Supercapacitor to Provide Ancillary Services With Control Coordination

This paper proposes a dynamic frequency support scheme of a supercapacitor energy storage system (SCESS) in coordination with run-of-the-river-based pumped storage hydropower (PSH) to enhance the short-term frequency stability in a power system that has a high penetration of renewable energy. To achieve this, the proposed coordinated frequency controller (CFC) enables the SCESS and PSH plant to provide the frequency response. The CFC scheme employs a dynamic droop characteristic in parallel with an integral controller and a distribution function. The dynamic droop characteristic determines the power production for frequency regulation employing a variable gain, which varies with the total capacity of the frequency control units and magnitude of the system frequency error with time; the gain increases with the frequency error, and thereby, arresting the frequency nadir at a higher level than in the conventional droop characteristic. In addition, the distribution function dispatches the power from the dynamic droop and integral controller to the control units in proportion to their headrooms; furthermore, the distribution function considers a sudden loss of generation from an SCESS by its operational constraint during the frequency support. Thus, the proposed dynamic frequency support scheme can enhance the short-term frequency stability for a frequency event.