A multiloop system stability margin study using matrix singular values. [for wing flutter suppression and drone lateral attitude control]

A stability margin evaluation method in terms of simultaneous gain and phase changes in all loops of a multiloop system is presented. A universal gain-phase margin evaluation diagram is constructed by extending an existing method using matrix singular value properties. Using this diagram and computing the minimum singular value of the system return difference matrix over the operating frequency range, regions of guaranteed stability margins can be obtained. Examples are presented for a wing flutter suppression and a drone lateral attitude control problem. The use of a return difference matrix eigenvalue plot in the complex plane is discussed.