Abstract
The general method to suppress the axial force of the permanent magnet synchronous motor (PMSM) direct-drive turbine is to increase the number of balance devices, such as balance disks and special bearings, to counteract its influence, but this also leads to complex system structure and higher mechanical losses. Aiming to solve the above issue, this paper presents a novel PMSM structure with a conical-rotor (CR). Due to its adaptive equilibrium of axial force and simple structure of rotor with turbine, the CR-PMSM can help improve the system efficiency. Both surface-type and interior-type motors are analyzed, and the axial magnetic force of CR-PMSM is studied in detail. The 3-D finite-element method (FEM) is used to model and simulate the machine, and the magnetic-field distribution, axial magnetic force and driving performance are obtained. Also, the control rule of d-axis current is analyzed to achieve the adaptive equilibrium of axial force. A 2.0 kW, 6000 r/min prototype motor is fabricated and tested to validate the theory.
Highlights
IntroductionThanks to their high energy transfer efficiency and high torque density, permanent magnet synchronous motor (PMSM) direct-drive high-speed turbines (such as turbo-compressors and turbo-expanders, etc.) have been widely accepted
Thanks to their high energy transfer efficiency and high torque density, permanent magnet synchronous motor (PMSM) direct-drive high-speed turbines have been widely accepted.to ensure the safe and reliable operation of the system, the axial force of the turbine under the impact of high-speed working-fluid flow should be balanced, which is usually accomplished by using mechanical devices such as balance disks, mechanical linkages, sliders and special bearings, which significantly increase the system complexity and bring more losses.the axial force changes aperiodically due to the influence of temperature, pressure and flow of the working fluid, so the impeller blades will collide with the volute and experience vibration and friction, causing abnormal wear and tear of the bearings, balance plates and springs
The rotor of the CR-PSMSM can be moved outside in an axial direction which decreases the air-gap flux density and increases the effective space between the stator and the rotor, so the axial magnetic force of the motor can be adjusted by changing the current or the the air-gap length to balance the axial force of the turbine
Summary
Thanks to their high energy transfer efficiency and high torque density, PMSM direct-drive high-speed turbines (such as turbo-compressors and turbo-expanders, etc.) have been widely accepted. This paper presents an axial force suppression method for motor-turbine systems by using a CR-PMSM instead of increasing the number of balance devices. The rotor of the CR-PSMSM can be moved outside in an axial direction which decreases the air-gap flux density and increases the effective space between the stator and the rotor, so the axial magnetic force of the motor can be adjusted by changing the current or the the air-gap length to balance the axial force of the turbine. In [8] a 3-D finite element model was used to simulate the magnetic-field distribution of the air gap, flux weakening, and driving performance in CR-PMSM according to rotor axial displacement, instead of changing the current angle. 2.0 kW, 6000 r/min prototype CR-PMSM with a cone angle of 6.0â—¦ is designed and built, and tests of the motor-turbine system are carried out to validate the theory
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