit description of power flow and manipulation of power flow in the drive system is given. The mechanisms by which the hydraulic machines are adjusted to manipulate power flow, are examined in detail so that their contribution to the dynamic behaviour of the total drive system can be described. , Experimental measurements are used to obtain a reliable description of the dynamic response of the adjustment mechanisms. An analytical model of the dynamic behaviour of the drive system is presented in block diagram format. The inherent multiple-input-multiple-output characteristic of the drive system with secondary controlled hydraulic motors is discussed. The block diagram is simplified to create linearized transfer functions that will depict the input-output-relationships. The effect of an accumulator on the dynamic response of the system is also given. Digital simulation programmes are constructed from the analytical model. The requirements of a vehicle traction system are interpreted and used as guidelines to conduct a functional design of the control system layout. The delivery of torque and the restriction of wheel spin for each of the wheel drive units, which is realised by secondary controlled hydraulic motors, are described in detail. A hypothetical drive system is considered and quantitive control system design information is generated, using the simulation programmes. Some aspects of the dynamic response of the system are discussed and it is shown that the adjustment mechanism has a big influence on the overall dynamic response of the system.

A novel control strategy for segmented long-stator permanent magnet linear synchronous motors is presented that is particularly suited to ropeless hoisting. The stator (primary) is segmented into modular sections that are shorter than the moving reaction plate (secondary) and a single voltage source inverter per conveyance is used to power the energised sections. Efficient partial excitation of the stator is achieved with an intermediate switching layer placed between the stator sections and the inverter. The common voltage supplied to the sections is controlled with any standard motor vector control technique. Computer simulation and a purpose-built laboratory prototype show the strategy to be effective. There is scope for future research into full sensorless control of the proposed arrangement and a method of further modulating the supply voltage for those stator sections that are only partially covered by the reaction plate, particularly when operating at higher speeds. Stemming from initial efforts to mathematically model the linear motor, a novel electromagnetic modelling approach was formulated. This hybrid magnetic-equivalentcircuit (MEC) and finite element method (FEM) approach is suited to efficient dynamic simulation and is explicated with a worked example. The method yields accurate results when compared with pure FEM. An MEC formulation is used for highly-permeable polygonal regions, whereas the magnetic field outside these regions is solved, by superposition, as the combined effect of boundary conditions that interface with those MEC regions and any magnetic sources. The required parameter sets for solving the field outside the regions represented as MECs are purely dependent on the geometry of the problem space and are thus precomputed. The force acting on a chosen group of moving components is calculated using an approximation of the Maxwell Stress Tensor method. Future research could address the present limitation that the highly-permeable regions are meshed using exclusively-rectangular flux tube elements. A dynamic simulation model that caters for the discontinuities of a segmented stator was ultimately derived using an extended space-vector approach and its implementation as a generic Simulink R blockset is detailed. The motor parameters are determined from static FEM solutions over the range of reaction plate displacement, assuming no magnetic saturation.

No description available.

by Poon Ting-kwun, Wan Hung-koon. / Abstract in Chinese. / Thesis (M.B.A.)--Chinese University of Hong Kong, 1981. / Bibliography: leaves 79-80.

An integrated starter/alternator (ISA) has been proposed for the future 42 V PowerNet, which combines both starter and alternator functions into a single electrical machine with bidirectional power flow ability. This thesis presents analysis, design, modeling and experimental results of the direct torque controlled ISA system based on a low voltage induction machine. The classical direct torque controlled ISA based on switching-table is systematically for an ISA evaluated in this thesis. The simulation and experimental results show that the direct torque control (DTC) concept can be successfully extended to the ISA application. An improved DTC of the ISA based on direct stator flux vector is presented to reduce the drawbacks of high torque and flux ripples of the classical DTC. Robust design of the controller ensures the system is not sensitive to the variation of rotor resistance. By controlling the electromagnetic torque of the induction machine quickly, the required dc bus voltage can be well regulated within the 42 V PowerNet specifications. Another improved DTC of the ISA with direct torque and flux control is also studied. Compared to the direct flux vector control scheme, the calculation of the commanded voltage vector in this scheme only requires the derivative of the stator flux magnitude, which is a dc quantity. In addition, both torque and flux are regulated directly with two independent closed-loops. This scheme is relatively insensitive to the noise. The thesis proposed compensation methods to reduce the effects of switch voltage drops and dead-time on the estimation of the stator flux. Experimental results confirm that the estimation error is reduced with compensation for both motoring and generating modes of the ISA. A closed-loop type of sliding mode flux observer is proposed to reduce the estimation error of the stator flux. Both Simulation and experimental results confirm that the proposed sliding mode observer is insensitive to the stator resistance variation and sensor offsets. A loss minimized scheme with power factor control for the ISA is proposed in this thesis. It provides a simple solution for the efficiency improvement of the induction machine without requiring any speed or load information. The effectiveness of the direct torque controlled induction machine for an integrated starter/alternator system has thus been confirmed and well supported by the studies presented in this thesis.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Synchronous machines provide a practical way to control reactive power consumption of a plant. One of the main advantages of using synchronous motors in a plant is their ability to generate reactive power for plant loads. A new control scheme for synchronous motor excitation systems is developed to automate reactive power consumption. The system performs adaptive control based on the real time data and keeps the power factor within a specified range. The system can also be used to improve voltage drop during large induction motor starts. Power system behavior as a result of applying the adaptive control is studied under different operating scenarios using power system analysis software. Results and conclusions are based on mathematical simulation and experimental measurements of a prototype system. / Graduation date: 2003

A Brushless, Doubly Fed Machine (BDFM) attempts to combine the advantages of conventional induction and synchronous types of electrical machines by its unique architecture. The validation of BDFM designs in an actual test environment requires the estimation of the BDFM model parameters from actual experimentation. Accurate values for the parameters are also required by controllers that will be used in the future with specific objectives in mind. This study deals with the design of an estimation scheme to evaluate the parameters for a BDFM, dynamic model. Experimental results are presented. Conventional, practical estimation schemes are based generally on a number of experiments carried out at different operating points, or are limited to estimating a few parameters. The thrust of this work is towards developing a technique that can evaluate all parameters of the BDFM model around the same operating point, and, with limited number of experiments. The parameter estimation scheme is developed with practical implementation in mind. The constraints of the experimental procedure are outlined. The validity of the estimation scheme has been established by tests on a laboratory prototype of the BDFM. / Graduation date: 1995

This research deals with the comparison of fault signatures in induction motors. The primary objective is to study and analyze the similarities in the electrical and mechanical fault signatures, and to determine the suitability of the former for effective motor fault detection. Currently, vibration analysis is the dominant means for mechanical fault detection for use in condition-based maintenance. The use of electrical signatures for mechanical fault detection in electric motors is becoming of interest. Due to its cost-effective nature and ease of use, electrical sensors are preinstalled at the motor switchgear by manufacturers. However in order to achieve this for mechanical faults, a systematic comparison between the vibration signatures and electric current signatures must be performed to study the effectiveness of such an approach. The behavior of vibration signatures as measured through tri-ax accelerometers installed at both in-board and out-board sides, and the three phase motor current signatures as compared to their corresponding healthy baselines is analyzed through a sequence of signal processing algorithms. The procedure is carried out for different types of mechanical faults including broken rotor bars, air-gap eccentricity, mechanical imbalance and deteriorating bearings staged on motors of different make and power rating. A comparison is then made between the two fault indicators derived from mechanical and electrical measurements, respectively.