自动化外文翻译-住宅用燃料电池测试台的微电脑控【中文4140字】 【PDF+中文WORD】
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中文4140字
PDF+中文WORD
自动化外文翻译-住宅用燃料电池测试台的微电脑控【中文4140字】
【PDF+中文WORD】
自动化
外文
翻译
住宅
燃料电池
测试
微电脑
中文
4140
PDF
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自动化外文翻译-住宅用燃料电池测试台的微电脑控【中文4140字】 【PDF+中文WORD】,中文4140字,PDF+中文WORD,自动化外文翻译-住宅用燃料电池测试台的微电脑控【中文4140字】,【PDF+中文WORD】,自动化,外文,翻译,住宅,燃料电池,测试,微电脑,中文,4140,PDF
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Journal of Power Sources 127 (2004) 319324Micro-computer control for a fuel cell test bench for residential useG. Heideck, M. Purmann, Z. StyczynskiInstitute of Power Systems, University of Magdeburg, 39106 Magdeburg, GermanyAbstractGreat efforts are presently being undertaken to develop fuel cell applications. The Chair of Electrical Power Networks and RenewableEnergy Sources at the University of Magdeburg operates a fuel cell test bench which is oriented to fuel cell applications for residential use.Like many test benches of this kind, the control of the plant is done by a classical programmable logic controller (PLC). After numerousmeasurements and tests were carried out, it could be noted that the process power of the PLC is limited considering the improvementof dynamic behaviour of a fuel cell system and taking over extensive calculation tasks. Furthermore, an automatic measuring procedureis desirable for long-term investigations. An interface is therefore necessary for the superordinate PC-based measurement and systemcontrol in order to vary specific parameters dependent on the experimental process which have not yet been realised. Additionally, it canbe noted that an economical and ecological operation of a fuel cell plant is only possible if the design considers the entire heating system.The combination of both tasks in a common control is useful. The micro-computer control as a standard solution is available for thesuperordinate combined control of heating systems and block-type thermal power stations using combustion engines. This control systemwill now be modified in close co-operation with the suppliers for the test stand control. 2003 Published by Elsevier B.V.Keywords: Micro-computer control; Fuel cell system; Overall efficiency; Heating system; Network adjustment1. IntroductionThis paper presents a micro-computer control concept fora fuel cell test stand which enables the automatic test standto operate and combines the fuel cell system with othersystem components like intermediate heat storage units orburners. The ecological, economical and technical advan-tages of the components can only be used by an intelligentand complex control.An economical and efficient operation of fuel cell systemsin residential applications essentially depends on the possi-bility to maximise the use of the generated thermal and elec-trical power. Reaching a high total efficiency in combinationwith a high electrical efficiency is the goal of the efforts.However, a high-energy output is only to be expected if anoptimal ratio exists between both kinds of energy. This ratiodependsontheconcretedemandofheatandelectricalenergyand the determined price for the generated electrical power.The fuel cell test bench at the Chair of Electric PowerNetworks and Renewable Energy Sources at the Otto-von-Guericke-Universitaet Magdeburg was put into operation 1year ago. The test bench has been in operation for approx-Corresponding author.E-mail addresses: guenter.heidecket.uni-magdeburg.de (G. Heideck),mathias.purmannet.uni-magdeburg.de (M. Purmann).imately 1500h. More than 500 characteristics were mea-sured. The dynamic as well as the stationary behaviour de-pendent on the important process parameters were recorded.The stack is designed to generate approximately 500Welectrical power and consists of 25 single cells. Accordingly,the peripheral components are designed to supply this stackwith the necessary process media. The fuel hydrogen for thestack is produced by an electrolyser which was bought inparallel with the installation of the test stand. It generatesabout 1m3/h hydrogen. For the necessary air supply of thestack, the compressed air system of the building is used.The control of the process medias hydrogen and air wereovertaken by two mass flow controllers. Further parameterswhich determine the electrical power generation like thestack temperature and the humidity of the process mediawere measured by a PC-based data-acquisition system.Table 1 shows the parameters which were actually con-trolled by the PLC-system S7/200 and recorded by thedata-acquisition system 1.2. Hardware description of the controlThe central element of the control is the processor MPC555 (32-bit at 40MHz), a joint development of Motorola andIBM. It is installed on a controller board with a great number0378-7753/$ see front matter 2003 Published by Elsevier B.V.doi:10.1016/j.jpowsour.2003.09.029320G. Heideck et al./Journal of Power Sources 127 (2004) 319324Table 1Measured analogue parameters and their usageSerial numberDescriptionIndicatedProcessedExpensed1Stack voltage2Stack current3Temperature H2output4Temperature H2input5Temperature air humidifier6Temperature cooling water heating7Temperature heat exchanger input8Temperature heat exchanger output9Temperature air input10Temperature air output11Temperature cooling water before stack12Temperature cooling water after stack13Rate of flow H214Rate of flow Air15Rate of flow cooling water16Humidity air after stack17Pressure H2before stack18Pressure H2after stack19Pressure air before stack20Pressure air after stackof peripheral components like external flash storage unit,real-time clock, and integrated 46-bit floating-point-unit.Most of the signals can not be directly connected to the envi-ronment. For this purpose, the board is attached to a carriermotherboard. On this carrier motherboard in addition to thepower supply, are the switching elements for the adaptationand the preparation of the signals to the process as well asa set of interfaces which are necessary for communication2.The carrier motherboard requires only one 24V powersupply. The other necessary voltages are generated on themotherboard and for all functional units connected to theenvironment, separate safety devices exist.The operation of the control unit should be made via anoperator screen. An illuminated LCD display with 16 linesand 40 columns is therefore inserted. As the display hasgraphic capacities sequences can be directly presented. Fournavigation buttons and two separate buttons are availablefor the input of parameters and operation modes but an al-phanumeric keyboard with at maximum 78 press buttonscan also be connected. The connection between keyboardand controller can be made via the communication ports.The concrete number and the kind of individual inputs andoutputs can be seen in Fig. 1, which also shows the controldesign.A special feature of the control is the possibility of freelymounting the analogue inputs. Additionally, sensors with-out signal conditioning can be connected with appropriatemounting of the board. Table 2 shows a choice of con-nectable sensors and the corresponding prescribed mount-ing. Naturally, the necessary filters for failure-free recordingof the signals are considered. Several interfaces are availablefor communication with the environment. These interfacesare in detail: two serial interfaces RS 232 for the connection of a PC,a notebook or a modem; two CAN-Businterfaces make possible the connection ofadditional MPC-555 controls, other process controls withtheir own hardware unit and also CAN-Modules for theextension of inputs and outputs; an interface RS 485, used for excitation of bus capablecredits such as Grundfos credits and an Ethernet interfacethat allows for the connection of personal computer netsand ISDN modem makes the simple entrance possible tothe Internet 3.The carrier motherboard has a size of approximately300mm 300mm and is preferably installed on therear-side of the control cabinet behind the display so that noplace is blocked on the mounting board in the control cabi-net. There the necessary electromechanic and the electronicFig. 1. Carrier board with the single modules Foto: energiekontor Han-nover.G. Heideck et al./Journal of Power Sources 127 (2004) 319324321Table 2Choice of connectable sensors and the corresponding prescribed mountingSerialnumberDescription ANAINType ()Ra (?)R+; R (?)RF2 (?)CF (?F)RF1 (?)RS (?)Jumper(yes/no)RV (?)1Temperature sensor KTY 81/210T800.0001000.000200.0000.22200.0005.0002Temperature sensor Pt 1000Tp800.000450.00033.0000.22100.0005.0003SwitcherK800.000200.0000.22200.00016205.0004Current 20 to +20mAP+800.0001600.000200.0000.22200.000685Current 420mAIA800.0003200.000200.0000.22200.0001566Solar cell “RESOL”12m5200.0005.0000.225.0001007Gas sensorGS800.0001600.000500.0000.22250.0008ac net voltage (isolated)W800.0001600.00049.9000.22250.0001279Thermocouple Type KNCN800.00010000.0001.0000.225.00010010Voltage of LambdasondeL1000.000100.0001.00100.00025000011dc voltage 30V30U200.000200.0000.221000.000Amplifier resistor: Ra, R+, and R; filter capacitor/resistor: CF, RF2, RF1; shunt: RS; pull-up resistor: RV.Fig. 2. Implemented microcontroller solution with input/output and switch-ing modules Foto: energiekontor Hponents for the load circuits including the 24V powerunit can be installed (Fig. 2) 4.3. Software descriptionThe designer of the hardware has developed this con-trol as a superordinate control system for innovative powerstations, e.g. with condensing boiler cascades, block-typepower stations, intermediate storage units, solar facilities,and heat pumps as well as heating circuits and hot waterpreparation with low return pipe temperatures. The ecolog-ical, economical and technical advantages of the compo-nents can only be used effectively by using such a complexcontrol system. For the processor MPC555 different operat-ing systems like Linux, RTOS and software programs likesoftware codes written with the programming language Ccan be used. The developers have decided to use the multi-tasking operating system “Real TimeOperatingSystem-UniHannover” (RTOS-UH). The operating system is responsi-ble for the internal organisation of the computer system andvery often makes possible the further use of older programcodes or codes which are written by changing softwareteams. The present program is written in the standard lan-guage PEARL which was specifically developed for controland supervisory tasks. In order to use as many tools as pos-sible of available software and the extensive experiences ofthe software developers, the team at LENA also decided touse the standard language “PEARL”. Software tools likevoltage, frequency and power monitoring for the combinedheat and power unit (CHP) can almost be incorporated intothe program of the fuel cell system without adaptation. Bugscan be limited and the development time can be shortenedby using proven software tools. C-Compiler for the oper-ating system RTOS-UH are available, so that parts of theprogram which are written in the programming language Cand/or C+ and run under Windows or Linux run also un-der RTOS-UH. In this way, C-code can be imbedded with-out problems into the PEARL program. The chosen displayprovides a menu control working nearly exclusively withplaintext. So the operation can be significantly improved.Linearities can also be presented with a good resolutionon account of the graphical capabilities of the display.Therefore, programmed day or week load curves can bevisualised. The real-time clock with an integrated calendarsupplies the system with the desired real-time references.The extensively programmed disturbance and alarm man-agement also uses the possibilities of the real-time clockand is helpful for limiting downtimes during the operationof the fuel cell system. The extensive remote control possi-bilities are discussed in one of the following sections 4.4. Planned extensions4.1. Hydrogen humidificationFor the expansion of stack investigations a humidifierfor hydrogen was planned and constructed according to theconcept of the air humidifier. In this manner, it is possibleto determine the dependence of the power generation on thehumidification degree of hydrogen and to optimally controlthe humidity. The possible water mass transported by theair mainly depends on the temperature of the hydrogen so322G. Heideck et al./Journal of Power Sources 127 (2004) 319324that the water content can be specified by controlling thehumidifier temperature. It is, however, necessary that thetube between the humidifier and the stack is well insulatedto prevent a cooling of the hydrogen and therefore a con-densation of the water on the way to the stack. Otherwise,the tube has to be additionally heated between humidifierand stack. Therefore, the heating control can be overtakenby the supervisory control.4.2. Air supplyThe existing test stand is supplied with air from the com-pressed air system of the building. A mass flow controllerregulates the air flow in accordance with the set point de-faulted by the PLC. Since fuel cell facilities for residentialuse generally use the compressed air generated by their owncompressors, the air supply of the system will be conceptu-ally adapted. An air compressor with a power control waschosen to supply the fuel cell system with low energy con-sumption and low pressure losses. It was particular abouthigh efficiencies under full and part load at the selection ofthe compressor and the motor. However, in the case of thisconcept, the control must generate the required actuator sig-nal. For this purpose, the volume flow and the temperatureof the air are to be measured. Fig. 3 shows the constructionof the new air system.4.3. Heating integrationThe main goal of the integration of a stationary fuel cellsystem into a heating system is the full use of generated heatto improve the total energy balance. The best way to achievethe defined goal is the operation of the heating system atlow return pipe temperatures. A low return pipe temperatureallows the cooling of the waste air below the dew point. Ad-ditionally, a higher temperature difference between the stackand heating circuit can be reached. The stack temperatureof a PEM fuel cell is often situated between 60 and 80C.A heat exchanger is necessary for decoupling the pressurelevels of the heating system and the stack. In order to limitthe size of the exchanger a temperature difference of 10Kbetween supply temperature of the fuel cell and supply tem-StackHumidifierPressureregulatingvalveSurroundingairExhaustairCompressorFig. 3. Scheme of the planned air supply.perature of the heating circuit has to be considered. So onlysupply temperatures of 60C without additional heating canbe reached. This value is still acceptable for low-temperatureheating systems and hot water preparation. In order to bemore independent of the fuel cell temperature there is theidea to use surplus hydrogen in a catalytic burner and there-fore to raise the temperature level. Simultaneously, it is pos-sible to influence the ratio between heat and electrical powergeneration and to meet the demand of heat and electricalpower. This is a difficult task for the proposed control sincethe control parameters must be permanently matched.In order to improve the number of full operating hoursand to make possible a more effective power generation dur-ing peak load times without wasting heat the installationof an intermediate heat storage unit can be economicallyand ecologically promising. The storage unit can be alsoused for pre-warming the stack. However, for this purposean additional three-way valve and a connection to the up-per part of the heat exchanger is necessary. If the rotationspeed of the pumps are controlled via a pulse width mod-ulation (PWM) the storage unit can be optionally chargedand discharged. Fig. 4 shows the scheme of the test benchwhich is extended by the corresponding components. Forthe control of the energy fluxes a complex control system isrequired which precisely knows the system conditions. Thementioned micro-computer control is designed for this task.4.4. Grid-connection/power supply monitoringThe investigations on the test bench are focused on thegrid connected operation. In this operating mode, the gen-erated electric energy is used to cover the local internalconsumption, e.g. in a house. The surplus is then fed into theelectric power network of the grid utility and compensated.The actual benefit results in the decreased purchase of elec-tric energy since the compensation for the fed-in electricenergy is lower than the price of the purchased energy. How-ever, the generated electric power can only be reasonablyused if it conforms to the parameters of the power network.For this reason, direct current of the fuel cell with a lowvoltage level has to be transformed into alternating currenton a higher voltage level. While the adaptation of the kindG. Heideck et al./Journal of Power Sources 127 (2004) 319324323*Fig. 4. Scheme of the superordinate heating system of the fuel cell test stand.of current is solved by well-known concepts of inverters, thelow voltage level of the fuel cell proves more problematic.The fuel cell stack which is integrated into the test stand hasan open-circuit voltage at about 23V and a voltage of about12V under full load. For a single-phase operation a voltagelevel is required which is approximately 30 times higherthan the voltage level of the fuel cell. The converter used atthe chair consists of a boost converter and an inverter. Thisconcept results in a relatively low efficiency caused by thevoltage adaptation. Therefore, it is planned to increase thedc voltage of the fuel cell to a dc voltage of 400V by usinga step-up switching regulator and to transform the directcurrent into an alternating current by installing a standardinverter. The step-up switching regulator and the invertedrectifiers can be directly controlled with the describedmicro-computer control. Fig. 5 shows the block diagram ofthis concept by which a higher efficiency is expected 5.4.5. Remote monitoringService and fast reaction when problems occur are in-creasingly becoming important sales arguments. This hasresulted in the use of remote monitoring and modern distur-DC / AC ConverterInverter modulPower networkDC- Fuel-Cell13V / 35AfU Z,DC-Link400VNetworkmonitoringFig. 5. Block diagram of the concept for voltage and current adaptation.bance management. With the available Ethernet interface,the connection of an ISDN modem is both easy and possible.Remote monitoring, remote control and remote diagnosticsare realisable both via the Internet and
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