Optimal interface based on power electronics in distributed generation systems for fuel cells

A hybrid system comprising a fuel cell stack and a battery bank was developed, built and tested in this research work. This hybrid system was built to supply both DC and AC outputs. The voltage levels set on electrical interconnection points are achieved with several power conditioning stages controlled by Pulse Width Modulation (PWM). The main advantage of this system is its excellence as a test bench, since it allows testing system performance at different voltage-restricted interconnecting points. Besides, power electronics are observed to play an essential role in distributed generation systems. The applications of the developed hybrid system extend from Auxiliary Power Units (APU) in vehicles (cars, buses or trains) to Uninterruptible Power Systems (UPS) in hospitals, nursing homes, hotels, office buildings or schools.     

Solid oxide fuel cell systems for distributed power generation and cogeneration

Solid oxide fuel cell (SOFC) is a promising technology for decentralized power generation and cogeneration. This technology has several advantages: the high electric efficiency, which can be theoretically improved through integration in power cycles; the low emissions; and the possibility of using a large variety of gaseous fuels.     

Pem fuel cells for transportation and stationary power generation applications

We describe recent activities at Los Alamos National Laboratory devoted to polymer electrolyte fuel cells in the contexts of stationary power generation and transportation applications. A low cost/high performance hydrogen or reformate/air stack technology is being developed based on ultra-low platinum loadings and non-machined, inexpensive elements for flow-fields and bipolar plates. On-board methanol reforming is compared to the option of direct methanol fuel cells in light of recent significant power density increases demonstrated in the latter.     

Development of a high-efficiency hydrogen generator for fuel cells for distributed power generation

A collaborative effort between Intelligent Energy and Cal Poly Pomona has developed an adsorption enhanced reformer (AER) for hydrogen generation for use in conjunction with fuel cells in small sizes. The AER operates at a lower temperature (about 500 °C) and has a higher hydrogen yield and purity than those in the conventional steam reforming. It employs ceria supported rhodium as the catalyst and potassium-promoted hydrotalcites to remove carbon dioxide from the products. A novel pulsing feed concept is developed for the AER operation to allow a deeper conversion of the feedstock to hydrogen. Continuous production of near fuel-cell grade hydrogen is demonstrated in the AER with four packed beds running alternately. In the best case of methane reforming, the overall conversion to hydrogen is 92% while the carbon dioxide and carbon monoxide concentrations in the production stream are on the ppm level. The ratio of carbon dioxide in the regeneration exhaust to the one in the product stream is on the order of 10³.     

High-temperature fuel cells for power generation

Hybrid systems consisting of series-connected high-temperature solid-electrolyte fuel cells (HTSEFCs) thermally coupled to coal gasifiers show great potential for overall efficiencies of nearly 60% for the production of electricity from coal. This paper describes a steady-state model for the prediction of HTSEFC voltage, current and power density. The HTSEFC model is essentially a distributed parameter electrical network that includes the effects of mass transfer resistance (concentration polarization), chemical kinetic resistance (activation polarization), as well as all relevant electrical resistances (ohmic losses). This electrical network representation leads to a finite-difference discretization which, in effect, divides the fuel cell into many simple current-flow sections. Furthermore, the model computes the fuel and oxidant stream compositions as functions of axial length from energy and mass balances performed on each fuel cell slice. The model yields results that compare favorably with the published experimental data from Westinhouse.     

SmartGrid: Future networks for New Zealand power systems incorporating distributed generation

The concept of intelligent electricity grids, which primarily involves the integration of new information and communication technologies with power transmission lines and distribution cables, is being actively explored in the European Union and the United States. Both developments share common technological developmental goals but also differ distinctly towards the role of distributed generation for their future electrical energy security. This paper looks at options that could find relevance to New Zealand (NZ), in the context of its aspiration of achieving 90% renewable energy electricity generation portfolio by 2025. It also identifies developments in technical standardization and industry investments that facilitate a pathway towards an intelligent or smart grid development for NZ. Some areas where policy can support research in NZ being a “fast adapter” to future grid development are also listed.This paper will help policy makers quickly review developments surrounding SmartGrid and also identify its potential to support NZ Energy Strategy in the electricity infrastructure. This paper will also help researchers and power system stakeholders for identifying international standardization, projects and potential partners in the area of future grid technologies.     

基于PVsyst的分布式并网光伏发电系统效率分析与优化研究

针对分布式并网光伏发电系统各环节功率损耗量大、系统综合效率(PR,Performance Ratio)较低的问题,文章首先全面分析了影响光伏系统效率的各个因素,定性和定量研究其功率损耗机制,并结合项目建设经验给出各影响因子的效率损失典型值。然后从系统设计角度出发,提出各影响因素功率损耗的优化方法。最后利用PVsyst光伏系统仿真平台,按照所提出的优化策略对光伏系统直流线路设计方案进行改进。实例仿真结果表明,优化后的系统年均发电效率提高0.31%,年均发电量提高4 053 k Wh,并产生可观的经济效益。     

小规模分布式光伏发电系统用户侧经济性分析

从用户侧角度研究了小规模分布式光伏发电系统的经济性。以内部收益率、静态投资回收期及全寿命期净收益为指标,建立了分布式光伏发电系统的经济分析模型;以湖北省武汉市和宜昌市为代表,以典型配置的光伏发电系统为范例,验证了经济性分析模型的正确性。文章深入研究了发电上网率、系统可用率、政府补贴及单位造价等因素对分布式光伏系统经济性的影响,还研究了政府补贴与单位造价的耦合关系。     

Unit sizing and cost analysis of stand-alone hybrid wind/PV/fuel cell power generation systems

An economic evaluation of a hybrid wind/photovoltaic/fuel cell (FC) generation system for a typical home in the Pacific Northwest is performed. In this configuration the combination of a FC stack, an electrolyser, and hydrogen storage tanks is used as the energy storage system. This system is compared to a traditional hybrid energy system with battery storage. A computer program has been developed to size system components in order to match the load of the site in the most cost effective way. A cost of electricity, an overall system cost, and a break-even distance analysis are also calculated for each configuration. The study was performed using a graphical user interface programmed in MATLAB.     

Feasibility analysis of fuel cells for combined heat and power systems in the tertiary sector

The aim of this paper is to present a feasibility analysis of the application of fuel cells for a combined heat and power system with grid connection in the tertiary sector. Although the analysis considers Spanish data, the methodology proposed is developed to be applicable at the EU level.The current legislative framework is analysed in order to establish the suitability of the payment scheme considered for the sale of surplus electricity from these systems. The paper also establishes criteria for the optimal design of distributed generation systems based on fuel cells from a technical, economic and environmental point of view, presenting the strategies that should be implemented to promote the future implantation of these systems and their progressive introduction to the market.     

基于PEMFC分布式发电系统的动态特性分析

分析了质子交换膜燃料电池(PEMFC)的机理模型,在此基础上运用MATLAB的Simulink仿真工具,建立了PEMFC发电系统带负载模型。通过仿真,分析了负载对PEMFC电堆的各项动态特性(燃料的流量、效率、输出电压等)的影响,以及DC/DC、负载端的电压响应。仿真结果中负载电压呈三相交流正弦波形,表明搭建的整个PEMFC发电系统是基本正确的,为实现PEMFC并网的实时分析和动态优化提供了理论依据和参考方法。     

Hybrid renewable energy systems for power generation in stand-alone applications: A review

It has become imperative for the power and energy engineers to look out for the renewable energy sources such as sun, wind, geothermal, ocean and biomass as sustainable, cost-effective and environment friendly alternatives for conventional energy sources. However, the non-availability of these renewable energy resources all the time throughout the year has led to research in the area of hybrid renewable energy systems. In the past few years, a lot of research has taken place in the design, optimization, operation and control of the renewable hybrid energy systems. It is indeed evident that this area is still emerging and vast in scope. The main aim of this paper is to review the research on the unit sizing, optimization, energy management and modeling of the hybrid renewable energy system components. Developments in research on modeling of hybrid energy resources (PV systems), backup energy systems (Fuel Cell, Battery, Ultra-capacitor, Diesel Generator), power conditioning units (MPPT converters, Buck/Boost converters, Battery chargers) and techniques for energy flow management have been discussed in detail. In this paper, an attempt has been made to present a comprehensive review of the research in this area in the past one decade.     

Numerical analysis of electrical power generation and internal reforming characteristics in seal-less disk-type solid oxide fuel cells

For seal-less type solid oxide fuel cells, its power generation characteristics and distribution of the gas composition depend on not only the electrochemical reaction, but also complex kinetics and transport phenomena, because the internal reforming reaction and the water-gas shift reaction take place together with reverse diffusion of the ambient gas from the surroundings of the cell. The purpose of this paper is to theoretically explain the experimental results of the anodic concentration profile of gaseous species previously reported in a practical seal-less disk-type cell which used pre-reforming methane with steam as a fuel. A numerical model that takes into account the transport phenomena of the gaseous species and the internal reforming reaction with the water-gas shift reaction together with the assumption of the cell outlet boundary condition was constructed to numerically analyse the gas composition distribution and power generation characteristics. Numerical analyses by the model were conducted for the several cases reported as the experiment. The calculated results in the anode gas concentration profile and in the voltage–current characteristics show good agreement with the experimental data in every case, and then the validity of the simulation model was verified. Therefore, the model is useful for a seal-less disk-type cell which is operated by a fuel including non-reformed methane.     

PEM fuel cells analysis for grid connected applications

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.     

Exergy analysis of PEM fuel cells for marine applications

Fuel cells have a promising potential use in stationary and mobile power generation systems, as well as in automotive, aerospace or marine industries. At present, the main field of marine applications of fuel cells is submarines. Hydrogen/oxygen polymer electrolyte membrane (PEM) fuel cells are commonly used in this field. Storage of oxygen in liquid form is the optimal solution. Hydrogen can be stored in carbon-nanofibres or metallic hydrides, for example, or in liquid fuels, as alcohols, with further generation of the hydrogen required on-board. The objective of this study is to perform an exergetic analysis of two possibilities of using PEM fuel cells on surface ships and submarines: hydrogen/oxygen PEM fuel cells fed with hydrogen generated by reforming of methanol, and Direct Methanol Fuel Cells directly fed with liquid methanol. To do this, exergy losses and exergetic efficiencies are calculated for both configurations at selected optimal operation points.     

Dynamic modeling,simulation and control design of an advanced micro-hydro power plant for distributed generation applications

A small-scale hydropower station is usually a run-of-river plant that uses a fixed speed drive with mechanical regulation of the turbine water flow rate for controlling the active power generation. This design enables to reach high efficiency over a wide range of water flows but using a complex operating mechanism, which is in consequence expensive and tend to be more affordable for large systems. This paper proposes an advanced structure of a micro-hydro power plant (MHPP) based on a smaller, lighter, more robust and more efficient higher-speed turbine. The suggested design is much simpler and eliminates all mechanical adjustments through a novel electronic power conditioning system for connection to the electric grid. In this way, it allows obtaining higher reliability and lower cost of the power plant. A full detailed model of the MHPP is derived and a new three-level control scheme is designed. The dynamic performance of the proposed MHPP is validated through digital simulations and employing a small-scale experimental set-up.