Variable speed drives (VSDs): These drives change the speed of a motor by changing the input voltage and can be used with both AC and DC motors.
Variable frequency drives (VFDs): Variable frequency drives also control the speed of a motor, but they do so by changing the voltage and frequency and can thus only be used with AC motors.
We keep both as they are different:
Variable speed drives (VSDs): These drives change the speed of a motor by changing the input voltage and can be used with both AC and DC motors.
Variable frequency drives (VFDs): Variable frequency drives also control the speed of a motor, but they do so by changing the voltage and frequency and can thus only be used with AC motors.