Optimization based energy control for battery/super-capacitor hybrid energy storage systems

Batteries have been widely used as electrical energy storage units nowadays. However, due to their low power-density, it is usually necessary to combine batteries with other energy storage units, such as super-capacitors, in hybrid energy systems. In this paper, an optimization based control strategy is proposed to improve the energy efficiency as well as battery life time for battery semi-active hybrid systems. Sharing the similar idea as average current strategy but without any predefined driving cycle, this strategy aims to converge the current of the battery pack to the average current of the test trip by mainly enforcing the energy left in the super-capacitor pack to be same as its initial state while to maintain the current variation as small as possible. To achieve those two objectives, a two-objective optimization problem, whose objectives represents the preferences of the battery and supercapacitor packs, is formed and easily solved by using KKT conditions at any control point. The simulation results of this strategy are compared with those from average current strategy, and show that the proposed strategy can achieve comparable performance.