Multiphase Buck Converter with Minimum Time Control Strategy for RF Envelope Modulation

Power amplifier supplied with constant supply voltage has very low efficiency in the transmitter. A DC-DC converter in series with a linear regulator can be used to obtain voltage modulation. Since this converter should be able to change the output voltage very fast, a multiphase buck converter with a minimum time control strategy is proposed. To modulate supply voltage of the envelope amplifier, the multiphase converter works with some particular duty cycle (i/n, i=1, 2 ... n, n is the number of phase) to generate discrete output voltages, and in these duty cycles the output current ripple can be completely cancelled. The transition times for the minimum time are pre-calculated and inserted in a look-up table. The theoretical background, the system model that is necessary in order to calculate the transition times and the experimental results obtained with a 4-phase buck prototype are given

Multiphase transformer-coupled converter: two different strategies for energy conversion

The operation of a multiphase topology, ideally, without energy storage presents the advantage of achieving very high efficiency over a wide load range as well as a fast dynamic response. However, ideal no-energy storage operation also implies a limitation in the regulation capability of the topology, the output voltage can only take discrete values. These features (high efficiency and discrete regulation capability) of the proposed energy conversion strategy enable the topology as a candidate for `DC-DC transformer' applications. The advantages, drawbacks and the operating principle of this concept, implemented with a `closed chain' magnetic structure have been already presented. In this work, the minimum energy storage operation, is applied to two different magnetic structures. These magnetic structures are called `closed chain' and `pyramidal' the main advantage of the `pyramidal' coupling structure is to improve the size of the converter without increasing the operating frequency. Both magnetic structures are analyzed, compared and experimentally implemented.

New Considerations in the Input Filter Design of a Three-Phase Buck-Type PWM Rectifier for Aircraft Applications

An EMI filter for a three-phase buck-type medium power pulse-width modulation rectifier is designed. This filter considers differential mode noise and complies with MIL-STD-461E for the frequency range of 10kHz to 10MHz. In industrial applications, the frequency range of the standard starts at 150kHz and the designer typically uses a switching frequency of 28kHz because the fifth harmonic is out of the range. This approach is not valid for aircraft applications. In order to design the switching frequency in aircraft applications, the power losses in the semiconductors and the weight of the reactive components should be considered. The proposed design is based on a harmonic analysis of the rectifier input current and an analytical study of the input filter. The classical industrial design does not consider the inductive effect in the filter design because the grid frequency is 50/60Hz. However, in the aircraft applications, the grid frequency is 400Hz and the inductance cannot be neglected. The proposed design considers the inductance and the capacitance effect of the filter in order to obtain unitary power factor at full power. In the optimization process, several filters are designed for different switching frequencies of the converter. In addition, designs from single to five stages are considered. The power losses of the converter plus the EMI filter are estimated at these switching frequencies. Considering overall losses and minimal filter volume, the optimal switching frequency is selected.

Non-linear gain - look-up table based approach for modeling a family of DC to DC converters based on transient response analysis

The purpose of this work is to propose a structure for simulating power systems using behavioral models of nonlinear DC to DC converters implemented through a look-up table of gains. This structure is specially designed for converters whose output impedance depends on the load current level, e.g. quasi-resonant converters. The proposed model is a generic one whose parameters can be obtained by direct measuring the transient response at different operating points. It also includes optional functionalities for modeling converters with current limitation and current sharing in paralleling characteristics. The pusposed structured also allows including aditional characteristics of the DC to DC converter as the efficency as a function of the input voltage and the output current or overvoltage and undervoltage protections. In addition, this proposed model is valid for overdamped and underdamped situations.

Optimum Design of an Envelope Tracking Buck Converter for RF PA using GaN HEMTs

In this paper, filter design methodology and application of GaN HEMTs for high efficiency Envelope Amplifier in RF transmitters are proposed. The main objectives of the filter design are generation of the envelope reference with the minimum possible distortion and high efficiency of the amplifier obtained by the optimum trade-off between conduction and switching losses. This optimum point was determined using power losses model for synchronous buck with sinusoidal output voltage and experimental results showed good correspondence with the model and verified the proposed methodology. On the other hand, comparing to Si MOSFETs, GaN HEMTs can provide higher efficiency of the envelope amplifier, due to superior conductivity and switching characteristics. Experimental results verified benefits of GaN devices comparing to the appliance of Si switching devices with very good Figure Of Merit, for this particular application

Red adaptativa de conmutación suave para convertidor trifásico en puente activo completo para aplicaciones de vehículos eléctricos

En éste artículo se presenta el control adaptativo de un circuito auxiliar para conseguir conmutaciones suaves en todo el rango de carga en los semiconductores principales de un convertidor cargador de baterías trifásico basado en doble puente activo. Mediante este sistema se consigue tener ZVS en todo el margen de carga, sin ser necesaria la modificación de los parámetros del circuito ni de los semiconductores principales. Los principios de operación de este circuito y su control se comprobarán experimentalmente en un convertidor cargador de baterías de características similares al utilizado en el HYBRID TOYOTA PRIUS

Serial or Parallel Linear-Assisted Switching Converter as Envelope Amplifier: Optimization and Comparison

This paper presents a theoretical analysis and an optimization method for envelope amplifier. Highly efficient envelope amplifiers based on a switching converter in parallel or series with a linear regulator have been analyzed and optimized. The results of the optimization process have been shown and these two architectures are compared regarding their complexity and efficiency. The optimization method that is proposed is based on the previous knowledge about the transmitted signal type (OFDM, WCDMA...) and it can be applied to any signal type as long as the envelope probability distribution is known. Finally, it is shown that the analyzed architectures have an inherent efficiency limit.

Series combination of a switched dc-dc converter and a linear regulator for high frequency RF envelope amplifier

Classical linear amplifiers such as A, AB and B offer very good linearity suitable for RF power amplifiers. However, its inherent low efficiency limits its use especially in base-stations that manage tens or hundreds of Watts. The use of linearization techniques such as Envelope Elimination and Restoration (EER) allow an increase of efficiency keeping good linearity. This technique requires a very fast dc-dc power converter to provide variable voltage supply to the power amplifier. In this paper, several alternatives are analyzed to implement the envelope amplifier based on a cascade association of a switched dc-dc converter and a linear regulator. A simplified version of this approach is also suitable to operate with Envelope Tracking technique.

Single-Stage Grid-Connected Forward Microinverter with Boundary Mode Control

This paper presents a microinverter to be integrated into a solar module. The proposed solution combines a forward converter and a constant off-time boundary mode control, providing MPPT capability and unity power factor in a single-stage converter. 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 for the proposed solution are provided, regarding the inductance value, transformer turns ratio and frequency variation during a line semi-cycle. 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 100W prototype are enclosed

Stability and Transient Performance Assessment in a COTS-Module-Based Distributed DC/DC System

This paper introduces a method to analyze and predict stability and transient performance of a distributed system where COTS (Commercial-off-the-shelf) modules share an input filter. The presented procedure is based on the measured data from the input and output terminals of the power modules. The required information for the analysis is obtained by performing frequency response measurements for each converter. This attained data is utilized to compute special transfer functions, which partly determine the source and load interactions within the converters. The system level dynamic description is constructed based on the measured and computed transfer functions introducing cross-coupling mechanisms within the system. System stability can be studied based on the well-known impedance- related minor-loop gain at an arbitrary interface within the system.

Teaching digital control of switch mode power supplier

This paper explains the methodology followed to teach the subject `Digital control of power converters'. This subject belongs to the research master on `Industrial Electronics' of the Universidad Politécnica de Madrid. The subject is composed of several theoretical lessons plus the development of an actual digital control. For that purpose an ad hoc dc-dc converter has been designed and built. The use of this board together with some software tools seems a very powerful way for the students to learn the concepts from the design to the real world

Teaching Magnetic Design using CAD tools

Design of magnetic components is a multivariable problem. There are many different combinations of shapes, sizes and materials for the core with many diameters for the wires. So it is difficult to find the optimum design without a great number of iterations. Analytically only a few combinations are usually studied but it is very easy to take into account all the combinations using a CAD tool [1]. In this work the CAD tool used is PExprt (ANSYS [2]) which is being developed at UPMCEI.

Uso de Herramientas de Simulación Electrónica como Apoyo Docente en Electrónica de Potencia

El objetivo de este trabajo es el mostrar cómo las herramientas de simulación electrónica pueden apoyar didácticamente al profesor en la enseñanza de asignaturas relacionadas con la electrónica de potencia. Se va a presentar un ejemplo guiado de uso de este tipo de herramientas en para el diseño del circuito de control de un convertidor CC/CC para una aplicación de alimentación dual en el entorno del automóvil. Para diseñar el circuito de control es necesario determinar en primer lugar la respuesta en frecuencia del convertidor. Se va a hacer uso del programa Simplorer con la biblioteca SMPS Library como herramienta de simulación para este ejemplo. Existen modelos en dicha biblioteca que permiten obtener la respuesta en frecuencia del circuito de forma directa. Este artículo explica los pasos que deben seguirse para diseñar el circuito de control de un convertidor Buck multi-fase usando tanto modelos promediados como modelos conmutados.

Envelope amplifier based on switching capacitors for high efficiency RF amplifiers

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.

Three-level cell topology for a multilevel power supply to achieve High

This paper presents an envelope amplifier solution for envelope elimination and restoration (EER), that consists of a series combination of a switch-mode power supply (SMPS), based on three-level voltage cells and a linear regulator. This cell topology offers several advantages over a previously presented envelope amplifier based on a different multilevel topology (two-level voltage cells). The topology of the multilevel converter affects to the whole design of the envelope amplifier and a comparison between both design alternatives regarding the size, complexity and the efficiency of the solution is done. Both envelope amplifier solutions have a bandwidth of 2 MHz with an instantaneous maximum power of 50 W. It is also analyzed the linearity of the three-level cell solution, with critical importance in the EER technique implementation. Additionally, considerations to optimize the design of the envelope amplifier and experimental comparison between both cell topologies are included.