Hi

I have a motor drive modelled in simulink making use of Space Vector PWM and I'm having a few problems with stability. I have a PI current controller on the front end and I'm trying to tune the PI Values to get a stable response....at the moment I get a ripple on the current (and hence torque) waveform.

I've done a block analysis (in terms of continous 's' domain) and the result is a second order response. THis lets me choose an wn (bandwidth) and zeta(damping factor)...I chose wn=1000Hz and zeta=0.707 which gives P=2 I=5000. My first thoughts were "eeek the integral gain is huge" but trying to manually tune P&I has not give me a better response.

I'm currently working out my control action each PWM cycle. I get the feeling this is the wrong thing to do? but slowing the control down e.g working out the control every other PWM period increases the current and torque ripple. So I'm confused as to what the link is between choice of Bandwidth with PI values and Choice of bandwidth from the controler sampling frequency.

Presumably my system bandwidth....whatever it is needs to be significantly less than the PWM frequency for stable operation? Do I need to perform a discrete analysis of the system?

Thanks in advance for your help....once I get this controller stable I can get to hardware and have some fun

Steve Minshull