Modelling, analysis and design of integrated magnetics for modern power electronic circuits

Abstract

In power electronics, magnetic components, such as transformers and inductors, are important devices used for energy storage/transfer, galvanic isolation, filtering and power splitting. Modern power electronic circuits, such as AC/DC converters with power-factor-correction and poly-phase DC/DC converters, often require the use of multiple magnetic components. It is well known that a significant percentage of the material cost of power electronic circuits is due to magnetic components. A large percentage of the space requirement also comes from magnetic components. The use of integrated magnetics is attractive because it can reduce the cost and space requirements of magnetic components and/or achieve special functions in the power electronic circuits. This thesis introduces a method to use z-parameters to model the interface between an electric circuit and a magnetic component. Using this model the electrical equivalent circuit of any complex integrated magnetic component can be developed easily. This provides a powerful tool for the analysis and design of integrated magnetics. A methodology of converting the z-parameter model of a complex integrated magnetic component into an equivalent-circuit model using the principle of duality has also been developed. The design of integrated inductors and transformers using z-parameter model is studied. In order to demonstrate the practical applications of the integrated inductor/transformer and its z-parameter model, a single-switch regulator with power-factor-correction, using a single integrated magnetic component, is built. Based on the same example, the problem of uneven magnetic flux density in an integrated magnetic component is examined. A possible solution to the problem is also proposed. In order to demonstrate the practical applications of the integrated transformer/transformer, a bi-directional pulse-current sensor is designed and built for use in bi-directional PWM DC-DC converters. The uses of integrated magnetics for poly-phase converters are studied. A two-phase forward converter using an integrated transformer/inductor (which consists of two step-down transformers and two output-filtering inductors wound on a standard EE-core), a four-phase forward convener using an integrated transformer (which consists of four step-down transformers wound on a standard ETD-core) and an (N+X)-phase forward converter using an expandable integrated transformer (which consists of N+X step-down transformers wound on an assembly of UI-cores) are designed. Based on their equivalent-circuit models, all these converters are analysed. The theoretical analyses have been verified by both simulated and experimental results. In all designs of this thesis, standard core structures are used to increase the commercial value of the proposed integrated magnetics.