It is preferable for the retired batteries to balance their states of health (SOH) in the battery energy storage system (BESS) since it can prolong the system lifetime and reduce the maintenance burden. So far, the corresponding balancing techniques mainly focus on either the SOH balancing among packs or the SOH balancing of cells inside a pack. This paper further proposes the multilayer SOH equalization scheme to equalize all cells' SOHs of large-scale BESS by comprehensively combining the pack SOH balancing strategy and the commercial cell equalization techniques. It is noted that the balancing schemes for pack and cell cannot be simply superimposed since packs and cells have totally different connection modes and are equipped with different types of balancing circuits. In specific, the modular multilevel converter (MMC) is assumed to coordinate the pack and cell SOH equalization schemes, where the charging/discharging power per submodule is properly adjusted according to the extent of cell SOH deviation and the extent of pack SOH deviation together. Matlab simulation and experimental results of a 10kWh MMC-BESS prototype verified the performance of the proposed method.

Smoothing power fluctuations and arranging reserves play a more crucial role in the secure and economic operation of the active distribution network (ADN), as the high penetration rate of uncertain renewable energy sources (RES) increases. In this article, a multitimescale ADN optimal dispatching model based on stochastic model predictive control (SMPC) is proposed to track the random fluctuation of RES and address the operation risk. First, load shedding and RES curtailment risk are quantified by a conditional value at risk based on the probability distribution and a reserve arrangement strategy considering the tradeoff between reserve cost and operation risk is further proposed. Second, the copula theory is introduced to establish a high-dimensional RES prediction error model for the purpose of capturing its spatial–temporal characteristics. Furthermore, according to prediction error distribution, based on the scenario method, typical RES output scenarios for the day-ahead, intraday, and real-time stages are generated. Then, a multitimescale optimal dispatching framework based on SMPC is established in which the outputs of units are optimized and coordinated under different time scales. Finally, simulation results on a modified IEEE 33-bus power system demonstrated the superiority of the proposed method in tracking the fluctuation of RES and also verify the effectiveness of the method to improve the economy of system operation.

The presence of a low density area is beneficial to the facilitation of the underwater pulsed spark discharge, which can be achieved by artificially injecting gas bubble in between the inter-electrode gap. The generation of intensive acoustic waves by such gas-bubble-guided spark discharges makes them promising underwater acoustic sources in multiple practical applications. This paper is aimed at comprehensive investigation of the guiding effect of the injected bubble on the pre-breakdown process of underwater pulsed spark discharges and potential correlations between their subsequent electrical and acoustic parameters with the purpose of optimizing the acoustic emission. The breakdown probability and the pre-breakdown delay were used to evaluate the general facilitation effect brought by the injected bubble. Experimental and numerical works have been conducted and allow observation on the dynamics of the injected bubble under the influence of the applied voltage. Different guiding modes of the injected bubble for plasma streamers' propagation have been observed regarding its relative position. The characteristics of the electrical properties of gas-bubble-guided spark discharges, including the plasma resistance and the plasma energy density, were analyzed by relating them with the breakdown voltage. The dependency of the acoustic wave amplitude and the acoustic efficiency on these electrical parameters was verified, which provides solid regulation principles for the optimization of the plasma-acoustic system for target practical applications.

Cross-linked polyethylene (XLPE) carries a high fire risk. In this paper, a cone calorimeter is used to carry out radiation ignition experiments, and the heat release rate (HRR), mass loss rate (MLR) and other combustion parameters of XLPE cables under three kinds of radiation intensity are measured. By comparing the ignition time and HRR of samples under different conditions, the following conclusions are drawn: (1) The ignition time of XLPE cables decreases significantly with the increase in external thermal radiation intensity. The critical ignition heat flux (CHF) is about 16.24 kW/m². (2) The HRR curve of XLPE is consistent with the characteristics of hot, thick material. The HRR rises rapidly to the first peak after ignition and then rapidly decreases. Then, it slowly rises to the second peak. Finally, it slowly decays until the combustion stops. (3) The first peak values of HRR of XLPE under different radiation intensities are almost the same. The time for the second peak of HRR is shorter, and the value is larger with the increase in external thermal radiation intensity. (4) The cable ignition model is established, which can simulate the cable ignition time well under different radiant heat flow conditions. (5) Based on the mathematical model, the ignition time trend with the thickness of sheath layer and conductive core layer as variables is deduced.