Simulink Control Design™ - MathWorks

Preventing Saturations

So far we have only specified a desired response time for the outer (speed) loop. This

leaves systune free to allocate the control effort between the inner and outer loops.

Saturations in the inner loop suggest that the proportional gain is too high and that some

rebalancing is needed. One possible remedy is to explicitly limit the gain from the speed

command to the outputs of the P and PI controllers. For a speed reference of 2000 rpm

and saturation limits of plus/minus 5, the average gain should not exceed 5/2000 =

0.0025. To be conservative, we can try to keep the gain from speed reference to controller

outputs below 0.001. To do this, add two gain requirements and retune the controller

gains with all three requirements in place.

% Mark the control signals as points of interest so that they can be

% referenced in the gain requirements

addPoint(ST0,{'Current PID','Speed PID'})

% Limit gain from speed demand to control signals to avoid saturation

MG1 = TuningGoal.Gain('Speed Demand (rpm)','Speed PID',0.001);

MG2 = TuningGoal.Gain('Speed Demand (rpm)','Current PID',0.001);

% Retune with these additional requirements

ST2 = systune(ST0,[TR,MG1,MG2]);

Final: Soft = 1.39, Hard = -Inf, Iterations = 42

The final gain 1.39 indicates that the requirements are nearly but not exactly met (all

requirements are met when the final gain is less than 1). Use viewGoal to inspect how

the tuned controllers fare against each requirement.

figure('Position',[100,100,560,550])

viewGoal([TR,MG1,MG2],ST2)

13 Control System Tuning Examples