A generic FPGA-based PWM generator with automatic device fault recovery for fuel cell,interleaved, multi-phase and multi-switch DC/DC boost converters

This paper describes the simulation and implementation of a generic FPGA-based PWM generator with automatic device fault recovery. This PWM generator is applied to multi-switch DC/DC boost converters for fuel cell applications; these converters have gained attention due to its reliability, equally-distributed power losses and reduced part count. In this paper, three different driving schemes for one phase and different legs are described and one driving scheme has been finally chosen. The operation of the proposed PWM generator with simulations and experimental results are shown. This PWM generator with automatic fault recovery, brings more reliability and fault robustness to fuel cell boost converters, making suitable to use in electric vehicle and uninterruptible power supplies (UPS). The method used in the PWM generator described on this paper, allows to change the number of devices working in DC/DC conversion, increasing the switching frequency and the duty cycle of the power switches, ensuring a DC/DC conversion without interruption.     

Efficient soft-switched boost converter for fuel cell applications

The dc voltage generated from fuel cell is low in magnitude, unregulated and load dependent. Hence, it is required to be regulated and boosted by high performance dc-dc converter. In this paper, a fully soft-switched pulse-width-modulated dc-dc boost converter has been proposed for fuel cell applications. The proposed converter operates at high switching frequency with high efficiency and large power to volume ratio. A laboratory prototype model of the proposed converter has been designed and fabricated for charging a battery bank at 110 V from a fuel cell stack SR-12 of Avista Lab. The experimental results were found in close agreement with the predicted behavior.     

Non-isolated multiphase boost converter for a fuel cell with battery backup power system

This work describes a step-up non-isolated DC/DC converter aimed for fuel cell stand-alone power systems. The proposed converter has the following features: simple structure based on the basic boost topology that reduces the number of components; it uses the interleaving technique in order to reduce the current ripple at the input and output sides, reduction of the inductors size, higher frequency that reduce the output filter capacitor and easier power losses management. In addition, the use of an inner current control loop in the input side assures power sharing and easy module parallelization. The converter feeds a backup battery that maintains a DC voltage level at the main bus. An outer battery-charging loop controls the converter. Experimental validation is given for a four-phases 1 kW prototype at 100 kHz PWM switching frequency connected to a Nexa Ballard (1.2 kW-46 A) PEM fuel cell.     

A suitable model plant for control of the set fuel cell−DC/DC converter

In this work a state and transfer function model of the set made up of a proton exchange membrane (PEM) fuel cell and a DC/DC converter is developed. The set is modelled as a plant controlled by the converter duty cycle. In addition to allow setting the plant operating point at any point of its characteristic curve (two interesting points are maximum efficiency and maximum power points), this approach also allows the connection of the fuel cell to other energy generation and storage devices, given that, as they all usually share a single DC bus, a thorough control of the interconnected devices is required. First, the state and transfer function models of the fuel cell and the converter are obtained. Then, both models are related in order to achieve the fuel cell+DC/DC converter set (plant) model. The results of the theoretical developments are validated by simulation on a real fuel cell model.     

Power switch failures tolerance and remedial strategies of a 4-leg floating interleaved DC/DC boost converter for photovoltaic/fuel cell applications

In recent years, many researchers have proposed new DC/DC converters in order to meet the fuel cell requirements. The reliability of these DC/DC converters is crucial in order to guarantee the availability of fuel cell systems. In these converters, power switches ranked the most fragile components. In order to enhance the reliability of DC/DC converters, fuel cell systems have to include fault-tolerant topologies. Usually, dynamic redundancy is employed to make a fault-tolerant converter. Despite this kind of converter allows ensuring a continuity of service in case of faults, the use of dynamic redundancy gets back to increase the complexity of the converter. In order to cope with reliability expectations in DC/DC converters, floating interleaved boost converters seem to be the best solution. Indeed, they have much to offer for fuel cells and DC renewable energy sources (i.e. photovoltaic system), including reduced input current ripple and reliability in case of faults. Despite the offered benefits of this topology, operating degraded modes lead up to undesirable effects such as electrical overstress on components and input current ripple increasing. The aim of this paper is to carry out a thorough analysis of these undesirable effects and to propose remedial strategies to minimize them.     

Design and experimental validation of a high voltage ratio DC/DC converter for proton exchange membrane electrolyzer applications

This paper deals with hydrogen production via water electrolysis, which is considered the most attractive and promising solution. Specifically, the use of renewable energy sources, such as wind electric power generators, is hypothesized for supplying the electrolyzer, aiming to strongly reduce the environmental impact. In particular, micro-wind energy conversion systems (μWECSs) are attractive for their low cost and easy installation. In order to interface the μWECS and the electrolyzer, suitable power conditioning systems such as step-down DC-DC converters are mandatory. However, due to the requested high conversion ratio between the DC bus grid, i.e. the output of a three-phase diode rectifier connected to the output of the electric generator, and the rated supply voltage of the electrolyzer, the classic buck converter alone is not suitable. Therefore, a converter is proposed and designed, consisting of a buck converter, a full-bridge IGBT converter, a single-phase transformer, and a diode bridge rectifier; LC filters are also included between buck and full-bridge converters, and at the output of the diode bridge rectifier with the aim of reducing the ripple on currents and voltages. The components of the described physical system from the output of the three-phase rectifier up to the electrolyzer are then modeled assuming the transformer as ideal, and the model is employed for designing a PI-type controller. Experimental results are provided in order to demonstrate the effectiveness of the developed converter and its control for these applications.     

Robust control of four-phase interleaved boost converter by considering the performance of PEM fuel cell current

Hydrogen associated with Proton Exchange Membrane Fuel Cell (PEMFC) as the prime candidate energy is becoming attention in transportation. However, the cost and the service lifespan are the main reasons that limit PEMFC wide application. In this paper, the super-twisting sliding mode (STSM) controller is designed for a four-phase interleaved boost converter (IBC) coupled with a PEMFC. The proposed controller can enhance the robustness of the output voltage while reducing the PEMFC current overshoot as much as possible for protection under a certain limitation of the PEMFC current ripple. The stability of the proposed controller is proved by the Lyapunov theorem. A typical proportional-integral (PI) controller based on ac small-signal model is designed for further comparison and discussion. The effectiveness of the STSM controller is further evaluated through experimental results obtained with a 1 kW fuel cell system based on a real-time hardware-in-the-loop system.     

Minimum time current controller design for two-interleaved bidirectional converter: Application to hybrid fuel cell/supercapacitor vehicles

In fuel cell hybrid vehicles (FCHV) with a supercapacitor (SC) used as auxiliary source of hybridization, classical SC converters limit the current tracking performance due to the presence of a large input inductance. A hardware solution to this issue consists in using an interleaved converter topology that enables considerably reducing the input inductance. To optimize interleaved converters usage, an intelligent control scheme that maximizes closed-loop performance in current tracking must be designed. For that purpose, we design two controllers: a transient-state controller and a steady-state one. The first controller is a bang-bang one that guaranties a fast transition from the initial condition to some closed region around the reference. The second controller ensures the local asymptotic stabilization of a certain desired limit cycle and is based on switching surfaces design. The proposed control scheme performances and robustness are evaluated through simulations with piece-wise constant source and reference current. Performances are also evaluated on a battery-like supercapacitor vehicle using an urban driving cycle.     

A high voltage ratio and low stress DC–DC converter with reduced input current ripple for fuel cell source

A new single-switch non-isolated dc–dc converter with high-voltage gain and reduced semiconductor voltage stress is proposed in this paper. The proposed topology is derived from the conventional boost converter integrated with self-lift Sepic converter for providing high voltage gain without extreme switch duty-cycle. The reduced voltage stress across the power switch enables the use of a lower voltage and R_DS-ON MOSFET switch, which will further reduce the conduction losses. Moreover, the low voltage stress across the diodes allows the use of Schottky rectifiers for alleviating the reverse-recovery current problem, leading to a further reduction in the switching and conduction losses. Furthermore, the “near-zero” ripple current can be achieved at the input side of the converter which will help improve the fuel cell stack life cycle. The principle of operation, and theoretical are performed. Experimental results of a 100 W/240 V_dc output with 24 V_dc input voltage are provided to evaluate the performance of the proposed scheme.     

Comprehensive analysis and design of multi-leg fuel cell boost converter

This paper presents the design and development of a practical multi-leg fuel cell boost converter. The applied multi-leg topology and the interleaved switching method can effectively reduce fuel cell current ripple to meet the suggested limitation of 4%. Input inductors play a critical role for ripple current reduction, while output capacitors are used for specified output voltage performance. In the selection of the input inductors and the output capacitors, this paper uniquely presents an analytic method for obtaining optimum parameter values. The design considerations include leg number, switching frequency, output loads, and dynamic response. Novel equivalent models with equivalent series resistors for multi-leg boost converters are proposed. This model can simplify the analysis of multi-leg converters and is thus used for compensation design. To verify the analytic results, Intersil ISL6556B integrated circuit is used to implement two-, three-, and four-leg fuel cell boost converters rated 1000 W. Finally, the experimental results show that the four-leg one can have lower ripple factor than its two- and three-leg counterparts, and meet the limitation of fuel cell output current ripple factor of 4%.     

Computationally efficient multi-phase models for a proton exchange membrane fuel cell: Asymptotic reduction and thermal decoupling

Generally, multi-phase models for the proton exchange membrane fuel cell (PEMFC) that seek to capture the local transport phenomena are inherently non-linear with high computational overhead. We address the latter with a reduced multi-phase, multicomponent, and non-isothermal model that is inexpensive to compute without sacrificing geometrical resolution and the salient features of the PEMFC - this is accomplished by considering a PEMFC equipped with porous-type flow fields coupled with scaling arguments and leading-order asymptotics. The reduced model is verified with the calibrated and validated full model for three different experimental fuel cells: good agreement is found. Overall, memory requirements and computational time are reduced by around 2-3 orders of magnitude. In addition, thermal decoupling is explored in an attempt to further reduce computational cost. Finally, we discuss how other types of flow fields and transient conditions can be incorporated into the mathematical and numerical framework presented here.     

Online electrochemical impedance spectroscopy detection integrated with step-up converter for fuel cell electric vehicle

Declining reserves of the crude oil and increasingly serious environmental pollution have emphasized the requirement of a suitable substitute to our actual petroleum-based automobile market. An environmentally-friendly and efficient power generation device based on a sustainable energy source is attractive to settle this issue and realize cleaner production. Proton Exchange Membrane Fuel Cell (PEMFC), which achieves zero emission, modular construction, high energy conversion ratio and etc., has been treated as one of the most promising solution for automobile applications. Nevertheless, many technical restrictions such as relatively short life cycle have still to be conquered before satisfying the requirements of large-scale commercialization.Electrochemical Impedance Spectroscopy (EIS) is an effective technique for fault detection of electrochemical system. This paper presents an on-line EIS detection strategy based on the proposed fuel cell stack connected step-up converter. No additional equipment is required compared with conventional detection process. Furthermore, the proposed 6-phase Interleaved Boost Converter (IBC) based on Silicon Carbide (SiC) semiconductors and inverse coupled inductors has achieved low input current ripple, high efficiency, high voltage gain ratio, high compactness and high redundancy. Benefiting from these advantages, the lifespan of fuel cell stack can be extended. The proposed online EIS detection has been realized and the results have been compared with theoretical analysis.     

Integrated modeling and control of a PEM fuel cell power system with a PWM DC/DC converter

A fuel cell powered system is regarded as a high current and low voltage source. To boost the output voltage of a fuel cell, a DC/DC converter is employed. Since these two systems show different dynamics, they need to be coordinated to meet the demand of a load. This paper proposes models for the two systems with associated controls, which take into account a PEM fuel cell stack with air supply and thermal systems, and a PWM DC/DC converter. The integrated simulation facilitates optimization of the power control strategy, and analyses of interrelated effects between the electric load and the temperature of cell components. In addition, the results show that the proposed power control can coordinate the two sources with improved dynamics and efficiency at a given dynamic load.     

Single-switch boost-buck DC-DC converter for industrial fuel cell and photovoltaics applications

The realization of dc-dc converters performs a vital function in exploiting renewable energy sources such as solar photovoltaic (PV) and fuel cell applications. This paper demonstrates a single-switch unidirectional buck-boost dc-dc converter for continuous power flow control, excluding the hybrid switched-capacitor. The proposed converter utilizes a limited number of passive components, only four diodes and three inductors required, in addition to six capacitors. The converter can operate at a wide input voltage range with continues input current. The converter has experimented under real-time conditions with 660 W PV system. The obtained efficiency ranges from 93% to 98%. Furthermore, the converter has interfaced with 550 W fuel cell operated under different fuel pressure. The realized efficiency ranges from 91% to 97%. The maximum measured inductance current ripple is limited to under 0.70 A in both scenarios, whereas 0.16 V is the maximum output voltage ripple.     

Fuzzy logic based MPPT controller for high conversion ratio quadratic boost converter

In this study, a maximum power point tracking DC–DC quadratic boost converter for high conversion ratio required applications is proposed. The proposed system consists of a quadratic boost converter with high step-up ratio and fuzzy logic based maximum power point tracking controller. The fuzzy logic based maximum power point tracking algorithm is used to generate the converter reference signal, and the change in PV power and the change in PV voltage are selected as fuzzy variables. Determined membership functions and fuzzy rules which are design to track the maximum power point of the PV system generates the output signal of the fuzzy logic controller's output. It is seen from MATLAB/Simulink simulation and experimental results that the quadratic boost converter provides high step-up function with robustness and stability. In addition, this process is achieved with low duty cycle ratio when compared to the traditional boost converter. Furthermore, simulation and experimental results have validated that the proposed system has fast response, and it is suitable for rapidly changing atmospheric conditions. The steady state maximum power point tracking efficiency of the proposed system is obtained as 99.10%. Besides, the output power oscillation of the converter, which is a major problem of the maximum power point trackers, is also reduced.     

Thermally integrated fuel processor design for fuel cell applications

Effective thermal integration could enable the use of compact fuel processors with PEM fuel cell-based power systems. These systems have potential for deployment in distributed, stationary electricity generation using natural gas. This paper describes a concept wherein the latent heat of vaporization of H₂O is used to control the axial temperature gradient of a fuel processor consisting of an autothermal reformer (ATR) with water gas shift (WGS) and preferential oxidation (PROX) reactors to manage the CO exhaust concentration. A prototype was experimentally evaluated using methane fuel over a range of external heat addition and thermal inputs. The experiments confirmed that the axial temperature profile of the fuel processor can be controlled by managing only the vapor fraction of the premixed reactant stream. The optimal temperature profile is shown to result in high thermal efficiency and a CO concentration less than 40 ppm at the exit of the PROX reactor.     

Energy management of fuel cell/battery/ultracapacitor in electrical hybrid vehicle

This paper describes an energy management algorithm for an electrical hybrid vehicle. The proposed hybrid vehicle presents a fuel cell as the main energy source and the storage system, composed of a battery and a supercapacitor as the secondary energy source. The main source must produce the necessary energy to the electrical vehicle. The secondary energy source produces the lacking power in acceleration and absorbs excess power in braking operation. The addition of a supercapacitor and battery in fuel cell-based vehicles has a great potential because it allows a significant reduction of the hydrogen consumption and an improvement of the vehicle efficiency. Other the energy sources, the electrical vehicle composed of a traction motor drive, Inverter and power conditioning. The last is composed of three DC/DC converters: the first converter interfaces the fuel cell and the DC link. For the second and the third converter, two buck boost are used in order to interface respectively the ultracapacitor and the battery with the DC link. The energy management algorithm determines the currents of the converters in order to regulate accurately the power provided from the three electrical sources. This algorithm is simulated with MATLAB_Simulink and implemented experimentally with a real-time system controller based on dSPACE. In this paper, the proposed algorithm is evaluated for the New European Driving Cycle (NEDC). The experimental results validate the effectiveness of the proposed energy management algorithm.     

A family of high gain fuel cell front-end converters with low input current ripple for PEMFC power conditioning systems

Since the output voltage of the proton exchange membrane fuel cell (PEMFC) is relatively low and load-dependent, a high-performance fuel cell front-end converter is required to achieve boost and power regulation in PEMFC systems. In response, a novel family of high gain fuel cell front-end converters with low input current ripple is proposed. The proposed topologies can substantially improve the voltage gain through the expansion and combination of active switched-inductor networks and passive switched-capacitor units. The introduced interleaved parallel structure is convenient to limit the current ripple on the input side to prevent accelerated aging of fuel cells, which is another prominent advantage. Meanwhile, the converters can achieve the automatic current sharing between parallel inductors and the low voltage stress on active switches and diodes. In this paper, the fuel cell model and topology derivation of the high gain fuel cell front-end converters are first analyzed. Then, it further describes the operating mode and steady-state performance of converters under the inductor current continuous conduction mode. The comparison with other converters shows that this converter is suitable for connecting the PEMFC to the high voltage DC bus. Finally, a 200 W, 20/180 V converter prototype is implemented, and the simulation and experiment prove the theoretical correctness and validate the superior performances of the proposed converters.     

Fabrication of high strength and a low weight composite bipolar plate for fuel cell applications

The bipolar plate is one of the most important components in a PEM fuel cell. A polymer composite bipolar plate possessing high strength (81 MPa) and high stiffness (20 GPa) has been developed by making use of carbon fiber network in a specific form as the filler component. Such high strength is very much desired, especially when the fuel cells are used for mobile applications, since it is the bipolar plate that provides mechanical support to all the other cell components. The addition of carbon black and the effect of particle size of the natural graphite flakes used as other reinforcements also play a crucial role in controlling the physical and electrical properties of the composite plates. The plate when used in the unit fuel cell assembly showed I–V performance comparable to that of the commercially available bipolar plates.     

A flexible paper-based hydrogen fuel cell for small power applications

In this work, a paper-based hydrogen fuel cell is developed without the need for hydrogen storage. Instead, an embedded aluminum foil inside the paper is utilized for in-situ hydrogen generation. The electrodes and current collectors are also deposited on the paper, leading to a lightweight, compact and flexible hydrogen fuel cell with an OCV reaching 0.93 V and a peak power density of 4 mW cm⁻². Benefited from the impeded hydroxyl ion diffusion, the hydrogen generation rate is well controlled, leading to a high faradaic efficiency of 72%. In addition, the cell can be operated under different bending angles with negligible power loss. Furthermore, it can be conveniently stacked in the same piece of paper for higher voltage and power outputs. Such a novel fuel cell design is especially suitable for powering various flexible devices with small rated power.