Direct integration of supercapacitors in CHB converter with low voltage components for Fast Frequency Reserve and enhanced response from Kaplan turbines

The paper investigates the feasibility, cost and performance of a Cascaded H-Bridge converter using low-voltage components and direct integration of supercapacitors to deliver short duration frequency regulatory services. Through coordination with a Kaplan turbine hydro power plant, the system may qualify for a further palette of regulatory power. Parallel MOSFET switches are considered as a low voltage alternative to high voltage IGBTs. Suitable configurations of supercapacitors in each submodule, number of submodules and configurations of switches are proposed to meet requirements for Fast Frequency Reserve with a nominal power of 5 MW within the limits of component ratings. A Matlab model is used to validate the function and performance of the converter. The system proposed meets criteria for supercapacitor balancing, temperature over semiconductor junctions while supplying Fast Frequency Reserve. The energy needed from the energy storage to meet activation time requirements for FCR-D when coordinated with the Kaplan turbine is quantified for two Kaplan turbine responses. A comparison of conduction and switching loss in the converter show that conduction loss from the internal resistance of the supercapacitors are the largest driver of loss in the system.