The use of Permanent Magnet Synchronous Machines (PMSMs) has become widespread across numerous applications and industries. Their high power density, efficiency and accuracy of control make them excellent choices, leading them to become the industrial standard. Two issues concerning PMSMs use in recent years have been associated with the elevated cost of rare earth materials required for the Permanent Magnet (PM) rotor poles and the reliance on a direct rotor position sensor such as an encoder. PMSMs require an accurate rotor position feedback within the control scheme, traditionally provided by an encoder or resolver. These devices are excellent at providing the realtime rotor position accurately but have a negative impact on the machine as a whole. Their use increases the size, weight and cost of the electrical machine, while reducing reliability and often limiting use in extreme environments. This has created motivation for sensorless control of PMSMs, which removes the need for a position sensor. Sensorless control can be categorized into two distinctive aspects. The first is the control scheme and focuses on how position dependent properties can be used to estimate rotor position. The second, which has had less focus, is the machine design. This is focused on the ability of a machine to act as a position sensor with clear position dependent properties. Self-sensing machine design is the common term applied to this field since in essence the machine acts as its own position sensor. This thesis is concerned with self-sensing oriented design. The work presented is focused on PMSMs with inset rotor topologies. A methodology was developed to assess the position tracking capability of a machine and incorporated within a traditional machine design optimization routine. The conceptual design of the machine emphasized a generic geometrical topology, accounting for practical material selections and construction techniques. This ensured the design outcome had widespread implications, as opposed to a novel machine design with limited commercial relevance.

Fossil fuels, which are the main energy sources of the current world, are running low and alternative ways of generating and storing different types of energies are becoming daunting missions. Renewable energy is very attractive because the source of the energy is often free and also environmentally friendly. The key issue to utilise the renewable energies in sustainable manner is how effectively store the energies and provide them on demand. Therefore, the significance of the energy storage devices has been widely recognised in recent time. Electrochemical capacitors (ECs), which are also commonly known as supercapacitors, are a type of the energy storage devices and the ECs are widely used as a back-up power boosting device to the batteries. Due to EC's low energy characteristics (typically, lower than 5 Wh/kg), their applications are limited. Therefore, main aim of this study is to enhance the energy characteristics of the ECs. In particular, aqueous ECs were examined due to a number of advantages offered by the water-based system. It was found that neutral aqueous electrolytes can expand the operating voltage close to 2 V (aqueous ECs commonly operate within 1 V) with advanced designs and hence result in remarkably higher energy. Moreover, the optimum condition of the neutral aqueous electrolytes was investigated by examining the effect of ion size, concentration and temperature. One of the main disadvantages of using the aqueous electrolytes in low temperatures was successfully resolved by using concentrated electrolytes (freezing point depressed up to -20°C). Mn02 with carbon materials were also used to construct asymmetrical ECs. The highest specific energy (Wh/kg) of the neutral aqueous ECs was achieved at 20 Wh/kg using unequal electrode design. This result is very much comparable to the Pb-acid battery. Based on the obtained data, larger scale (thicker and bigger electrode films) of the prototype ECs were constructed and their results correspond well with the results obtained from the smaller ECs. The data of the neutral aqueous ECs, which is contained in this thesis, suggest that the water-based ECs have a remarkable market potential.

The main aim of this project was to research, develop and test an induction motor drive not requiring a speed encoder, but which could be considered commercially viable by motor drives manufacturers, and which should aim to meet the follow requirements: • Dynamic torque performance and steady state speed-holding accuracy to be comparable with encodered vector controlled drives • Extensive and highly accurate knowledge of electrical and mechanical parameters of the motor and load not to be required • Extensive commissioning from an expert engineer not to be necessary • Algorithm not to rely on excessive computational capability being available The drive was to operate, in a stable manner, over speed and load ranges at least comparable with commercially available sensorless induction motor drives. The above requirements were set such that the developed sensorless technique may be considered for synchronised multi-motor process applications, where the advantages of a sensorless system could be exploited for hazardous, damp and hot conditions. The solution developed consists of a leading model-based sensorless method augmented with a speed estimator that tracks harmonics, seen in the stator terminal quantities, due to rotor slotting. The model-based scheme facilitates field-orientated control for dynamic performance. The slot harmonic speed estimator tunes the model for speed accuracy. Slot harmonics are identified using a recursive signal processing method termed the Recursive Maximum Likelihood - Adaptive Tracking Filter. This work is the first example of the method being developed into a practical sensorless drive system and the complete speed identifier is described, including set-up, pre-filtering and the minimal parameter considerations. Being recursive the method is computationally efficient, yet has accuracy comparable with that of FFT identifiers used in other work. The developed sensorless strategy was implemented practically on two motor drive systems. The performance of the scheme is shown to give encoder like speed holding accuracy and field-orientated dynamic performance. The two drives were also configured and tested as a speed synchronised pair, using applicable multi-motor control techniques, themselves compared and contrasted. The sensorless performance is demonstrated, alongside an encodered version acting as a benchmark, and the performance of the two schemes is shown to be highly comparable. The author has found no other example of sensorless techniques considered for use in multi-motor applications. The use of such a technique brings established advantages associated with encoder removal and allows multi-axis electronic synchronisation to be considered for parts of a process where an encoder may not be appropriate.

This thesis describes an investigation of three and five level diode clamped inverters for motor drive applications. The work was completed as a PhD project at the University of Nottingham with funding from EPSRC and Heenan Drives Ltd. The investigation of the three level converter describes the design, development, control and operation of an 11kW prototype. Included in the design is a review of typical switching strategies employed for control of the output voltage. New improvements to the sub-harmonic pulse width modulation method are presented which allow an improved output waveform to be obtained. The problem of DC link capacitor voltage balancing (Neutral Point Control) is addressed and a novel balancing control method is presented based on the addition of a DC offset to the modulation pattern. This method is verified through mathematical analysis and experimental operation. The operational limits of the control are analysed. Improvements to the technique are presented to expand its operating limits. The development of a prototype five level converter is then described. The design again features improvements to the sub-harmonic modulation strategy to provide enhanced output waveform generation, particularly for transient operation. The current demands on the DC link capacitors for the five level arrangement are analysed and it is concluded that the capacitors cannot be regulated by simple modifications to the output switching pattern. A novel circuit is presented to achieve capacitor balancing within the DC link. The circuit behaviour is described and analysed. Operation is confirmed through simulation and experimental implementation. High dynamic performance is demonstrated via the use of a vector controlled induction motor. Neutral point control is successfully achieved through a similar method to that used for the three level inverter. Having demonstrated the principle of operation of the three and five level inverters on low voltage prototypes, the thesis concludes with a review of the main considerations required to implement the configurations as medium voltage drives.

Recently, cooperative diversity system has become an effective way to mitigate multipath fading. This thesis concentrates on the performance analysis of cooperative diversity relaying system by considering several realistic limitations. These limitations are likely to exist in the real network and may cause the system performance degradation significantly. Consequently, it is valuable to produce the more accurate system evaluation for the development of network. Our research work is immersed in amplify-and-forward (AF) relaying protocol due to its simplicity. The effect of limitations such as correlated channels, signal-to-noise ratio (SNR) estimation errors and feedback delay are further studied. At first, we analyze the performance of a single antenna dualhop AF relaying system with correlated links in Nakagami-m fading channels by taking account of blind fixed-gain relaying (BFG), semiblind fixed-gain relaying (SFG), and variable-gain relaying (VG) schemes. Numerical results show that the link correlation can have a considerable effect on these schemes for specific ways of correlation, especially when the correlation coefficient is larger than 0.5. Then we investigate the effect of SNR estimation error which assumes relay selection performed under imperfect channel gain as well as imperfect noise power in Rayleigh fading channels. The numerical derivations of outage probability together with PDF and CDF of the estimated end-to-end SNR are verified and analyzed by simulation results. Finally, regarding the impact of outdated channel state information (CSI) due to feedback delay, we evaluate the performances of several generalized relay selection schemes based on multihop cooperative diversity over Rayleigh fading channels. Our results show that increasing the hop index may lead different peformance degradations for different relay selection schemes. Furthermore, it is also shown that selecting more relays in one hop does not necessarily lead to better performance. Again, simulation results verify the correctness of numerical derivation of outage probability.

Ever since the first mobile telephone call was made by a Motorola researcher in 1973, mobile technology has been growing rapidly to facilitate diverse ubiquitous services. Although cell based radio technology has proved beneficial for reliable long distance transmission, it is faced with challenges when deployed in an indoor environment. With the introduction of white LED - based communication entities at the start of the 21st century, radio and other technologies have become more interdependent, with the possibility for further expansion. Bearing in mind the sophistication offered, with the rapid developments witnessed in mobile telecommunications, this thesis presents an innovative alternative for cell phone connectivity in RF restricted or poor signal connectivity region. To address the research objective of offering uninterrupted signal connectivity in an indoor environment, the term Radio on Visible Light (RoVL) was introduced in this research. Furthermore, five major attributes influencing mobile signal transmission through visible light channels were identified and addressed. The bandwidth constraint offered by a white LED was tackled with an intelligent technique of frequency translation and mapping. In addition, an electronic predistorter was designed and implemented to address the nonlinearity in an LED. For efficient data manipulation, subcarrier continuous phase technique of modulation was introduced and hardware implemented for visible light communication, with a discussion on the LED number and arrangement for efficient illumination and data transmission. Despite the presence of significant research contributions in visible light technology, the study here is specifically focussed on integrating the GSM network with that of the optical wireless systems. The existing visible light entities provide service users with a one way broadband data transmission hub, unlike the dual channel support rendered by the RoVL device as presented in this research. The techniques proposed, backed up with interesting research observations and experimental results, clearly demonstrate the capability of supporting mobile communication through optical wireless channels. The methods proposed and techniques discussed shall lay foundation in supplementing the radio based mobile technology with optical wireless entities, opening new avenues for further research & development in this direction.

An advanced mathematical model of the Voltage Source Converters (VSC) suitable for optimal power flow (OPF) solutions using Newton’s method for augmented Lagrangian functions has been developed in this research, using first principles – this model is far more flexible and realistic than the existing VSC models aimed at fundamental frequency power systems studies. The nodal active and reactive powers of the VSC are suitably modified to accommodate more complex models corresponding to back-to-back, point-to-point and multi-terminal High Voltage Direct Current (HVDC) transmission links, within Newton’s OPF algorithm – the various model representations of the HVDC links use two or more VSC models, resulting in a new and more powerful way of VSC-HVDC representation. These models are subsequently used to interconnect otherwise independent AC systems. The new models are developed and presented in quite a comprehensive manner throughout the thesis. System simulations are carried out in order to illustrate the VSC-HVDC modelling flexibility in representing various modes of VSC-HVDC operation by selecting a range of control modes. It should be noticed that a straightforward extension of the VSC model yields a new STATCOM model of unrivalled modelling flexibility. It has been observed that the new models do not impair the strong convergence characteristics exhibited by Newton’s iterative method. As an integral part of this research, a computer program written in MATLAB has been developed to perform OPF system simulations. The program is capable of solving conventional power systems of an arbitrary complexity, multi-terminal VSC-HVDC transmission links and combined AC/DC transmission systems. It follows that less complex systems comprising one or more STATCOM, back-to-back and point-to-point VSC-HVDC can be solved with ease, using the Newton OPF computer program. It should be brought to attention that existing power systems commercial or distribution free packages with OPF facilities do not possess the advanced modelling capabilities exhibited by the new VSC model and its extensions, presented in this thesis.

Techniques of conventional chromatography do not always give convenient results. Analyses are often contaminated with detector noise and baseline drift. Continuous analysis is not possible and anomalous detector response can occur. This report proposes a method which overcomes these difficulties to a certain degree. A pseudo- random sequence controls the injections into a conventional column. Cross-correlation between input and output yields the chromatogram to within a constant factor. Sample valve and detector must be operated in a linear fashion. The resultant data analysis requires digital computation, but this can be carried out on-line.

The thesis is a presentation of published work with a commentary. The 25 publications cover the period from 1961 to 1974, and with one exception (on the subject of silicon transistor circuits) are in the general area of microwave electronics. Work on tunnel diode amplifiers includes a stability criterion, a measurement technique, amplifier designs for U.H.F. and X-band frequencies, and application to short hop radio-relay systems, General purpose computer programs for the analysis of microwave circuits are discussed. The method of using chain matrices, which has since found 0ide application, is presented. Work on microwave integrated circuits is presented which is mainly concerned which measurement techniques, and material and component properties. Measurement techniques are presented for thin dielectric films, rectangular dielectric plates, thin conducting metal films, and overlay capacitors. In each case microwave properties not previously obtained, are presented.

This thesis describes an investigation into the suitability of pulse frequency modulation (PFM) as a standard form of signal for representing quantities in process control. The encoding and decoding of PFM signals into both analogue and digital forms is examined in some detail. PFM is shown to be well suited for high accuracy telemetry at moderate cost, provided ample channel band-width is available. The processing of the information in PFM signals by means of binary logic devices is treated systematically. Functional building blocks are identified, and shown to be capable of performing all the basic algebraic and differential operations needed for control. The thesis concludes with an examination of applications and a discussion of PFM transducers, actuators and hierarchical control schemes. The performance constraints of two different process controllers are identified. Both controllers show ‘P+I’ action; one works continuously, the other has a cyclic action; both employ PFM techniques. They are shown to offer dynamic responses similar to those of conventional analogue controllers, in conjunction with high accuracy (e. g. errors less than ½%), computer compatibility and the facility for digital display.