On Stabilizing Sets of PI Controllers for Multiple Time Delayed Process

This paper considers the problem of stabilizing multiple time delayed processes using proportional integral (PD controller. The presented approach is based on finding all possible values of control parameters which will result in pure imaginary roots of closed loop characteristic equation under all process parameters fixed. The ergedic search of three PI control parameters are converted from the range of infinity to finite range by introducing trigonometric tangent function. After all possible stability boundaries are obtained, the Nyquist stability method is used to determine the actual stability region of the controller parameters. This method also permits design for simultaneous minimum gain and phase margin requirement. An illustrative example case is also presented.