Modeling and Control Design for a Bidirectional DC-DC Converter System for Cyclic Operation of a Reversible Solid Oxide Electrolysis Cell Stack

This paper presents a design of a bidirectional DC- DC power electronic converter system enabling cyclic operation for a Reversible Solid Oxide Electrolysis Cell (RSO EC) stack for steam electrolysis. The cyclic operation of the RSOEC stack is investigated, and two different equivalent circuit models are presented for the mathematical representation of the stack's electrical dynamics: The well-established steady-state Resistive model and a novel Voigt model. From these, two combined mathematical models of the bidirectional Buck-Boost converter supplying the RSOEC stack are derived using the small-signal averaging technique. For tracking the cyclic output current reference to an RSOEC stack, two Proportional Integral Derivative with derivative Filter (PIDF) controllers are designed using the two combined mathematical models derived. Finally, the performances of the two PIDF controllers for the bidirectional DC-DC converter systems are compared and validated through simulations. The simulation results confirm the bidirectional Buck-Boost converter's ability to deliver cyclic bidirectional output current and demonstrate that the control tuned based on the Voigt mathematical representation of the RSOEC stack yields superior closed-loop performance in accordance with the control design requirements.