Parallel Stator Winding Connection Of Permanent Magnet Synchronous Motor Without Neural Points Connected

Permanent magnet synchronous motor (PMSM) with high efficiency and powerdensity are widely used in electric vehicle. But PMSM applied in pure electric vehicleand hybrid cars are generally powered by batteries resulting in low-voltage andhigh-current problems. Low voltage means turns-in-series per-phase is less and highcurrent means total sectional area of winding wire is larger. Under ideal condition, thenumber of the stator parallel winding can be selected flexibly. In fact, magneticproperties of commercial permanent magnet have significant dispersion. Beside,excessive temperature rise and over current will also lead to local demagnetization.Serious inconsistency in magnetic properties will bring in different air gap magneticflux under each magnetic pole, which means different induced electromotive force ineach parallel branch. As a result, circulating current and additional loss generatesbetween parallel branches causing motor performance degradation.A stator winding connection type is proposed for the above-mentioned problems.That star connection groups are connected in parallel without any connection betweentheir neutral points is elaborated and winding connection in several different cases arelist. Symmetrical component method is used to analyze the circulating current in eachstator winding branch when take inconsistency of magnetic properties into account. Alow-voltage high-current PMSM is designed according to actual needs and motordesign theory and field-circuit coupled finite element method is applied for simulationanalysis on permanent magnet magnetomotive force, induced electromotive force andwinding circulating current.Analyses show turns-in-series per-phase can be flexibly adjusted and slot spacecan be effectively utilized in the motor adopting the novel winding connection type.Beside, motor performance and operating efficiency of frequency conversion drivingsystem are also improved. The simulation results demonstrate that lower circulatingcurrent and additional loss generated by inconsistency of permanent magnet in theproposed connection method compared with that with neural points connected.