Fixed-time sliding mode attitude control of a flexible spacecraft with rotating appendages connected by magnetic bearing

<abstract> <p>This study focuses on the attitude control of a flexible spacecraft comprising rotating appendages, magnetic bearings, and a satellite platform capable of carrying flexible solar panels. The kinematic and dynamic models of the spacecraft were established using Lagrange methods to describe the translation and rotation of the spacecraft system and its connected components. A simplified model of the dynamics of a five-degrees-of-freedom (DOF) active magnetic bearing was developed using the equivalent stiffness and damping methods based on the magnetic gap variations in the magnetic bearing. Next, a fixed-time sliding mode control method was proposed for each component of the spacecraft to adjust the magnetic gap of the active magnetic bearing, realize a stable rotation of the flexible solar panels, obtain a high inertia for the appendage of the spacecraft, and accurately control the attitude. Finally, the numerical simulation results of the proposed fixed-time control method were compared with those of the proportional-derivative control method to demonstrate the superiority and effectiveness of the proposed control law.</p> </abstract>

A novel permanent magnet bias hybrid thrust magnetic bearing with extremely simple structure for high-speed rotating machinery

This paper presents a novel permanent magnet (PM) bias hybrid thrust magnetic bearing (HTMB), which can be used to replace the traditional thrust magnetic bearings (TMBs) for high-speed rotating machinery. By adding two PM rings and by reducing the number of the control coils by half, this HTMB eliminates the bias current, reduces the number of amplifiers, and minimizes the magnetic bearing’s structure complexity and power consumption. The analytical modelling method of the HTMB is presented in this paper. Mathematical models for calculating the magnetic force capacity and the stiffnesses of this bearing are derived as simplified formulae, which can be used for the design, analysis, and control of this bearing. Electromechanical characteristics of the HTMB are analyzed, which is compared to the traditional TMB to demonstrate the advantages of the HTMB. The prototype of the HTMB is designed, analyzed, and fabricated, whereas, the 2-D FEM is used to verify the design and the analytical model. Finally, an experimental setup is constructed and tested. The analytical and experimental results indicate that the proposed novel topology of this HTMB is feasible and the presented analytical model is accurate.

Gain-Scheduled Control of Asymmetric Thrust Magnetic Bearing

The thrust position of the magnetic levitation rotor can be changed, bringing convenience to the practical application of cold compressors. This paper derives the mathematical model of asymmetric thrust magnetic bearings for a cold compressor and analyzes the changes in the system characteristics with the equilibrium position. By constructing PID controllers associated with the structural parameters of the magnetic bearing, the adaptive adjustment of the control parameters under different balanced position commands is realized. The simulation and experimental results prove that the gain-scheduled control method proposed in this paper can achieve a robust stability of the rotor in the range of 50 to 350 μm, and not at the cost of the response speed, adjustment time, and overshoot. The research results have reference significance for the structure design of asymmetric thrust magnetic bearings and play an important role in the commissioning and performance improvement of cold compressors.

A Full-Period Mathematical Model for a Hybrid-Rotor Bearingless Switched Reluctance Motor

A bearingless switched reluctance motor (BSRM) has the combined characteristics of a switched reluctance motor (SRM) and a magnetic bearing. The hybrid-rotor BSRM (HBSRM) discussed in the paper has a twelve-pole stator and an eight-pole hybrid rotor, which is composed of a cylindrical rotor and a salient-pole rotor. Although the asymmetry of the hybrid rotor makes the structure and magnetic field of the HBSRM more complex, it can always produce a significant amount of magnetic pulling force to levitate a rotor shaft at all the rotor angular positions of each phase, which is not available in a traditional BSRM. The classical mathematical model for a conventional BSRM is valid only when its rotor rotates from the start of the overlap position to the aligned position, and the radial force and torque derived from this model are discontinuous at the aligned positon, which is harmful to the motor’s stable operation. In this paper, a full-period mathematical model on the assumption that the gap permeance is cut apart by straight lines or improved elliptical lines for a 12/8-pole HBSRM is provided. On the basis of this mathematical model, the continuity of the radial force and torque at all the rotor angular positions can be guaranteed, and the fine characteristics of this mathematical model have been verified by simulations.