BiQuad-filter for active damping of low frequency oscillations in two-inertia drive systems

Usually the coupling between an electrical drive and Its mechanical load is designed with a high stiffness to avoid any eigenfrequency which could be excited by the drive itself or other influences. In some applications, however, a rather long coupling shaft cannot be avoided; consequently resonance problems most be expected due to the more or less elastic coupling between the drive and the load. A well-known method to overcome this problem is the application of mechanical damping elements. This paper presents the design and application of a so-called BiQuad filter which is implemented to suppress low frequency resonance oscillations by in active method instead of mechanical damping equipment The filter is placed either In the feedforward branch or in the feedback of the drive control loop. Practical results obtained by both versions of BiQuad filter application are presented and discussed with special respect to the influence of a current limitation, which is integrated in most commercial drive systems.