Energy management in Converter-Interfaced Renewable Energy Sources through ultracapacitors for provision of ancillary services

The ever-growing penetration of Converter-Interfaced Renewable Energy Sources (CI-RES) and the gradual decommission of synchronous generators (SGs) are posing several challenges to guarantee the stability and robustness of the electric power system. A possible solution to overcome the foreseen problems is to enable the provision of ancillary services (AS) by advanced CI-RES emulating the SG performance. However, given the fact that most of the CI-RES operate at maximum power point, it will be required to rely on energy storage systems (ESS) to deal with active power related ASs. The ESS integration can be done in a straightforward manner within the CI-RES DC bus by means of a DC/DC converter. It is required, however, an adequate DC energy management to properly control the DC bus voltage, the ESS energy and the power delivered to the grid by the primary power source. This is a major challenge which must be solved to unlock the AS provision by means of CI-RES. With this regard, the main contribution of the paper is the design of an energy management system to simultaneously regulate the CI-RES DC bus voltage using the UC and also maintain the UC voltage within their safety limits while a given AS is provided. The control strategy is validated experimentally using a prototype with results that reveal a reliable and stable operation