Research On High Speed Slotless Permanent Magnet Synchronous Motor With Integrated Inductance

High speed motor has many advantages such as small size, high power density, low inertia, fast dynamic response, high efficiency, has become a hot research topic in the field of motor, and has been widely used in the microturbine, spindle, flywheel energy storage, high speed centrifuge, high speed compressors and other fields. Take the flywheel energy storage system as the application background, this paper proposed a high speed slotless permanent magnet synchronous motor(HSS-PMSM) with integrated inductance, and the Halbach magnet array of the rotor, the stator structure with integrated additional inductance, the calculation method of the motor loss and the design of the cooling structure have been studied.Firstly, in this paper the slotless motor and the ring winding are combined, and a novel slotless motor with integrated inductance is proposed. The motor consist of a rotor with novel double layer Halbach magnet array and a slotless stator with integrated inductance. The structure and properties of this novel double layer Halbach magnet array is introduced detailed, and the advantages of the double layer Halbach magnet array are analyzed. The magnetic field analytical model of the Halbach array is established. The magnetic field analytical model of the Halbach array is analyzed using scalar magnetic potential. The expressions of the radial and tangential magnetic fields in space are obtained, and the expression of the backEMF is getting further. The magnetic field model is validated by comparing the result with the results of which got by using the finite element method and experimental. The flux density distribution curves and back-EMF curves obtained from three methods coincide, which verify the double layer Halbach magnet array can improve the sine of the air-gap flux density.Secondly, the features of the novel slotless stator with integrated additional inductance is introduced detailed, the mechanism of increasing additional inductance in the stator has been clarified. The inductance of the motor is calculated by using magnetic vector potential. The relationship between the stator’s additional inductance and the lateral groove dimensions is analyzed using the magnetic circuit method, and an accurate value of the additional inductance is obtained. The motor which with integrated inductance is simulated in Simulink, and compared with the general structure high speed slotless motors. The additional inductance of the motor and the current wave of the winding at running state are obtained through experimental measurements and are verified by comparing with the analytical and simulation results to prove the integrated inductance structure can reduce the harmonic winding current effectively.Thirdly, the loss of the new structure high speed slotless permanent magnet synchronous motor is studied. Considering the skin effect and proximity effect, the equivalent resistance changes of the winding caused by high frequency current is analyzed. The relationship between the eddy current losses of the motor and the stator winding spatial distribution field is analyzed. In order to reduce the eddy current losses in the rotor, a novel quasi-sinusoidal winding is proposed under the premise of slotless motors. The spatial harmonic of the winding’s line load, as well as the losses of the rotor due to eddy current are analyzed. The relationship between the eddy current loss and spatial distribution of the winding is derived by comparing with the traditional 12-slot single-layer full pitch winding and 24-slot double-layer short pitch winding. Consider the impact of current harmonics, the iron loss of the motor is calculated and the independence of the iron loss of the inside stator yoke and the outside teeth is pointed. The correctness of the analytical results is verified through experiments on the loss of the motor tested. And compared with the ordinary slotless motor, the new structure HSS-PMSM can effectively reduce rotor eddy current loss.Finally, the temperature field and the cooling structure of the motor is investigated. Based on the basic heat transfer theory, a three-dimensional temperature field model of the motor is established. The temperature distribution of the motor with forced air cooling is obtained by the temperature field calculation and the comparison with the measured temperature verifies the accuracy of the temperature field calculation results. In order to ensure a more stable operation of the motor, the chassis water cooling structure is designed, comparison with the ordinary slotless motor is made, which proved that the novel structure HSS-PMSM can reduce the temperature of rotor effectively. Furtherly, a direct winding cooling structure is proposed according to the characteristics of the motor structure of this paper. Three-dimensional temperature field simulation of the two water cooling structures are made. The results show that compared with the chasiss water cooling structure, the direct winding cooling structure can further reduce the temperature of the various parts of the motor, and make it can be applied to higher power density applications.