Hydrofly–FuelCellFinalReportDecember2005.doc

33UNIVERSITY OF IDAHODEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERINGInterfacing an Avista SR-12 Hydrogen Fuel Cell to the Analog Model Power System (AMPS)December 15, 2005Project by:Daniel HubbardSponsors/Advisors:Dr. Brian JUniversity of IdahoAdam LintDr. Herb HUniversity of IdahoChris CockrellCTable of ContentsI.Introduction4II.Project Description4A.Objective and Scope4B.Requirements4C.Significance of the Project5D.Background/History5E.Functional Specs5F.Constraints5G.Fuel Cell/AMPS Interface Solution5III.Method of Solution5A.Fuel Cell51)Types of Fuel Cells 352)Operation of the PEM Fuel Cell63)The Avista SR-12 PEM Fuel Cell64)Characterizing the SR-12 Fuel Cell65)Additional Considerations7B.DC/DC Converter7C.DC/AC Converter7D.Transformers7E.System Control81)DC to AC Converter8F.Zero-Crossing Detection91)Design Constraints102)Response Time103)Input Stage104)Active Feedback/Middle Stage105)Optoisolator/Output State116)Output Logic/Conditioning11IV.Design Simulation11A.DC/DC Converter11B.Inverter12C.Zero-crossing Detection Circuitry12V.Validation13A.Individual Components131)DC/DC Converter:132)Inverter133)Transformer134)Zero Detection Circuitry135)Software14B.Overall System Specifications14VI.Results14A.DC/DC Converter14B.Inverter14C.Transformer14D.Zero Detection Circuitry151)PCB Design/Construction152)PCB Testing/Error Analysis15E.Software151)Overall Flow Diagram152)Case 1 Waiting For Pulse163)Case 2 - Waiting for Falling Edge164)Case 3 - Calculations165)Case 4 Zero Crossing Analysis176)Case 5 PWM State17F.Overall System Results18VII.Manufacturing and Support18A.Product Life Cycle Report181)INTRODUCTION18a)Hardware Components and General Interface Design18b)Power Flow Control18c)Protection182)Design18a)Selection of Hardware Components18b)Software Programming and System Control19c)Hardware and Software Costs193)Implementation and Testing19a)Component Implementation19b)Component Testing19c)Interface Testing19d)Release Plans194)Maintenance19a)Zero Detection Board19b)Software19c)Other205)End of Life20B.Hardware Reliability Analysis201)INTRODUCTION202)System Failure Rate Calculations203)Failure Modes and FMECA Analysis20a)Potential Failure Modes20b)Ratings214)Conclusion21VIII.Budget21IX.Future Work21X.Conclusion22Appendices23Appendix A Absopulse BAP265 Series DC/DC Converter Data Sheet24Appendix B Tier Electronics DC/AC Inverter I/O Pins and Pinouts25Appendix C Zero Crossing Circuit Feedback Derivation27Appendix D Zero Detection Circuitry Simulation Results28Appendix E Zero Detection Circuitry PCB Board Design, Parts/Build List29Appendix F Zero Detection Circuitry Test Point Reference30Appendix F DSP Software34Appendix G Power Flow Calculations35Appendix H Personal Contributions36Hydrofly Fuel Cell Final Report(December 2005)Chris Cockrell, Daniel Hubbard, and Adam LintAbstract Alternative energy sources are a focus in the energy industry as the world realizes that its dependency on fossil fuels must diminish because of pollution, oil prices, or other factors. For this reason it is important that students at the University of Idaho have exposure to some of the alternative energy sources available in the 21st century. This report outlines a plan for interfacing an Avista SR-12 hydrogen fuel cell to the UI Analog Model Power System (AMPS). Fuel cell characteristics and system specifications are discussed along with simulation data for the entire system. However, the primary focus of the simulation data discussion is on the zero detection circuitry used for synchronizing the AC signal from the DC/AC converter with the utility frequency. The results of this simulation provide a method for implementing the design in hardware and show that the system will need to be designed to transfer a maximum of 200W to the AMPS.Index Terms: Hydrogen Fuel Cell, Alternative Energy, Zero-Crossing Detection, Synchronization, Voltage Regulation, Voltage Conversion, Analog Model Power System.I. IntroductionTHIS report outlines an interface design for transferring power from an Avista Hydrogen Fuel Cell to the Analog Model Power System. Additional Information on the interface, design, simulations, and data sheets can be found on the Hydrofly: Fuel Cell Project CD and project folder.II. Project DescriptionA. Objective and ScopeThe project objective is to interface an Avista SR-12 hydrogen fuel cell to the University of Idaho Analog Model Power System (AMPS). This project will allow the fuel cell to provide supplemental power to the AMPS. Overall power quality and capacity are not important in this project, as the main goal is to simply create the interface. Protection circuitry is important to shield the fuel cell and the interface design from voltage surges or faults on the AMPS and to protect users of the AMPS.B. RequirementsIn coordination with project sponsors, the requirements for this project are as follows: 1) Operation of the Fuel Cell must be better documented.a. ECE students must be able to initialize and shut down the fuel cell in a safe and timely manner.b. ECE students must be able to identify and efficiently correct problems that arise as a result of fuel cell operation.2) The power converters must be simulated to show knowledge of their operation.a. The DC to DC power converter for the fuel cell must accept 18-36V DC and regulate it to 120V DC at the output. A tolerance of 0.1% is acceptable. b. The DC to AC power converter for the fuel cell must invert the regulated DC voltage to a sinusoidal three-phase 208V line-to-line AC voltage 2%. c. All power converters, transformers, and other circuitry used in this design must be capable of handling 200W peak power though, ideally, only 100W will ever pass through them.3) The overall system must provide power to the AMPS.a. The fuel cell, when interfaced to the AMPS, must provide positive three phase AC power flow into the model power system.b. The interface design must include protective circuitry to ensure that surges on the AMPS do not damage the fuel cell, either of the converters, the transformer, or the zero detection circuitry. 4) The fuel cell system must be able to synchronize with the AMPS without drawing excessive current.a. “Excessive” will be classified as any current above the rated conditions for the fuel cell: 5.5A at 18VDC on the output of the Fuel Cell.b. Maximum phase error will need to be determined by circuit analysis after measuring the line impedance of both the fuel cell system and the AMPS.C. Significance of the Project The AMPS provides students with the opportunity to explore and understand a typical power transmission system. The ECE department wishes to expand and improve this system to include alternative energy sources. This project will further facilitate the learning experience for students and enable them to experiment with new technologies in the power industry. Ultimately, this project will benefit power companies as UI students apply their knowledge in the workforce. D. Background/HistoryIn the mid-1990s, the University of Idaho acquired the Analog Model Power System (AMPS) from Idaho Power 1. The AMPS is located in the basement of the Buchanan Engineering Laboratory on UIs main campus in Moscow, Idaho. The purpose of AMPS is to provide an understanding of the operation of a power transmission and distribution system. The main source of power is from the local utility company, Avista. Currently, a generator is also interfaced with the AMPS to provide additional power to the system and increase complexity of system that can be analyzed. In addition to the generator, the UI has obtained an Avista SR-12 Hydrogen Fuel Cell from Genesis Fueltech 2. This fuel cell represents one of many alternative energy sources available in the 21st century.E. Functional SpecsIn cooperation with project sponsors, a set of functional specifications were created in order to meet the goals presented by the project sponsors. The overall specifications for the interface are: A 3-phase AC signal must present on the AMPS 18-36V DC input from the Fuel Cell Output 208V +/- 2 % (L-L 3-phase) Output Voltage at 60Hz +/- 0.2Hz Power flow of 45W for the interfaceInterface must fit on cart with dimensions 32” x 27” x 18” (2 shelves)*not including fuel cell, transformers or inductor bankF. Constraints Since the hydrogen fuel cell is creating power and the goal of this project is to transfer power from it to the AMPS, the interface must not draw power from the AMPS since it would defeat the purpose of the interface and possibly damage the fuel cell or other components in the design. It must be easy to operate and simple to maintain. All safety precautions must be properly labeled to ensure the users safety. Operation must also be simple enough so that it can be properly documented in a users manual and repeated if others were to use the interface. Other constraints for the system include but are not limited to cost, reliability and performance.G. Fuel Cell/AMPS Interface Solution A graphical representation of the design can be seen below in a functional block diagram (Figure 1). For the interface, a DC/DC converter is connected to the output of the hydrogen fuel cell to regulate the wide range DC output voltage (18-36VDC) to a constant level (120V). The DC voltage is then sent through a custom-programmed DC/AC converter that converts the 120VDC signal to a three-phase AC signal at 60 hertz. The 3-phase AC signal is then sent through three single-phase transformers that will step up the voltage to 208V line-to-line. The 3-phase AC signal is sent through a 3-phase inductor bank before being connected in parallel to the AMPS. To correctly interface the resulting 3-phase AC signal to the AMPS, the three phase signal must be synchronized with the three phase signals already on AMPS. Zero detection circuitry connected to the three phases on AMPS will provide the DC/AC converter with the required timings and phase information necessary for proper synchronization and fault detection.DCDCDCACTrans-formers and inductor bankINPUT18-36V DC120V DC 1%AC 3-phaseSynchronous Freq.Output: 208VLL OUTPUT208V 2%AC 3-phaseSynchronous Freq.:Zero-Detection CircuitryControlY45WFigure 1 - Functional Block DiagramIII. Method of SolutionA. Fuel Cell1) Types of Fuel Cells 3There are five different types of fuel cells currently being operated and manufactured. Each is named for the type of electrolyte used in the individual cells. Alkaline fuel cells (AFCs) are the oldest design. AFCs have been used in the U.S. space program since the 1960s but are not widely used within the earths atmosphere because of their susceptibility to contamination due to impurities in the air. Because they require pure hydrogen and oxygen to operate, they must be operated in special containment environments, which make them expensive and impractical for terrestrial use.Solid oxide fuel cells (SOFCs) are capable of supplying as much power as large utility grade generators but operate at much higher temperatures than other types of fuel cellsaround 1000C. SOFCs require more maintenance than other fuel cells because of their high temperature, but they are potentially more efficient because the steam generated by the high temperature operation can be used to power turbines and generate more electricity. Molten carbonate fuel cells (MCFCs) run at lower temperatures than SOFCs but still have the capability of generating steam. Their lower temperature (around 600C) makes them cheaper than SOFCs, but they still surpass other types of fuel cells with respect to cost.Phosphoric acid fuel cells (PAFCs) have a much lower operating temperature than SOFCs or MCFCs, but they have a longer warm-up time than proton exchange membrane fuel cells (PEMs). PEMs are relatively cheap to manufacture and maintain, and they operate at temperatures around 80C. They also have a fast startup time and are small and portable compared to the other types of fuel cells. This makes them suitable for a wide variety of applications, including vehicles. A PEM fuel cell has been donated to the University of Idaho ECE department and will be used to complete this project.2) Operation of the PEM Fuel CellProton exchange membrane fuel cells undergo a chemical reaction similar to that of a battery. As shown in Figure 2, the hydrogen molecules are stripped of their electrons by a thin membrane that has been specially treated to only conduct positively charged ions. The electrons flow through a load and to the cathode where two oxygen atoms will combine with the hydrogen ions to create water and heat. Figure 2 - PEM Chemical Reaction3) The Avista SR-12 PEM Fuel CellIn 2003, the University of Idaho ECE department acquired a 500W Avista SR-12 PEM fuel cell from Genesis Fueltech. This unit contains 12 fuel cell cartridges, and was once capable of providing 500W peak power with a variable DC voltage range of 23V to 43V 2. Since its manufacture in 1999, its capabilities have degraded and its characteristics have changed. For this reason, several load tests were performed on the fuel cell to re-characterize it. These tests have been discussed in the remainder of this section.4) Characterizing the SR-12 Fuel CellThe values shown in Table 1 and Table 2 reveal that the actual voltage range of the fuel cell differs from that discussed in “Avista SR-12 PEM Hydrogen Fuel Cell” 2. Fletcher claims that the voltage range is 23 43V DC, but by performing three separate tests, it can be shown that the actual voltage range is 18 36V DC if not overloaded. When overloaded, the fuel cell may drop below 18V DC and will draw current from the startup batteries for a short period of time before shutting down. This smaller voltage range greatly reduces the cost of a suitable DC to DC converter. Table 1 shows the results of tests one and two a no load test and a 100W load test. Note that for the nine and ten minute marks for the loaded test, the values were not available because the fuel cell failed because of weak batteries. More information about troubleshooting fuel cell operation is available in the system interface users manual. Table 1 - Preliminary Fuel Cell Voltage LevelsNo Load100 W Loadtimevoltagetimevoltage1 min.291 min.232 min. 312 min. 23.13 min. 303 min. 24.124 min.284 min.24.185 min.295 min.24.156 min.306 min.24.127 min.317 min.24.148 min.298 min.24.069 min.299 min.N/A10 min.3110 min.N/AThe results of the third test a variable load test which shows much of the range of the fuel cell voltage, including overloaded conditions, are presented in Table 2. This table shows load data obtained by connecting a resistive load to the fuel cell while operating under nominal conditions. Figure 3 shows a linear operation which is characteristic of most proton exchange membrane fuel cells. This graph more concretely verifies the voltage range presented in section 3.1.3, though an overload condition causes it to fall below the 18V limit. When significant current is seen on the two 12V batteries used to power the internal circuitry, the fuel cell should be considered overloaded. To reduce battery drain, and to stay within specifications, the fuel cell should not be run in an overloaded condition.Table 2 - Fuel Cell Loading CharacteristicsVVI (Load)AP (load) WI (Batteries) AR 350.310.50.0002116.6734.80.413.920.000487.00350.4140.000387.5034.50.517.250.000369.0033.60.826.880.000342.0031.71.857.060.000317.6129.22.5730.000311.6830.52.473.20.000412.71302.6780.000311.5428.92.880.920.000310.3228.33.290.560.00038.8427.83.391.740.00048.4226.84.1109.880.00016.5426.64.4117.040.00016.052551250.05175.0025.74.9125.93.00935.2423.46.84237.14Figure 3 - Fuel Cell Loading Curve5) Additional ConsiderationsThe load tests reveal that the fuel cell is capable of supplying just over 100W of power before overload conditions occur. This loss efficiency can be attributed to the aging fuel cell cartridges. These cartridges depend on moisture content to operate well, and they have lost some of their ability to self-humidify. To try to correct this, a bubble humidifier filled with de-ionized water was connected in line with the hydrogen to increase the humidity in the system. Theoretically, this would noticeably increase the capabilities of the fuel cell; however, after testing the fuel cell with the humidifier attached, no noticeable change in power was detected. Over time, the humidification may increase the power capability or lifespan of the fuel cell. Regardless, all components in the design have been designed to withstand 200W peak power from the fuel cell.B. DC/DC ConverterTo successfully regulate the output voltage from the fuel cell, the DC/DC converter is required to meet the following specifications: Wide input voltage range: 18-36V Constant output voltage: 120V 1% Pow