Active vibration reduction of high-rise buildings has received practical applications since 1989. However, most of them only utilizes feedback controller. Earthquake excitations have certain characteristics in frequency spectrum. It is well known that the modern control theory can take the characteristics of disturbance into consideration. One of the authors presented a feedforward augmented controller design method by taking account of the dynamics of disturbance in 1988 , and confirmed that the feedforward augmented controller achieves higher performance than the ordinary feedback controller. Moreover, in 1993, he showed that the robustness of the method is enhanced by the use of Hinfinity control theory which is known as an effective mean to obtain robust feedback controller .
Meanwhile, the fact that the active systems always need power supply often restricts the performance of the systems. For examples, most of practical systems are not activated under ordinary circumstances to decrease the driving cost, for the actuators for high-rise buildings require huge energy. Besides, the active systems may not be effective if there is not enough power supply in disasters like large earthquake. Under such circumstances semi-active vibration control systems which need no energy supply may be more preferable for high-rise buildings subjected to earthquake excitation.
Many design methods to realize semi-active vibration control system are already presented. One idea is to replace active control elements by using variable passive elements and approximate active control force by varying the elements. In this case, active control methods can be applied to obtain active controller which directs target force. Some studies based on LQG control theory have been already performed and achieved good performance. It is expected that the performance of semi-active control systems is modified by applying such feedforward augmented controller instead of ordinary feedback controller.
In this paper, the performances of active and semi-active controllers which accommodate the dynamics of disturbance are investigated and compared. A feedforward augmented active vibration controller is designed according to the method shown in the paper . And a design method of semi-active robust vibration controller is also presented. In the method, nonlinear Hinfinity control theory is introduced to compensate the decrease of control effect due to the replacement of active elements to passive. The benchmark building subjected to earthquake excitations is applied as a control object, while a dynamic vibration absorber is utilized as control device. Computer simulations are carried out to verify the control performances of the obtained systems.
 K. Yoshida, T. Shimogo and H. Nishimura, Optimal Control of Random Vibration by the Use of an Active Dynamic Vibration Absorber (Experimental Considerations on the Effect of the Control with Feed forward Link), JSME International Journal, Ser. III, Vol.31, No.2, 387-394 (1988).
 S. Kang and K. Yoshida, Vibration Isolation Control with Feed forward Link using Hinfinity Control Theory, Proceedings of the JSME International Conference on Advanced Mechatronics, 645-649 (1993).