Hi. I am having some difficulty getting my head around direct torque control. What I have understood is that stator voltage and rotor current is measured. Stator voltage gives an estimate of the flux linkage. Then the rotor current combined with the use of flux linkage vector gives a measurement of torque. The flux and torque are then compared with the reference values and PWM waveform changed accordingly.

My questions are

1. How does the flux linkage get estimated from stator voltage?

2. Why does flux need to be compared with a reference value? ( I thought torque is the main thing we are looking at and if it deviates then we can alter the flux which in turn alters the torque)


Any guidance would be great

 

How does the flux linkage get estimated from stator voltage?

EMFs are generated, which in turn are then typically processed digitally.

Why does flux need to be compared with a reference value? ( I thought torque is the main thing we are looking at and if it deviates then we can alter the flux which in turn alters the torque)

Flux control can be useful for different things, such as starting and braking where controlled ramping is implemented. Flux stability is more important when load driving.

 

Isn't the torque proportional to the flux? Controlling the flux is essentially controlling the torque right? Or have I misunderstood?

 

to some degree, as one would ask, doesn't current also affect torque. Flux, or more specifically the orientation of opposing fields between stator and rotor, has the potential to nullify substantial current variance, but one wants to avoid that by maximizing the torque effects of current.

I had the pleasure of commissioning ABB drives for topdrives used in drilling. Initially, the drive ran an ID run, which rotated the motor and gathered magnetic information about that motor, which it then used as drive parameters.

Some theory that may help;
http://yantrabazaar.com/Documents/DTC VS Field Oriented.pdf