Sensorless Vector Control VFD
Sensorless Vector Control is included in nearly all VFD manufacturers offerings. The difficulty remains in maintaining 100 Torque at Zero Speed and the truth is that very few can accomplish that standard of performance. As the title of the type of control suggests, the typical control scheme involves measurement of the opposing fields vectors, and this gets very difficult to do when you minimize the field to reach zero speed, i.e. the application of a Zero Hertz field. It is recommended that you seek out those who can offer, the highest accuracy control as close to Zero speed as possible in a Sensorless Vector drive. DTC (Direct Torque Control) within a Sensorless Vector Drive was developed by ABB to accomplish just that type of control.
The most common speed-sensorless strategies do not control torque at zero speed. There are ways to control torque at zero speed without a speed sensor, but they are a bit trickier and mostly require specific types of motors.
For example, it is possible to perform a sensorless torque control at zero speed of a Permanent Magnet Synchronous Motor with high frequency signal injection. This is already applied in industry.
The most common speed-sensorless strategies do not control torque at zero speed. There are ways to control torque at zero speed without a speed sensor, but they are a bit trickier and mostly require specific types of motors.
For example, it is possible to perform a sensorless torque control at zero speed of a Permanent Magnet Synchronous Motor with high frequency signal injection. This is already applied in industry.
