Influence of Clamping Bolts on Electromagnetic Performance of PMSM Machines and Its Restraining Methods

The clamping bolts and bolt-holes can be employed to stack the steel laminations in permanent magnet machines. Their influence on the electromagnetic performance is analyzed in this paper, including the electromagnetic torque, open-circuit torque, phase back-EMFs, and circulating current loss. A restraining method of dummy bolt-hole is proposed to achieve both balanced phase back-EMFs and zero circulating currents in bolts. The ratio of bolt-hole edge thickness to bolt-hole radius is optimized to compensate the reduction of stator yoke caused by bolt-holes. Besides, a method of open bolt-hole edge is proposed to restrain the circulating currents. Furthermore, structure analyses are conducted to prove the reliability of the electromagnetic design. The proposed method is verified by experiments on a prototype machine.