Hao Jiang

To address issues such as the susceptibility of traditional magnetic bearings (MBs) to corrosion by liquid media when employed in pump systems, this paper proposes a canned MBs structure. The design incorporates a shielding sleeve made of high-strength low-conductive metal material to protect the MBs core from rust, corrosion, and immersion in the liquid medium. Furthermore, considering the significant eddy current effects introduced by the shielding sleeve, the model of the canned MBs is established. This model is used to analyze the influence of different shielding sleeve materials and thicknesses on the performance of the canned MBs. Based on the derived influence patterns and available manufacturing techniques, an appropriate material and thickness for the shielding sleeve are selected. A prototype is then fabricated to validate the performance of the proposed canned MBs.

This article deals with the issue of manufacturing processes leading to rotor surface losses through analytical, finite element analysis (FEA) and experimental methods. Based on experiments, it is found that the rotor surface losses make the rotor temperature of radial magnetic bearings (MBs) higher than expected, and thermal ablation appeared on the rotor surface. First, we investigate the mechanism of rotor surface loss in radial MBs using an improved analytical method. The FEA is then used to validate the analytical results and explore the correlation between the degree of short-circuit faults on the rotor surface and the surface losses. This yields a more comprehensive understanding of the loss characteristics and provides ideas for improving manufacturing methods to reduce surface losses. Finally, a simple method of rotor outer circle machining, namely finish turning with fine feed, is proposed. Comparison prototypes were manufactured using the proposed method and the conventional method. The results demonstrate that the proposed method can effectively reduce the rotor surface losses of radial MBs.

Magnetic bearings (MBs) enable the rotor to run at high speed without lubrication due to no mechanical contact. However, the inherent hysteresis of ferromagnetic materials affects the support characteristics, reducing the design performance and stability margin of MBs, especially for axial MBs using materials with high coercive force. To analyze and compensate for the hysteresis effect on the electromagnetic force in axial MBs, an efficient method is proposed in this paper. Firstly, the hysteresis properties of the ferromagnetic materials are simulated by the Preisach model, and the B - H relationships under any external magnetic field can be determined. Taking into account the non-ideal factors such as hysteresis and saturation effects, the nonlinear magnetic circuit model of the axial MBs is established. The magnetic flux density working point under different control currents and eccentric displacements can be determined through iterative calculation, and then the air gap flux density distribution and electromagnetic force of the axial MBs are calculated. On this basis, the adverse effects of hysteresis on the bearing capacity and system stability of axial MBs are analyzed. A compensation algorithm is designed based on the inverse model to reduce the hysteresis effect. The inverse model is approximated modeled by the Lissajous curve. Finally, the proposed analysis and control methods are verified by the finite element method (FEM) or experiments. The results show that the proposed analysis method is capable of accomplishing good accuracy and requires less computation time than FEM, it can be applied to arbitrary current variation processes. In addition, the phase lag of the system is effectively improved with the compensation algorithm.

Parameter identification enables active magnetic bearing (AMB) to obtain more state information, which can be used for control optimization, condition monitoring, and fault diagnosis for rotating machinery. Due to the limitation of working principle and modeling accuracy, the traditional parameter identification methods show inherent disadvantages in cost, applicability or precision. Thus, this article proposes an accurate multiparameter identification method without any instrumentation. This method takes into account the electromagnetic force coupling caused by the asymmetric magnetic circuit, the nonlinearity caused by the saturation effect, together with the uncertain parameters caused by machining and assembly errors, temperature, etc. First, the coupled nonlinear magnetic circuit model of the AMB is established by the reluctance network method, and the influence of nonideal factors on the electromagnetic force is treated. Second, a novel experimental method for parameter identification is presented. According to the equilibrium relationship between the electromagnetic force and the supporting load, the force balance equations of the rotor under different working conditions are obtained. Taking the supporting parameters and uncertain geometric parameters as the parameters to be identified, the multiparameter identification model is established. Finally, the proposed method is validated by the finite element method and experiments. The results show that the method can accurately identify the air gap length, rotor origin, static supporting load, and stiffness of the AMB.

To solve the problem that coupled magnetic flux and saturation of active magnetic bearing (AMB) cannot be taken into account in the traditional magnetic circuit calculation method together, this paper proposes a novel analytical calculation method based on distributed magnetic circuit method (DMCM). First, a magnetic circuit model with multiple magnetic circuits is built, we can obtain the initial flux density of each section by magnetic circuit calculation. Next, the magnetomotive force (MMF) of each magnetic circuit is calculated by the B-H curve of the ferromagnetic material. Then, the air-gap flux density under each magnetic pole center is obtained by further iterative calculations according to the magnetic potential error. On the basis, the flux density distribution along the air-gap circumference is obtained by one-dimensional (1D) relative permeance function, and thus the bearing capacity is derived and a loss calculation method is introduced. Finally, the finite element method (FEM) and experimental results show that the proposed method is feasible and effective.