Power controller

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Block diagram

In industry, power controllers are all electronic devices that can be used to set power (or current or voltage) variably from 0-100%. Typically these are thyristor controllers .

Control types

  • The amplitude control by means of pulse width modulation (PWM) determines the power through the ratio of the switch-on time to the pause time during a fixed period and is the most common type of control. This type of control is ideal for sluggish processes.
  • The pulse packet control (also: pulse group operation) as a subtype of PWM ensures targeted switching of individual full waves of the network with the aim of avoiding long on or off phases.
  • With phase control , each individual half-wave is cut directly. The non-sinusoidal current curve of the phase control causes considerable disturbances in the supplying power grid. Since current and voltage do not have the same signal curve, this results in what is known as control or harmonic reactive power .

Whether phase control or full wave control can be used in the process depends very much on the load used and the requirements of the application.

Control

The power controllers are normally controlled using one of the following methods in order to bring the desired control value from the controller to the power controller:

  • The most common method for controlling power controllers is analog control with a standard signal of 0-10 V, which comes from a PLC or similar. To do this, an analog output is required for each individual power controller, as well as a digital enable output for the entire system.
  • An alternative is the transmission of the analog control values ​​by means of a serial data telegram via digital outputs. For this purpose, a digital output for the data is required for each individual power controller, as well as a digital output for the cycle for the entire system.
  • The most complex method is control via an industrial bus . Here z. B. Profibus DP, Modbus or CAN bus are used. This means that power controllers can be ideally integrated into the overall system control.

Monitoring functions

Modern power controllers are equipped with a number of monitoring functions that enable safe and stable operation. These include a. Monitoring of fuse failure, wire break, load break, failure of load voltage or auxiliary voltage, undervoltage, failure and partial failure of thyristor controller, temperature monitoring.

Three-phase motor

The types of control mentioned are suitable to a limited extent for the soft start of three-phase motors and not at all for speed control . Frequency converters are mainly used here.

further reading

  • Manfred Schleicher, Winfried Schneider; Electronic power controller basics and tips for the practitioner ISBN 978-3-935742-04-7