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Implementation and Modeling of Online Efficiency Optimization Techniques for High-Frequency dc-dc Converters in Automotive Applications
Get PDFIn recent years, the automotive industry has been characterized by a growth in the field of electronics. This growth concerns many aspects in the car design such as energy efficiency, safety, x-by-wire systems, connectivity and comfort. For this reason, while in the past electronic power consumption was negligible with respect to the total car energy consumption, a particular attention is paid nowadays to the efficiency of these devices. Furthermore, there is a political and social pressure to reduce CO2 emissions that results in penalties and taxes for those companies who do not comply with the limits imposed by national and international targets. It is clear that failure to meet these standards causes a loss of competitiveness and profit. Therefore many efforts have been made during the last years by the automotive industry to find affordable solutions to improve the energy efficiency of each part of the vehicle.
For small power devices such as safety systems (airbag, adaptive cruise control, collision avoidance etc...), vehicle networking, body (windows drivers, led driver etc...) the state of the art technologies belong to the class Smart Power Technology (SPT). Such class of technologies allows to include in the same chip die low voltage digital and analog devices like MOSFET and bipolar transistors (smart part) and power devices like high voltage DMOS (power part). The smart part of the technology is used by designers to implement systems like over temperature, short circuit protection and over voltage management circuits, while the power part is used to implement the power stage.
The most widespread class of power stages is so far represented by linear regulators because of their relative simplicity, low noise, small size and low cost. The major weakness, however, is their typically poor efficiency. As a consequence, although linear regulators still represent the main source of profit, the automotive silicon industry is investing more in highly efficient solutions such as switching converters.
The main reasons that obstruct the diffusion of switched-mode power supplies in low power automotive applications are the additional costs and additional area consumption caused by the need to include bulky inductors.
Goal of this Ph.D. research is to explore on the fly efficiency optimization strategies, also known as online efficiency optimization techniques, in which the converter is dynamically brought to its maximum efficiency operating point regardless of the specific operating conditions.
This research activity is conducted through the collaboration between Infineon Technologies Italia and the Department of Information Engineering (DEI) of the University of Padova within the framework of a contract of Apprenticeship in Higher Education and Research, and focuses on modeling and design of efficiency optimization techniques for high-frequency dc-dc converters in automotive applications. Part of the research activity has been developed during a six months visiting period at the Colorado Power Electronics Center of the University of Colorado at Boulder, under the supervision of Prof. Dragan Maksimovic.
The approach followed during the research activity aims to transfer the hardware complexity from the power stage, that is typically the most expensive part, to the control stage. In this regard, the digital control appears a natural choice enabling the possibility to explore advanced control strategies and modulation schemes that exploit the degrees of freedom offered by the converter for purpose of regulation and efficiency optimization. Moreover, being the compactness one of the major issues, the soft switching capability become a crucial aspect allowing to thereby increase the switching frequency without compromise the converter efficiency and to reduce the passive component size.
The thesis is organized as follows. First of all, a general overview of the automotive power electronics is presented in order to clarify the motivation of this research.
The first part of the thesis focuses on the steady state analysis of the Dual Half Bridge converter with particular regard to the efficiency characterization.
Such topology is considered, in both its resonant and non-resonant versions, because of its degrees of freedom inherently available in the converter modulation space.
Control strategy are proposed that allow to accomplish the output voltage regulation and an online efficiency optimization.
In systems like the one under consideration, the controller moves the converter from one operating point to a new one every time a new event occurs (for example a load step or battery line variation).
For this reason, a wide area of the control space can be potentially spanned during the normal operations, therefore an accurate dynamic analysis is mandatory to ensure the stability of the system throughout the entire control space.
For this reason another important topic analyzed in this thesis is the dynamic study of digitally controlled Dual Active Bridge converters.
The dynamics introduced by uniformly sampled phase shift modulators and combined phase shift and pulse width modulators is analyzed in detail and incorporated into a multi-harmonic small-signal model valid for both the resonant and non resonant dual half-bridge topologies.
All the results presented in this thesis are validated both via simulations and experiments made on discrete components prototype
Small-signal modeling of uniformly sampled phase shift modulators
No full textPhase shift modulation (PSM) is a commonly used technique for controlling the active power flow in resonant dc-ac and dc-dc converters. Although traditionally developed as an analog modulation scheme, digital PSM is being increasingly used in conjunction with advanced multi-variable digital controllers and online efficiency optimization algorithms. While analog PSM is known not to introduce additional dynamics from a small-signal standpoint, the analysis disclosed in this work indicates that discrete-time, or uniformly sampled, PSM introduces a transport delay of small-signal nature. Furthermore, and in close analogy with the theory of uniformly sampled pulse width modulators, such delay depends on the modulator carrier type as well as on the converter operating point. The paper first clarifies the modeling procedure for describing the small-signal dynamics of uniformly sampled phase shift modulators. Secondly, it provides an extension of traditional phasor modeling to digital phase-controlled converters, allowing to account for the additional modulator dynamics in the design of the closed-loop compensation. Theoretical findings are validated via simulation and experimental results
Small-signal modeling of combined phase shift and pulse width uniformly sampled modulators
No full textMulti-variable digital controllers exploiting a combination of phase shift and pulse width modulation (PSM+PWM) have recently been investigated as methods for simultaneously achieving output voltage regulation and efficiency optimization in dc-dc Series Resonant Converters. This paper discusses the small-signal dynamics of such combined phase shift and pulse width modulators when implemented digitally, and clarifies how the dynamical contributions of PSM+PWM around the generic harmonic of the switching rate can be expressed in the framework of dynamic phasor modeling. The study extends known results for uniformly sampled pulse width and phase shift modulators, illustrating the effects of sampling delays on the modulator output dynamics. Furthermore, results indicate that, in general,
PWM and PSM individually induce both amplitude and phase modulation in the converter phasor dynamics. Closed-form results
are presented for the generic harmonic of the modulated signal. Theoretical findings are validated via simulation and experimental
results
Multi-harmonic small-signal modeling of digitally controlled dc-dc series resonant converters
No full textThis paper addresses the problem of small-signal modeling of digitally controlled dc-dc series resonant converters when controlled using a combination of phase shift and pulse width modulation. Examples of such combined modulation techniques have been recently proposed as part of online efficiency optimization controllers, in which the regulator acts on both the phase shift between the input and output legs and the duty cycle of one of the converter legs. This paper extends the dynamic phasor approach, employed for instance when a pure phase shift control is used, to a more general multi-harmonic model which accounts for the effects of duty cycle modulation on both the
baseband components and the switching frequency components. Theoretical findings confirm the need for an extended model in
order to fully capture the converter dynamics. Simulations and experimental results are presented to validate the approach
Two-dimensional online efficiency optimization technique for dual active bridge converters
No full textThis paper proposes an online efficiency optimization technique for Dual Active Bridge (DAB) Converters. Simultaneous output voltage regulation and efficiency optimization are achieved through an advanced modulation scheme by exploiting the degrees of freedom offered by the DAB topology and with no requirements of preliminary calibration or converter characterization. A digital closed-loop controller implements voltage regulation and a two-dimensional optimization algorithm which continuously tracks the converter optimal efficiency point. The optimization loop relies on the simplex algorithm, which can be implemented in a hardware-efficient manner and without involving gradient calculations. Experimental results on a digitally controlled 196 kHz, 12 V-to-5 V, 10 W DAB prototype are reported confirming the effectiveness of the technique
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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