1,721,123 research outputs found
High Efficiency Power Converters for Vehicular Applications
Full text linkThe use of power electronics in the electrical propulsion systems leads to the optimal and efficient utilization of the traction motors and the energy sources (batteries and/or fuel cells) through the recourse to suitable power converters and their proper control. Power electronics is also used for implementing the multiple conversions of the energy delivered by the sources to feed the various loads, most of them requiring different waveforms of voltage (ac or dc) and/or different levels of voltage. This work focuses on the solutions aimed at improving the efficiency of power converters for vehicular applications, which is of great importance because of the limited amount of energy that can be stored in the electric vehicles. The study takes into consideration both the traction applications and the battery charging applications whether it is done by conductive means or by wireless power transfer (WPT) systems. The improvement in traction drive efficiency results in an increment of the drivetrain efficiency of the vehicle, leading to an extension in the driving range, while the employment of efficient power converters is required to charge batteries with increasingly large capacity. The losses of power devices are even more significant when they operate at high frequencies to compact the size of the filter elements and/or the transformers. The losses of power devices can be minimized by making the commutation soft or by replacing the conventional devices with the new generation devices based on wide bandgap (WBG) semiconductor materials. In this work, the properties of the WBG semiconductor materials are illustrated and the operation of the devices based on these materials are analyzed to grasp better their characteristics and performance. The losses of individual devices (i.e. diode, IGBT, MOSFET) as well as the operation of power converters for various applications are examined in detail.
To evaluate the performance of the SiC devices in electric vehicle applications, an AC traction drive for the propulsion of a typical compact C-class electric car has been considered. Two versions of the inverter have been investigated, one built up with conventional Si IGBTs and the other one with SiC MOSFETs, and the losses in the semiconductor devices of the two versions have been found along the standard New European Driving Cycle (NEDC). By comparing the results, it is emerged that the usage of the SiC MOSFETs reduces the losses in the traction inverter of about 5%, yielding an equal increase in the car range. To complete the study, calculation of the efficiency has been extended to the whole traction drive, including the traction motor and the gear.
Afterwards, a power factor correction (PFC) circuit, which is commonly used to mitigate the distortion in line current, has been studied. The study is started by considering the basic and the interleaved PFC configurations and by defining their circuit parameters. After selecting the interleaved configuration, the magnitude of voltages and currents in the PFC rectifier has been determined and the values obtained have been verified by a power circuit simulation software. The digital signal processing (DSP) has been also studied as it is used for the control operation of the PFC. At last, a prototype of PFC rectifier with interleaved configuration is designed. The design process and the specification of the components are described in brief.
A prototype of synchronous rectifier (SR) is designed for the output stage of a WPT system. With respect to conventional rectifiers, in SRs the diodes are replaced by MOSFETs with their antiparallel diodes. MOSFETs are bidirectional devices that conduct with a low voltage drop. During the dead time, the diodes in antiparallel to the MOSFETs are conducting. At the end of dead-time, signals are applied at the MOSFET gates that make conducting all along the remaining period, thus reducing the conduction losses. The dead-time length is optimized by using fast switching devices based on SiC semiconductor materials. The prototype is designed and tested at the line frequency. The experimental results obtained from the prototype corroborate both the analytical results and the simulation results. As SR exhibits is working with high efficiency at the line frequency, it is expected that at the higher operating frequencies of the WPT systems, the performance of SR will be even better.
A DC-DC isolated power converters used to setup the battery charger through wire system are studied. Two topologies of DC-DC converters, i.e. Dual Active Bridge (DAB) and Single Active Bridge (SAB) converters, are considered. For both the topologies operation are described at steady state. For SAB converter, two possible modes of operation are examined: discontinuous current conduction (DCM) and continuous current conduction (CCM). Soft-switching operation of both SAB and DAB converters, obtained by the insertion of auxiliary capacitors, is analyzed. Moreover, the soft-switching operating zone for the two converters are found as a function of the their output voltages and currents. Finally, the comparative analysis of soft-switching operation of SAB versus DAB converter is presented.
The thesis work has been carried out at the Laboratory of “Electric Systems for Automation and Automotive” headed by Prof. Giuseppe Buja. The laboratory belongs to the Department of Industrial Engineering of the University of Padova, Italy
Formal upscaling and numerical validation of unsaturated flow models in fractured porous media
No full textIn this work, we consider a mathematical model for describing flow in an unsaturated porous medium containing a fracture. Both the flow in the fracture as well as in the matrix blocks are governed by Richards' equation coupled by natural transmission conditions. Using formal asymptotics, we derive upscaled models as the limit of vanishing ε, the ratio of the width and length of the fracture. Our results show that the ratio of porosities and permeabilities in the fracture to matrix determine, to the leading order of approximation, the appropriate effective model. In these models the fracture is a lower dimensional object for which different transversally averaged models are derived depending on the ratio of the porosities and permeabilities of the fracture and respective matrix blocks. We obtain a catalogue of effective models which are validated by numerical computations.Acknowledgements
The work of K. Kumar and F. A. Radu was partially supported by the Research Council of Norway through the projects Lab2Field no. 811716, IMMENS no. 255426, CHI no. 25510, MICAP no. 811696 and Norwegian Academy of Science and
Statoil through VISTA AdaSim no. 6367. I. S. Pop was supported by the Research Foundation-Flanders (FWO) through the Odysseus programme (project GOG1316N), the project G051418N, and by Statoil through the Akademia agreement
Computational mathematics aspects of flow and mechanics of porous media
No full textThis Special Issue contains a series of fourteen papers that resulted from the Lorentz workshop in Leiden in the period of May 22-25 in 2018
Impact of SiC MOSFET traction inverters on compact-class electric car range
No full textThe advent of power devices based on Wide BandGap
(WBG) semiconductor materials, like the Silicon Carbide (SiC)
MOSFETs, can improve the overall performance of the power
converter systems, by reducing the conversion losses and
enabling operation at higher switching frequency. This paper
analyzes the range extension of electric vehicles (EVs) ensuing
from the adoption of SiC devices for the traction inverter. As a
case study, a compact-class electric car equipped with a Silicon
(Si) IGBT traction inverter is considered. After introducing the
driving cycle used to evaluate the range, the time graphs of
currents and voltages applied by the inverter to the traction
motor along the driving cycle are calculated. A loss model for Si
and SiC devices is then formulated, and the losses of the Si IGBT
inverter over the driving cycle are found and compared to the
losses obtainable with a SiC MOSFET inverter. For the case
study, the analysis shows that a SiC MOSFET inverter can
extend the electric car range up to 5
Quantitative Analysis of Efficiency Improvement of a Propulsion Drive by Using SiC Devices: A Case of Study
Full text linkOne of the emerging research topics in the propulsion drive of the electric vehicles is the improvement in the efficiency of its component parts, namely, the propulsion motor and the associated inverter. This paper is focused on the efficiency of the inverter and analyzes the improvement that follows from the replacement of the silicon (Si) IGBT devices with silicon carbide (SiC) MOSFETs. To this end, the paper starts by deriving the voltage-current solicitations of the inverter over the working torque-speed plane of the propulsion motor. Then, a proper model of the power losses in the inverter over a supply period of the motor is formulated for the two types of device, including the integrated freewheeling diode. By putting together the voltage-current solicitations and the device power losses, the efficiency maps of the Si IGBT and SiC MOSFET inverters are calculated and compared over the torque-speed plane. The results for the Si IGBT inverter are supported by measurements executed on a marketed C-segment compact electric car, while the SiC MOSFET loss model is validated by an on-purpose built test bench. Finally, the overall efficiency of the propulsion drive is calculated by accounting for the motor efficiency. Main outcomes of the paper is a quantitative evaluation of both the improvement in the efficiency achievable with the SiC MOSFETs and the ensuing increase in the electric car range
Power and control characteristics of an isolated three-port DC-DC converter under DCM operations
No full textIsolated multiport DC-DC converters offer an efficient solution to meet the increasing demand of integrating energy delivery elements (EDEs) of various type like renewable energy sources (RESs), energy storage devices (ESDs) and mains. This paper deals with an isolated three-port DC-DC converter (3PC): two ports are connected to EDEs, respectively to a RES and an ESD, and a port is connected to the load. The 3PC characteristics in terms of power capabilities and control laws are investigated for two discontinuous conduction mode (DCM) operations and two operational working situations. The DCM operations are i) full DCM (FDCM), with all the ports operating in DCM, and ii) mixed discontinuous conduction mode, with the ESD-connected port operating in DCM and the other ports in continuous conduction mode. The working situations are i) both EDEs deliver power to the load, and ii) RES delivers power to ESD and the load. The theoretical findings are explicated by waveforms and diagrams
Mathematical Modeling, Laboratory Experiments, and Sensitivity Analysis of Bioplug Technology at Darcy Scale
No full textIn this paper, we study a Darcy-scale mathematical model for biofilm formation in porous media. The pores in the core are divided into three phases: water, oil, and biofilm. The water and oil flow are modeled by a generalized version of Darcy's law, and the substrate is transported by mechanical dispersion, diffusion, and convection in the water phase. Initially, there is biofilm on the pore walls. The bio-film consumes substrate for production of biomass and modifies the pore space, which changes the rock permeability. The model includes detachment of biomass caused by water flux and death of bacteria, and it is implemented in the MATLAB Reservoir Simulation Toolbox (MRST). We discuss the capability of the numerical simulator to capture results from laboratory experiments. We perform a novel sensitivity analysis based on sparse-grid interpolation and multiwavelet expansion to identify the critical model parameters. Numerical experiments using diverse injection strategies are performed to study the impact of different porosity/permeability relationships in a core saturated with water and oil. Introduction After primary and secondary production, up to 85% of the oil remains in the reservoir (Patel et al. 2015). Microbial improved and enhanced oil recovery (MIEOR) is one of the secondary and tertiary methods to increase the oil production using microorganisms (Wood 2019). Bioplug technology is an MIEOR strategy that comprises plugging the most permeable zones in the reservoir, which provokes water to flow through new paths, and recovering the oil in these new zones. However, microorganisms could also form biofilms in undesirable zones in the reservoir, leading to negative effects such as a decrease in water injectivity. Therefore, understanding the mechanisms involved in the development of biofilms is important to control their formation. The bioplug technology is intended for use on the field scale but to perform field-scale experiments is both time consuming and economically infeasible. Experiments in microsystems allow us to observe processes in greater detail, which leads to improvement of the experimental methods in core-scale experiments before field applications. For example, in Liu et al. (2019), the effects of flow velocity and substrate (also referred to as nutrients/food) concentration on biofilm in a microchannel was studied, finding values of substrate concentration and flow velocity for a strong plugging effect. Core samples from reservoirs can be used to study changes in permeability because of biofilm formation; for example, in Suthar et al. (2009), two-phase flow experiments were performed to study the selective plugging strategy for MIEOR. In that study, the MIEOR effects increased the oil recovery by approximately 25%. Mathematical models of bioplug technology are important because they help to predict the applicability of this MIEOR strategy and to optimize its benefits. In Kim (2006), a mathematical model for single-phase flow was proposed that includes changes of rock porosity and permeability as a result of biofilm growth. The author calibrated the model using data from experiments in silica sand columns and performed a simple sensitivity analysis (one-at-a-time technique) of a few model parameters. Li et al. (2011) built a mathematical model for two-phase flow including the effects of bio-surfactants and biomass on improving oil recovery. The authors also performed a simple sensitivity analysis of a few model parameters and compared the numerical results for two different porosity/permeability relationships. They concluded that MIEOR could enhance the oil recovery substantially if a larger capillary number is achievable. Nielsen et al. (2016) built a two-phase-flow mathematical model for MIEOR that included a decrease in oil/water interfacial tension by produced surfactants and selective plugging by microbes and metabolic products. The authors studied the oil recovery for diverse injection strategies, changing the pore volumes injected and substrate concentration at a fixed-flow rate. In Dzianach et al. (2019), the authors present a recent review of mathematical models of biofilms for diverse purposes. They concluded that cooperation between various disciplines is required to develop novel models. In this work, we present a two-phase core-scale model of bioplug technology. To our knowledge, this is the first mathematical model for two-phase flow and permeable biofilm. This mathematical model is the result of a research project where microbiologists, physicists, chemists, and mathematicians were involved. A detailed description of this project and previous publications can be found in Landa-Marbán (2019). In contrast to Li et al. (2011), in this work, we perform simulations to find at which part (low, medium, or high porosity) of five porosity/permeability relationships the oil recovery is more sensitive. Unlike Nielsen et al. (2016), we study the oil recovery for several injection strategies by changing the substrate concentration, flow rate, and injection direction. Sensitivity studies of mathematical models are of great interest because they provide estimates of the influence of the inputs (e.g., physical parameters) on a quantity of interest (e.g., biofilm formation). In Brockmann et al. (2006), a regional steady-state sensitivity analysis was performed to identify parameters with the largest impact on a mathematical model for deammonification in biofilm systems. Sensitivity analysis by means of Sobol decomposition provides rigorous estimates of parameter dependencies but are prohibitively expensive to compute if the number of parameters is large. This is remedied for smooth problems by first computing spectral (generalized polynomial chaos) expansions in the parameters, which then leads to efficient evaluation of the sensitivity indices via post-processing of spectral coefficients (Sudret 2008). The latter method was used in Landa-Marbán et al. (2019), where a global sensitivity analysis was performed using Sobol indices to identify the critical parameters of a pore-scale model for permeable biofilm. In this paper, we introduce a different approach that can also be used for nonsmooth mathematical models in the dependent parameters, where spectral expansions with global smooth-basis functions are not a robust choice. We propose a two-stage method where we first useThe work of DLM, GB, BFV, KK, PP, and FAR was partially supported by the Research Council of Norway through Projects IMMENS 255426, MICAP 268390, and CHI 255510. ISP was supported by the Research Foundation-Flanders Belgium, through the Odysseus program (Project G0G1316N) and an Akademia grant from Equinor ASA. The authors also appreciate the support from Equinor ASA related to the experimental work reported herein
- …
