In the coming decades, electrical energy networks will gradually change from a traditional passive network into an active bidirectional one using concepts such as these associated with the smart grid. Power electronics will play an important role in these changes. The inherent ability to control power flow and respond to highly dynamic network will be vital. Modular power electronics structures which can be reconfigured for a variety of applications promote economies of scale and technical advantages such as redundancy. The control of the energy flow through these converters has been much researched over the last 20 years. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a Cascaded H-Bridge converter, configured to function as a solid state substation. The work considers the derivation and application of Dead Beat and Model Predictive controllers for this application and scrutinises the technical advantages and potential application issues of these methodologies. Moreover an improvement to the standard Model Predictive Control algorithm that include an intrinsic modulation scheme inside the controller and named Modulated Model Predictive Control is introduced. Detailed technical work is supported by Matlab/Simulink model based simulations and validated by experimental work on two converter platforms, considering both ideal and non-ideal electrical network conditions.

The alternative components in an electric/flywheel propulsion system are reviewed, including different continuously variable transmissions (CVT's), and a new arrangement is proposed for electric vehicles, called the "Sussex propulsion system". Computer simulations are developed which show the effects of using flywheel energy storage, as opposed to electrical regenerative braking, for a large urban delivery van, which originally incorporated an electronically-controlled motor. Vehicle performance and energy consumption are compared over different driving cycles, and the result of varying the flywheel energy capacity is shown. The design and operation of an experimental rig is described and the experimental results are compared with those obtained from a computer simulation,, in order to test the validity of the mathematical models. The results show that for urban use, an electric delivery van fitted with the Sussex propulsion system has a substantially reduced energy consumption and better performance than a comparable conventional electric vehicle. Therefore, an electric vehicle in the future would require a smaller, cheaper installed battery pack or would have a greater range between recharging.

A Turbo-Pascal program has been developed that will aid a circuit designer to determine which of a set of "real" circuits will best match the associated "ideal" circuit or in choosing components for a given circuit. Study one examined the Sallen and Key second-order active low-pass circuit. Wn (mean), Wn (standard deviation), Q (mean), and Q (standard deviation) were examined as a function of Q desired, distribution type and component tolerance. The sensitivity of the circuit was calculated both numerically and through program execution. In Study two a set of reference graphs were generated to compare several second order low pass, high pass, and band pass filter classes as a function of component distribution and tolerance. Study three compares the behavior of several orders of low pass MFM (Maximally Flat Magnitude) Leapfrog filters. Amax (maximum gain), Wmax (frequency of maximum gain), and the 3dB frequency were examined. (Abstract shortened with permission of author.)

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The work in this thesis focuses on the characterization, modeling and emulation of both the supercapacitor and the new supercapattery energy storage device. The characterization involves the selection of dynamic models and experimental methodologies to derive model parameters. The characterizing processes focus on predicting short-term device dynamics, energy retention (self-discharging) and losses and round-trip efficiency. A methodology involving a pulse current method is applied for the first time to identify a model parameter to give fast device dynamic characteristics and a new constant power cycling method is used for evaluating round-trip efficiency. Experimental results are shown for a number of supercapacitor and supercapattery devices and good results are obtained. The derived models from the characterization results are implemented into the emulator system and the emulator system is used to mimic the dynamic characteristics of a scaled-up 1kW supercapattery device. The thesis also addresses voltage equalizing circuits and reports a study that investigates efficiency, a cell voltage deviation and voltage equalizing time for different control methods.

This thesis is concerned with two main lines of work which have followed parallel and complementary paths. The first one consists in using the technique of subharmonic sampling to investigate the frequency stabi lity of microwave oscillators using a convenient low frequency replica. The second line has been concerned with a detailed study of the Allan variance and the dependence of this variance on the operation of digital frequency counters, with special emphasis on the effects of 'dead-time'. This has led to the concept of an 'extended' variance over a time window NT obtained by averaging elementary estimates over a window T. After Chapter 1 which contains an overview of the basic concepts of frequency stability and summarises current measurement systems, Chapter 2 discusses in detail the operation of digital frequency counters and related mathematical modelling of the operation. As indicated above the chapter concludes with an original method of obtaining an extrapolated measurement of the two pair Allan variance. Chapter 3 extends the sampling theory to the down-conversion of a microwave signal using trapezoidal pulses with the objective of generating a low frequency replica. Recovery of the sampled signal, optimisation techniques and noise limitations are discussed in detail. Based on these considerations Chapter 4 explains the experimental equipment developed; it allows a microwave signal of up to 3 GHz to be translated down into the range 5 MHz to 7.5 MHz using a sampling gate driven by a variable width pulse generator coherent with a highly stable 5 MHz clock. Chapter 5 discusses the data acquisition and processing together with the calibration and checks of the experimental apparatus. Verification of the operation showed good agreement with the theoretical calculations and with an alternative mixing technique. The thesis concludes with Chapter 6 where after a detailed overview of the research work suggestions are given for further work.

<p> Power system is the backbone of modern society. Traditionally, over 90% of the electrical energy is produced by power generation systems driven by steam turbines. Recently, with the development of renewable energy resources, wind energy conversion systems are the proven solutions for the next generation sustainable energy resources. Stability and performance of these power systems are the primary concerns of power system engineers. To better characterize the dynamical behaviors of power systems in practical applications, time delays in the feedback state variables, systems modeling uncertainties, and external disturbances are included in the state space model of the power system in this work. Linear matrix inequality based robust and resilient controllers satisfying the H_infinty performance objective for time delayed power systems are proposed. Fixed time delays are assumed to exist within the system state and input signals. The system model is assumed to have unstructured bounded uncertainties and L_2 type of disturbances. Furthermore, controller gain perturbations are assumed to be of additive type. The proposed control techniques have been applied to variable speed permanent magnet synchronous generator based wind energy conversion systems, and electrical power generation systems driven by steam turbine. Computer simulations conducted in MATLAB show the eectiveness of the proposed control algorithms.</p>

In the past 2 decades the increasing intensive use of non-linear loads has resulted in a substantial reduction of power quality in electric power systems. Current harmonics produced by non-linear loads, such as power electronic converters and electrical drives cause a number of problems in power distribution networks. In more recent years this problem has affected also smaller distribution grids like for example in aircrafts, due to the so called "more electric aircraft" trend, consisting in the replacement of most of hydraulic/pneumatic actuators with electronically controlled electromechanical devices. Electrically powered actuation is becoming more attractive due to technology advances in bespoke equipment among which electrical motors, magnetic materials, electronic control circuits and power devices. Power electronics converters are required to control electrical power and are necessary for example for actuator motor drives and to convert variable frequency (360-800Hz) in the next generation of civil aircraft to a constant frequency supply bus for various loads or to a DC supply bus. Although the presence of electrically powered equipment is desirable for weight and fuel cost reduction, the increase of electrical systems on board, and above all the presence of power electronic subsystems, brings severe challenges to aircraft power system distribution interns of power quality. The aim of this research project is to investigate Shunt Active Filter (SAF) solutions to improve the quality of power of on-board grids. In particular advanced control strategies will be studied in order to enhance the SAFs' operation in maintaining high power quality in these particular power networks. Anyway, only harmonics compensation will be addressed, as considered SAF are not intended to alleviate other power quality potential issues such as current unbalance between phases, reactive power compensation. This research project presents the specific application of a wide-band current control method based on Iterative Learning Control (ILC) for aircraft power networks, and introduces enhanced design strategies to increase compensation accuracy and improve the robustness of the SAF control system by using a P-type ILC controller. Due to the fact that a variable supply frequency (360Hz - 800Hz) is adopted in the power networks of newly released aircrafts, this research project presents a close investigation of the P-type ILC current controlled SAF system in such application (together with the standard fixed 400Hz supply), and hence identifies suitable modifications for the SAF system control to provide an effective and accurate current harmonic cancellation during the supply frequency variation. Considering both simulation and experimental results, it can be concluded that the proposed SAF control proved to be very effective for accurate reduction of current harmonics on aircraft power grids with both fixed and variable supply frequency, using ordinary equipment and reasonable switching frequency and also ensuring good dynamics in transient conditions.