Please describe eight (8) of the non-linear algorithms found in the handout material. Please describe to the best of your ability, when these algorithms can be used.
Standard algorithms are used in control systems to reduce the errors between the measured variables and the set-point.it uses three components proportional, derivative and integral and then summing these components to get the desired output.
Derivative on PV
It is a nonlinear algorithm this algorithm is widely used in the applications of derivatives .When there is a change in load the derivative parameters only act and they do not act when there is change in the set point.
Derivative and Proportional on PV.
This algorithm is used for the tuning of PID controllers. In this algorithm, the integral component is used to handle errors caused by changing the set-point value and derivative and proportional components are used to eliminate the error caused by load changes. If the proportional gain is too large it will make the PV to oscillate.
SP Filtering
In this algorithm Using SP filter on the set-point reduces the overshoot it I also recommended to use tuning parameters because the set-point is too oscillatory and can be attenuated by tuning.
P2ID (error squared).
It is a nonlinear function and is increased with the increase in the magnitude of the errors. Small deviation from the set-point result in little change in the controller and large deviation are result in stronger control action (large error). To achieve this purpose, the error is squared before it gets input into the controller. It is also used in moore controller.
PI2D (integral squared).
For the purpose of better compensating for the variable dead times in the processes, the integral parameter is squared. This algorithm removes overshoot for level loops due to the removal of integral action as the process variable nears the setpoint and the error approaches to zero.
PID + gap.
For this algorithm, a tolerance of a certain range of error is accepted, neglecting the error altogether. The controller output remains the same for that range of error. If the error is outside the given accepted error range, regular parameters of tuning are applied. This algorithm helps in maximizing the life of control elements in the application that have high tolerance for variability in output quality and error.
PID + gap + adaptive tuning.
In this algorithm, the integral action is removed during the time when the error is in the gap. This helps in combating valve stiction. The proportional action, however, is reduced to battle hysteresis and non-linearity. The uses for this algorithm include the applications incorporating pneumatic control valves.
