Design of a multirate PD control system for improvement in the steady-state intersample response

Abstract

The present paper proposes a new design method for a multirate system, in which the continuous-time plant is controlled by updating the discrete-time control input, in which the sampling interval of the plant output is an integer multiple of the hold interval of the control input. In the multirate system, the intersample response might oscillate even if the sample response converges to the reference response because the control input can vary between sampling instants. In the present paper, a multirate proportional-derivative control system is enhanced such that the steady-state intersample ripples are eliminated. In the proposed method, the intersample response can be improved independently of the sample response because an existing closed-loop response is maintained. Moreover, the control performance is not affected by the phase lag caused by the integral compensation because the integral compensation is not used for the elimination of the intersample ripples. Finally, in order to control a plant with unknown or time-varying parameters, the designed multirate control system is extended to a self-tuning controller. As a result, an unknown or time-varying plant can be controlled using the proposed method.