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Unscheduled charging of Electric Vehicles (EVs) may shift voltage unbalance beyond the desired limit. Effects of uncoordinated charging of EVs were assessed by calculating voltage magnitudes and voltage unbalances at the end node of a residential feeder. The assessment was illustrated by presenting loading conditions of distribution transformers and distribution lines. Power losses of these components also have been recorded. Four uptakes of EVs were considered based on the number of EVs per phase. These cases were simulated considering daily profiles of residential loads and EV loads. A 50% EVs uptake has led to an excessive voltage unbalance with a 3-phase 4-wire connection. However, only a 25% EVs uptake caused the violation of voltage unbalance with a 3-phase 3-wire connection. Therefore, 4-wire connections permit more uptake of EVs on the network than 3-wire connections, before voltage unbalances exceed their limits.

Abstract:In this paper, the charging loads of electric vehicles were controlled to avoid their impact on distribution networks. A centralized control algorithm was developed using unbalanced optimal power flow calculations with a time resolution of one minute. The charging loads were optimally reallocated using a central controller based on non-linear programming. Electric vehicles were recharged using the proposed control algorithm considering the network constraints of voltage magnitudes, voltage unbalances, and limitations of the network components (transformers and cables). Simulation results showed that network components at the medium voltage level can tolerate high uptakes of uncontrolled recharged electric vehicles. However, at the low voltage level, network components exceeded their limits with these high uptakes of uncontrolled charging loads. Using the proposed centralized control algorithm, these high uptakes of electric vehicles were accommodated in the network under study without the need of upgrading the network components.

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<p>This paper presents applications of lithium-sulfur (Li-S) energy storage batteries, while showing merits and demerits of several techniques to mitigate their electrochemical challenges. Unmanned aerial vehicles, electric cars, and grid-scale energy storage systems represent main applications of Li-S batteries due to their low cost, high specific capacity, and light weight. However, polysulfide shuttle effects, low conductivities, and low coulombic efficiencies signify key challenges of Li-S batteries, causing high volumetric changes, dendritic growths, and limited cycling performances. Solid-state electrolytes, interfacial interlayers, and electrocatalysts denote promising methods to mitigate such challenges. Moreover, nanomaterials have capability to improve kinetic reactions of Li-S batteries based on several properties of nanoparticles to immobilize sulfur in cathodes, stabilizing lithium in anodes while controlling volumetric growths. Li-S energy storage technologies are able to satisfy requirements of future markets for advanced rechargeable batteries with high-power densities and low costs, considering environmentally friendly systems based on renewable energy sources.</p>