The magnetic suspended dual‐rotor system (MSDS) can effectively increase the thrust weight ratio of aeroengines. However, the MSDS dynamic characteristics have rarely been investigated. In this research, a MSDS with the outer rotor supported by two active magnetic bearings (AMBs) is designed, and the PID control is employed. The Riccati transfer matrix method using complex variables is adopted to establish the MSDS dynamic model. Subsequently, the influences of AMBs’ control parameters on the MSDS dynamic characteristics are explored. According to the analysis, two rigid mode shapes remain unchanged with the variation of the relationship between their corresponding damped critical speeds (DCSs). Moreover, the rigid DCSs disappear with large derivative coefficient. Eventually, the validity of the dynamic model and the appearance of rigid DCSs are verified.

High-speed operation is a crucial approach for achieving high power density of drive motors for new energy vehicles. However, mechanical strength of the rotor has become the primary bottleneck in the development of high-speed drive motors. Adopting a multi-bridge structure can effectively enhance the mechanical strength of the V-shaped rotors widely used in interior permanent magnet synchronous motors (IPMSMs). Firstly, based on the equivalent centroid principle, the centrifugal forces generated by the rotor’s pole shoes and permanent magnets are calculated. An improved centrifugal force method is proposed to establish an analytical mechanical model of the multi-bridge V-shaped rotor structure. This method comprehensively considers the force conditions, deformation constraints, and material properties of the magnetic bridges. Additionally, stress concentration is taken into account to ensure the accuracy of the model. The effects of various structural parameters on the maximum mechanical stress and deformation are then analyzed. These parameters include the V-angle, pole shoe angle, and the dimensions of three types of magnetic bridges, namely, the central bridge, air-gap bridge, and middle bridge. Finally, recommendations for selecting structural parameters in the mechanical strength design of multi-bridge V-shaped rotors are summarized. The effectiveness of the proposed rotor structure is verified through finite element method and experiments.

The magnetic suspended dual-rotor system applied in more electric aero-engine can eliminate the wear and lubrication system of mechanical bearings and solve the vibration control issue of system effectively, which provides the possibility to improve the performance of aero-engine significantly. This research focuses on the unbalance response of the magnetic suspended dual-rotor system. First, a structure of dual-rotor system supported by two active magnetic bearings and two permanent magnetic bearings is presented. With proportional derivative (PD) control adopted, the bearing characteristics of active magnetic bearings are modeled as the equivalent stiffness and equivalent damping, and the permanent magnetic bearings are modeled as elastic support. Then, the Riccati transfer matrix method with good numerical stability is used to establish the model of the magnetic suspended dual-rotor system unbalance response. Subsequently, the validity of the present formulation has been tested against some known results available in literature and the simulation results obtained by finite element method (FEM). Finally, the dynamic characteristics of the unbalance response are investigated. The results reveal that the influence of the inner rotor imbalance excitation on the magnetic suspended dual-rotor system unbalance response is much larger than that of the outer rotor imbalance excitation. In addition, the critical speeds increase with the proportional coefficient, and the derivative coefficient can affect the amplitudes of the unbalance response, but not critical speeds. From the perspectives of the maximum bearing capacity and maximum displacement of active magnetic bearing-rotor system, the possibility of the magnetic suspended dual-rotor system safely crossing the critical speeds of the first three orders is investigated.

Due to the elimination of wear and lubrication system and effective solution to the vibration control issue, magnetic suspended dual-rotor system (MSDS) offers the possibility to significantly enhance the performance of aero-engines. However, research on MSDS vibration characteristics under fixed-point rubbing with the consideration of nonlinear support characteristics of active magnetic bearing (AMB) has rarely been addressed. In this research, an improved EF model of AMB is proposed by equivalent magnetic circuit method and verified by finite element model. Then, the Lankarani-Nikravesh model is employed to describe the impact force during rubbing process. On this basis, the rubbing dynamic model is established by finite element method and verified by comparing with the experimental results in literature. Finally, the MSDS vibration characteristics are explored, and some interesting phenomena are found. Fixed-point rubbing will cause abundant frequency components equally spaced around the combined frequency components of rotor rotational speeds at different frequency intervals. Due to the stimulation of the AMB nonlinear EF, the fractional frequency component of MSDS second-order critical speed emerges in a certain speed range and implies potential instability of the system, and the rotational speed corresponding to the initial appearance of this frequency component will decrease when fixed-point rubbing occurs. With the decrease of proportional coefficient and the increase of differential coefficient, the maximum normal impact force in the rubbing process decreases.

Magnetic suspended dual-rotor systems (MSDS) provide the potential to significantly improve the performance of aero-engines by eliminating the wear and lubrication system, and solve vibration control issues effectively. However, the nonlinear dynamics of MSDS with rubbing is rarely investigated. In this work, the nonlinear support characteristics of active magnetic bearings (AMBs) are described by the equivalent magnetic circuit method, the impact force is characterized by the Lankarani–Nikravesh model, and the nonlinear dynamic model is established using the finite element method. On this basis, the influence of speed ratio on the nonlinear dynamics is investigated. Simulation results show that the fundamental sub-synchronous vibration of period n is the dominant motion of MSDS, where n is determined by the speed ratio. The frequency components of sub-synchronous vibrations of period k are integer multiples of the minimum dimensionless frequency component 1/k, where k is a positive integral multiple of n. Quasi-periodic and chaotic vibrations are more likely to occur near critical speeds, and their main frequency components can be expressed as a variety of combined frequency components of the rotating frequency difference and its fractional frequency. To reduce the severity of fluctuating stresses stemming from complicated non-synchronous vibrations, speed ratios, corresponding to smaller n and AMB control parameters attenuating vibration amplitude or avoiding critical speeds, are suggested.