1,720,964 research outputs found
A Per-Phase Power Controller allowing Smooth Transitions to Islanded Operation
No full textThis paper presents a droop-based controller for grid-tied three-phase inverters. The controller allows to regulate the inverter output power while operating grid-tied, to support the local grid voltage while operating islanded, and to seamlessly transition into this latter mode of operation. The use of the traditional droop control scheme for per-phase power control would lead to unequal frequencies among the phase voltages, which is not acceptable. Instead, the proposed controller allows independent power references tracking at each of the phases of a three-phase inverter while grid-tied and a proper transition into the islanded operation. Per-phase power control is crucial for several important services in modern smart power networks, like demand-response and distributed unbalance compensation. Simulation and experimental results considering a laboratory-scale prototype are reported and discussed to validate the proposed controller
An Oversampled Hysteresis Modulation for Shaping the Output Impedance of Droop-Controlled Boost Converters in DC Microgrids
No full textDroop control is a common method to share power among Distributed Energy Resources (DERs) in DC microgrids. In order to reduce the DC bus voltage variations during the load transient conditions, a resistive-capacitive output impedance is needed. This can be done by implementing a fast voltage controller for the converters or using a bulky output capacitance. This paper analyses an oversampled hysteresis controller for the droop controller of boost converters. Due to the higher controller bandwidth, a resistive-capacitive output impedance is obtained with a small output capacitor. The paper proposes a design approach for hysteresis droop-controlled converters, including the design of frequency-dependent droop coefficients. Experimental results on a 3kW-380V boost prototype verify the validity of the proposed solution
Limiting power cycling stress in power MOSFETs by active thermal control
Full text linkIn this work we propose a system which is able to actively control the temperature of a power MOSFET, in order to limit the temperature swing and hence to reduce the power/thermal cycling effect. To this purpose a dedicated driving circuit, allowing to control the gate voltage of the switching device under investigation, is used in a synchronous buck converter. Therefore, power losses can be modulated in order to reach the desired temperature through self-heating effects. The implemented control system is able to compensate the non-linear relationship between the gate voltage and the on-resistance. Moreover, to improve the response of the system, a predictor has been implemented, having the capability of on-line tuning the thermal resistance of the device. Experimental results are reported to demonstrate the suitability of this solution to control the temperature in the semiconductor device. The reduction of temperature swing under power and thermal cycling is also demonstrated
Asymmetric Digital Dual-Edge Modulator for Dynamic Performance Improvement of Multiloop-Controlled VSI
No full textThis article proposes the architecture and a graphical-based analysis for a digital asymmetric dual edge (ADE) carrier-based pulsewidth modulator. In its digital version, it retains some advantages offered by the analog implementation. Indeed, in single-sampling operation, the phase delay introduced by this modulator is always less than or equal to the one obtained with the trailing-triangle edge (TTE) carrier. Moreover, by combining the advantages given by the ADE carrier and the double sampling of the modulating signal, it is possible to realize a digital modulator with a null phase delay. Since the proposed ADE-carrier-based digital pulsewidth modulator (DPWM) operates at a variable switching frequency, synchronization strategies between the carrier and the sampling instants may be required for some applications. Reliable synchronism correction architectures are, therefore, proposed and discussed. The developed model is validated through simulation and experimentally on a 27.5-kHz 9-kW single-phase voltage-source inverter case study. The experimental tests include a comparison with the DPWM architecture based on the TTE carrier
PRBS-based loop gain identification and output impedance shaping in DC microgrid power converters
No full textDue to potential dynamic interactions among dc microgrid power converters, the performance of some of their control loops can vary from the designed behavior. Thus, online monitoring of different control loops within a dc microgrid power converter is highly desirable. This paper proposes the simultaneous identification of several control loops within dc microgrid power converters, by injecting orthogonal pseudo-random binary sequences (PRBSs), and measuring all the loop gains in one measurement cycle. The identification results can be used for different purposes such as controller autotuning, impedance shaping, etc. Herein, an example of output impedance estimation and shaping based on locally-measured loop gains is presented. The proposed identification technique and its application in output impedance shaping are validated on an experimental dc microgrid prototype, composed of three droop-controlled power converters
Per-Phase Power Controller for Smooth Islanded Transitions in Three-Phase Three-Wire Systems
Full text linkThis manuscript describes the operation of a droop-based controller for three-phase converters in the case of the absence of a neutral connection to the grid. The controller is capable of output power tracking and smooth transitions into the islanded operation. While independent per-phase control of the converter output power is possible if a neutral connection is present, its absence implies additional constraints to be considered. Focusing on this latter case, the controller described herein allows the independent control of the active power at the output of each phase of the converter and a smooth transition to the islanded operation. These features are paramount in future smart power systems, such as smart microgrids, for implementing demand–response, power-flow management, and uninterrupted power operation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
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