| According to the problems of high cost, low transmission efficiency and serious vibration and noise in engineering machinery and equipment of metallurgy, mine and electric power filed, this dissertation proposes a kind of proper fractional slot winding in low voltage low speed PMSM (permanent magnet synchronous motor).To improve efficiency in low load rate, reduce harmful arc and cut down system cost, stator winding is designed into independent multi-branch structure.The electromagnetic design, parameter selection and strength check method of low voltage low speed megawatt grade multi-branch PMSM is analyzed combined with low speed and high torque multi-pole permanent magnet motor design features. Analytical analysis is derived. And weaken method of cogging torque is given. Effective ways to weaken cogging torque are as follows:choosing optimal pole arc coefficient, using skew stator slot, asymmetric airgap and magnetic slot wedge.Conception of proper fractional slot winding is proposed and its advantages and disadvantages are analyzed. The condition to form proper fraction slot winding PMSM symmetric winding is derived. This dissertation proposes two methods of winding arrangement. Calculation method of distribution coefficient is given basing harmonic analysis.Then by analysis harmonic amplitude, advantages of proper fraction slot winding are studied. It can improve slot utilization, back emf waveform and motor efficiency, reduce weight of copper, and weaken harmonic magnetic field and cogging torque. Influence to stable running and accurate control which caused by vibration and noise is weakened too.A 1300kW,120 poles low voltage low speed megawatt grade multi-branch PMSM is manufactured. Experimental results show that the methods to weaken cogging torque and structure of proper fraction slot winding proposed in this dissertation is effective and reasonable.
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