Commits on Mar 21, 2021

1. Update approach to anti-wind-up in PID.c …

   Current approach (re-written to be more concise, although possibly less clear):
   
     I = I + deltaT * Ki * mean_error;
     I = (I>limImax) ? limImax : ((I<limImin) ? limiImin : I);
   
     /* Calculate out from P, I, and D, then clamp */
     out = P + I + D;
     out = (out>limMax) ? limMax : ((out<limMin) ? limiMin : out);
   
   Example where this fails, or at least performs poorly:
   
   - Assume
   
     P = 90%; D = 0%; I = 20%; limImax=50%; limMax = 100%;
   
     /* I < limImax, so no anti-windup is in effect; however ... */
   
     out = P + I + D;                    /* => 110%, i.e. out is over-saturated */
     out - (out>limMax) ? limMax : ...;  /* => 100%, out is clamped, but I is not */
   
   New approach:
   
     I = I + deltaT * Ki * mean_error;   /* Same */
     /* Remove static limiting of I */
   
     /* Same */
     out = P + I + D;
     out = (out>limMax) ? limMax : ((out<limMin) ? limiMin : out);
   
     /* New - solve for I from [out=P+I+D] above */
     I = out - (P + D);   /* [I] will not change unless out is being clamped

   

   drbitboy committed Mar 21, 2021
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