Using blending control to suppress multi-frequency disturbances

In this paper, rejecting multi-frequency narrow-band disturbances is formulated as a control blending problem according to each disturbance characteristic. Each disturbance rejection is accomplished by using H₂ optimal control method. Based on all the H₂ optimal controls, the blending technique is employed to yield a single controller which is capable to achieve the rejection for all disturbances. Rejections for two and three disturbances through the control design for the VCM actuator in a hard disk drive are taken as application examples in the current paper. Simulation and experimental results show that the ultimate controller results in a simultaneous attenuation to disturbances with frequencies higher or lower than the closed-loop system bandwidth. Moreover, the method turns out to be able to lift phase and thus prevent phase margin loss when it is used to deal with disturbances near bandwidth.