268 research outputs found
A novel architecture of a bidirectional bridgeless interleaved converter for EV battery chargers
This paper presents a novel architecture of a
bidirectional bridgeless interleaved converter for battery
chargers of electric vehicles (EVs). The proposed converter is
composed by two power stages: an ac-dc converter that is used to
interface the power grid and the dc-link, and a dc-dc converter
that is used to interface the dc-link and the batteries. The ac-dc
converter is an interleaved bridgeless bidirectional boost-type
converter and the dc-dc converter is a bidirectional
buck-boost-type converter. The proposed converter works with
sinusoidal grid current and with high power factor for all
operating power levels, and in both grid-to-vehicle (G2V) and
vehicle-to-grid (V2G) operation modes. In the paper is described
in detail the proposed converter for EV battery chargers: the
circuit topology, the principle of operation, the power control
theory, and the current control strategy. Several simulation
results for both G2V and V2G operation modes are presented.Fundação para a Ciência e Tecnologia (FCT
Comparison of current-source and voltage-source shunt active power filters for harmonic compensation and reactive power control
This paper presents the comparison between two
three-phase Shunt Active Power Filters (SAPFs), one with
Current-Source Inverter (CSI) and the other with
Voltage-Source Inverter (VSI), which are used to compensate
current harmonics and to control reactive power. The control
algorithm of both SAPFs is based on the Instantaneous Reactive
Power Theory (p-q Theory). The comparison here presented
focuses on the Total Harmonic Distortion (THD) and RMS
values of the compensated currents, and in the Total Power
Factor (TPF) of the installation.Fundação para a Ciência e a Tecnologia (FCT
A novel concept of unidirectional bridgeless combined boost-buck converter for EV battery chargers
This paper presents a novel concept of
unidirectional bridgeless combined boost-buck converter for
electric vehicles (EVs) battery chargers. The proposed converter
is composed by two power stages: an ac-dc front-end converter
used to interface the power grid and the dc-link, and a dc-dc
back-end converter used to interface the dc-link and the
batteries. The ac-dc converter is a bridgeless boost-type
converter and the dc-dc converter is an interleaved buck-type
converter. The proposed converter operates with sinusoidal grid
current and unitary power factor for all operating power levels.
Along the paper is described in detail the proposed converter for
EV battery chargers: the circuit topology, the different stages
describing the principle of operation, the power control theory,
and the current control strategy, for both converters. Along the
paper are presented several simulation results for a maximum
power of 3.5 kW.Fundação para a Ciência e Tecnologia (FCT
Tube-jack testing for irregular masonry walls: Regular masonry wall testing
This paper presents the continued development of a novel non-destructive testing method termed tube-jack
testing. The goal of the tube-jack system is to provide an enhanced and less destructive method than traditional flatjack testing for determination of mechanical characteristics and local stress states in irregular masonrywalls. Single tubejack testswere performed, using previously developed rubber tube-jacks, in regular masonry walls of granite and cementlimemortar. A traditional flat-jack test was also performed in the same masonry wall. Conclusions suggest that tube-jacks are successful in applying pressure to the masonry at low
stress states.The authors would like to acknowledge the Fundação para a Ciência e Tecnologia, which supported this research work as a part of the Project “Improved and innovative techniques for the diagnosis and monitoring of historical masonry”, PTDC/ECM/104045/2008
Alkali Iodide Deep Eutectic Solvents as Alternative Electrolytes for Dye Sensitized Solar Cells
PTDC/QEQ- QFI/1971/2014
POCI- 01-0145-FEDER-016387Different alkali deep eutectic solvents (DES), such as LiI:nEG, NaI:nEG, and KI:nEG, have been tested as electrolytes for dye sensitized solar cells (DSSCs). These DSSCs were prepared using pure DES or, alternatively, DES combined with different amounts of iodine (I2). The most important parameters, such as open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF), and the overall conversion efficiency (η), were evaluated. Some DES seem to be promising candidates for DSSC applications, since they present higher VOC (up to 140 mV), similar FF values but less current density values, when compared with a reference electrolyte in the same experimental conditions. Additionally, electrochemical impedance spectroscopy (EIS) has been performed to elucidate the charge transfer and transport processes that occur in DSSCs. The values of different resistance (Ω·cm2) phenomena and recombination/relaxation time (s) for each process have been calculated. The best-performance was obtained for DES-based electrolyte, KI:EG (containing 0.5 mol% I2) showing an efficiency of 2.3%. The efficiency of this DES-based electrolyte is comparable to other literature systems, but the device stability is higher (only after seven months the performance of the device drop to 60%).publishersversionpublishe
A novel multilevel solid-state transformer for hybrid power grids
This paper presents a new proposed topology of a
solid-state transformer (SST) for application in hybrid power
grids (ac and dc), in which the possibility of operating with
various voltage levels (multilevel) in both sides is the main
characteristic. At the interface with the power grid (primary
side), the proposed SST consists of an ac-dc converter in Y
configuration that guarantees operation with five levels in each
phase-to-neutral voltage. To establish the hybrid power grid on
the secondary side, the SST is composed of a dc-ac converter in
Y configuration to establish an ac-grid, also operating with five
levels in each phase-to-neutral voltage, and by a dc-dc converter
to establish a dc-grid, which operates with three voltage levels.
The interface between the converters of the primary side and
the secondary side is guaranteed by an intermediary isolated
dc-dc converter. As fundamental requirements, the proposed
SST operates with balanced and sinusoidal currents on the
primary side, and with balanced and sinusoidal voltages on the
secondary side (ac-grid), as well as controlled voltages and
currents on the dc-grid. Throughout the paper, the proposed
topology for the SST is described in detail, with the operating
principle of each converter being presented. The obtained
results, both on steady-state and transient-state, for several
main operating conditions, prove the correct functioning of the
proposed SST, highlighting important features that
contextualize the operation of the proposed SST in smart grids.This work has been supported by FCT -Fundacao para a Ciencia e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT
Mass spectrometry parameters optimization for the 46 multiclass pesticides determination in strawberries with gas chromatography ion-trap tandem mass spectrometry
Multiclass analysis method was optimized in order to analyze pesticides traces by gas
chromatography with ion-trap and tandem mass spectrometry (GC-MS/MS). The influence of some
analytical parameters on pesticide signal response was explored. Five ion trap mass spectrometry
(IT-MS) operating parameters, including isolation time (IT), excitation voltage (EV), excitation time
(ET),maximum excitation energy or “q” value (q), and isolationmass window (IMW) were numerically
tested in order to maximize the instrument analytical signal response. For this, multiple linear
regression was used in data analysis to evaluate the influence of the five parameters on the analytical
response in the ion trap mass spectrometer and to predict its response. The assessment of the five
parameters based on the regression equations substantially increased the sensitivity of IT-MS/MS in
the MS/MS mode. The results obtained show that for most of the pesticides, these parameters have a
strong influence on both signal response and detection limit.Using the optimized method, a multiclass
pesticide analysis was performed for 46 pesticides in a strawberry matrix. Levels higher than the limit
established for strawberries by the European Union were found in some samples
Unified power converter based on a dual-stator permanent magnet synchronous machine for motor drive and battery charging of electric vehicles
An electric vehicle (EV) usually has two main power converters, namely one for the motor drive system and another for the battery-charging system. Considering the similarities between both converters, a new unified power converter for motor drive and battery charging of EVs is propounded in this paper. By using a single unified power converter, the cost, volume, and weight of the power electronics are reduced, thus also making possible a reduction in the final price of the EV. Moreover, the proposed unified power converter has the capability of bidirectional power flow. During operation in traction mode, the unified power converter controls motor driving and regenerative braking. Additionally, during operation in battery-charging mode, with the EV plugged into the electrical power grid, the unified power converter controls the power flow for slow or fast battery charging (grid-to-vehicle (G2V) mode), or for discharging of the batteries (vehicle-to-grid (V2G) mode). Specifically, this paper presents computer simulations and experimental validations for operation in both motor-driving and slow battery-charging mode (in G2V and V2G modes). It is demonstrated that the field-oriented control used in the traction system presents good performance for different values of mechanical load and that the battery-charging system operates with high levels of power quality, both in G2V and in V2G mode.This work was supported by the Portuguese Foundation of Science and Technology
(FCT) (in Portuguese, Fundação para a Ciência e Tecnologia) within the R&D Units Project Scope:
UIDB/00319/2020. This work was also supported by the FCT Project DAIPESEV PTDC/EEIEEE/30382/2017 and by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017. T.J.C.S.
is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by the FCT
The effect of levodopa on postural stability evaluated by wearable inertial measurement units for idiopathic and vascular Parkinson’s disease
BACKGROUND:
Postural stability analysis has shown that postural control is impaired in untreated idiopathic Parkinson's disease (IPD), even in the early stages of the disease. Vascular Parkinson's disease (VPD) lacks consensus clinical criteria or diagnostic tests. Moreover, the levodopa effect on postural balance remains undefined for IPD and even less so for VPD.
OBJECTIVE:
To characterize postural stability, using kinematic analysis with wearable inertial measurement units, in IPD and VPD patients without clinical PI, and to subsequently analyze the response to levodopa.
METHODS:
Ten patients with akinetic-rigid IPD and five patients with VPD were included. Clinical and postural stability kinematic analysis was performed before and after levodopa challenge, on different standing tasks: normal stance (NS), Romberg eyes open (REO) and Romberg eyes closed.
RESULTS:
In the "off state", VPD patients had higher mean distances and higher maximal distance of postural sway on NS and REO tasks, respectively. VPD patients maintained a higher range of anterior-posterior (AP) postural sway after levodopa. In the absence of PI and non-significant differences in UPDRS-III, a higher mPIGD score in the VPD patients was mainly due to gait disturbance. Gait disturbance, and not UPDRS-III, influenced the degree of postural sway response to levodopa for VPD patients.
CONCLUSION:
Quantitative postural sway evaluation is useful in the investigation of Parkinsonian syndromes. VPD patients have higher AP postural sway that is correlated with their gait disturbance burden and also not responsive to levodopa. These observations corroborate the interconnection of postural control and locomotor networks
- …