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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 subject of this paper falls under the development of power electronics for more electric aircraft systems. The study concerns the design of a converter whose function is to generate a 300-V dc bus from a standard 28-V dc avionic network. Various systems, such as motor drives, need to be connected to the 28-V dc network. Their design could be simplified significantly, and standardized, by introducing this intermediate 28–300-V stage. The step-up converter in the proposed configuration is integrated as a part of the system. The power specification is 10 kW, which leads to very high-current values on the 28-V side. The choice of the converter topology, therefore, needs to match this central constraint. The proposed converter uses six boost cells, associated to constitute a series–parallel architecture. This arrangement leads to significantly more optimal sizing for high step-up ratios than conventional boost-cell configurations. Cell interconnection is implemented by means of a monolithic InterCell transformer to reduce the weight of the magnetic part. This paper describes the topology, design, and construction of the lab prototype, as well as experimental results obtained during testing. [ABSTRACT FROM PUBLISHER]

This paper presents fast test protocols for ageing IGBT modules in power cycling conditions, and a monitoring device that tracks the on-state voltage V CE and junction temperature T J of IGBTs during ageing test operations. This device is implemented in an ageing test bench described in previous papers, but which has since been modified to perform fast power cycling tests. The fast test protocols described here use the thermal variations imposed on IGBT modules by a test bench operating under Pulse Width Modulation conditions. This test bench reaches the maximal values of power cycling frequencies attainable with a given module packaging in order to optimize test duration. The measurement device monitors V CE throughout the ageing test that is needed to detect possible degradations of wire bonds and/or emitter metallization. This requires identifying small V CE variations (a few dozen mV). In addition, the thermal swing amplitude of power cycling must be adjusted to achieve a given ageing protocol. This requires measuring junction temperature evolution on a power cycle, which is carried out by means of V CE measurement at a low current level (100 mA). Experimental results demonstrate the flexibility of this test bench with respect to various power cycling conditions, as well as the feasibility of the proposed on-line monitoring methods. [ABSTRACT FROM AUTHOR]

Recent uninterruptible power supply (UPS) systems, in the medium power range (a few 100 kW), are based on a three-power stage topology including a rectifier, an inverter, and a dc-dc converter. The dc-dc converter ensures the charger/discharger function necessary for battery management. The monolithic intercell transformer (ICT) described in this paper is dedicated to such a charger/discharger, of which the nominal power is 137 kW. This dc-dc converter is comprised of eight interleaved cells that are interconnected by the ICT. The first part of this paper briefly presents the full UPS system and the topology of the eight-cell charger/discharger arranged around the eight-phase monolithic ICT. The second part suggests a model and emphasizes the design specificities of the monolithic ICT. The final design is provided by an optimization routine, checked in the end by different 2-D and 3-D finite-element simulations, both electromagnetic and thermal. The third part describes the construction of the ICT prototype. It is then placed in a test bench that reproduces the conditions of future operations and provides current balance conditions. Finally, the experimental results obtained for the 137-kW nominal power validate design parameters and confirm the interest of the ICT solution. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the ageing of insulated-gate bipolar transistor (IGBT) power modules. The aim is to identify the effects of power cycling on these devices with high baseplate temperatures (60 ^\circ\C to 90 ^ \circ\C) and wide temperature swings (60 ^\circ \C to 100 ^\circ\C). These values for thermal stresses have been defined according to automotive applications. The test conditions are provided by two types of test benches that will be described in this paper. The changes in electrical and thermal indicators are observed regularly by a monitoring system. At the end of the test (reaching damage criterion or failure), different analyses are performed (acoustic scanning and SEM imaging), and the damage is listed systematically. Nineteen samples of 600-V 200-A IGBT modules were thus aged using five different power-cycling protocols. The final summary of results shows that ageing mechanisms mainly concern wire bonds and emitter metallization, with gradual impact depending on protocol severity. [ABSTRACT FROM AUTHOR]

Presents a study which examined the application of soft-switching in imbricated-cell multi-level converters. General properties of a hard-switched multicell converter; Analysis of the auxiliary resonant commutated pole multicell converter.

Suggests a way of building a multi-load/single converter system based on the use of a series-resonant ZVS inverter, supplying several resonant loads. Converter topologies for low power induction heating; Description of the proposed system; Simulations and experimental test results.

A correction to the article "Analytic Design Method Based on Homothetic Shape of Magnetic Cores for High-Frequency Transformers," which appeared in the previous issue is presented.