Control of Energy Storage System Integrating Electrochemical Batteries and Supercapacitors for Grid-Connected Applications

The implementation of ancillary services in renewable energy based generation systems requires controlling bidirectional power flow. For such applications, integrated energy storage systems (ESSs) in such generation platforms have emerged as a promising solution. However, a large variety of ESS solutions are available in the market, and even hybrid systems are proposed to optimize the overall performance. In this regard, the integration of supercapacitors (SCs) and electrochemical batteries is an attractive and feasible solution, as it takes the most of the combination of the large storage capacity of batteries with the high dynamic performance of SCs. This combination enables the implementation of energy and power services, such as inertia emulation, black start, or power oscillation damping among others. This solution avoids oversizing ESS and enlarges the battery lifetime, since the SCs absorve the high dynamic response meanwhile the battery feeds an attenuated power profile. This paper presents a strategy to manage mixed energy storage technologies, composed by a direct connection of a battery and an SC bank interfaced through a dc-dc converter. A power control loop distributes the power flow through each element in order to achieve an optimized performance, meanwhile, it permits to provide grid-frequency support and minimizes the number of cycles applied to the battery. The analysis made and the initial sections are endorsed by simulation and experimental results collected in a 50-kW test-bench.