C. Alonso

Practical Implementation of a High-Frequency Current Sensing Technique for VRM

Inductor current tracking in high-frequency DC/DC converters is not effortless, especially when high current and low voltages loads are demanded. This paper proposes a simple technique to obtain a good resolution in the inductor current measurement obtaining an equivalent voltage image which can be used for a high-frequency PWM controller. This strategy of measurements is generic and it has been validated by simulations. Our experimental results are obtained with very low output voltages and several loads between 10mA to high currents covering the needs of portable and embedded VRM applications.

Synthesis of PWM-based power gyrators

A systematic procedure to synthesize power gyrators operating at constant switching frequency is presented. Based on the gyrator equations, topological constraints on the power stage are first established and two types of gyrators, i.e., G and R, are defined. Subsequently, the equivalence between ideal sliding-dynamics and PWM zero-dynamics is used to derive the control law of the duty cycle. As a result, new gyrator structures are eventually disclosed. Namely, the buck converter with input filter and the Cuk converter are shown to have stable characteristic of a G-gyrator if damping networks are inserted and certain parametric conditions are satisfied. Similarly, a boost converter with output filter is also shown to behave as a power R-gyrator with stable dynamics.

An adaptive control developed for Multi-Phase Converters based on look-up tables and applied to photovoltaic conversion systems

This paper presents an Adaptive Multi-Phase Converter (AMPC) used as a perfect matching stage to improve the global energy production and conversion efficiency of a photovoltaic power conversion system. A control law was specially developed to guarantee high conversion efficiency, even in presence of a constantly changing operating point, which is the main constraint in a traditional photovoltaic system design. Another control law was designed to reduce the stress on the components of each converters phase and then to insure a higher life time for the system. Through this control, we proposed a rotation algorithm that guarantees an homogeneous aging of the phases and increases the average lifetime of the converter. Examples of guidelines of these control laws are presented with their impact on the efficiency. An experimental prototype has been designed to evaluate the performances of this proposed adaptation stage and to validate this concept in real field operating conditions.

Analysis and design of digital predictive current-mode control techniques for high-frequency VRMs

Digital predictive techniques are nowadays an attractive option for current-mode controlled voltage regulator modules. This article examines the implementation of two digital predictive control laws and their application in a typical case for this kind of loads. The simulation results presented in this paper illustrate the pros and contras of both techniques.

Comparative study of the optimal number of phases for interleaved Voltage regulator modules

This paper studies several solutions to choose the most appropriated number of phases for a high- current low-voltage interleaved voltage regulator module (VRM). Several criteria have been considered as transient responses, harmonic contents (EMI levels) or converter efficiency to find the optimal topology of the converter. A theoretical comparison between classical single-phase converters with those multi-phased has been established. Finally, we have extracted some results to determine the optimal number of phases.

Adaptive digital synchronous P&O MPPT algorithm for Photovoltaic DC power conversion

This paper presents an implementation of a new fast, robust and accurate Maximum Power Point Tracking (MPPT) technique for Photovoltaic (PV) applications. This algorithm uses an adaptive perturbation generator coupled with a synchronous data acquisition process. A variable offset is added to the perturbation in order to provide the control signal for the Digital Pulse Width Modulation (DPWM) stage that commands the switching of the DC/DC converter. Thanks to a Proportional Integral (PI) control of the offset variation, the overall dynamic behavior of the MPPT algorithm is enhanced by one order of magnitude. The adaptive control of the perturbation amplitude allows to minimize the steady state error of the MPPT algorithm, while insuring good operation at low power when the signal over noise ratio is poorer, this without the need of a high precision sampling system. This control strategy has been first validated through simulations. Experimental results are then demonstrated using a Boost converter with the presented advanced P&O MPPT control algorithm in real operating conditions for battery charging.

FPGA-based digital voltage-current controller for a buck converter

This paper introduces an analysis and design of a digital controlled double loop voltage-current for a buck converter. Taking into account the implementation requirements, the chosen platform was an Field-Programmable Gate Array (FPGA). This paper also shows in detail the analog-digital interface. The study is completed by a detailed analysis of the FPGA programming including states machines and logic diagrams. Finally, theoretical results are validated with extensive simulations.

Optimizing losses in multilevel inverters

Losses generation in a multilevel inverter leg are analyzed in this paper for N=2, 3, 4, and 5 levels. An N-level inverter is modeled as the superposition of N-1 elementary buck converters to simplify the losses analysis. The results of the analysis show that the efficiency of a multilevel inverter can increase when the number of levels increases if an appropriate device selection is made. SABER simulations and experimental results in a 500 W 5-level prototype confirm the analytic predictions.

Control and design of a hybrid energy storage system

The increasing deployment of intermittent renewable energy sources (RESs) around the world has revealed concerns about the power grid stability. To solve this problem, a massive use of storage systems is needed. The main goal of this work is to develop a hybrid energy storage system (HESS) combining several storage devices with complementary performances. In this paper, lead-acid batteries and supercapacitors (SCs) are associated in order to deliver a pulsed current. An innovative cascade control with anti-windup tracking manages the power sharing between a buck and a boost converters connected to the same DC bus. Analog control circuits and power converters have been designed to evaluate the performances of the HESS in real conditions.

Rotational adaptative-multilevel converter control strategy based on FPGA

In this paper, a control method for autonomous changing the number of parallel driven DC-DC converter is proposed. In order to improve efficiency of the parallel driving, the number of parallel driven converters is dynamically changed for the variations of output power. Taking into account the implementation requirements, the chosen platform was an Field-Programmable Gate Array (FPGA). This paper also shows in detail the analog-digital interface. The study is completed by a detailed analysis of the FPGA programming including states machines and logic diagrams. Finally, an experimental comparison with a typical single converter topology is done.