GPS-X Technical Reference

347 Tools Object
PID in Position Form
With derivative kick protection OFF:
Equation 12.19
With derivative kick protection ON
Equation 12.20
Equation 12.21
Position and Velocity Forms
The velocity form is obtained by differencing the position form of the PID controller.
When using the velocity form, one calculates the change in the value of the manipulated
variable that is to be implemented, as opposed to the absolute value calculated by the
position form of the algorithm. The velocity form has certain advantages over the
position form; in particular, it is naturally protected against reset or integral windup. This
condition occurs when a persistent, nonzero setpoint error results in a large value of the
integral mode of the PID, forcing the control action to `saturate' (i.e. to maintain the
manipulated variable at its minimum or maximum value). Even when the setpoint error
returns to zero, the control action remains saturated when the position form of the PID
algorithm is used. When using the velocity form, the control action can return within the
control range after one sampling period.
GPS-X Technical Reference