In this paper, we propose a novel charge-equalization circuit for series-connected batteries. The circuit is composed of an intermediate resonant energy tank, formed by an inductor and a capacitor, and selection switches connected to each battery. The advantage of the proposed circuit is that an exchange of unbalanced charge can be established between any two batteries via the intermediate energy tank. In addition, more than one adjacent battery can serve as a charge-transference party on either side through proper activation of the associated selection switches. Moreover, by virtue of the resonant tank, zero-current switching can be achieved to significantly reduce the transference losses. A laboratory circuit with a control unit was designed for eight 2.5 Ah lithium iron phosphate (LiFePO4) batteries in series. The test results demonstrate that the proposed charge-equalization circuit can realize charge balance effectively. With the charge-equalization circuit, the worst open-circuit voltage difference can be reduced to less than 20 mV under offline conditions, which helps the batteries operate more efficiently.
The purpose of this study was to examine the fracture toughness of epoxy-based graphene nanocomposites. The single edge notched bending (SENB) samples with precrack tips were created by either tapping or sliding methods. For the tapping method, a single tap was conducted on a razor blade such a crack with a length of 2 mm was instantly propagated. For the sliding method, a razor blade was slid forward and backward into the samples, and a crack was generated with the blade edge. The SENB samples with graphene loadings (0.15 and 0.3 wt%) were subjected to three-point bending tests to evaluate fracture toughness. Results indicated that the graphene loading did not considerably affect the fracture toughness of the samples with tapping-induced precrack tips. However, the fracture toughness of the samples with sliding-induced precrack tips decreased as the graphene loading increased. For the 0.3-wt% graphene nanocomposites, the fracture toughness levels of the samples with sliding- and tapping-induced precrack tips were equal. In order to explicate the experimental results, the plastic zone sizes around the crack tip were evaluated using finite element analysis. For the sharp precrack tips (tapping method), the plastic zone was comparatively small (brittle behavior); hence, the effect of graphene on the inception of crack extension was minimal. Nevertheless, for blunt crack tips (sliding method), the plastic zone was larger and the size decreased as graphene loading increased; thus, the fracture behavior measured from the sliding method was dramatically influenced by the graphene loading.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.