Home

state of the art of the automatic control and monitoring system from

image

Contents

1. the scan time for this PLC is Ims Kword of program and 0 225 ms for the I O e an ordinary PC computer Pentium 133 MHz for developing the graphical user interface in order to minimize the control program as much as possible some calculations are also done here also all data used for historical trends are stored on the computer hard disk e an Allen Bradley DTAM Micro module for developing a text user interface Rockwell95 this is used only if the graphical one breaks down From the software point of view it results from the requirements analysis that the control program must perform the following operations e monitoring and controlling different parameters flows pressures temperatures levels and so on using different actuators motors valves switches handling the alarms re starting and stopping the system changing between different operation modes automatic manually etc e other specific functions The Advanced Programming Software APS from Allen Bradley was used in developing the control program Rockwell95 APS is a dedicated software environment for industrial control The resulting program is of type ladder logic and was developed using an IBM PC compatible computer and then downloaded into the PLC For the user interface development the InTouch SCADA package on a PC is used Wonderware94 The display windows that formed the user interface are linked with the PLC using Dynamic Data Exchange DDE
2. Language created by MGA Software MGA95 MGA96 Through simulation we tried to maintain the PT1 pressure around 2 bars TT8 around 55 C and TT12 at around 70 C according to the C case from the Table 1 The following equations that are characterizing the heating process from the heat exchangers Popa896 d Q oo amn Si 4 tiin ta Eten 1 Qy M16 2 ry tm d t ose otan Tta Vi tte Ca ttan s1 T lt s1 m a e 2 O 0 8 Q 0 8 nm nho Sra a7 4 Ja 4 Pe Jala Where Ee OT gg ee tiin t input output temperature for primary agent tyjin t 51 input output temperature for secondary agent M Ms quantity of water from the primary secondary heat exchanger Qi Qs the flow from the primary and secondary agent in the heat exchanger r f global coefficient for the heat exchange Qimax Qsimax Maximum flow for fully opened valves in the primary secondary heat exchanger After the simulation our new startegy model for the heat station was accepted as a realistic one and with a rational functioning after studying the results obtained For the considered cases the validation of the proposed model was made with data collected from the real system and the results were as we expected After the validation of all cases we started to implement our new strategy for the heat station by making changes in the PLC program These are our mains working issues at present 4102 2 3
3. rector of University of Oradea who created the possibility for this project to exist REFERENCES Halang91 Halang W A Stoyenko A D 1991 Constructing Predictable Real Time Systems Kluwer Academic Publishers 254pp Kopetz92 Kopetz H 1992 Time Triggered versus Event Triggered Systems Proc International Workshop on Operating Systems in the 90s and Beyond Vol 563 pp45 67 Parr95 Parr E A 1995 Programmable Controllers An Engineer s Guide Newnes an imprint of Butterworth Heinemann Ltd Oxford pp325 Rockwell95 Rockwell Automation 1995 Allen Bradley Automation Systems pp345 Table 1 Possible cases for winter and summer Zmaranda95 Zmaranda D 1995 Automatic Control and Monitoring System for the District Heating System at the University of Oradea United Nations University Reports Reykjavik Iceland pp23 Rockwell94 Rockwell automation 1994 Advanced programming Software User Manual Reference Manual pp567 Wonderware90 Wonderware Corporation 1990 DDE Sever Allen Bradley Serial pp69 Wonderware94 Wonderware Corporation 1994 InTouch User s Guide pp489 Popa86 Popa B 1986 Thermotechnician Engineer Manual Editura Tehnica Bucharest pp123 Philips96 Phillips C I Harbor R D 1996 Feedback Controlled Systems Prentice Hall International pp436 MGA95 MGA Software 1995 ACSL Reference Manual Edition 11 1 pp3
4. The return geothermal water from the heating processes leaves the station in a common pipe and is discharged in the river Peta or to cascaded users The DH district heating network is a closed system directly connected to the elements in the buildings and heated indirectly by geothermal water in four plate exchangers The heating period has an average of 172 days year and in summer time the distribution network is emptied Two of the three circulation pumps P 5 7 are used to circulate water in the closed DH network to deliver heat to the buildings Two make up water pumps P8 9 are used to ad water into the closed DH network to maintain its static pressure within predetermined limits to compensate it for leakage Controller RG5 is used to control the supply temperature TT8 for the district heating network This regulator utilizes the control valve CV2 to regulate the flow of the geothermal water to the DH exchanger to heat the supply water TT8 in the district heating network The controller RG6 utilizes CV4 to regulate the pressure inlet to the DH heat exchanger The function of P8 and P9 is to keep return pressure PT5 the static pressure in the system The DHW domestic hot water is produced indirectly by heating up cold water from the University s fresh water supply in a plate heat exchanger with geothermal water There are two plate exchangers and one is for reserve The system is operated continuously all year around The pumping s
5. cases considering also the initial conditions MGA96 So the equations characterizing the statically regime of the heat station are Popa86 QO C tin T bies thin 7 b gites tries 2 QC Gin bres Qo Cries bain K S in baies ries si bain 2 2 C 2 0 re sires siin tan K Sy Q ki tN Pye 7 Pa Ca Riin WP a Pa ko VPs 7 Px Qo 21 22 where Q flowrate through the heat exchanger used for DH Q flowrate through the heat exchanger used for DHW Qo total flowrate from the well tiin ties input output temperature for the heat exchanger used for DH tzin toies input output temperature for the heat exchanger used for DHW K K global coefficients for the heat exchange in the heat exchangers S So surfaces for the heat exchange ko ki Kam flow coefficients for valves CVO CV5 CV4 Px pressure to be maintained corresponds to PT1 Pa atmospheric pressure Ps well pressure In the mean time the dynamically regime is characterized by the following equations d d Pp 16 Cii T fe Rate tiie JF tjk s ti tases Cuse T ir ECAT dt 2 1 d Tea Cam Paice Lae e Crzies Fein lk ny Coin s2iec Cries aai 2 a e T dt dt IQ d Pe Pe Fs eas P x gt The simulation language chosen was ACSL GM the Graphic Modeller from Advanced Continuous Simulating
6. 67 MGA96 MGA Software 1996 ACSL Graphic Modeller Version 4 1 pp124 Symbol Name Final control Process value Preset value element A SUMMER RG8 Supplied water temperature CV5 TT12 50 55 C RG7 Water pressure in the heat exchanger CV3 PT7 2 2 5 bar B WINTER P1 not functioning and the pumps functioning RG6 Water temperature in the secondary circuit CV4 TT8 65 75 C RG8 Supplied water temperature CV5 TT12 50 55 C C WINTER P1 not functioning and the pumps by passed RG6 Water temperature in the secondary circuit CV4 TT8 65 75 C RG8 Supplied water temperature CV5 TT12 50 55 C D WINTER P1 and the pumps are not functioning RG6 Water temperature in the secondary circuit CV4 TT8 65 75 C RG8 Supplied water temperature CV5 TT12 50 55 C 4103 analyze the current situation P d erform processing actions ecide on measures to take actuate measures po deltaT time Figure 1 The basic cycle of a control system P8 P9 Legend TT PT FT RG CV DH DHW CW P5 P6 P7 X X4 temperature transmitter pressure transmitter flowrate transmitter controller control valve motor for valve control district heating domestic hot water cold water cv6 C
7. Proceedings World Geothermal Congress 2000 Kyushu Tohoku Japan May 28 June 10 2000 STATE OF THE ART OF THE AUTOMATIC CONTROL AND MONITORING SYSTEM FROM THE GEOTHERMAL PLANT FROM THE UNIVERSITY OF ORADEA ROMANIA PRESENT AND PERSPECTIVES Doina Zmaranda Gianina Gabor University of Oradea 5 Armatei Romane St 3700 Oradea Romania University of Oradea 5 Armatei Romane St 3700 Oradea Romania Key Words control system Programmable Logic Controller PLC user interface ABSTRACT In its first part the paper intends to describe the main features of the already implemented automatic control and monitoring system from the University of Oradea from the implementation point of view including aspects regarding the software and hardware In the second part of the paper some future perspectives of this existing system will be outlined Between these there are some important directions in which we already start to work on First there are the modifications that we have done to the implemented system these result after a period of almost two years of continuously running the system Because the system is at this moment unique in our country another aspect regarding the future perspectives deals with the way in which it is used for training students from our university However the system described in the paper turns the attention to tools and techniques that help us building such complex systems in a safe and secure way 1 IN
8. TRODUCTION The automatic control and monitoring system for the geothermal plant from the University of Oradea was already described from the structural and functional point of view in Zmaranda95 1 1 The system structure The controlled plant is composed of 3 parts the well station the pump station and the heat station The system functions in the following way e the geothermal water is extracted from the well station using a deep well pump if the necessary flowrate is greater than the artesian one e the water is then stored into a reservoir tank which acts as an accumulator and also separates the production network from the distribution network e from the reservoir tank the water is pumped through the pump station to the heat station In the heat station the water is not directly utilised but through 4 heat exchangers the water that comes out from these heat exchangers flows into the distribution network and heats the university campus buildings 1 2 The control system structure In order to implement the automatic system for this geothermal plant the general hardware and software 4099 configuration was established based on the application requirements Philips96 From the hardware point of view the following devices were used e an Allen Bradley PLC SLC 5 03 Programmable Logic Controller equipped with multiple I O modules and a non interruptible power supply for developing the control program Rockwell94
9. Training the students using the implemented control system The system already implemented is in present intensively used for the teaching purposes The students study the following issues e the importance of the geothermal energy and its main directions of utilization e the main possibilities of geothermal energy utilization in our country e the main methods and tools used for automating geothermal plants creating and implementing simulation programs using ACSL creating control programs using APS software from Allen Bradley creating and implementing user interfaces using Wonderware InTouch software means of optimization of the system functions through control parameters modification In order to improve the security of the control system we have the possibility to train the operators using the simulation program The simulation program gives us the possibility to test the system response without connecting it to the real plant Different scenarios can be tested and the human response and behavior can be also evaluated In the future we also intend to create a summer school for training personal to work into the geothermal plants from operator to system engineer level 3 CONCLUSIONS In this paper some specific problems associated with the implementation of control systems for geothermal plants were considered It was demonstrated that the joint goals of predictability and determinism could be achieved using the cyclic paradigm b
10. W Figure 2 Schematic diagram for the heat station pressure controller CW cold water DHW Qo DHW ro yRG11 Q2 bin q tezics r Ml ti RG6 Mi eE wn ee CV4 Px CV5 Cascade usage Peta CVO k NV eee t RG8 ths ra tories H 7 e3 well no 4796 ue DH district heating CW cold water Figure 3 The simplified model of the new strategy for the heat station 4104
11. aT CASE model WITH sensors AND actuators DO EVERY Nth deltaT BEGIN operation operation IF situation_predicate THEN operation operation IF situation_predicate THEN operation operation END mode2 WITH sensors AND actuators DO EVERY Nth deltaT BEGIN operation operation IF situation_predicate THEN operation operation startup_mode WITH sensors AND actuators DO EVERY Nth deltaT BEGIN END ENDCASE It is obvious that the basic structure of the software presented above corresponds to the fundamental cyclic paradigm presented in This approach also provides a strong mechanism for focusing upon the essential issues of the specific application domain This cyclic approach was used for developing the control program for the geothermal plant from the University of Oradea The control program implemented into the PLC runs forever and every module is implemented as a separate subroutine So the structure of the program developed with this software corresponds to the general structure presented above The time base here deltaT is the time scan of the controller and it depends of processor speed as ell as the length of the control program In order to improve the time scan the modules subroutines were so created in order to minimize the length of the control program all modules that perform additional calculations were moved if possible on the PC computer In its curre
12. ased on resource adequacy The automatic control and monitoring system for the geothermal plant from the University of Oradea demonstrates that for a wide category of automatic control systems the cyclic approach is a simple but a feasible solution in order to achieve predictability and determinism Such a control system needs a permanent maintenance and improvement in order to obtain an optimum functionality In its second part this paper tries to present some of the recently modifications done into the system as a result of a two years functioning analysis All the modifications implemented lead to a better system performance but also improve the knowledge about the system behavior By using this control system in the teaching process we try to create specialists in this domain that will be able in the future to exploit in the modern way the existing geothermal resources from our country ACKNOLEDGEMENTS The authors of this paper would like to express their gratitude to all the colleagues from the University of Oradea who participate in the development and maintenance process of the geothermal plant from the University of Oradea Special thanks to all staff members of Orkustofnun Iceland especially to Dr Ingvar Fridleifsson for their efficient training in geothermal matters Also to all the staff from Rafhonnun Ltd were this project initially started Finally we want to express our gratitude to Prof Dr Ing Teodor Maghiar
13. ation greater than the sampling period of the trigger task deltaT are guaranteed to be observed A strong advantage of applying a solution based upon timing intervals is the possibility to treat hardware and software faults in a reasonable manner This advantage accrues due to having simultaneous control over the continuous processing being done and the rate at which it is being performed Using the cyclic approach a fault may only have local time effects but the system will automatically stabilize itself in succeeding time periods The main advantage of the time driven approach is that a better error detection and confinement can be achieved Halang91 Also for critical measurements it is also possible to build time series for 4100 a suitable number of cyclic periods and apply interpolation in the presence of a fault in order to approximate a missing measurement These series may also be continually calculated and applied for determining the reasonability of measurements over time The cyclic approach views the modules like subroutines of a main program Consequently the program structure should be based upon the partitioning of application into modules depending on functionality and when necessary on time constrains that are coupled together using a control structure A general structure is presented below This partitioning leads to a set of operations each operation performing a specific function DO forever DO during delt
14. communication protocol in order to transfer data Wonderware90 2 MODIFICATIONS TO THE EXISTING SYSTEM In order to obtain a better functionality of the system several modification were done to the initial implemented control system The main goal of these modifications is to obtain a better performance of the system as well as a higher reliability than in the previous version 2 1 Improving the reliability and predictability of the software program by using the cyclic approach One of the simplest ways of developing automatic and control systems is using the cyclic approach In the latest years there has been a lack of research in respect to exploiting the cyclic approach in automatic control systems This is mainly due to the fact that the simplifying fundamental properties seemingly do not provide significant academic research challenge Practical applications prove that this wrong because up to now the time based approach was an essential ingredient in reducing the complexity and achieving mapping simplifications in the form of bulk synchronous processing The cyclic approach paradigm is based on a philosophy of resource adequacy that is it relies upon the assumption that there are sufficient resources to guarantee that all processing requirements are met on time Kopetz92 If processing resources are not sufficient to accomplish all processing there are two means of achieving resource adequacy employing faster processing eleme
15. nt version the control program consists of 29 program files modules 92 data files 6828 instructions and uses approximately 200 I O signals The scan time obtained with this program were approximately 100ms which includes program time scan I O time scan and actuators delays as well as the trigger task overhead This corresponds to the application needs the controlling and monitoring system for the Oradea University Geothermal Plant is a relatively slow real time control system and consequently all time constants imposed are of the order of magnitude of one ore more minutes Zmaranda95 so that a scan time period of approximately 100ms means that it could be a maximum delay in treating an exceptional situation of 200ms which is more than acceptable It can be observed that the number of modules is relatively big but only 25 of the modules deal with normal functioning of the system The rest of them 75 are dealing with handling exceptional situation such as alarms for example which rarely appear This protection although increasing the program length was necessary for obtaining robust software Parr95 2 2 Improving the control strategy for the heat station The heat station s function is to heat up the buildings DH district heating of the University and to supply them with domestic hot water DHW These processes are operated indirectly i e the geothermal water is used indirectly in plate exchangers to supply heat energy
16. nts or paralleling and distributing functions to multiple processing elements nodes Given this paradigm the programmed application logic could be divided into short code segments each of these parts having a uniform structure and a pre defined functionality The most essential timing property is deltaT which is the interval which establish cyclic execution frequency The value of deltaT must be established on a rational application dependent basis This is the central issue in constructing automatic control systems upon a cyclic approach so each particular application requires proper engineering risk and trade off analysis in order to determine the appropriate execution frequency properties Two contradictory requirements must be accomplished when establishing the value for deltaT first the deltaT parameter must be long enough to permit all processing to be accomplished and second the deltaT parameter must be sufficiently short to insure stability of the system so every critical situation can be properly handled Usually a trigger task is used to regularly capture the state of the environment This trigger task is a periodic task that evaluates a trigger condition on a set of temporally accurate real time variables The result of a trigger task can be a control signal that activates another application task Kopetz92 Since data either external or internal is sampled at the frequency of the trigger task only those data with dur
17. tation of 4101 the fresh water delivers water for the buildings from our university and for the heat station by intermittent control of the pumps So the PT8 is varying between 2 4 bars The domestic hot water is produced with constant supply temperature TT12 with the aid of the controller RG7 The RG7 controller utilizes the control valve CV3 to regulate the flow of the geothermal water to the DHW heat exchanger to heat up the DHW water to the supply temperature TT12 The controller RG8 utilizes the control valve CV5 to regulate the pressure inlet to the DHW heat exchanger The on off control valve CV6 is used to protect the plate heat exchanger from excessive differential pressure across the plates due to the excessive fresh water supply system PT8 Together with a group of specialists from the University of Oradea we analyzed the system control automation Figure2 and we realized that the behavior of the controllers RG5 RG6 depends on the behavior of RG7 RG8 controllers In this case the valves CV4 and CV5 are working opening and closing very often to keep the temperatures to the preset values To eliminate this inconvenient we proposed another strategy presented in By introducing a pressure controller in the DHW we obtained all the new possible control loops Table presents all the possible cases for winter and summer In order to simulate the new strategy we created a model using equations from both dynamically and statically

Download Pdf Manuals

image

Related Search

Related Contents

  2468 フュートレック    EPREUVE FACULTATIVE D`AEROMODELISME    Package Content ..........................................................  Kenroy Home 32479CH Instructions / Assembly  1985-KB-HelpSystems - Center for LifeLong Learning & Design (L3D)  

Copyright © All rights reserved.
Failed to retrieve file