I'm controlling a Permanent Magnet DC motor with PWM for a treadmill. I'm using a reflective sensor with 6 pulses per rev to get a speed feedback. So I'm actually doing "speed control" directly, but not "torque control". So I have two specific questions:
1- Do I need direct torque control for this application by measuring the current? Or a combination of speed and torque control where a cascade PI is needed?
2- Do I strictly need to know the DC motor parameters (R, L, K, J, B) in order to do speed control?
It's okay I can vary the speed by changing the duty cycle. But, beyond a simple analogy of pulse-width-modulation, I know it should be a whole lot more complicated than that.
Best Answer
1-No not necessarily. You need to control the torque, since in a treadmill you want at a specific setting a constant speed no matter how much the load varies, and the speed loop will make sure that happens. however adding internal torque loop ( cascade PID ) could help with improving response and better disturbance rejection if it is needed.
2-Not at all, but you have to work with trail and error to tune your PID loop and do a lot of testing to ensure stability at all settings and loads.