Effect of Weighting Strategies on Taguchi-Based Optimization of the Four-Stage Constant Current Charge Pattern

Abstract

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.