Catania University students section (Italy)
A NEW SMART SENSING DEVICE FOR TARGET
DETECTION
Salvatore Cutrona, Cristian Lombardo, Giovanni Re
1. INTRODUCTION
In this paper a new displacement sensing device, based on a smart signal processing, is discussed. The main feature of the proposed system is its insensitivity to both the target material and the influence parameters (e.g. light condition). As an example, the sensor can be minded as a useful tool for visual impaired people, to help their navigation in unknown place, being (for this purpose) the material-free feature much more important than the resolution. Moreover, the developed device has the advantage to be a low cost system.
2. AN OVERVIEW OF THE SENSING DEVICE
The sensing system is composed by two parts: the first part is dedicated to signal transmission while the second part allows to process the received signals. The working principle of the proposed system is shown in Figure 1.
The main target of the device is to detect the distance of remote objects independently to both their nature and environmental condition. To fix this target the information related to the distance cannot be obtained by processing the amplitude of the reflected signals. Infact, the signal level is strictly correlated to the target material [1]. A different codification of the target distance information is hence proposed.
Figure 1. The schematisation of the developed sensing device.
Three signals with different frequency are emitted by three infrared (IR) devices, placed with known inclination; the reflected signal are received by three IR detectors.
The transmitting transducers are placed to a height about 170 cm while the receiving transducers are placed at three different heights (e.g. on a stick to be kept in vertical position), as shown in Figure 2.
As can be observed, several information on the target position can be obtained with a few number of devices, by suitably processing the signals detected by the receivers. For example, from a theoretical point of view, each target in Figure 2 can be univocally detected on the basis of the receivers response combination. It should be observed that the information on the discrete position of the target can be easily extended to an information on a distance range, due to the emission corner of each sensor.
Figure 2. The theoretical map for the transmitted and reflected signals.
Moreover, the sensing device configuration can be chosen in order to improve the system resolution in the extreme low region of the working range.
3. THE CONDITIONING CIRCUITS
In this section, a conditioning topology for the considered device, giving suitable performance, is described.
Emitter block: the emitted signals (one for each emitting device) are generated by three astable multivibrators and a buffer current device driving the emitter transducers, as shown in Figure 3.
Figure 3. The emission block.
The adopted trasducer is a suitable infrared diode emitter, allowing to detect the target up to 200 cm [2].
Receiver block: this is the heart of the system; each receiver (three in the described topology) consists of the blocks reported in Figure 4.
Figure 4. The receiver block.
The first stage is an IR receiver device carefully chosen to avoid the influence of environmental parameters (e.g. light, temperature). To detect the emitted signals three selective amplifiers are required. To bypass the filtering problem, PLL circuits (phase locked loop) have been adopted, giving a logical output signal when a fixed frequency is present on its input gate.
The last stage, dedicated to the elaboration of the logic signals given by the PLL, represents the smart unit of the proposed device.
4. THE EXPERIMENTAL SET UP
In order to test the performance of the proposed device an experimental set-up has been implemented. In particular, the smart processing unit has been implemented in LabVIEW, a development tool for virtual instrument by National Instruments. In order to process the logic signals a combinatory logic net has been implemented. The front panel of the developed instrument is reported in Figure 5; it represents a possible case of signal combination. Due to the interaction between the detected signals, the proposed sensing device is able to detect distances as far as 240 cm with step of 60 cm. The possibility to develop new signal processing tool using non linear algorithm (such us fuzzy logic) and analog microcontroller is under consideration.
Figure 5. The front panel of the virtual instrument implementing the smart unit of the sensing device.
Bibliography
1. Ernest O. Doebelin, Measurement Systems, McGRAW-HILL BOOK COMPANY, third edition, 1985.
2. R. Pallas-Areny, J. Webster, Sensors and signal conditioning, John Wiley & Sons, Inc., 1991.
Adsorption kinetic measurement with capacitance sensors
S. Cavallaro, G. Finocchiaro, L. Gambino, M. Musumeci
1. INTRODUCTION
Comprehension and control of interaction between proteins and solid surfaces finds important applications in various fields. In the last twenty years the study of protein adsorption has been of particular interest compared to synthetic materials biomedical applied. It seems, in fact, that the more or less, emocompatibility of biomaterials depends on protein adsorption processes, many scientists have focussed their attention on the adsorption of various proteins, such as -globulin and albumin [1]. The aim of such study is to establish a logical connection between the biocompatibility of a material and the interaction mechanism of these with the main proteins that can be found in the blood plasma. Today, thought, the study concentrates on the adsorption of an only component, because of its great complexity and the great number of doubts about it.
2. PROTEIC ADSORPTION PROBLEM
Many studies, particularly Vromans [2-6], show that proteins adsorb on every surface.
The main interaction forces which can involve a protein are ionic or electrostatic type, due to the attraction or repulsion of two or more groups carrying a neat charge, or interaction of the hydrophobic kind generated by the interaction of hydrogen and in the end reaction of charge transfer. Among these, the most important component, referring to protein adsorption, is given by hydrophobic interactions (of entropic nature).
Adsorption of a protein on a solid surface gives way to an important change of conformation structure [7]. Conformation and orientation that the protein acquires are critical parameters which influences the adsorbed quantity of the solid surface. If the protein structure is modified during the adsorption, the protein is said to be denatured, it means that it is tertiary structure is destroyed with the consequent loss of its biological activity.
The protein adsorption phenomenon on solid surfaces, can be followed in terms of isotherm of adsorption and kinetic, where the quantity of protein adsorbed is followed versus the bulk concentration or versus time. Experimental evidence, suggests that protein adsorption phenomenon is of a dynamic kind.
Many thermodynamic models have been created in order to interpret the interaction between protein molecule and surfaces. In particular if the protein molecules adsorb in a monolayer and the adsorption is completely reversible (there are not interaction between the adsorbed molecules) the adsorption isotherm follows the so called Langmuir isotherm:
where indicates surface concentration of the protein adsorbed layer by the surface unit, C is solution concentration, while and C0 are constants and indicate respectively the coverage of monolayer and the concentration of monolayer adsorption. This simple isotherm together with the respected adsorption kinetic are illustrated in figure 1(a). Figure 1(b) illustrates what happens if the molecules are reversibly adsorbed in one conformation (or orientation) but may change orientation or conformation to a second irreversibly form. Figure 1(c) shows a similar situation where the new conformational needs a larger area on the surface and hence the conformational change introduced an extra desorption of molecules. Figure 1(d) illustrates dynamic situation where a protein molecule is adsorbed in one conformation (or orientation) and undergoes a fast conformational change loading to a situation where molecules of forms 1 and 2 compete for the same area on the surface.
Figure 1. Some hypothetical situations which may occur during protein adsorption
The polymers have been chosen in an opportune way from among the many synthetic materials used in the biomedical applications. For this study it has been decided to use different nature polymers: a polysilossan already widely tested as biocompatible material and on which studies of cellular adsorption have been already done, the PHMS (a mostly inorganic polymer, with the main chain made of oxygen and silicon), and the P2VP, of exclusively organic nature (its components are carbon, hydrogen and nitrogen), frequently used for implant in biomedicine.
Polymers has been deposited as a thin film on inert substratum through the 'spin-coating' technique.
The PHMS was prepared by means of deposition on silicon slices, operating for 60''at the speed of 3000 rotations per minute.
The P2VP was laid down in the same way (30'' at the speed of 2000 per minute) on silicon wafers.
Proteins are biological macromolecules which carry out a specific function; they are, in various numbers, in various succession and in various proportions, the result of copolymerisation of the twenty natural amino acids. We have examined Human Serum Albumin (HSA) which is one of the most abundant protein of blood plasma.
As it is known protein adsorption is influenced not only by the properties of the solid surface but also by the properties of the protein itself [8].
Albumin has a globular structure developing an ellipsoid. The polypeptic chain which characterizes such a protein is made of 609 amino acids linked through 17 sulphide bridges. According to literature, such a protein can be classified as "soft"[9]. All proteins having a low internal stability which consequently, during adsorption, allows conformation changes, belong to this class. Another substance which has been studied is the l-cysteina , it is a (-amino acid which contains the tiolic group. Cysteina can be found in neutral watery solutions such as dipolar ions or zwitterions. The cysteina contains - SH sulphidrilic groups which is particularly important because it allows the formation of disulphide bridges (-S-S-) among different protein chains and among the folds of a single chain.
Sensor structure
In this section the structure of the used sensor will be illustrated. We shall use a two electrode capacitive sensor with cylindrical structure , the first electrode is used as a fixed potential while the second is in contact with the polymer under examination. Figure 2 illustrates a differential circuit, carried out on a wafer whose output voltage is proportional to the difference of entry capacitance. When the protein or the amino acid, dissolved in the tampon solution, comes into contact with the sensible electrode, they modify the complex capacitance (in both the real part and the imaginary one) causing a variation in the output voltage both module and phase[10].
Figure 2. Differential circuit
The equations which regulate the output voltage are:
 |
 |
where and are respectively the equivalent admittance to the capacities and . Being in a sinusoidal regime it is possible to take into account phasors for both the input and output signals; the following relations derived from (2) and (3) by Eulero's formula:
 |
 |
 |
 |
where and are the phase displacement of V
1 and V2, with respect to the entry signal VS; GA and GB are the conductance relative to the admittances YA and YB; the resistances R1=R2=R4=680 k while R3 is a regulated trimmer while the choice of the signal in entry is made on the basis of the interval of frequencies we are interested in. An alimentation of V was used and the integrated amplifier TL082.
Figure 3 Photo with visible electrodes
The lateral surface of the cylindrical capacitance is made of a sheet of copper which acts as a shield
Having fixed potential (i.e. ground). The sensible element is made of silicon wafer covered in copper on which a polymer is deposited by means of a ' spin coating' process. This sensor is put into a polyetilene pot (an inert material to the used substance) on whose upper surface is bored a hole which allows the introduction of the solution. To annul the effect of the solution on the final capacity, solvent is inserted first and later, during the insertion of the solute the acquisition of data is carried out. The solute is prepared in a solution of maximum concentration and then is diluted in order to obtain different quantities of concentration. So the reference and measurement electrodes (we are working with a differential structure) are put in the same conditions and the measure of module and phase variation of output voltage is only due to the insertion of the solute.
Results and Conclusion
From the results, it is evident that there is a higher adsorption speed from the cysteina with regard to albumin. In fact, at the maximum solving concentration in the tampon solution (bi-distilled water for cysteina and phosphate tampon for albumin), it is noted that cysteina reaches to the absorption curve's elbow in about two minutes while the time for albumin is much longer.
This trend is shown also in the variation phase although the last mentioned undergoes less detachment of the initial value with regard to the value of the module. About the behaviour of the some substance in different concentration, it has been observed that the kinetic is slightly slowed when the quantity of protein or amino acid in solution goes down.
After acquisition, data have been elaborated and mediated to diminish error.
In reference to what has been said an adsorption hypotheses, it is realized, by the elaborated data, that the trend is plausible as you can see in figure 1.
Moreover it is established, with accuracy, the required time to the end of adsorption process; in literature, in fact, there are qualitative data only while it is obtained quantitative data for used substances too.
Reference
[1] M. Malmsten, D. Muller, and B. Lassen J. of Colloid and Interface Science 193, 88-95 (1997)
[2] Vroman, L.: Blood, Natural History Press,(1966)
[3] Macritchie, F.: Adv.Protein Chem. 32,283-326 (1978)
[4] Andrade, L.D. ed.Protein Adsorption New York, Plenum Press (1985)
[5] Vroman L. Nature 196, 476-7 (1962)
[6] Vroman L. Thromb. Diath. Haemorrh. 10, 455 (1966)
[7] J.D. Andrade and V. Hlay,"Principles of protein adsorption"
[8] B. Lassen and M. Malmsten, J. of Colloid and Interface Science, 186, 9-16, no. CS964529 (1997)
[9] N.L.Burns, K.Holmberg, and C.Brink, J. of Colloid and Interface Science, 178, 116-122, no 0099 (1996)
[10] L.K.Baxter "Capacitive Sensors-Design and Application" IEEE Press (1997)
Development of an OPC Client
Michele Brischetto, Maila Mazzone and Sandro Spadaro
In a factory information are managed in three levels:
Process control information architecture
First level: Field Management. At this level information provide data on device state.
Second level: Process Management. Include Distributed Control System (DCS) and SCADA System to control manufacturing process.
Third level: Business Management. At this level information collected
from process are integrated whit financial management systems.
So, it is needed a standard and independent way to access data provided by different sources, either device placed in the first level or database.
The key to realise this integration is an efficient and independent communication architecture based on data access and not on data type.
The target of Opc is just to achieve the goals discussed above.
OLE for Process Control (OPC) provides a standard mechanism by which a data source can communicate to any client application in a standard mode. So it is possible for hardware vendors to offer their buyers, servers with OPC interface, allowing in this way any client to connect their server devices.
Applications that work with different OPC Servers
An OPC Server is a server that provides the following OPC interfaces:
OPC DataAccess Server,
OPC Alarm&Event Server,
OPC HistoricalData Server.
Who writes this article focalised his attention on the OPC DataAccess Server interface, designing and realising an OPC Client who has been called OPCClient.
At high level an OPC DataAccess Server is made up of the following objects: Server, Group, Item and Browser.
OPC Server object maintain information about server and acts as container for OPC Group objects.
OPC Group object provides mechanisms to contain and logically organising OPC Items. For each Group the client can define one or more OPC Items.
OPC Item represent connections to data sources within server. Any access to an OPC Item happens through the OPC Group that "contains" the Item. Any Item have associated a Value, a Quality and a TimeStamp. Note that Items are not the sources of data, but only links to them. The OPC Item should be thought as the address of the data source and not as the physical source to which the address is referred.
The OPC Browser object is a collections of branches and leafs, where the leafs represent the Items accessible through the path represented by branches. Browsing is optional. If the server doesn't support it, the CreateBrowser method will not create this object.
OPC Data Access Server object model
OPCClient 1.0.0 has been realised by Visual Basic® 6.0 using the OPC Data Access Automation inteface.
Main Form
OPCClient can provide the list of servers present in the machine specified by the IP address or by the correspondent URL. If any address is specified, then is provided the list of OPC Servers of the local host.
Via the "Connetti" button it is possible to realise the connection to the selected OPC Server.
The Server's properties can be obtained by the "Proprieta" button. These information are visualised on a secondary form.
For each server the information collected are the following:
For each
StartTime:
it indicates the time the server started runningCurrentTime: it indicates the current time from the server.
LastUpadateTime: it indicates the time of the last server's update.
MajorVersion: it is the server's major version.
MinorVersion: it is the server's minor version.
BuildNumber: it is an integer indicating the server's build number.
VendorInfo: it is a string containing information on the server's vendor.
ServerState: it is a code indicating the server's state.
LocaIID: it indicates the locale that can be utilised to localise strings returned from the server.
BandWidth: it is server's specific and indicates the available bandwidth's percentage.
ServerName: it is the name of the server that the client connected to via Connect().
ServerNode: it is the node name of the server that the client connected.
The "Disconnessione" button realise the disconnection from server and free all the resources used.
The "Aggiungi" button allows to create and add a new group. The new group created will have the name and update rate specified in the textbox.
Allows to brows the resource offered by server, which organisation may be either hierarchical or flat.
In the first case items are grouped forming a tree structure with branches (a certain subset of items) e leafs (any single Item).
For a flat organisation only items are showed.
OPCClient allows a server's resources browsing in a friendly way.
After a group has been selected it is possible to add it a new Item. An item can belong to different groups simultaneously.
Selecting a group and using the "Proprieta Items" button, it is possible to show a form containing information about items owned by the selected group.
These are: ItemID, Value, DataType, Quality and TimeStamp.
The form is updated second the update rate set for the group.
Selecting an item it is possible modify the value making OPCClient an useful tool to control and to analyse a manufacturing process.
It is also possible to modify the update rate of each group and eliminate an item of the group. It is finally possible to eliminate all entire group.
Remote Web Process Control in Internet with OPC and SSL
Nunzio Torrisi
Abstract
In this paper a possible implementation of a distributed process control system for Internet is described. Internet is a best effort and insecure network. Any workstation connected to the Internet is vulnerable to clandestine invasion from seekers or profiteers. How can we combine the timeless of manufacturing process control to such an insecure and sometimes low-speed network? The answer depends on how to integrate the Internet into the design of manufacturing control. The approach proposed in the paper combines the scalability and flexibility offers, through the use of an OPC compliant manufacturing system, the reliability of SSL protocol and the simplicity of the Web browser interfaces. The OPC standard interfaces link different fieldbus networks and distribute the process control over a local network by Microsoft DCOM inter-process protocol technology. In the top level of the system a web server, SSL enabled, exchanges data process with one or more OPC servers by DCOM. The end user of remote control does not need to configure a complicate inter-process protocol and learns a graphical user interface for each particular OPC client of different vendor but uses only a web browser SSL enable.
1. Introduction
Security is a basic feature for each process control system. The use of control PC based in the distributed control system has integrated step-by-step the technologies of process control and computer networks. In particular, the integration of Internet in the local network of manufacturing system requires the choice which control function export in Internet and network architecture screen the security problems of Internet. It is not possible to include the Internet inside any kind of control or feedback-loop but we can use the Web to collect and communicate data keeping all the time critical functions under control of the local processor. For instance, we can set up limit parameters, show graphical trends, browse online documentation of a single device on fieldbus network or update a firmware. This use of Web does not require timeless but only a secure Internet access for the control application. A reliable and secure solution for every Internet application over Web is to integrate the SSL protocol with HTTP protocol. The architecture of this system is based on the integration of software packages with OPC interfaces and web technology with SSL protocol. The possibility of this integration is provided by Microsoft DCOM(Distributed Component Object Model) technology.
OPC stands for OLE for Process Control(OLE = Object Linking and Embedding). It defines interfaces for the access data items such as: process signals, alarms, events and so on. It is an industry standard for data exchange between applications. Several industrial networks of different hardware vendors follow the OPC specifications and simplify the I/O driver development. Having a standard makes it possible that different software packages can connect and communicate with different devices. If a vendor of an industrial network makes a data server OPC compliant there are already all kinds of OPC clients available that can access the OPC server. An OPC server provides a reliable inter-process protocol by DCOM technology and an OPC client installed on PC remotely manages the OPC server[1].
SSL stands for Secure Socket Layer. It is a protocol layer which may be placed between a reliable connection-oriented network layer protocol and the application protocol layer. SSL provides secure communication between a client and a server by allowing mutual authentication, the use of digital signatures for integrity, and encryption for privacy. It is a standard de facto in the internet security(see, e.g., [2] and references there in). The use of both these technologies improves the security of a system providing at the same time scalability and flexibility.
2. Architecture
The overall architecture consists of two parts: the manufacturing system and the client, a remote PC which sends and receives data by a web browser.
There are several reasons for choosing an architecture where an OPC server workstation and the Web server workstation are separated. The two workstations have different software requirements and need different Operating System.
The data flow in a manufacturing system, where a fieldbus network is divided in periodic flow and asynchronous flow. The periodic flow is generated by periodic processes which produce variables with a fixed time to live. If a consumer process would take this variable it must observe the limits, called deadlines, fixed by the time to live[3]. The Operating System of OPC server workstation must schedule processes to provide timeless in time critical processes keeping all deadlines.
There are two families of operating systems available on the market:
- GPOS(General Purpose Operating System): Windows, Unix.
- RTOS(Real Time Operating System): QNX, RTX, LinuxRT.
An RTOS ensures that the network software and the application software share processor time with appropriate priorities. On the other hand the primary goal of the Operating system of a Web server is to process an indefinite number of multiple, simultaneous browser requests. Most of Web server software respond to multiple requests by spawning processes, one for each request. Each process has its own copy of server. If there are too many simultaneous requests the web server can consume all the available system memory. Another difference that prompts to separate Web server workstation from OPC server workstation is the possible interference between the priority of TCP/IP stack and the priority of time critical variables.
The architecture of the manufacturing system proposed can be represented by three layers: Web server level, OPC server level and fieldbus level.
The fieldbus level can include many different fieldbus networks as PROFIBUS or Lonwork. For each type of fieldbus network there is a specific fieldbus protocol: Lonwork uses Lontalk, PROFIBUS uses a 802.4 modified and so on.
The goal of OPC server level is collect all data of fieldbus level and to make uniform the access to variables incoming from different fieldbus[4]. Several hard tests on OPC and DCOM systems have reported good performance[5][6]. In this level the inter-process protocol is DCOM then the Web server, such as an OPC Client, can retrieve data process by DCOM protocol. In these two level the priority is the timeless for periodic flow, the data requests incoming from Web server are served such as asynchronous flow. The Web server level includes the workstation with an Operating System dedicated to Internet network, such as Windows NT Server, and a Web server software SSL enabled. Inside the html pages shared by Web server we can export controls through the use of ActiveX control and Java Applets. The communication protocol between Web server and Web browser is HTTPS. This stands for HTTP + SSL protocol. The SSL handshake protocol provides mutual authentication to ensure the identity of remote user with Web server. The integrity of the data transmitted is protected by digest algorithm such as MD5, SHA or SHA1[7]. Besides, a strong encryption after SSL handshake protocol is not needed then we can set the Web server with a fast cryptography algorithm such as RC4 40 bit-keys and reduce the CPU load.
This is a transparent architecture for a remote user of the manufacturing system because he views and interacts with only the Web server. The interface for an OPC server is not an OPC client but becomes a simple html page with embedded an ActiveX control or a Java Applet. If the user of remote control uses MS Internet Explorer the ActiveX control into the web page can be the same control of a local OPC client because the Microsoft ActiveX technology is integrated in MS Internet Explorer[8]. Alternately the user of remote PC can use the control by Java Applet. Every objects, ActiveX or Java Applets, inside html pages work into the browser-program context and the information about the remote process is inserted in the frame of HTTPS protocol[2]. The web server uses SSL protocol for each remote connection to encrypt the data flow and to protect against spoofing. Without SSL anyone can read the HTTP data flow through the base64 code table and use false network addresses to access to the manufacturing system.
3. Conclusion
The Secure Socket Layer provides a very high security level. A possible attack may be tried only by a one or more supercomputer able to compute a large algebra operations in a short time. But the use of supercomputers is restricted by law and only particular agency such as FBI can use them[2].
This architecture enables the remote user to interacts with the manufacturing system through a standard Web browser instead of built-in hardware switches and displays. With this capability, we eliminate the cost of the user interface hardware. We can replace switches and displays by using icons and an html editor that give the user look and feel of a panel but without hardware cost.
Another feature of the browser interface is that the remote user can control the system from any desktop computer. The user can choose any available computer for day-to-day operations: update firmware, diagnose problems, set limits, test a single device and so ones.
Another advantage to save cost up is network delivered device documentation. Not only do we save the cost of printing and shipping maintenance, but also increase the value to the user by linking operation of device with the appropriate section of the documentation.
The discerning reader can find different points of view about these kinds of problems in [9].
References
[1] Richard C. Harrison, Intellution Inc. "OPC DCOM White Paper", Intellution Inc. 1998 [www.opcfoundation.org]
[2] Nunzio Torrisi, "Web Security and SSL" [http://www.isa.iit.unict.it/~ntorrisi]
[3] Orazio Mirabella, University of Catania, "Esigenze dei sistemi di controllo di processo e loro legame con il sistema di comunicazione" [http://RetidiCalcolatori.iit.unict.it/Dispense/FieldBus]
[4] SC34/WG07 - "Possible Architecture of Automated Systems" - [www.opcfoundation.org]
[5] Richard C. Harrison, Intellution Inc. "DCOM, OPC and Performance Iusses", Intellution Inc. 1998 [www.opcfoundation.org]
[6] Al Chisholm, Intellution Inc. "The Performance and Throughput of OPC", Rockwell Software Inc. 1998
[7] Netscape Communications Corporation, "How SSL Works", [http://developer.netscape.com/tech/security/ssl/howitworks.html]
[8] Microsoft Corporation, "DCOM Architecture" [http://www.microsoft.com/com/tech/DCOM.asp]
[9] Scenix Semiconductor Inc., "The Embedded Internet", [http://www.scenix.com]
Study of an Electric Vehicle with an Additional Photovoltaic Panel and a Power Unit
Salvatore Argentino, Adriano Basile
Introduction
The current state of the environment, with the high degree of pollution, produced an improvement on studies which try to use alternative and renewable sources of energy. This project concerns the analysis, from an energetic point of view, of an electric four wheels vehicle (EV). The vehicle is mainly powered by a set of accumulators, charged by a conventional electric power line, but, in order to increase its autonomy, it is possible to add some photovoltaic (PV) panels and when required also to activate a Power Unit (PU) that restores the charge on the accumulators.
The system under examination has been studied through a program Matlab, that thanks to an intuitive graphic interface allows us to set all the parameters of the system in a dynamic way. It allows therefore to analyse the energetic performances of any combination of the devices of the system: the electric vehicle, the photovoltaic panels and the power unit.
Particularly we have examined the energetic behavior of the vehicle electric MELEX 743, on which 4 panels UNI-SOLAR US-64 have been installed and a generator HONDA EU1000i.
We compared all the three power sources, and through suitable graphs it is possible to appraise residual energy in the accumulator. Once established the time when the vehicle is switched on, the duration of the journey, the initial energy of the accumulator etc., we can know in advance if the vehicle is able or not to reach its destination.
Characteristics of the electric vehicle
Calculation of the power of the driving gear
To appraise the power needed by the motor we have calculated the power required in relationship with the performances desired
The power required for the motion can be deduced by the following relationship:
P
r= [W CRR (sin x + cos x ) g + CRA v2 + W a] vwhere:
- x is the angle of inclination of the plan of the motion in comparison to the horizontal one;
- g is the acceleration of gravity;
- v is the instant speed of the vehicle;
- a is the acceleration of the vehicle;
- W is the total weight;
- CRA is the coefficient of aerodynamic resistance;
- CRR is the coefficient of resistance to the rolling.
Cycle of operation of the motor
We have considered the following operating regime as the typical cycle of the motor:
The graph shows the lines of motion uniformly accelerated, the lines of motion with constant speed, and the duration of the run of 136 seconds that correspond to 650m. The speed on the ordinate is in percentage of the maximum speed of the vehicle.
Energetic contribution of the photovoltaic panel
The power supplied by the system PV has been calculated instant for instant with the following relationship:
P
v = NumP * PotNom * Irrag; Where:- NumP is the number of installed panels;
- PotNom is the power supplied nominally by every single panel;
- Irrag is the percentage of irradiation in comparison to the maximum value of power irradiated by the sun.
The curve that describes the solar irradiation during the day is shown in the figure:
Energetic contribution of the power unit
The power supplied by the PU is constant and equal to its nominal power, naturally up to depletion of the fuel.
Examined case
The electric vehicle taken into consideration is a vehicle with four wheels for the transport of persons for circulation on the road. The main parameters of the electric vehicle, relevant to the present study, are the followings ones:
Model: Melex 743
Length [mm]: 2710
Width [mm]: 1220
Empty Weight [kg]: 350
Maximum speed [Km/h]: 25
Max Number of passengers: 4
Autonomy with a single charge [km]: 100
Electric motor: 48V DC, series traction, 2.1 HP to 3200rpm
Accumulators: eight 6V accumulators with high capacity and electronic static power control CURTIS.
The dimensions of the vehicle allow us to assemble on its roof up to 4 photovoltaic panels US-64 with a small side leaning part (26cm).
Model US-64
Nominal power [W] 64
Length [mm] 1366.10
Width [mm] 741.20
Thickness [mm] 31.80
Weight [kg] 9.17
Cost excluded taxes [Euro] 475
The PU used in the mathematical model is the following:
Model: Honda EU 1000i
Nominal power [W]: 900
Autonomy [h]: 4
Capacity reservoir [lt]: 3.3
Empty Weight [kg]: 13
The PU is turned on when the charge of the accumulator goes down under 20% of its maximum value and it is turned off when it exceeds 50% up to depletion of the fuel.
According to the characteristics of the EV, with a complete charge of the accumulator (2000 Wh) the vehicle is able to run 100 km in 5.37 h. The energetic maximum contribution given by the photovoltaic units(4 panels) is of 2082 Wh that give an autonomy to the EV of 5.59 hours equal to 104 km, while the contribution of the PU is 3600 Wh that give an autonomy of 9.67 hours which correspond to 180 km. From these results it is deduced that a complete charge of the accumulator is got with an exposure of the EV for a whole day to the sun. Besides such results represent the maximum values we can obtain from the various power sources, and cannot be considered valid in a real case. For this reason we decided to appraise the contribution of the photovoltaic energy to the motion of the EV in a practical case. The simulation has considered two cases with either 2 and 4 panels PV, 130 Km crossing (200 runs type) with departure at 8:00 o'clock; the data mentioned are represented in the following figure:
Results of the simulation with 2 panels PV:
The graph of the powers is the following:
The behavior of the charge of the accumulator is shown in the following figure:
As it can be noticed by the graph, in absence of the generator , the energy in the accumulator is totally used, with the consequent arrest of the EV.
The results in terms of performances obtained are:
As it can be noticed, with the use of the photovoltaic energy the consumption of fuel in the PU is reduced to less than 50%, this way reducing the polluting in the atmosphere.
Resulted of the simulation with 4 panels PV:
The graph of the powers is the following:
The behavior of the charge of the accumulator is shown in the following figure:
It must be noticed that the power unit doesn't enter in operation in the complete system and therefore the red and blue curves result overlapped. Besides the EV doesn't arrive to stop.
From this graph we note that there are not energetic contributions from the PU.
The results in terms of performances obtained are:
In this last case, with the use of the photovoltaic energy no power has been required to the PU and therefore there are no polluting issues in the atmosphere.
Conclusions
Following the tests performed in the case under examination it can be noticed that, with the use of 4 photovoltaic panels rather than 2 the power unit is no more necessary, saving up, therefore, its cost with is comparables to the additional expense for the two additional panels. Moreover we obtain the total absence of polluting issues.
Another advantage that is obtained with the use of 4 panels is the possibility to reload completely the accumulator by exposing the vehicle to the sun for a whole day, while with the use of only 2 panels 2 days would be necessary. In this way we save up therefore the electric energy supplied by the power line.