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The installation of the combined energy generation system at West Beacon Farm, Loughborough, Leicestershire commenced in 1988, since when it has steadily grown in both generating capacity and operating complexity. It now consists of three electrical generating sources: two 25kW fixed speed horizontal axis wind turbines, a 6kWp photovoltaic array consisting of both monocrystalline and polycrystalline cells and a 15kW combined heat and power unit which also provides 38kW of thermal energy. Electricity is stored in a 184kWh lead acid battery, and also imported and exported from the grid. Previous research on the system was limited, due to lack of detailed system information and time. Therefore the aim of this research project has been to develop a more detailed and accurate computer model of the system that enables the present operating strategy to be evaluated, together with the effects on the system of changing this strategy. The outcome will be to optimize the generating cost and to provide a model with the flexibility to investigate the conditions in other hybrid systems.

The research in this thesis has undertaken a technical, economic and environmental appraisal of three gas-fired, small-scale Combined Heat-and-Power (CHP) systems together with a study of the UK's electricity supply industry (ESI) and CHP market. The purpose of each system is to attempt to utilise more of the heat and/or electricity output from the CHP unit. Within the non-technical research area, three scenarios for the evolution of the ESI have been developed to help establish how changes to forces acting within the industry might affect the development of the UK CHP market. New applications of several strategic management analysis tools were used to develop and select the following scenarios: (i) New and reduced CO₂ limits set by the Climate Control Conference + stricter environmental legislation; (ii) Changes to the Pool mechanism for pricing electricity; (iii) Business as usual. It was concluded that in isolation scenarios 1 and 3 would aid the expansion of the CHP market, whereas scenario 2 is likely to hinder it. The selection of the scenarios and the implications for the ESI and CHP market are supported by the opinions of 'industry specialists', which were solicited in a survey specifically undertaken for this study. The investigation into the first of the three technical systems involves the substitution of two separate CHP units in place of a single larger unit. The intention is to operate the larger of the two CHP units at maximum output to satisfy the base heat-load and to use the second unit for meeting peak loads. The results for five test-cases were produced via a newly-developed predictive model, and indicated that it is possible, for one of the case studies considered, to achieve shorter pay-back periods when using the double-unit - with a higher availability of 95% - rather than the single-unit system. In the other two cases (where CHP is a viable economic option), longer pay-back periods ensue by the installation of the two unit rather than the single-unit system. The operation of the two-unit system can potentially increase energy-utilisation from the CHP units at one of the other sites. Furthermore, the proposed system can offer, in some cases, significant secondary benefits, which could encourage a potential investor in the technology. These benefits include the increased heat-and-electricity output, increased availability from the system, back-up from the secondary unit if one unit fails. The second system determines the viability of an integrated small-scale CHP and TES system. Another predictive model was developed and tested on five test-cases. It was found that there is insufficient potential for the system and that the potential is limited by the following factors: (i) CHP-sizing methodology, (ii) the relatively high capital cost for TES hardware and installation, (iii) the relatively low economic value attributed to heat and (iv) the availability of low-priced off-peak electricity. An industrial case study provided a rare and useful operational example of the proposed system and the findings indicated that the heat-store could reduce the energy and monetary expenditures by up to 2.8% of the site's annual gas usage, displacing approximately 30 tones Of CO₂ emissions each year. However, because of the high financial cost of the TES components and installation, the pay-back period produced would rarely be acceptable to a prospective investor, except in exceptional circumstances. Finally, the viability of an integrated CHP/absorption chiller system was investigated. The effectiveness of these types of systems are dependent on several factors, namely: the source-water temperature from the hot-engine CHP unit - for a high COP - and the cooling load at the site, the cooling demand at the site and the temperature of the cooling water. A first-stage predictive model was developed to determine the initial appropriateness of the installation of the integrated system at a local hospital for the first time. The indications were that the cooling demand was too low and the surplus waste-heat from the CHP unit insufficient to make the system viable at the site. A second working-system was studied with a full CO₂ investigation undertaken. The intention was to compare the total CO₂ emissions for the integrated CHP and absorption chiller system with those for a similarly sized vapour-compression system. The results indicate that the installed system will produce 0.30kg CO₂/kWhcoolth compared with 0.27 kg and 0.32kg for two different types of vapour compression systems at design conditions. If the CHP heat output is increased - to supply all of the heat required by the absorption chiller - then the proposed system can displace up to 0.06 kg CO₂ per kWhcoolth at design conditions and 0.10 kg CO₂ per kWh of cooling delivered for lower cooling water temperatures. This represents a reduction of 22% and 40% respectively, when compared with the vapour-compressions system.

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No description available.

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When islanding occurs, power supply from the main grid is interrupted which causes a problem when distributed generators continue to provide power into distributed networks. An islanding situation should be detected accurately soon after the island is formed. Because failure to trip the islanded distributed resource can lead to a number of problems for the resource and the connected load. Although ROCOF islanding detection method is the most commonly employed anti-islanding protection technique, it provides fast detection and easily implementation. It is sensitive to the system disturbance. Therefore, the application of the ROCOF relay to detect system islanding has been limited. This thesis proposes a solution to enhance the performance of the ROCOF relay by cooperation with rate of change of power or v2/p interlock function. During system load variation, the false operation of ROCOF relay can be blocked effectively. It is validated by applied in grid-connected synchronous generator, Doubly-fed Induction generator (both simulation and experiment) and microgrid. The principle of rate of change of power or v2/p interlock function are presented in this thesis. The new interlock function v2/p with ROCOF relays works well for different types of DGs within a short detection time without introducing perturbation into the system, which are the advantages over other active and hybrid islanding detection methods. The performances characteristics of ROCOF relays for DGs islanding detection (i.e. frequency measuring methods, measuring windows, generator inertia constant, relay settings and load power factor) are investigated. In addition, two other islanding detection methods (impedance measurement (active method) and the Total Harmonic Method) are applied to the grid-connected DFIG distributed system, the comparison and effectiveness of these two methods utilized in islanding and load changing conditions are also discussed.

The face of electricity generation, transmission and distribution is changing due to economic, technology and environmental incentives. Recently, interactive and intelligent electricity grid structures which consist of interconnected small/medium sized generators, power electronic technologies and energy storage elements have been developed to address the major shortcomings of the traditional electricity grid structure. Microgrids are key elements of these emerging grid structures. Although microgrids are accepted as possible solutions to power quality and power stability issues in ac power systems, the uncertainty in the ability of microgrids to cope with severe fluctuating load and fault conditions is a major concern in the operation of these new grid structures. This project was aimed at improving frequency control within a microgrid. Four objectives were identified and addressed to meet this aim. I. A weak microgrid network using an emulated internal combustion engine generator and associated loads was modelled. The emulation of a diesel generating set was achieved with a vector controlled induction motor driving a synchronous generator. The diesel engine emulation was achieved by incorporating a single delay into the speed control loop of the vector controlled induction motor. The modelled microgrid network is a very useful tool for the development of novel control schemes for frequency control within a microgrid. II. Simulation studies were carried out to investigate how a weak power system can be strengthened through the use of enhanced STATCOM and Supercapacitor energy storage. This assisted in understanding the limitations and performances of the novel algorithms proposed for frequency control improvement. III. Novel open and closed loop control algorithms for frequency control within a microgrid were proposed. The advantage of the open loop control scheme is its simplicity but the functionality of the control action is limited with the knowledge of the diesel engine transfer function and load current being important requirements. A closed loop control scheme was employed to address the limitations of the open loop control scheme. IV. A laboratory prototype of the microgrid network was developed and used in validating the novel control schemes proposed. The thesis describes the novel algorithms for frequency control using an intelligent STAtic COMpensator (STATCOM) and SuperCapacitor Energy Storage System (SCESS). The benefits and effectiveness of the proposed algorithms are given in the simulation and experimental results.

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