Digital tracking techniques for MIMO swept sine control testing

Multiple-Input Multiple-Output (MIMO) swept sine excitation is nowadays largely used in the environmental and modal testing of aerospace structures. One of the advantages of swept sine excitation is the possibility of effectively control to a (safe) reference level the response of critical sensors, relying on information from a low level System Identification test executed prior to the test. System Identification errors during the actual sine sweep runs require on-line MIMO feedback control. One of the main challenges of applying MIMO feedback control algorithms to swept sine excitation is the need for accurate amplitude and phase tracking techniques. This paper proposes two different solutions to this challenge: a DFT-based sweeping Harmonic Estimator and a Digital Tracking Filter, with fixed and variable bandwidth. The analysis of the two techniques is followed by the integration of the proposed tracking algorithms to an innovative frequency domain feedback control technique for MIMO swept sine control testing.