Simple topologies for single phase AC line conditioning

This paper presents a variety of single phase AC line conditioning approaches. The topologies use a minimal number of devices and feature buck-boost voltage regulation capability without a transformer, while preserving a neutral connection which is common with the input AC line. The simplest form of the converter is seen to be an AC voltage regulator with output voltage range of 0-2 p.u. with reasonable line current waveform. Modifications allow the circuit to operate with fully controlled input current. The circuit can be further extended to provide significant ride-through capability without using a battery. Finally, a full function single phase UPS can also be realized if required. The paper contains analytical, simulation and experimental results     

An improved full-bridge zero-voltage switching PWM converter usinga two-inductor rectifier

An improved full-bridge ZVS PWM power convertor using a two-inductor rectifier DC/DC power converter is presented in this paper. For this improved topology, the main devices are switched under zero-voltage (ZVS) conditions using the energy stored in the secondary filter inductors. In addition, it utilizes the low leakage inductance of a coaxial winding transformer to reset the currents in the rectifier diodes and eliminate the secondary voltage spike. The two-inductor rectifier has only one diode conduction drop in addition to frequency doubling in the output capacitor. The secondary filter size in the proposed topology is rather small. The advantages of the new topology include a wide load range with ZVS, no lost duty cycle due to diode recovery, no secondary voltage spikes, in addition to high power density and high efficiency     

Design considerations for high-frequency coaxial winding powertransformers

The use of coaxial windings to create low-loss, low-leakage-reactance, power transformers for use in high-frequency soft-switched DC/DC and resonant converters has been demonstrated by M.H. Kheraluwalest al. (1990). Some of the important loss aspects of the design of coaxial winding transformers are examined, including the influence of the skin effect on winding resistance, the variation of core loss caused by nonuniform core flux density, and the choice of the principle dimensions and aspect ratios for maximum efficiency. Experimental measurements on a 50 kVA, 50 kHz unit are included to confirm portions of the analytical results and suggested design procedures     

Flux-based active filter controller

This paper presents a synchronous frame flux-based control method for a parallel active filter application. The flux-based controller directly implements the inverter switchings in the synchronous reference frame by a hysteresis rule-based carrier-less pulse-width modulation (PWM) strategy to achieve high current bandwidth. This paper addresses the issues and impact on parallel active filtering requirements for utility interface of commonly used harmonic front-ends. The synchronous frame flux-based controller provides additional insights for harmonic current compensation requirements. Simulation results provide the validation of the flux-based active filter controller to meet IEEE Standard 519 recommended harmonic standards for large rated nonlinear loads under balanced and unbalanced supply conditions     

Development of a freestanding copper antiscatter grid using deep X-ray lithography

A prototype freestanding copper antiscatter grid with parallel lamellar walls has been fabricated using deep X-ray lithography and electroforming. The freestanding copper grid has square shaped lamellar walls that are 25 m thick and 1 mm tall with a 550 m period. For mammography applications, the lamellar walls have to be aligned to a point X-ray source of the X-ray system. To achieve this goal, we investigated a dynamic double-exposure technique. Our progress in using stacked exposures and use of the photoresist SU-8, both to reduce fabrication cost, is also presented.We would like to thank Francesco De Carlo, Judith Yaeger, Joseph Arko and Shenglan Xu for their assistance. Use of the APS was supported by US Department of Energy, Office of Sciences, under Contract No. W-31-109-ENG-38. We thank SRI CAT for the support of this research. The work is supported by NIH SBIR Phase II Grants: 2 R44 CA76752-02 and 5 R44 CA76752-03.This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

Distributed FACTS—A New Concept for Realizing Grid Power Flow Control

Flexible AC transmission systems (FACTS) devices are used to control power flow in the transmission grid to relieve congestion and limit loop flows. High cost and reliability concerns have limited the widespread deployment of FACTS solutions. This paper introduces the concept of distributed FACTS (D-FACTS) as an alternative approach to realizing cost-effective power flow control. By way of example, a distributed series impedance (DSI) and a distributed static series compensator (DSSC) are shown that can be clipped on to an existing power line and can, dynamically and statically, change the impedance of the line so as to control power flow. Details of implementation and system impact are presented in the paper, along with experimental results.     

Design considerations for charge equalization of an electricvehicle battery system

Charge equalization for series-connected battery strings has important ramifications on battery life. It enhances the uniformity of the battery cells and, hence, improves the life of the battery as a whole. A new charge equalization technique for a series string of battery cells has been recently proposed by the authors. The basic technique utilizes a simple isolated DC-to-DC power converter with a capacitive output filter along with a multiwinding transformer. The possibility of integrating the trickle charge function with the charge equalization function is potentially very attractive, as it can lead to an efficient and low-cost implementation     

Acoustic noise reduction in sinusoidal PWM drives using a randomlymodulated carrier

Acoustic noise in an inverter-driven electric machine can be reduced by avoiding the concentration of harmonic energy in distinct tones. One method to spread out the harmonic spectrum without the use of programmed PWM (pulse width modulation) is to make the switching pattern random. It is proposed that the switching pattern can be randomized by modulating the triangle carrier in sinusoidal PWM with bandlimited white noise. All of the advantages of sinusoidal PWM are preserved with this technique. These include, real-time control, linear operation, good transient response, and a constant average switching frequency. By controlling the bandwidth and RMS value of the bandwidth limited noise modulation, it is shown that the instantaneous variation in switching frequency and the bandwidth of the energy spectrum in the machine can be specified within predetermined limits. Experimental results show the absence of acoustic noise concentrated at specific tones, which is present in conventional sinusoidal modulation     

New high power DC-DC converter with loss limited switching and lossless secondary clamp

A new isolated high frequency high power DC-DC converter full bridge topology employing one resonant "soft" switching pole that is zero voltage switched and one phase-shifted hard switching pole with loss limited switching for primary switching is presented. The devices in the loss limited pole do not have resonant capacitors across them, but exhibit significantly lower losses than conventional hard switching as the energy dissipation is limited by the finite energy stored in the leakage inductance. This unique combination of zero voltage switching and loss limited switching reduces the switching loss in all primary devices to lower levels. Isolation is achieved by a coaxially wound high frequency transformer with ultra low leakage which increases throughput and efficiency. A novel nondissipative secondary rectifier clamp allows excellent control of reverse recovery energy. Converters that produce 128 kW at 25 kHz have been developed and are commercially available. As this topology exhibits complete control of all parasitic loss mechanisms, it can be easily scaled to higher power levels.     

Harmonic Reduction in Synchronous Chopper-Converter Combinations

The synchronous chopper-converter combination has previously been shown to be suitable for moderate to high power ac/dc converter applications. Operation at unity displacement factor, however, was seen to be accompanied by a significant increase in the harmonic compensation requirements. Techniques for reducing the input harmonic current levels in the synchronous chopper-converter combination are investigated. Operating the synchronous chopper at higher frequencies allows selective harmonic elimination but results in restricted output voltage control. The use of a multiphase synchronous chopper yields greatly improved input characteristics but requires additional power components. A compromise solution involves a single-phase chopper operated at different frequencies over its operating range.