Analysis of Active Suspension Systems with Hydraulic Actuators

Most of the existing active suspension studies assume that an ideal force actuator exists and will carry out the commanded force accurately. In reality, due to the interaction between the hydraulic actuator and suspension system, the lightly damped modes of the plant will generate lightly damped zeros (LDZ) for the servo-loop system, which confines the closed-loop performance to a low frequency range. Converting the active suspension problem formulation into a displacement control problem, as suggested by several recent papers, will not solve this problem. Four candidate remedies to reduce the effect of the LDZ are studied and their potentials and limitations are discussed.