Control of a Civil Structure Using an Electric Machine with Semiactive Capability

Abstract

This paper concerns the implementation of a brushless DC machine as a force actuator, for use in suppressing vibrations in civil structures. The machine has the dual capability of operation as an active as well as semiactive device. It operates semiactively by using the machine as a generator to convert mechanical energy to electrical energy which is then dissipated. The electrical network uses electronic switching to control the power flow from the machine. With the machine shaft connected to a gear reducer and ballscrew mechanism, the result is a device that resembles a linear damper with a controllable damping coefficient. The only external electrical power required is that which is needed to support the control system intelligence and to control the transistors, enabling the device to be operated on battery power. As an example of an application of such an actuator, simulations are performed in which the semiactive device is used to control a three-story structural model, with acceleration feedback control. The structural control system design approach is the well-established “clipped-optimal” method. Results suggest that this actuator is effective in simultaneously suppressing the interstory drifts and the absolute accelerations of the structure. A comparison is made to a similar configuration using a magnetorheological damper as the semiactive force device.