Knowhow: Motor Driven Systems

Variable Speed Drives (VSD) are used in systems where the speed of an electric motor requires to be controlled.

Due to the switching frequencies of the power electronics components within the VSD,  in certain circumstances,  electrical interference can be transferred to the electrical supply and to the electric motor.

This interference can manifest itself in a number of visible and invisible symptoms - VSD tripping, motor judder,  motor shaft bearing failure,  burned-out motor windings,  spurious faults within electronic control systems and unnecessarily high power consumption.

Electro-Magnetic Compatability (EMC) filters or Electro-Magnetic Interference (EMI) filters are designed to remove the higher frequencies of electrical interference that can result from a VSD power swithcing circuits.

Sinusoidal Filters,  dV / dT Filters and Chokes remove the lower-order frequencies of electrical interference that can result from a VSD power swithcing circuits.

Since both filters and chokes minimise the effects of electro-magnetic interference,  the also reduce the generation of this interference and therefore are an effective way of reducing the overall energy consumption of motor driven systems.

Braking Resistors are used where rapid decelleration of electric motors or where electric motors have heavy loads.  The VSD switches in the braking resistor whenever there is too much kinetic energy within the motor driving circuit,  to dissipate the excess energy by transferring the electrical energy into heat energy and preventing over-voltage damage to the VSD.