J.A. Cobos

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.

Review and Comparison of Step-Up Transformerless Topologies for Photovoltaic AC-Module Application

This paper presents a comprehensive review of step-up single-phase non-isolated inverters suitable for ac-module applications. In order to compare the most feasible solutions of the reviewed topologies, a benchmark is set. This benchmark is based on a typical ac-module application considering the requirements for the solar panels and the grid. The selected solutions are designed and simulated complying with the benchmark obtaining passive and semiconductor components ratings in order to perform a comparison in terms of size and cost. A discussion of the analyzed topologies regarding the obtained ratings as well as ground currents is presented. Recommendations for topological solutions complying with the application benchmark are provided.

A simple dc-dc converter for the power supply of a cochlear implant

A resonant topology based on class-E is presented as the power supply of a cochlear implant. This topology has the important advantage of a small number of components and a grounded single switch. Zero voltage switching can be achieved, which significantly reduces switching losses and improves efficiency. A circuit has been designed, built and tested in order to check the feasibility of the topology for the mentioned contactless application. The results are very good, the efficiency has been clearly improved compared to the former system and the autonomy has increased.

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.

Improving power factor correction in distributed power supply systems using PWM and ZCS-QR SEPIC topologies

The single-ended primary inductance converter (SEPIC) presents several advantages over boost and flyback topologies which make this converter convenient for use as a power factor preregulator (PFP). Due to this fact, both the pulsewidth modulation (PWM) and the zero-current switched quasi-resonant (ZCS-QR) SEPIC used as PFPs are studied. Stress in components and operation in continuous and discontinuous conduction mode are considered in the PWM case, while the use of full-wave and half-wave resonant switches is considered in the ZCS-QR case. The study of the PWM SEPIC used as a PFP reveals that both types of PFP control, multiplier approach and voltage-follower approach, can be used in PWM SEPIC, the first one when it operates in continuous conduction mode and the second one when it operates in discontinuous conduction mode. Regarding the ZCS-QR SEPIC used as PFP, both types of resonant switch (half-wave and full-wave) can be used.<<ETX>>

Magnetic integration for interleaved converters

In this paper several techniques for integration of magnetic components in interleaved converters are analyzed. Magnetic components define the way the energy is transformed. Several opposite approaches can be considered: from decoupled integrated inductors to tightly coupled inductors. The integration of inductors in the same core for multiphase converters is especially analyzed from the point of view of size, losses and coupling.

Multilevel Power Supply for High-Efficiency RF Amplifiers

In radio systems linear power amplifiers (class A, B or AB) are usually used as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has low peak-to-average power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a combination of multilevel converter and linear regulator. The proposed solution can reproduce any signal with maximal spectral component of 2 MHz and give instantaneous maximal power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, it has up to 15% higher efficiency than linear regulator that is used as a conventional solution. Additionally, the algorithm for selection of voltage levels for the multilevel converter is explained, as well.

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>>

Miniaturised battery charger using piezoelectric transformers

Piezoelectric materials are a technology that in recent years have raised enormous interest for their possible use as power transformers. Their main features are high power densities, absence of electromagnetic noise and high voltage isolation capability. This paper presents the results obtained in a prototype of a miniaturized battery charger for mobile phones. Due to the reduced size of the piezoelectric transformers, the charger has been introduced in a plug type case, smaller than a matchbox.

Nonlinear digital control breaks bandwidth limitations

The bandwidth achievable by using linear control in SMPS is limited either by the switching frequency or by the robustness of the system. Fast transient response requires high switching frequency. However, lower switching frequencies could be more suitable to maximize efficiency. On the other hand, if high switching frequency is not a problem, high bandwidth is difficult to obtain because of noise, plant variation and non-idealities of the error amplifier. This paper proposes two different approaches based on the combination of nonlinear control with linear control to break these limitations. These strategies are applied for dynamic voltage scaling and two prototypes are built to validate the concepts.