Showing papers by "J.A. Cobos published in 2012"
TL;DR: In this paper, the potential of power electronics for energy savings in four major application fields, buildings and lighting, power supplies, smart electricity grid, and industrial drives, is investigated.
Abstract: Power electronics is a key technology for the efficient conversion, control, and conditioning of electric energy from the source to the load. In this paper, the potential of power electronics for energy savings in four major application fields, buildings and lighting, power supplies, smart electricity grid, and industrial drives, is investigated. It is shown that by wider adoption of power electronics in these areas, the current European Union electricity consumption could be reduced by 25%. The technology challenges for exploiting this potential for all the four areas are identified in the paper.
87 citations
TL;DR: In this paper, a hysteretic mixed-signal controller for high-frequency switchmode power supplies that achieves both very fast transient response and constant switching frequency under steady-state operation is presented.
Abstract: A hysteretic mixed-signal controller for high-frequency switch-mode power supplies that achieves both very fast transient response and constant switching frequency under steady-state operation is presented. The mixed-signal controller combines three control loops: analog nonlinear current loop, digital linear voltage loop, and digital frequency loop. To eliminate the sampling delay associated with conventional digital controllers and improve the transient response performance, the fast nonlinear loop is built with a simple analog hardware. The nonlinear current loop is designed based on the hysteretic control of the output capacitor current. To guarantee the constant switching frequency, under different operating conditions, a digital frequency loop is proposed and implemented. The digital frequency loop eliminates undesirable switching frequency variation, associated with the conventional hysteretic controllers, by digitally adjusting the hysteretic bands around the output voltage reference. The controller operation is experimentally verified with a 5-MHz buck converter. Experimental results demonstrate fast transient response while the constant switching frequency is maintained under steady-state operation.
46 citations
TL;DR: In this paper, a power amplifier with high linearity based on the envelope elimination and restoration (EER) technique is proposed, which provides up to 100 W of peak power and tracks sine waves up to 2 MHz.
Abstract: This letter describes a power amplifier (PA) with high linearity based on the envelope elimination and restoration (EER) technique. PAs based on this technique are composed of a highly efficient nonlinear PA (class E) that performs phase modulation and a wide bandwidth envelope amplifier that supplies the nonlinear PA and has to inject the envelope through power supply modulation. The design of the envelope amplifier is a complicated task due to the tradeoff between demanded high efficiency and very wide bandwidth. In order to obtain a reasonably high efficiency and very wide bandwidth, a solution based on the multilevel converter in series with a linear regulator is proposed. It provides up to 100 W of peak power and tracks sine waves up to 2 MHz. The class E amplifier has been optimized for high-efficiency (near 85%) and high-frequency (120 MHz) operation. The experimental results presented in this letter validate the proposed solutions for the envelope and phase amplifier, demonstrate that the implemented EER PA can handle up to 100 W of peak power, and highlight its high linearity (around 40 dB of attenuation of the intermodulation products) and high efficiency (up to 25% less power losses than an ideal class B amplifier).
41 citations
09 Mar 2012
TL;DR: In this article, the state of the art of the power converters used as envelope amplifiers in this application where a fast output voltage variation is required is analyzed and several important parameters such as efficiency, bandwidth, and output voltage range are discussed.
Abstract: Over the past few years, RF power amplifiers are taking advantage of the switched dc-dc converters to use them in several architectures that may improve the efficiency of the amplifier, keeping a good linearity. The use of linearization techniques such as envelope elimination and restoration and envelope tracking requires a very fast dc-dc power converter to provide variable voltage supply to the power amplifier, but theoretically, the efficiency can be much higher than using the classical amplifiers belonging to classes A, B, or AB. The purpose of this paper is to analyze the state of the art of the power converters used as envelope amplifiers in this application where a fast output voltage variation is required. The power topologies are explored and several important parameters such as efficiency, bandwidth, and output voltage range are discussed. Some of these topologies are compared in terms of efficiency for a particular set of specifications.
40 citations
TL;DR: In this paper, a multilevel converter is implemented by employing voltage dividers based on switching capacitors, and the implemented envelope amplifier can reproduce any signal with a maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, the implemented prototypes have up to 20% higher efficiency than linear regulators used as a conventional solution.
Abstract: Modern transmitters usually have to amplify and transmit signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, 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 high peak-to-average power ratio. The Kahn envelope elimination and restoration technique is used to enhance the efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class E) with a highly efficient envelope amplifier in order to obtain a linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a multilevel converter in series with a linear regulator. The multilevel converter is implemented by employing voltage dividers based on switching capacitors. The implemented envelope amplifier can reproduce any signal with a maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, the implemented prototypes have up to 20% higher efficiency than linear regulators used as a conventional solution.
39 citations
16 Nov 2012
TL;DR: In this article, an output impedance correction circuit is used to inject or extract a current n-1 times larger than the output capacitor current, thus virtually increasing the value of the output capacitance during transients.
Abstract: This study is related to the improvement of the output impedance of the buck converter by means of introducing an additional power path that virtually increases the output capacitance during transients. It is well known that in voltage regulation module applications, with wide load steps, voltage overshoots and undershoots may lead to undesired performance of the load. To solve this problem, high-bandwidth high-switching-frequency power converters can be applied to reduce the transient time or a big output capacitor can be applied to reduce the output impedance. The first solution can degrade the efficiency by increasing switching losses of the MOSFETS, and the second solution is penalizing the cost and size of the output filter. The output impedance correction circuit, as presented here, is used to inject or extract a current n-1 times larger than the output capacitor current, thus virtually increasing n times the value of the output capacitance during the transients. This feature allows the usage of a low-frequency buck converter with smaller capacitor but satisfying the dynamic requirements.
31 citations
09 Mar 2012
TL;DR: In this article, a single-stage solution combining a forward converter with a constant off-time boundary mode control, providing MPPT capability and unity power factor, is presented for a 50W@110V photovoltaic panel.
Abstract: This paper presents a micro-inverter to be integrated into a photovoltaic panel. The proposed single-stage solution combines a forward converter with a constant off-time boundary mode control, providing MPPT capability and unity power factor. The transformer structure of the power stage remains as in the classical DC-DC forward converter. Transformer primary windings are utilized for power transfer or demagnetization depending on the grid semi-cycle. Furthermore, bidirectional switches are used on the secondary side allowing direct connection of the inverter to the grid. Design considerations regarding the inductance value, transformer turns ratio and frequency variation during a line semi-cycle are provided. The decoupling of the twice the line frequency power pulsation is also discussed, as well as the maximum power point tracking (MPPT) capability. Simulation and experimental results for a 50W@110V prototype are enclosed.
18 citations
09 Mar 2012
TL;DR: In this paper, the theoretical limitations of this architecture regarding its efficiency were discussed and two possible way of its implementation was presented. And the benefits of the new emerging GaN technology for this application have been shown as well.
Abstract: Envelope Tracking (ET) and Envelope Elimination and Restoration (EER) are two techniques that have been used as a solution for highly efficient linear RF Power Amplifiers (PA). In both techniques the most important part is a dc-dc converter called envelope amplifier that has to supply the RF PA with variable voltage. Besides high efficiency, its bandwidth is very important as well. Envelope amplifier based on parallel combination of a switching dc-dc converter and a linear regulator is an architecture that is widely used due to its simplicity. In this paper we discuss about theoretical limitations of this architecture regarding its efficiency and we demonstrate two possible way of its implementation. In order to derive the presented conclusions, a theoretical model of envelope amplifier's efficiency has been presented. Additionally, the benefits of the new emerging GaN technology for this application have been shown as well.
12 citations
09 Mar 2012
TL;DR: In this article, the authors present a method to analyze robust stability and transient performance of a distributed power system consisting of commercial converter modules interconnected through a common input filter, which is based on the use of four transfer functions, which are measurable from the converter input and output terminals.
Abstract: The paper presents a method to analyze robust stability and transient performance of a distributed power system consisting of commercial converter modules interconnected through a common input filter. The method is based on the use of four transfer functions, which are measurable from the converter input and output terminals. It is shown that these parameters provide important information on the power module sensitivity to the interactions caused by the external impedances. Practical characterization for the described system structure is performed introducing special transfer functions utilized for the interactions assessment. Experimental results are provided to support the presented analysis procedure.
8 citations
09 Mar 2012
TL;DR: In this paper, an adaptive control for the auxiliary circuit, called ARCN (Auxiliary Resonant Commutating Network), used to achieve ZVS in full active bridge converters under a wide load range.
Abstract: This paper presents an adaptive control for the auxiliary circuit, called ARCN (Auxiliary Resonant Commutating Network), used to achieve ZVS in full active bridge converters under a wide load range. Depending on the load conditions, the proposed control adapts the timing of the ARCN to minimize the losses. The principle of operation and implementation considerations are presented for a three phase full active bridge converter, proposing different methods to implement the control according to the specifications. The experimental results shown verify the proposed methodology.
4 citations
09 Mar 2012
TL;DR: In this article, a contactless transformer model using finite element analysis (FEA) is proposed to simulate Inductive Coupling Power Transfer (ICPT) systems with good accuracy of the transformer and reduce the fabrication time.
Abstract: A contactless transformer model is proposed in this paper using Finite Element Analysis (FEA). This model can be used to simulate Inductive Coupling Power Transfer (ICPT) systems with good accuracy of the transformer and reduce the fabrication time of these systems. The model not only takes into account the geometry of the windings but also the frequency effects in them. As the transformer does not have a magnetic core, it is complicated to model because the flux is expanded in the area around the windings. In order to obtain a very accurate model, it is necessary to use a 2D/3D field solver.