: > Gc = 10(1+s/58.4)(1+s/100)/(1+s/8)(1+s/700) : >
: > my plant is : > Gp = 100/s(1+s/100)(1+s/1000). : >
: > I successfully simlutate and prove a stable design with the goals of : > velocity constant = 1000 : > phase margin = 50 deg. : >
: > Now, I am converting this controller to a minor loop controller and : > have successfully suimulated it and verified stability of the minor : > loop and overall plant---but I have some questions that I don't : > understand: : >
: > 1) by basing the design on the previously determined Gc, do I need to : > worry about velocity constant? (ie will the minor loop feedback have : > to be re-adjusted to guarantee kv=1000)? : >
: > 2) my original gaincrossover was calculated to be about 140 rad/s. : > Unexpectedly, the Bode plots for the minor loop compensator move the : > gain crossover from 140 to about 60. Is this to be expected? if so, : > why? : >
: > My matlab/simulink seem to indicate all is OK--I'm just bugged by the : > fact of gain crossover frequency moving so far to the left and giving : > a more sluggish step-response than the supposed equivalent series : > lead-lag compensator? : >
: > My web searches have yields nothing useful on minor loop : > techniques/comparisons. : >
: > My approximated minor feedback block is: : >
: > 0.0125s/(1+s/58.4) and is applied around the (1/(1+s/100)) term of the : > plant. : >
: > Comments? : >
: > THanks, : >
: > Bo : : After looking up "minor loop" on the web, I checked not one, but two of : the references on my shelves -- neither of them refer to them. That's a : relief.
I had seen inner loops refered to as minor loops before. I too refer to them as inner loops.
: I'd be interested to know if there's any technical difference between : the terms "inner loop" and "minor loop".
I haven't seen anything that indicates they are not the same. : : I'm not sure if this illuminates anything for you, but if you have a : loop of the form : : _ .--------. _ .--------. : / \ | | / \ | | : ------>| + |-->| |-->| + |-->| |----o------>
: \_/ | | \_/ | | | : A '--------' A '--------' | : | | | : | | .--------. | : | | | | | : | '-----| |----o : | | | | : | '--------' | : | | : '----------------------------------------' : (created by AACircuit v1.28.6 beta 04/19/05
: : then the "minor loop" compensation isn't much but a fancy way of adding : feed-forward.
A minor loop is not the same as feed forward. Feed forwards are open loop gains that are proportional to the reference and its derivatives and summed with the output of closed loop sections to form the control output. I don't see how an inner loop can be mistaken for a feed forward.
There is another form of feed forward where the reference is run through a filter so there is an exaggerated pseudo reference. This is similar to leading the donkey with a carrot by slightly exaggerating the path.
The rest of your desciption is good.