The motor control approach you choose for your variable frequency drive (VFD) can considerably impact costs, efficiency, and the application’s overall performance. Understanding which method works best for your situation is integral to a successful application.
There are multiple methods for motor control, the most common being volts per hertz (V/f), V/f with an encoder, open loop, and closed loop. Keep reading to learn more about these methods and pick which is best for your motor-controlled application.
Volts per hertz is the simplest form of motor control of the four. People commonly refer to it as a “plug-and-play” method because of how simple and ready to use it is. For example:
V/f is most often used with machine tool, spindle, fan, and pump applications if there is a chance that operations could cap 1,000 Hz. It is also the only approach that lets multiple motors run from one VFD. If all your motors need to start and stop at the same time and follow the same speed, this method is the best for your situation.
The minimum running speed that VFDs must achieve to control a motor can be calculated by multiplying the maximum frequency by the 1:40 ratio:
At 50 Hz maximum frequency
1/40 = .025
50 x .025 = 1.25
A drive using V/f control can control a motor down to 1.25 Hz
Single parameters to select preset V/f patterns can be used in the program that are enhanced for certain applications. Custom patterns for distinct operations can also be programmed by users.
V/f with an encoder is more obscure than V/f Hz but can be added to V/f motor control under two circumstances:
Using open-loop vector (OLV) motor control allows speed and torque to be controlled separately.
OLV is the preferred method for users needing more custom motor control over their applications. This method suits a wider variety of applications because of a higher starting torque at much lower speeds and the availability of four-quadrant torque limits.
Using torque limits can prevent damage to your machines and can be set separately for each quadrant. Operators can pick a program with a torque limit into the VFD.
No feedback, never ensuring that the motor shaft is responding
Like OLV, closed-loop vector (CLV) motor control utilizes an algorithm to establish output voltage. However, a downside to this method is the requirement of an encoder. CLV motor control is best for applications that hold loads without moving (elevators, cranes, etc.).
Torque-control mode is available in CLV motor control, which favors torque over speed. This application is best for winders/rewinders, capping, and other similar uses.
Motor control methods for VFDs are imperative for everyday operations in facilities everywhere. It is important to know which is best for your application to achieve better performance overall.
No matter your specific application, Motion Ai is a perfect starting point for finding your perfect motor control method. We have experts on standby to help whenever you need for whatever you need. Contact Motion Ai today to speak to a specialist.