PI controller:
PI controller has the cascaded proportional and integral modes. The main advantage of this control mode is that the one-to-one correspondence of the proportional mode is available and the integral mode eliminates the inherent offset. In the present mode, the integral function provides the required new
controller output, thereby allowing the error to be zero after a load change. The integral feature effectively provides a reset of the zero error output after a load change occurs. The analytical expression for this mode can be given as
The characteristics of the PI mode:
i) When the error is zero, the controller output is fixed at the value that the integral term had when the error went to zero.
ii) If the error is not zero, the proportional term contributes a correction, and the integral term begins to increase or decrease the accumulated value [initially, pI(0)], depending on the sign of the error and the direct or reverse action.
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