Control of fuel cell power output

A simplified dynamic model for fuel cells is developed, based on the concept of instantaneous characteristic, which is the set of values of current and voltage that a fuel cell can reach instantaneously. This is used to derive a theorem that indicates the conditions under which the power output of fuel cells can, in theory, be perfectly controlled. A fuel cell connected to a DC/DC converter is simulated numerically, with a control system based on switching rules in order to control the converter’s output voltage. The resulting transients settle in about 5–10 ms. The converter is then used as an actuator in a cascade control loop to control the torque output of a DC electric motor with a PI controller in the external loop. In this loop, the resulting in transients settle in less than 0.2 s.     

Mathematical modeling and steady-state analysis of a proton-conducting solid oxide fuel cell

This paper presents a study of mathematical modeling and steady-state analysis of a proton-conducting solid oxide fuel cell (SOFC). The SOFC has a SrCe_0.95Yb_0.05O_3?α (SCY) electrolyte and two platinum electrodes. A mathematical model of the SOFC is first developed. The model captures electrochemical processes as well as the transport phenomena. The existence of steady-state multiplicity in the cell under three modes of constant ohmic load, potentiostatic and galvanostatic operations is studied. Simulation results show that a multiple steady-states region exists at low inlet fuel and air temperatures under constant ohmic load and potentiostatic operations. The occurrence of ignition and extinction in the cell solid (electrolyte, anode and cathode) temperature is reported. This result is in agreement with those for oxygen ion-conducting solid oxide fuel cells in which the existence of steady-state multiplicity has been attributed to the dependence of the electrolyte oxygen-ion conductivity on temperature. This work shows that concentration and temperature multiplicities coexist.     

安全操控下5 kW固体氧化物燃料电池电堆预测控制器设计

基于5 kW固体氧化物燃料电池(SOFC)电堆,考虑建模仿真—2温度层模型在模型精度与复杂度上做了更好的折中,可以更有效地应用于控制器设计.本文首先对2温度层模型在常用稳态工作点附近采用泰勒级数展开,获得其状态空间方程.然后考虑其安全操作特性,设计了两种带约束的预测控制器:即面向SOFC电堆的快速负载跟踪与燃料亏空控制...     

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.     

固体氧化物燃料电池温度特性的T-S模糊建模

固体氧化物燃料电池（SOFC）工作温度对于其输出电特性的性能起着重要的作用。由于电池在电化学反应过程中,温度特性呈现强非线性等特性,采用常规机理建模后难以在该模型的基础上较好地管理温度特性。为此,设计了面向控制的改进型T-S模型的模糊建模方法来解决此难题。实验仿真结果表明该模糊模型能精确拟合温度动态响应的映射特性,为下一步控制算法的实现奠定了良好的基础。     

Control‐oriented fault detection of solid oxide fuel cell system unknown input on fuel supply

As the solid oxide fuel cell (SOFC) system work environment is a high‐temperature environment for a long time, it is difficult to obtain the SOFC stack internal state change directly. When the fault occurs, it is difficult to determine where the fault occurs. Moreover, the existing literature ignores the impact of faults, which creates many problems for SOFC system control. Therefore, a state observer‐based fault detection method, which is used to detect the input flow sensor fault and the fuel input fault, is proposed. Their advantage is that they do not need data processing. To realize the fault detection, the observer is used to track the changes of SOFC stack chamber temperature. To obtain the observer estimation parameter, an approach from the actual stack structure parameters is employed to approximate the observer parameters. The results show the proposed fault detect method can judge fuel input fault type quickly and shield the disturbances signals from the sensor effectively. The proposed method also can be used to other operating points or air input fault.     

A 2D model for shape optimization of solid oxide fuel cell cathodes

A topology optimization method is used to identify the optimal shape of the nano-composite cathode of a solid oxide fuel cell (SOFC). A simplified analysis model is used in computations aimed at reducing ohmic losses by optimizing the shape of the cathode to minimize resistance. The model of the SOFC is reduced to a periodic, 2D conduction problem with design-dependent ionic transfer boundary conditions. Special techniques are introduced to avoid physically inadmissible designs that would otherwise be allowed by the 2D model. Isoperimetric constraints on the perimeter and the amount of material are used in the problem. Numerical examples are provided to discuss the effect of material properties and the resource restrictions introduced by the constraints. The methodology discussed can be applied to similar problems involving design-dependent boundary conditions.     

Optimal experiment design for autoregressive model with output power constraints

The output power constraint problem of optimal experiment design for an autoregressive model is considered. It is shown that besides the known minimum variance control law design, aD- optimal experiment consisting of sinusoidai input test signals without feedback can be obtained by solving a set of nonlinear equations. Two examples are also given to illustrate this design methodology.     

Identification of Wiener models for dynamic and steady‐state performance with application to solid oxide fuel cell

This work is concerned with identification of Wiener models (a linear dynamic part connected in series with a nonlinear dynamic one). A neural network with one hidden layer is used as the nonlinear block of the model, two network configurations are considered. For model identification three algorithms are described. In the first case model accuracy only in transient conditions is considered, only the dynamic data is used for model training. In the next two algorithms model accuracy in both transient and steady‐state conditions is considered, dynamic and steady‐state data sets are used. The steady‐state model errors are taken into account by an additional term in the minimized cost‐function or by additional inequality constraints. For comparison of discussed algorithms and model structures, identification of a Wiener model of a solid oxide fuel cell (SOFC) process is considered. It is shown that the best results are obtained by the algorithm 2 which minimizes at the same time both dynamic and steady‐state model errors, additional constraints used in the algorithm 3 are computationally quite demanding.     

Dynamic modeling,simulation, and MIMO predictive control of a tubular solid oxide fuel cell

Solid oxide fuel cells are a promising option for distributed energy stationary power generation that offers efficiencies up to 50% in stand-alone applications, 70% in hybrid gas turbine applications and 80% in cogeneration. To advance SOFC technology sufficiently for widespread market penetration, the SOFC must demonstrate improved cell lifetime from the status quo. Much research has been performed to improve SOFC lifetime using advanced geometries and materials, and in this research, we suggest further improving lifetime by designing an advanced control algorithm based upon preexisting mechanical stress analysis [1]. Control algorithms commonly address SOFC lifetime related operability objectives using unconstrained, SISO control algorithms that seek to minimize thermal transients. While thermal fatigue may be one thermal stress driver, these studies often do not consider maximum radial thermal gradients or critical absolute temperatures in the SOFC. In addition, researchers often discuss hot-spots as a critical lifetime reliability issue, but as previous stress work demonstrates, the minimum cell temperature is the primary thermal stress driver in tubular SOFCs modeled after the Siemens Power Generation, Inc. design. In this work, we present a dynamic, quasi-two-dimensional model for a high-temperature tubular SOFC combined with ejector and prereformer models. The model captures dynamics of critical thermal stress drivers and is used as the physical plant for closed-loop simulations with a constrained, MIMO model predictive control algorithm. Closed-loop simulation results demonstrate effective load-following, operability constraint satisfaction, and disturbance rejection.     

Lateral phase change random access memory cell design for low power operation

In this paper, we present a novel lateral cell design for phase change random access memory (PCRAM) that features an improved thermal management to efficiently reduce the current consumption during reset operation. Simulation, fabrication and electrical characterization results of the lateral concept are presented.     

一种频率稳定的低功耗振荡器电路设计

设计了一种频率稳定的低功耗张弛振荡器电路。采用恒流源对电容两端同时充电和放电,然后将电容两端电压送入后级比较器进行判决,使得输出频率只与恒流源电流、电容以及比较器比较窗口相关。该电路采用GSMC 0.18μm CMOS工艺,在5 V电源电压以及室温条件下仿真,输出频率为123.6 kHz,平均电流消耗为2.67μA;在2 V～5.5 V电源电压和-40℃-+85℃的温度变化范围内,输出频率精度在-6.5%-1.3%范围内。     

Measurement of thermodynamic activity of zirconia in yttria-stabilized zirconia electrolyte for solid oxide fuel cell application

The Knudsen effusion mass spectrometry technique was applied to determine the activity of ZrO₂ in 8 mol% yttria-stabilized zirconia (8YSZ) in the temperature range from 2200 K to 2500 K. The minor ZrO₂⁺ ion current was used in calculations instead of the prevailing ZrO⁺ signal. The phase stability of the samples and their negligible interaction with the cell material was proved by XRD-analysis. The activity of ZrO₂ was obtained to be 0.84 ± 0.04 independent of temperature. This fact allows estimating the same value of activity in the operating temperature range of solid oxide fuel cells (SOFCs).     

基于低阈值单元的高性能低功耗设计方法

在高性能IC设计中对高低两种阈值电压技术进行比较,利用低阈值电压降低动态功耗的手段实现降低总功耗的目标,并分析出了两种阈值电压低功耗设计各自适应的电路类型。首先对40nm工艺中标准单元的内部功耗、时序、尺寸进行分析。接着在相同延时下对高阈值和低阈值两种标准单元所设计的反相器链时序电路的功耗进行对比分析。最后基于Benchmark和AES两种类型电路,分别采用高阈值和低阈值进行综合,对比得出在相同时钟周期下更低功耗的设计所对应的阈值电压设计方式。结果显示,在相同的时钟频率下,对动态功耗占据总功耗比例极大的电路使用低阈值设计得到的功耗更低。同样,在动态功耗比例不是极大的电路中,当低阈值综合的slack为正时,以及当高阈值综合的slack为负、低阈值的slack为0时,用低阈值设计功耗更低;而当高阈值、低阈值综合的slack都为0时,用高阈值设计功耗更低。     

高输入电压单端反激式开关电源设计关键问题

讨论了高输入电压情况下单端反激式开关电源设计中的关键问题,如变压器设计中的匝数较多、漏感引起的尖峰电压及缓冲回路设计及器件选择等问题,并提出了相应的解决策略。提供了详细的实验波形,充分验证了方案的正确性,为后续开发者提供了参考。     

An adaptive non-linear observer for the estimation of temperature distribution in the planar solid oxide fuel cell

Minimising the thermal gradients is extremely important in a planar solid oxide fuel cell (SOFC) for improving the cell life. The estimation of the temperature distribution in the cell is necessary to achieve this objective through suitable control, since they are not generally measurable. In this work, we have designed a non-linear adaptive observer for estimating the temperatures inside the hydrogen fed planar SOFC. The observer design is based on a lumped parameter model of the SOFC. The stability of the proposed observer is proven using the Lyapunov function method and is based on the concept of input-to-state stability for cascaded systems. The simulations show that the developed observer can track the temperature and species concentration profiles in the planar SOFC during step changes in the cell current. The adaptive observer presented is valid for a wide operating range, requires fewer variables to be measured, and is robust to fluctuations in the inlet flows.     

Distributed generation system control strategies with PV and fuel cell in microgrid operation

Control strategies of distributed generation (DG) are investigated for different combination of DG and storage units in a microgrid. In this paper the authors proposed a microgrid structure which consists of a detailed photovoltaic (PV) array model, a solid oxide fuel cell (SOFC) and various loads. Real and reactive power (PQ) control and droop control are developed for microgrid operation. In grid-connected mode, PQ control is developed by controlling the active and reactive power output of DGs in accordance with assigned references. Two PI controllers were used in the PQ controller, and a novel heuristic method, artificial bee colony (ABC), was adopted to tune the PI parameters. DGs can be controlled by droop control both under grid-connected and islanded modes. Droop control implements power reallocation between DGs based on predefined droop characteristics whenever load changes or the microgrid is connected/disconnected to the grid, while the microgrid voltage and frequency is maintained at appropriate levels. Through voltage, frequency, and power characteristics in the simulation under different scenarios, the proposed control strategies have demonstrated to work properly and effectively. The simulation results also show the effectiveness of tuning PI parameters by the ABC.     

Modeling and cycling control of carbonate fuel cell power plants

A mathematical process model for an internal reforming molten carbonate fuel cell power plant is discussed in this paper. The dominant thermal and chemical dynamic processes are modeled for the cell stack array and balance-of-plant, including cathode gas preparation, heat recovery, and fuel processing. Physical data is obtained from a 2 MW system design that was a precursor to a demonstration plant operated at the City of Santa Clara, CA, USA. Steady state validation for several load points is provided for the cell stack array and a load cycling control system is described and tested under ramping operation between load points.     

独立、并网双模式户用光伏发电装置的研究与设计

针对户用光伏发电系统的特点和要求进行了系统的研究与设计。系统设计将独立逆变与并网逆变相结合,使系统既可以工作在独立逆变状态,为负载提供正弦交流电源,也可以工作在并网逆变状态,将太阳的能量或蓄电池的能量回馈到电网。本系统采用TI公司32位定点DSP芯片TMS320F2812为控制核心,利用PIC16F877A单片机构成系统的人机操作界面。本文所设计的系统具有完善的保护功能、键盘监控和液晶显示、串口通讯功能,为家庭使用提供了方便。实验结果验证了方案的可行性。     

高精度多通道的电能质量测试仪前向通道设计

介绍了以锁相环电路控制的高精度多通道的电能质量测试仪的前向通道的设计，结合具体电路图分析了锁相环芯片CD4045和14位A／D芯片MAX125功能及其应用。