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A Virtual Laboratory Environment for Control Design of a Multivariable Process
12th IFAC Symposium on July Philadelphia, PA, USAin 12th 7-9, IFAC2019. Symposium on Advances Advances in Control Control Education Education July 7-9, Philadelphia, PA, 12th IFAC2019. Symposium on Advances Control Education July 7-9, 2019. Philadelphia, PA, USA USAin Available online at www.sciencedirect.com July 7-9, Philadelphia, PA, USAin Control Education 12th IFAC2019. Symposium on Advances July 7-9, 2019. Philadelphia, PA, USA
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IFAC PapersOnLine 52-9Control (2019) 15–20 Design of a Multivariable Process A Virtual Laboratory Environment for A Virtual Laboratory Environment for Control A Virtual Laboratory Environment for Control Design Design of of aa Multivariable Multivariable Process Process A Virtual Laboratory Environment for Control Design of a Multivariable Process Javier Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** A Virtual Laboratory Environment for Control Design of a Multivariable Process
Javier Gustavo Javier Sotomayor-Moriano*. Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** Pérez-Zúñiga** Mario Soto*** Javier Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** Mario Soto*** Mario Soto*** Javier Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** Mario Soto*** Engineering Department, Pontifical Catholic University of Peru, PUCP, Lima, Peru. Mario Soto*** Engineering Department, Pontifical Catholic University of PUCP, Peru. Engineering Department, Pontifical Catholic University of Peru, Peru, PUCP, Lima, Lima, Peru. (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). Engineering Department, Pontifical Catholic University of Peru, PUCP, Lima, Peru. (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). Engineering Department, Pontifical Catholic University of Peru, PUCP, Lima, Peru. (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). Abstract: This paper describes the development of a virtual laboratory environment (VLE) that allows Abstract: This papercontrol describes the development development ofvirtual virtual laboratory environment (VLE) that allows allows Abstract: paper describes the aa virtual laboratory environment (VLE) that students toThis perform design practice in aof plant from remote locations through a web Abstract: This papercontrol describes the development a virtual laboratory environment (VLE) that system allows students to perform control design practice in aaof virtual plant from remote locations through web students perform practice in virtual plant from remote through aa web browser. to The proposed VLEdesign facilitates to learn concepts; such as, design oflocations controllers and Abstract: This paper describes the development a virtual laboratory environment (VLE) that system allows students perform control practice in aof virtual plant from remote through awith weba browser. to The proposed VLEdesign facilitates to learn learn concepts; such as, design design oflocations controllers and system browser. The proposed VLE facilitates to concepts; such as, of controllers and identification of multivariable processes using a simulation environment, and an industrial device students to control in a concepts; virtual from remote locations through awith web browser.model Theperform proposed VLEdesign facilitates to learn suchis as, design of controllers anditssystem identification of multivariable processes using simulation environment, and an an industrial device with identification of processes using aa simulation environment, and industrial device reliable ofmultivariable a benchmark plant.practice Architecture of the plant VLE explained and evidence of use isaa browser. The proposed VLE facilitates to learn concepts; such as, design of controllers and system identification of multivariable processes using a simulation environment, and an industrial device with reliable model of a benchmark plant. Architecture of the VLE is explained and evidence of its use is reliable of a benchmark plant. Architecture of tool the VLE explained andwide evidence of its use isa showed. model The proposed VLE represents an education that isis user friendly, availability, with identification of multivariable processes using a simulation environment, and an industrial device with reliable model of a benchmark plant. Architecture of the VLE is explained and evidence of its use isa showed. The proposed VLE represents an education tool that is user friendly, wide availability, with showed. proposed VLE represents education tool that is allows user friendly, wide student availability, graphicalThe interface capabilities and lowancost maintenance, that to improve skillswith by reliable model of a benchmark plant. Architecture of the VLE is explained and evidence of its use is showed. The proposed VLE represents an education tool that is user friendly, wide availability, with graphical interface capabilities and low cost maintenance, that allows to improve student skills by graphical interface and low cost maintenance, that allows to improve student skills by connecting the theorycapabilities and practice. showed. The proposed VLE represents an education tool that is user friendly, wide availability, with graphical interface capabilities and low cost maintenance, that allows to improve student skills by connecting the theory and practice. connecting the theory design, and practice. Keywords: Control System Virtual environment, Multivariable graphical interface and low cost maintenance, that allows to Controllers, improve student skills by © 2019, IFAC (International Federation ofidentification, Automatic Control) Hosting by Elsevier Ltd. All rights reserved. connecting the theorycapabilities and practice. Keywords: Control design, System identification, identification, Virtual Virtual environment, environment, Controllers, Controllers, Multivariable Multivariable Keywords: Control design, System process. the connecting theory and practice. Keywords: Control design, System identification, Virtual environment, Controllers, Multivariable process. process. Keywords: Control design, System identification, Virtual environment, Controllers, Multivariable process. 1. INTRODUCTION server) and the view (which runs on the client) (Heradio, process. 1. server) and the (which runs the (Heradio, 1. INTRODUCTION INTRODUCTION server) The andinterface the view viewmust (which runs on onthrough the client) client) (Heradio, 2016). be available Internet. 1. INTRODUCTION server) and the view (which runs on the client) (Heradio, 2016). The interface must be available through Internet. In control education, the use of a virtual environment is an 2016). The interface must be available through Internet. The validity ofview experimental results implies that data 1. INTRODUCTION server) and the (which runs on the client) (Heradio, 2016). The interface must be available through Internet. In control education, the use of a virtual environment is an In controloption education, the use of a virtual environment is an The validity of experimental results implies that excellent to perform control design experimental tasks data The validity of experimental results implies that data obtained from the VLE must be very close to data that 2016). The interface must be available through Internet. In control education, the use of a virtual environment is an excellent option to control tasks excellent optionmodel to perform perform control design design experimental tasks The using a proper of a benchmark plant experimental (physical system). validity of experimental results implies that data obtained from the VLE must be very close to data that from the VLE must be very close to data that obtained from the physical system. Thus, the mathematical In control education, the use of a virtual environment is an excellent option to perform control design experimental tasks using type proper modelcan of aabebenchmark benchmark plant (physical system). using aa proper model of (physical This of tool used for plant teaching and system). research obtained The validity of experimental results implies that data from the VLE must be very close to data that from the physical system. Thus, the mathematical obtained from the physical system. Thus, the mathematical model of the benchmark plant must comply with operating excellent option to perform control design experimental tasks using a proper model of a benchmark plant (physical system). This type type of of tool tool can can be be used used for for teaching teaching and and research research This purposes. from the VLE must be very close to data that obtained from the physical system. Thus, the mathematical model of the benchmark plant must comply with operating model of the benchmark plant must comply withworking operating (behavior of physical system) when as using a proper modelcan of abebenchmark (physical This type of tool used for plant teaching and system). research conditions purposes. purposes. obtained from the physical system. Thus, the mathematical model of the benchmark plant must comply with operating conditions (behavior of physical system) when working as conditions (behavior system) when workingcan as simulation model in of thephysical VLE; therefore, the student This type of tool can be used for teaching and research purposes. Among the requirements that are demanded to the VLE are: model of the benchmark plant must comply with operating conditions (behavior of physical system) when working as simulation model in the VLE; therefore, the student can simulation in the VLE; therefore, thedesign studentusing can analyze themodel performance of his/her control purposes. Among the requirements that are demanded to the VLE are: Among the requirements that areappropriate demanded resources to the VLE user-friendly, wide availability, in are: the conditions (behavior of physical system) when working as simulation model in the VLE; therefore, the student can analyze the analyze data. the performance performance of of his/her his/her control control design design using using reliable Among thevalidity requirements that areappropriate to the tests, VLE user-friendly, wide resources in the user-friendly, wideofavailability, availability, appropriate resources in are: the simulation interface, the results ofdemanded the simulation low model in the VLE; therefore, the student can analyze the performance of his/her control design using reliable data. data. Among thevalidity requirements that areappropriate to the tests, VLE user-friendly, wideetc. resources in are: the reliable interface, of the of the low interface, validity ofavailability, the results results ofdemanded the simulation simulation tests, low cost maintenance, Traditional labs involve high control costs, associated with analyze thehands-on performance of his/her design using reliable data. user-friendly, wide availability, appropriate resources in the interface, validity of the results of the simulation tests, low cost Traditional involve high costs, with cost maintenance, maintenance, etc. etc. Traditional hands-on labs involve high2009). costs, associated associated with equipment, space andlabs staff (Gomes, Thus, reducing reliable data.hands-on interface, validity of the results simulation tests, low cost maintenance, etc. Traditional hands-on labs involve high costs, associated with space and staff (Gomes, 2009). Thus, reducing To make interaction easy with ofthetheuser, the concepts of equipment, equipment, space and (Gomes, cost maintenance is staff possible using2009). VLEThus, and reducing Internet cost maintenance, etc. Traditional hands-on labs involve high costs, associated with equipment, space and staff (Gomes, 2009). Thus, reducing To interaction the the of possible using VLE Internet To make make images interaction easy with the user, user,systems the concepts concepts of cost dynamic and easy virtualwith interactive are used, cost maintenance maintenance ishands-on possible using VLE and and tools Internet resources instead of is labs. The interactive that To make interaction easy with the user, the concepts of equipment, space and staff (Gomes, 2009). Thus, reducing cost maintenance is possible using VLE and Internet dynamic images and virtual interactive systems are used, instead of labs. interactive tools dynamictheimages interactive systems used, resources where changeandofvirtual an active element in thearegraphic resources instead of hands-on hands-on labs. The The interactive tools that are available on Internet represent a great stimulus for that the To make interaction easy with theelement user, the concepts of cost dynamic virtual interactive systems maintenance ishands-on possible using VLE and tools Internet resources instead of labs. The interactive that where the change an active in the are on represent aa great stimulus for the where theimages changeandof ofan animmediate active element in and thearegraphic graphic windows generates update a used, new are available available on Internet represent great stimulus for the development of Internet engineering learning (Sotomayor, 2017) dynamic images and virtual interactive systems are used, where the change of an active element in the graphic resources instead of hands-on labs. The interactive tools that are available on Internet represent a great stimulus for the windows generates an immediate update and a new development of engineering learning (Sotomayor, 2017) windows generates an immediate updatethe and presentation of the environment, visualizing effecta ofnew the development of the engineering 2017) Currently, under concept oflearning "Internet(Sotomayor, of Things" (IoT), where the change of an active element in the graphic windows generates an immediate update and a new are available on Internet represent a great stimulus for development of engineering learning (Sotomayor, 2017) presentation of the environment, visualizing the effect of the Currently, under the concept of "Internet of Things" (IoT), presentationmodifications of the environment, effect of the the performed (Heradio,visualizing 2016; Hu, the 2014). Currently, under idea the concept "Internet of Things" main design of VLE of is to use a web platform(IoT), asthea windows generates an immediate update and a new presentation of the environment, visualizing the effect of the development of engineering learning (Sotomayor, 2017) Currently, under the concept of "Internet of Things" (IoT), performed modifications (Heradio, 2016; Hu, 2014). the main design idea of VLE is to use a web platform as performed modifications (Heradio, 2016; Hu, 2014). the main designstructure, idea of VLE to use a web platform as aa communication and aislocal host as a user interface presentation of the environment, effect of the communication performed modifications (Heradio,visualizing 2016; Hu, the 2014). Currently, under the concept of "Internet of Things" (IoT), the main design idea of VLE is to use a web platform as a structure, and a local host as a user interface communication structure, and a local host as a user interface 2017). It is desirable that, the VLE is programmed software of (Jie, performed modifications (Heradio, 2016; Hu,with 2014). the main design idea of VLE is to use a web platform as a communication structure, and a local host as a user interface (Jie, 2017). It is desirable that, the VLE is programmed with software of 2017). It is desirable the VLE is programmed with software of (Jie, easy access. Tothat, achieve the requested requirements, the VLE The proposed VLE with 4 coupled tanks (4CT) system communication structure, and a local host as a user interface (Jie, 2017). It is desirable the VLE is programmed with software of easy access. To achieve the requirements, the easy access. Tothat, achieve thea requested requested requirements, the VLE VLE should be programmed in generally purpose programming The proposed VLE with 4 tanks (4CT) system The 2017). proposed VLE withapplication 4 coupled coupled(Web tanksServer (4CT)app) system on a web server that (Jie, It is desirable that, the VLE is programmed with software of consists easy access. To achieve the requested requirements, the VLE should be programmed in a generally purpose programming should be that programmed in a generally purposeand programming language allows easy implementation simplified The proposed VLE with 4 coupled tanks (4CT) system consists on a web server application (Web Server app) that consists on a web server application (Web Server app) that links to a desktop application (Desktop app) that is easy access. To achieve the requested requirements, the VLE should be programmed in a generally purpose programming language that and allows easy (Fabregas, implementation andHere, simplified language that allows easy implementation and simplified The proposed VLE with 4 coupled tanks (4CT) system maintenance updates 2013). it is consists on a web server application (Web Server app) that links to a desktop application (Desktop app) that is links to a desktop application (Desktop app) that is previously downloaded by each user. In Desktop app, an should be programmed in a generally purpose programming language that allows easy implementation and simplified maintenancetheand and updates (Fabregas, 2013). Here, object it is is consists maintenance (Fabregas, Here, it on a web server application (Web Server app) that considered use updates of Python, which is2013). a dynamic, links to a desktop application (Desktop app) that is previously downloaded by each user. In Desktop app, an previously downloaded by each user. In Desktop app, an interactive 3D simulation runs of the 4CT system that language that allows easy implementation and simplified maintenance and updates (Fabregas, 2013). Here, it is consideredand the use use of Python, Python, programming which is is aa dynamic, dynamic, object considered the of which to a desktop application (Desktop app) that is previously downloaded by each user. In Desktop app, an oriented multipurpose languageobject for links interactive 3D simulation runs system interactive with 3D the simulation runs of ofappthe thefor4CT 4CT system that that Web server a permanently maintenance and updates (Fabregas, Here, it for is connects considered the use of Python, whichapplications. is2013). a dynamic, object oriented multipurpose programming language previously downloaded by each user. In Desktop app, an oriented and and multipurpose programming language for developing both desktop and web Likewise, interactive 3D simulation runs of the 4CT system that connects permanently connects with with ofthe thetheWeb Web server app for permanently user server and to app load for the aadesigns of the considered the use of Python, whichapplications. is a dynamic, object oriented and multipurpose programming language for authentication developing both desktop and web developing bothto desktop and web applications. Likewise, interactive 3D simulation runs ofapp thefor 4CT system Python allows develop complex scientific andLikewise, numeric connects with the Web server adesigns permanently authentication of the user and to load the of the authentication of the user and to load the designs of that the students to be evaluated. The interactive 3D simulation oriented and multipurpose programming for connects with the Web server app for a permanently developing both desktop web applications. Likewise, Python to develop complex scientific and numeric Python allows allows to develop and complex scientific and numeric applications with features that facilitate data language analysis and authentication of the user and to load the designs of the students to be evaluated. The interactive 3D simulation students to be evaluated. The interactive 3D simulation (included in the Desktop app) allows the student to perform developing both desktop and Likewise, Python allows develop complex scientific and numeric applications with features that facilitate data analysis applications with features that facilitate data Python analysis and authentication of the user and to load the designs of the visualization. Intothis regard, theweb IEEEapplications. ranked as and the tests students to be evaluated. The interactive 3D simulation (included in the Desktop app) allows the student to perform (included in the Desktop app)system allowsidentification the student totasks. perform of controller design and For Python allows develop complex scientific and numeric applications with features data Python analysis visualization. In this regard, the IEEE ranked as the visualization. Intolanguage this regard, the facilitate IEEE ranked Python as and the tests students to be evaluated. The interactive 3D simulation #1 programming inthat 2018 (Cass, 2018). (included in the Desktop app) allows the student to perform of controller design and system identification tasks. For of controller design tasks. For this purpose, the user canand testsystem his/heridentification design by connecting applications with features data Python analysisas and visualization. In language this regard, the facilitate IEEE the tests #1 in 2018 (Cass, 2018). #1 programming programming language inthat 2018 (Cass,ranked 2018). (included in the app) allows the student totasks. perform tests of controller design and this purpose, the user test his/her design by connecting this purpose, theDesktop user can testsystem his/her design byalso connecting the Desktop app with acan Matlab script.identification The user has For the In VLE, students use regard, an interface in which a physical visualization. In language this the IEEE ranked Pythonsystem as the tests #1 programming in 2018 (Cass, 2018). of controller design and system identification tasks. this purpose, the user can test his/her design by connecting the Desktop app with a Matlab script. The user also the In VLE, students use an interface in which a physical system the Desktop app with Matlab script. The userdeveloped also has has For the of doing the alatter with a program in In VLE, students use an interface in which amodel. physical was replaced with a reliable mathematical Thesystem VLE option #1 programming language in 2018 (Cass, 2018). this purpose, the itwith user can test his/her design by connecting the Desktop app alatter Matlab script. The user also has the In VLE, students use an interface in which a physical system option of doing the with a program developed in was replaced with a reliable mathematical model. The VLE option of doing the latter with a program developed in Python. Finally, is possible to test the implementation of was replaced with a reliable TheonVLE allows a decoupling of the mathematical model (whichmodel. can run the the Desktop appusing with aalatter Matlab script. The userdeveloped also has the option of doing the with atext program in In VLE, students use an interface in which a physical system was replaced with a reliable mathematical model. The VLE Python. Finally, it is possible to test the implementation of allows a decoupling of the model (which can run on the Python. Finally, it is possible to test the implementation of his/her solution structured routine developed in allows a decoupling of the model (which can run on the of doing the latter with a program developed Python. Finally, it is possible to test the implementation of was replaced with a reliable TheonVLE allows a decoupling of the mathematical model (whichmodel. can run the option his/her solution using a structured text routine developed in his/her solution using a structured text routine developed in Finally, using it is possible to test implementation his/her solution a structured textthe routine developed of in allows a decoupling of the model (which can run on the Python. Copyright © 2019 IFAC 15 his/her solution using a structured text routine developed in 2405-8963 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Copyright © 2019 IFAC 15 Copyright 2019 responsibility IFAC 15 Control. Peer review© of International Federation of Automatic Copyright ©under 2019 IFAC 15 10.1016/j.ifacol.2019.08.116 Copyright © 2019 IFAC 15
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Where: Ai : Cross section of the tank i (𝑐𝑐𝑐𝑐2 ); ai : Cross section of the tank outlet i (𝑐𝑐𝑐𝑐2 ); hi : Water level in the tank in i (𝑐𝑐𝑐𝑐); 𝑢𝑢𝑖𝑖 : voltage applied to Pump i and the corresponding flow is 𝑘𝑘i ui ; The flow to Tanks 1 to 4 are: 𝑞𝑞1 = 𝛾𝛾1 𝑘𝑘1 u1 , 𝑞𝑞2 = 𝛾𝛾2 𝑘𝑘2 u2 , 𝑞𝑞3 = (1 − 𝛾𝛾2 )𝑘𝑘2 u2 and 𝑞𝑞4 = (1 − 𝛾𝛾1 )𝑘𝑘1 u1 (𝑐𝑐𝑐𝑐3 /s); g: Acceleration of gravity (𝑐𝑐𝑐𝑐/s 2); qi : Input flow to the tank (𝑐𝑐𝑐𝑐3 /s); γi : Opening parameter of the 3-way valve. 𝑘𝑘i : Voltage parameter (𝑐𝑐𝑐𝑐3 /Vs). The modified configuration is shown in Fig. 2.
an industrial device that is a programmable logic controller (PLC). Therefore, the Desktop app allows a connection with Matlab, Python and a PLC with TCP / IP communication. This article is structured as follows: Section 2 describes the mathematical model and operating conditions of 4CT system. Section 3 explains the development of the VLE and describes connectivity of a desktop application with Matlab, Python and industrial device to check the design of controllers or perform system identification tasks. Section 4 describes how the development of skills is achieved by using the proposed VLE; therefore, an example of checking a design of controllers for the 4CT system is shown. 2. MODEL OF THE FOUR COUPLED TANKS SYSTEM The 4CT system is a benchmark plant, which is useful for teaching and research purposes of multivariable processes control design. It allows different operating configurations; also it is possible to represent this system as nonlinear or linear, exposing students to broader practical issues. The two most widely used configurations are the known as basic configuration and as the modified configuration. From these, with the closing and/or opening of some of the valves that make up the system, it is possible to obtain other configurations. The process inputs are 𝑢𝑢1 and 𝑢𝑢2 as input voltages to the pumps and the outputs are 𝑦𝑦1 and 𝑦𝑦2 as level measurements of Tanks 1 and 2. Fig. 1 shows the basic configuration of 4CT system presented by Johansson (Johansson, 2000; Alvarado, 2006).
Fig. 2. Modified configuration of the four-tank process (Numsomran, 2008).
The respective flow balance leads to a non-linear model, which is present in Numsomran (Numsomran, 2008). In the 4CT system model (for each configuration) used in the proposed VLE has been considered the specifications of physical 4CT system located in the Advanced Control Lab at PUCP (Fig. 3), in which: • Maximum flow delivered by the pumps: 266.7 𝑐𝑐𝑐𝑐3 /s. • Pipe diameter: 1.27 𝑐𝑐𝑐𝑐. • Maximum height in tanks: 40 𝑐𝑐𝑐𝑐.
Fig. 1. Basic configuration of the four coupled tanks process (Alvarado, 2006).
The flow balance is made for each tank and a non-linear model is obtained (Johansson, 2000; Alvarado, 2006): 𝑑𝑑ℎ1 𝑑𝑑𝑑𝑑 𝑑𝑑ℎ2 𝑑𝑑𝑑𝑑 𝑑𝑑ℎ3 𝑑𝑑𝑑𝑑 𝑑𝑑ℎ4 𝑑𝑑𝑑𝑑
=− =− =− =−
𝑎𝑎1 𝐴𝐴1 𝑎𝑎2 𝐴𝐴2 𝑎𝑎3 𝐴𝐴3 𝑎𝑎4 𝐴𝐴4
𝑎𝑎
𝛾𝛾1𝑘𝑘1
1 𝑎𝑎4
𝐴𝐴1 𝛾𝛾2𝑘𝑘2
�2𝑔𝑔ℎ1 + 𝐴𝐴3 �2𝑔𝑔ℎ3 + �2𝑔𝑔ℎ2 + 𝐴𝐴 �2𝑔𝑔ℎ4 + 2
�2𝑔𝑔ℎ3 + �2𝑔𝑔ℎ4 +
(1−𝛾𝛾2 )𝑘𝑘2 𝐴𝐴3 (1−𝛾𝛾1 )𝑘𝑘1 𝐴𝐴4
𝐴𝐴2
𝑢𝑢1
(1)
𝑢𝑢2
(2)
𝑢𝑢2
(3)
𝑢𝑢1
(4)
Fig. 3. Four coupled tanks pilot plant. Advanced Control Lab (PUCP)
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Validation works allowed to verify that the model matched with physical 4CT system behavior. Likewise, data obtained when working with the model and the physical system were very close. On the other hand, some typical disturbances (added in the Desktop app) could be included in the model for a greater similarity with real operation of a physical system.
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program for communication with Matlab, Python and a PLC. The Desktop app runs an interactive 3D simulation of the model of the 4CT system whose dynamics represent adequately the real behavior of the physical laboratory plant shown in Fig. 5 based in the mathematical model presented in Section II. Using this model, the user will be able to carry out controller design tests and system identification tasks through a communication with a test routine in real time. The effect of control design implementations will be reflected in a 3D model view, and the interaction with the application will be in real time. The 3D model is developed in Blender, which is a free and Open 3D Creation Software based in Python. The blender game engine mode is used to perform the plant simulation as a video game. The blender game engine has a game logic that can be programmed in Python. The 3D model of the plant can be observed as shown in Fig. 5.
3. DEVELOPMENT OF THE VIRTUAL LABORATORY ENVIRONMENT In the following, the proposed VLE is summarized, as a novel interactive remote approach in which a virtual world is combined with a real physical system surrounding. The architecture of the VLE shown in Fig. 4 consists of a “Web server app” and a local application “Desktop app”.
Fig 4. Web server and Desktop apps architecture. Fig. 5. 3D model View of the Desktop app.
Description of the main components of the VLE
The Web Server app is developed through the integration of HTML, CSS, Javascript and Python.
3.1 Web Server app The student accesses to Web server app with a username and password previously assigned according to course registration. Within this application, the student can download the desktop application, review the assigned works and upload his/her results to be graded by the instructor.
3.4 Test routine for checking the controller design Once the student finished the homework of controller design, he/she makes the implementation. Controller implementation is performed first using a script in Matlab. This script (to be executed in Matlab) represents the controller to be tested with the 4CT system. In this case, the script can be tested by connecting Matlab with the Desktop app as many times as necessary during the time permitted. An optional stage is to implement the controller using a script in the open source language Python connecting it with the Desktop app to test it as many times as necessary. Finally, when the first stage is successfully fulfilled, the student implements his/her controller using the structured text language (IEC 61131-3) to practice in an industrial device (PLC) which connects with the Desktop app.
3.2 Communication between the Desktop app VLE and the Web server app This communication is made using a local network (LAN) within the campus; the computers with the desktop application are in a computer lab for simultaneous work of the students with instructor’s support. 3.3 Desktop app The Desktop app is an application that contains the model of the 4CT system as well as the libraries and the necessary 17
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3.5 Test routine for system identification tasks
application that contains the model of the system with Matlab.
System identification tasks that could be performed with this tool are: I/O data collection, model validation and model implementation.
4. Within Matlab, Pyhton or structured text, the student will be able to develop the modeling or controller design tasks, testing their performance with the virtual plant as many times as he/she considers necessary during the authorized time.
For I/O data collection of 4CT system, a Matlab script developed by the student, which will run on Matlab, is used.
5. When the student finishes the practice, he/she must save and send his/her work, which will be automatically sent to the Web server application for a later evaluation.
The collected I/O data are used to perform system identification procedures in homework stage in order to obtain a 4CT system model (Zhu, 2001).
6. Finally, the student can select another practice or close session.
Once the model is obtained in homework stage, a validation task is performed using a Matlab script, comparing the output of the model with the output of the 4CT system against the same inputs and disturbances. After the 4CT system model is validated, the user could implement it using the structured text language (IEC 611313) in an industrial device (PLC) which connects with the Desktop app. The model implemented in an industrial device would allow the development of model-based control strategies for the benchmark plant (Camacho, 2007; Gouta, 2017). Communication between the Desktop app and test routine For communication between the Desktop app and test routine, a client-server TCP/IP based-architecture is used, the objective is to have a bidirectional communication between them, as seen in Fig. 6.
Fig. 7. Flow chart of the proposed VLE
4. USING THE VLE Nowadays, control-engineering education needs to achieve an understanding of mathematics behind the concepts and practice in implementing theoretical solutions in real plants. In order to achieve the development of skills in control design, the proposed VLE is used to:
Fig 6. Types of test routines allowed by the desktop application.
In the following, we describe the use of the VLE, shown in the flow chart of the Fig. 7: 1. The student enters the local application installed in a PC of a computer lab, access with an account assigned by the instructor of the course.
• Describe the operation of the system. • Explain how the physical characteristics of the components influence the operation of the system.
2. Once the student performs this authentication, the local application connects with the web application and the student is authorized to use the system for a specific time to verify and select one of the tasks assigned by the instructor for control design or modeling work.
• Expose students to design and modeling issues. • Practice in implementing control strategies. • Check the design of controllers or perform system identification tasks.
3. Next, the student decides to start the practice, and a communications port will open to connect the local
• Practice with different operating conditions of the system and obtain new control design solutions. 18
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case, the controllers generate the control variables u1 and u2 (see Fig. 1) as inputs of pumps 1 and 2 respectively.
In the desktop application, it is possible to choose a system operation configuration as well as include disturbances. It is also possible to switch a control mode: manual or automatic.
As a result of homework stage using the design method (Garrido et al., 2012), PI-Control algorithms are obtained.
Checking the design of controllers
Using the script in Matlab and by means of connecting with the Desktop App, simulations are performed with the designed PI-Control. Here, to evaluate system dynamics with basis configuration against disturbances, the latter are considered (through their effect) as variations in valve openings defined by the parameters γ1 and γ2 . Two cases were evaluated to check disturbance rejection effectiveness of designed PI-Control.
The design of a controller involves obtaining its algorithm in order to achieve certain desired system characteristics. By checking the design of their controllers, students will be able to verify if the system with proposed algorithms reaches the desired characteristics. For checking the design of controllers, this tool allows the user in real time to: • Choose a configuration of 4CT system.
In Fig. 9 is shown the system time response for 𝛾𝛾1 = 0.6 and 𝛾𝛾2 = 0.7. In this case, the system effectively reaches the desired level values in tanks 1 and 2.
• Program the control algorithms in a Matlab script, Python script and in a structured text routine. • Handle the experiment (start, stop, reset, control mode: manual/automatic). • Generate system input signals. • Simulate the system dynamics (behavior of variables). • Visualize the system dynamics in a 3D model view. • Collect input/output variables data. In the 4CT system, the desired characteristics relate to transient response of levels of tanks. If “basic configuration” is chosen, the control objective would make levels of lower tanks of 4CT system reach the desired values despite disturbances. Once the design of controllers is completed, the test routine is connected with the Desktop app. At executing the simulation, the user can visualize an animation of the operation of 4CT system (Fig. 8). In addition, it is possible to observe the behavior of variables (levels of lower tanks) through graphs generated by the virtual model in the Desktop app.
Fig. 9. Simulation for γ1 = 0.6 and γ2 = 0.7
In Fig. 10 is shown the case when γ1 + γ2 = 1. In this case, the control is not able to reach the desired values of the level of tanks 1 and 2; however, the system reaches stationary values.
Fig. 8. Desktop app for γ1 = 0.6 and γ2 = 0.7.
Checking the design of PI-Control One of the approaches for control of multivariable processes is using decoupling control with two PI controllers. In this
Fig. 10. Simulation for γ1 = 0.5 and γ2 = 0.5
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2019 IFAC ACE 20 June 1-3, 2016. Bratislava, Slovakia
Javier Sotomayor-Moriano et al. / IFAC PapersOnLine 52-9 (2019) 15–20
Once the students finished checking the design of theirs controllers by means of evaluating the transient response of the levels of lower tanks of 4CT, they elaborate a report that must be uploaded to the Web Server app.
Fabregas, E. (2013). Plataformas interactivas de experimentación virtual y remota. Cap 3, pp. 85-125. Tesis doctoral UNED, Madrid, España. Garrido, J., Vázquez, F., and Morilla, F. (2012). Centralized multivariable control by simplified decoupling. Journal of Process Control, 22(6):1044-1062. Gomes, L. (2009). Current trends in remote laboratories, IEEE Transactions on Industrial Electronics 56, pp. 4744-4756. Gouta, H., Saïd, S.H., Barhoumi, N., and M’Sahli, F. (2017). Generalized predictive control for a coupled four tank MIMO system using a continuous-discrete time observer. ISA Transactions. Vol. 67, pp. 280-292. Heradio, R., De la Torre, R., and Dormido, S. (2016). Virtual and remote labs in control education: A survey. Annual Reviews in Control 42, 1-10. Hu, W., Zhou, H., Liu, L., Zhong, L. (2014). Web-based 3D Interactive Virtual Control Laboratory Based on NCSLab Framework. Int. Journal of Online and Biomedical Engineering (iJOE). Vol 10, No 6. Jie, L., Wei, Y., Nan, Z., Xinyu, Y., Hanlin, Z., and Wei, Z. (2017). A Survey on Internet of Things. Architecture, Enabling Technologies, Security and Privacy, and Applications. IEEE Internet of Things Journal, vol. 4, no.5, pp. 1125-1142. Johansson, K. (2000). The Quadruple-Tank Process; A Multivariable Laboratory Process with an Adjustable Zero. IEEE Transactions on Control Systems Technology, Vol. 8, no. 3., pp. 456-465. Numsomran, A., Tipsuwanporn, V., and Tirasesth, K. (2008). Modeling of the modified quadruple-tank process. Proceedings of SICE Annual Conference, Vols 1-7, pp, 783-788. Sánchez, J., Esquembre, F., Martin, C., Dormido, S., Pastor, R., and A. Urquía. (2005). Easy Java Simulations: an Open- Source Tool to Develop Interactive Virtual Laboratories Using MATLAB/Simulink. Vol. 21, No. 5, pp. 798-813. Tempus Publications. UNED, Madrid, España. Sotomayor, J., and Pérez-Zuñiga, C.G. (2017). Cuadernos de Innovación en la Docencia. Dirección Académica del Profesorado. Pontificia Universidad Católica del Perú. Zhu, Y. (2001). Multivariable System Identification For Process Control. Elsevier. Eindhoven University of Technology, Eindhoven, The Netherlands.
It is also possible to use Python script to test the designed PIControl with open source software and elaborate the respective report. Finally, the implementation of PI-Control in structured text is developed and drawn up a final report. Through this reports, instructors will be able to evaluate the development of student skills in design of controllers. 6. CONCLUSIONS The proposed VLE facilitates the development of skills of engineering students in control design of multivariable processes, in this way, before implementation on physical systems, simulations and animations can be carry out to practice theoretical solutions. A novel interactive “virtual laboratory environment” for a 4 coupled tanks system that could be used in control education to check the design of their controllers and perform system identification tasks was presented. The Web server and Desktop application architecture proposed are user-friendly and demands low cost maintenance. Desktop app allows a connection with Matlab, Python and a PLC with TCP / IP communication. A case of use the proposed VLE when checking the design of controllers is presented. Simulations of system dynamics were performed to check the design of PI-Control. FUTURE WORK Development of resources (hardware and software) for interactive work between the VLE and the physical plant (remote lab) for use in process control education.
REFERENCES Alvarado, I., Limon, D., García, W., Alamo, T., and Camacho, E. (2006). An Educational Plant Based on the Quadruple- Tank Process. 7th IFAC Symposium on Advances in Control Education. vol. 8, no.6, pp. 82-87. Elsevier. Astrom, K.J., and Murray, R.M. (2008). Feedback Systems An Introduction for Scientists and Engineers. Princeton University Press. Camacho E.F and Bordons C. (2007). Model Predictive Control. Advanced Textbooks in Control and Signal Processing. Springer-Verlag London. Cass, S. (2018). The 2018 Top Programming Languages. Journal IEEE Spectrum. Dormido, R.,Varga, H., Duro, N., Sánchez, J.,DormidoCanto, S., Farias, G., Esquembre, F., and Dormido, S. (2008). Development of Web-Based Control: The ThreeTank System. IEEE Transactions on Education, vol.51, no.1, pp. 35-44.
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ScienceDirect
IFAC PapersOnLine 52-9Control (2019) 15–20 Design of a Multivariable Process A Virtual Laboratory Environment for A Virtual Laboratory Environment for Control A Virtual Laboratory Environment for Control Design Design of of aa Multivariable Multivariable Process Process A Virtual Laboratory Environment for Control Design of a Multivariable Process Javier Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** A Virtual Laboratory Environment for Control Design of a Multivariable Process
Javier Gustavo Javier Sotomayor-Moriano*. Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** Pérez-Zúñiga** Mario Soto*** Javier Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** Mario Soto*** Mario Soto*** Javier Sotomayor-Moriano*. Gustavo Pérez-Zúñiga** Mario Soto*** Engineering Department, Pontifical Catholic University of Peru, PUCP, Lima, Peru. Mario Soto*** Engineering Department, Pontifical Catholic University of PUCP, Peru. Engineering Department, Pontifical Catholic University of Peru, Peru, PUCP, Lima, Lima, Peru. (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). Engineering Department, Pontifical Catholic University of Peru, PUCP, Lima, Peru. (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). Engineering Department, Pontifical Catholic University of Peru, PUCP, Lima, Peru. (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). (e-mail: *jsotom@ pucp.edu.pe, **gustavo.perez@ pucp.pe, *** mario.soto@ pucp.pe). Abstract: This paper describes the development of a virtual laboratory environment (VLE) that allows Abstract: This papercontrol describes the development development ofvirtual virtual laboratory environment (VLE) that allows allows Abstract: paper describes the aa virtual laboratory environment (VLE) that students toThis perform design practice in aof plant from remote locations through a web Abstract: This papercontrol describes the development a virtual laboratory environment (VLE) that system allows students to perform control design practice in aaof virtual plant from remote locations through web students perform practice in virtual plant from remote through aa web browser. to The proposed VLEdesign facilitates to learn concepts; such as, design oflocations controllers and Abstract: This paper describes the development a virtual laboratory environment (VLE) that system allows students perform control practice in aof virtual plant from remote through awith weba browser. to The proposed VLEdesign facilitates to learn learn concepts; such as, design design oflocations controllers and system browser. The proposed VLE facilitates to concepts; such as, of controllers and identification of multivariable processes using a simulation environment, and an industrial device students to control in a concepts; virtual from remote locations through awith web browser.model Theperform proposed VLEdesign facilitates to learn suchis as, design of controllers anditssystem identification of multivariable processes using simulation environment, and an an industrial device with identification of processes using aa simulation environment, and industrial device reliable ofmultivariable a benchmark plant.practice Architecture of the plant VLE explained and evidence of use isaa browser. The proposed VLE facilitates to learn concepts; such as, design of controllers and system identification of multivariable processes using a simulation environment, and an industrial device with reliable model of a benchmark plant. Architecture of the VLE is explained and evidence of its use is reliable of a benchmark plant. Architecture of tool the VLE explained andwide evidence of its use isa showed. model The proposed VLE represents an education that isis user friendly, availability, with identification of multivariable processes using a simulation environment, and an industrial device with reliable model of a benchmark plant. Architecture of the VLE is explained and evidence of its use isa showed. The proposed VLE represents an education tool that is user friendly, wide availability, with showed. proposed VLE represents education tool that is allows user friendly, wide student availability, graphicalThe interface capabilities and lowancost maintenance, that to improve skillswith by reliable model of a benchmark plant. Architecture of the VLE is explained and evidence of its use is showed. The proposed VLE represents an education tool that is user friendly, wide availability, with graphical interface capabilities and low cost maintenance, that allows to improve student skills by graphical interface and low cost maintenance, that allows to improve student skills by connecting the theorycapabilities and practice. showed. The proposed VLE represents an education tool that is user friendly, wide availability, with graphical interface capabilities and low cost maintenance, that allows to improve student skills by connecting the theory and practice. connecting the theory design, and practice. Keywords: Control System Virtual environment, Multivariable graphical interface and low cost maintenance, that allows to Controllers, improve student skills by © 2019, IFAC (International Federation ofidentification, Automatic Control) Hosting by Elsevier Ltd. All rights reserved. connecting the theorycapabilities and practice. Keywords: Control design, System identification, identification, Virtual Virtual environment, environment, Controllers, Controllers, Multivariable Multivariable Keywords: Control design, System process. the connecting theory and practice. Keywords: Control design, System identification, Virtual environment, Controllers, Multivariable process. process. Keywords: Control design, System identification, Virtual environment, Controllers, Multivariable process. 1. INTRODUCTION server) and the view (which runs on the client) (Heradio, process. 1. server) and the (which runs the (Heradio, 1. INTRODUCTION INTRODUCTION server) The andinterface the view viewmust (which runs on onthrough the client) client) (Heradio, 2016). be available Internet. 1. INTRODUCTION server) and the view (which runs on the client) (Heradio, 2016). The interface must be available through Internet. In control education, the use of a virtual environment is an 2016). The interface must be available through Internet. The validity ofview experimental results implies that data 1. INTRODUCTION server) and the (which runs on the client) (Heradio, 2016). The interface must be available through Internet. In control education, the use of a virtual environment is an In controloption education, the use of a virtual environment is an The validity of experimental results implies that excellent to perform control design experimental tasks data The validity of experimental results implies that data obtained from the VLE must be very close to data that 2016). The interface must be available through Internet. In control education, the use of a virtual environment is an excellent option to control tasks excellent optionmodel to perform perform control design design experimental tasks The using a proper of a benchmark plant experimental (physical system). validity of experimental results implies that data obtained from the VLE must be very close to data that from the VLE must be very close to data that obtained from the physical system. Thus, the mathematical In control education, the use of a virtual environment is an excellent option to perform control design experimental tasks using type proper modelcan of aabebenchmark benchmark plant (physical system). using aa proper model of (physical This of tool used for plant teaching and system). research obtained The validity of experimental results implies that data from the VLE must be very close to data that from the physical system. Thus, the mathematical obtained from the physical system. Thus, the mathematical model of the benchmark plant must comply with operating excellent option to perform control design experimental tasks using a proper model of a benchmark plant (physical system). This type type of of tool tool can can be be used used for for teaching teaching and and research research This purposes. from the VLE must be very close to data that obtained from the physical system. Thus, the mathematical model of the benchmark plant must comply with operating model of the benchmark plant must comply withworking operating (behavior of physical system) when as using a proper modelcan of abebenchmark (physical This type of tool used for plant teaching and system). research conditions purposes. purposes. obtained from the physical system. Thus, the mathematical model of the benchmark plant must comply with operating conditions (behavior of physical system) when working as conditions (behavior system) when workingcan as simulation model in of thephysical VLE; therefore, the student This type of tool can be used for teaching and research purposes. Among the requirements that are demanded to the VLE are: model of the benchmark plant must comply with operating conditions (behavior of physical system) when working as simulation model in the VLE; therefore, the student can simulation in the VLE; therefore, thedesign studentusing can analyze themodel performance of his/her control purposes. Among the requirements that are demanded to the VLE are: Among the requirements that areappropriate demanded resources to the VLE user-friendly, wide availability, in are: the conditions (behavior of physical system) when working as simulation model in the VLE; therefore, the student can analyze the analyze data. the performance performance of of his/her his/her control control design design using using reliable Among thevalidity requirements that areappropriate to the tests, VLE user-friendly, wide resources in the user-friendly, wideofavailability, availability, appropriate resources in are: the simulation interface, the results ofdemanded the simulation low model in the VLE; therefore, the student can analyze the performance of his/her control design using reliable data. data. Among thevalidity requirements that areappropriate to the tests, VLE user-friendly, wideetc. resources in are: the reliable interface, of the of the low interface, validity ofavailability, the results results ofdemanded the simulation simulation tests, low cost maintenance, Traditional labs involve high control costs, associated with analyze thehands-on performance of his/her design using reliable data. user-friendly, wide availability, appropriate resources in the interface, validity of the results of the simulation tests, low cost Traditional involve high costs, with cost maintenance, maintenance, etc. etc. Traditional hands-on labs involve high2009). costs, associated associated with equipment, space andlabs staff (Gomes, Thus, reducing reliable data.hands-on interface, validity of the results simulation tests, low cost maintenance, etc. Traditional hands-on labs involve high costs, associated with space and staff (Gomes, 2009). Thus, reducing To make interaction easy with ofthetheuser, the concepts of equipment, equipment, space and (Gomes, cost maintenance is staff possible using2009). VLEThus, and reducing Internet cost maintenance, etc. Traditional hands-on labs involve high costs, associated with equipment, space and staff (Gomes, 2009). Thus, reducing To interaction the the of possible using VLE Internet To make make images interaction easy with the user, user,systems the concepts concepts of cost dynamic and easy virtualwith interactive are used, cost maintenance maintenance ishands-on possible using VLE and and tools Internet resources instead of is labs. The interactive that To make interaction easy with the user, the concepts of equipment, space and staff (Gomes, 2009). Thus, reducing cost maintenance is possible using VLE and Internet dynamic images and virtual interactive systems are used, instead of labs. interactive tools dynamictheimages interactive systems used, resources where changeandofvirtual an active element in thearegraphic resources instead of hands-on hands-on labs. The The interactive tools that are available on Internet represent a great stimulus for that the To make interaction easy with theelement user, the concepts of cost dynamic virtual interactive systems maintenance ishands-on possible using VLE and tools Internet resources instead of labs. The interactive that where the change an active in the are on represent aa great stimulus for the where theimages changeandof ofan animmediate active element in and thearegraphic graphic windows generates update a used, new are available available on Internet represent great stimulus for the development of Internet engineering learning (Sotomayor, 2017) dynamic images and virtual interactive systems are used, where the change of an active element in the graphic resources instead of hands-on labs. The interactive tools that are available on Internet represent a great stimulus for the windows generates an immediate update and a new development of engineering learning (Sotomayor, 2017) windows generates an immediate updatethe and presentation of the environment, visualizing effecta ofnew the development of the engineering 2017) Currently, under concept oflearning "Internet(Sotomayor, of Things" (IoT), where the change of an active element in the graphic windows generates an immediate update and a new are available on Internet represent a great stimulus for development of engineering learning (Sotomayor, 2017) presentation of the environment, visualizing the effect of the Currently, under the concept of "Internet of Things" (IoT), presentationmodifications of the environment, effect of the the performed (Heradio,visualizing 2016; Hu, the 2014). Currently, under idea the concept "Internet of Things" main design of VLE of is to use a web platform(IoT), asthea windows generates an immediate update and a new presentation of the environment, visualizing the effect of the development of engineering learning (Sotomayor, 2017) Currently, under the concept of "Internet of Things" (IoT), performed modifications (Heradio, 2016; Hu, 2014). the main design idea of VLE is to use a web platform as performed modifications (Heradio, 2016; Hu, 2014). the main designstructure, idea of VLE to use a web platform as aa communication and aislocal host as a user interface presentation of the environment, effect of the communication performed modifications (Heradio,visualizing 2016; Hu, the 2014). Currently, under the concept of "Internet of Things" (IoT), the main design idea of VLE is to use a web platform as a structure, and a local host as a user interface communication structure, and a local host as a user interface 2017). It is desirable that, the VLE is programmed software of (Jie, performed modifications (Heradio, 2016; Hu,with 2014). the main design idea of VLE is to use a web platform as a communication structure, and a local host as a user interface (Jie, 2017). It is desirable that, the VLE is programmed with software of 2017). It is desirable the VLE is programmed with software of (Jie, easy access. Tothat, achieve the requested requirements, the VLE The proposed VLE with 4 coupled tanks (4CT) system communication structure, and a local host as a user interface (Jie, 2017). It is desirable the VLE is programmed with software of easy access. To achieve the requirements, the easy access. Tothat, achieve thea requested requested requirements, the VLE VLE should be programmed in generally purpose programming The proposed VLE with 4 tanks (4CT) system The 2017). proposed VLE withapplication 4 coupled coupled(Web tanksServer (4CT)app) system on a web server that (Jie, It is desirable that, the VLE is programmed with software of consists easy access. To achieve the requested requirements, the VLE should be programmed in a generally purpose programming should be that programmed in a generally purposeand programming language allows easy implementation simplified The proposed VLE with 4 coupled tanks (4CT) system consists on a web server application (Web Server app) that consists on a web server application (Web Server app) that links to a desktop application (Desktop app) that is easy access. To achieve the requested requirements, the VLE should be programmed in a generally purpose programming language that and allows easy (Fabregas, implementation andHere, simplified language that allows easy implementation and simplified The proposed VLE with 4 coupled tanks (4CT) system maintenance updates 2013). it is consists on a web server application (Web Server app) that links to a desktop application (Desktop app) that is links to a desktop application (Desktop app) that is previously downloaded by each user. In Desktop app, an should be programmed in a generally purpose programming language that allows easy implementation and simplified maintenancetheand and updates (Fabregas, 2013). Here, object it is is consists maintenance (Fabregas, Here, it on a web server application (Web Server app) that considered use updates of Python, which is2013). a dynamic, links to a desktop application (Desktop app) that is previously downloaded by each user. In Desktop app, an previously downloaded by each user. In Desktop app, an interactive 3D simulation runs of the 4CT system that language that allows easy implementation and simplified maintenance and updates (Fabregas, 2013). Here, it is consideredand the use use of Python, Python, programming which is is aa dynamic, dynamic, object considered the of which to a desktop application (Desktop app) that is previously downloaded by each user. In Desktop app, an oriented multipurpose languageobject for links interactive 3D simulation runs system interactive with 3D the simulation runs of ofappthe thefor4CT 4CT system that that Web server a permanently maintenance and updates (Fabregas, Here, it for is connects considered the use of Python, whichapplications. is2013). a dynamic, object oriented multipurpose programming language previously downloaded by each user. In Desktop app, an oriented and and multipurpose programming language for developing both desktop and web Likewise, interactive 3D simulation runs of the 4CT system that connects permanently connects with with ofthe thetheWeb Web server app for permanently user server and to app load for the aadesigns of the considered the use of Python, whichapplications. is a dynamic, object oriented and multipurpose programming language for authentication developing both desktop and web developing bothto desktop and web applications. Likewise, interactive 3D simulation runs ofapp thefor 4CT system Python allows develop complex scientific andLikewise, numeric connects with the Web server adesigns permanently authentication of the user and to load the of the authentication of the user and to load the designs of that the students to be evaluated. The interactive 3D simulation oriented and multipurpose programming for connects with the Web server app for a permanently developing both desktop web applications. Likewise, Python to develop complex scientific and numeric Python allows allows to develop and complex scientific and numeric applications with features that facilitate data language analysis and authentication of the user and to load the designs of the students to be evaluated. The interactive 3D simulation students to be evaluated. The interactive 3D simulation (included in the Desktop app) allows the student to perform developing both desktop and Likewise, Python allows develop complex scientific and numeric applications with features that facilitate data analysis applications with features that facilitate data Python analysis and authentication of the user and to load the designs of the visualization. Intothis regard, theweb IEEEapplications. ranked as and the tests students to be evaluated. The interactive 3D simulation (included in the Desktop app) allows the student to perform (included in the Desktop app)system allowsidentification the student totasks. perform of controller design and For Python allows develop complex scientific and numeric applications with features data Python analysis visualization. In this regard, the IEEE ranked as the visualization. Intolanguage this regard, the facilitate IEEE ranked Python as and the tests students to be evaluated. The interactive 3D simulation #1 programming inthat 2018 (Cass, 2018). (included in the Desktop app) allows the student to perform of controller design and system identification tasks. For of controller design tasks. For this purpose, the user canand testsystem his/heridentification design by connecting applications with features data Python analysisas and visualization. In language this regard, the facilitate IEEE the tests #1 in 2018 (Cass, 2018). #1 programming programming language inthat 2018 (Cass,ranked 2018). (included in the app) allows the student totasks. perform tests of controller design and this purpose, the user test his/her design by connecting this purpose, theDesktop user can testsystem his/her design byalso connecting the Desktop app with acan Matlab script.identification The user has For the In VLE, students use regard, an interface in which a physical visualization. In language this the IEEE ranked Pythonsystem as the tests #1 programming in 2018 (Cass, 2018). of controller design and system identification tasks. this purpose, the user can test his/her design by connecting the Desktop app with a Matlab script. The user also the In VLE, students use an interface in which a physical system the Desktop app with Matlab script. The userdeveloped also has has For the of doing the alatter with a program in In VLE, students use an interface in which amodel. physical was replaced with a reliable mathematical Thesystem VLE option #1 programming language in 2018 (Cass, 2018). this purpose, the itwith user can test his/her design by connecting the Desktop app alatter Matlab script. The user also has the In VLE, students use an interface in which a physical system option of doing the with a program developed in was replaced with a reliable mathematical model. The VLE option of doing the latter with a program developed in Python. Finally, is possible to test the implementation of was replaced with a reliable TheonVLE allows a decoupling of the mathematical model (whichmodel. can run the the Desktop appusing with aalatter Matlab script. The userdeveloped also has the option of doing the with atext program in In VLE, students use an interface in which a physical system was replaced with a reliable mathematical model. The VLE Python. Finally, it is possible to test the implementation of allows a decoupling of the model (which can run on the Python. Finally, it is possible to test the implementation of his/her solution structured routine developed in allows a decoupling of the model (which can run on the of doing the latter with a program developed Python. Finally, it is possible to test the implementation of was replaced with a reliable TheonVLE allows a decoupling of the mathematical model (whichmodel. can run the option his/her solution using a structured text routine developed in his/her solution using a structured text routine developed in Finally, using it is possible to test implementation his/her solution a structured textthe routine developed of in allows a decoupling of the model (which can run on the Python. Copyright © 2019 IFAC 15 his/her solution using a structured text routine developed in 2405-8963 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Copyright © 2019 IFAC 15 Copyright 2019 responsibility IFAC 15 Control. Peer review© of International Federation of Automatic Copyright ©under 2019 IFAC 15 10.1016/j.ifacol.2019.08.116 Copyright © 2019 IFAC 15
2019 IFAC ACE 16 June 1-3, 2016. Bratislava, Slovakia
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Where: Ai : Cross section of the tank i (𝑐𝑐𝑐𝑐2 ); ai : Cross section of the tank outlet i (𝑐𝑐𝑐𝑐2 ); hi : Water level in the tank in i (𝑐𝑐𝑐𝑐); 𝑢𝑢𝑖𝑖 : voltage applied to Pump i and the corresponding flow is 𝑘𝑘i ui ; The flow to Tanks 1 to 4 are: 𝑞𝑞1 = 𝛾𝛾1 𝑘𝑘1 u1 , 𝑞𝑞2 = 𝛾𝛾2 𝑘𝑘2 u2 , 𝑞𝑞3 = (1 − 𝛾𝛾2 )𝑘𝑘2 u2 and 𝑞𝑞4 = (1 − 𝛾𝛾1 )𝑘𝑘1 u1 (𝑐𝑐𝑐𝑐3 /s); g: Acceleration of gravity (𝑐𝑐𝑐𝑐/s 2); qi : Input flow to the tank (𝑐𝑐𝑐𝑐3 /s); γi : Opening parameter of the 3-way valve. 𝑘𝑘i : Voltage parameter (𝑐𝑐𝑐𝑐3 /Vs). The modified configuration is shown in Fig. 2.
an industrial device that is a programmable logic controller (PLC). Therefore, the Desktop app allows a connection with Matlab, Python and a PLC with TCP / IP communication. This article is structured as follows: Section 2 describes the mathematical model and operating conditions of 4CT system. Section 3 explains the development of the VLE and describes connectivity of a desktop application with Matlab, Python and industrial device to check the design of controllers or perform system identification tasks. Section 4 describes how the development of skills is achieved by using the proposed VLE; therefore, an example of checking a design of controllers for the 4CT system is shown. 2. MODEL OF THE FOUR COUPLED TANKS SYSTEM The 4CT system is a benchmark plant, which is useful for teaching and research purposes of multivariable processes control design. It allows different operating configurations; also it is possible to represent this system as nonlinear or linear, exposing students to broader practical issues. The two most widely used configurations are the known as basic configuration and as the modified configuration. From these, with the closing and/or opening of some of the valves that make up the system, it is possible to obtain other configurations. The process inputs are 𝑢𝑢1 and 𝑢𝑢2 as input voltages to the pumps and the outputs are 𝑦𝑦1 and 𝑦𝑦2 as level measurements of Tanks 1 and 2. Fig. 1 shows the basic configuration of 4CT system presented by Johansson (Johansson, 2000; Alvarado, 2006).
Fig. 2. Modified configuration of the four-tank process (Numsomran, 2008).
The respective flow balance leads to a non-linear model, which is present in Numsomran (Numsomran, 2008). In the 4CT system model (for each configuration) used in the proposed VLE has been considered the specifications of physical 4CT system located in the Advanced Control Lab at PUCP (Fig. 3), in which: • Maximum flow delivered by the pumps: 266.7 𝑐𝑐𝑐𝑐3 /s. • Pipe diameter: 1.27 𝑐𝑐𝑐𝑐. • Maximum height in tanks: 40 𝑐𝑐𝑐𝑐.
Fig. 1. Basic configuration of the four coupled tanks process (Alvarado, 2006).
The flow balance is made for each tank and a non-linear model is obtained (Johansson, 2000; Alvarado, 2006): 𝑑𝑑ℎ1 𝑑𝑑𝑑𝑑 𝑑𝑑ℎ2 𝑑𝑑𝑑𝑑 𝑑𝑑ℎ3 𝑑𝑑𝑑𝑑 𝑑𝑑ℎ4 𝑑𝑑𝑑𝑑
=− =− =− =−
𝑎𝑎1 𝐴𝐴1 𝑎𝑎2 𝐴𝐴2 𝑎𝑎3 𝐴𝐴3 𝑎𝑎4 𝐴𝐴4
𝑎𝑎
𝛾𝛾1𝑘𝑘1
1 𝑎𝑎4
𝐴𝐴1 𝛾𝛾2𝑘𝑘2
�2𝑔𝑔ℎ1 + 𝐴𝐴3 �2𝑔𝑔ℎ3 + �2𝑔𝑔ℎ2 + 𝐴𝐴 �2𝑔𝑔ℎ4 + 2
�2𝑔𝑔ℎ3 + �2𝑔𝑔ℎ4 +
(1−𝛾𝛾2 )𝑘𝑘2 𝐴𝐴3 (1−𝛾𝛾1 )𝑘𝑘1 𝐴𝐴4
𝐴𝐴2
𝑢𝑢1
(1)
𝑢𝑢2
(2)
𝑢𝑢2
(3)
𝑢𝑢1
(4)
Fig. 3. Four coupled tanks pilot plant. Advanced Control Lab (PUCP)
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Validation works allowed to verify that the model matched with physical 4CT system behavior. Likewise, data obtained when working with the model and the physical system were very close. On the other hand, some typical disturbances (added in the Desktop app) could be included in the model for a greater similarity with real operation of a physical system.
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program for communication with Matlab, Python and a PLC. The Desktop app runs an interactive 3D simulation of the model of the 4CT system whose dynamics represent adequately the real behavior of the physical laboratory plant shown in Fig. 5 based in the mathematical model presented in Section II. Using this model, the user will be able to carry out controller design tests and system identification tasks through a communication with a test routine in real time. The effect of control design implementations will be reflected in a 3D model view, and the interaction with the application will be in real time. The 3D model is developed in Blender, which is a free and Open 3D Creation Software based in Python. The blender game engine mode is used to perform the plant simulation as a video game. The blender game engine has a game logic that can be programmed in Python. The 3D model of the plant can be observed as shown in Fig. 5.
3. DEVELOPMENT OF THE VIRTUAL LABORATORY ENVIRONMENT In the following, the proposed VLE is summarized, as a novel interactive remote approach in which a virtual world is combined with a real physical system surrounding. The architecture of the VLE shown in Fig. 4 consists of a “Web server app” and a local application “Desktop app”.
Fig 4. Web server and Desktop apps architecture. Fig. 5. 3D model View of the Desktop app.
Description of the main components of the VLE
The Web Server app is developed through the integration of HTML, CSS, Javascript and Python.
3.1 Web Server app The student accesses to Web server app with a username and password previously assigned according to course registration. Within this application, the student can download the desktop application, review the assigned works and upload his/her results to be graded by the instructor.
3.4 Test routine for checking the controller design Once the student finished the homework of controller design, he/she makes the implementation. Controller implementation is performed first using a script in Matlab. This script (to be executed in Matlab) represents the controller to be tested with the 4CT system. In this case, the script can be tested by connecting Matlab with the Desktop app as many times as necessary during the time permitted. An optional stage is to implement the controller using a script in the open source language Python connecting it with the Desktop app to test it as many times as necessary. Finally, when the first stage is successfully fulfilled, the student implements his/her controller using the structured text language (IEC 61131-3) to practice in an industrial device (PLC) which connects with the Desktop app.
3.2 Communication between the Desktop app VLE and the Web server app This communication is made using a local network (LAN) within the campus; the computers with the desktop application are in a computer lab for simultaneous work of the students with instructor’s support. 3.3 Desktop app The Desktop app is an application that contains the model of the 4CT system as well as the libraries and the necessary 17
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3.5 Test routine for system identification tasks
application that contains the model of the system with Matlab.
System identification tasks that could be performed with this tool are: I/O data collection, model validation and model implementation.
4. Within Matlab, Pyhton or structured text, the student will be able to develop the modeling or controller design tasks, testing their performance with the virtual plant as many times as he/she considers necessary during the authorized time.
For I/O data collection of 4CT system, a Matlab script developed by the student, which will run on Matlab, is used.
5. When the student finishes the practice, he/she must save and send his/her work, which will be automatically sent to the Web server application for a later evaluation.
The collected I/O data are used to perform system identification procedures in homework stage in order to obtain a 4CT system model (Zhu, 2001).
6. Finally, the student can select another practice or close session.
Once the model is obtained in homework stage, a validation task is performed using a Matlab script, comparing the output of the model with the output of the 4CT system against the same inputs and disturbances. After the 4CT system model is validated, the user could implement it using the structured text language (IEC 611313) in an industrial device (PLC) which connects with the Desktop app. The model implemented in an industrial device would allow the development of model-based control strategies for the benchmark plant (Camacho, 2007; Gouta, 2017). Communication between the Desktop app and test routine For communication between the Desktop app and test routine, a client-server TCP/IP based-architecture is used, the objective is to have a bidirectional communication between them, as seen in Fig. 6.
Fig. 7. Flow chart of the proposed VLE
4. USING THE VLE Nowadays, control-engineering education needs to achieve an understanding of mathematics behind the concepts and practice in implementing theoretical solutions in real plants. In order to achieve the development of skills in control design, the proposed VLE is used to:
Fig 6. Types of test routines allowed by the desktop application.
In the following, we describe the use of the VLE, shown in the flow chart of the Fig. 7: 1. The student enters the local application installed in a PC of a computer lab, access with an account assigned by the instructor of the course.
• Describe the operation of the system. • Explain how the physical characteristics of the components influence the operation of the system.
2. Once the student performs this authentication, the local application connects with the web application and the student is authorized to use the system for a specific time to verify and select one of the tasks assigned by the instructor for control design or modeling work.
• Expose students to design and modeling issues. • Practice in implementing control strategies. • Check the design of controllers or perform system identification tasks.
3. Next, the student decides to start the practice, and a communications port will open to connect the local
• Practice with different operating conditions of the system and obtain new control design solutions. 18
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case, the controllers generate the control variables u1 and u2 (see Fig. 1) as inputs of pumps 1 and 2 respectively.
In the desktop application, it is possible to choose a system operation configuration as well as include disturbances. It is also possible to switch a control mode: manual or automatic.
As a result of homework stage using the design method (Garrido et al., 2012), PI-Control algorithms are obtained.
Checking the design of controllers
Using the script in Matlab and by means of connecting with the Desktop App, simulations are performed with the designed PI-Control. Here, to evaluate system dynamics with basis configuration against disturbances, the latter are considered (through their effect) as variations in valve openings defined by the parameters γ1 and γ2 . Two cases were evaluated to check disturbance rejection effectiveness of designed PI-Control.
The design of a controller involves obtaining its algorithm in order to achieve certain desired system characteristics. By checking the design of their controllers, students will be able to verify if the system with proposed algorithms reaches the desired characteristics. For checking the design of controllers, this tool allows the user in real time to: • Choose a configuration of 4CT system.
In Fig. 9 is shown the system time response for 𝛾𝛾1 = 0.6 and 𝛾𝛾2 = 0.7. In this case, the system effectively reaches the desired level values in tanks 1 and 2.
• Program the control algorithms in a Matlab script, Python script and in a structured text routine. • Handle the experiment (start, stop, reset, control mode: manual/automatic). • Generate system input signals. • Simulate the system dynamics (behavior of variables). • Visualize the system dynamics in a 3D model view. • Collect input/output variables data. In the 4CT system, the desired characteristics relate to transient response of levels of tanks. If “basic configuration” is chosen, the control objective would make levels of lower tanks of 4CT system reach the desired values despite disturbances. Once the design of controllers is completed, the test routine is connected with the Desktop app. At executing the simulation, the user can visualize an animation of the operation of 4CT system (Fig. 8). In addition, it is possible to observe the behavior of variables (levels of lower tanks) through graphs generated by the virtual model in the Desktop app.
Fig. 9. Simulation for γ1 = 0.6 and γ2 = 0.7
In Fig. 10 is shown the case when γ1 + γ2 = 1. In this case, the control is not able to reach the desired values of the level of tanks 1 and 2; however, the system reaches stationary values.
Fig. 8. Desktop app for γ1 = 0.6 and γ2 = 0.7.
Checking the design of PI-Control One of the approaches for control of multivariable processes is using decoupling control with two PI controllers. In this
Fig. 10. Simulation for γ1 = 0.5 and γ2 = 0.5
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Once the students finished checking the design of theirs controllers by means of evaluating the transient response of the levels of lower tanks of 4CT, they elaborate a report that must be uploaded to the Web Server app.
Fabregas, E. (2013). Plataformas interactivas de experimentación virtual y remota. Cap 3, pp. 85-125. Tesis doctoral UNED, Madrid, España. Garrido, J., Vázquez, F., and Morilla, F. (2012). Centralized multivariable control by simplified decoupling. Journal of Process Control, 22(6):1044-1062. Gomes, L. (2009). Current trends in remote laboratories, IEEE Transactions on Industrial Electronics 56, pp. 4744-4756. Gouta, H., Saïd, S.H., Barhoumi, N., and M’Sahli, F. (2017). Generalized predictive control for a coupled four tank MIMO system using a continuous-discrete time observer. ISA Transactions. Vol. 67, pp. 280-292. Heradio, R., De la Torre, R., and Dormido, S. (2016). Virtual and remote labs in control education: A survey. Annual Reviews in Control 42, 1-10. Hu, W., Zhou, H., Liu, L., Zhong, L. (2014). Web-based 3D Interactive Virtual Control Laboratory Based on NCSLab Framework. Int. Journal of Online and Biomedical Engineering (iJOE). Vol 10, No 6. Jie, L., Wei, Y., Nan, Z., Xinyu, Y., Hanlin, Z., and Wei, Z. (2017). A Survey on Internet of Things. Architecture, Enabling Technologies, Security and Privacy, and Applications. IEEE Internet of Things Journal, vol. 4, no.5, pp. 1125-1142. Johansson, K. (2000). The Quadruple-Tank Process; A Multivariable Laboratory Process with an Adjustable Zero. IEEE Transactions on Control Systems Technology, Vol. 8, no. 3., pp. 456-465. Numsomran, A., Tipsuwanporn, V., and Tirasesth, K. (2008). Modeling of the modified quadruple-tank process. Proceedings of SICE Annual Conference, Vols 1-7, pp, 783-788. Sánchez, J., Esquembre, F., Martin, C., Dormido, S., Pastor, R., and A. Urquía. (2005). Easy Java Simulations: an Open- Source Tool to Develop Interactive Virtual Laboratories Using MATLAB/Simulink. Vol. 21, No. 5, pp. 798-813. Tempus Publications. UNED, Madrid, España. Sotomayor, J., and Pérez-Zuñiga, C.G. (2017). Cuadernos de Innovación en la Docencia. Dirección Académica del Profesorado. Pontificia Universidad Católica del Perú. Zhu, Y. (2001). Multivariable System Identification For Process Control. Elsevier. Eindhoven University of Technology, Eindhoven, The Netherlands.
It is also possible to use Python script to test the designed PIControl with open source software and elaborate the respective report. Finally, the implementation of PI-Control in structured text is developed and drawn up a final report. Through this reports, instructors will be able to evaluate the development of student skills in design of controllers. 6. CONCLUSIONS The proposed VLE facilitates the development of skills of engineering students in control design of multivariable processes, in this way, before implementation on physical systems, simulations and animations can be carry out to practice theoretical solutions. A novel interactive “virtual laboratory environment” for a 4 coupled tanks system that could be used in control education to check the design of their controllers and perform system identification tasks was presented. The Web server and Desktop application architecture proposed are user-friendly and demands low cost maintenance. Desktop app allows a connection with Matlab, Python and a PLC with TCP / IP communication. A case of use the proposed VLE when checking the design of controllers is presented. Simulations of system dynamics were performed to check the design of PI-Control. FUTURE WORK Development of resources (hardware and software) for interactive work between the VLE and the physical plant (remote lab) for use in process control education.
REFERENCES Alvarado, I., Limon, D., García, W., Alamo, T., and Camacho, E. (2006). An Educational Plant Based on the Quadruple- Tank Process. 7th IFAC Symposium on Advances in Control Education. vol. 8, no.6, pp. 82-87. Elsevier. Astrom, K.J., and Murray, R.M. (2008). Feedback Systems An Introduction for Scientists and Engineers. Princeton University Press. Camacho E.F and Bordons C. (2007). Model Predictive Control. Advanced Textbooks in Control and Signal Processing. Springer-Verlag London. Cass, S. (2018). The 2018 Top Programming Languages. Journal IEEE Spectrum. Dormido, R.,Varga, H., Duro, N., Sánchez, J.,DormidoCanto, S., Farias, G., Esquembre, F., and Dormido, S. (2008). Development of Web-Based Control: The ThreeTank System. IEEE Transactions on Education, vol.51, no.1, pp. 35-44.
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