This thesis is a detailed study of how two error correction schemes affect the precision of shaft position estimation in state-observer techniques for sensorless control surface-mounted Permanent Magnet Synchronous Motors (PMSM), variance correction and variable PI regulation. A novel sensorless estimation technique based on Linear Kalman Filter (LKF) through constant variance correction is proposed and compared with the conventional Flux Linkage Observer (FLO) method and other state-estimation sensorless control techniques namely, Extended Kalman Filter (EKF), variable variance correction, Single Dimension Luenberger (SDL) observer and Full-Order Luenberger (FOLU) observer both through variable PI regulation. These five sensorless control techniques for PMSM are successfully implemented in the same lab-based hardware platform, i.e. full digital float-point-type DSP control inverter-fed PMSM system. Experiments are reported on each sensorless method covering position estimation, speed response, self-startup and load behaviour. Intensive analysis has also been carried out on the impact of error correction of estimated position on the steady/dynamic PMSM characteristics with different sensorless approaches. The experiment demonstrates that the novel Linear Kalman Filter can achieve the minimum average position estimation error throughout the electrical cycle of the five sensorless estimation techniques during no load operation at rated speed and also makes PMSM capable of self-startup for any initial rotor position except the dead area. A speed response experiment for LKF shows that individual speed estimation can be extracted directly from LKF state estimation for sensorless control PMSM. Experiments on the five sensorless methods proves that position error correction scheme is the dominating factor for state estimation sensorless control PMSM and better dynamic/steady control performance can be achieved using a variance correction scheme applied in EKF/LKF than with variable PI regulation applied in SDL/FOLU. The thesis also concludes that the novel Linear Kalman Filter is an optimised cost-effective sensorless estimation method for the PMSM drive industry compared with classic and Flux Linkage observers/Extended Kalman Filters.

This research investigates a novel method for energy saving in a point-to-point actuation of a pneumatic system. The method predicts the system's actuation using the Gas Law and the actuator model, and commits air supply cut-off at the time when the energy in the actuator is sufficient to complete the actuation task. Experimental implementation is compared with simulation. The effect of the method is compared with conventional no cut-off and end-stroke cut-off actuations. Lumped and finite difference methods are used for transmission line and system actuation modelling. The transmission line, actuator and control valves are modelled and integrated for the system actuation simulation and comparisons between simulation and measured data are performed. Pressure oscillation in the transmission line exists and is captured by stimulating the air dynamics using a new transmission line experimental method. The friction model of the pneumatic actuator is determined by experiment and applied to the energy saving control system as well as the computer modelling algorithm. The determination of pneumatic transmission line bulk modulus is performed through experiment due to the confidentiality of Young's modulus value needed for its calculation. Significant effect has been achieved in implementation and it is found that cut off at end-stroke and cut-off using model prediction can reduce the amount of air potential energy wasted in conventional actuation by up to 43.5% and 80.2% respectively. However the actuation time of predicted cut-off increases by up to 25%.

Coal combustion looks set to continue in the near future, however, with the pressure being put on power generators, by the UK government, to reduce carbon emissions, ways of reducing CO₂ emissions are constantly being sought Co-firing of biomass in pulverised coal-fired boilers is one possible solution. An investigation into this technology has been carried out with particular attention being paid to combustion modelling techniques. Following a comprehensive review of related literature two tasks were carried out the simulation of a 500kW downfired furnace using the FLUENT CFD code, and the development of a universal boiler performance prediction tool. During the CFD task, blends of 5%* and 10%th sewage sludge and pure coal were simulated. Particle impaction rates were predicted on two deposition probes however, the task highlighted the need to produce a high quality computational grid as part of the modelling process. In the second task empirical correlations, later to be replaced by artificial neural networks, were derived, which could predict the temperature profile, deposition performance and corrosion performance of a full-scale boiler. These models were tested using predictions for the 618MWth Langerlo boiler and the 1316MWth Cottham boiler, producing consistent results. These results were found to satisfy what was expected from the literature.

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The main objective of this work was to investigate silicon based nanoscale interfaces with other exciting materials and to investigate their applicability to photovoltaics. In this context, quantum confined silicon nanocrystals (Si NCs) were synthesised and methods used to manipulate surface properties in order to maintain desirable opto-electronic properties. Additionally, a spray deposition technique was developed in order to integrate Si NCs more effectively with organic-inorganic halide perovskite, for opto-electronic conversion and photovoltaic applications. One of the most important findings of this work is the control and understanding of Si NC oxidation that presented ideal conditions for the non-metallic growth of carbon nanotubes (CNTs), and the production of a Si NC-CNT nanocomposite. It was experimentally determined that the growth of CNTs was reliant on small nanocrystal assemblies (< 100 nm) coupled with an oxide shell thickness of at least 1 nm, before acting a suitable catalyst. Secondly, practicality of spray technique was demonstrated for perovskite solar devices where surface chemistry and subsequent change in electronic structure affected performance. Through optimizing the absorber thickness the short-circuit current density was increased from 4.9 mA/cm2 to 22.3 mA/cm2, increasing overall power conversion efficiency from 0.83% to 5.22%. Sprayed thin films however showed increased surface degradation that affected the stability under continued illumination, highlighting potential limitations existing for deposition technique. Following, third generation solar cells based on perovskite-quantum dot architectures with p-doped and n-doped Si NCs were fabricated for the first time. The Si NCs embedded within perovskite film absorbed diffusing moisture and became oxidized due to their hydrophilic nature which consequently slowed the chemical decomposition of the perovskite. The slowed degradation allowed composite perovskite-quantum dot devices to perform better under continued illumination with short- circuit current density reaching around 20 mA/cm2 and efficiencies above 6 %. Efforts were made towards an all Si NC heterojunction devices where mixing with perovskite in the solution phase allowed for more compact films that showed rectifying behaviour and demonstrated working devices.

The majority of the worldwide installed power inverters today are voltage source inverters followed by current source inverters where the concluding decision lies with the performance of the applications besides the usual economic reasons. Recent active development in the current source inverter areas has seen the emerging of various generalized multilevel current source inverter topologies analogous to the existing multilevel voltage source inverter families. To date, the multilevel current source inverter families have been classified principally by the physical appearance of their basic structures and also by the number of current sources employed. The existing multilevel current source inverter topologies are unpopular for present applications due to reasons such as big sizes, high control complexity and low reliability; which circumstances are often associated to massive component counts and multiple requirements of current sources. Therefore, this research has been focused on the single-phase single-source generalized multilevel current source inverter for this apparent advantage; where this thesis proposed a novel generalized multilevel current-source inverter topology with the lowest component utilization while employing just a single current source. In addition, the proposed topology can conveniently achieved dc current balance with a simple low frequency switching strategy for the five- and nine-level current outputs. From comparison analysis, the proposed topology has significantly less number of components employed compared to the nearest topology, which implies low implementation cost. The experimental results verify the characteristics and performances of the proposed topology acquired by computer simulations.

The use of renewable sources of energy is becoming increasingly important role in electricity generation. Wind energy is the fastest growing renewable energy source and is making a significant contribution to meeting the energy demands while still reducing CO2 emissions. In designing generators for installation in wind turbines, characteristics of high efficiency and low cost are among the first to consider. As the number of installed wind turbines increases across the world, questions of turbine component failure and repair are also receiving much attention. This PhD starts with the investigation of modern wind turbine generator design with a focus on electrical generator and its operation. The finite element analysis of an off-the-shelf 55 kW doubly fed induction generator is used as a case study in order to investigate its design and improve the machine performance. The main work of this PhD is on a novel approach by surrogate-based analysis and the optimisation of winding design and rewinding design based upon the doubly fed induction generator for energy efficiency improvement. Surrogate models of the machine are constructed using Latin Hypercube sampling and the Kriging modelling. Having validated the surrogate models, the particle swarm optimisation algorithm is developed and applied to find the optimal solution. Assuming a winding failure occurs mid-life of the wind turbine, three optimisation plans have been studied for the repair and re-design of the stator and rotor winding separately and in combination. To validate the optimisation results, an improved testing standard is developed to test doubly fed induction generator. The original machine is then rewound following the optimised plan and tested to determine the difference in performance. By comparing the two machines, improved performance is achieved both in optimisation simulation and experiments. Finally an annual wind speed profile at a specific location (Albemarle site) is analysed to estimate wind power. The Weibull distribution of the wind speed data is combined with the turbine topologies for estimating the annual wind energy production. The annual power generation from the two machines is compared to validate the proposed technology.

A technology move, known as the More Electric Aircraft, is resulting in the use of electric motor drives and power electronic converters to replace the hydraulic, pneumatic and mechanical power systems that are used onboard aircraft. The application of high performance multi-pulse rectifiers as the input stage of the power conversion circuits for actuators and motor drives is becoming typical in aircraft systems, and the growing use of rectifier-front-end equipment is resulting in more stringent power quality limits being placed on load current harmonics. This Thesis describes the development of an active injection technique for a 12-pulse rectifier that uses the natural harmonic ripple of the rectifier to produce high-quality input currents. The injection technique utilises a single low-rated active device that carries approximately 2.9% of the load current, and it potentially offers two important advantages over previously reported ripple injection techniques. First, there is no need to use an injection transformer, avoiding the associated weight penalty. Second, the active device may be driven with either low-frequency pulses or high-frequency, pulse-width modulation to produce 24/36-pulse operation or multi› level PWM operation respectively. The resultant input currents are almost sinusoidal, the line current THD being 2.36%for the 24-pulse operation and 1.06%for the PWM operation. The active injection technique uses a phase-locked loop control strategy that synchronises the injector operation with the harmonic ripple frequency of the rectifier. The circuit operation, idealised waveforms, modulation strategy and design are explained together with Micro-Cap simulation and experimental results, which are presented from a 4 kW prototype to illustrate and examine the circuit performance in both 24/36-pulse and PWM operating modes.

The Unified Power Flow Controller (UPFC) is an advanced Flexible AC Transmission System (FACTS) device that can be controlled to condition alternating voltage and alternating current simultaneously. In this project the use of a reverse connected UPFC topology has been investigated for the improvement of poor power quality at distribution voltage and power levels, namely voltage distortion due to voltage sags and current distortion due to non-linear loads. A three-phase, reverse connected UPFC model, based on two back-to-back connected two-level Voltage Sourced Converters (VSCs) has been modelled in software and tested. To validate the voltage conditioning part of the UPFC, and therefore one half of the software model, a hardware model using one three-phase two-level VSC was constructed and used to condition the load voltage. with a supply voltage distortion due to voltage sags. . With both the software and hardware models voltage sag magnitudes between 0% and 100% are considered. along with phase angle jumps between 00 and 400^ to determine the level of compensation power required from the DC voltage source energy storage. The emphasis on the control was to operate the system as fast as possible and therefore provide a degree of compensation to the fastest of unpredictable power quality disturbances. A preferred control technique was identified for each element of the RC-UPFC.

This thesis addresses some of the challenges that arise when the new smart grid paradigm is applied to power systems. In particular, novel control strategies are designed to deal in a decentralized matter with the increasing complexity of the network. Two main areas are investigated: participation to frequency control of variable-speed wind turbines and management of large populations of competing agents (e.g. micro-storage devices and "smart appliances") that exchange energy with the system. The first part of this work presents two different techniques that allow wind turbines to provide frequency response: following the trip of a large power plant, the turbines population increases its aggregate generated power, reducing the resulting drop in frequency. A first method models the wind turbines as stochastic hybrid systems: the generators switch randomly between two operative modes characterized by different efficiency and generated power at equilibrium. Transitions are driven by frequency-dependent switching functions: single generators behave randomly while large populations perform deterministically, changing the total power in response to frequency variations. The second proposed control strategy allows a prescribed increase in generation, distributing the control effort among the individual turbines in order to maximize the duration of frequency support or minimize the resulting kinetic energy losses. The second part of the thesis deals with large populations of agents which determine their operation strategy in response to a broadcast price signal. Micro-storage devices performing energy arbitrage are initially considered: each agent charges/discharges during the day in order to maximize its profit. By approximating the number of devices as infinite, modelling the population as a continuum and describing the problem through a differential game with infinite players (mean field game), it is possible to avoid synchronicity phenomena and determine an equilibrium for the market. Finally, the similar case of flexible demand is analyzed, with price-responsive appliances that schedule their power consumption in order to minimize their energy cost. Necessary and sufficient conditions for the existence of a Nash equilibrium are provided, extending the results by introducing time-varying constraints on the power rate and considering partial flexibility of the devices.