SPR-condition free command generator tracking method-application to electrohydraulic servo

The command generator tracking (CGT) method is considered and relaxation of the strictly positive real (SPR)-condition is studied for the input tracking of oscillatory waves given by the superposition of sinusoids. A direct adaptive algorithm is proposed which is free from the SPR-condition without making use of the plant augmentation. The algorithm is simple to allow a compact analog controller, applicable to any plant order, and works well in the presence of weak nonlinearity. The experimental test to an electrohydraulic servo shows good tracking performances