基于BOOST变换器的MFC最大功率跟踪控制

针对微生物燃料电池存在的输出功率低、运行稳定性差等问题,建立微生物燃料电池仿真实验平台,设计改进的扰动观测最大功率跟踪控制算法,通过调节Boost变换器的占空比,对微生物燃料电池进行最大功率跟踪控制。仿真实验结果表明,改进的扰动观测最大功率跟踪控制能及时追踪微生物燃料电池的最大功率点,显著提高稳态输出功率并减小输出功率脉动,有效改善微生物燃料电池的供电质量。     

Development of solid oxide fuel cell and battery hybrid power generation system

Solid oxide fuel cell hybrid generation system is the best scheme for the load tracking of off-grid monitoring stations. But there are still potential problems that need to be addressed: preventing fuel starvation and ensuring thermal safety while meeting load tracking in hybrid power generation system. In order to solve these problems, a feasible hybrid power generation system structure scheme is proposed which combined SOFC subsystem and Li-ion battery subsystem. Then a model of the hybrid power generation system is built based on the proposed system structure. On this basis, an adaptive controller, include the adaptive energy management algorithm and current feedforward gas supply strategy, is applied to manage the power-sharing in this hybrid system as well as keep the system operating within the safety constraints. The constraints, including maintaining the bus voltage at the desired level, keeping SOFC operating temperature in safety, and mitigating fuel starvation are explicitly considered. The stability of the proposed energy management algorithm is analyzed. Finally, the developed control algorithm is applied to the hybrid power generation system model, the operation result proves the feasibility of the designed controller strategy for hybrid generation system and effectively prevent fuel starvation and ensure thermal safety.     

ANFIS-MPPT control algorithm for a PEMFC system used in electric vehicle applications

Fuel cell has been considered as one of the optimistic renewable power technologies for the automotive applications. The output power of a fuel cell is immensely dependent on cell temperature and membrane water content. Hence, a maximum power point tracking controller is essentially required to extract the optimum power from the fuel cell stack. In this paper, an adaptive neuro-fuzzy inference system based maximum power point tracking controller is presented for 1.26 kW proton exchange membrane fuel cell system used in electric vehicle applications. In order to extract the optimum power, a high step-up boost converter is connected between the fuel cell and the BLDC motor. The duty cycle of the converter is controlled by using ANFIS reference model, so that the maximum power is delivered to the BLDC motor. The performance of the proposed controller is tested under normal operating conditions and also for sudden variations in the cell temperatures of the fuel cell. In addition to this, to analyze the effectiveness and tracking behaviour of the proposed controller, the results were compared with those obtained using the fuzzy logic controller. Compared to the fuzzy logic controller, the proposed ANFIS controller has increased the average DC link power by 1.95% and the average time taken to reach the maximum power point is reduced by 17.74%.     

Adaptive operation strategy of a polymer electrolyte membrane fuel cell air system based on model predictive control

The present article investigates a model predictive control-based operation strategy of an automotive fuel cell air system. For this purpose, a nonlinear model of a fuel cell system is derived, which is linearized and discretized around the current operation point during each time sample. This model is combined with a cost function taking into account power reference tracking and hydrogen minimization. Additional system constraints ensure a safe and robust operation. Subsequently, the adaptive and efficiency-optimal behavior of the model predictive controller is demonstrated based on a simulation study of different scenarios with varying power profiles. Furthermore, the thermal derating behavior of this control is studied using an exemplary situation with critical thermal conditions. Finally, the model predictive control approach is compared with a validated map-based operation strategy highlighting the potential of reducing the hydrogen consumption by 3% while decreasing the risk of harmful operation conditions.     

On tracking robustness in adaptive extremum seeking control of the fuel cell power plants

In this paper is proposed an optimization approach, based on optimal utilization of the power harmonics from the probing signal by including a band-pass filter in the feedback loop of the extremum seeking control (ESC) scheme. The ESC is used to track the maximum power point (MMP) of fuel cell power, and presence of the first and second power harmonics in the probing signal assure this tracking capacity. The MPP tracking robustness is improved by including the third power harmonics into the probing signal, given for probing signal amplitude a time adaptive variation depending of third derivate of the fuel cell power. The MPP tracking is demonstrated and the ESC robustness is proved by simulation in case of using a recommended current ripple factor.     

Development of a proton exchange membrane fuel cell cogeneration system

A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.     

Harvesting of PEM fuel cell heat energy for a thermal engine in an underwater glider

The heat generated by a proton exchange membrane fuel cell (PEMFC) is generally removed from the cell by a cooling system. Combining heat energy and electricity in a PEMFC is highly desirable to achieve higher fuel efficiency. This paper describes the design of a new power system that combines the heat energy and electricity in a miniature PEMFC to improve the overall power efficiency in an underwater glider. The system makes use of the available heat energy for navigational power of the underwater glider while the electricity generated by the miniature PEMFC is used for the glider's sensors and control system. Experimental results show that the performance of the thermal engine can be obviously improved due to the high quality heat from the PEMFC compared with the ocean environmental thermal energy. Moreover, the overall fuel efficiency can be increased from 17 to 25% at different electric power levels by harvesting the PEMFC heat energy for an integrated fuel cell and thermal engine system in the underwater glider.     

Building air conditioning system using fuel cell: Case study for Kuwait

Air conditioning machines in Kuwait consume more than 75% of electric energy generated at peak load time. It is in the national interest of Kuwait to decelerate the continuous increase of peak electric power demand. One way to do this is to install for new complexes or high-rise apartments buildings distributed utilities (isolated small power plants), mainly for air conditioning A/C systems. Fuel cells are among the alternatives considered for distributed utilities.This paper discusses the use of commercially available phosphoric acid fuel cell PAFC, known as ONSI P25 to operate air conditioning systems for big buildings in Kuwait.The proposed fuel cell, which is usually delivered with built-in heat exchanger for hot water, is operated by natural gas and uses a propylene glycol-water loop to recover thermal energy. The PAFC has 200 kW nominal electric power capacity, and produces thermal energy of 105 kW thermal energy at 120 °C, and 100 kW at 60 °C.The performance characteristics for the proposed fuel cell are very well documented. In the present study, it is suggested that the fuel cell operates combined mechanical vapor compression and absorption water chillers to utilize the fuel cell full output of electric power and waste heat. Also, to meet the required A/C cooling capacity system by the limited fuel cell power output, it is proposed to use cold storage technique. This allows fuel cell power output to supply the needed energy for average as well as peak A/C system capacity.     

Maximum power point tracking of a proton exchange membrane fuel cell system using PSO-PID controller

Fuel cells output power depends on the operating conditions, including cell temperature, oxygen partial pressure, hydrogen partial pressure, and membrane water content. In each particular condition, there is only one unique operating point for a fuel cell system with the maximum output. Thus, a maximum power point tracking (MPPT) controller is needed to increase the efficiency of the fuel cell systems. In this paper an efficient method based on the particle swarm optimization (PSO) and PID controller (PSO-PID) is proposed for MPPT of the proton exchange membrane (PEM) fuel cells. The closed loop system includes the PEM fuel cell, boost converter, battery and PSO-PID controller. PSO-PID controller adjusts the operating point of the PEM fuel cell to the maximum power by tuning of the boost converter duty cycle. To demonstrate the performance of the proposed algorithm, simulation results are compared with perturb and observe (P&O) and sliding mode (SM) algorithms under different operating conditions. PSO algorithm with fast convergence, high accuracy and very low power fluctuations tracks the maximum power point of the fuel cell system.     

Adaptive maximum power point tracking control of fuel cell power plants

A fuel cell's output power depends nonlinearly on the applied current or voltage, and there exists a unique maximum power point (MPP). This paper reports a first attempt to trace MPPs by an extremum seeking controller. The locus of MPPs varies nonlinearly with the unpredictable variations in the fuel cell's operation conditions. Thus, a maximum power point tracking (MPPT) controller is needed to continuously deliver the highest possible power to the load when variations in operation conditions occur. A two-loop cascade controller with an intermediate converter is designed to operate fuel cell power plants at their MPPs. The outer loop uses an adaptive extremum seeking algorithm to estimate the real-time MPP, and then gives the estimated value to the inner loop as the set-point, at which the inner loop forces the fuel cell to operate. The proposed MPPT control system provides a simple and robust control law that can keep the fuel cell working at MPPs in real time. Simulation shows that this control approach can yield satisfactory results in terms of robustness toward variations in fuel cell operation conditions.     

Transient power characteristic measurement of a proton exchange membrane fuel cell generator

An experimental study on the transient power characteristics of a fuel cell generator has been conducted. The generator is hybridized by a proton exchange membrane (PEM) as the main power source and a lithium-ion battery as the secondary power source. power-conditioning module consisting of a main bidirectional converter and an auxiliary converter has been designed to manage the hybrid power of the generator that copes with fast dynamics of variable loads. Sensors embedded in the generator have measured the electrical properties dynamically. It was found that the present power-conditioning scheme has well controlled the power flow between the fuel cell stack and the battery by regulating the power flow from or to the battery. In addition, the thermal management system using pulse width modulation (PWM) schemes could limit the operation temperature of the fuel cell generator in a designed range. Furthermore, the dynamics of electrical efficiency of the generator are found to be parallel with those of the net system power. Finally, the stability and reliability of the fuel cell generator is proven by the rational dynamic behaviors of thermal and electrical properties for over 30-h demonstration.     

SOFC cogeneration system for building applications, part 1: Development of SOFC system-level model and the parametric study

A thermal and electrochemical model is developed for the simulation of Solid Oxide Fuel Cell (SOFC) cogeneration system in this study. The modeling algorithms of electrochemical and thermal models are described. Since the fuel cell stack itself is only a single component within the whole SOFC system, the modeling of the balance-of-plant (BOP) components is also performed to assess the system-level performance. Using the new model, a parametric analysis is carried out to investigate the effects of fuel flow rate, extent of methane gas pre-reforming, fuel utilization factor, recycling rate of cathode gas and cell voltage on the overall system performance. As a result of the parametric study, fuel flow rate, cell voltage, fuel utilization and recycling rate of cathode gas turned out to improve system power output. In addition, the internal reforming turned out to have advantage over external reforming in terms of system power supply.     

Two-loop controller for maximizing performance of a grid-connectedphotovoltaic-fuel cell hybrid power plant

Maximizing performance of a grid-connected photovoltaic (PV)-fuel cell hybrid system by use of a two-loop controller is discussed. One loop is a neural network controller for maximum power point tracking, which extracts maximum available solar power from PV arrays under varying conditions of insolation, temperature, and system load. A real/reactive power controller (RRPC) is the other loop. The RRPC achieves the system's requirements for real and reactive powers by controlling incoming fuel to fuel cell stacks as well as switching control signals to a power conditioning subsystem. Results of time-domain simulations prove not only the effectiveness of the proposed computer models of the two-loop controller but also its applicability for use in stability analysis of the hybrid power plant     

Performance evaluation of an energy recovery system for fuel reforming of PEM fuel cell power plants

This paper describes an energy recovery system that recovers waste thermal energy from a fuel cell stack and uses it for fuel reforming purposes. The energy recovery system includes a throttling valve, a heat exchanger, and a compressor, and is coupled with a coolant loop of the fuel cell stack. The feed stock of a fuel reformer, which is primarily a mixture of water and fuel, is vaporized in the heat exchanger and is compressed to a sufficiently high pressure before it is ducted into the fuel reformer. The performance of a fuel cell power plant equipped with the energy recovery system is evaluated. The results indicate that the power plant efficiency can be increased by more than 40% compared to that of a fuel cell power plant without the energy recovery system. Additionally, up to 90% of the waste heat generated in the fuel cell stack is recovered. As a result, the required heat dissipation capacity of the radiator that is used for cooling the fuel cell stack can be drastically reduced.     

Discharge dynamics of coupled fuel cell and metal hydride hydrogen storage bed for small wind hybrid systems

In small hybrid wind systems, excess wind energy is stored for later use during the deficit power generation. Excess wind energy can be stored as hydrogen in a metal hydride storage bed and reused later to generate power using a fuel cell. This paper deals with the discharge dynamics of the coupled fuel cell and metal hydride storage bed during the power extraction. Thermal coupling of the fuel cell and metal hydride bed is also discussed. The waste heat generated in the fuel cell is removed using a water coolant. The exit fuel cell coolant stream is passed through the metal hydride storage bed to supply the necessary heat required for desorption of hydrogen from the bed. This will also lead to a reduction in the load on the radiator. The discharge dynamics and the thermal management of the coupled system are demonstrated through a system simulation model developed in Matlab/Simulink platform.     

Dynamic modeling and evaluation of solid oxide fuel cell - combined heat and power system operating strategies

Operating strategies of solid oxide fuel cell (SOFC) combined heat and power (CHP) systems are developed and evaluated from a utility, and end-user perspective using a fully integrated SOFC-CHP system dynamic model that resolves the physical states, thermal integration and overall efficiency of the system. The model can be modified for any SOFC-CHP system, but the present analysis is applied to a hotel in southern California based on measured electric and heating loads. Analysis indicates that combined heat and power systems can be operated to benefit both the end-users and the utility, providing more efficient electric generation as well as grid ancillary services, namely dispatchable urban power.Design and operating strategies considered in the paper include optimal sizing of the fuel cell, thermal energy storage to dispatch heat, and operating the fuel cell to provide flexible grid power. Analysis results indicate that with a 13.1% average increase in price-of-electricity (POE), the system can provide the grid with a 50% operating range of dispatchable urban power at an overall thermal efficiency of 80%. This grid-support operating mode increases the operational flexibility of the SOFC-CHP system, which may make the technology an important utility asset for accommodating the increased penetration of intermittent renewable power.     

Automotive fuel cell engine test cell design and its thermal flow analysis

A test cell for automotive PEM fuel cell engine is introduced and designed. Similarities and differences of facilities between PEM fuel cell engine and inner-combustion engine are illustrated. It turns out that, the air treatment, exhaust gas, cooling and electrical facilities are quite similar, the fuel treatment, power load type, ventilation and air-conditioning are quite different, while the vibration isolation and noise elimination facilities are completely simplified. Furthermore, a thermodynamic model is proposed to analysis the heat flow in fuel cell engine test cell. The Monte Carlo Simulation method is applied to get the proportion of outgoing thermal flows. A thermal flow rule of 4.5/4.5/0.6/0.4 is proposed as rule of thumb for cell designer.     

A new topology of fuel cell hybrid power source for efficient operation and high reliability

This paper analyzes a new fuel cell Hybrid Power Source (HPS) topology having the feature to mitigate the current ripple of the fuel cell inverter system. In the operation of the inverter system that is grid connected or supplies AC motors in vehicle application, the current ripple normally appears at the DC port of the fuel cell HPS. Consequently, if mitigation measures are not applied, this ripple is back propagated to the fuel cell stack. Other features of the proposed fuel cell HPS are the Maximum Power Point (MPP) tracking, high reliability in operation under sharp power pulses and improved energy efficiency in high power applications. This topology uses an inverter system directly powered from the appropriate fuel cell stack and a controlled buck current source as low power source used for ripple mitigation. The low frequency ripple mitigation is based on active control. The anti-ripple current is injected in HPS output node and this has the LF power spectrum almost the same with the inverter ripple. Consequently, the fuel cell current ripple is mitigated by the designed active control. The ripple mitigation performances are evaluated by indicators that are defined to measure the mitigation ratio of the low frequency harmonics. In this paper it is shown that good performances are obtained by using the hysteretic current control, but better if a dedicated nonlinear controller is used. Two ways to design the nonlinear control law are proposed. First is based on simulation trials that help to draw the characteristic of ripple mitigation ratio vs. fuel cell current ripple. The second is based on Fuzzy Logic Controller (FLC). The ripple factor is up to 1% in both cases.     

Performance and thermal stresses in functionally graded anode-supported honeycomb solid-oxide fuel cells

Enhancing the performance of anode supported honeycomb solid-oxide fuel cells via operating at higher temperatures is of great interest. However, working at a higher temperature leads to a significant rise in thermal stresses over the allowable limit. Thus, in the current study, functionally graded electrodes are considered to avoid cell failure due to higher thermal stresses. To assess the cell performance and thermal stress distribution, a theoretical investigation of a solid-oxide fuel cell with a honeycomb configuration using functionally graded electrode compositions is conducted through a comprehensive 3D model. The developed model includes the charge transport, mass and momentum transport, energy conservation, electrochemical reaction kinetics, and elastic stress. The model is numerically simulated and validated with the available experimental data. Results indicate that using functionally graded electrodes with grading index m = 1 significantly improves the fuel cell's performance, with an improvement in power density reaching around 60%. In addition, the most beneficial improvement is to reduce thermal stresses at elevated temperatures, for which the maximum value of equivalent stress is reduced to 85% less than the conventional electrode at a temperature of 1150 °C. Accordingly, the fuel cell's maximum power density can be obtained by operating at elevated temperatures with safe thermal stresses. These improvements are particularly attractive for applications requiring compact, reliable, and high-power devices based on fuel cell technology.     

Thermal and electrical energy management in a PEMFC stack – An analytical approach

An analytical method has been developed to differentiate the electrical and thermal resistance of the PEM fuel cell assembly in the fuel cell operating conditions. The usefulness of this method lies in the determination of the electrical resistance based on the polarization curve and the thermal resistance from the mass balance. This method also paves way for the evaluation of cogeneration from a PEMFC power plant. Based on this approach, the increase in current and resistance due to unit change in temperature at a particular current density has been evaluated. It was observed that the internal resistance of the cell is dependent on the electrode fabrication process, which also play a major role in the thermal management of the fuel cell stack.