Research on special low-speed, high-torque permanent magnet synchronous motor for screw pump

With the requirement of energy conservation and environmental protection, current induction motor (IM) with gear box for screw pump is unqualified. This paper investigates a special low-speed, high-torque permanent magnet synchronous motor (PMSM) to directly drive the screw pump without gear box. Design constraints are surveyed for the special PMSM, both from the motor´s structure and performance. To reduce cogging torque, analytical analysis is done first. Then, a method is proposed that is combination of fractional-slot winding and optimized pole-arc coefficient based on the cogging torque´s analytical expression. Computed aided design (CAD) is adopted for PMSM designing. The magnetic field and load performance are analyzed with the finite element method (FEA). The PMSM with a rating of 1000 Nm and 125 rmp is designed, manufactured and compared with induction motor to verify the proposed method.