Real‐time optimal energy management for a fuel cell/battery hybrid system

An energy management strategy is proposed for a class of fuel cell/battery hybrid systems. In such hybrid systems, a fuel cell system is the main power source, and a lithium‐ion battery is the auxiliary power source. In order to manage the system power at the next moment in a reasonable way, a load current filter with bounded estimation errors is designed to estimate the load current. Then, a real‐time optimal energy management algorithm is proposed to optimize economy consumption of the hybrid system. By taking current change rate of the fuel cell and the state of charge into consideration and taking reasonable model simplifications, the optimization problem can be described as a quadratic programming problem. Then a general purpose solver is proposed to solve the quadratic programming problem based on the alternating direction method of multipliers. The efficiency of the proposed solver is much faster than computing interior point method or active set method. Simulation results in MATLAB/SIMULINK are carried out to validate the significant effectiveness and efficiency of the proposed management strategy.     

汽油Mn杂质对氧传感器特性的影响

氧传感器是闭环控制的汽车发动机电系统的核心部件之一。利用氧传感器检测汽车尾气成分,调节空燃比,可以获得较高的汽油燃烧效率和较好的三元催化系统的净化效率。使用过程中,汽油中的杂质会影响氧传感器的性能。试验研究了汽油中Mn杂质对氧传感器性能的影响。结果表明：Mn杂质严重影响氧传感器的性能。Mn杂质沉积在传感器表面,与铂电极发生反应,导致传感器失效,从而导致排放尾气的净化率降低。     

A simulation of aircraft fuel management system

Aircrafts usually have several fuel tanks, and there are fuel transfers among these tanks along a flight. These transfers are controlled with valves, and may follow several alternative paths, since structural fuel system redundancies are provided for evident reasons. An on board program for the management and reconfiguration of the fuel system must be developed and tested. The article introduces an aircraft fuel management system simulation, which provides a platform for the study of the fuel system logic and sequencing that the on board program must implement for normal flights and for malfunction cases. The simulation environment can be easily modified and extended, for instance to consider the use of new components. A specific example is considered: an aircraft with six tanks in the wings and a tail tank. The article presents a two-layer model, the use of the model for simulation experiments, and some illustrative examples.     

A microreactor for hydrogen production in micro fuel cell applications

A silicon-chip based microreactor has been successfully fabricated and tested for carrying out the reaction of methanol reforming for microscale hydrogen production. The developed microreactor in combination with a micro fuel cell is proposed as an alternative to conventional portable sources of electricity such as batteries due to its ability to provide an uninterrupted supply of electricity as long as a supply of methanol and water can be provided. The microreformer-fuel cell combination has the advantage of not requiring the tedious recharging cycles needed by conventional rechargeable lithium-ion batteries. It also offers significantly higher energy storage densities, which translates into less frequent "recharging" through the refilling of methanol fuel. The microreactor consists of a network of catalyst-packed parallel microchannels of depths ranging from 200 to 400 /spl mu/m with a catalyst particle filter near the outlet fabricated using photolithography and deep-reactive ion etching (DRIE) on a silicon substrate. Issues related to microchannel and filter capping, on-chip heating and temperature sensing, introduction and trapping of catalyst particles in the microchannels, flow distribution, microfluidic interfacing, and thermal insulation have been addressed. Experimental runs have demonstrated a methanol to hydrogen molar conversion of at least 85% to 90% at flow rates enough to supply hydrogen to an 8- to 10-W fuel cell.     

Modelling,dynamics and control of a portable DMFC system

A dynamic model for a direct methanol fuel cell and its ancillary units is presented, in which all ancillary units perform only one operation each. The system’s losses and main dynamics (cathodic oxygen fraction, anodic methanol concentration, stack temperature, system water holdup) are analysed for stability and time constants. The system is found to be stable in all of its dynamics except for that of water holdup. The influence of external conditions, such as temperature and humidity, on system feasibility is analysed; the capability of system autonomous operation depends essentially on environmental conditions and on the chosen air excess ratio. Decoupled single-input, single-output controllers, some of which employing feedback, are applied to maintain the system at a certain set point. System simulations are performed, confirming the performance of the proposed controllers, their ability to stabilise the water holdup, and the absence of interaction-induced oscillations; the system can be started up in about ten minutes with the presented parameters.     

Fabrication and characterization of a passive silicon-based direct methanol fuel cell

This paper reports on the fabrication and characterization of a passive silicon microfabricated direct methanol fuel cell (μDMFC). The main characteristics of the device are its capability to work without complex pumping systems, only by capillary pressure, and the fact that its performance is not affected by the device orientation. A simple fabrication process based in deep reactive ion etching (DRIE), allows obtaining a reliable and low-cost final device. The device consists of two silicon microfabricated plates mounted together with a commercial membrane electrode assembly (MEA). The impact of current collector design on microfuel cell performance is explored and current–voltage (I–V) and current–power (I–P) curves of the device at different methanol concentration and orientation are presented. Optimal performance was obtained for methanol concentrations between 3 and 5 M, achieving a maximum power density of 12 mW/cm². The results obtained in this work demonstrate the feasibility of the device and give a guideline for design and conditions optimization.     

基于Fluent的微型直接甲醇燃料电池阳极流场结构分析

微型直接甲醇燃料电池中阳极流场结构对电池的性能有着重要的影响。为了合理设计阳极流场结构,改善甲醇燃料在阳极流场中的分布,采用计算流体动力学(CFD)软件Fluent对微型直接甲醇燃料电池进行建模并仿真分析。分析比较了点型、平行和蛇形3种不同流场图案下得到的压降与流速分布,得出蛇形流场能够更有利于甲醇燃料的均匀分配。在此基础上分别建立不同流道宽度(800,400,200,100μm)的蛇形流场模型,通过仿真计算甲醇燃料的分布情况来分析其对燃料电池性能的影响,并结合实验结果进行对比得出流道宽度为200～400μm之间为优化值。     

Modeling and identification of a PEM fuel cell humidification system

A theoretical model of a humidifier of proton exchange membrane （PEM） fuel cell systems is developed and analyzed first in this paper. The model shows that there exists a strong nonlinearity in the system. Then, the system is identified using a wavelet networks method. To avoid the curse-of-dimensionality problem, a class of wavelet networks proposed by Billings is employed. The experimental data acquired from the test bench are used for identification. The one-step-ahead predictions and the five-step-ahead predictions are compared with the real measurements, respectively. It shows that the identified model can effectively describe the real system.     

Nonlinear time-variant model of the PEM type fuel cell for automotive applications

This paper deals with nonlinear dynamic modeling of the Proton Exchange Membrane Fuel Cell (PEMFC) dedicated for automotive applications. A time-variant state space model taking into account most of internal phenomena is built. Based on electrical and diffusion approaches, the model proposes a more complete equivalent circuit including all cell components. The proposed circuit couple between gas diffusion, membrane water content, temperature, activation, ohmic and concentration losses, as well as double layer and geometrical capacitances. Similarly to engine vehicles, the model consider the hydrogen flow rate as input controlled by the pilot to change vehicle’s speed. Urban and highway driving cycles similar to those of Nissan LEAF are simulated. Simulation results show that the model responds to both low and high dynamics of power demand. Results reveal that membrane humidity has a considerable effect on the cell’s efficiency. This offer the opportunity to use the model, in a future work, to improve the fuel cell’s efficiency through the control of humidity. The model is validated by experimental tests on a 50 W PEMFC.     

两种固体氧化物燃料电池系统的故障建模与仿真对比研究

固体氧化物燃料电池(SOFC)系统的建模方式较多,而基于机理模型的故障诊断是能够通过系统的动态趋势辨别故障的有效手段之一,但该方法对机理模型的准确性有要求.此外,不同的燃料供给系统采用的系统结构也是有差异的,进而导致在相同故障下SOFC系统的动态响应也是不同的.因此,本文基于两种燃料供应方式,提出了分别以纯氢气和天然气作为燃料的SOFC系统结构,并基于原有机理知识进行MATLAB/Simulink系统建模.经与真实SOFC系统实验对比,搭建的系统模型能够有效模拟系统在无故障状态下的动态变化;另外,在无故障模型的基础上,分别加入两类常见故障,其一为风机故障,其二为燃料供应管路泄露.最后通过仿真分析,明确了所搭建模型的合理性,且发现了两种燃料供应对SOFC系统热响应特性是不同的,对SOFC系统故障的检测和设备选型具有重要意义.     

Capillary-driven pumping for passive degassing and fuel supply in direct methanol fuel cells

In this paper we present a new concept of creating and using capillary pressure gradients for passive degassing and passive methanol supply in direct methanol fuel cells (DMFCs). An anode flow field consisting of parallel tapered channels structures is applied to achieve the passive supply mechanism. The flow is propelled by the surface forces of deformed CO₂ bubbles, generated as a reaction product during DMFC operation. This work focuses on studying the influence of channel geometry and surface properties on the capillary-induced liquid flow rates at various bubbly gas flow rates. Besides the aspect ratios and opening angles of the tapered channels, the static contact angle as well as the effect of contact angle hysteresis has been identified to significantly influence the liquid flow rates induced by capillary forces at the bubble menisci. Applying the novel concept, we show that the liquid flow rates are up to thirteen times higher than the methanol oxidation reaction on the anode requires. Experimental results are presented that demonstrate the continuous passive operation of a DMFC for more than 15 h.     

A Methanol-Tolerant Gas-Venting Microchannel for a Microdirect Methanol Fuel Cell

As a byproduct, gas is constantly generated from the electrochemical reactions of direct methanol fuel cells (DMFCs). In the anodic channel of a DMFC, the gas forms bubbles, which leads to bubble clogging and pressure buildup if the device is miniaturized. Bubble clogging increases the flow resistance in microchannels, calling for excessive power consumption for fuel delivery. Pressure buildup aggravates the undesired crossover of methanol. In order to solve those problems, this paper introduces a gas-venting microchannel that directly removes gas bubbles from the two-phase flows of gas and methanol solution without leakage. By employing a hydrophobic nanoporous membrane, successful venting is achieved for both water and methanol fuel with a concentration of as high as 10 M. The fuel is contained without leakage under overpressures of as high as 200 kPa for both water and 10-M methanol, fulfilling the requirement of the current- as well as next-generation microdirect methanol fuel cells. A 1-D venting rate model is developed and experimentally verified for elongated bubbles. The reported bubble removal approach is also useful for other microfluidic devices, in which the accidental introduction of gas bubbles is prevalent.     

On-line detection of toxic components using a microbial fuel cell-based biosensor

Safe drinking water without toxic chemicals is crucial for people's health. A recently developed sensor for the detection of toxic components in water is the microbial fuel cell (MFC)-based biosensor. In this biosensor, substrate consumption rate and metabolic activity of bacteria are directly related to the electric current. A reduction in current under otherwise similar conditions is an indication of toxic inhibition. Under steady state conditions, current can be described by the Butler–Volmer–Monod (BVM) model. Knowing which parameters of this model change under toxic contamination can give an indication on the type of toxicity. The model requires that the substrate concentration is known. It is shown in this paper that is not possible to estimate both the substrate concentration as well as the BVM parameters on-line from current data at constant overpotential. However, it appears that substrate concentration and substrate consumption rate can be estimated on-line, and that after a linear reparametrization the BVM parameters can be estimated by ordinary least-squares techniques from a polarization curve that is generated as soon as a suspect change in current occurs. Analysis shows that a weighted least-squares method is necessary to secure a good fit at the overpotentials where current is most sensitive to changes in kinetic parameters. A protocol for on-line detection of toxicity and for detection of the type of kinetic inhibition is provided.     

A decoupled controller for fuel cell hybrid electric power split

The power management of a hybrid system composed of a fuel cell, a battery and a DC/DC power converter is developed. A decoupled control strategy is proposed, aimed at balancing the power flow between the stack and the battery and avoiding electrochemical damage due to low oxygen concentration in the fuel cell cathode. The controller is composed of two components. The first controller regulates the compressor, and as consequence the oxygen supplied to the cathode, via a classic proportional–integral controller. The second controller optimally manages the current demanded by the fuel cell and battery via linear-quadratic control strategy acting on the converter. The closed-loop performance has been tested both in simulation and in real-time simulation using a microprocessor for the controller.     

Model-based diagnosis for proton exchange membrane fuel cells

Proton Exchange Membrane Fuel Cell (PEMFC) systems are more and more presented as a good alternative to current energy converters such as internal combustion engines. They suffer however from insufficient reliability and durability for stationary and transport applications. Reliability and lifetime may be improved by suitable fault detection and localization.Traditionally, fault diagnosis in fuel cell systems needs the knowledge of number of parameters, which might require a special inner parameter monitoring setup. This is difficult, even impossible with respect to fuel cell stacks geometry. Moreover, with respect to the transportation application that aims at minimizing the embedded instrumentation, simple diagnosis methods involving non-intrusive and easy-to-monitor parameters are highly desired in PEMFC systems.We present in this paper a flooding diagnosis procedure based on black-box model. This diagnosis method allows automating the flooding diagnosis and the parameters used are minimal, low-cost and simple to monitor. The model inputs are some variables that are critical for water management in the PEMFC and consequently for fuel cell performances while the output is a variable that can be monitored in a non-intrusive way and can be used to detect flooding (namely pressure drop through the cathode).The flooding diagnosis procedure is based on the analysis of a residual obtained from the comparison between an experimental and an estimated pressure drop. The estimation of this latter is ensured by an artificial Neural Network that has been trained with flooding-free data. Fault detection is obtained by means of a residual analysis.It has been successfully tested under different experimental conditions including non-flooding and deliberately induced flooding as well as a succession of the two states of health. A proposition to include drying out problems is given as perspective to this work.     

Modeling,state estimation and nonlinear model predictive control of cathode exhaust gas mass flow for PEM fuel cells

Polymer electrolyte membrane fuel cells are efficient energy converters and provide electrical energy, water and oxygen depleted air with a low oxygen content as exhaust gas if fed with air. Due to their low emission of greenhouse gases and noise they are investigated as replacement for auxiliary power units currently used for electrical power supply on aircraft. Oxygen depleted air, called ODA-gas, with an oxygen concentration of 10–11% and a low humidity can be used for tank-inerting on aircraft. A challenging task is controlling the fuel cell system for generation of dehumidified ODA-gas mass flow while simultaneously keeping bounds and gradients on control inputs. This task is attacked by a nonlinear model predictive control. Not all system states can be measured and some states measured exhibit a significant time delay. A nonlinear state estimation strategy builds the entire system state and compensates for the delay. The nonlinear model predictive control and the state estimation are derived from the system model, which is presented. Simulation and experimental results are shown.     

乏燃料组件跌落速度的理论计算和数值模拟

针对乏燃料组件在乏燃料池的水中吊运时有可能发生跌落的情况,通过理论近似解和CFD数值模拟两种方法计算乏燃料组件跌落速度.结果表明两种方法得到的跌落速度相近,最大误差小于5%,都可以用于跌落过程的模拟;采用CFD数值模拟还可以得到乏燃料组件下降过程中周围流场和压强的变化.虽然乏燃料组件的跌落速度逐渐增大,但跌落加速度变化不大,表明水对组件的阻力影响较小.     

柴油机油量执行器的干扰估计滑模控制方法

油量执行器是电控分配泵的核心部件之一,其直接控制着柴油发动机的燃油喷射量.模型非线性与外部扰动是油量执行器系统中不可避免的影响因素,前期的许多研究忽略了这些非线性,使得闭环系统性能并不理想.本文考虑了旋转电磁铁和复位弹簧等非线性特性的建模,得到了油量执行器系统的数学模型.进而,在基于模型对系统非线性进行抵消之后引入扩张状态观测器对系统外部干扰和不确定性进行估计,设计了基于扩张状态观测器的滑模控制律.该控制律在保证鲁棒性的同时,可以使得切换增益幅值更小,有利于减小滑模控制的抖振问题.最后,通过MATLAB/Simulink仿真和dSPACE平台实验验证了所提方法的可行性和有效性.     

应用虚拟仪器的精细水煤浆制备过程控制技术

为了提高精细水煤浆的质量,开发了一种应用虚拟仪器的水煤浆制备过程自动控制系统。系统采用PX I总线硬件结构达到稳定的性能,采用模糊逻辑控制压力和超声频率实现生产工艺参数优化,使水煤浆粒度及其分布达到内燃机使用的要求。     

Modeling and control of a PEM fuel cell system: A practical study based on experimental defined component behavior

In this contribution, the dynamical behavior of a polymer electrolyte membrane (PEM) fuel cell system is modeled; related control approaches are developed. The system model used for experimental and modeling purposes describes a 1.2 kW PEM fuel cell stack and an air blower. Due to the dynamical fuel cell–blower interaction the fuel cell stack and the blower model are validated to real systems respectively. Additionally, a feedback based on PI-control is used for hydrogen pressure control with an anode inlet valve. This controller is able to eliminate a stationary error between the anode and cathode pressures. For principal investigations three control approaches, a classical static feed-forward control approach, a state-space feedback control, and a novel gain-scheduling approach are developed, applied, and compared. As result, it can be shown that the feed-forward approach lacks in performance recovering the excess oxygen ratio to the desired level. The state-space feedback control shows stationary error. The introduced gain-scheduling control approach leads to a fast excess oxygen ratio recovery without stationary deviations.