A medium-frequency transformer with multiple secondary windings for grid connection through H-bridge voltage source converters

Although the power output of today's wind turbine has exceeded 7 MW, the voltage rating of the most common generator is below 700 V. A low-frequency transformer is commonly used to step-up the voltage to the grid voltage level, e.g. 11 kV or 33 kV. These heavy and bulky low-frequency transformers significantly increase the volume and weight of nacelle. To achieve a compact and light nacelle, a medium-voltage converter with series-connected H-bridge (SCHB) topology would be an attractive technology for future wind turbines. However, the SCHB converter requires multiple isolated and balanced DC sources, which makes the application not straightforward. As an alternative approach to generate multiple isolated and balanced sources a prototype transformer with six secondary windings, 1.26 kVA and 10 kHz, is designed and developed for 1 kV five levels SCHB multilevel converters. The experimental results show that the proposed system may be attractive in grid based renewable energy systems. © 2012 IEEJ Industry Appl Soc

Design and implementation of a compact highly efficient 472kHz radio frequency generator for electrosurgery

2011 Summer.Includes bibliographical references.This thesis explores the utilization of modern design practices and advance technologies to reduce the size of traditional 472kHz radio frequency generators used for electrosurgery. Achieving the reduced size requires an innovative approach to increase the overall efficiency to lower the internal heat dissipation allowing the overall package size to shrink. This thesis covers the selection and design process to achieving the final topology of an innovative approach utilizing a variation of the Class-D amplifier to produce a resonance type power saturation amplifier. While using a high-efficiency power source to control the amplifier voltage rails, and to control the amplitude of the output signal will produce a sinusoidal power source capable of driving a radio frequency surgical scalpel

Accurate copper loss analysis of a multi-winding high-frequency transformer for a magnetically-coupled residential micro-grid

© 2017 IEEE. Improvements in characteristics of magnetic materials and switching devices have provided the feasibility of replacing the electrical buses with high frequency magnetic links in micro-grids. This effectively reduces the number of voltage conversion stages, and the size and cost of the renewable energy system. It also isolates the converter ports, which increases the system safety and facilitates bidirectional power flow and energy management. To design the magnetic link optimally, an accurate evaluation of copper loss of the windings considering both current waveforms and parasitic effects is required. This paper studies the accurate copper loss analysis of a three-winding high-frequency magnetic link for residential micro-grid applications. Due to the non-sinusoidal nature of the voltage and currents, the loss analysis is carried out on a harmonic basis taking into account variations of phase shift, duty ratio and amplitude of waveforms. The high frequency skin and proximity effects have are taken into account. The maximum and minimum copper loss operating points of the converter and their dependency on the phase shift and duty ratio of the waveforms are studied and simulation results are presented

Copper loss analysis of a multiwinding high-frequency transformer for a magnetically-coupled residential microgrid

© 2018 IEEE. Improvements in characteristics of magnetic materials and switching devices have provided the feasibility of replacing the electrical buses with high-frequency magnetic links in small-scale microgrids. This can effectively reduce the number of voltage conversion stages, size, and cost of the microgrid, and isolate the sources and loads. To optimally design the magnetic link, an accurate evaluation of copper loss of the windings considering both the current waveforms and parasitic effects are required. This paper studies the copper loss analysis of a three-winding high-frequency magnetic link for residential microgrid applications. Due to the nonsinusoidal nature of the voltages and currents, the loss analysis is carried out on a harmonic basis taking into account the variations of phase shift, duty ratio, and amplitude of the waveforms. The high-frequency parasitic phenomena including the skin and proximity effects are taken into account. The maximum and minimum copper loss operating conditions of the magnetic link and their dependency on the phase shift angle and the duty ratio of the connected waveforms are studied. A prototype of the microgrid including the magnetic link is developed to validate the theoretical analysis, evaluate the microgrid efficiency, and perform the loss breakdown

High speed high power electrical machines

DEng ThesisHigh Speed High Power (HSHP) electrical machines push the limits of electromagnetics, material capabilities and construction techniques. In doing so they are able to match the power performance of high speed turbomachinery such as gas turbines, compressors and expanders. This makes them attractive options for direct coupling to such machinery as either a power source or as a generator; eliminating the need for gearboxes and achieving a smaller system size and greater reliability. The design of HSHP machines is a challenging, iterative process. Mechanical, electromagnetic and thermal constraints are all placed on the machine shape, topology, operating point and materials. The designer must balance all of these constraints to find a workable solution that is mechanically stable, can work within the available electrical supply and will not overheat. This thesis researches the fundamental origins and interaction of the mechanical, electromagnetic and thermal constraints on electrical machines. Particular attention was paid to improving the accuracy of traditional mechanical rotor design processes, and improving loss estimation in inverter fed machines. The issues of selecting an appropriate electric loading for low voltage machines and choosing effective, economic cooling strategies were explored in detail. An analytical iterative design process that combines mechanical, electromagnetic and thermal design is proposed; this process balances the need for speed versus accuracy for the initial design of a machine, with Finite Element Analysis used only for final validation of performance and losses. The design process was tested on the design and manufacture of a 1.1MW 30,000rpm PM dynamometer used in an industrial test stand. The machine operating point was chosen to meet a gap in the industrial machines market and exceed the capabilities of other commercially available machines of the same speed. The resulting machine was successfully tested and comfortably meets the performance criteria used in the design process

Analysis and optimization of the efficiency of induction heating applications with litz-wire planar and solenoidal coils

Optimization of the efficiency of an induction heating application is essential in order to improve both reliability and performance. For this purpose, multi-stranded cables with litz structure are often used in induction heating applications. This paper presents an analysis and optimization of the efficiency of induction heating systems focusing on the optimal copper volume of the winding with respect to different constraints. The analysis is based on the concept of a one-strand one-turn coil, which captures the dissipative effects of an induction heating system and reduces the number of variables of the analysis. An expression for the efficiency of the induction heating system is derived. It is found that, with the geometry and the other parameters of the system fixed, efficiency depends on the copper volume of the windings. In order to use this result to optimize the efficiency of an application, volume restrictions, the packing factor and the window utilization factor are also considered. The optimum frequency for an induction heating system is also studied in this work. An experimental verification for both planar and solenoidal cases is also presented