Dynamic Demand Technology (DDT) developed by Open Energi Ltd. adjusts the power consumption of demand to react rapidly to changes in grid frequency without undermining the inherent control of loads. In this thesis, DDT is used to regulate the power consumption of domestic refrigerators and industrial bitumen tanks for grid frequency control. The feasibility of the loads to participate in frequency response services is studied. Refrigerators are connected throughout the power system and thus have great potential to be used for frequency control. A frequency controller based on the DDT is applied to refrigerators so that their power consumption varies with frequency deviations autonomously and proportionally. The technique maintains the temperature control of refrigerators and causes little adverse impact on their cold storage of food. A thermodynamic model of refrigerators is developed and validated through field tests on a number of refrigerators at the premises of the Indesit Company. The refrigerator models equipped with frequency control are then integrated into a simplified Great Britain (GB) power system model to investigate their capability for grid frequency control. Results show that the refrigerators change their power consumption in order to reduce deviations of grid frequency. Approximately 500 MW of frequency response is provided by 40 million refrigerators when frequency dropped to below 49.5 Hz. The frequency control is faster than that provided by frequency-sensitive generation. DDT is also applied to bitumen tanks. Frequency control is developed which is similar to refrigerators. A thermodynamic model of bitumen tanks equipped with the frequency control is developed and validated through field tests. The tank models are then connected to the GB power system model to study the capability of industrial heating loads for grid frequency control. Results show that tanks provide frequency control in a manner similar to and faster than that of frequency-sensitive generation. Approximately 72 MW of frequency response is provided by 5,000 bitumen tanks. A participant in the Firm Frequency Response (FFR) service is required to deliver a minimum response of 10 MW. Loads with low power consumption need to be aggregated in order to participate. The availability of refrigerators and of tanks for ABSTRACT ii frequency response varies over a day and is measured through field tests at different times of the day. Based on the measurements of availability, the number of refrigerators and tanks to be aggregated for delivering more than 10 MW of response over a day is calculated. Simulations are carried out with an aggregation of 591 bitumen tank and 622,980 refrigerator models. Results show that more than 10 MW of response is able to be delivered. For the future GB power system, fast control of frequency is required because of the reduction in system inertia caused by the large-scale use of converter connected generation. A case study is carried out to test the impact of the fast control of loads on the frequency of the future power system. Refrigerator models representing 40 million refrigerators and 500 tank models are connected to the GB power system model with reduced system inertia of 3.1 s. Results show that with the use of DDT, the frequency drop after a sudden loss of 1.8 GW generation is halted quickly and the magnitude of the drop reduced significantly (from 1 Hz to 0.4 Hz).

Differential interferometric synthetic aperture radar (InSAR) is a well used technique for measuring deformations, but often suffers greatly from effects due to atmospheric differences occurring between different SAR images. Recently a new set of techniques have been developed called Persistent Scatterer techniques, which take advantage of the high number of SAR images available to try and model out the atmospheric effects. To aid this process, all present techniques make use of a Digital Elevation Model (DEM) to remove the interferometric phase due to topography, but as a consequence this contaminates the phase values with an unknown error due to the DEM, which has to be modelled out in the processing chain. In this thesis a new Persistent Scatterer (PS) method is proposed that does not use a DEM to remove the topographic phase component, but rather one of the interferograms used in the study, and hence does not need to calculate topographic height corrections. This is achieved by using the Integer Ambiguity Search (IAS) 3-Pass differential technique. The developed algorithms are then tested and assessed over two test sites in central London, UK. The overall conclusions of the research are summarised below. The IAS 3-pass differential interferometry method gives a differential result that is more consistent with 2-pass results than with traditional 3-pass results. By using the IAS 3-pass method, it is possible to do a PS InSAR analysis without recourse to a DEM or needing to derive any topographic information. The developed IAS PSInSAR algorithms have been tested using simulated data, which has shown that the methods developed can identify small scale target motion over a period of a few years. The IAS PSInSAR algorithms were also tested using real SAR data, the results of which are consistent with GPS results of the test site and previous independent investigations.

Researchers all over the world are looking for ways of continuing the evolution of mobile communication technology to its fifth generation (5G). Providing high data rate information transfer to highly mobile users over time varying communication channels remains a shared obstacle. In this thesis, we contribute to these global efforts by providing further fundamental understanding of time varying channels in 5G mobile communication systems and overcome the obstacle. First, we reopen the door of research in the field of time varying communication channels. The door has almost been closed before by a well-accepted conclusion related to the types of channels. It was ‘proven’ that mutual information rate of the uniformly symmetric variable noise finite state Markov channel (USVNFSMC) was maximized by input signals of maximum information entropy. The result means time varying channels and time invariable channels are identical, regarding information rate maximization over input signal probability distribution. We provide evidence that assumptions for the results are not valid for time varying channels and replace them with more practical ones. We confirm, via input signals of non-uniform independent distribution and first order Markov chain, that the mutual information rate of the USVN-FSMC is maximized by input signals with information redundancy. Second, we provide a solution which dramatically reduces the waste of communication resources in estimating channel state information of time varying mobile communication channels. The orthodox method in dealing with time varying channels is that, the channel is “cut” to pieces in time domain to look like a sequence of time invariable channels for the purpose of state estimation. By doing this the capacity loss is staggering for n-times higher carrier frequency channels and n-dimensional multiple input and multiple output channels, eliminating almost entirely the capacity gain of these two most promising capacity-increasing techniques for 5G. We define the simplest finite state Markov model for time varying channels to explain the essential difference between information processing of time varying channels and time invariable channels. We prove that the full information capacity of the model can be achieved by the differential type encoding/decoding scheme without employing any conventional channel state estimator.

The thesis is concerned with the study of the dynamic responses of a supercritical coal-fired power plant via mathematical modelling and simulation. Supercritical technology leads to much more efficient energy conversion compared with subcritical power generation technology so it is considered to be a viable option from the economic and environmental aspects for replacement of aged thermal power plants in the United Kingdom. However there are concerns for the adoption of this technology as it is unclear whether the dynamic responses of supercritical power plants can meet the Great Britain Grid Code requirement in frequency responses and frequency control. To provide answers to the above concerns, the PhD research project is conducted with the following objectives: to study the dynamic responses of the power plant under different control modes in order to assess its compliance in providing the frequency control services specified by the Great Britain Grid Code; to evaluate and improve the performance of the existing control loops of the power plant simulator and in this regard a controller based on the Dynamic Matrix Control algorithm was designed to regulate the coal flow rate and another controller based on the Generalized Predictive Control algorithm was implemented to regulate the temperature of the superheated steam; to conduct an investigation regarding frequency control at the power plant level followed by an analysis of the frequency control requirements extracted from the Grid Codes of several European and non-European countries. The structure and operation of the supercritical power plant was intensively studied and presented. All the simulation tests presented in this thesis were carried out by the mean of a complex 600 megawatts power plant simulator developed in collaboration with Tsinghua University from Beijing, China. The study of the conducted simulation tests indicate that it is difficult for this type of power plant to comply with the frequency control requirements of the Great Britain Grid Code in its current control method. Therefore, it is essential to investigate more effective control strategies aiming at improving its dynamic responses. In the thesis, new Model Predictive Control power plant control strategies are developed and the performance of the control loops and consequently of the power plant are greatly improved through implementation of Model Predictive Control based controllers.

It is widely acknowledged that the world needs to reduce the level of greenhouse gas emissions. It is proposed to use potentially cleaner renewable energy sources to replace fossil fuels, and thus reduce greenhouse gas emissions. A significant challenge facing renewable energy sources, however, is that the power generation facilities are often located far from the load centres, meaning that new high capacity long-distance transmission systems would need to be built. This is a particular issue since there are increasing difficulties in obtaining approval to construct new overhead lines (OHL). An alternative is gas-insulated lines (GIL), a system for the transmission of electricity over long distance and is considered as a viable technical solution in places where OHL cannot be constructed. The currently adopted gas medium in GIL, however, is sulphur hexafluoride (SF₆), which is a potent greenhouse gas. Trifluoroiodomethane (CF₃I) has been proposed as an alternative insulation medium to SF6 in GIL, and this thesis investigates the potential of using a CF₃I gas mixture in GIL applications. It is hoped that the research can lead to a new form of environmentally friendly power transmission system that could cope with the increasing power demand in large metropolitan areas, and contribute to the reduction of SF6 usage in the high-voltage industry. The literature survey reviewed the research work on CF₃I gas and its mixtures to date. Several research gaps were identified, and these informed the investigations carried out in this research. Reduced-scale coaxial test systems with the electric field properties of a full-scale 400 kV GIL were designed, developed and fabricated. The designs were simulated using COMSOL to ensure that the highest field would be along the centre of the conductor. The effective ionisation coefficients of various CF3I gas mixtures were calculated using BOLSIG+, which provided estimated values for the critical reduced field strength of each gas mixture. Extensive laboratory tests using a standard lightning impulse (1.2/50) were conducted on the fabricated prototypes using various CF₃I/CO₂ and CF₃I/N₂ gas mixtures to determine the 50% breakdown voltage. The breakdown characteristics of CF3I gas mixtures were examined for pressure, geometric ratio, impulse polarity, buffer gas and mixture content. Based on the measured breakdown voltage and calculated critical reduced field strength of various CF3I gas mixtures, a two-stage streamer/leader mathematical model was developed to evaluate the reduction in field strength at higher pressures. A comparative study was carried out on CF3I gas mixtures in a rod-plane electrode configuration under standard lightning impulse and steep-front square impulse waveforms. This investigation focused on the V-t characteristics of CF3I gas mixtures in this particular configuration. A phase equilibrium experiment was also carried out to determine the boiling point of various CF3I gas mixtures.

On British electricity distribution networks, the phase to which single phase loads and generators are connected is, in most cases, unknown. There is concern that large imbalances in connection will limit the capacity of the network to support distributed generation as well as the electrification of heating and transport. The roll-out of Smart Metering in Britain, expected to be completed by the end of 2020, provides Distribution Network Operators with a means to predict the phase of single phase connections and more accurately assess the impact of increased distributed generation. This thesis examines these possibilities. There are three main sections: 1. Development of a steady state LV feeder modelling program allowing for flexible definition of connection imbalance and suitable for use with a supercomputer. 2. Development of a stochastic method to assess the combined influence (on voltages, currents and losses) of connection imbalance and photovoltaic generation. 3. Creation of an algorithm for the prediction of phase connections using Smart Meter Data, based on the GB smart metering proposals. The LV feeder model uses an unbalanced load flow based on network reduction and re-expansion with nodal analysis. It was validated using PSCAD. The feeder model uses a TNS earthing arrangement; this was shown to be equivalent to TN-C-S in normal operation, allowing for simpler modelling. A metric for connection imbalance was introduced – the highest proportion of houses connected to any phase. The model is capable of varying connection imbalance by changing the phase to which each house is connected. The connection imbalance was varied by randomly allocating houses to different phases. Demand profiles were created stochastically and PV generation was added to a varied proportion of houses (0 to 100% in 10% steps). More than 19 million unbalanced load flow calculations were performed using a supercomputer. It was found that, for a typical urban feeder serving residential properties, connection imbalance is not a significant problem for DNOs until it becomes severe (>60% of houses on one phase). The phase identification algorithm combines two methods found in the literature; voltage measurement clustering and solution of the subset sum problem. It uses vii smart meter voltage profiles and active power profiles with current measured at the supply substation. It correctly predicted the phase connection for 97% of smart meters, using simulated data representing a set 100 different connection configurations, across 6 different days (different sets of demand profiles) with a measurement averaging timeframe of 30 minutes.

From the point of view of energy importance and the environmental impacts associated with conventional energy production methods, and for the purpose of low-grade waste heat recovery, this thesis demonstrates an investigative approach to develop and test a novel, environmentally friendly small-scale Rankine based power generation prototype system. To fulfil the aim, a range of systems of different technologies, and employing different working fluids were investigated to identify the most efficient, cost-effective system for the application. These systems are the absorption power generation system, and the flood expansion power generation system employing CO2/Lubricant mixture as the working fluid, the CO2 SRC power system, and finally the ORC system employing newly developed HFOs and HCFOR1233zd(E) refrigerants. The CO2/lubricant working fluid mixture was experimentally investigated and thermodynamically modelled. The performance of the investigated systems was theoretically evaluated by computer simulations. The results revealed that the ORC outperformed all other investigated systems, achieving thermal efficiency and net thermal power output of 14.36% and 4.81 kW respectively with R1233zd(E). In addition, the evaluation confirmed the capability of the new refrigerants to replace conventional refrigerants. A small-scale R1233zd(E) ORC prototype system utilising a specially developed scroll expander was constructed and tested. In the First Experiment, an automotive motor was utilised as the electric generator. The system’s optimum performance was 7.87% thermal efficiency, 1.39 kW expander power output, and 180 W electric power output. The main source of performance limitation was identified as the lower capability of the steam humidifier heat source, in addition to the speed mismatch between the expander and the motor, the poor performance of the circulation pump, and the piping configuration in relation to the positions of heat exchangers. Piping and the position of heat exchangers were altered, the motor was replaced by an alternator and the second experiment commenced in which the best overall experimental performance of 7.6% thermal efficiency, 1 kW expander power output, 246 W electric power output, was achieved. Very poor pump efficiency and a large power loss through the power transmission mechanism to the alternator were observed. Upon completion of the experiments, the theoretically predicted performance was validated, and the experimentally obtained results were compared to those of similar ORCs from literature. The comparison revealed that for the utilised expander type, a mass flow rate of 0.074 kg/s, and a pressure ratio of 4.5, achieves the best expander efficiency of 75%. From an economic point of view, the R1233zd(E) ORC was shown to be a very attractive and safe investment even for scaled- up systems. The thesis concluded that the ORC technology remains the most efficient, flexible technology for low-grade heat recovery, and the evaluation of R1233zd(E) for the first time expressed the attractive potentials of the refrigerant in ORC applications. Finally, justified recommendations were made to replace the heat source and refrigerant pump and to test other types of expander in order to improve the performance of the R1233zd(E) ORC prototype system.

In this thesis, a number of semi-blind structures are proposed for Orthogonal Frequency Division Multiplexing (OFDM) based wireless communication systems, with Carrier Frequency Offset (CFO) estimation and Independent Component Analysis (ICA) based equalization. In the first contribution, a semi-blind non-redundant single-user Multiple-Input Multiple-Output (MIMO) OFDM system is proposed, with a precoding aided CFO estimation approach and an ICA based equalization structure. A number of reference data sequences are carefully designed and selected from a pool of orthogonal sequences, killing two birds with one stone. On the one hand, the precoding based CFO estimation is performed by minimizing the sum cross-correlations between the CFO compensated signals and the rest of the orthogonal sequences in the pool. On the other hand, the same reference data sequences enable the elimination of permutation and quadrant ambiguities in the ICA equalized signals. Simulation results show that the proposed semi-blind MIMO OFDM system can achieve a Bit Error Rate (BER) performance close to the ideal case with perfect Channel State Information (CSI) and no CFO. In the second contribution, a low-complexity semi-blind structure, with a multi-CFO estimation method and an ICA based equalization scheme, is proposed for multiuser Coordinated Multi-Point (CoMP) OFDM systems. A short pilot is carefully designed offline for each user and has a two-fold advantage. On the one hand, using the pilot structure, a complex multi-dimensional search for multiple CFOs is divided into a number of low-complexity mono-dimensional searches. On the other hand, the cross-correlation between the transmitted and received pilots is explored to allow the simultaneous elimination of permutation and quadrant ambiguities in the ICA equalized signals. Simulation results show that the proposed semi-blind CoMP OFDM system can provide a BER performance close to the ideal case with perfect CSI and no CFO. In the third contribution, a semi-blind structure is proposed for Carrier Aggregation (CA) based CoMP Orthogonal Frequency Division Multiple Access (OFDMA) systems, with an ICA based joint Inter-Carrier Interference (ICI) mitigation and equalization scheme. The CFO-induced ICI is mitigated implicitly via ICA based equalization, without introducing feedback overhead for CFO correction. The permutation and quadrant ambiguities in the ICA equalized signals can be eliminated by a small number of pilots. Simulation results show that with a low training overhead, the proposed semi-blind equalization scheme can provide a BER performance close to the ideal case with perfect CSI and no CFO.

A Quadrupole Mass Spectrometer (QMS) is an instrument for measuring concentrations of atoms and molecules by separating atomic and molecular ions according to their mass-to-charge ratios (m/z). It consists primarily of an ion source, quadrupole mass filter (QMF) and detector. Generally, QMF resolution can be improved by increasing the number of rf cycles of the alternating electric field the ion experiences when passing through the mass filter. In order to improve the resolution, the dimensions of the QMF or the operating parameters are to be changed. However geometric modifications to improve performance increase the manufacturing cost and usually the size of the instrument. A low cost method to increase the resolution of a given QMS is the application of magnetic field to the mass filter. The work is mainly concerned with the performance of a QMS under the influence of magnetic field. Significant improvement in QMS performance was obtained under certain magnetic field conditions, and these have been explained in terms of our theoretical model developed in the University of Liverpool. The theoretical approach assumed in the model is that the QMF contains hyperbolic rods as electrodes and that the magnetic field acts over the full length of the mass filter assembly. This model is capable of accurate simulation of spectra allowing the user to specify different values of mass spectrometer dimensions and applied input signals. The model has been upgraded for better sensitivity, and to simulate the QMF at very high number of rf cycles. Simulation and experimental results were presented for different conditions. This work also demonstrates the modeling of mass spectra of gases using the theoretical model for stability zones 1 and 3. The performance of QMF operating in stability zones 1 and 3 has been derived and a relationship between maximum obtainable resolution and scan line is obtained.

Power electronic converter systems play an important role in the interconnection of renewable energy sources in microgrids and utility grid. The interface between energy sources and microgrids is usually implemented by digitally controlled power inverters. This thesis provides a discrete modelling and design method for the digitally controlled inverters in microgrids. The fundamentals and background of digital control of power inverters are introduced. The small-signal models for digital pulse-width-modulations (PWMs) with delay effects are derived. Based on the models, the controllers can be designed using several methods according to the block diagrams. The simulation software and experimental environment for the digitally controlled inverters are described. For inverters operating in parallel, a linear voltage control scheme with duty-ratio feedforward is proposed. The control parameters are chosen according to the stable operating condition derived in z-domain. The closed-loop transfer function and output impedance for both the classical controller and the proposed controller are derived theoretically. A comparison reveals the advantages of the proposed control scheme: a unity closed-loop gain, no phase shift, good current sharing and low total harmonic distortion (THD) of the output voltage. The theoretical results are verified by the experimental setup of a system with two digitally controlled inverters connected in parallel. For digitally controlled grid-connected inverters with LCL filters, new small-signal z-domain models are deduced. The proposed methods model the inverters including different delay effects under most possible circumstances, which allows a direct design for controllers in z-domain. The stability boundaries obtained from the root loci of the classic models and the proposed models are compared to the simulation results, showing that the proposed z-domain models are more accurate in predicting instabilities. Experimental results are presented, showing the proposed models are also capable of predicting the values of control variables at the true sampling instants. The phase-shifted modulated multisampled multilevel inverter is studied. The filter current ripple frequency of the multilevel inverters is increased by the phase-shifted PWM. The small-signal z-domain model is derived. Compared to the bipolar switched inverter, the multisampled multilevel inverter is characterized by the capability of achieving higher feedback control gains, which improves the control performance. An experimental prototype based on a 10 kHz switching frequency, 80 kHz sampling frequency five-level single-phase H bridge inverter is tested to demonstrate the validity of the analysis.