W.A. Cronje

High-permittivity ceramic dielectrics for tuning transmission in power electronic converters

The fabrication and application of high-permittivity ceramic materials for use in power electronic circuits are investigated. The ability to manufacture materials with a wide range of epsilon /sub r/ values and the influence of dielectric permittivity on the circuit behaviour of a converter employing planar connections are studied. It is shown conclusively that the circuit behavior of a power electronic circuit can be modified by only varying the properties of the materials used for supporting the connections. This mechanism can be used to improve the power transmission characteristics of the connections. Methods are described whereby the dielectric properties of BaTiO/sub 3/-based materials can be varied over a very wide range of 4<or= epsilon /sub r/<or=1300. The material is manufactured in the form of tiles that can be used to support connections, acting both as insulation and as a medium to help control circuit performance.<<ETX>>

Loss modeling and thermal measurement in planar inductors-a case study

This paper covers the experimental investigation and theoretical calculation of losses in a planar inductor under load. Finite-element software is used to perform the loss calculations. Thermally controlled experiments are performed for a range of frequencies to validate the corresponding finite-element method loss calculations. The thermal dependence of the loss mechanisms is also considered.

A systematic approach to modelling of layout parasitics in converters-initial formulation

This paper investigates methods for modelling the effects of layout parasitics in converters. Modelling of parasitics is growing in importance with the advent of modern power switching devices, since EMI and unexpected device degradation might result when the layout parasitics are neglected. A systematic approach is taken to find a suitable engineering solution for the modelling of layout parasitics in converters employing state-of-the art planar construction methods and good correspondence with experimental results is obtained.

Adjusting circuit parasitics to optimize converter switching transient behaviour

It is shown that the influence of parasitic energy storage in a physical converter circuit on converter operation can be modeled with equivalent lumped element circuits that allow SPICE simulations of complete converter circuits by inclusion of the equivalent circuits. The proposed techniques are demonstrated by an example, and the simulated results are verified experimentally. It is shown that the use of high-permittivity ceramic dielectric materials can significantly change the electromagnetic behavior of connecting structures. The concepts can be applied to practical structures and used to improve the converter behavior-for instance, by using the parasitic capacitance for snubbing. This obviates the need for discrete snubber components, leading to circuits with reduced component count, volume, and mass. The main advantage of the method is the significantly reduced switch stresses due to reduced overshoot and oscillation amplitudes. As a result, the switching device ratings can be reduced while maintaining circuit reliability.<<ETX>>

Combined numeric and analytic methods for foil winding design

A new approach to eddy current analysis in foil windings, using a combination of numerical and closed form analytical solutions, is proposed. The method requires less computing power, is faster than finite element methods and is more accurate than traditional one-dimensional closed form analytical techniques. The method is applied to a foil winding inductor and its accuracy is compared to a finite element solution of the same problem.<<ETX>>

An experimental evaluation of losses in planar Litz structures

Planar magnetic structures are gaining popularity in power electronics, however they have drawbacks in high current and high frequency applications. The main drawback is the poor current distribution in the planar conductor, which arises from the proximity and skin effects. This leads to a high AC resistance, which increases the conduction losses. In This work the principle of the Litz wire is applied to the planar conductor. It has already been demonstrated that this technique can reduce the effective AC resistance of the planar conductor. To date however it has only been demonstrated at very low signal levels through impedance measurements. In This work the reduction in loss is demonstrated experimentally at high powers under real operational conditions. The work is carried out with various configurations of Litz interconnections, and the losses characterised by means of impedance and calorific measurements.

Construction and modelling of a planar multi-layer electromagnetically integrated LCCT component

This paper describes the design and construction of a multi-layer multi-turn planar electromagnetic structure. This structure has the same functionality of a conventional discrete inductor, transformer and two capacitors. The structure was applied in a single switch single stage unity power factor converter. A 100 watt experimental converter was constructed and evaluated. An identical converter was constructed using conventional discrete components and the two compared. The integrated structure was analysed and an existing transmission line model is expanded to include multiple turns.

Converter layout parasitic extraction and modelling-continuation of a systematic approach

The continuation of a systematic investigation into converter parasitic effects is presented. The emphasis is placed on effects due to power stage layout. The use of analytical equations specifically, and the creation of suitable SPICE models to enable designers to predict possible detrimental effects, are investigated. Simulation versus experimental results for single switch converters and a two switch converter are compared.

Adjusting structural impedances for optimal electric power transmission at circuit and system level in electronic power conversion equipment

A novel use of dielectric materials, with permittivity values that can vary over a wide range (5<or= epsilon /sub r/<or=1200), for optimizing switch-node operation of power electronic circuitry is discussed. The method can be applied to power connections at circuit level or at the system level with benefits such as reduced system losses and improved operational safety of active devices. Two experimental examples illustrating the general principle of impedance matching in power electronic circuits are given. One method applies conventional materials to match a gate turn-off thyristor gate triggering circuit while the other applies new high epsilon /sub r/ ceramic materials to match the load connection of a chopper to its load. The proposed planar connection geometries are suitable for low cost/mass production. Existing CAD/CAM facilities can be used in the design and manufacturing processes. Commercially available analysis programs can be used for the design phase.<<ETX>>

Application of evolutionary computation in power electronics

An overview is given of possible evolutionary programming applications in power electronics CAD/E. Evolutionary programming is discussed in terms of the procedures and advantages. An overview of the requirements and concerns in power electronics CAD/E is given. Then the possible ways of applying evolutionary programming to address the concerns are discussed.