R. Prieto

Single phase power factor correction: a survey

New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal. In addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase and low power applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

Power factor correction: a survey

New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions to this problem to obtain sinusoidal line current and in addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

A full procedure to model high frequency transformer windings

A full procedure to model high frequency magnetic components has been developed. A finite element analysis (FEA) tool is used to compute the frequency behavior of the windings, taking into account geometry and frequency effects, like skin, proximity, interleaving, gap and end effects. The capacitive effects among the windings of the components are also taken into account. From these data, a model for the windings is developed by means of discrete components and differential equations that present the same frequency behavior as the actual component. Although the model has been developed for behavioral simulators, it can also be used in electrical simulators.<<ETX>>

A new driving scheme for synchronous rectifiers: single winding self-driven synchronous rectification

Single winding self-driven synchronous rectification (SWSDSR) approach is a new driving circuit that overcomes the limitations of the traditional driving schemes, becoming an interesting alternative to supply new electronic loads such as microprocessors. Traditional self-driven synchronous rectification (SDSR) technique has shown very good performance to improve efficiency and thermal management in low-voltage low-power DC/DC converters, however it can not be extended to the new fast dynamic, very low voltage applications. SWSDSR scheme is based on an additional winding in the power transformer (auxiliary winding). It allows for maintaining the synchronous rectifiers (SRs,) on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes it possible to drive properly the SRs even in very low voltage applications, 1.5 V or less. Coupling of the windings strongly affects the performance of the SWSDSR technique. The influence of the coupling between the different windings is analyzed through simulations of different transformers designed for the same application. Models of transformers are generated with a finite element analysis (FEA) tool. Goodness of the SWSDSR scheme is validated through experimental results.

A new family of single stage AC/DC power factor correction converters with fast output voltage regulation

Off line converters should be designed to drain almost sinusoidal current from the utility to accomplish international regulations about harmonic injection. A common approach is to use power factor pre-regulators, that is usually, cascaded by a DC/DC converter to obtain a fast regulated output voltage in the load or DC bus. There are also several single stage solutions that make these two tasks using one single converter, obtaining advantages from the point of view of efficiency, size or cost. In this paper, a new family of single stage AC/DC circuits is proposed. With these converters, a high power factor and a tight regulated output voltage are achieved. This family has advantages such as efficiency and size over the two stage structure, and simplicity over other single stage solutions.

Design issues of a core-less transformer for a contact-less application

A set of rules for designing coreless transformers for contactless applications is presented in this paper. In contactless transference of energy, there is a relative big separation distance between the coils, so coupling is low. Several simulations have been performed with an FEA tool studying different technologies and winding strategies in order to quantify the improvements in coupling and resistance for different gaps. The analysis has been done for the transcutaneous transformer of a human-body implant, but the conclusions can be extended to any kind of coreless transformer for a contact-less application. The results are consistent with the measurements.

Impedance-Based Stability and Transient-Performance Assessment Applying Maximum Peak Criteria

The impedance-based stability-assessment method has turned out to be a very effective tool and its usage is rapidly growing in different applications ranging from the conventional interconnected dc/dc systems to the grid-connected renewable energy systems. The results are sometime given as a certain forbidden region in the complex plane out of which the impedance ratio--known as minor-loop gain--shall stay for ensuring robust stability. This letter discusses the circle-like forbidden region occupying minimum area in the complex plane, defined by applying maximum peak criteria, which is well-known theory in control engineering. The investigation shows that the circle-like forbidden region will ensure robust stability only if the impedance-based minor-loop gain is determined at the very input or output of each subsystem within the interconnected system. Experimental evidence is provided based on a small-scale dc/dc distributed system.

A simple single-switch single-stage AC/DC power converter with fast output voltage regulation

In this paper a simple single-stage AC/DC converter, based on the flyback topology, is presented. With a single switch, a fast-regulated output voltage is achieved and although the line current is not sinusoidal, the converter complies with the standard IEC 1000-3-2 for low frequency harmonics in the medium power range. The major advantages of this converter are its size and the efficiency. Design guidelines, analysis of the line current and extensions to other topologies are analyzed. Experimental results are included in the paper.

Model of the capacitive effects in magnetic components

A model for the capacitive effects in magnetic components for switch mode power supplies (SMPS) has been developed. It can be applied to multiwinding transformers. A finite element analysis (FEA) tool is used to compute the frequency behavior of the magnetic component, taking into account geometry and materials. The parameters of the model can be calculated before the magnetic component is built. An accurate capacitances modeling is expected to be crucial for common-mode EMI transmission modeling. The model takes into account winding floating voltages and the capacitance among each winding. Several model levels with different degrees of freedom are proposed. Some experimental results comparing the actual magnetic component results with the behavioural simulator results, are presented.<<ETX>>

Optimizing the winding strategy of the transformer in a flyback converter

This work presents a study of the influence of the winding strategy in the parameters of the flyback transformer. A frequency and geometry dependent model generated from FEM simulations has been employed in order to study the influence of the position of the windings on the leakage energy and AC resistance. A study of the interleaving technique in the flyback transformer has also been developed using the FEM solver. Conclusions of the advantages of the interleaving technique in the flyback transformer compared with its application in common transformers have been extracted. The influence of the leakage inductance in primary and secondary windings has been studied by means of SPICE simulations. The final goal of this paper is to obtain winding strategy design rules to minimize the leakage inductance and AC resistance in order to optimize power converter performance.