Hi
I'm attempting to control a brushed DC motor using an analogue PWM chip inside a feedback loop. I'm currently doing some modelling in simulink with a proportional controller, a pwm stage, a motor's electrical component I=(V-E/(Ls+R) and a current as the feedback. My input demand is therefore torque or current.
I have a problem such that when I increase the proportional loop gain so that I get a decent step response, the input to the pwm module tends to follow the internal sawtooth reference signal, causing the pwm output to do stange things......It tends to output a much higher frequency signal as the pwm input makes multiple transitions above and below the sawtooth waveform during one cycle.
Now, is this just a practical limit when a pwm module is placed in the feedback loop (control action limited to 0-100% pwm)? or am I overlooking something somewhere???
Thanks for any advice in advance
Cheers
Steve Minshull