Ambroise Schellmanns

Multiwinding transformers: a successive refinement method to characterize a general equivalent circuit

A lumped component equivalent circuit has been developed by our team to model the linear electrical behaviour of any two winding transformer. Its topology is independent of sizes and technology and a general method of characterization, based exclusively on external impedance measurements, has been presented. Unfortunately, when some key frequencies are out of the range of the measuring apparatus, many of its components remain unevaluated. Owing to a new understanding of magnetic and electrostatic coupling, a several step approach is presented. At each step a more accurate circuit proven to be effective in electronic simulation, is fully characterized. This method suits whatever the number of windings and experimental data will be presented for two and three winding transformers.

Equivalent circuits for transformers based on one-dimensional propagation: accounting for multilayer structure of windings and ferrite losses

In a recent paper, we linked the electromagnetic power propagation in a two-winding transformer to an electrical equivalent circuit. This study pointed out that an electrical equivalent circuit can be associated with each layer (conductor, insulator, ferrite) passed through, and that connecting all of these elementary circuits together leads to the equivalent circuit of the entire component. Propagation was assumed to be one-dimensional, and each winding was supposed to be made of a single layer of turns. In this paper, we first investigate the consequences of the multilayer structure of each winding, following the above approach. Skin and proximity effects are taken into account this way, and theoretical results are compared with experimental data. Then, we focus on the representation of the linear behavior of the ferrite core. On the basis of an experimental approach, it is shown that an accurate equivalent circuit must include a capacitor. This is consistent with the high permittivity of the material.

Representing electrical behaviour of transformers by lumped element circuits: a global physical approach

This paper proposes equivalent circuits to represent the external electrical behaviour of multiwinding transformers. All aspects of the linear behaviour, including resonances and inter-winding devices to currents, are taken into account. The global physical components approach leads to general lumped element circuits such that only element values change from one component to another. All the element values of the proposed circuits are deducible from external electrical measurements with no need for extra information regarding shape, size, used technology and, even, turn numbers. This paper includes two parts. The first one focus on the representation of linear loss free magnetic coupling. How to represent leakage of multi-winding transformers and what measurements to choose to fully and accurately characterise magnetic coupling are among the investigated subjects. In the second part, representation of stray capacitors is studied: how to represent the electrostatic behaviour of multi-winding transformers and what measurements to choose to fully and accurately characterise these components.

Modeling of a New SOI Bidirectional Bipolar Junction Transistor for Low-Loss Household Appliances

In this paper, a new monolithic bidirectional bipolar junction transistor with full turn-off control is studied due to technology computer-aided tools. The structure is built on a symmetrical transistor using silicon-on-insulator technology, which functionality relies on reduced surface field and base shielding effects. These concepts allow high drift doping concentrations and a thin and/or lowly doped base. Such a structure is suitable for bidirectional household appliances within a confined environment where power dissipation is a critical parameter.

Development and Static Mode Characterization of a New Low-Loss AC Switch Based on Super-gain BJT

This paper deals with an innovative low-loss AC switch, named as TBBS (transistor based bidirectional switch), based on the association of super-gain BJTs developed by the GREMAN laboratory. The main characterization results of the super-gain BJT are reminded to identify the key parameters that are essential to build the TBBS. A complete characterization database in static mode of this new AC switch is discussed. In particular, its forward and reverse-biased features have been measured to see the evolution of the DC current gain as a function of the current density. The TBBS makes sense when using the super-gain BJT (bipolar junction transistor) in reverse mode. It means that the reverse DC current gain has to be sufficient (at least higher than 1 compared with the conventional BJT one). This new AC switch is bidirectional in current and voltage, totally controllable (turn-on and turn-off) and the most attractive solution in terms of on-state power losses. Further, its manufacturing process is as easier as existing device such as triac.

1D-propagation based equivalent circuits for transformers: accounting for multi-layer structure of windings and ferrite losses

A previous paper established the link between the electromagnetic power propagation and electrical equivalent circuit of the two-winding transformer. This study pointed out that an electrical equivalent circuit can be associated with each layer (conductor, insulator, ferrite) gone through, and that linking all these elementary circuits together leads to the equivalent circuit of the entire component. Propagation is assumed to be 1D and each winding is supposed by a single layer of turns. The aim of this paper is to follow the same approach to investigate the consequences of first, the multi-layer structure of each winding and second, the observed behavior of Mn-Zn magnetic cores. Theoretical results are compared to experimental data.

Electrical modeling of a new super-gain BJT dedicated to an innovative 600V AC switch

This paper deals with the static electrical modeling of the super-gain BJT which is dedicated to an innovative 600V AC switch solution which it gives birth to. As power bipolar component, its electrical modeling is based on the Gummel-Poon model which is widely accepted and used by researchers as well as circuit simulators such as Pspice. All of the model parameters are extracted from device characterization data via extraction mathematical equations. The modeling of the super-gain BJT is mainly composed of two separate parts which is respectively the forward-biased modeling and the reverse-biased modeling. The characterization test bench is presented, than the extraction methods of respective parameter category are also introduced in this paper as well as the data processing method. The validation of the extracted model parameters will be done by comparing the SPICE simulation results with experimental ones under the same condition. The comparison result proves a good coherence between simulations and experimentations.

Measurement bench for near field characterisation of wound components

In switching power electronics, wound components radiate magnetic fields, which can disturb surrounding components, especially other transformers or magnetic components. The aim of this paper is to present the preliminary study of an experimental bench, dedicated to the measurement of the near magnetic field of these components. Mechanical aspects related to the positioning of the device under test, electrical supply of the component, instrumentation and probing are investigated. Measurements are performed up to 1 MHz, then problems to overcome in order to reach testing at 10 MHz are studied. The bench is validated using single turn loop field and experimental results are given for inductors.