With rapid progress in microelectronics technology, high-performance Integrated Circuits (ICs) bring huge challenge to design the power supplies. Fast loop response is required to handle the high transient current of devices. Power solution size is demanded to reduce due to the size reduction of integrated circuits. The best way to meet these harsh requirements is to increase switching frequency of power supplies. Along with the benefits of increasing switching frequency, the power supplies will suffer from high switching loss and high gate charge loss as these losses are frequency dependant losses. This thesis investigates the best topology to minimize the switching loss. The Series-Parallel Resonant Converter (SPRC) with current-doubler is mainly analyzed for high frequency low voltage high current application. The advantages and disadvantages of SPRC with current-doubler are presented. A new adaptive synchronous rectifiers timing control scheme is also proposed. The proposed timing control scheme demonstrates it can minimize body diode conduction loss of synchronous rectifiers and therefore improve the efficiency of the converter. This thesis also proposes two families of new resonant gate drive circuits. The circuits recover a portion of gate drive energy that is total lost in conventional gate drive circuit. In addition to reducing gate charge loss, it also reduces the switching losses of the power switches. Detail operation principle, loss analysis and design guideline of the proposed drive circuits are provided. Simulation and experimental results are also presented. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-01-29 22:37:09.812

No description available.

This research studied the tractive performance of integrated steering-drive systems by investigating a two-wheel-drive vehicle having two independent rear drive wheels and non-driven steerable front wheels. The feasibility of integrating the steering and drive systems and the performance advantages that may be obtained was investigated. In order to demonstrate the feasibility of the concept, the steering system and the drive system of a test vehicle were integrated using a computer with a specially-developed program. The software algorithm developed for the program used the mathematical relationship between the rear drive wheel speeds and the steer angles of the non-driven front wheels to set the steer angles. A test-bed vehicle was fitted with instrumentation to implement the computer-integrated system. The circuitry of the hydraulic lines of the hydraulically-driven test vehicle was modified to allow changes in drive configuration. These changes are not possible with conventional vehicles. The test vehicle could be configured for the following steering-drive configurations: open differential rear drive with steerable front wheels, independent rear drive wheels with front castors, locked differential rear drive with steerable front wheels and the computer-integrated steering-drive system developed. The sensors on the vehicle allowed data collection for characterising the vehicle and wheels. omputer models were developed for the various steering-drive configurations from the force relationships, longitudinal slip relationships, vehicle geometry and turning geometry. Characteristics of the test vehicle's wheels for use in the models were measured experimentally. he models were used to simulate the behaviour, and calculate the tractive performance, of the four steering-drive configurations in various situations but actual tests were not able to be conducted with the available resources. Unlike previous models, the models of this research used force and longitudinal slip information rather than power input and power output to produce values for drawbar efficiency. theoretical analysis was conducted into the optimal slip conditions for maximum tractive efficiency. The analysis was conducted using a more rigorous mathematical analysis than previous researchers and used a thorough graphical analysis to substantiate the mathematical analysis. Previous studies concluded that under all traction conditions the efficiency of slip will be a maximum when the slip of each wheel is equal. This research revealed that, contrary to the previous literature, efficiency of slip will not be a maximum when the slip of each wheel is equal under non-uniform traction conditions. The simulations were focussed on turning situations, non-uniform traction conditions and traversing slopes. The optimal slip conditions and steer angles for turning situations were also investigated and analysed. The computer-integrated steering-drive system achieved a drawbar pull 50% higher than that for a conventional open differential when undertaking a 10 m radius turn with non-uniform traction conditions. Under these conditions, the drawbar efficiency of the computer-integrated steering-drive system was 5% greater than that for the open differential at the lower drawbar pull. It was concluded that it is feasible and beneficial to use a computer-integrated steering system. Vehicles using such a system would operate more effectively and efficiently when turning under load, moving across slopes and in non-uniform traction conditions. More effectiveness was provided through greater drawbar pull and higher drawbar efficiency. / thesis (PhD)--University of South Australia, 2005.

This works systematically presents various strategies to reduce both differential mode (DM) and common mode (CM) noise using a passive filter in a dc-fed motor drive. Following a standard approach a baseline filter is first designed to be used as reference to understand and compare the available filter topologies. Furthermore, it is used to analyze the grounding scheme of EMI filter and more specifically provide guidelines to ground single or multi stages filter. Finally, the baseline filter is investigated to recognize the possible solutions to minimize the size of the whole filter. It turns out that the CM choke and DM capacitors are the two main downsides to achieve a small EMI filter. Therefore, ideas are proposed to improve the CM choke by using other type of material such as nano crystalline core, different winding technique and new integrated method. A material comparison study is made between the common ferrite core and the nano crystalline core. Its advantages (high permeability and saturation flux density) and drawback (huge permeability drop) are analyzed thought multitudes of small and large signals tests. A novel integrated filter structure is addressed that maximizes the window area of the ferrite core and increases its leakage inductance by integrating both CM and DM inductances on the same core. Small- and large-signal experiments are conducted to verify the validity of the structure showing an effective size reduction and a good improvement at low and high frequencies. To conclude, a final filter version is proposed that reduce the volume of the baseline filter by three improve the performances in power tests. / Master of Science

Advances in electro-mechanical actuation have encouraged revolutions in automobile design which promise to increase fuel efficiency, reduce costs, improve safety and performance, and allow a wider range of architectural choices for the vehicle designer and manufacturer. This is facilitated by the concept of an intelligent corner (IC). The IC consists of traction, steering, camber, and suspension actuators working together to control the forces generated at the wheel/surface interface, allowing complete control of vehicle motion with completely active, as opposed to passive, systems. The most critical actuator to the longitudinal performance of an IC vehicle is the traction system, envisioned in this case as a hub mounted electro-mechanical actuator connected directly to the wheel. This traction actuator consists of a number of primary and supplementary components, including a prime mover, gear train, clutch, brake, bearings, seals, shafts, housing, etc. The consideration of these components in the design of an in-hub electric drive actuator is the subject of this report. Currently, gear trains are used in automobiles to match the operating speed of an internal combustion engine (ICE) to the speed of the vehicle on the road. The same need is anticipated for the hub drive wheel, although with fewer reduction ratio choices due to the responsiveness of the electric motor. Specifying a gear train design includes selecting a gear train architecture, and designing the gears to handle the expected loads. A review of gear design and gear train architectures is presented. A number of electric machines are used in industrial, and now more commonly, vehicle applications; of these, the switched reluctance motor (SRM) represents an excellent candidate for a vehicle prime mover due to its ruggedness, broad torque speed curve, low cost, and simplicity. Integrating the motor and gear train into an electro-mechanical actuator with multiple speeds requires consideration of other ancillary components. Brief design guides are presented for clutches, brakes, bearings, seals, and the structure for the in-hub wheel drive. Given the analytical descriptions of the drive wheel components, methods for managing the numerous design parameters are developed and expanded. Actuator specifications are chosen based upon meeting various vehicle performance requirements such as maximum speed, gradeability, acceleration, and drawbar pull. A proposed parametric drive wheel design is presented to meet the requirements of a generic heavy vehicle. The design demonstrates the feasibility of actuator technology that can be used to increase the performance, maintainability, and refreshability of hybrid electric vehicles while allowing open architecture paradigms to lower costs and spur new levels of manufacturing and innovation. / text

As machine topologies and technologies mature, the fundamental function of the device is honed. Direct drive machines have the potential to launch the renewable energy sector into a new era of large scale, reliable, offshore power generation. With advancements in new technologies, such as superconductivity, the reduction of generator mass due to incorporation of machine and device structures, the continued advancements in component and system reliability; direct drive generators have the ability to outsize geared wind systems and simplify submerged linear and rotary power generation. The research held within this thesis will focus on improving direct drive power take off systems for offshore renewable energy power generation by splitting the area into four parts. The first part will discuss the various methods of energy extraction within the offshore and marine environment. The future of the sector will be discussed, and a forecast of technological advancement and existing reliability issues will be provided based on current data. The second part will focus on drive trains and direct drive generators, assessing the current topologies and suggesting alternatives that may thrive in a variety of large and small offshore renewable machines. The third part investigates the application of novel linear bearings in direct drive systems for offshore and submerged operation. A brief study of the loads found in wave applications will be presented and the testing of several polymer bearing materials will be outlined. The final part will discuss the potential benefits of flooding the airgap of a direct drive generator with sea water for marine applications. Results will be presented from two linear test rigs and the marinisation of devices will conclude the report.

No description available.

This thesis describes four novel superconducting machine concepts, in the pursuit of finding a suitable design for large offshore wind turbines. The designs should be reliable, modular and light-weight. The main novelty of the topologies reside in using a single loop shaped stationary superconducting field winding, which eliminates the rotating transfer couplers and electric brushes or brushless exciters. Furthermore, the electromagnetic forces in the superconducting wire are also eliminated, which simplifies the design and manufacturing of the cryostat and the support structure. Among the four topologies presented, the claw pole type machine is the most promising one. The rotor of the machine composes of claw-poles made from laminated electrical sheets, the superconducting field winding and the armature winding are stationary. The machine is analysed using 3D FEA simulations and a small linear machine prototype is manufactured to verify the simulations. For large scale applications, a double-sided claw pole machine is proposed, which has balanced magnetic attraction forces in the rotor. The machine has a modular cryostat structure, which increases the availability of the machine. Thus, even if a fault occurs in the cryocoolers or in the armature coils, the rest of the machine can operate at partial load until the maintenance is performed. Moreover, it is much easier to replace the faulty parts, as full disassemble of the machine is not required, and a small on-site crane can be used. As a result, it offers operational advantages over the existing superconducting topologies. A 10 MW, 10 rpm generator design is presented, which has a diameter of 6.6 m and an axial length of 1.4 m. The total active mass of the generator is 58 tonnes, and the structural mass is 126 tonnes, which gives a total mass of 184 tonnes. There are four independent cryostats and two independent armature windings in the machine to improve modularity. The biggest advantage of the design is the significantly less superconducting wire usage compared to any other designs; 10 MW machine just needs 15 km of MgB2 wire at 30 K. Thus, it is believed that the proposed topology is a very cost effective and suitable candidate for a successful entry to the wind turbine market.

Floating wind turbines (FWTs) are considered a new lease of opportunity for sustaining growth from offshore wind energy. In recent years, several new concepts have emerged, with only a few making it to demonstration or pre-commercialisation stages. Amongst these, the spar-buoy based FWT has been extensively researched concept with efforts to optimise the dynamic response and reduce the costs at acceptable levels of performance. Yet, there exist notable lapses in understanding of these systems due to lack of established design standards, operational experience, inaccurate modelling and inconsistent reporting that hamper the design process. Previous studies on spar-buoy FWTs have shown inconsistencies in reporting hydrodynamic response and adopted simplified mooring line models that have failed to capture the coupled hydrodynamic behaviour accurately. At the same time, published information on drive-trains for FWTs is scarce and limited to geared systems that suffer from reliability issues. This research was aimed at filling the knowledge gaps with regard to hydrodynamic modelling and drive-train research for the spar-buoy FWT. The research proceeds in three parts, beginning with numerical modelling and experimental testing of a stepped spar-buoy FWT. A 1:100 scale model was constructed and tested in the University of Edinburgh’s curved wave tank for various regular and irregular sea states. The motion responses were recorded at its centre of mass and nacelle locations. The same motions were also simulated numerically using finite element method based software, OrcaFlex for identical wave conditions. The hydrodynamic responses were evaluated as Response Amplitude Operator (RAO) and compared with numerical simulations. The results showed very good agreement and the numerical model was found to better capture the non-linearities from mooring lines. A new design parameter, Nacelle Magnification Factor, was introduced to quantify coupled behaviour of the system. This could potentially encourage a new design approach to optimising floating wind turbine systems for a given hub height. The second part of the research was initiated by identification of special design considerations for drive-trains to be successfully integrated into FWTs. A comparative assessment of current state of the art showed good potential for directdrive permanent magnet synchronous generators (PMSG). A radial flux topology of the direct-drive PMSG was further examined to verify its suitability to FWT. The generator design was qualified based on its structural integrity and ability to ensure minimal overall impact. The results showed that limiting the generator weight without compromising air-gap tolerances or tower-foundation upgrades was the biggest challenge. Further research was required to verify the dynamic response and component loading to be at an acceptable level. The concluding part of research investigated the dynamic behaviour of the directdrive generator and the various processes that controlled its performance in a FWT. For this purpose, a fully coupled aero-hydro-servo-elastic model of direct-drive FWT was developed. This exercise yet again highlighted the weight challenge imposed by the direct-drive system entailing extra investment on structure. The drive-train dynamics were analysed using a linear combination of multi-body simulation tools namely HAWC2 and SIMPACK. Shaft misalignment, its effect on unbalanced magnetic pull and the main bearing loads were examined. The responses were found to be within acceptable limits and the FWT system does not appreciably alter the dynamics of a direct-drive generator. Any extra investment on the structure is expected to be outweighed by the superior performance and reliability with the direct-drive generator. In summary, this research proposes new solutions to increase the general understanding of hydrodynamics of FWTs and encourages the implementation of direct-drive generators for FWTs. It is believed that the solutions proposed through this research can potentially help address the design challenges of FWTs.

For adaptive motion control of an autonomous vehicle, operating in a generally structured environment, position and velocity feedback are required to ascertain the vehicle location relative to a reference. Whilst the literature offers techniques for guiding vehicles along external references, autonomous vehicles should be able to navigate between despatch locations without the need to rely on external guidance systems. Considerations of the vehicle stability and manoeuvrability favour a vehicle design with four independently steered wheels. A new motion control methodology has been proposed which utilises the geometric relationship of the angular displacements and the rotations of the wheels to estimate the longitudinal and lateral motions of the vehicle. The motion controller consists of three building blocks: the motion control system comprising the position tracking and the motion command generation; the electronic system comprising a data acquisition system and proprietary power electronics; the mechanical system which includes an undercarriage enabling permanent contact of the wheels with the floor. The components have been designed not only to perform optimally in their specific functions but also to ensure full compatibility within the integrated system. For reliable deduction of the wheel rotations with a high degree of accuracy a dedicated data acquisition interface has been developed, which enables data to be captured in parallel from four optical encoders mounted directly on the wheel axles. Parallel sampling of the angular wheel position and parallel actuation of all steering motors improves the accuracy of the system state and gives a higher degree of certainty. Considering only circular motion of the vehicle, a method for calculating the steering angles and wheel speeds based on the complex notation is presented. By cumulating the displacement vectors of the vehicle motion and the location of the centre of rotation between consecutive samples of the controller, the path of the vehicle is estimated. The difference between the nominal and the deduced centre of rotation is determined to minimise deviations from the reference trajectory and to allow the controller to adapt to changes in the road/tyre interface characteristics. The individual mechanical and electronic components have been assembled and tested. Additionally, the performance of the electronic interface has been evaluated on a purpose built test-bed. For the experimental validation of the methodology, a simple method of mapping the centre of curvature with a pen mounted at the nominal centre of rotation has been proposed. Experiments have been conducted with both the steering angles fixed to their theoretical values for the nominal centre of rotation and with the proportional steering controller enabled. The results from the latter method have shown a significantly reduced deviation from the nominal centre of rotation. The data captured of the angular wheel positions and steering angle settings has been analysed off-line. Good agreement is obtained between the deduced and the actual centres of rotation for the measurements averaged over 1.5 seconds. A number of different centres of rotation have been investigated and the required steering angles to compensate for the deviation have been plotted to form a control surface for the motion controller. The deviation between the estimated and the actual centre of curvature was less than 1.6% and adequate results could be obtained with the proportional steering controller.