Cogging Torque Suppression of Interior Spoke-Type Permanent Magnet Synchronous Motors with Rotor Trapezoidal Groove
Wu Shengnan1, Tong Yueyang1, Tong Wenming2
1. School of Electrical Engineering Shenyang University of Technology Shenyang 110870 China; 2. National Engineering Research Center for Rare-Earth Permanent Magnet Machines Shenyang University of Technology Shenyang 110870 China
Abstract：To solve the problems of ample cogging torque and severe torque fluctuation of interior permanent magnet synchronous motors (IPMSM), an interior spoke-type IPMSM cogging torque suppression method with a trapezoidal groove structure of the rotor core is proposed. This method can effectively reduce the harmonic proportion of cogging torque and no-load back electromotive force of the motor, as well as the torque fluctuation of the motor. Firstly, the cogging torque calculation formula of the IPMSM with a semi-closed groove is derived by an analytical method. Changing the polar arc coefficient and air gap shape of the permanent magnet motor can effectively suppress cogging torque. For the interior spoke-type structure, a new method for reducing the cogging torque is proposed. A new expression for calculating the polar arc coefficient is proposed to change the shape of the air gap and the polar arc coefficient by changing the shape and size of the grooving. Secondly, taking a 14-pole 12-slot interior spoke-type permanent magnet synchronous motor as an example, the influence of trapezoidal groove height on cogging torque is explored by finite element simulation. The cogging torque decreases with the increase in notch height. At the same time, the influence of the short-side opening angle and the long-side opening angle of the trapezoidal groove on the cogging torque is analyzed under the combination of three common pole grooves: 14-pole 12-slot, 10-pole 12-slot, and 16-pole 18-groove. Combined with the cogging torque calculation formula, polar arc coefficient calculation formula, and finite element simulation analysis, the trapezoidal groove selection formula is given. In addition, this paper compares the no-load back EMF, back EMF harmonic proportion, cogging torque, and torque fluctuation of the slot-less rotor, rectangular slot rotor structure, and the optimized trapezoidal slot rotor structure permanent magnet synchronous motor. The cogging torque of the trapezoidal rotor is reduced by 90.9% and 83.6% compared with the rectangular groove rotor and the slot-less structure. The output torque of the slot-less structure motor is low, and the torque fluctuation of the trapezoidal slot motor is 54% lower than that of the rectangular slot motor when the output torque of the slot-less structure motor is close. The torque output performance of the motor is stable. Finally, the motor no-load test and static cogging torque test were carried out. The effective value of the no-load back electromotive force of the test prototype was 7.75 V. The cogging torque was 6 mN·m with an error of 2.92%. The experimental errors are all within the allowable range, verifying the effectiveness and practicability of the finite element simulation. This paper provides an effective method to solve the problem of significant cogging torque and torque fluctuation of IPMSM.
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