Dynamic thermal rating (DTR) is a technique that can effectively reduce the complexity of the decision-making processes for a smart grid. IoT-based DTR monitoring systems can be used to achieve reliable and low-cost remote monitoring of power grids, but this method is heavily reliant on collecting accurate real-time meteorological data by sensors deployed on the power lines. However, deploying sensors on each span of the line may not be feasible, due to the high cost of such sensors. Thus, this study proposes a modified binary particle swarm optimization (MBPSO) strategy to solve multi-objective combinational decision problems. The proposed method is able to determine the minimum number of sensors required to achieve nearly ideal performance. A 161 kV line located between Xizhi and Minquan, part of the Taiwan Power Company transmission system, was selected as the experimental target. The MBPSO algorithm was solved based upon hourly meteorological data provided by Taiwan’s Central Weather Bureau. The results obtained with the proposed method show that only one sensor needs to be deployed on the 3rd span of the line to effectively monitor more than 89.6% of high conductor temperature events, and the root mean square error on the reconstructed conductor temperature distribution is less than 0.8 ∘C.

For overhead power grids, unexpected serious line sagging of extra-high voltage transmission lines would easily lead to major blackouts. Different direct and indirect sag measuring methods have been proposed, but they all have their own limitations. In this study, an Internet of Things (IoT)-based sag-monitoring system is proposed, which is able to perform real-time detection of line sags. The whole system has been deployed on two 161-kV lines for long-term field testing. The effectiveness of the proposed sag-monitoring system is verified through both theoretical calculation and field measurements. In this sag-monitoring system, a sag-sensing module is equipped with an embedded triaxial accelerometer to detect line sags at different spans of a single circuit. A catenary equation that takes temperature dependency into consideration is derived, so the measured accelerometer parameters can be converted to accurate line sag values. The long-term testing results show that the proposed sag-monitoring system yields an average error of 2.09%. The average differences between the sag values coming from the proposed system and a commercial sag measuring device are relatively small (between 0.57% and 4.14%), which proves that the sag values provided by the proposed system are reliable and accurate in the long-term testing. In addition, compared to the other existing sag measuring methods, the advantages of employing the proposed system are high measurement accuracy, and enabling wide field implementation, online monitoring, long-term field operation, and real-time transmission.

This study presents a preliminary investigation report on an aging-level-based (ALB) charging strategy that is possible to extend the battery lifespan by varying the charge current according to the state of health of a cell as opposed to the standard constant-current constant-voltage (CC-CV) and a four-stage constant current (4SCC) methods. Tests of Sanyo UR14500P lithium-ion batteries in the cylindrical shape with a nominal voltage of 3.7 V and a rated capacity of 840 mAh have been carried out. The results demonstrate that the ALB charging with a CC charge profile is able to slow down the cell capacity fade by 3.84% compared with the standard CC charging after 120 cycles, which increases the lifetime of 40 cycles to 50 cycles. Besides, the ALB charging with a 4SCC charge profile is able to slow down the cell capacity fade by 2.55% compared with the standard 4SCC charging after 100 cycles, which prolongs the lifetime of 30 cycles to 40 cycles. Nevertheless, the ALB charging strategy with both the CC and 4SCC charge profiles has much longer charging time than those with the standard charging method, and the charging time increases by 22.5% and 10.71%, respectively.

This communication presents an improved design and implementation of a broadband circularly polarized antenna that features a size reduction, good axial-ratio bandwidth and good return loss bandwidth. The circuit comprises one Schiffman phase shifter that is used to obtain a wideband phase difference of 90°, and a pair of orthogonally positioned linearly polarized slot antennas with equal radiation strength that are used to accomplish a circular polarization by combining the horizontally and vertically polarized waves with a Wilkinson power divider. Measured results show that the 3 dB axial-ratio bandwidth of the proposed antenna can reach 81.5% (1.6-3.8 GHz), and the 10 dB return loss bandwidth is 100% (1.48-4.47 GHz).

This article proposes an experimental test to examine the effect of weighting strategies on Taguchi-based optimization of the four-stage constant current (4SCC) charging method. The performance objectives used in the test include charging time, normalized discharge capacity, charging efficiency, average cell temperature rises, and energy losses. To simplify the optimization problem, a scalarization approach incorporating multiobjective functions into a single solution is utilized in this article. There are two types of weights in the scalarization: equal and unequal weights. In the equal weighting strategy, each performance objective is equally important. In the unequal weighting strategy, by contrast, unequal weights represent the performance priority of an objective function. To investigate the effect of the equal weighting strategy, an equal weight of 1/5 is given to each performance objective. For the unequal weighting strategy, this article adopts a random integer ranging from 1 to 5, and a floating-point value from 0 to 1, so the sum of all weights will be equal to 1. The test utilizes Sanyo UR14500P batteries in the cylindrical shape with a nominal voltage of 3.7 V and a rated capacity of 840 mAh. The experimental results show that the charging efficiency remains approximately the same regardless of which weighting strategy is adopted. The equal-weighted 4SCC charging yields the largest nominal charged capacity (96.7%), the longest charging time (102 min), and the smallest average cell temperature rise (1.714 °C). Considering charging time reduction, however, the performance of the unequal-weighted 4SCC charging is significantly better than that of the equal-weighted 4SCC charging. In addition, the energy losses brought by applying the equal- and unequal-weighted 4SCC charging are roughly the same.

This paper assesses the behavior of electrical output for a Ballard Mark V 35-cell 5 kW PEMFC (proton exchange membrane fuel cell) stack-based dc-dc power conversion for applications in autonomous underwater vehicles (AUVs) under load changes. Since the fuel cell produces dc output voltage that is unregulated, pulsewidth modulated (PWM) dc-dc converters are connected to the output of the studied fuel cell for converting the unregulated voltage into a desired voltage level. The fuel cell model includes the double-layer charging effect, gases diffusion in the electrodes, and the thermodynamic characteristic. Moreover, PWM dc-dc converters are assumed to operate in continuous-conduction mode (CCM), and the compensator is designed with voltage-mode control. The models of the study's fuel cell and PWM dc-dc converters have been implemented in a Matlab/SIMULINK™ environment. The results show that the output voltages of the studied PEMFC connected with PWM dc-dc converters during a load change are stable.