Modeling And Magnetic Field Analysis Of A New Double-Layer Magnetic Pole Permanent Magnet Motor

Owing to their advantages such as low losses,high efficiency and torque density,permanent magnet(PM)brushless machines are widely used in the national protection,industrial and agricultural production,daily life and other aspects.The electromagnetic performance of the conventional magnetic pole PM brushless machine has to be improved.The electromagnetic performance of a PM brushless machine with double-layer combined poles is investigated in this paper.A finite element method is used to analyze the two-dimensional magnetic fields in a PM brushless DC motor with single-layer/double-layer magnetic pole.A control circuit is presented for simulation.The air-gap flux density,back electromotive force,and electromagnetic torque waveforms for two motors are shown and compared.The results shown that the double-layer PM brushless DC motor has better electromagnetic performance.A PM brushless machine with double-layer hybrid magnetic poles is modeled and analyzed.The upper magnetic pole is the traditional surface-mounted type and parallel magnetized,while the lower magnetic pole is the surface-inserted type and parallel magnetized with variable magnetization angle.The influence of the ratio of the upper to lower magnet thickness and the magnetization angle of the lower magnet on the air-gap flux density is investigated.On the basis of the air-gap flux density in the PM machine with upper/lower magnetic pole,the air-gap flux density in the PM machine with double-layer hybrid magnetic poles is derived.Besides,the optimal air-gap flux density,optimal back electromotive force,and optimal electromagnetic torque for the PM machine are derived.Compared with the conventional parallel magnetization PM machine,the double-layer PM machine not only saves materials,but also has better electromagnetic performance.Finally,the analytical results are verified by finite element method.A permanent magnet brushless machine with double-layer two-segment Halbach is modeled.On the basis of solving Laplacian and quasi-Poissonian equations,and the analytical formula of air-gap flux density in the permanent magnet machine with double-layer two-segment Halbach is obtained by superposition method.For the commonly used tooth and slot structure in stators,an improved Carter's coefficient is used to calculate the equivalent air-gap length.The analytical expressions of the air-gap flux density,back electromotive force and electromagnetic torque of thedouble-layer two-segment Halbach PM machine are obtained.The optimal pole-to-arc ratio for the PM machine with single-layer/double-layer two-segment Halbach is obtained by using a method of separating variables.Therefore,the maximum fundamental radial air-gap flux density is derived.Compared with the single-layer two-segment Halbach structure,the optimal fundamental radial air-gap flux density of the double-layer two-segment Halbach structure is larger,thus having better electromagnetic performance.