A parametric design method of direct digital control with transient response requirements

This paper presents a new parametric method of designing a direct digital controller for a discrete time linear time-invariant plant so that it satisfies the given transient response specifications like overshoot and settling time. The controller structure of R-S-T type is considered. We first transform the discrete time closed loop model into the w-domain by the w-transform. A reference characteristic polynomial in w-domain is determined by using the characteristic ratio assignment(CRA), so that the corresponding closed-loop model in w-domain meets the desired time response specifications. Then, this characteristic polynomial is transformed into the z-domain. Finally, applying the model matching method with this discrete time target polynomial, a satisfactory digital controller can be obtained. We show through a numerical example how the proposed method can be used and we also compare the result with those of conventional methods.