Features of Motor VFD

Modern DC and AC motors provide useful features when using electric motors as final control elements. Here are some common features that are seen in both VSDs and VFDs.

  • Speed limiting
  • Torque limiting
  • Limitation of acceleration (speed of change)
  • Limitation of deceleration (speed of change)
  • Braking by DC injection (apply DC to an engine to convert it into an electromagnetic brake)
  • Dynamic braking (convert the motor into an electromagnetic brake)
  • PWM frequency adjustment
  • Plugging
  • Regenerative braking

Some of these limiting parameters are not only useful for prolonging the life of the motor, but can also help to prolong the life of the mechanical equipment driven by the motor. It is certainly advantageous.

If an engine is equipped with a digital network communication capability (eg Modbus), it is usually possible for a host system, such as a PLC or DCS, to update these control parameters while the engine is running.

For a VSD or VFD to adequately and safely control an electric motor, that drive must be programmed with the motor nameplate data (rated voltage, rated current, maximum speed, etc.)

If an engine is not properly configured With these “base” parameters, you can even damage the motor, for example, if the controller is configured to output more current than the motor is rated. As such, it is recommended that you first program these parameters in an engine unit before configuring any other unit parameter.


Instrumentation Engineer

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