Control of energy storage system integrating electrochemical batteries and SC for grid-connected applications

Ancillary services offered by renewable energy sources frequently requires the capability of bidirectional power flow and power reserve, so an energy storage system (ESS) is a solution for this requirement. A large variety of ESS solutions are in the market, and frequently are mixed to optimize the global performance. This paper presents the integration of supercapacitors (SC) and electrochemical batteries for grid-supporting applications. The large operating voltage range of a SC requires a power conversion stage to adapt the energy stored into a common dc-bus composed by a battery bank. This is achieved through bidirectional dc-dc interleaved buck/boost converters feeding a common higher-voltage dc-bus, composed by the battery. In order to integrate the energy storage mix to the grid, through a grid-supporting inverter, a power control loop has been implemented with the goal of take advantage of the high dynamic performance of the SC bank and high reserve capacity of the battery system.