Search

Hydrogen is an important alternative as a clean fuel for industry and power-to-gas energy storage. The water electrolysis process is a promising technology in green hydrogen production where proton exchange membrane (PEM) technology has been keenly interested. Industrial large-scale PEM electrolyzers need a high current power supply. When connected to an alternating current (AC) source, high current power rectifiers are used to convert AC to DC. Currently, the most commonly used topology in large-scale PEM electrolysis systems is the thyristor-based topology due to its technology maturity and low cost. However, this topology presents several drawbacks in terms of power quality and consequently leads to higher stack-specific energy consumption (SEC) and additional losses. In the present research, we demonstrate the potential power quality improvement for a 20 MW PEM water electrolysis system by rectifier topology upgrade. Rather than traditional thyristor-based topology, a 3-phase interleaved buck rectifier topology is proposed. The new topology presents advantages on both AC and DC sides via a validated simulation model, which is built using MATLAB/Simulink and then validated with experimental data from an industrial 20 MW PEM water electrolyzer at Air Liquide's Bécancour plant. Results show a great improvement in terms of power factor, Total Harmonic Distortion (THD), and DC-current ripple reducing the total losses and the SEC of the PEM stack, especially under partial load. Towards a higher power efficiency, the proposed rectifier topology may be considered in the construction of future large-scale PEM systems. • Reported the power quality of the world's largest PEM water electrolyzer (20 MW). • Modeled the power electronics performance for the 20 MW PEM water electrolyzer. • Validated the numerical model using test data from the 20 MW PEM hydrogen plant. • Proposed power quality improvement using topology optimization. [ABSTRACT FROM AUTHOR]

This paper presents a new fault-tolerant operation method of multiphase stacked interleaved Buck converter for green hydrogen production. An improved topology and new fault-tolerant control strategy is proposed. Multi-mode fault-tolerant operation of multiphase stacked interleaved Buck converter for different performance requirements of electrolyzer in hydrogen production system is realized. The multiphase stacked interleaved Buck converter can not only achieve elimination of output current ripple in normal operation mode, but also adopt different fault-tolerant modes according to different demands of electrolyzers in case of failure of any phase of converter. The proposed method is able to improve the availability of multiphase stacked interleaved Buck converter, reduce the times of equipment shutdown, and ensure the continuous operation of hydrogen production system from renewable energy sources. The effectiveness of the proposed method has been verified by experimental results. • An new topology and fault-tolerant control strategy is proposed for green hydrogen production. • The proposal not only achieves the current ripple elimination, but fault-tolerant operation in case of failure. • The proposed solution improves the system operation performance and reliability. • Experimental investigation of the proposed solution is provided. [ABSTRACT FROM AUTHOR]

Since the two last decades, hydrogen production has been attracting the attention of the scientific community thanks to its inherent very low pollution when energy coming from renewable energy sources (RESs) are used. However, it implies the use of DC/DC converters to interface source and load. These conversion systems must meet several requirements from current ripple point of view, energy efficiency, and performance to preserve the sustainability of hydrogen production. This article proposes the design and realization of a stacked interleaved buck converter to supply a proton exchange membrane electrolyzer. The converter is designed to ensure a low output current ripple and a suitable dynamic response to guarantee the reliability of the electrolyzer. A theoretical analysis of the converter, taking into account the dynamic model of the electrolyzer, and the design of the control system based both on feedforward and a feedback action is provided. The stability of the control system is discussed as well. The effectiveness of the model and the control algorithm has been verified by simulation and experimental results on a PEM electrolyzer at laboratory scale; the extension to higher power levels is discussed at the end. • Current requirements of DC-DC converters for electrolyzers are emphasized. • A stacked interleaved step-down converter is proposed for electrolyzers. • The controller is designed based on the electrical model of the electrolyzer. • The developed control has been validated both by simulations and experimentally. • The results demonstrate the effectiveness of the control to enhance performance. [ABSTRACT FROM AUTHOR]

In recent years, the use of electrolyzers to produce cleanly and efficiently hydrogen from renewable energy sources (i.e. wind turbines, photovoltaic) has taken advantage of a growing interest from researchers and industrial. Similarly to fuel cells, DC/DC converters are needed to interface the DC bus with the electrolyzer. Usually, electrolyzers require a low DC voltage to produce hydrogen from water. For this reason, a DC/DC buck converter is generally used for this purpose. However, other DC/DC converter topologies can be used depending on the feature of the electrolyzer and electrical grid as well. The main purpose of this paper is to present the current state-of-the-art of DC/DC converter topologies which can be combined with electrolyzers. The different DC/DC converter topologies are compared in terms of output current ripple reduction, conversion ratio, energy efficiency, and power switch fault-tolerance. Besides, remarks on the state-of-the-art and remaining key issues regarding DC/DC converters are provided. [ABSTRACT FROM AUTHOR]

This study aims to investigate the development of an Electrical Circuit Model (ECM) that represents the behavior of a PEM fuel cell system. The ECM parameters are identified based on sets of impedance data obtained by using a characterization process known as Electrochemical Impedance Spectroscopy (EIS). In this process, a small magnitude of alternating current sweeping a broad spectrum of frequencies is superimposed on a DC current drawn from the fuel cell while measuring the resulting voltage response. The measured impedance is fitted to an ECM using a nonlinear least-square fitting method. The proposed ECM is able to reflect the voltage response of the system to current ripples and represent the effect of the compressor. The proposed model is validated using a commercial fuel cell power module. In general, such model representation is useful for analyzing the effects of the operating conditions on the fuel cell performance, efficiency and durability. It also helps in comprehending the effects of current ripple on the fuel cell while operating with power-conditioning units [ABSTRACT FROM AUTHOR]

Abstract: In this paper a simple model for evaluating current ripple effects on commercial PEM fuel cells is presented. The model is formulated starting from the Randles equivalent circuit and extending it assuming a dielectric relaxation of the material to represent dynamic processes in the frequency range typical of inverter current ripple. The proposed equivalent circuit is experimentally validated on a 14 kW commercial Morphic PEM fuel cell at the frequencies of interest. Finally the effects of current ripple on losses and fuel cell efficiency are discussed. [Copyright &y& Elsevier]

Abstract: Polymer electrolyte fuel cells (PEFCs) fed by hydrogen were investigated with the aim of highlighting their behaviour during grid connected (GC) operation. Starting from the analysis of the systems working under practical conditions on the utility grid, the study was addressed to the materials degradation during GC applications. Endurance tests on 5 kW pre-commercial PEFC fuel cell systems were carried out at direct current constant load and in GC configuration. An evidence of disturbance on the FC system power output was observed. The study was focused on Low Frequency (LF) 100 Hz noise (current ripple) that can mainly affect the fuel cell performance and lifetime. In order to evaluate the issues that occurred on the active components of a PEMFC, when subjected to a current ripple, electrochemical characterizations were performed on single cells of 5 cm2 subjected to a dynamic load. Post mortem physico-chemical analyses showed materials degradation on the cathode catalyst associated to the current ripple. [Copyright &y& Elsevier]