In order for a complex system to work properly and take advantage of an integrated control system, the user must be able to control the most complete gear in the device itself - the motor. Mechanical work that used to be done by humans required control of torque, acceleration and deceleration rates, braking, and many other measures managed by control systems. But it's the ability to control speed accurately and efficiently that makes everything work.
To control motor speed in a range of applications, designers long ago created two different ways to manage motor speed. One is a variable frequency drive (VFD). In a VFD, the speed of the motor is changed by changing the voltage and frequency. Therefore, VFDs can only be used with AC motors. The second is a variable speed drive (VSD). Here, the VSD controls the motor speed only by changing the input voltage, allowing the VSD to be used for both AC and DC motors. There are other differences between the capabilities of the two drives. Aside from the difference between AC and DC motors, the application plays the biggest role in choosing the right drive. So what is the difference between VSD and VFD?
The efficiency of the motor and its impact on the chosen system type will again depend on the requirements of the application. So what is the difference between a VSD and a VFD in terms of energy efficiency?
Generally speaking, VFDs are more energy efficient and save more energy than VSDs. Multiple motors can be connected to a VFD. This enables them to control other elements in the system, such as pumping systems or HVAC. By controlling the motor on system elements such as valves, actuators, dampers, etc., the load on the motor can be optimized and less energy is required.
Another way VFDs save energy compared to VSDs is their ability to gradually increase the speed of the motors of system components. This reduces the stress on all motors in the system and reduces the energy when accelerating or accelerating. Typically, VFDs can achieve up to 97% efficiency at full load. This is somewhat related to HP, as the HP of the motor drops. Those over 10HP can still achieve up to 90% efficiency, while lower HP motors will drop significantly depending on size and load.
What is the difference between a VSD and a VFD, in general, with the advent of smart motor control, using a VFD to control numerous motors is a more efficient solution. Other energy-saving aspects where VFDs are superior to VSDs include regenerative enhancements to return power back to the grid, and the fact that power usage in systems using VFDs uses only the energy needed to drive equipment needs.