Fast frequency response provision from large-scale hydrogen electrolyzers considering stack voltage-current nonlinearity

This paper investigates the fast frequency response (FFR) capability of large-scale hydrogen electrolyzers (HEs) and their contribution to frequency control in low-inertia conditions, with focus on understanding the impacts of stack voltage-current (V-I) nonlinearity. We propose a HE stack model which includes a variable internal resistance to capture its V-I nonlinear behaviour. We then study the negative impacts of this nonlinearity on HE FFR capability and its mitigation solutions via proposing design specifications for the HE power-electronics interface (PEI) (DC-DC-AC) control. To do so, first we highlight the need for simultaneous stack voltage-current control in HE active power (FFR) control and propose a relevant cascaded V-I controller for stack-side converter via novel HE stack equivalencing with a capacitor. Second, we modify the DC-link voltage level in the HE PEI to avoid the stack V-I nonlinear effect. Simulation results show how the stack V-I nonlinearity might limit the HE FFR potential and how the proposed PEI controller represents an effective solution.