A fuzzy compensation-Koopman model predictive control design for pressure regulation in proton exchange membrane electrolyzer

Abstract

Proton exchange membrane (PEM) electrolyzer have attracted increasing attention from the industrial and researchers in recent years due to its excellent hydrogen production performance. Developing accurate models to predict their performance is crucial for promoting and accelerating the design and optimization of electrolysis systems. This work developed a Koopman model predictive control (MPC) method incorporating fuzzy compensation for regulating the anode and cathode pressures in a PEM electrolyzer. A PEM electrolyzer is then built to study pressure control and provide experimental data for the identification of the Koopman linear predictor. The identified linear predictors are used to design the Koopman MPC. In addition, the developed fuzzy compensator can effectively solve the Koopman MPC model mismatch problem. The effectiveness of the proposed method is verified through the hydrogen production process in PEM simulation.

1. Introduction

Hydrogen plays an important role in developing an environmentally friendly energy system in the future of the world. Compared to non-renewable fossil fuels, hydrogen is used as a source of energy or fuel and may be the ideal energy carrier [1] due to its high energy content by mass without emitting pollutants or greenhouse gases. Traditionally, hydrogen can be produced from various sources including oil, natural gas, and coal. However, these methods of hydrogen production are highly polluting. In today's global low-carbon development, hydrogen production from water electrolysis is the most promising way. Hydrogen production by water electrolysis can use electrical or thermal energy generated from nuclear or renewable sources (i.e. wind and solar) with no carbon emissions during the process. There are three main types of water electrolysis hydrogen production technologies, depending on the type of electrolyzer: Alkaline water electrolysis (AWE), proton exchange membrane (PEM), and solid oxide electrolysis cells (SOEC) [2].

The poor quality of the hydrogen produced and the need for additional treatment are the drawbacks of AWE hydrogen production. The expensive electrode and electrolyte materials as well as the prolonged start-up and shutdown times are SOEC's drawbacks. Although the PEM technique has many advantages such as compact system design, higher hydrogen purity, faster transient response, higher current density, and higher voltage efficiency. However, the main disadvantages of PEM electrolyzer are the higher cost of components and lower durability compared to the alkaline electrolyzer [3], which severely limits the use of PEM electrolysis. Moreover, the high-pressure operation of the electrolyzer facilitates the delivery of hydrogen to the end user and reduces the energy consumed by further compression and storage of hydrogen. However, according to Fick's law of diffusion, gas permeability increases significantly with increasing pressure [4]. Correa et al. [5], Han et al. [6], and Koponen et al. [3] investigated the effect of the operating pressure on the electrolyzer performance from aspects including energy consumption, activation overpotential, efficiency, etc. The drawn conclusion shows that hydrogen production could be maximized by controlling the stack hydrogen outlet pressure as close to the storage pressure as possible, while the specific energy consumption of the PEM water electrolyzer increased at higher hydrogen outlet pressure. In summary, PEM water electrolysis needs to be carried out at appropriate operating pressures in many practical situations.