PID controller and Antenna Azimuth

Introduction:

PID is the combination of different function for controlling devices in control system engineering. Most important of them are proportional, integral and derivative function that’s why it is named as PID. They are used in controlling various industrial instruments automatically like flow rate, temperature, pressure, position controlling in azimuth antenna.








Before PID:

                    Before PID, all regulation task are usually done manually like if you have to keep constant temperature of water discharge from an industrial gas fired heater, an operator has to watch a temperature gauge abd adjust a gas control valve accordingly. If the water temperature becomes high, operator has to close the gas control valve a bit, enough to bring the temperature back to desired value. If the water becomes too cold, he has to open the valve again.

Automatic Control Using PID:

                                                                           To relieve our operator from tedious task of manual control, we automate the control by installing PID controller. PIC has a set point SP that the operator can adjust to desired temperature. There is also an actuator or positioner so that the output can be changed by moving value. As said previously PID has proportional, integral and Derivative control functions.

 

--Proportional Control: It changes the controller output in proportional to error.
--Integral Control:  It produces a long term corrective change at controller output.
--Derivative Control:  It makes control loop faster with less over shoot.

Schematic and Block Diagram:

• Proportional Term:     The proportional term produces an output value that is proportional to the current error value. The proportional response can be adjusted by multiplying the error by a constant Kp, called the proportional gain constant. The proportional term is given by: A high proportional gain results in a large change in the output for a given change in the error. If the proportional gain is too high, the system can become unstable (see the section on loop tuning). In contrast, a small gain results in a small output response to a large input error, and a less responsive or less sensitive controller. If the proportional gain is too low, the control action may be too small when responding to system disturbances. Tuning theory and industrial practice indicate that the proportional term should contribute the bulk of the output change.

•   Integral Term:          The contribution from the integral term is proportional to both the magnitude of the error and the duration of the error. The integral in a PID controller is the sum of the instantaneous error over time and gives the accumulated offset that should have been corrected previously. The accumulated error is then multiplied by the integral gain     

• Derivative Term:        The derivative of the process error is calculated by determining the slope of the error over time and multiplying this rate of change by the derivative gain.The magnitude of the contribution of the derivative term to the overall control action is termed the derivative gain.

Impulse Response:

Conclusion and Last words:

                        Initially the system was unstable when we applied a step response, we have seen through MATLAB plot the system is unstable, using sisotool we get a proper compensator by setting poles or zeros then we get proper value of gain for compensator. With its proportional, integral and derivative mode the PID controller is the most popular method of control by a great margin. If properly tuned, the three mode of controlling can be achieved.

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