The main difference between VFD (Variable Frequency Drive) and VSD (Variable Speed Drive) is that a VFD controls the speed of AC motors by changing the frequency and voltage of the power supply, while a VSD is a general term used for any drive that controls motor speed — whether it’s an AC motor or a DC motor. In short, all VFDs are VSDs, but not all VSDs are VFDs.
A VFD works by converting fixed-frequency AC power into variable-frequency AC power, allowing precise control of motor speed and torque. A VSD, on the other hand, can include different types of speed control systems — such as DC drives for DC motors or hydraulic and mechanical speed control systems. So, if you are using an AC motor, a VFD is the specific type of VSD you’ll use. The key takeaway: VFD is for AC motor speed control, while VSD is a broader category that covers both AC and DC motor applications.