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Soft-switching inverters can achieve high efficiencies and low switchdv/dtanddi/dt, but often impose additional stress on the switches due to their resonant behavior. Multicell converters, on the other hand, can process high voltages by arranging the switches to share the stress. This paper proposes a buck–boost multicell soft-switching inverter with inherent cell voltage balancing. Both the current and voltage stresses are shared by the cells. Soft-switching conditions are achieved for all switching transitions without any need for auxiliary circuitry or clamps. A multiple-winding transformer transfers energy between the terminals and provides galvanic isolation. An analytical study and experimental results on a 1200-W prototype verify the operation of the inverter. [ABSTRACT FROM AUTHOR]

This paper presents a novel single-stage soft-switched high-frequency-link three-phase dc–ac converter topology. The topology supports unidirectional dc to ac power flow and is targeted for applications like grid integration of photovoltaic sources, fuel cell, etc. The high frequency magnetic isolation results in reduction of system volume, weight, and cost. Sine-wave pulsewidth modulation is implemented in dc-side converter. Though high-frequency switched, dc-side converter is soft switched for most part of the line cycle. The ac-side converter active switches are line frequency switched incurring negligible switching loss. The line frequency switching of ac-side converter facilitates use of high voltage blocking inherently slow semiconductor devices to generate high voltage ac output. In addition, a cascaded multilevel structure is presented in this paper for direct medium-voltage ac grid integration. A detailed circuit analysis considering nonidealities like transformer leakage and switch capacitances, is presented in this paper. A 6-kW three-phase laboratory prototype is built. The presented simulation and experimental results verify the operation of the proposed topologies. [ABSTRACT FROM AUTHOR]

This paper presents a modified methodology for calculating static capacitance values between conductors with a circular cross section. Two forms of coil's stacking were considered, perfectly in 90° and each layer embedded in the previous one. Finite element simulations were carried out to determine the capacitance values for a 5 × 5 array arrangement, taking into account the two stacking forms. It was observed that depending on the position of the turn in the coil, it could present different capacitances values for the adjacent turns. A comparison between the proposed and existing methods for over isolated conductors was performed as well. The proposed method displayed good agreement with simulation and experimental results. The gain of the proposed method can be even more appreciated when comparing results for over insulated conductors. [ABSTRACT FROM AUTHOR]

A 10-year reanalysis of the PacIOOS Hawaiian Island Ocean Forecast System was produced using an incremental strong-constraint 4-D variational data assimilation with the Regional Ocean Modeling System (ROMS v3.6). Observations were assimilated from a range of sources: satellite-derived sea surface temperature (SST), salinity (SSS), and height anomalies (SSHAs); depth profiles of temperature and salinity from Argo floats, autonomous Seagliders, and shipboard conductivity–temperature–depth (CTD); and surface velocity measurements from high-frequency radar (HFR). The performance of the state estimate is examined against a forecast showing an improved representation of the observations, especially the realization of HFR surface currents. EOFs of the increments made during the assimilation to the initial conditions and atmospheric forcing components are computed, revealing the variables that are influential in producing the state-estimate solution and the spatial structure the increments form. [ABSTRACT FROM AUTHOR]

Incipient discharges formed in natural ester oil due to corona activity, surface discharges and particle movement were investigated using UHF technique. When the applied voltage magnitude is increased, on the inception of discharges, the peak to peak magnitude of the voltage of the UHF signal formed also increases. After certain applied voltage magnitude increase, if it is reduced, the magnitude of UHF signal formed is much higher than the magnitude of the signal formed when the voltage is increased. This phenomenon is observed with all the three types of discharges. Cross Recurrence plot (CRP) can be effectively used to determine the Time Difference Of Arrival (TDOA) of UHF signals. Self-similarity Recurrence Quantification Analysis (RQA) parameter is found to be more suitable technique to estimate the TDOA of UHF signals. CRP method is used to estimate TDOA correctly, even with low signal to noise ratio and it is found to be superior to Cross-correlation technique in estimating the TDOA. Estimated TDOA of UHF signals are validated and incipient discharge source is localized by adopting the non-iterative technique. [ABSTRACT FROM AUTHOR]

This paper deals with the design, the setup, and the operation of a rotating contactless energy transfer (CET) system. The system is used to replace the slip rings of an electrical excited synchronous machine and to transfer energy onto the rotor of the machine without mechanical contact. A compensation topology with an autoresonant circuit to generate the high frequency voltage is presented. Furthermore, the required parameters of the CET system are calculated. Based on these calculations, the system consisting of the power electronics, the compensation network, the magnetic path, the control system, and the electrical excited synchronous machine with controller, is set up. Finally, the calculated parameters are verified by measurements. [ABSTRACT FROM AUTHOR]

High frequency isolated dc–ac converters are becoming popular in on-board auxiliary inverters for railway applications. Compared to conventional fixed dc-link inverter (FDCLI), pulse dc-link inverter (PDCLI) has simpler circuit topology and higher power density, but greatly different control algorithm. This paper is going to study the application possibility of PDCLI for railway auxiliary inverter, and will be concerned with algorithm and their performance comparison between approximately independent hybrid modulation (AI-HM) and six-pulse demodulation hybrid modulation for PDCLIs, including fundamental principle and harmonic performance of output voltage under zero portion effect. Then a piecewise compensation of modulation wave and a carrier phase-shift strategy are proposed to improve the output voltage quality of AI-HM under zero portion effect. The simulation and experimental results, as well as the output filter parameter comparison are provided to verify the theoretical analysis and the feasibility of the proposed strategies. [ABSTRACT FROM PUBLISHER]

In a permanent magnet synchronous motor (PMSM) drive system, high-frequency (HF) pulsating voltage signal injection has demonstrated high accuracy to estimate the initial rotor position. However, a conventional signal demodulation method may face the problems of long convergence time and limited system stability, owing to the low-pass filter (LPF) used in signal demodulation process. Thus, a direct signal demodulation method is proposed, in which, the LPF is removed to improve system stability and dynamic property. A direct demodulation collection is generated to extract the position deviation signal from estimated q-axis HF current. Recursive discrete Fourier transform is employed to calculate the amplitude of estimated d-axis HF current, thus an amplitude normalized technique is implemented to reduce the effects of HF signal and PMSM. Meanwhile, the stability and dynamic property are compared between the conventional and proposed method, with the aid of D-partition technique and amplitude–frequency characteristics diagram. Furthermore, a novel magnetic polarity detection method is put forward based on the magnetic saturation, which has a high signal-to-noise ratio. Finally, the experimental results on three PMSM drive systems prove that the proposed method is practicable and effective. [ABSTRACT FROM PUBLISHER]

Current fed dual active bridge converters for photovoltaic generation may typically require a given leakage or extra inductance in order to provide proper control of the currents. Therefore, the many researches have been focused on the leakage inductance control of high frequency transformer to integrate an extra inductor. In this paper, an asymmetric winding arrangement to get the controlled leakage inductance for the high frequency transformer is proposed to improve the efficiency of the current fed dual active bridge converter. In order to accurate analysis, a coupled electromagnetic analysis model of transformer connected with high frequency switching circuit is used. A design optimization procedure for high efficiency is also presented using design analysis model, and it is verified by the experimental result. [ABSTRACT FROM AUTHOR]

In this paper, a class of single-phase Z-source (ZS) ac–ac converters is proposed with high-frequency transformer (HFT) isolation. The proposed HFT isolated (HFTI) ZS ac–ac converters possess all the features of their nonisolated counterparts, such as providing wide range of buck-boost output voltage with reversing or maintaining the phase angle, suppressing the in-rush and harmonic currents, and improved reliability. In addition, the proposed converters incorporate HFT for electrical isolation and safety, and therefore can save an external bulky line frequency transformer, for applications such as dynamic voltage restorers, etc. The proposed HFTI ZS converters are obtained from conventional (nonisolated) ZS ac–ac converters by adding only one extra bidirectional switch, and replacing two inductors with an HFT, thus saving one magnetic core. The switching signals for buck and boost modes are presented with safe-commutation strategy to remove the switch voltage spikes. A quasi-ZS-based HFTI ac–ac is used to discuss the operation principle and circuit analysis of the proposed class of HFTI ZS ac–ac converters. Various ZS-based HFTI proposed ac–ac converters are also presented thereafter. Moreover, a laboratory prototype of the proposed converter is constructed and experiments are conducted to produce output voltage of 110 Vrms / 60 Hz, which verify the operation of the proposed converters. [ABSTRACT FROM AUTHOR]

Analysis of lightning transients in cable systems necessitates accurate calculation of ground return impedances (GRIs) in high-frequency regions. EMT-type programs used for transient analyses incorporate various methods for calculation of GRI. Most of these methods include assumptions and approximations, the validity of which needs to be questioned at high frequencies. In particular, the common approximation of the neglecting effect of displacement currents should be reviewed. The purpose of this paper is to evaluate commonly used GRI calculation methods in terms of their accuracy and validity in high-frequency regions. In this study, GRI calculation methods are analyzed and compared, the effect of displacement currents is evaluated, and validity ranges of the basic calculation formula (Pollaczek formula) are discussed. It is shown that for high-resistivity and high-permittivity soil cases, the effect of displacement currents must be taken into account in high-frequency regions. Most default calculation routines in EMT-type programs neglect this effect. Therefore, it is very important to review and understand the calculation methods used in EMT-type programs before employing them in high-frequency transient analyses. Moreover, it is shown that in most of the practical cases the basic calculation formula (Pollaczek formula) is valid for the frequency range of interest for lightning studies. [ABSTRACT FROM AUTHOR]

This work investigates high-frequency measurements for the contribution to the understanding of different stall inception types in high-speed multistage compressors. A 3.5-stage high-speed axial multistage compressor is investigated with a 2 MW test rig in the Laboratoire de Mécanique des Fluides et d’Acoustique (LMFA) at Ecole Centrale de Lyon, France. Two different types of instabilities arise in this compressor as a function of shaft speed. At part speed, a controversy called “rotating instability” type flow field modulation is identified with the measurements. New results are the demonstration of the periodic behavior of this instability and the analogy to classical frequency modulation, periodic to one revolution of the instability. Furthermore, the amplitude of the instability is modulated by the time period of a rotor revolution. At nominal speed, the abrupt spike type stall inception is detected, taking usually less than five rotor revolutions. [ABSTRACT FROM AUTHOR]

In this paper, the design procedure of a 14.4 kV output voltage, 100 kHz transformer with an isolation voltage of 115 kV using Litz wire is presented. All design models, including a generalized magnetic model for the leakage and the loss calculations as well as an electrical model for the parasitic capacitance estimation for the transformer are derived and proven by measurements. For designing the insulation, a comprehensive design method based on an analytical maximum electrical field evaluation and an electrical field conform design is used. The resulting design is verified by long and short term partial discharge measurements on a prototype transformer. [ABSTRACT FROM AUTHOR]

Parasitic capacitances of the high-frequency (HF) transformer used in dc–dc converter impact harmonic analysis of the transformer and interactions with the converter. Resonant frequencies of open- and short-circuit impedances characteristics (ICs) have been widely used to extract parasitic capacitances of HF transformers, but it was reported that some resonant frequencies were unobtainable as they were too high where the ICs fluctuated heavily, and parasitic capacitances remained unevaluated. In this paper, resonance features of ICs and voltage transfer characteristics (TCs) are investigated, and a new frequency of voltage TC is used for extracting parasitic capacitances. By analyzing inner links of known impedance resonant frequencies, why and which resonant frequencies are likely to be unobtainable is revealed. Furthermore, a new frequency corresponding to zero of TC, accounting for parallel resonance between leakage inductance and mutual capacitance of the two windings, is used to extract parasitic capacitances. With this new frequency mutual capacitance of the windings is evaluated, and missing equation due to unobtainable impedance resonant frequency is added. Besides, merits and limitations of extracting parasitic capacitances based on ICs and TCs are analyzed. These techniques are verified with several HF transformer prototypes in the laboratory. [ABSTRACT FROM AUTHOR]

To transmit constant powers particularly at light load, the isolated dual active bridge (DAB) with conventional dual-phase-shift (DPS) control exhibits large variations of currents, losses, and efficiencies if there is a small change of outer phase shift ratio, which is caused by the change of command to adjust power transmission. This is mainly because of the narrow operation region of outer phase shift ratio if the conventional DPS modulation is used. To solve this problem, a novel DPS control with bidirectional inner phase shifts for the DAB is developed to reduce the current surge in the high-frequency transformer, which can stabilize the output power with high efficiency. From the analysis of operation modes and power characteristics of the proposed DPS control, it is shown that due to wider operation region of outer phase shift ratios compared with the conventional DPS control in which the inner phase shifts of both the primary and secondary H-bridges are in the same direction, lower surge current can be obtained in the change of phase shift command, which results in stable power transmission particularly at light load without scarifying the efficiency. Moreover, the DAB of using the proposed DPS control can transmit bidirectional energy with the inner and outer shift ratios of 0–1. For experimental verifications, the test results are also presented in this paper. [ABSTRACT FROM AUTHOR]

Spatial-saliency-tracking-based high-frequency (HF) pulsating carrier injection method is widely employed in permanent-magnet synchronous machines sensorless control. In order to avoid the problems of long convergence time, potential start-up failure and limited system stability existing in tracking observers, a strategy to inject three HF pulsating voltages with different frequencies and amplitudes into ABC frame is proposed in this paper. With the proposed method, three frequency components in the response current signals are demodulated and then combined together to calculate the rotor position directly. Different from the conventional method, the proposed solution utilizes both d- and q-axis carrier current instead of only the q-axis carrier current to enhance the acquisition of the rotor position information. Meanwhile, a new signal processing strategy is developed to completely eliminate the effects of system delay. Furthermore, the compensation of cross-saturation effect is deduced in detail to improve the accuracy of rotor position estimation. In addition, magnetic polarity detection is implemented with the same proposed solution by demodulating the second harmonic components from the response current signals, which simplifies the magnetic polarity process. Finally, the experimental results demonstrate that the proposed strategy can obtain an accurate rotor position with good steady-state and dynamic performance. [ABSTRACT FROM AUTHOR]

Recent improvements in magnetic material characteristics and switching devices have generated a possibility to replace the electrical buses with high-frequency magnetic links in microgrids. Multiwinding transformers (MWTs) as magnetic links can effectively reduce the number of conversion stages of renewable energy system by adjusting turn ratio of windings according to the source voltage level. Other advantages are galvanic isolation, bidirectional power flow capability, and simultaneous power transfer between multiple ports. Despite the benefits, design, and characterization of MWTs are relatively complex due to their structural complexity and cross-coupling effects. This paper presents all stages of numerical design, prototyping, and characterization of an MWT for microgrid application. To design the transformer for certain value of parameters, the reluctance network method is employed. Due to the iterative nature of transformer design, it presented less computation time and reasonable accuracy. A prototype of designed transformer is implemented using amorphous magnetic materials. A set of experimental tests are conducted to measure the magnetic characteristics of the core and series coupling and open-circuit tests are applied to measure the transformer parameters. A comparison between the simulation and experimental test results under different loads within the medium-frequency range validated both design and modeling procedures. [ABSTRACT FROM AUTHOR]

The high-frequency transformer is an important device in the modern electrical system, and the performance requirement for this device has recently become more and more important. Thus, it is necessary to model high-frequency transformer accurately and the key is to calculate the capacitance. In this paper, the capacitance of the foil winding in the high-frequency transformer is calculated by using the static capacitance model and the finite-element method (FEM), respectively. The relative error is about 0.4% by comparing the FEM. To calculate the capacitance of solid wire accurately, a new static capacitance model is proposed considering that the actual electric field lines gradually changed in the windings. Compared with the finite-element model, the proposed model is more accurate than the traditional models. The capacitances of two wires calculated by the proposed model and the finite-element model are 115.56 and 114.76 pF, respectively. The dynamic capacitance of transformer windings is analyzed by considering the uneven charge distribution. A dynamic capacitance analytical model is present by considering the eddy current effect. The result of the dynamic capacitance is 49.81 pF. It is found that the dynamic capacitance is lower than the static capacitance according to the static capacitance and the dynamic capacitance analytical model. [ABSTRACT FROM PUBLISHER]

With the background of power supplies for high-precision apparatuses, an isolated high-frequency dc–ac converter based on a differential output structure is proposed. It is composed of two phase-shifted full bridges (PSFBs) that share a common half-bridge as the lagging leg on the primary side. Two current-doubler synchronous rectifiers (CDRs) constitute the differential output structure on the secondary side. The ac output is synthesized by the two PSFB-CDRs generating the same dc bias and phase-reversed ac components. Compared with traditional solutions, the new circuit has the potential capability to obtain an ultralow distortion output voltage without using special control or compensations. Moreover, zero voltage switching is realized in the primary circuit within a wide load range, whereas zero current switching is achieved in the secondary circuit. Operation principles are analyzed, and a 1-kW prototype is built to validate the proposed scheme. [ABSTRACT FROM PUBLISHER]

Frequency-dependent leakage inductance is often observed. The high-frequency eddy current effects cause a reduction in leakage inductance. The proximity effect between adjacent layers is responsible for the reduction of leakage inductance. This paper gives a detailed analysis of high-frequency leakage inductance and proposes an accurate prediction methodology. High-frequency leakage inductances in several interleaved winding configurations are also discussed. Interleaved winding configurations actually give a smaller degree of reduction of leakage induction at high frequency. Finite-element analysis simulation and measurement validate the models. [ABSTRACT FROM AUTHOR]

This paper conducts modeling and controller design for a SEries-connected Output Universal Link (SEOUL) converter. The SEOUL converter was proposed to interface multiple distributed power sources to the grid with a reduced amount of reactive components. It employs a high-frequency (HF) transformer instead of a bulky line-frequency transformer like solid-state transformers (SSTs). In addition, it does not use a large dc-link capacitor at the input side and reduces the size of the input filter. This is inherently possible due to its original operating characteristic. The input phase current is not actively controlled but synthesized indirectly by HF power transfer between input and output sides of the SEOUL converter. Therefore, it is important to properly control the HF power transfer part, on which this paper focuses. An analytic model is developed, and a control strategy is proposed based on the model with a decoupling control method. The developed model and the proposed control method were verified by experiments. [ABSTRACT FROM PUBLISHER]

When operating higher up in frequency, the copper losses in transformer windings will significantly rise due to enhanced skin and proximity effect. This leads to a high need to develop new methods to accurately evaluate winding losses at higher frequencies. This paper investigates the effect of different geometrical parameters at a wide range of frequencies in order to propose a pseudoempirical formula for winding loss calculation in high-frequency transformers. A comprehensive analysis of the edge effect and ac resistance is done by performing more than 12 300 2-D finite element simulations on foil and round conductors. Unlike previous studies which mostly focused on specific case studies with limited applications, this model provides very high accuracy, especially where the most common analytical models drastically underestimate the winding losses, with a wide-range applicability which could be of interest for designers to avoid time consuming FEM simulation without compromising with the accuracy. Several transformers are built and the model is experimentally verified with a good agreement. [ABSTRACT FROM AUTHOR]

The increase of transmission frequency reveals more merits than low- or medium-frequency distribution among different kinds of power applications. High-frequency inverter serves as source side in high-frequency ac (HFAC) power distribution system (PDS). However, it is complicated to obtain a high-frequency inverter with both simple circuit topology and straightforward modulation strategy. A novel switched-capacitor-based cascaded multilevel inverter is proposed in this paper, which is constructed by a switched-capacitor frontend and H-Bridge backend. Through the conversion of series and parallel connections, the switched-capacitor frontend increases the number of voltage levels. The output harmonics and the component counter can be significantly reduced by the increasing number of voltage levels. A symmetrical triangular waveform modulation is proposed with a simple analog implementation and low modulation frequency comparing with traditional multicarrier modulation. The circuit topology, symmetrical modulation, operation cycles, Fourier analysis, parameter determination, and topology enhancement are examined. An experimental prototype with a rated output frequency of 25 kHz is implemented to compare with simulation results. The experimental results agreed very well with the simulation that confirms the feasibility of proposed multilevel inverter. [ABSTRACT FROM AUTHOR]

In this paper, a novel modular cascaded multi-level converter with multiwinding high-frequency (MWHF) transformer is proposed for medium- or high-voltage applications. In the proposed converter, a cascaded H-bridge rectifier (CHBR) is connected directly with the input ac source while the traditional step-down transformer is no longer necessary. Then, an isolated dc-dc converter composed by a group of H-bridge converters and a MWHF transformer with high power density is used to isolate the dc buses produced by the CHBR. The equivalent circuit and mathematical model of the MWHF transformer and the high frequency (HF) converter are obtained firstly in this paper. Then, the voltage stability under unbalanced loads is analyzed and the naturally balance ability is verified. To accelerate the dc bus voltage balancing process, a voltage balance control algorithm based on energy exchange between different transformer windings is proposed that is realized by accomplishing the phase shift adjustment of the terminal voltages on different windings. Simulations and experiments are implemented to verify the performance of the proposed converter and voltage balance algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage bidirectional high-frequency transformer (HFT) link dc/ac converter topology for a three-phase adjustable magnitude and frequency PWM ac drive. This type of converters find a wide range of applications including UPS systems, drives involving renewable energy sources (Solar, Fuel cell), and energy storage systems (typically low voltage dc to high voltage PWM ac). The HFT results in reduction in cost and weight along with a considerable increase in power density. The adverse effects of common-mode voltage are well known in this kind of applications. The proposed topology along with a modulation technique reduces common-mode voltage to practically zero and generates high-quality output voltage waveform comparable to conventional space vector PWM (CSVPWM). A source-based commutation method, presented in this paper, to commute the energy stored in the leakage inductance of the HFT resulting in the following advantages 1) no need for any auxiliary circuits with passive components; 2) almost complete recovery of the leakage energy; 3) soft switching of the output side converter for all load conditions; and 4) minimization of common-mode voltage switching due to commutation. The converter along with the suggested control has been analyzed in detail. The presented simulation and experimental results confirm the operation of the proposed converter. [ABSTRACT FROM AUTHOR]

This letter presents a new zero-voltage-switching (ZVS) isolated dc–dc converter which combines a boost half-bridge (BHB) cell and a full-bridge (FB) cell, so that two different type of power sources, i.e., both current fed and voltage fed, can be coupled effectively by the proposed converter for various applications, such as fuel cell and supercapacitor hybrid energy system. By fully using two high- frequency transformers and a shared leg of switches, number of the power devices and associated gate driver circuits can be reduced. With phase-shift control, the converter can achieve ZVS turn-on of active switches and zero-current switching (ZCS) turn-off of diodes. In this letter, derivation, analysis, and design of the proposed converter are presented. Finally, a 25–50 V input, 300–400 V output prototype with a 600 W nominal power rating is built up and tested to demonstrate the effectiveness of the proposed converter topology. [ABSTRACT FROM AUTHOR]

This paper presents a parallel-circuit Class-E amplifier that maintains it operating characteristics even when the output capacitance of the transistor is greater than the optimum shunt capacitance. The finite dc feed inductor in the parallel circuit topology is replaced by a transmission-line compensation circuit to eliminate the limitations on the operating frequency imposed by the output capacitance. Theoretical formulas for the circuit elements of the proposed network are derived in detail, and the analysis is validated by simulation and measurement. The measured maximum output power of 40.1 dBm, drain efficiency of 77.5%, and power-added efficiency of 70.8% were obtained at 2.8 GHz with a 29.4-dBm input power. These measurements show a similar or better level of efficiency and output power that is reported for other amplifiers at lower frequencies using the same transistor. [ABSTRACT FROM AUTHOR]

A new mode matching method is presented for the electromagnetic scattering from large cavity-backed apertures. The new method is based on the expansion of the field inside the cavity by the standard modes, and a periodic extension of the field on the cavity aperture to the whole ground plane. The computation cost is low by solving only the coefficients of the modes. Numerical examples are presented to show the efficiency of the approach. [ABSTRACT FROM AUTHOR]

Integration of passive magnetic devices is essential in the design of highly efficient power converters. This is due to the necessity to conserve as much space as possible for modern devices such as thin LED TVs and small bright LED illumination. This paper focuses on this multiphysics issue and presents a novel integrated magnetic system (IMS), investigated by the finite element method (FEM). Two different FEM approaches are applied to prove the accuracy of the analyzed data. Both magnetic systems have been developed with a novel capacitor layer design. This provides the system with the required resonance tank integrated in the conductor arrangement, without any interference to the transformer section or vice versa. [ABSTRACT FROM PUBLISHER]

This paper presents the design of new high-frequency transformer isolated bidirectional dc-dc converter modules connected in input-series-output-parallel (ISOP) for 20-kVA-solid-state transformer. The ISOP modular structure enables the use of low-voltage MOSFETs, featuring low on-state resistance and resulted conduction losses, to address medium-voltage input. A phase-shift dual-half-bridge (DHB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero voltage switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Furthermore, an adaptive inductor is proposed as the main energy transfer element of a phase-shift DHB converter so that the circulating energy can be optimized to maintain ZVS at light load and minimize the conduction losses at heavy load as well. As a result, high efficiency over wide load range and high power density can be achieved. In addition, current stress of switching devices can be reduced. A planar transformer adopting printed-circuit-board windings arranged in an interleaved structure is designed to obtain low core and winding loss, solid isolation, and identical parameters in multiple modules. Moreover, the modular structure along with a distributed control provides plug-and-play capability and possible high-level fault tolerance. The experimental results on 1 kW DHB converter modules switching at 50 kHz are presented to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents a novel measuring system for partial discharge (PD) measurements in Gas Insulated Systems (GIS) using high frequency current transformers (HFCT). The system is based on the measurement of the induced PD currents in the GIS enclosure. In opposition to the existing antenna technologies that measure the radiated energy in the very high frequency/ultra-high frequency (VHF/UHF) range, the proposed system measures the PD conducted currents in the high frequency (HF) range and below. The foundation of the measurements together with a detailed explanation of the sensor installed conveniently at the bolts of the GIS spacer are presented. An experimental study on the current distribution in the GIS enclosure is described to evaluate the impact of the sensor on the measurements. Laboratory experiments have been performed that show the suitability of this method to properly measure particle discharges caused by corona, surface and free moving particle discharges in SF6. Discharges in the range of 1 to 4 pC have been properly measured. An analysis to evaluate the performance of the method is shown, in comparison to VHF/UHF antenna measurements. The potential benefits of this novel technique rely on the small attenuation of PD signals in the GIS components in the HF range and sample rate reductions. Finally, a discussion on the potential applicability of present cluster and charge calculation techniques to the proposed PD GIS measurement using HFCT is presented. [ABSTRACT FROM AUTHOR]

An integrated balancing transformer is proposed for a high frequency parallel AC-LED drive circuit using a LLC resonant converter. The design and implementation of the integrated balancing transformer are presented. The experimental results for the converter with the integrated transformer are provided to show the validity of the proposed technique. [ABSTRACT FROM AUTHOR]