Wednesday, August 3, 2011

PLC as System Controller

The monitoring and control system implementation for the motor induction based on technology of programmable logic controller (PLC) is explained. Also, the hardware and software implementation for protection and speed control with the results acquired from tests on the performance of induction motor is presented. The PLC associates the parameters of operational to the speed requested by the user and checks the system through normal operation and under trip situations. The induction motor system tests driven by inverter and managed by PLC establish a higher accurateness in regulation of speed as compared to a conventional control system of Vf. The PLC control efficiency is improved the synchronous speed at high speeds up to 95%. Therefore, PLC establishes as a very flexible and efficient tool in electric drives control industry.

A Programmable Logic Controller is a microprocessor-based control system, the purpose is for automation processes in industry. It utilizes a programmable memory for the storage of internal instructions of user-orientated for executing particular functions for example arithmetic, logic, and timing. It can be programmed to activate, sense, and control the equipment of industry and, thus, integrates an I/O points number, which enable electrical signals to be lined. The process input and output devices are linked to the PLC and the control program is penetrated into the memory of PLC.

In the application, it manages via analog and digital inputs and outputs the unreliable speed operation of load-constant an induction motor. The PLC constantly observes the inputs and triggers the outputs based on the control program. This system of PLC is modular type created of particular hardware building blocks, which plug straightly into a bus of proprietary: a input-output modules I/O, CPU, a power supply unit, and a program terminal. Such as modular advance has the benefit that the first configuration can be extended for other future appliances for example, the systems of multi-machine or computer connecting.

The configurations can be gotfrom this setup.
1. A system of closed-loop control for stable operation of speed, constructed with load current feedback and speed feedback. The motor of induction makes a variable load, is supplied by an inverter, and the PLC manages the output of inverter.
2. A system of open-loop control for variable operation of speed. The motor of induction makes a variable load and is supplied by an inverter with mode of constant control. The PLC is not triggered.
3. The standard operation of variable speed. The motor of induction takes a variable load and is supplied by a constant frequency, constant voltage standard supply of three-phase.

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