No description available.

In the area of performance analysis of the Shaded Pole Induction Motors (SPIMs),much research has been done with different equivalent circuit models, but the results are generally not satisfactory. The emergence of Finite Element (FE) methods provides an opportunity to take a fresh look at the design of SPIMs and this forms the backbone of my research. In the research, a more accurate two-dimensional time-stepping eddy-current FE model was developed. The multi-slice technique, justified as the more efficient way to consider the effect of a skewed rotor, has been adopted in the model. For the first time,the end-ring resistance was investigated under the condition that the end-ring current distributes itself non-sinusoidally along the circumferential direction in the end-ring area. An instantaneous non-uniform end-ring resistance model was therefore presented and coupled with the two-dimensional multi-slice FE model. Thus, compared with using the normal two-dimensional FE model, the three-dimensional nature of electric machines, e.g. the skew and end-ring, could be considered more properly by using the proposed FE Model. Meanwhile, the harmonics, the skin effect and the saturation of the permeable parts can all be taken into account with the new model. On the other hand, in order to reduce the computing time required, by the time-stepping technique, a variable step size method was adopted and a more reliable method of estimating the truncation error of time-stepping has been developed. Additionally, by coupling the external circuits equations directly to the field equations, the time cost was further reduced and the performance of a SPIM including current and torque might be obtained immediately after the systems equations were solved. With the developed two-dimensional FE model, the effects of variation of design parameters, including air gap profile, pole bridge, the skew, rotor slot number and closed-slot rotor, have been investigated. By introducing a new harmonic analysis method based directly on the time-stepping finite element method, the effect of different designs on the spatial harmonic in the air gap field and the time harmonic in the rotorbar current can be learned. The optimisation technique was applied to the design of SPIMs in order to obtain a proper combination of the design variables. A more efficient global-local hybrid search algorithm that combines the Genetic Algorithm with the direct search method was proposed in this study. To meet the demand of either speed or accuracy, a multi-slice fixed-mesh model of SPIMs was built up and used to calculate of the motor performance, the objective function of the optimisation. Because the optimisation program was based on FE analysis directly, an automatic re-mesh scheme depending on the optimisation variables was required and therefore developed in this research as well. A great performance improvement was achieved when applying the proposed optimisation method to maximising the starting torque. Finally, In order to validate the result of the two-dimensional, multi-slice FE model proposed, a PC-based experimental rig has been set up. With this test rig, two SPIMs have been tested in both the steady state and the transient state and the measuring results proved the accuracy of the analysis model developed in the study.

No description available.

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.