Abstract
This paper investigates the dynamic behaviour of a typical rotor-active magnetic bearings (AMBs) system with delayed feedback. The method of multiple scales is used to obtain the averaged equations in the case of primary resonance and 1/3 subharmonic resonance. The effect of short delay in feedback loop of system on the resonances is studied with respect to the steady-state response and stability of the system. Results of the studies show that time delay not only influences the amplitude and phase of primary resonance and 1/3 subharmonic resonances, as well as resonance region, but also has a significant effect on threshold of excitation amplitude that can induce 1/3 subharmonic resonance.