What is a VSD?

A Variable Speed Drive (VSD) is an electronic power converter that produces a multi-phase, variable frequency output to drive a standard AC induction motor. It can control the motor speed, direction, torque and mechanical power output. By implementing this type of control a very close match between motor speed and the process requirements of the driven machine may be achieved.

A VSD may also be referred to as a drive, frequency converter, adjustable speed drive, variable frequency drive or inverter. They are usually available as standalone devices and are connected to the motor's electrical supply. VSD are classed by power and range from tens of Watts through to several MW, available in single phase AC, 3 phase AC and DC families.

VSDs are extremely versatile and offer a high degree of motor control where motor speeds can be continuously and accurately varied, whilst the torque is also adjusted to suit. Different options are available to cover a variety of applications; basic VSD designs are used in simple applications such as fan and pump control whereas more complex versions might be used for very precise speed and torque control.

Energy Saving

In many applications variable speed control can lead to a substantial reduction in energy use. The use of VSDs is particularly effective in fan and pump applications where they might be used to replace mechanical methods of output regulation; here an exponential relationship exists between the machine speed (and output) and the energy used, so that a 20% reduction in speed could lead to a 50% reduction in energy.