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improve anti-windup #59

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improve anti-windup #59

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f546538
improve anti-windup
mestrode Mar 11, 2021
c906cd4
back calculation of anti windup
mestrode Mar 12, 2021
6aa2240
remove derivative part in back calculation
mestrode Mar 13, 2021
4992c84
integrator: without filtering
mestrode Mar 13, 2021
0bd97de
correction for neg limitation
mestrode Mar 13, 2021
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19 changes: 12 additions & 7 deletions src/common/pid.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -27,26 +27,31 @@ float PIDController::operator() (float error){
// u_p = P *e(k)
float proportional = P * error;
// Tustin transform of the integral part
// u_ik = u_ik_1 + I*Ts/2*(ek + ek_1)
float integral = integral_prev + I*Ts*0.5*(error + error_prev);
// antiwindup - limit the output
integral = _constrain(integral, -limit, limit);
// u_ik = u_ik_1 + I*Ts*e(k)
float integral = integral_prev + I*Ts*error;
// Discrete derivation
// u_dk = D(ek - ek_1)/Ts
float derivative = D*(error - error_prev)/Ts;

// sum all the components
float output = proportional + integral + derivative;
// antiwindup - limit the output variable
output = _constrain(output, -limit, limit);


// limit the acceleration by ramping the output
float output_rate = (output - output_prev)/Ts;
if (output_rate > output_ramp)
output = output_prev + output_ramp*Ts;
else if (output_rate < -output_ramp)
output = output_prev - output_ramp*Ts;

// limit abs value of output and antiwindup for integrator
if (output > limit) {
output = limit;
integral = output - proportional;
} else if (output < -limit) {
output = -limit;
integral = output - proportional;
}

// saving for the next pass
integral_prev = integral;
output_prev = output;
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