Thierry Martire

Optimization of the Supply Voltage System in Interleaved Converters Using Intercell 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

Passive wind energy conversion system association of a direct-driven synchronous motor with vernier effect and a diode rectifier

The increase of the performances of wind turbine systems passes through the removal of the speed-increasing gear which is generally located between the blades and the alternator and thus the direct drive of this last. In this article we will show that the association of a direct-driven synchronous motor with Vernier effect and a diode rectifier is possible and makes it possible to achieve interesting objectives of costs and performances. We will present the studied electric system, the characteristics of the vertical axis wind turbine which drive the motor, then we will comment the results obtained in the study through simulations of the association of the motor with a diode rectifier. These results are perfectly in agreement with the measurements taken on the system studied at the laboratory.

Estimation of rotor eddy-current losses for high speed SPMSM

Surface-mounted permanent magnet synchronous machine (SPMSM) is widely used in various fields due to its high power density and reliability (compressors, turbine generators...) [1], in our case it is used in aeronautics. However, in high-speed operations eddy-current losses can be important and lead to a damage because of an overheating (PM detachment, demagnetization...). Therefore, it is important to estimate these losses during the design phase. This paper describes a technique to estimate rotor eddy-current losses (magnets and sleeve) for the design of 25 kW, 10.5 krpm 3-phase motor by means of both analytical and finite-element approach. Firstly, we study the spatial variation of the magnetic flux density in the magnets and the sleeve. Consequently, it results a segmentation of magnet and sleeve according to the half of slot pitch. Secondly, we estimate the maximum variation of magnetic flux density (36 mT in the summit of magnets, 125 mT in the sleeve) by finite-element analysis (COMSOL Multiphysics). Finally, this paper presents the result of computation of rotor eddy-current losses (97 Watt).

Near-field electromagnetic tomography applied to current density reconstruction in metallized capacitors

A nonintrusive method of current cartography inside a component is presented. The measurement of the current density in metallized film capacitors has numerous applications, including nondestructive testing, new component design, and validation of existing models on current distribution in capacitors. The method is based upon the measurement of the magnetic field created by a capacitor and the current density reconstruction by means of inverse problem methodology. The experimental setup comprises of a radio-frequency generator operating between 10 to 1000 MHz, a near-field probe, an XY positioning table and a computer used for control and data acquisition. The first results confirm that, near some frequencies, the current density in the capacitor becomes nonhomogeneous and increases dramatically in some areas.

On-line [T J , V ce ] monitoring of IGBTs stressed by fast power cycling tests

This paper describes a part of a larger supervision system able to monitor the on-state voltage VCE and the junction temperature TJ of IGBT in operation. That system is associated to an ageing test bench stressing IGBT modules by power cycling. All along the ageing test, it is necessary to supervise VCE, always measured in the same conditions of junction temperature and collector current, in order to detect possible degradations of wire bonds and/or emitter metallization. In addition, the thermal swing amplitude of the power cycling must be adjusted to realize a given ageing protocol. That requires measuring the junction temperature evolution on a power cycle to choose the initial electrical conditions providing the wished temperature swing and then, to regularly verify the stability of this thermal stress during the ageing test. The temperature measurement needed for both monitoring is carried out by means of VCE measurement at low current level (100mA), that intrinsic on-stage voltage being a well-known thermo sensitive parameter. The first section describes briefly the ageing test bench, that places the power IGBT modules in operating conditions close to those of real world (PWM operations), and presents the thermal stress protocol applied to the devices, the aim being to define the context in which the measurements have to be made. The second section presents, on the one hand, the principle of an automated measurement of VCE(100A-125°C), made in steady-state, to detect a possible degradation of the top part of IGBT dies, on the other hand, the dynamic measurement of the junction temperature in operation, i.e. in power cycling conditions generated by the PWM modulation. In both cases, experimental results are shown that demonstrate the feasibility and the good accuracy of these monitoring methods.

Portable installation for space charge measurements on full-size high voltage cable loops based on a multicell power converter

The development and the qualification of polymer-insulated high voltage dc cables require the measurement of the space charge in order to ensure that charge accumulation does not result in high internal fields leading to breakdown. The aim of this work is to set up a portable installation to be used for space charge measurements on long cable loops (up to 100 m) and high conductor sections (up to 2500 mm2). Its principle is based on a transient heating of the cable core or of the outer conducting screen by Joule effect for generating a thermal pulse of several degrees, which, by crossing the insulation, generate a capacitive current measured by a current amplifier (inner heating thermal method). This requires the ability to obtain and to control a high current (up to 12 kA) during a given period of time. The use of ac current heating requiring significant apparent power, it can hardly be used for such a goal. We propose a set-up based on a coupled inductor parallel multicell power buck converter, with a topology especially designed for generating and controlling high currents during short periods of time. The design and the manufacturing of the converter are described. The validation of a base cell delivering 600 A through tests on power cable is presented.

A high current multi-cell buck converter using intercell transformers: Modeling and design of a 1200 amps, 12-phase prototype

This paper deals with the design of high power density DC/DC buck converter for portable bench space charge measurements in full-size HVDC cables. The design of a coupled interleaved buck converter used for delivering the necessary regulated high transient current (up to 1200A during one or two seconds) is presented. The structure is original regarding its compacity and the use of an innovative, small and compact structure of magnetic coupling called InterCell transformer (ICT) which guarantees an excellent filtering of the output current. Experimental results are included in order to confirm the effectiveness and the advantages of the proposed structure. Thermal step current measurements are included in order to validate the application principle on aged power cable loops.

A Versatile Inverter for Educational Purposes

This paper presents an experimental chopper-inverter system which we use for most of our lab work in power electronics. The system is based on an IGBT three-phase voltage inverter and a FPGA control board. According to the configuration chosen by the user, this set can constitute a converter in a predefined list ranging from the simple non reversible buck converter up to the three-phase PWM power inverter with constant V/f modulation. A detailed description of the experimental system is given. In addition some practical examples of use in power engineering labs are illustrated experimentally