Hello Everybody

I am developing PWM DC brush motor driver. I have tested the drivers avilable in the market. It is found that when I command 0 velocity the motor
is giving zero speed but I am also getting torque at zero speed. The rotor of the motor is very stiff. Can anybody explain this.

My other question is I have seen an integrator in current loop. why is another integrator required when there is one in speed loop?

thanks

Badly needed answer.

Vikas

 

Vikas, If there is nothing attached to the motor shaft, there is no torque. As soon as you grab it and start to try to turn it, it develops torque to fight that. If it has a velocity loop (which it does), the stiffness will be very high. You could get the full torque of the motor with an imperceptible movement of the shaft. This is because of the integrator. It will continue to integrate any error until it drives the error back to zero. Then it will stop integrating, but hold the torque at that value. Any servo loop must have a net single integration in its open loop to function properly. Are you familiar with Bode diagrams? This means each of the position, velocity, and torque loops must have a net integration. Send me your snail mail address and I'll send you a paper discussing the three loops and their Bode diagrams.

Tom Thomas B. Bullock, President Industrial Controls Consulting Div. Bull's Eye Marketing, Inc. 104 S. Main St., Suite 320 Fond du Lac, WI 54935
Ph: 920: 929-6544
Fax: 920: 929-9344
E-mail: [email protected]