VFD Sensorless Vector and V/Hz Control

Most modern day variable frequency drives (VFD) will offer V/Hz control, sensorless Vector control and optionally closed loop control for full field orientation control method. The V/Hz control is retained for applications generally whereby a high torque speed or dynamic control is not required such as applications like centrifugal pumps and fans, or lightly loaded applications.

Although it can be argued that in modern Sensorless Vector VFDs the motor modeling and speed of the MCU's is such that they can just about cope with all applications.
In the V/Hz modes again this is advantageous for setting the V/F characteristics to match those of the load such as in fans whereby a quadratic curve may be required for torque speed, or in applications such as high speed spindle drives (high frequency applications), where vector control is not required.

My experience of Sensorless Vector VFD is that modern generation VFD are much more efficient against V/F drives especially for applications like hoists / lifts as they can control the load requirement in all four quadrants so both positive and negative torques in lifting and lowering, I would also argue if set correctly the Sensorless Vector VFD will achieve full motor torque at 1 Hz or lower, allowing for very efficient mechanical brake control.

If used with a VFD of one frame larger than the motor rated current, then the VFD even in open loop mode can produce 100% torque at 0 speed.

Also the more modern VFDs these days will generally have control modes for PM Motors making for even more efficient operation and performance.

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