Emmanuel Sarraute

A Theoretical Approach to InterCell Transformers, Application to Interleaved Converters

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.

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

Analytical static modelling and optimization of electrostatic micropumps

Having developed a mechanical law with a simple elementary model of membrane deflection, we demonstrate the static instability of such a system under electrostatic actuation and provide an analytical solution for the membrane position. This allows us to highlight the sticking effect and the hysteresis phenomenon of the pump strike volume due to the nonlinearity of such excitation. We determine a parameter optimization procedure for the dimensions of the electrostatic actuated membrane in order to achieve maximum volume displacement.

Piezoelectric transformer for integrated MOSFET and IGBT gate driver

In this paper, a new complementary gate driver for power metal-oxide semiconductor field-effect transistors and insulated gate bipolar transistors is presented based on the use of a piezoelectric transformer (PT). This type of transformer has a high integration capability. Its design is based on a multilayer structure working in the second thickness resonance mode. A new design method has been used based on an analytical Mason model in order to optimize the efficiency, the available power at the transformer secondary ends, and the total volume. This design method takes into account mechanical losses and heating of the piezoelectric material; it can be extended to predict the characteristics of the PT: gain, transmitted power, efficiency, and heating of piezoelectric materials according to load resistance. A prototype of a PT rated for an inverter-leg gate driver was fabricated and tested experimentally. All calculated characteristics have been confirmed by measurements. Satisfactory results have been obtained in driving a 10-A/300-V/10-kHz chopper. Moreover, a study has been carried out about the propagation of common mode currents between the top-switch and the bottom-switch of the inverter leg throughout the driver in order to avoid cross-talking failures.

Piezoelectric micro-transformer based on PZT unimorph membrane

In this paper, a piezoelectric micro-transformer processed in a SOI (silicon-on-insulator) wafer is presented. The micro-transformer consists of a unimorph circular membrane (PZT/silicon). The manufacturing uses an original method consisting of a deposition by sputtering and a etching by lift-off of thin material layers. This transformer is intended to supply micro-systems requiring a very low amount of energy. An analytical model has enabled us to determine the electrical equivalent circuit of the transformer, to express the resonance frequencies and to plot the deflection and strain shapes of the membrane. A mechanical characterization has been carried out by interferometry and an electric characterization has been conducted using a first prototype.

Optimization of the geometry of electrostatic micromotors using only analytical equations

Since electrostatic motors require very high voltages and do not exert great efforts on the usual dimensional scale, their design and optimization are not well known, but on the millimetre and micrometre scales, this kind of motor seems to present interesting qualities. The optimization of electrostatic micromotors is generally based on the use of numerical finite-element methods. Because of the numerous possible geometrical combinations, this type of optimization takes a lot of time and must be reperformed for each application. In this paper, we present the optimization of variable capacitance motors based solely on an analytical model of the stator - rotor capacity. For each application, this model allows determination of the optimal geometrical dimensions of the electrostatic micromotor depending on the fabrication process used.

Multiphase coupled converter models dedicated to transient response and output voltage regulation studies

In order to study transient response and output voltage regulation in multiphase coupled buck converter, it is proposed two models of interleaved coupled buck converter. These two models provide accurate current and voltage waveforms for any value of duty cycle. In the first part, the two proposed models are described in details. In the second part, it is shown the interest of this approach to study dynamic behaviour and determine compensation filters for voltage regulation in a multiphase coupled buck converter.

Modular control of parallel isolated micro-converters dedicated to conversion network

In this paper, an original control method used to regulate a micro-converter is presented. A network of micro-converters is dedicated to photovoltaic or bio-battery power conversion applications. This network combines several micro-converters in parallel to provide a high output current. Each micro-converter (5V, 2A) use a multi-leg transformer with several coupled inductors. A modular approach for the control of each internal switching cell is chosen. It consists in an original masterless control method used to generate a perfect shift of the interleaved carrier phases using a self-alignment process, and to provide the balancing of the internal inductor currents. At last, the control of a micro-converter is implemented in an integrated circuit with a targeted 1MHz switching frequency.

A new method to design piezoelectric transformer used in MOSFET and IGBT gate drive circuits

This paper is situated in the continuity of our works focused on the use of piezoelectric transformer (PT) in MOSFET/IGBT gate drives. In this paper, a new design method for a gate drive PT is presented. We have previously demonstrated that this kind of transformer can be successfully used in insulated MOSFETs/IGBTs gate drive circuits. An optimized multi-layered PT working in the second thickness mode has been studied for transmitting signal and energy in a gate drive circuit. Based on an analytical Mason model, the design method gives the minimal size of the multi-layer PT. Thickness of the PT is given by its mechanical resonance frequency and by maximum electrical field in the material. This method takes into account mechanical losses and heating of the piezoelectric material. Area of the PT is calculated considering the required secondary power P/sub 2/ and heating of the material. This analytical design method can be extended to predict the characteristics of the PT: gain, transmitted power, efficiency and heating of piezoelectric materials according to load resistance. A prototype of a PT based on this design process was fabricated and tested experimentally. Piezoelectric material used for primary and secondary layers is lead titanate, PbTiO/sub 3/, polarized along the thickness. Insulation between the primary and the secondary is achieved by a 300 /spl mu/m thickness layer of alumina, Al/sub 2/O/sub 3/. All calculated characteristics have been confirmed by measurements.

Simulation of self-control of an electrostatic micromotor for an intravascular echographic system

Abstract In this paper, the possibility of using an electrostatic micromotor for an intravascular echographic system is studied. For this given application, the advantage of a micromotor is the absence of a long cable between motor and mirror. This advantage is real only if the micromotor speed can be controlled. In fact, electrostatic micromotors are often used with a step-by-step power supply but, for low mean angular speed (2000 rpm), the rotation is not regular with this type of command. So, we propose herein a self-control command based on the rotor-position control carried out by a capacitance measurement.