Question

could someone describe briefly the two main methods of tuning a PID controlled system and say which one would not be suitable for tuning a critical system such as a power plant. The answer should not be too long (maximum 500 words) and preferably not hand written. Thanks

Answer 1

Two methods of tuning of PID controlled system.

1.Trial and Error method

2.Zeiger-Nichols method

1.TRIAL AND ERROR METHOD :

This is simple method for tuning a pid controller. The trial and error method become relatively easy.

Set integral and derivative terms to zero first and then increase the proportional gain until the output of the control loop oscillates at a constant rate. This increase of proportional gain should be in such that response the system becomes faster provided it should not make system ustabe. Once the P response is fast enough . set the integral term. so that the oscillations will be gradually reduced. Change this Integral value untill the state error is reduced. but it may increase overshoot.

Once P and integral parameters have been set to a desired values with minimal steadty state error, increase the derivative term decrease the overshoot of the controller response

2. Ziegler-Nichols Method:

It is another method for tuning PID controllers.Ziegler and Nichols presented two classical methods for determining values of proportional gain ,Integral time and derivative timebased on transient response characteristics of a given plant or system.

It is performed by setting the integral and derivative gains to zero. The proportional gain Kp is then increased until reaches the ultimate gain Ku at which the output of the control loop has stable and consisent oscillations.Ku ans the oscillation period are used to set the P,I,and D gains depending on thetype of xontroller used.

The ziegler -Nicholas tuning creates a 'quater wave decay". This is an acceptable result for some purposes ,but not optimal for all applications.

Best method for tuning of PID controlled system is Ziegler -Nichols Method.