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This Thesis examines the operation and dynamic characteristics of the dual-interleaved boost converter with interphase transformer. Due to its inherent high efficiency and potential for miniaturisation, the circuit is of particular interest for the emerging applications in electric vehicle power trains, for example to interface a low voltage fuel cell or battery to a high voltage traction system. The steady-state analysis of the converter focuses on understanding the shapes of the interphase transformer currents and identifying the boundary condition for continuous conduction of the transformer windings. The analysis Is also seen to be applicable to a modified version of the converter in which the freewheel diodes are replaced by a second pair of transistors, enabling zero voltage switching by appropriate choice of the interphase transformer inductance. The analysis predicts approximately the boundary of zero voltage switching operation.

This thesis mainly presents two intelligent approaches to the Asset Management (AM) of power substations, which include an Evidential Reasoning (ER)-based document ranking approach to an Ontology-based Document Search Engine (ODSE) for the Information Retrieval (IR) of power substations and an Association Rule Mining (ARM)-based Dissolved Gas Analysis (DGA) approach to the Fault Diagnosis (FD) of power transformers.

A flywheel energy store comprises a motor/generator driving a flywheel where the noload losses are reduced so that half of the stored energy remains available after six hours of coasting. Analysis of the permitted level of losses is followed by discussion of how the losses can be minimised. The merits of induction and permanent magnet machines are compared in terms of their coasting losses. There is discussion of zero-power magnetic bearing systems developed to suspend vertical-axis energy-storage flywheels. With permanent magnet material in the magnetic circuit, an electronic control system can hold the airgap at the otherwise unstable point of equilibrium, where the attractive force due to the magnetic flux exactly balances the weight of the flywheel. Under steady state conditions the power dissipated in the control coil is virtually zero. The torque generation characteristic of an induction machine is explained from first principles. This is followed by an equivalent circuit analysis that is specific to operation at a constant flux level with a variable supply frequency and voltage. The supply voltage for constant flux operation is specified as a function of the rotational speed and the absolute slip frequency. An all-digital, three-phase inverter developed for use with an induction motor gives four-quadrant control of the torque applied to a load. A low cost incremental shaft encoder and straightforward digital logic allows precise and instantaneous generation of absolute slip frequency. A modified PWM switching topology minimises switching losses and maximises the utilisation of the DC link voltage. The inherent speed of the all-hardware design and its precise control of slip frequency, make it ideal for highspeed motors or for drives requiring frequent and rapid reversal. A new design for an ironless stator winding for a permanent magnet motor/generator minimises electromagnetic drag when coasting. The winding meets the predicted reduction in drag torque and provides an extremely pure sine wave output with very low source impedance.

Switching operations within high voltage substations will radiate transient electromagnetic fields. This was not a problem for electromechanical devices found within the substations. However, with the introduction of new technology equipment (microelectronics) into the substations for measurement, communication, protection and control purposes, there is a growing concern that radiated fields due to switching could cause interference to the normal operation of electronic equipment. This could lead to complete system disturbances and ultimately complete blackout. There is therefore the need to quantity the magnitude of radiated fields within the substation environment.

Electrical systems are subject to a wide variety of power quality problems which can interrupt production processes, affect sensitive equipment, and cause downtime. Several power quality studies show that harmonics and voltage sags have been identified as the most serious problems facing industrial customers today, especially in small independent grids which employ distributed generation units.

A novel probabilistic method has been developed for modelling the operation of energy storage in electricity systems with significant amounts of wind and solar powered generation. This method is based on a spectral analysis of the variations of wind speed and solar irradiance together with profiles of electrical demand. The method has been embodied in two Matlab computer programs: Wind power only: This program models wind power on any time scale from seconds to years, with limited modelling of demand profiles. This program is only capable of modelling stand-alone systems, or systems in which the electrical demand is replaced by a weak grid connection with limited export capacity. 24-hours: This program models wind power, solar PV power and electrical demand, including seasonal and diurnal effects of each. However, this program only models store cycle times (variations within a time scale) of 24 hours. This program is capable of modelling local electrical demand at the same time as a grid connection with import or export capacity and a backup generator. Each of these programs has been validated by comparing its results with those from a time step program, making four Matlab programs in total. All four programs calculate the power flows to and from the store, satisfied demand, unsatisfied demand and curtailed power. The programs also predict the fractions of time that the store spends full, empty, filling or emptying. The results obtained are promising. Probabilistic program results agree well with time step results over a wide range of input data and time scales. The probabilistic method needs further refinement, but can be used to perform initial modelling and feasibility studies for renewable energy systems. The probabilistic method has the advantage that the required input data is less, and the computer run time is reduced, compared to the time step method.

Thesis (D. Tech. Engineering : Electrical ; Dept. Applied Electronics and Electronic Communications) -- Vaal University of Technology / Two methods to convert an AC current source to an AC voltage source are presented. Both methods make use of a current transformer to provide energy extraction from the main system while maintaining galvanic isolation between the main system and the output system. Control is via a pulse width modulation scheme in both instances. The ftrst method uses a storage element to provide a DC voltage, which feeds an inverter that supplies the AC load with a voltage source. The second method does not use a storage element but is a direct AC current source to AC voltage source converter employing a current transformer. This has not been done before. A possible application of this study is in the extraction of power from high voltage transmission lines without the conventional substation and rural grid to supply small users such as the telecommunication industry.