Using the combination of batteries and ultra-capacitors to improve the performance and flexibility for energy storage systems

A certain number of batteries are connected in series to raise the DC bus voltage in energy storage systems (ESSs). The ratings of the discharging and charging currents of the batteries are limited. As a result, the dynamic performance of the battery cannot meet the requirements in some ESSs, which are installed to smooth the power from wind power generators. This paper proposes a structure that is a combination of ultra-capacitors and traditional batteries. With the help of the ultra-capacitors, two goals are achieved: (i) the terminal voltage is enhanced, and (ii) the dynamic performance of the ESS is improved. Control of the proposed ESS is discussed, and an experimental prototype is built to validate the working schemes. The proposed solution is highly modularized, and thus the electrical energy modules can be easily removed and installed.