PLCBasedMonitoringControlSystemforInductionMotorPLC.docx

1、PLCBasedMonitoringControlSystemforInductionMotorPLCDesign and Implementation of PLC-Based Monitoring Control System for Induction MotorAbstract：The implementation of a monitoring and control system for the induction motor based on programmable logic controller (PLC) technology is described. Also, th

2、e implementation of the hardware and software for speed control and protection with the results obtained from tests on induction motor performance is provided. The PLC correlates the operational parameters to the speed requested by the user and monitors the system during normal operation and under t

3、rip conditions. Tests of the induction motor system driven by inverter and controlled by PLC prove a higher accuracy in speed regulation as compared to a conventional control system. The efficiency of PLC control is increased at high speeds up to 95% of the synchronous speed. Thus, PLC proves themse

4、lves as a very versatile and effective tool in industrial control of electric drives.Keywords：Computer-controlled systems, computerized monitoring, electric drives, induction motors, motion control, programmable logic controllers (PLCs), variable-frequency drives, voltage control.I. INTRODUCTIONSinc

5、e technology for motion control of electric drives became available, the use of programmable logic controllers (PLCs) with power electronics in electric machines applications has been introduced in the manufacturing automation 1, 2. This use offers advantages such as lower voltage drop when turned o

6、n and the ability to control motors and other equipment with a virtually unity power factor 3. Many factories use PLCs in automation processes to diminish production cost and to increase quality and reliability 49. Other applications include machine tools with improved precision computerized numeric

7、al control (CNC) due to the use of PLCs 10. To obtain accurate industrial electric drive systems, it is necessary to use PLCs interfaced with power converters, personal computers, and other electric equipment 1113. Nevertheless, this makes the equipment more sophisticated, complex, and expensive 14,

8、 15.Few papers were published concerning dc machines controlled by PLCs. They report both the implementation of the fuzzy method for speed control of a dc motor/generator set using a PLC to change the armature voltage 16, and the incorporation of an adaptive controller based on the self-tuning regul

9、ator technology into an existing industrial PLC 17. Also, other types of machines were interfaced with PLCs. Thereby, an industrial PLC was used for controlling stepper motors in a five-axis rotor position, direction and speed, reducing the number of circuit components, lowering the cost, and enhanc

10、ing reliability 18. For switched reluctance motors as a possible alternative to adjustable speed ac and dc drives, a single chip logic controller for controlling torque and speed uses a PLC to implement the digital logic coupled with a power controller 19. Other reported application concerns a linea

11、r induction motor for passenger elevators with a PLC achieving the control of the drive system and the data acquisition 20. To monitor power quality and identify the disturbances that disrupt production of an electric plant, two PLCs were used to determine the sensitivity of the equipment 21. Only f

12、ew papers were published in the field of induction motors with PLCs. A power factor controller for a three-phase induction motor utilizes PLC to improve the power factor and to keep its voltage to frequency ratio constant under the whole control conditions 3. The vector control integrated circuit us

13、es a complex programmable logic device (CPLD) and integer arithmetic for the voltage or current regulation of three-phase pulse-width modulation (PWM) inverters 22.Many applications of induction motors require besides the motor control functionality, the handling of several specific analog and digit

14、al I/O signals, home signals, trip signals, on/off/reverse commands. In such cases, a control unit involving a PLC must be added to the system structure. This paper presents a PLC-based monitoring and control system for a three-phase induction motor. It describes the design and implementation of the

15、 configured hardware and software. The test results obtained on induction motor performance show improved efficiency and increased accuracy in variable-load constant-speed-controlled operation. Thus, the PLC correlates and controls the operational parameters to the speed set point requested by the u

16、ser and monitors the induction motor system during normal operation and under trip conditions.II. PLC AS SYSTEM CONTROLLERA PLC is a microprocessor-based control system, designed for automation processes in industrial environments. It uses a programmable memory for the internal storage of user-orien

17、tated instructions for implementing specific functions such as arithmetic, counting, logic, sequencing, and timing 23, 24. A PLC can be programmed to sense, activate, and control industrial equipment and, therefore, incorporates a number of I/O points, which allow electrical signals to be interfaced

18、. Input devices and output devices of the process are connected to the PLC and the control program is entered into the PLC memory (Fig. 1).Fig. 1. Control action of a PLC.In our application, it controls through analog and digital inputs and outputs the varying load-constant speed operation of an ind

19、uction motor. Also, the PLC continuously monitors the inputs and activates the outputs according to the control program. This PLC system is of modular type composed of specific hardware building blocks (modules), which plug directly into a proprietary bus: a central processor unit (CPU), a power sup

20、ply unit, input-output modules I/O, and a program terminal. Such a modular approach has the advantage that the initial configuration can be expanded for other future applications such as multimachine systems or computer linking. III. CONTROL SYSTEM OF INDUCTION MOTORIn Fig. 2, the block diagram of t

21、he experimental system is illustrated. The following configurations can be obtained from this setup.a) A closed-loop control system for constant speed operation, configured with speed feedback and load current feedback. The induction motor drives a variable load, is fed by an inverter, and the PLC c

22、ontrols the inverter V/f output.b) An open-loop control system for variable speed operation. The induction motor drives a variable load and is fed by an inverter in constant V/f control mode. c) The standard variable speed operation. The induction motor drives a variable load and is fed by a constan

23、t voltage-constant frequency standard three-phase supplyThe open-loop configuration b) can be obtained from the closed-loop configuration a) by removing the speed and load feedback. On the other hand, operation c) results if the entire control system is bypassed. IV. HARDWARE DESCRIPTIONThe control

24、system is implemented and tested for a wound rotor induction motor, having the technical specifications given in Table I. The induction motor drives a dc generator, which supplies a variable R load. The three-phase power supply is connected to a three-phase main switch and then to a three-phase ther

25、mal overload relay, which provides protection against cur- rent overloads. The relay output is connected to the rectifier, which rectifies the three-phase voltage and gives a dc input to the insulated gate bipolar transistor (IGBT) inverter. Its technical specifications 25 are summarized in Table II

26、. The IGBT inverter converts the dc voltage input to three-phase voltage output, which is supplied to the stator of the induction motor. On the other hand, the inverter is interfaced to the PLC-based controller.Fig.2 Electrical diagram of experimental system.TABLE I INDUCTION MOTOR TECHNICAL SPECIFI

27、CATIONSTABLE II INVERTER TECHNICAL SPECIFICATIONSThis controller is implemented on a PLC modular system 5, 2628. The PLC architecture refers to its internal hardware and software. As a microprocessor-based system, the PLC system hardware is designed and built up with the following modules 2937: cent

28、ral processor unit (CPU) discrete output module (DOM) discrete input module (DIM) analog outputs module (AOM) analog inputs module (AIM) power supply.Other details of the PLC configuration are shown in Tables III and IV.A speed sensor is used for the speed feedback, a current sensor is used for the

29、load current feedback, and a second current sensor is connected to the stator circuits 32. Thus, the two feedback loops of the closed-loop system are setup by using the load current sensor, the speed sensor, and the AIM. A tachogenerator (permanent magnet dc motor) is used for speed sensing. The ind

30、uction machine drives its shaft mechanically and an output voltage is produced, the magnitude of which is proportional to the speed of rotation. Polarity depends on the direction of rotation. The voltage signal from the tachogenerator must match the specified voltage range of the AIM (05 V dc and 20

31、0- internal resistance). Other PLC external control circuits are designed using a low-voltage supply of 24 V dc.V. SOFTWARE DESCRIPTIONPLCs programming is based on the logic demands of input devices and the programs implemented are predominantly logical rather than numerical computational algorithms

32、. Most of the programmed operations work on a straightforward two-state “on or off” basis and these alternate possibilities correspond to “true or false” (logical form) and “1 or 0” (binary form), respectively. Thus, PLCs offer a flexible programmable alternative to electrical circuit relay-based control systems built using analog devices.The programming method used is the ladder diagram method. The PLC system provides a design environment in the form of software tools running on a host computer terminal which allows ladder diagrams to be develop