Direct-Drive Conical-Rotor Permanent Magnet Synchronous Generator for Turbo-Expander, Accounting for Adaptive Equilibrium of Axial Force

The permanent magnet synchronous generator (PMSG) has been widely employed in high-speed direct-drive turbo-expander for distributed energy generation. However, for conventional PMSG based turbo-expander system, expensive mechanical balance devices should be installed on the rotor to restrain the axial force of turbine impeller under high-speed flow, which may cause both complex system structure and higher manufacturing cost. Thus, in this paper, a direct-drive conical-rotor PMSG (CR-PMSG) for turbo-expander is developed, which can generate an axial magnetic force as equilibrant to counteract the axial force of turbine impeller without mechanical balance device, so as to reduce the system complexity, improve the operating performance and extend the operating cycle. First, the structural features of the CR-PMSG are introduced and the basic principle of axial force balance is analyzed. Then, a 1.5 kW, 6000 rpm CR-PMSG with cone angle of 6° is designed. Using 3-D finite element analysis, the axial force of turbine impeller, the axial magnetic force of the rotor, and the electromagnetic performance are simulated. Also, the control strategy of d, q-axis currents is obtained to achieve the adaptive equilibrium of axial force. Finally, a CR-PMSG prototype is fabricated and tested to validate the theory.