No description available.

No description available.

No description available.

No description available.

The thesis presents a speed-control scheme for a separately-excited DC motor using a microprocessor. The control strategy incorporates both armature-voltage control and spill-over field weakening. The armature voltage is controlled in closed loop using a lead term in series with an integral term. The analogue Lead-Integral (LI) controller parameters were obtained and optimised by observing the system time response in successive digital simulations. The parameters determined provide the motor with a fast response and minimum speed overshoot during transient operations. The analogue LI controller was emulated to form a digital filter using the bilinear transformation and implemented in a 16-bit microprocessor using floating point arithmetic.

A portable high speed digital electronic DRAM radiation detection system was designed and constructed at the University of Surrey. The electronics system was designed around a Fully Programmable Gate Array (FPGA) acting as the DRAM controller. The system was controlled by a Personal Computer (PC) which also acquired and stored the data. The system control software was developed using the C language and written at the University of Surrey, the system was designed for use with 4 different types of Dynamic Random Access Memory (DRAM) chips acting as detectors mounted on separate boards from the controller. This was so that the main electronics could be placed in a shielded area whilst the detector is exposed to a radiation field. This is especially important in neutron fields where activation of components can be a significant problem. The radiation response of decapsulated 1 Mbit and 4 Mbit DRAMs to alpha particles was examined. There were six different devices in all, three 1 Mbit standard power devices, two 4 Mbit standard power devices and one 4 Mbit low power DRAM. These DRAMs were tested under different operating conditions of operating voltage, memory data pattern, cycle time and incident a-particle energy. Each DRAM was examined and their peak responses in terms of these factors was determined and compared to previous experiments with earlier DRAMs, all six devices were found to show an increase in soft error rate (SER) when the operating voltage of the DRAM was decreased. This was in agreement with previous experiments. This continued until an optimum was reached, if the operating was decreased below the optimum then the SER of the devices would quickly fall to zero, which was an unexpected effect. Two devices, the Hyundai 1 Mbit device and the Hitachi 4 Mbit ZIG-ZAG device exhibited a strong dependence on memory pattern with the Hyundai having no response with a 0000 pattern and a peak SER with a 1111 pattern. The Hitachi device had it's highest SER at 0000 and it's lowest at 1111. The other devices all exhibited some pattern dependence but it was not as marked as in these two devices. The devices all showed a lower SER for higher energy alpha particles (~5 MeV) with the SER increasing as the incident alpha particle energy decreased until a maximum SER was reached. As the incident energy was decreased further the SER would begin to fall again. This was also in agreement with previous DRAM experiments. The highest SER of the DRAMs tested was that of the 4 Mbit low power DRAM (manufactured by Toshiba), which had an SER of 224.25 s-1, more than 25 times that of the next most sensitive device, the 1 Mbit Hyundai standard power DRAM with a peak SER of 8.27 s-1. Unfortunately, due to an undetected fault in the low power header board the Toshiba device was not available to be used in the positron and neutron experiments. The 1 Mbit standard power devices (as they were more sensitive than the 4 Mbit standard power devices) were taken to the MRC Cyclotron Unit in London to try and detect a variety of positron emitters (11C, 15O, 18F 68Ge). Unfortunately, these experiments were not successful and the 1 Mbit devices did not appear to have enough sensitivity to be able to detect any of these particles. The 1 Mbit devices were also taken and irradiated in a neutron beam from the CONSORT-II research reactor at Imperial College, the devices were irradiated both bare and coated with a thermal neutron to charged particle converter material, the converter used was 6LiF and was deposited directly onto the bare silicon die of the DRAM, in both cases thermal neutrons were detected by the DRAMs. Further possible experiments with a larger range of low power DRAMs to investigate their apparently high SER rates are discussed, including further experiments with positrons and neutrons. The implications of further miniaturisation of the controller and header boards for remote inspection purposes are also discussed.

No description available.

The inherent advantages of the induction motor in variable speed drive applications can now be realised in a cost-effective manner as a result of recent advances in power electronics and microelectronics. This thesis is devoted to the advancement of the use of induction motors in variable speed applications, and describes the analysis, simulation and implementation of a variable speed induction motor drive. The state-space method lends itself as an ideal approach both for digital computer modelling and design of modem controller and was therefore adopted for the analysis and simulation of the drive system. The simulation was developed by means of a low cost personal computer package called MATLAB that has been designed to facilitate matrix operations. The use of such a specialized software package provided a 'user-friendly' operating environment with error messages identifying problem areas during program development. The resulted computer model of the drive system offers high flexibility and modularity and can be readily incorporated into further analysis and real-time controller design. Experimental results of the drive demonstrated good correlation with the model at both steady and transient states and the validity of the model is therefore confirmed. The experimental drive system was developed by means of transputers and its associated programming language occam. It was a flexible and comprehensive drive system comprising: (i) an on-line user interactive environment facilitated by the Transputer Development System; (ii) a 3-phase inverter bridge as the power conditioning unit; and (iii) a signal processing unit by means of a multi-transputer network system. The adoption of the transputer and occam enabled parallel processing to be achieved cost effectively in the drive system. The specifications of the drive system developed included on-line speed change, dynamic braking and programmable soft-start. Vector-control was also incorporated for good dynamic response. Experimental results of the specified functions of the drive are provided to confirm the proposed specifications of the drive. Further research areas on the present system are proposed, so that a viable industrial implementation may be contemplated.

This thesis is mainly devoted to the investigation of speed control methods of three phase, cage rotor induction motors with particular emphasis being given to vector control and direct torque control techniques. Modern control strategies such as vector control and direct torque control are investigated as well as the conventional methods such as open loop (constant V/f) operation. A number of different pulse width modulation (p.w.m.) waveform generation strategies are simulated and discussed and their application to the above speed control systems fully investigated. A 3kW, three phase induction motor drive has been designed and experimental data obtained from it in order to verify the results achieved by simulation. It is shown that direct torque control achieves decoupling of the motor torque and the motor flux without the use of a co-ordinate transform. A variation of the direct torque control algorithm has also been developed and implemented. It is shown, that by using different switching tables for the selection of voltage vectors, the performance of direct torque control can be further improved. Further insight into the nature of direct torque control has been gained from the study of the effect of the application of inverter switch settings, or the application of corresponding voltage vectors, on the motor flux and torque. It has been found that the range of torque variation of the motor drive system depends strongly on both the motor load torque and the motor speed. The results of the work reported indicate that the range of torque variation for a drive system which strongly depends on motor load torque and motor speed is considerably reduced by the novel direct torque control system resulting from the research. The control algorithms have been implemented on 32 bit micro processors which facilitate the use of parallelism in both the hardware and the software design. The resulting system is capable of controlling a three phase induction motor with variable voltage and variable frequency with control strategies such as six step operation, symmetric and asymmetric regular and natural sampled p.w.m. waveforms, sigma delta modulation methods, space vector modulation techniques, flux vector control and direct torque control.

A general model is developed describing the performance of positive displacement flowmeters. This model allows to predict the performance of any positive displacement meter if 8 coefficients describing the meter design are known. The logic is that a flowmeter performs at a defined pressure loss for a given speed. This pressure loss times flowrate is then energy balanced against all internal loses. Pressure loss and speed are the reasons for leakage. Rotational speed times the theoretical swept volume is the theoretical flowrate and this flowrate, when combined with leakage flow can be used to calculate the effective or true flowrate. The 8 coefficients describe the influence of the design of a meter on laminar leakage flow, turbulent leakage flow, speed related leakage flow, viscous friction, mechanical friction, constant friction, impulse energy losses and ball bearing friction, respectively. This model was applied to a twin-screw type displacement flowmeter which uses two helical rotors which form separate pockets and allow the flow-rate of the fluid to be measured. Based on the general prediction model it was found that for this type of flowmeter mainly two coefficients are the reasons for deviation from linearity. These are the constant friction power losses KC produced by mechanical sliding and the turbulent leakage flow losses Kt ur . When the values of KC and Ktur are zero then the error against flowrate is constant. A complete model of an actual twin-screw type displacement flowmeter was realised, determining all 8 loss coefficients. In order to do so, tests with a twin-screw type displacement flowmeter have been carried out on the overall meter performance, leakage flow losses and bearing friction. The theoretical work includes the determination of all 8 coefficients based on a study of the rotor geometry of the meter and a calculation of the fluid forces and torques acting on the rotors. The theoretical results of the final performance prediction model were compared with experimental results and show a good accordance. It was found that one optimal circumference clearance value can be determined for every different fluid property and flowrate. The flowmeter performance may be increased by minimising mechanical sliding and turbulent leakage flow losses.