Semi-active Control

Introduction

Active control systems rely entirely on external power to operate the actuators and supply the control forces. In many applications, such systems require a large power source, which makes them costly (this is why there has been very few cars equipped with fully active suspensions) and vulnerable to power failure (this is why the civil engineering community is reluctant to use active control devices for earthquake protection). Semi-active devices require a lot less energy than active devices; and the energy can often be stored locally, in a battery, thus rendering the semi-active device independent of any external power supply. Another critical issue with active control is the stability robustness with respect to sensor failure; this problem is especially difficult when centralized controllers are used.