Javier Uceda

Control of Distributed Uninterruptible Power Supply Systems

In the last years, the use of distributed uninterruptible power supply (UPS) systems has been growing into the market, becoming an alternative to large conventional UPS systems. In addition, with the increasing interest in renewable energy integration and distributed generation, distributed UPS systems can be a suitable solution for storage energy in micro grids. This paper depicts the most important control schemes for the parallel operation of UPS systems. Active load-sharing techniques and droop control approaches are described. The recent improvements and variants of these control techniques are presented.

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.

The discontinuous conduction mode Sepic and Cuk power factor preregulators: analysis and design

Sepic and Cuk power converters working as power factor preregulators (PFP) in the discontinuous conduction mode (DCM) present the following desirable characteristics for a PFP: (1) the power converter works as a voltage follower (no current loop is needed); (2) the theoretical power factor is unity; and (3) the input current ripple is defined at the design stage. Besides, input-output galvanic isolation is easily obtained. This paper analyzes the operation of both power converters as DCM-PFP. Design equations are derived, as well as a small-signal model to aid the control loop design. Both simulation and experimental results are presented that are in agreement with the theoretical analysis and complement the work.

Static and dynamic modeling of tapped-inductor dc-to-dc converters

Six different topologies of tapped-inductor dc-to-dc converters derived from buck, boost and buck-boost topologies are analyzed. Both dc and ac analysis in continuous and discontinuous operating modes are considered. The influence of the tapped inductor turn ratio (λ) is very important in the circuit behaviour. Particulary in the poles and zeros distribution of the transfer function. Some important conclusions about the dynamical characteristics of converters are derived from this study. Theoretical results are compared with those obtained from experiment carried out on some prototypes. Generalized conclusions are presented considering classical buck, boost and buck-boost (non tapped-inductor) as a particular case of these converters.

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 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.

Study of the applicability of self-driven synchronous rectification to resonant topologies

Synchronous rectification techniques applied to high-frequency resonant topologies are studied. The on-resistance reduction of the MOSFET synchronous rectifier produces an increase of the parasitic capacitances. A selection of the resonant topologies where these capacitances are absorbed by the resonant tank, allowing self-driving of the synchronous rectifier, is presented. High efficiency has been obtained in a low-output-voltage (5 V and 3.3 V) forward ZVS-MRC with resonant synchronous rectification. Layout effects appeared to be very important at high switching frequencies. Even better results are expected in a hybrid prototype using specific low gate resistance MOSFETs as synchronous rectifiers.<<ETX>>

Modeling High-Frequency Multiwinding Magnetic Components Using Finite-Element Analysis

This paper presents a magnetic component equivalent circuit as well as a methodology to extract its parameters by using a finite- element analysis tool. The model is valid for any kind of magnetic component-transformers and gapped and nongapped inductors-and takes into account frequency and geometry effects such as skin, proximity, interleaving, gap, and end effects. An additional model for capacitive effects may be coupled with the previous one to obtain a more precise result. The impedances in this model represent not only the self terms, but also all mutual terms shared between the windings. Because the simplification of concentrating impedances in one winding is not invoked, simultaneous conduction of all windings (such as forward-like converters) or in alternate conduction of the windings (such as flyback-like converters) can be accurately simulated. The parameters of these self and mutual impedances are frequency dependent, so the model represents the frequency behavior of windings in detail. This allows simulating components with nonsinusoidal currents like the ones present in switched-mode power supplies, provided there is no saturation of magnetic materials. This is not a serious limitation of the model because this kind of power supply works in linear (no-saturation) mode. When there is saturation, the core model determines the component behavior. Applying the model to several actual components has shown its usefulness and accuracy. Details concerning model parameters extraction are presented here with simulation and measurement results.

Simplified control strategy for hybrid active filters

Nowadays, hybrid filtering is an important alternative to improve line performance when supplying high-power nonlinear loads. This paper presents a simple and low cost control strategy for hybrid filter as an alternative to other more complex algorithms, in some specific applications. The proposed control strategy is recommended for a utility interface with three-phase diode bridge rectifier front-end due to its high displacement power factor. It has been tested by simulations (both steady-state and transient analysis) and by experimental verification, where good results are obtained. It can be seen that using this control strategy, acceptable harmonic levels according to IEEE-519 standard are obtained. Also a different connection of the passive filter is experimentally verified, allowing the reduction of passive filter capacitors.

Study of 3-D magnetic components by means of "double 2-D" methodology

The magnetic field in many magnetic components, namely toroids and EE cores, has a three-dimensional (3-D) distribution. Energy and losses calculation in these particular structures makes necessary the use of 3-D techniques that accounts for all 3-D effects. The calculation of the energy and losses is needed in order to obtain any transformer model. This paper presents a procedure that allows the calculation of energy and losses in 3-D structures using two-dimensional (2-D) approaches. This procedure accounts for 3-D effects, solving each magnetic component by means of two different analyses but using 2-D finite-element analysis (FEA) solvers instead of 3-D. The main advantages of this procedure are that all geometrical and frequency effects are taken into account using 2-D FEA solvers. 3-D FEA solvers are not applicable to analyze most practical cases because of the complexity in the geometry. Therefore, the use of this method is not only advantageous from the point of view of time reduction, but also it is a solution for many cases where 3-D solvers are not a feasible solution. Some experimental results illustrate the application of the methodology, which is especially useful to study the influence of the winding strategy in toroidal structures and to design integrated magnetics in order to adjust the coupling coefficient between each pair of windings before the component construction.