A Complete Frequency Response Service Scheme using PV-Supercapacitor Cascade Topology

Frequency response services have become more important than ever in an increasingly inertia-less power system. A promising way to provide such services in a photovoltaic (PV) system is by hybridizing with supercapacitors (SC) due to their high power density, long operating cycles and fast response. The challenge, however, with a PV/SC system is what topology can effectively integrate such devices with so low and variable voltage, as well as how to control them for optimal utilization of their very limited capacity. This paper builds upon a previously introduced PV/SC cascade topology and proposes a complete control scheme for frequency services. A power segregation mechanism infers how the power demand is shared between SC and PV array, accounting for the operational boundaries of the former and occasionally deciding short-term curtailments for the latter. The proposed scheme involves also a voltage recovery function to slowly get the SC voltage back to the steady-state value after a disturbance, the latter being calculated via a newly introduced methodology. MATLAB/Simulink simulations validate the control efficacy under a series of frequency disturbances.