A SISO Linear System with An Unstable Inner Loop and Its Application to Zero Moment Point (ZMP) Control

An analysis of a cascade control system constructed by an inner and an outer feedback loop is presented. It differs from other researches, because the inner feedback loop is unstable. The control method is motivated by balance stabilization of a humanoid robot based on the zero moment point (ZMP) principle where the effectiveness is well-known experimentally. This paper generalizes the control method, and analyzes the stability and the robustness w.r.t. parameter variations of the plant and external disturbances. Some examples to the ZMP control and a simple linear system are described and the simulation results are shown