Control Law Design for MISO System in the Presence of Actuator Position Limit Constraint

Abstract

This article is about including the actuator position limit constraint while designing PD controller based on output feedback pole placement methodology for a multi-input-single-output (MISO) system. While designing control law for MISO system, designer has additional degrees of freedom which can be utilized in many ways to achieve different time and frequency domain specifications. One such goal can be to maximize the control availability at any instant of time in the presence of growing disturbance moment. In the paper it is shown that if the proportional path gains of all the loops are constrained to be in the ratio of the maximum value (actuator saturation limit) of control input of respective loops, then at steady state, total control demand will always be distributed to different control power plants in the ratio of their maximum control availability. Designing control law with the inclusion of actuator saturation limit, as constraint on proportional path gains, helps in ensuring the stability of the whole closed loop system by postponing saturation to higher disturbance values. Efficacy of the proposed method is demonstrated on a real life problem of attitude control law design for a typical launch vehicle.