Internet based SCADA System for Dc Motor Control using PLC *Muhammad Yasir Zaheen, **Muhammad Rehan, ***Fahad Ahmed Siddiqui, ****Syed Waqad Ali Hashmi and *****Muhammad Shujaat Kamal
Abstract: Most of the industrial units are spread across vast areas with different units installed at remote distances. DCS and SCADA based systems are widely used in industrial control process to overcome these vast distances. SCADA provides additional supervisory parameters by keeping the record of past performance and providing the feedback to supervisors. Most of the applications in the industry involve controlling of conveyer belt with variable load. The possibility of driving these conveyors can be either DC or AC motors. The problem occurs with AC motor in controlling of variable load on conveyer belt. The system model of AC motor is inherently nonlinear and hard to control if the load keeps on getting varied. This paper provides a solution for the both above said possibilities as a single scenario. SCADA system is implemented for the control of a dc motor driving a pump at a remote location controlling flow of any liquid to a certain plant. This provides a centralized control for the supervisor of multiple units without the need of moving from one station to another. Wireless connections are used to inter connect the substations to the master unit using internet. This provides even greater flexibility and convenience by eliminating the need of wires scattered all over the plant. The implemented system acquired the data in real time and the collected data was managed for the supervisor in order to improve the performance of the overall process. Index Terms – Automation, DC Motor Control, PID, SCADA
I INTRODUCTION PID control is widely used these days to control different industrial processes where the system model is linear and time invariant. Even though most of the real life processes are neither linear nor time invariant, but slight variations can be done away as far as they are not making the system unstable or creating a lot of disturbance. Designers use linear approximations in order to convert the nonlinear system equation to a linear one [1]. So it can be said that as far as the output is satisfactory, PID is the tool of choice of most developers due to its simplicity and ease.
Most of the industries these days have the covered area spanning upon miles of land, and even units can be placed as far away as different cities. Checking and monitoring at every step in industry gives easy and reliable production management [2]. It has always been of great importance to control such remote units without the need of physical presence of any supervisory staff on site. This simply increase the overall cost of the process control and the human negligence error would also be increased. This paper is presenting an automation system to control and monitor speed of DC pumps installed at different remote locations from a centralized location. These provide the convenience to the supervisory staff and reduce the cost of individual visits to monitor the performance of the pumps. Supervisory control and data acquisition (SCADA) system is popular to control over plant processes and their continuous monitoring. As the motor control requirements are no longer confined to the limited working boundary, but can be required to be controlled over great distances, it gives reliable and local control of each pump station through remote PLC and SCADA computers [3]. In order to attain the maximum benefit from SCADA systems, it should be connected to internet. Internet communication system can handle large amount of data within a very short time [4]. Authorize person can have secure plant access from any remote location using a standard web browser on their PCs. SCADA is state of the art technology when it comes to the online system monitoring and control through internet technologies[5]. The interface between MATLAB and PLC is provided using OPC toolbox available in the MATLAB and OPC Server for SIMATIC S7 used to program PLC. This OPC connectivity provides the interface for the sensor readings from pump to be fed to PID model in MATLAB and convey back the control parameters to the RTU for system
*Electronic Engineering Department, SSUET,
[email protected] **Electronic Engineering Department, SSUET,
[email protected] ***Electronic Engineering Department, SSUET,
[email protected] ****Electronic Engineering Department, SSUET,
[email protected] *****Electronic Engineering Department, SSUET,
[email protected]
control. Even though it was possible to use the PID module for the PLC, but this setup was implemented to test and try different algorithms for plant control in the future. The rest of the paper is organized as follows; part 2 describes the overall model along with SCADA frame work. Part 3 give a brief description of the software used with part 4 detailing about hardware used in the system. In the end, part 5 defines the Control model of DC motor along with DC drives. Part 6 is the conclusion of the whole project. II OVERALL SYSTEM MODEL This paper presents dc motor control through PLC using SCADA system. According to the presumed scenario different dc motors are mounted at remote locations very far from the central control room. GUI is used to get the control parameters from the user and provide the overall outlook about the system performance. These control parameters are passed to the RTU units through internet. TCP/IP Protocols are used to send the data over the internet and Ethernet modules are used over the PLC to enable them for online communication. RTU decode these control signals and pass the information to the dc drive which controls the dc motor of the pump. RTU collects the data about the rpm of the motor and the flow generated. This data is sent back to the MTU for processing and generating the correct control parameter. The SCADA software passes this information to the MATLAB over OPC connectivity for PID calculation. This step could have been implemented over PLC, but this setup will help in future analysis and comparison of different control algorithms. After processing the inputs, the generated output is sent back to SCADA software for implementation. Figure 1 completely explains the overall working of the system and elaborates the connectivity between different components and modules of the system.
Fig. 2: Control Process Diagram III HARDWARE SCHEME OF CONTROL PROCESS Consider a PLC is generating the control signal with comparison of feedback signal and reference signal (desired speed) to regulator block. The operation of regulator block is to compares the current feedback signal and reference current signal generated from PLC and finally generate a signal for DC drive. Now DC drive run the DC motor at reference speed. Figure: 2 explain the complete process of hardware scheme at RTU. Figure 3, elaborates the system flowchart. The system starts with the input of desired speed at the MTU. The GUI screen is used as an interface to input the desired speed in to the system. The speed will be process at MTU and the respective control signal is transmitted from MTU to RTU. PLC receives the signal and compares it with the current speed of the DC motor at RTU. As the difference found, PLC will generate new control signal to DC Drive and finally DC drive runs the DC motor at specific set point send by user from MTU. START
GUI
PC
Data Transmission (MTU to RTU)
PLC
Speed Difference
No
Yes Dc drive
Dc Motor
End
Fig. 1: Overall Model of SCADA System
Fig. 3: Flowchart of the system
A. DC Motor Controlling Dc motor generally operated from armature voltage and/or field voltage. The variance of said parameters of dc motor is dedicated use to control speed of dc motor. Mathematical analysis is below in which eq. 1 shows the armature voltage and eq. 2 shows the field voltage (1) (2) We are using dc motor to derive a conveyer with variable load. The torque characteristic can be analyzed through following equations. The electromagnetic torque produce by dc motor is expressed as (3)
Fig. 4: Controlled thyristor based DC Drive As motor is connected to conveyer, therefore,
(4) Where express as
(6)
is the armature back and it can be (5)
Where, is the load torque (Nm), J is the load inertia ( ) and B is the viscous friction coefficient (Nm/rad/s)
Fig. 5: Snapshot of Graphical User Interface
V RESULTS AND CONCLUSION The system is implemented to remotely monitor and control different DC pumps located at considerable distances from control room. Software is designed using Simatic S7 to configure SCADA system connecting the central unit to RTUs using internet. These RTUs are controlling the DC pumps and monitoring the speed of DC motor. In this experiment, RTUs are designed using PLCs, but the option of dedicated RTU is available in the market to be used. This speed is sent to control unit which transfer the data to MATLAB. Interconnection between Simatic S7 and MATLAB is created using OPC connectivity. MATLAB implemented the PID control and return the control parameters to the SCADA to return back to RTUs. The control values generating from MATLAB and transmitted over the internet are then fed to DC drive which in turn controlled the firing delay between thyristor pairs. This controlled the overall output power and voltage level of the DC drive. The speed of the motor is directly proportional to the applied voltage on its input. Hence by varying the output voltage of DC Drive, the speed of the motor can be controlled. The results achieved from the experimentation and beta tests showed that the DC pumps operated under varying circumstances with satisfactory performance. The steady state error and settling time is reduced and overshoot is also controlled, yet not completely removed. This is done to reduce the rise time as much as possible because the pump application can sustain slight overshoot without much disturbance to the mechanical setup. In case of an application where the system is prone to overshooting of the output, PID gains are calculated to tradeoff the rise time with complete elimination of overshoot.
This setup can be used in educational institutions to train the students Electrical and Electronic Engineering in the fields of industrial automation and control system design. This will give them a chance to implement their theoretical knowledge in real life scenarios and get some hands on experience of implementing the SCADA system and comparison between different control algorithms. In future, current experimentation setup can be used to further implement different control algorithms like adaptive control, LQR control or fuzzy control instead of PID and their result can be compared against the processing power required in the execution of the algorithm. Furthermore, the PID and other algorithms can be moved to the embedded platform in order to take the design further towards real life product development. REFERENCES [1] Jui-Hong Horng, “Hybrid MATLAB and LabVIEW with neural network to implement a SCADA system of AC servo motor”, Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, Keelung, Taiwan, Advances in Engineering Software 39 (2008) 149–155. [2] Yucel Cetinceviz, Ramazan Bayindir,” Design and implementation of an Internet based effective controlling and monitoring system with wireless field bus communications technologies for process automation”, ISA Transactions 51 (2012) 461–470. [3] Z. Tugee OZCAN, “Wastewater Treatment with SCADA Application”, the Chamber of Electrical Engineering, Kocaeli. [4] K. C. Lin, L. -R. Chang-Chien, “A Remote Supervisory Control for Motor Driving System Using Windows Mobile-based Pocket PC”, Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan. [5] Zafer Aydogmus and Omur Aydogmus, “A WebBased Remote Access Laboratory Using SCADA”, IEEE Transactions on Education, VOL. 52, NO. 1, February 2009.
