Investigating electrical contact resistance losses in lithium-ion battery assemblies for hybrid and electric vehicles

Lithium-ion (Li-ion) batteries are favored in hybrid-electric vehicles and electric vehicles for their outstanding power characteristics. In this paper the energy loss due to electrical contact resistance (ECR) at the interface of electrodes and current-collector bars in Li-ion battery assemblies is investigated for the first time. ECR is a direct result of contact surface imperfections, i.e., roughness and out-of-flatness, and acts as an ohmic resistance at the electrode-collector joints. A custom-designed testbed is developed to conduct a systematic experimental study. ECR is measured at separable bolted electrode connections of a sample Li-ion battery, and a straightforward analysis to evaluate the relevant energy loss is presented. Through the experiments, it is observed that ECR is an important issue in energy management of Li-ion batteries. Effects of surface imperfection, contact pressure, joint type, collector bar material, and interfacial materials on ECR are highlighted. The obtained data show that in the considered Li-ion battery, the energy loss due to ECR can be as high as 20% of the total energy flow in and out of the battery under normal operating conditions. However, ECR loss can be reduced to 6% when proper joint pressure and/or surface treatment are used. A poor connection at the electrode-collector interface can lead to a significant battery energy loss as heat generated at the interface. Consequently, a heat flow can be initiated from the electrodes towards the internal battery structure, which results in a considerable temperature increase and onset of thermal runaway. At sever conditions, heat generation due to ECR might cause serious safety issues, sparks, and even melting of the electrodes.     

Rotor/Stator Internal Phase to Phase Fault Detection in Three-Phase Wound Rotor Induction Machines

Abstract

This paper presents a novel method based on Magnetic Equivalent Circuit (MEC) to model the wound rotor three-phase induction machine under healthy and faulty conditions. Different parameters of machine such as the number of poles, number of slots, winding configuration and dimension can be selected based on designed properties of a given machine. Internal phase to phase fault is also detected by stator current signature analysis in dq frame. Saturation effect is modeled by a tunable function as well as the core nonlinearity characteristic is considered. Finally, Finite Element Method (FEM) is used to evaluate the accuracy of the proposed MEC model. Short computational time of MEC method shows that this model is suitable for electrical machine modeling and analysis.     

Design optimization of a pattern reconfigurable microstrip antenna using differential evolution and 3D EM simulation‐based neural network model

In this work, design optimization of a varicap diode loaded antenna consisting of four identical rectangular microstrips is presented as a pattern reconfigurable antenna at 5.2 GHz. The microstrips are printed on the front of a FR4 substrate with the dimensions of 40 mm × 25 mm and ε _r = 4.6, h = 1.58 mm and probe‐fed via a coupling using a rectangular microstrip line symmetrically placed between them. In first stage, S₁₁ of the antenna are obtained as its real and imaginary parts as continuous functions of geometry of the microstrip components within 3 to 7 GHz using multi‐layer perceptron (MLP) trained and validated by 3D EM simulated data. In order to determine the most suitable (MLP) architecture and training algorithm, 20 different MLP architectures are tested. Then, S₁₁ are optimized with respect to the geometry parameters using differential evolution algorithm and MLP based model. The antenna is prototyped with the optimally selected parameters and measured. From the comparison of simulation and measurement results, it can be observed that the measurement results agree with the simulation results, thus it can be concluded that the proposed antenna is a simple and successful design subject to the design purposes with together its design methodology.     

Development of the ball-spine algorithm for the shape optimization of ducts containing nanofluid

ABSTRACT

In this paper a novel shape design method is introduced for the numerical solution of inverse heat convection problems (IHCPs) of nanofluids. The proposed method is a novel extension of the ball-spine algorithm (BSA) inverse method, which is recently adapted for inverse heat transfer problems (IHTPs). Here it is shown how, by a novel physical-sense remedy, the method is applicable to IHCPs as well. In this respect, after validation of the proposed method, two types of IHCPs are introduced and numerically solved. In both types of introduced inverse problems, the objective is shape optimization of a duct containing such steady-state incompressible laminar nanofluid flow that it satisfies a prescribed heat flux distribution along the walls of the geometry. The results show merits and robustness of the BSA application in capturing the target geometry corresponding to a given heat flux distribution in forced heat convection problems with a low computational cost.     

A New Verifiable Multi-secret Sharing Scheme Based on Bilinear Maps

In a (t, n)-threshold multi-secret sharing scheme, several secrets are shared among n participants in such a way that any t (or more) of them can reconstruct the secrets while a group of (t − 1) can not obtain any information. Therefore, when such schemes are used to distribute sensitive information over a network, fault tolerance property is achieved since even if n − t of the nodes go out of function, the remaining t nodes suffice to recover the information. In 2009, Wang et al. proposed a verifiable (t, n)-threshold multi-secret sharing scheme (WTS) based on elliptic curves in which the secrets can change periodically [Wireless Pers. Commun., Springer-Verlage, doi:. In this paper, we propose a verifiable (t, n)-threshold multi-secret sharing scheme based on bilinear maps. Our scheme does not require a secure channel and participants can verify the shares pooled in the reconstruction phase. Our proposed scheme is multi-use such that in order to change the secrets, it is sufficient to renew some public information. Furthermore, the proposed scheme is flexible to the threshold value. Therefore, our proposed scheme has all the merits of (WTS), however, we achieve two major improvements. First when the secrets are to be changed, we require to publish fewer public values. This reduction can be very important in certain applications such as steganographic use of secret sharing schemes. The second is that (WTS) is designed with the assumption that the number of secrets (m) is equal to the threshold t so that the case m > t is handled by repeating the scheme é \fracmt ù{\left\lceil \frac{m}{t}\right\rceil} times. However, in designing the scheme we do not assume any restrictions on the number of secrets.     

An efficient inverted organic solar cell with improved ZnO and gold contact layers

This paper presents a high efficiency (～3.8%) inverted organic photovoltaic devices based on a P3HT:PCBM bulk heterojunction (BHJ) blend with improved electron- and hole-selective contact layers. Zinc oxide (ZnO) nanoparticle films with different thicknesses are deposited on the transparent electrodes as a nano-porous electron-selective contact layer. A thin gold film is used between the BHJ photoactive layer and the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), which improves the wettability and significantly enhances the stability of the device (>50 days of air exposure). Photovoltaic device parameters such as power conversion efficiency (PCE) and external quantum efficiency (EQE) are systematically examined for inverted devices with different thicknesses of ZnO and gold layers in comparison to the non-inverted and reference inverted devices with no contact layers. The optimized organic devices with ZnO and Au contact layers show exceptional short circuit currents (in excess of 13 mA/cm²), in comparison to the reference devices, which is related to increased quantum efficiency of the device observed in measured EQE experiments. These results are important for development of high efficiency and stable all-printed organic solar cells and point out the role of contact layers, in particular, ZnO conductivity and morphology in the device performance.     

Improvement properties of nylon fabric by corona pre-treatment and nano coating

This article tries to represent a supplemental method based on surface modification in order to optimizing the per cent of nano cohesion to give the better performances, such as antibacterial resistance and UV-blocking characteristic (especially in nano-ZnO), which nanoparticles carry inherently. Corona treatment was used to modify the surface of Nylon 6 fabrics in Sixdifferent conditions (related to power and passages). Treated fabrics were dyed with acidic dye and imbued with nano-ZnO simultaneously and antibacterial property, dye absorption and UV-blocking characteristic of samples were investigated. Scanning electron microscopy (SEM) was used to observe a porous Nylon fibre consisting of nano-ZnO. By increasing the power and number of passages of the corona atmosphere in which samples were contacted with, the water absorption increased. The result demonstrated that by increasing power and passages of corona treatment, dye absorption decrease likely due to the increase of the nano-ZnO cohesion. UV blocking increased in relation with increasing power and passages of corona treating. Results from antibacterial property on samples showed that by increasing the power and passages of corona treatment, the fabrics became more resistance to Staphylococcus aureus and Escherichia coli bacteria.     

Novel polyfuran/functionalized multiwalled carbon nanotubes composites with improved conductivity: Chemical synthesis,characterization, and antioxidant activity

Novel composites containing very small quantities of functionalized multiwalled carbon nanotubes (MWCNTs‐COOH; 0.025, 0.050, and 0.075 g), and furan were synthesized via in situ chemical oxidative polymerization. The polymerization was carried out in nitromethane at room temperature using anhydrous iron (III) chloride (FeCl₃) as an oxidant. The nanocomposites were characterized by Fourier transform infrared, ultraviolet–visible, X‐ray diffraction, differential scanning calorimetry, and field emission scanning electron microscopy. All synthesized composites were crystalline and showed good solubility in dimethyl sulfoxide and N‐methyl 2‐pyrrolidone. The conductivity of composites was measured with a four‐probe method, and it was found that the electrical conductivity increased by increasing the amount of MWCNTs‐COOH. The maximum electrical conductivity value (6.68 × 10⁻⁴ S cm⁻¹) was obtained for polyfuran/MWCNTs‐COOH (1:0.075, v/w). The resulting composites were analyzed for their antioxidant activity using 2,2‐diphenyl‐1‐picrylhydrazyl assay. The results showed that the antioxidant activity of the composites increased by increasing the amount of MWCNTs‐COOH in nanocomposite. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers