Applied Mechanics and Materials Vol. 150

Abstract: The authors’ former works demonstrated that a passive magnetic (PM) rotator supported merely by PM bearings has a minimal speed, above which it can stabilize its equilibrium, under the function of a so-called Gyro-effect. It is unclear, however, by which factors is this minimal speed determined. This paper investigated the factors affecting the minimal stable speed of permanent maglev rotator, namely, the rotating inertia and PMB force. Two novel permanent maglev turbine models were designed: Model A---one stator and three rotors which have the same size but different rotational inertias; Model B---one rotor and one stator, but the stator has been devised with three different passive magnetic bearings: 1. a pair of small magnetic rings; 2. a pair of big magnetic rings; and 3. both of the two pairs of magnetic rings. Four Hall sensors distributed evenly at the turbine’s stator were used to detect the rotor’s eccentricity, and the speed sensor measured rotating speed. The calculated models of rotor’s eccentricity were established respectively for the two turbine models; the rotor’s eccentricity measuring system was built up and the rotor’s eccentricity of the two turbines was measured. The experimental data demonstrated that the rotational inertia of three rotors in the model A is 6.293×10-5 kg•m2, 1.074×10-4 kg•m2 and 2.081×10-4 kg•m2 respectively, and the corresponding minimal speed for suspension are 4597rpm, 3030rpm and 2222rpm respectively; in the model B, the magnetic force between the stator and rotor in the three cases is 92.12N, 123.48N, 212.66N respectively, corresponding to the minimal speed for suspension---3730rpm, 3120rpm and 2195rpm respectively. The results exhibited that same as the permanent maglev heart pump, permanent maglev turbines also have gyroscopic effect, which makes the rotors maintain stable suspension. And the minimal speed for suspension has a negative correlation with the rotor’s rotational inertia, namely, the bigger the inertia of the rotor, the smaller the required speed for suspension; the minimal speed for suspension also has a negative correlation with the magnetic force between the stator and rotor, that is, the larger the magnetic force, the smaller the rotating speed for suspension. Smaller minimal speed means better stability of the system, thereafter larger inertia or larger bearing force means better stability; besides, larger difference between minimal speed and performance speed of the rotator means better stability, it’s suggested permanent maglev be applied in high speed rotary machines.

Abstract: Magnetic suspended wind turbine generator is widely studied due to its low loss, low maintenance cost and high reliability. However, affected by the small stiffness of magnetic bearing, the generator shaft supported by magnetic bearing will be eccentric. Therefore, the performance of generator will be affected. A horizontal axial magnetic suspended wind turbine generator is designed in this paper. The variations of shaft eccentricity and Maxwell force of rotor supported by different bearing stiffness are studied. The results show that the shaft eccentricity affects the performance of generator; and the bearing stiffness is the key to reduce those effects. The magnetic bearing designed in this paper can meet the requirements of generator.

Abstract: Magnetic suspension system is nonlinear and unstable essentially. It is according to the principle of nonlinear system having same topological structure near the operation point with the linear system that linear control arithmetic for a nonlinear system is adopted. The system is easy to lose stabilize and diverge when subjected to interference or system parameters variation. Suspension mass is a key parameter of a magnetic suspension system and suspension mass variation has great influence on the dynamic characteristic of a magnetic suspension system. The influence of suspension mass variation on the dynamic characteristic of a magnetic suspension system under the PID control condition is discussed. The relationship between dynamic characteristic and structure as well as control parameters of the magnetic suspension system is reached by means of experimental method.

Abstract: There are some problems in the permanent magnetic circuit of the current permanent magnet biased magnetic bearings, such as small magnetic force, low magnetic flux density and lack of self-stabilization. To solve this problem, a new hybrid radial magnetic bearing structure has been proposed. The nonlinear model and linearization equation of the new hybrid radial magnetic bearing capacity has been established by current molecular method and virtual displacement theorem. It is found that the permanent magnetic bearing can achieve self-stabilization in the radial degrees of freedom and can reduce the total displacement of negative stiffness. The results show that the air gap flux density is greatly improved by the new hybrid magnetic bearing with Halbach array structure. Current stiffness and displacement rigidity is closely related to initial current and initial gap of the equilibrium position. Near the equilibrium position, current stiffness and displacement rigidity are linear relationship. With the increase of air gap, it remains a good linearity. While with the decrease of air gap, it presents nonlinear characteristics..

Abstract: According to electromagnetic theory, A single degree of freedom mathematical model of AMB system was established. We design a variable parameter PID controller based on the model. And the simulation results express that the variable parameters PID controller was better in the lots of indicators compared with the traditional PID controller.

Abstract: Feedforward control method to control vibration in the active vibration isolation system was discussed. By introducing the FIR filter as the feedforward link, using the mean-square deviation of system error as the performance index and utilizing the LMS algorithm to obtain the optimal parameters of controller, the design of adaptive feedforward controller was fulfilled. The simulation results showed that: for the active vibration isolation system with regularly vibration source, adopting adaptive filter method of feedforward control has notable effect. The contrast experiment with using the PID controller further verified the simulation results.

Abstract: It is important to clarify the rotor eddy current losses in bearingless permanent magnet synchronous (BPMSM) for temperature rising to induce irreversible demagnetization. In this paper, the torque and radial suspension force producing mechanisms of BPMSM are introduced. The relative motion relationships among radial suspension force, rotor magnetic field and suspension winding magnetic field are analyzed. The necessary conditions of producing stable controllable radial suspension force in single direction are concluded. The rotor eddy current losses in BPMSM with PB=PM+1 and PB=PM-1 are calculated and compared using 2D time-steeping finite element method. The research results have shown that the BPMSM with PB=PM+1 is the most suitable for high speed operation with the minimum eddy current losses in rotor.

Abstract: Vertical axis wind turbine (VAWT) plays one of the important roles in wind power equipments. When joining the magnetic levitation technology, the VAWTs can effectively reduce the friction torque to improve startup performance and increase the power coefficient. At the same time, the mechanical vibration can be reduced, and its actual functioning time can be extended. In this paper, the structure, working principle and mathematical model were introduced respectively with an intention to present the magnetic supporting structure of a VAWT. Then the self adaptive integral-type sliding mode control (AISMC) was offered and designed. Compared with convention-al PID control, the simulations show that the system under the AISMC control has a better dynamic response and robust characteristic.

Abstract: The mathematic models of an interior permanent magnet synchronous motor (IPMSM) are deduced in this paper. A novel sensorless control strategy for IPMSM is proposed. An extended flux is systematically derived by using the proposed extended flux estimating method. The shaft position and speed of the motor are obtained. The simulation control system is built based on Matlab and a TMS320LF2407 digital signal processor is used to execute the rotor position estimation and rotor speed estimation. Several experimental and simulation results are provided to validate the control strategy.

Abstract: When the permanent magnet synchronous motor is operated at a low speed. The rotor position and speed are very difficult to estimate using the extended flux or back EMF method. A novel modified current slope estimating method is used to estimate the rotor position and speed in low speed in this paper. The mathematical models of an interior permanent magnet synchronous motor (IPMSM) are deduced. The basic principle of modified current slope method is introduced. The simulation control system is built based on Matlab and a TMS320LF2407 digital signal processor is used to execute the rotor position and speed estimation. The experimental and simulation results have shown that the rotor position and speed can be accurately estimated in a low-speed operating region.