Both VFD (Variable Frequency Drive) and VSD (Variable Speed Drive) are used to control the speed of motors, but the difference lies in how they do it. A VFD specifically controls the speed of an AC motor by varying the frequency and voltage of the power supply. On the other hand, VSD is a broader term — it can refer to any device that controls motor speed, including VFDs (for AC motors) and DC drives (for DC motors).
So, saying which is “better” depends on your motor type and application. For AC induction or synchronous motors, a VFD is the better choice because it offers precise speed control, energy savings, and protection features like soft start and overload safety. If you’re dealing with DC motors, then a DC-based VSD would be used. In short, a VFD is a type of VSD, and it’s the preferred option in most modern industries since AC motors are more common today.