A Soft-Switched Multi-Port Converter for PV/Supercapacitors Hybrid Systems Enabling Frequency Response Services

Supercapacitors (SC) have superior performance for frequency response services in grid-tied photovoltaic (PV) systems owing to high power density. However, their variable voltage makes PV/SC hybridization quite challenging. The current body of literature lacks solutions that offer either a substantial step-up gain for the SC ports when controlled as a voltage source or a significant capability for high current discharging when controlled as a current source. To tackle this concern, this paper proposes a new compact multi-port dc/dc converter that integrates SC at the PV side by modifying the standard boost converter with three additional switches (two switches are soft switched and one is hard switched with low voltage) and three diodes. This topology allows SC operation at almost their entire voltage range, while a decoupling control method ensures separate regulation of the PV array and SC. The complete control scheme leverages both the SC and PV array for frequency response and comprises voltage recovery and protection for the SC. The proposed system is supported by theoretical analysis and design recommendations, as well as experimental validation results on a 675 Watt lab prototype.