[5]
The PMs are face-mounted with tile shape and radial polarization (see Fig. 2), with suitable pole embrace, polarization and circumferential length are confirmed as.
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[7]
Leakage in the gap mainly depends on magnetic shield and PM shape, within permit, wider magnetic shield will be better. Inner gap magnet flux is.
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[8]
Where ， According to air gap and magnet polarization length, the operating point of PM and iron length for inner motor are.
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[10]
Where are inner radius and outer radius of inner rotor; is flux density of iron for inner rotor. The shaft diameter of inner motor is available. The tooth width and slot deep of inside the stator are.
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[12]
αp is pole embrace, and τs1 , tooth span of inside stator; Klt1, leakage coefficient of inner gap and Klt1= Bg1/ Bm1. Allow for current density Jc and electric loading Ks1, the slot section area of inside stator is.
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[13]
Where Ris is inner radius of stator, Ks1, electric loading of inside stator; Jc , current density; kcu filling coefficient of copper; Ns , the number of slots; β , the span angle of each slot. The inner radius of stator is easily completed when slot shape is fixed. The depth of stator yoke is.
DOI: 10.7763/ijiee.2013.v3.331
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[14]
Where kds is the translation coefficiency of trapezoid to rectangle. B Design of Outer Motor The main task of outer motor design is that according to electromagnetic coupling and size restriction of 2 motors, confirm the size, electric and magnetic loading and other parameters. The outer motor shares some common parameters with internal portion: the slot number , current density and so on. Refering to (4) (5), electric charge and magnet load of 2 motors are inverse proportion to their diameters, operating point is (15). Apparently, lower flux density is need for outer motor, so ferrite is used to decrease the cost.
DOI: 10.1109/cefc.2016.7815959
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[15]
According to FEA (finite element analysis) results, there is almost no coupling when the flux of 2 motors are parallel. In other words, 2 motors need iron yoke respectively. So the stator yoke depth of out motor dys2 can be computed as.
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[16]
In conclusion, the stator yoke depth of anti-rotary PMSM is summation the of 2 motors: dys =dys1+ dys2 (17) The design work of the outer motor, including outer gap, tooth, slot can refer to inner motor. Design Procedure The design procedure of anti-rotating PMSM is as Fig. 4. Due to multiple design objectives of each motor, and electromagnetic coupling and structure restriction of the two motors, iterative calculation is essential to achieve the objective motor. Fig. 3 Inner rotor motor Fig. 4 Design procedure of anti-rotary PMSM Pprototype Design This section will analyze the parameter effects on motor main performance based on the equations derived previous and FEA. Efficiency and torque density in different aspect ratio and diameter ratio of outer rotor to inner rotor are deduced in Fig. 5 and Fig. 6. The fixed parameters are as follows: 3 phase, 1000 turn/m, 6 poles, pole embrace 0. 75, NFeB PMs are employed in inner motor with resistance of 1. 2T, and ferrit PMs are employed in outer motor. Fig. 5 Efficiency, torque density value in different aspect ratio Fig. 6 Efficiency, torque density value in different diameter ratio A Aspect Ratio The ratio of diameter to length is an important parameter to efficiency, torque density, cost and mass of anti-rotary PMSM. Fig. 5 shows efficiency, torque density value in different ratio of diameter to length. B Diameter Ratio of Outer Rotor to Inner Rotor Diameter ratio of outer rotor to inner rotor has much to do with efficiency, torque density, cost and mass of anti-rotary PMSM. Fig. 6 shows efficiency, torque density value in different diameter ratio of outer rotor to inner rotor. C Data of Portery According to design process and fixed parameters, in pursuit of the biggest torque density with the efficiency above 0. 87, a prototype is designed, whose ratio of diameter to length 1. 6, diameter ratio of outer rotor to inner rotor 1. 5, torque density and efficiency 0. 82N m/cm3 and 0. 872 respectively in steady state. When the PMs polarization in 2 rotors are in the same direction, their flux travle in series. When opposite, their flux in parallel. See Fig. 7 and Fig. 8. Fig. 7 Flux in series Fig. 8 Flux in parallel Conclusion To attain the objective anti-rotary PMSM, different permanent magnetic material and different design methods are employed to design inner motor and out motor respectively, then integrated in aspect of electromagnetic coupling and size restriction. The parameter value is computed via analytics, and FEA testified the effectiveness of design procedure. References.
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