PLC based drives and converters

May 14 • Notes • 2804 Views • 4 Comments on PLC based drives and converters

PLC based drives and converters

It stands for Programmable logic controller. It is a machine controller that activates relays and other input and output units from  stored programs. Additional modules support motion control and other functions.

PLC ha been gaining popularity because it has following advantages:

  • Cost is affordable  for controlling systems.
  • It can be applied again  to control other systems  easily and very fast.
  • Computation abilities allow more sophisticated control.
  • Trouble shooting aids makes programming easier and reduce downtime.
  • The reliable components can be used for long years.

Relays are used to control electrical drives because relays allow power to be switched ON and OFF without a mechanical switch and it is common to use relays to make simple logical control device.

PLC based control of drives

plc based drive

plc based drivers and conductors

The PLC based architecture is utilized for I/O intensive control applications. Based upon banks of relays that are scanned, or polled, by a central processor, the PLC provides a low cost for those familiar with its logic programming language. Integeration of the motion, I/O operator interface, and additional cards that are plugged in its backplane.

The additional of scanning points decreases the polling rate of any individual point, and can thus lead to lower machine response. Because PLCs have not historically concentrated on motion control, plug-in indexers or those that communicate. Because these indexers boards often include their own microprocessor, they prevent slow polling rates, but incorporate a separate programming language. In general, this comprise is acceptable for all but most complicated motion/ machine applications.

A PLC based indexer is designed to accept data from PLC in the form of I/O communication. Typically, the information is in BCD format. The BCD information may select a program to execute, a distance to move, a time delay, or any other parameter requiring a number. The PLC is well suited to I/O actuation, but poorly suited to perform complex operations such as math and complicated decisson making. The motion control functions are separated from PLC’s processor and thus do not burden in scan time.

PLC selects and executes the required motion sequences  that are programmed from the host when the controller is in stand alone mode, and stored in non volatile memory via the I/O interface.

AC – AC Converters

Converters are the devices which converts the a constant ac voltage to the variable ac voltage of the same frequency.The power flow to the load can be controlled by controlling the rms value of the applied voltage.

The applications of the ac voltage converter are

1)industrial heating

2)light control

3)speed control for the induction motor

4)on load transformer tap changer

The ac voltage controller are divided into 2 parts

1)single phase controller – operates for the single phase source

2)three phase controller –operates on the three phase source

Controls and the techniques

Since the input to the ac voltage  controller is ac it is always line commuted.so the forced commutation is not needed.

Two types of the controls needed are

Integral cycle control- as the name suggests  the ac supply is connected to the load for certain number of the cycles and is turned off for the another certain number of the cycles.They are switches on by the gate pulses at the zero voltage crossing of the input voltage.

Phase angle control

Here the thyristors( switches) are connected to the loads to an ac source for the portion of the each cycle of the input voltage.

Dc to DC converter or chopper is the static device which converts the fixed input dc voltage to the variable dc output voltage.It can be regarded as the dc equivalent of the ac transformer. Asthey behave in the identical manner.

Advantages-

Smooth voltage control ability

High efficiency

Fast response and the regeneration capability

Application-

Speed control of the dc drives

Trolley cars

Marine hoists etc.

Diode converters-Ths type of the convertors converts the  AC voltage into the fixed DC voltage.The input voltage to the rectifier may be either  single phase or three phase

DC to DC converters– It converts the fixed DC into variable DC and vice-verse.The dc output voltage is controlled by the duty cycle.

 Related questions and answers

1) Explain the term PLC

It stands for Programmable logic controller. It is a machine controller that activates relays and other input and output units from  stored programs. Additional modules support motion control and other functions

2)Give some advantages of the Programmable logic controller.

* These are cost effective.

* It can be reapplied to the control system and it is fast to respond.

* Computation abilities allow more sophisticated control.

* Trouble shooting aids makes programming easier and reduce downtime.

*The components are reliable and can be used for long period.

3)state the control techniques used in the convertors??

Controls and the techniques

Since the input to the ac voltage  controller is ac it is always line commuted.so the forced commutation is not needed.

Two types of the controls needed are

Integral cycle control- as the name suggests  the ac supply is connected to the load for certain number of the cyclesand is turned off for the another certain number of the cycles.They are switches on by the gate pulses at the zero voltage crossing of the input voltage.

Phase angle control

Here the thyristors( switches) are connected to the loads to an ac source for the portion of the each cycle of the input voltage

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4 Responses to PLC based drives and converters

  1. Rachita Mishra says:

    A Programmable Logic Controller, PLC or Programmable Controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. follow this for the betterment.

  2. patlakshi Jha says:

    PLC which is known as Programmable Logic Controller . It has now become one of the most important topic and application in the field of Electronics. It has got wide range of applications and uses. These are used in industries various big electronics companies for different purposes.

  3. Shilpa Ranjan says:

    PlC is a great part of electronics and electrical . To imagine these fields without it is unimaginable. This article gives the idea about the PLC. These are basically programs which controls the different parts of machines..!!!

  4. Ritika Savita says:

    PLCs are a major part of electronics that are used extensively. they provide the programming usage for various controllable operations & are used everywhere.

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