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This paper presents an original design option dedicated to output-filtered pulsewidth modulation inverters used in uninterruptible power systems, embedded networks, or motor drives operating on long cables. It is based on the coupling of interleaved inverter ceils by means of intercell transformers (ICTs) and is characterized by very good dynamic behavior on load transients, which is an important issue in such applications. ICT solutions are compared with the classical interleaved solutions using separate inductors. A specific design method is developed to achieve this comparison based on toroidal core shapes. The results obtained with a 600 V, 7.5 kW inverter show the usefulness of ICT-based designs, especially when nanocrystalline magnetic material is used; high specific power and very good dynamic performances are obtained. Index Terms--Embedded converters, intercell transformer (ICT), interleaved inverters, uninterruptible power system (UPS).

This paper presents the developments and the results of an analytic method elaborated to design isolated intercell transformers. These particular magnetic components are intended for multicell interleaved flyback converters recently proposed and well-suited to low-voltage, high-power applications. A specific 2-D model to evaluate the winding losses is included in the design process. The results, obtained for standard core shapes, allow defining the ranges of the main parameters, number of cells, and switching frequency, required for future realizations. Index Terms--Flyback converter, intercell transformer (ICT), interleaved converters, interphase transformers.

The theoretical advantage of InterCell Transformers over separate inductors is demonstrated in an interleaved power converter. Different practical ways to build InterCell Transformers are described. A theoretical approach dedicated to interleaved converters and InterCell Transformers analysis is presented. This analysis tool is used to understand and overcome the main drawback of InterCell Transformers. It is shown how the phase shifts between two adjacent phases must be modified to reduce the maximum flux density that influences core sizing and core losses. Index Terms--Coupled inductors, InterCell transformers, interleaved converters, interphase transformers.

An analytic formulation dedicated to the design of high-frequency power transformers is presented. This approach is based on the area product, and homothetic core shapes are considered. The temperature increase of the transformer is one of the main input data. Winding losses including the effect of eddy currents are calculated as well as core losses. An original model of magnetic losses valid over a wide frequency range of the common ferrite materials is introduced. The analytic formulation is validated by design examples concerning transformers that have been realized and tested. It is finally applied to study the evolution of power density versus operating frequency or power for different winding configurations or magnetic materials. Index Terms--AC resistance, winding losses.

An original converter composed of interleaved flyback is presented. The ceils are interconnected through intercell transformers replacing the standard multi-winding inductors used as insulation and storage magnetic device in the flyback. The combination of the interleaving effects and of the intercell transformer characteristics allows eliminating the mains limitations of the standard flyback due to the low performances of multiwindings inductors. In a first part, the different ways to interleave galvanic insulated converters as forward or flyback are briefly recalled. The second part presents the intercell transformers and shows that they can be used to interconnect interleaved converters cells. In the third and last part, this particular magnetic interconnection is applied to interleaved flyback cells and leads to create an 'intercell transformer flyback'. Its specific properties and advantages are described. Experimental results, obtained on a 2-kW test bench are finally presented. Index Terms--Coupled inductors, flyback, intercell transformer, interleaved converters, interphase transformers.

Interleaved power converters are now used in many different conversion systems involving various topologies (series or parallel) and related to different fields or loads. This paper deals with interleaved parallel commutation cells using coupling transformers with a possibly high number of cells. The first part of the paper is a reminder of the basics of magnetic couplers addressing monolithic as well as distributed implementations. The limits associated with the conventional supply of such couplers (supply voltages forming a direct polyphase system) are described. In the second part of the paper, an optimized voltage supply improving the performances of the system is introduced. Experimental results obtained on a seven-cells test bench validate the approach. Index Terms--Power converters, uninterruptible power supply (UPS) voltage regulator module (VRM).

The induction heating principle has been successfully introduced for about 20 years in domestic cooking appliances. The technical developments now concern the improvement of the current appliances and the introduction of new functions. So, one tendency is the design of multiwinding induction coils that are very adaptive concerning the shape and the power capability. This paper describes different original converter topologies designed to supply multiwinding coils, and, in addition, multicoil systems. The proposed topologies are based on particular use and associations of zero-voltage switching series-resonant converters. They are all characterized by a frequency-synchronized operating mode, in order to prevent any acoustic harm that could result from beating frequency-interferences. Index Terms--Frequency-synchronized power converter, induction heating, mnitiwinding induction coil, zero-voltage switching (ZVS) resonant power converter.

The test and the characterization of medium or high-power electronic converters, under nominal operating conditions, are made difficult by the requirement of high-power electrical source and load. In addition, the energy lost during the test may be very significant. The opposition method, which consists of an association of two identical converters supplied by the same source, one operating as a generator, the other as a receptor, can be a better way to do these test. Another advantage is the possibility to realize accurate measurements of the different losses in the converters under test. In the first part of this paper, the characteristics of the method concerning loss measurements are compared to those of the electrical or calorimetric methods, then it is shown how it can be applied to different types of power electronic converters, choppers, switched mode power supplies, and pulsewidth modulation inverters. In the second part, different examples of studies conducted by the authors, and using this method, are presented. They have varying goals, from the test of soft-switching inverters to the characterization of integrated gate-commutated thyristor (IGCT) devices mounted into 2-MW choppers. Index Terms--Integrated gate-commutated thyristor (IGCT) characterizations, inverter losses measurement, opposition method, reliability test in power electronics.

Power-factor-corrector (PFC) converters are now commonly used in low-power supply systems connected to ac networks. In addition to their basic PFC properties, they constitute the best technical solution to directly obtain the compatibility with a large range of ac voltages provided by different distribution networks around the world (typically, from 85 to 265 V rms). It is the main application of these converters. This function is achieved with an additional cost and volume, and this extra price to pay needs to be minimized. In this context, we first recall the main approaches of the design of conventional PFCs based on the boost converter topology. We emphasize the different critical points of the sizing that mainly concern the input choke and the silicon devices, in regard with the choice of the switching frequency. Few ways of improvement are then presented for these conventional PFCs. In a second part, always in the context of a large input voltage range, we consider the possibility to introduce the multi-level concept to reduce the input choke and filters. A solution using a multilevel Flying Capacitor Two-Cell converter is presented. It is shown that it can lead to a significant increase of the performances, with several options of sizing which can be suited to different requirements of the applications. Index Terms--Flying capacitor multicell converter, flying capacitors, multilevel converter, power-factor corrector (PFC).

The auxiliary resonant commutated pole (ARCP) multiceLl converter is a soft-switched variant of the multicell converter. It is shown in this paper that the ARCP technique can be very efficiently used in multicell flying capacitor converters. The main properties of the resulting soft switching multicell converter are very similar to those of the hard-switched version. They are presented and validated by simulations as well as experimental results. In practice, due to the damping, the ARCP multicell converter can suffer from switching faults as in two-level ARCP inverters, but in the case of a multicell converter failures can occur in different cells. So, the main control strategies are evaluated and the switching process is discussed step by step, taking account of the main imperfections of actual control circuits. When they can occur, the switching faults are described and analyzed. Finally, an original quasisoft switching control that should give a high safety of operation is proposed. Experimental results obtained with a 900 V-100 A ARCP multicell inverter leg are given and the performances are compared with those of a hard-switched multicell inverter leg of the same rating. Index Terms--ARCP, dual-thyristor, multicell flying capacitor inverter, safe control, soft-switching, switching faults.

The imbricated-cell multilevel converter is well suited to high power applications. It allows the series connection of n switches with natural voltage sharing between these switches enabled through the connection of n - 1 flying capacitors. This paper deals with the application of soft-switching on this topology; to date, only the hard-switching mode has been studied. The use of soft switching enables an increase of the switching frequency (resulting in the size reduction of the flying capacitors) without a decrease of the converter efficiency. Of the soft switching methods considered, the Auxiliary Resonant Commutated Pole (ARCP) technique was chosen due to the relative ease in which it can be incorporated into the converter topology. Furthermore, this technique offers numerous advantages: loss reduction, no added stress to the switches and compatibility with PWM control. The main properties of the ARCP multicell converter are the same as the hard-switched topology: an increase of the apparent output switching frequency and natural self-balancing of the flying-capacitor voltages. This paper presents the results of both simulations performed and measurements taken from an experimental set-up in order to study the viable system functioning. The introduction of soft-switching strongly complicates the theoretical study of the balancing mechanisms, however. As a result, the authors depend on simulations to validate the natural balancing effect during soft switching. Lastly, a general method of loss measurement is presented. Results show that the converter losses are reduced by at least 30%. Index Terms--ARCP, multicell converter, opposition method, soft switching, ZVS.

Multicell converters were introduced ten years ago and, over this period, their properties have been thoroughly analyzed. Since then, this concept has lead to some other innovative topologies which are briefly presented in this paper. Different ways to introduce soft switching in multicell converters are investigated. The concept of distributing power over several switches, giving more degrees of freedom and using less passive components, is extended further with the stacked multiceli topology. Finally, direct ac-ac converters using the multicell approach are described. Index Terms--AC-AC power conversion, insulated gate bipolar transistors, multilevel systems, power electronics, power systems harmonics, resonant power conversion, variable-speed drives.

Component counts and oversimplified reliability rules may lead to the conclusion that multilevel converters are less safe than two-level converters, just because they use more components. A better approach might be to consider that they use a different arrangement of components and also that the consequence of faults may be very different. This paper is focused on the study of the consequences of faults in hard-switching and soft-switching multicell converters. Solutions to minimize the consequences of major faults are described. Index Terms--Fault currents, fault detection, fault location, fault tolerance, insulated gate bipolar transistors, multilevel systems, power electronics, power systems harmonics.

Current measurements in power electronics or in EMI domains require high-performance probes. These probes must have a very wide bandwidth, be insensitive to electromagnetic interferences, and be able to measure large direct and alternating currents (ac-dc) without distortion. This paper will be limited to ac current probes. Various principles will be reviewed, in particular that based on the current transformer (CT); its limitations will be analyzed, and a solution based on a two-stage transformer will be proposed to extend low- and high-frequency performance. It will be shown that the use of new magnetic materials, such as the amorphous or the nanocrystalline, can improve large-current low-frequency operations, while preserving the smallest possible probe size. Various solutions will be provided to improve high-frequency operations. Different developments will be depicted; frequency and time-domain results will be presented. Index Terms - Amorphous magnetic materials, current measurements, current transformers, ferrite materials, HF transformers, magnetic tranducers, nanocristalline materials.

The induction heating appliances used for cooking generally include two or four inductors and in the most common solution, a converter is connected to each inductor. The main aim of this paper is to suggest a way of building a multi-load/single converter system, based on the use of a series-resonant ZVS inverter, supplying several resonant loads. The principle can be probably extended to different applications (dc-to-dc converters, high power induction heating applications) but our study has been restricted to a low power induction heating context. In order to make this study, suitable models for the loaded inductors had to be found. Therefore, in the first part of this document, a number of different electrical inductor models, from the basic L-R equivalent circuit to a representation taking into account eddy currents effects, are presented. The second part describes the multi-load operating principle with respecting ZVS conditions, by the analysis of an R-L inductor model. Finally, the third part completes this work with simulations, including a more realistic model of the inductors and the associated experimental validation. These emphasize the interest of this original system that is currently being evaluated for an industrial application. Index Terms--Induction heating, inductor modeling, multiload system, ZVS series-resonant inverter.