Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters

Harmonic content is inherent in switched-mode power supplies. Since the undesired harmonics interfere with the operation of other sensitive electronics, the reduction of harmonic content is essential for power electronics design. Conventional approaches to attenuate the harmonic content include passive/active filter and wave-shaping in modulation. However, those approaches are not suitable for resonant converters due to bulky passive volumes and excessive switching losses. This dissertation focuses on eliminating the undesired harmonics from generation by intelligently manipulating the spectrum of switching waveforms, considering practical needs for functionality.To generate multiple ac outputs while eliminating the low-order harmonics from a single inverter, a multi-frequency programmed pulse width modulation is investigated. The proposed modulation schemes enable multi-frequency generation and independent output regulation. In this method, the fundamental and certain harmonics are independently controlled for each of the outputs, allowing individual power regulations. Also, undesired harmonics in between output frequencies are easily eliminated from generation, which prevents potential hazards caused by the harmonic content and bulky filters. Finally, the proposed modulation schemes are applicable to a variety of DC/AC topologies.Two applications of dc/ac resonant inverters, i.e. an electrosurgical generator and a dual-mode WPT transmitter, are demonstrated using the proposed MFPWM schemes. From the experimental results of two hardware prototypes, the MFPWM alleviates the challenges of designing a complicated passive filter for the low-order harmonics. In addition, the MFPWM facilitates combines functionalities using less hardware compared to the state-of-the-art. The prototypes demonstrate a comparable efficiency while achieving multiple ac outputs using a single inverter.To overcome the low-efficiency, low power-density problems in conventional wireless fast charging, a multi-level switched-capacitor ac/dc rectifier is investigated. This new WPT receiver takes advantage of a high power-density switched-capacitor circuit, the low harmonic content of the multilevel MFPWMs, and output regulation ability to improve the system efficiency. A detailed topology evaluation regarding the regulation scheme, system efficiency, current THD and volume estimation is demonstrated, and experimental results from a 20 W prototype prove that the multi-level switched-capacitor rectifier is an excellent candidate for high-efficiency, high power density design of wireless fast charging receiver

Achieving monotonic variation of spectral composition in DC-DC converters using pulse skipping modulation

This paper presents a new type of pulse skipping modulation (PSM) in a dc-dc converter, which is controlled by a voltage mode scheme. The duty ratio of the pulses, instead of being constant as in the conventional PSM, is controlled using a voltage mode control scheme along with a feed-forward path of the input voltage and an adjustable voltage. In the conventional PSM, spectral composition varies nonmonotonically which results in problems due to electromagnetic interference (EMI). We show, both analytically and experimentally, that the proposed scheme results in monotonic spectral behavior for a wide range of input voltage and load resistance. Hence one can obtain the small signal model of the system. Because of the synchronism with the external clock, it facilitates the design of an input filter for reduction of EMI

Fatigue crack detection on structural steel members by using ultrasound excited thermography = Erkennung von Ermüdungsrissen in Stahlbauteilen durch ultraschallangeregte Thermografie

Ultrasound excitation of structural steel members leads to localised energy dissipation at existent fatigue cracks and thus allows for thermographic flaw detection. Essential effects on the defect-selective heating such as flaw size, plate thickness, crack mouth opening or static preload are systematically investigated. Laser vibrometry measurements of the crack edges, theoretical modelling of frictional heating and numerical simulations contribute to the understanding of the involved physics

18th IEEE Workshop on Nonlinear Dynamics of Electronic Systems: Proceedings

Proceedings of the 18th IEEE Workshop on Nonlinear Dynamics of Electronic Systems, which took place in Dresden, Germany, 26 – 28 May 2010.:Welcome Address ........................ Page I Table of Contents ........................ Page III Symposium Committees .............. Page IV Special Thanks ............................. Page V Conference program (incl. page numbers of papers) ................... Page VI Conference papers Invited talks ................................ Page 1 Regular Papers ........................... Page 14 Wednesday, May 26th, 2010 ......... Page 15 Thursday, May 27th, 2010 .......... Page 110 Friday, May 28th, 2010 ............... Page 210 Author index ............................... Page XII

Middle Atmosphere Program. Handbook for MAP. Volume 13: Ground-based Techniques

Topics of activities in the middle Atmosphere program covered include: lidar systems of aerosol studies; mesosphere temperature; upper atmosphere temperatures and winds; D region electron densities; nitrogen oxides; atmospheric composition and structure; and optical sounding of ozone

Investigations into a multiplexed fibre interferometer for on-line, nanoscale, surface metrology

Current trends in technology are leading to a need for ever smaller and more complex featured surfaces. The techniques for manufacturing these surfaces are varied but are tied together by one limitation; the lack of useable, on-line metrology instrumentation. Current metrology methods require the removal of a workpiece for characterisation which leads to machining down-time, more intensive labour and generally presents a bottle neck for throughput. In order to establish a new method for on-line metrology at the nanoscale investigation are made into the use of optical fibre interferometry to realise a compact probe that is robust to environmental disturbance. Wavelength tuning is combined with a dispersive element to provide a moveable optical stylus that sweeps the surface. The phase variation caused by the surface topography is then analysed using phase shifting interferometry. A second interferometer is wavelength multiplexed into the optical circuit in order to track the inherent instability of the optical fibre. This is then countered using a closed loop control to servo the path lengths mechanically which additionally counters external vibration on the measurand. The overall stability is found to be limited by polarisation state evolution however. A second method is then investigated and a rapid phase shifting technique is employed in conjunction with an electro-optic phase modulator to overcome the polarisation state evolution. Closed loop servo control is realised with no mechanical movement and a step height artefact is measured. The measurement result shows good correlation with a measurement taken with a commercial white light interferometer

Technology 2002: The Third National Technology Transfer Conference and Exposition, volume 2

Proceedings from symposia of the Technology 2002 Conference and Exposition, December 1-3, 1992, Baltimore, MD. Volume 2 features 60 papers presented during 30 concurrent sessions

Fatigue crack detection on structural steel members by using ultrasound excited thermography = Erkennung von Ermüdungsrissen in Stahlbauteilen durch ultraschallangeregte Thermografie

Ultrasound excitation of structural steel members leads to localised energy dissipation at existent fatigue cracks and thus allows for thermographic flaw detection. Essential effects on the defect-selective heating, such as flaw size, plate thickness, crack mouth opening or static preload, are systematically investigated. Laser vibrometry measurements of the crack edges, theoretical modelling of frictional heating and numerical simulations contribute to the understanding of the involved physics

Space Programs Summary No. 37-36

Research in systems, guidance and control, space sciences, engineering, telecommunications and propulsion for space exploration program