This thesis investigates the implementation of a practical control strategy for a simple wave energy converter in regular and irregular waves. Inspired by the neurophysiology of the lamprey, this work looks at the limitations of using this neural structure as a method for control of an articulated wave energy converter. Initially starting with a very simple mechanical model of a single heaving buoy, evolutionary techniques are employed to evolve a single lamprey segment that will be capable of acting as a controller. Without prediction of the incident wave, wide-bandwidth latching controllers, are evolved that show significant improvements over optimal damping in increasingly complex waveforms. More complex mechanical configurations are also investigated, expanding the simple heaving buoy into two and three interconnected buoys with power being developed through their relative motion. Neural latching controllers are evolved for these different configurations and it is shown that an effective neural latching controller cannot be evolved for more than two interconnected buoys. This thesis investigates the processes of producing a viable implementation of a latching strategy using neural oscillators as a non-linear feedback loop. It covers their performance in regular and irregular waves and demonstrates the limitations of latching control when applied to an articulated system.

Micro hydro power schemes are characterised by a power output of less than 100kW. They have been identified as a means of providing mechanical and electrical power for isolated communities in developing countries, with a view to increasing the rate of development in such communities. Nepal is one of the poorest countries of the world and, apart from hydro power, has little in the way of natural resources which it can use as a basis for development. It is essential, therefore, that this hydro resource is exploited efficiently. Large scale hydro power schemes benefit the country as a whole, but bring few benefits to the rural poor. Micro hydro power schemes supplying mechanical and electrical power can, however, have an immediate impact at this level. Small scale engineering projects in developing countries are constrained by factors which are not present in the developed world, such as lack of infrastructure, transport problems, communications problems and meagre materials and skills resources. Experiential knowledge is therefore as important as professional knowledge in the design and installation of micro hydro power schemes. When personnel leave the organisations which are involved in micro hydro power their skills are lost to the field. Expert systems and Decision Support Software (DSS) provide a method for capturing their experiential knowledge. The MICADO system of DSS is a software tool created to support engineers designing micro hydro power schemes and others who may be assessing the viability of such schemes. The software is intended for use in Nepal, but the evaluation routines can be applied to micro hydro power schemes elsewhere in the world. MICADO was programmed to specifications given by its user group in Nepal, and was constrained to run on hardware which was already available to them. It is configured on the commercially available CRYSTAL expert system builder, and runs on IBM PCs and compatibles.

No description available.

Three-phase four-leg voltage source inverters (VSIs) are widely used in distributed power generation applications, three-phase UPS systems and fault-mode operation of a balanced three-phase system where the balanced three-phase voltage output is required when the loads are unbalanced. A three-dimensional space vector modulation (3-D SVM) switching scheme, which is proved to be compatible with modern DSP implementation for a four-leg VSI, has the advantage of higher DC link utilization, less harmonic contents and less switching losses compared with sinusoidal PWM. Therefore it is the first choice of switching schemes for a four-leg inverter. Electromagnetic interference (EMI) which is associated with common-mode switching for a high voltage level power system can degrade the equipment performance and cause communication problems. The conventional 3-D SVM switching scheme exhibits high common-mode voltage (CMV) characteristics which may result in problems in high power applications. The 3-D SVM has the drawback of being complex which could become a software burden in computationally intense real-time control applications. Attempts to reduce the complexity of the 3-D SVM have been made by many researchers and new switching schemes such as carrier-based PWM proved to have the same performance. This thesis presents a switching scheme called near-state 3-D SVM that can reduce the CMV voltage level of a four-leg inverter by avoiding the use of the two zero switching states of the inverter. A laboratory test bench has been built to validate the proposed switching scheme. An in-depth analysis has been carried out for a four-leg inverter in terms of total harmonic distortion (THD) factor, current harmonic distortion factor, conduction losses and switching losses. The proposed switching scheme is analyzed and compared with the conventional 3-D SVM using the analysis method. Additionally, a simplified switching scheme which is still based on space vector theory is proposed. This simplified switching scheme remains compatible with vector control. Experimental results show that the simplified switching scheme has the same performance as 3-D SVM, with reduced program execution time. Abstract iii An output voltage control loop with current feed-forward term in d-q-0 coordinate, which is designed in the discrete-time domain, proves to be most compatible with a DSP-based control system. Experimental results demonstrate the performance of the control loop in both steady state and transient operation.

Maintaining power system stability has become a challenging task for engineers. A consequence of such factors is that power system damping of electro-mechanical oscillations is often reduced which could sometimes destabilise the power systems if the electro-mechanical oscillations are poorly/lightly damped. Decentralised power system stabilisers are often used to increase damping of local oscillation modes and to some extent to increase damping of inter-area oscillation modes. However, damping of inter-area oscillations modes by the local PSS is not quite effective as for local oscillation modes. Therefore, it is necessary to implement a new control strategy to enhance damping of inter-area oscillation modes. With today’s advancement of phasor measurement units (PMUs), global information, which contains valuable information about the existence of inter-area oscillation modes, could be possibly used as inputs to mitigate inter-area oscillations as the literature suggests. The aim of this thesis is to propose supervisory power system stabilisers (SPSS) which are based on Fuzzy Logic to improve damping of such electro-mechanical oscillations in particular inter-area oscillation modes. Three different structures of supervisory power system stabilisers are presented in this thesis. The inputs to the proposed supervisory damping controllers will use global signals, speeds and their derivatives; however, the structure of the inputs to the supervisory power system stabilisers is different depending on the structural design of SPSS. The uniqueness of each SPSS type proposed is that they all make use of the same control rules regardless to which power system is applied. The robustness of such control rules and proposed SPSS are verified on three different test systems as the results of the case studies demonstrate. The time domain simulations will highlight the impact of each SPSS type on the system response.

In recent years, wind energy has become one of the rapid growing renewableenergy sources. According to the new power report from the European Wind Energy Association (EWEA), it forecasts that by 2020 the European Union will achieve 20% of power generation from renewable-energy sources, e.g. wind, solar and bio-fuels. Wind energy is a clean and inexhaustible energy source. It is available in all locations, especially remote ones with rich wind resources and plentiful land, which are suitable for developing large-scale wind farms. Typically, there are two well-known strategies for operating wind turbine generator (WTG) systems, including a fixed-speed strategy and a variable-speed strategy. The former strategy is suitable for large-scale WTG systems, which are directly connected to a grid via capacitor banks for adjusting the generated reactive power. Most of the fixed-speed WTG systems employ pitch angle controllers for extracting maximum wind turbine power from wind. The main disadvantages of the fixed-speed strategy are: first, the mechanical torques are highly affected under rapid wind speeds, i.e. wind gusts, which cause power surges on a grid and second, additional expensive equipment, e.g. motors, actuators and drivers, are required to implement a pitch angle controller. In literatures, the first problem was tackled by keeping the reference pitch angle constant at rapid wind speed variations in order to decrease mechanical stresses on a wind turbine tower. Whilst, the variable-speed strategy has been widely employed for maximising the output power of WTG systems using maximum power point tracking (MPPT) controllers, which can be applied via power electronic converters. The power delivered by a WTG system is dependent on the swept area of a wind turbine, wind speeds, power coefficients of a wind turbine and the current v drawn from a generator. The only controllable factor is the power coefficient, which varies with operating tip speed ratios (TSR). For coming wind speeds, there is a unique optimal TSR that keeps power coefficients at its maximum value. In order to achieve the optimal TSR, it is required to control rotor speeds of a WTG system to follow reference rotor speeds, which can be produced by a TSR controller based on measurement or estimation of wind speeds. In Chapter 2, a comparison study between a classic direct field oriented controller (FOC) and an optimised direct FOC, has been presented. The proposed VTG system comprises a vertical-axis wind turbine (VAWT), a permanent magnet synchronous generator (PMSG), a three-phase controlled rectifier and a stand-alone DC load. The objectives of these controllers are for improving the efficiency and the dynamic performance of a WTG system as well as minimising rotor speed overshoots under rapid wind speed variations. The developed controllers are based on a well-known FOC method, through adjusting stator currents and consequently electromagnetic torque. FOC transforms three-phase stator currents into two currents in the rotational reference frame, i.e. d-axis and q-axis currents, using the Park transformation. These d-axis and q-axis currents act as DC currents. To apply FOC, reference rotor speeds or reference electromagnetic torques are required to generate reference q-axis currents, whilst reference d-axis currents are usually set as zero for minimising loss. It is important to note that the Park transformation needs the knowledge of rotor positions, which can be measured by an encoder. In practice, an encoder cannot measure an accurate initial position, which may lead to wrong calculations of d-axis and q-axis currents. It is worth noting that the parameters of a PI current controller are firstly tuned using a classic zero and pole placement method and secondly optimised using a particle swarm optimisation (PSO) algorithm. The PSO algorithm is adopted due to the following advantages: such as easy to implement with simulations in real-time, a high computational efficiency and stable convergence characteristics. An accurate model for a PMSG is important for the design of a high-performance PMSG control system, because the performance of such control systems is influenced by PMSG physical parameter variations under real operation conditions. In this research, electrical parameters of a PMSG are optimally identified, e.g. the stator resistance per phase, the stator inductance per phase and the rotor permanent magnet flux linkage, using also a PSO algorithm. It is important noting that the bounds of these parameters are obtained using standard tests, e.g. an open-circuit test, a short-circuit test and a load test. The aim is to increase the accuracy of parameter identification, reduce the search space of parameters and decrease the convergence time of a psa algorithm, i.e. the computation time required to reach an optimal solution. One of the difficulties for implementing the direct vector control strategy is the requirement to fix an anemometer close to wind turbine blades in order to obtain accurate wind speed measurements, otherwise inaccurate calculations of reference rotational speeds are obtained causing a WTG system not to rotate at optimal speeds. For cost and reliability consideration, a sensorless MPPT controller, which is based on a novel TSR observer is developed. The purpose of the proposed TSR observer is for estimating TSRs and consequently reference rotor speeds without the knowledge of wind speeds. The proposed TSR observer is based on the well-known perturbation and observation (P&O) method. It is also known as the hill-climbing searching method, which doesn't require any previous knowledge of wind turbine and generator characteristics. In spite of these advantages, it has some problems, which considerably decrease its dynamic performance. These problems include the steady-state oscillations around a maximum power point, a slow tracking speed, a perturbation process in a wrong direction and a high rotor speed overshoot under fast wind speed variations. In this research, these problems are tackled by using adaptive perturbation step sizes instead of fixed ones. For implementing the proposed MPPT controller, a costeffective power-electronics converter, which consists of a three-phase diode rectifier and a DC-DC boost converter, is constructed for experiments. Furthermore, a complete transfer function of the proposed system has been derived, which is employed to design a speed observer for estimating rotor speeds and consequently, rotor positions and for testing the stability of the developed rotor speed observers and controllers. In this thesis, another robust sensor less MPPT controller has been proposed for maximising the output power of a WTG system. A switch-mode rectifier (SMR), which includes a three-phase diode rectifier and a DC-DC boost converter without a boost inductance with an input capacitor filter for harmonic mitigation, is employed for implementing the proposed sensorless MPPT controller. The proposed sensorless MPPT controller is based on two novel observers, i.e. an adaptive sliding-mode observer (SMO) and an adaptive P&O algorithm. The former is used for estimating back-EMFs and consequently rotor speeds without the knowledge of rotor positions using an adaptive PMSG model in the stationary ex-/3 reference frame, an adaptive sliding gain and an adaptive cutoff-frequency LPF. The purpose is to eliminate the chattering effect (which occurs in conventional S1\,1Os ) and decrease estimation errors. The adaptive P&O algorithm is developed to estimate reference rotor speeds and optimal duty cycles based upon turbine coefficient errors and rotor speed errors, respectively. It uses adaptive variables compared with some widely used P&O algorithms, which use an adaptive perturbation step size but a fixed observation period. The adaptive variables are: (i) a perturbation step size, which decreases steady-state oscillations around optimal operating power points and (ii) an observation period, which is another contribution of this work. It increases the tracking speed and ensures that MPPT is always executed in the right direction with small rotor speed overshoots under fast wind speed variations. It should be noted that the developed sensorless MPPT controllers are experimentally validated using a WTG simulator. The data acquisition and control stage of the power electronic converters are implemented using a digital signal processing and control engineering (dSPACE) controller. In this thesis, the analysis of experimental results has been undertaken to verify the proposed observers and controllers. Finally, future research work is suggested.

This thesis presents research which shows that a helically configured Oscillating Water Column (OWC) could deliver improved performance compared to a conventional tube OWC, whilst saving a significant amount of draft. It is anticipated that savings in the deployment costs for this compact machine will outweigh any additional manufacturing costs. In order to prove the benefits of the helical concept, its performance relative to a conventional plain tube OWC was investigated in detail using scaled physical models. These models evolved during the course of the study, and refined models were developed. A variable impedance turbine simulator was also developed to test the models at their optimum conditions. The tests themselves were also refined leading to a high degree of confidence in the final result. A mathematical model was also adapted to model the performance of the physical models, and to help understand the physical processes involved in the system. With this series of improving physical models and tests, it has been shown that it is possible to achieve a 27% reduction in draft, with a 24% increase in power output.

Energy conversion efficiency is an important factor for the long-term feasibility of photovoltaic systems. Significant work has been carried out into improving the effectiveness of solar arrays in recent years. In addition, there has been substantial research into novel power converter topologies for maximum energy efficiency. However, in photovoltaic applications, even the most promising power converter topologies do not necessarily guarantee optimum performance under all operating conditions. For instance, the efficiency of the power conversion stage may be excellent during periods of high irradiance, but significantly lower in poorer light conditions. This work attempts to address this problem, by seeking to achieve higher energy conversion efficiency under sub-optimal conditions. In this thesis, stand-alone photovoltaic systems using DC-DC boost converters are considered. An interleaved boost converter with novel switch adaptive control scheme is designed to maximise system efficiency over a wider range of real-time operating atmospheric conditions and with different load conditions without incurring significant additional cost.

Experimental data are presented on the transient behaviour of an industrial scale shelland- tube condenser condensing steam from steam-air mixtures under reduced pressure. Models are developed for the dynamic simulation of a shell-and-tube condenser and for condensation in a single vertical tube. The unsteady behaviour of the UMIST condenser was examined by measuring the response of the system to step changes in the five key operating conditions. These are the pressure, steam load, air load, cooling water flowrate and cooling water inlet temperature. Step increases and decreases in each of these quantities were imposed. The responses of the system pressures, temperatures and flowrates are presented. Conclusions as to the underlying phenomena occurring are put forward. A model of a shell-and-tube condenser was developed within the DIY A dynamic simulation package, Hall et al (1988). This was used to simulate both steady and unsteady experiments using the UMIST condenser. The model was able to predict closely steady-state temperature and pressure profiles. The overall pressure drops with single-phase flow were predicted to within +5% and those with condensation to within ±10%. The simulated responses of the system to the step changes in operating conditions matched closely those seen experimentally. A model of condensation in a single vertical tube was developed within the SPEEDUP dynamic simulation environment, Perkins and Sargent (1982). The system investigated is that of condensation of a single vapour from a non-condensing gas. The condensation process was predicted using the film theory approach. The model was used to simulate the steady-state experimental data of G.Lehr (1972). Good agreement between the experimental and predicted Experimental data are presented on the transient behaviour of an industrial scale shelland- tube condenser condensing steam from steam-air mixtures under reduced pressure. Models are developed for the dynamic simulation of a shell-and-tube condenser and for condensation in a single vertical tube. The unsteady behaviour of the UMIST condenser was examined by measuring the response of the system to step changes in the five key operating conditions. These are the pressure, steam load, air load, cooling water flowrate and cooling water inlet temperature. Step increases and decreases in each of these quantities were imposed. The responses of the system pressures, temperatures and flowrates are presented. Conclusions as to the underlying phenomena occurring are put forward. A model of a shell-and-tube condenser was developed within the DIY A dynamic simulation package, Hall et al (1988). This was used to simulate both steady and unsteady experiments using the UMIST condenser. The model was able to predict closely steady-state temperature and pressure profiles. The overall pressure drops with single-phase flow were predicted to within +5% and those with condensation to within ±10%. The simulated responses of the system to the step changes in operating conditions matched closely those seen experimentally. A model of condensation in a single vertical tube was developed within the SPEEDUP dynamic simulation environment, Perkins and Sargent (1982). The system investigated is that of condensation of a single vapour from a non-condensing gas. The condensation process was predicted using the film theory approach. The model was used to simulate the steady-state experimental data of G.Lehr (1972). Good agreement between the experimental and predicted

Wind generation has emerged as an important renewable resource for power systems in recent years. However, the stochastic availability and variability of wind make scheduled generation dispatch complex. Therefore, a Coordinated Hydro and Wind Generation (CHWG) strategy is proposed to improve scheduled dispatch and thereby contribute to preservation of system stability, while offering access to wind energy at grid level. The CHWG is described in detail and a feasibility study has been conducted. In CHWG strategy, the hydroelectric generation is proposed for energy reserve and compensation in the context of wind power fluctuation in order to avoid curtailment of wind generation to benefit wind providers. An optimal dispatch model for CHWG proposed, which includes a wind forecasting confidence interval and electricity tariff. The boundary constraint and inertia coefficient of a particle swarm optimization algorithm are adopted and used to solve the optimal dispatch model. The model is applied to a wind farm system in North China to exemplify the proposed strategy. The following work and achievements are related to the use of the CHWG method. CHWG enhances the capacity of peak load regulation with offshore wind power integration. A model is presented to study the capacity of peak load regulation with offshore wind power integration. Meantime, a CHWG strategy mode is adopted to provide peak load regulation and some measures are proposed to improve regulation. A power system model is used to demonstrate that wind power fluctuations can readily render Over-frequency generator tripping (OFGT) and under-frequency load shedding (UFLS) mal-operation. Using the proposed CHWG strategy, a coordinated approach is proposed to resolve problems associated with OFGT and UFLS and preserve system stability. Finally, a risk assessment model (RAM) for wind generator tripping is established and verified by simulation results from a provincial Power Grid of China on line data.