1,355,515 research outputs found
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
The middle Permian pyrophyllite-rich ferruginous bauxite, northwestern Iran, Irano–Himalayan karst belt: Constraints on elemental fractionation and provenance
No full textThe pyrophyllite-rich ferruginous (PRF) bauxites in northwestern Iran from the Irano–Himalayan karst belt are deposited on the paleokarst of the middle Permian carbonate sequence of the Ruteh Formation. They were selected from the lowermost part of weathered profiles from 9 karst bauxite deposits, belonging to different stratigraphic positions. These bauxite deposits share similar mineralogical and geochemical features. Powder-XRD analyses show that the bauxites consist of diaspore, hematite, and pyrophyllite, with lesser amounts of goethite, rutile, anatase, illite, and clinochlore. Among minor constituents, single crystals, such as monazite, florencite, and zircon, were detected by SEM–EDS analyses. The positive Ce anomaly of the PRF bauxites (1.0–2.2), the relevant depletion of mobile elements, and values of the La/Y ratio (1.0–3.2) indicate that the PRF bauxites formed in a well-drained environment, characterized by a prevailing alkaline environment, promoting the stability of Fe (oxyhydr)oxides. The mineralogical composition of the PRF bauxites affects the distribution of trace elements: the redox-sensitive trace elements Ni, Cr, Co, Ce, U, and V are probably controlled by Fe (oxyhydr)oxides, whereas most of high field strength elements, such as critical metals Hf and Nb, are hosted in the pool of resistant minerals. Gallium co-varies with Al2O3, indicating this critical trace metal is distributed by diaspore. Phosphate-bearing minerals probably played an efficient role in concentrating light (LREE: LaSm) and heavy (HREE: EuLu plus Y) rare earth elements during the generation of the PRF bauxites. The mineralogical control on the distribution of LREE and HREE, coupled with the preferential complexation of HREE in an alkaline environment clearly affect the (La/Yb)ch and (LREE/HREE)ch fractionation ratios. Based on the ThZr and TiO2–Zr binary diagrams, the concentration of trace elements Zr, Cr, and Ga, bivariate plots of Ta (ppm) versus Al2O3 (wt%) and TiO2 (wt%), and the discriminant function 3 against discriminant function 4 variation diagram, basalt rocks within carbonate bedrocks of the Ruteh Formation have considered to be a probable provenance for the PRF bauxites, similar to some bauxite deposits from the Mediterranean-type karst bauxite belt of different ages, especially northern and northwestern Iran and western India
High-bandwidth droop-based controllers for DC and AC microgrids
Full text linkDue to the reduction in the transmission and distribution losses, the overall system costs and the CO2 emissions, distributed power generation based on sustainable and green resources, such as photovoltaic and wind have been exploited over the past decades. Grouping several mentioned power resources together with some loads as well as some energy storage systems is so-called a microgrid environment. Also, in microgrids, as the sources are near the loads, the power quality, efficiency, and reliability will be significantly increased. Microgrids are also a smart choice for remote locations that are not reachable by the main grid. Microgrids have three different architectures, DC, ac, and hybrid. DC microgrids bring some advantages over their AC counterpart. For instance, the inductive voltage drop is removed in a DC system. But still, AC microgrid is more compatible with the nature of many DERs such as wind and electric motors load. These facts make it valuable to consider both AC and DC microgrids for research activities. Sharing loads automatically between parallel resources in microgrids is an important aspect. A primary level control like the droop control solution can be used to share the power among parallel resources without any communication. Droop control is a simple approach that mostly applies to parallel DERs to ensure their stability. In AC systems, it generates the output reference voltage magnitude and voltage frequency of the DG units based on their reactive (Q–V) and active power (P–F) values and in DC systems, It functions by introducing virtual resistance in line to equalize current sharing or by controlling voltage magnitude based on active power (P–V). This dissertation focuses on performance improvement of droop-controlled converters, mainly in the following three aspects: i) a novel Dual-Edge (DE) PWM suitable for DC/AC and DC/DC converters with reduced modulation delay, and a graphical-based analysis for its dynamic behavior, and its effect on output impedance and stability; ii) reduction of DC bus capacitance while maintaining tight DC bus voltage regulation in DC microgrids; iii) Per-Phase Power Controller in AC Microgrids with smooth transfer from the power flow control to droop control, allowing AC microgrids to seamlessly disconnect from upstream grids.Due to the reduction in the transmission and distribution losses, the overall system costs and the CO2 emissions, distributed power generation based on sustainable and green resources, such as photovoltaic and wind have been exploited over the past decades. Grouping several mentioned power resources together with some loads as well as some energy storage systems is so-called a microgrid environment. Also, in microgrids, as the sources are near the loads, the power quality, efficiency, and reliability will be significantly increased. Microgrids are also a smart choice for remote locations that are not reachable by the main grid. Microgrids have three different architectures, DC, ac, and hybrid. DC microgrids bring some advantages over their AC counterpart. For instance, the inductive voltage drop is removed in a DC system. But still, AC microgrid is more compatible with the nature of many DERs such as wind and electric motors load. These facts make it valuable to consider both AC and DC microgrids for research activities. Sharing loads automatically between parallel resources in microgrids is an important aspect. A primary level control like the droop control solution can be used to share the power among parallel resources without any communication. Droop control is a simple approach that mostly applies to parallel DERs to ensure their stability. In AC systems, it generates the output reference voltage magnitude and voltage frequency of the DG units based on their reactive (Q–V) and active power (P–F) values and in DC systems, It functions by introducing virtual resistance in line to equalize current sharing or by controlling voltage magnitude based on active power (P–V). This dissertation focuses on performance improvement of droop-controlled converters, mainly in the following three aspects: i) a novel Dual-Edge (DE) PWM suitable for DC/AC and DC/DC converters with reduced modulation delay, and a graphical-based analysis for its dynamic behavior, and its effect on output impedance and stability; ii) reduction of DC bus capacitance while maintaining tight DC bus voltage regulation in DC microgrids; iii) Per-Phase Power Controller in AC Microgrids with smooth transfer from the power flow control to droop control, allowing AC microgrids to seamlessly disconnect from upstream grids
Simplified on-line monitoring system of MOSFET on-resistance based on a semi-empirical model
Full text linkThis work provides a solution allowing to monitor on-line the health of a power MOSFET adopted in a buck converter. In the considered application, the analysis is focused on the high-side switch, being a low-voltage power MOSFET. The monitoring system allows estimating the on-resistance of the device by measuring both output current and voltage drop across the switch. Moreover, a semi-empirical model is considered in order to account for the dependence of the on-resistance on operating temperature and gate driving voltage. The on-line implementation of such a model allows estimating on-resistance degradation in real-time with a high level of accuracy in a wide range of operating conditions. An on-line calibration procedure is also implemented in order to assess the on-resistance of fresh devices. Experimental results confirm the accuracy of the system (in conjunction with the proposed model) under different operating conditions: load current from 2A to 6A; device temperature up to 100°C and gate to source voltage (VGS) from 6V to 10.5V. In the abovementioned conditions, an accuracy ≤2.6% is experimentally found. Hence, the system is able to properly estimate the degradation of on-resistance due to ageing conditions
SEUPD@CLEF: Team Kalu on improving Search Engine Performance with Query Expansion and Re-Ranking Approach
No full textThis report provides a detailed description of the search engine system designed by Team KALU for the Conference and Labs of the Evaluation Forum (CLEF) LongEval LAB 2024 Task 1. The team, composed of students from the University of Padua, developed this system to efficiently index, search, and retrieve documents. We begin by outlining the problem and then go on to describe our system which mainly works on a collection of documents written in French language, then we explain the various methodologies we implemented. We present our experimental results and analyze them according to the techniques we employed. Finally, We present the outcomes of our experiments and discuss the different techniques used
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
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
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
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
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