Evaluation of linear DC motor actuators for control of large space structures

Abstract

This thesis examines the use of a linear DC motor as a proof mass actuator for the control of large space structures. A model for the actuator, including the current and force compensation used, is derived. Because of the force compensation, the actuator is unstable when placed on a structure. Relative position feedback is used for actuator stabilization. This method of compensation couples the actuator to the mast in a feedback configuration. Three compensator designs are proposed. The physical limits of the LDCM place limits on the bandwidth of the closed loop actuator.

A ten mode finite element model of a flexible space structure was used in simulations to examine all aspects of the actuator's performance. The performance of the actuator is compared for the three compensator designs. The actuator bandwidth is seen to be important in the actuator's effectiveness. Increasing actuator bandwidth resulted in a saturation nonlinearity in the actuator. The excitation capability of the actuator was examined to determine the authority of the actuator. The damping of the mast modes was examined to determine the effect of the feedback configuration of the actuator/mast system. Root locus techniques were used to explain changes in the vibrational modes of the structure due to the actuator compensation. Disturbance analysis was performed to quantify the effect of corrupted measurements on the purity of force generated by the actuator.