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Variable Frequency Drive vs Soft Starters

Variable frequency drives and soft starters are commonly regarded as same devices, when in fact they are completely different. The soft starter is a regulator for motor start-up and changes the output voltage only, not the frequency. The variable frequency drive is used for AC motors speed control and it can change both the output voltage and frequency at the same time.


The variable frequency drive for sale comes with a bigger price tag than the soft starters, because it offers more features and is more complex. Despite all that, these two devices protect the expensive connected equipment from damages that can be caused by uncontrolled torque. To help out to anyone in doubt regarding which one is better, let’s learn more about these two electronic devices.

Variable Frequency Drive

A variable frequency drive, shortly known as VFD, is an electronic device used for controlling and protecting the AC motor speed. It can control the motor speed during start and stop cycles and during the run cycle. The variable frequency drive is most commonly used where adjustable control, absolute speed control and energy savings are needed. The working principle of these devices is quite simple. They convert constant frequency and voltage input power to adjustable frequency and voltage source for AC induction motor control of the speed. The benefits of variable frequency drive over soft starter are:

Superior Versatility: Highly-advanced overload protection, digital and analog inputs/outputs, relay outputs, software programming, self-diagnostics and communications, variable frequency drives are incredibly versatile.

Energy Savings: When used for pumps, compressors or/and fans, variable frequency drives provide incredible energy savings. These devices are able to reduce power when not required, as well as reduce the peak energy demand.

Better Performance: The variable frequency drives provide a completely adjustable speed and provide a reliable starting, acceleration and stopping. Also, they provide a dynamic control of the torque, provide a smooth motion for some applications and maintain the speed of any equipment, making them perfect for a variety of manufacturing and industrial equipment.

Soft Starter

A soft starter is an electronic devices that helps protect the motor and connected equipment from damage from uncontrolled voltage. It reduces load and torque in power train and the electrical current surge of motors during start-up. Also, the soft starter helps in controlling the motor when accelerating to full speed, or in other words, when using a large inrush current.

Soft starters can be very beneficial to electrical systems that are limited in terms of capacity of current. Most commonly, soft starters are used where high inrush currents are required when starting a large-capacity motor, where torque control is a must, where avoiding pressure surges matters and where controlled start-up is needed.