The paper presents the energy density improvement using magnetic circuit analysis of the interior permanent magnet motor. The leakage flux from the conventional structure is improved with modified magnetic circuit to improve the energy and thereby the torque value. This is approached with a double stator structure design. The proposed structure is investigated with two design variations, namely, the double stator with thin pole shoe and the double stator with thick pole shoe motors. Variations in the mechanical parameters of the all the developed models are analyzed through the finite element analysis tool. In all investigations the magnetic source is fixed in both the permanent magnet volume and coil magnetomotive force, respectively, as 400 mm3 per each pole and 480 Ampere turns per pole. From the analysis the best fit magnetic structure based on the torque characteristics is derived and is fabricated for the same volume as that of the conventional structure for performance evaluations. It is found out that there is improvement on the motor constant square density for the proposed improved magnetic circuit through the best fit double stator with thick pole shoe by about 83.66% greater than that of the conventional structure.
Single phase interior permanent magnet (IPM) motors are adopted in many low cost applications such as in fan, blowers, and other domestic appliances [
This paper presents the analysis on the magnetic circuit design of single stator and double stator and the improvement in the magnetic energy of the double stator with magnetic circuit design. Analysis on the variations of the mechanical parameter that changes the optimal magnetic energy in the air gap that contributes to the generation of torque characteristics of the all structures is presented. Finite element analysis (FEA) is used as a numerical tool to derive the torque characteristics based on various combinations of taper parameters. The analysis result shows that minimum value of total harmonic distortion (THD) is found by optimizing the dimensions of the width of slot and that of the rotor. Also it is found that with reducing height of stator teeth a symmetrical torque waveform is evolved. The analysis is evaluated based on the value of the minimum total harmonic distortion (THD), the maximum fundamental torque
Figure
Parameters varied in this investigation.
Property | Values |
---|---|
Remanent flux density, |
1.28–1.32 |
Coercivity, |
>923 |
Intrinsic coercivity, |
>955 |
BH max, kJ/m3 | 318–342 |
Operating temperature, |
20°C to 120°C |
Conventional SSIPM. (a) Structural configurations; (b) fabricated SSIPM motor.
It comprises of a stationary stator and the rotational rotor that moves to develop the torque. With variety in design structure available in the literature, the above structure shows the conventional design with an outside stationary rotor and an inside cylindrical rotor coupled to the output shaft. The stator comprises of set of energised copper coils in succession to generate the magnetic flux. The stator flux interacts with the rotor, which is mounted inside the rotor in such a way that it can turn to align itself with the fields generated by the coils. This full alignment force generates torque, turning the rotor so that it moves the load through the shaft.
Figure
Magnetic circuit analysis of the SSIPM. (a) Magnetic flux flow path; (b) equivalent magnetic circuit flow.
The motivation on the introduction of magnetic circuit in the rotor part of the single stator interior permanent magnet (SSIPM) structure is proposed in this section. The design improvements in the magnetic circuit are highly influenced by the property of the material that is involved in the energy conversion process and also the effective area of energy conversion. From the first principles of magnetism, the reluctance in a magnetic circuit is given as
The reluctance magnetic circuit from the conventional single stator structure is converted to dual magnetic circuit using the double stator topology wherein the field magnetomotive force (mmf) is established through coil (
The rotor leakage flux from the SSIPM is catered with the introduction of another stator structure inside the machine, known as double stator interior permanent magnet (DSIPM) motor. It has two stators known as an outer and inner stator. Theoretically, this two magnetic circuits arrangement provides higher torque production compared to single stator since two air gaps are provided in between stator and rotor. Based on the magnetic equivalent circuit of this model, the flux has to go through 2
Magnetic circuit analysis of the DSIPM. (a) Magnetic flux flow path; (b) equivalent magnetic circuit flow.
However, there is a large area of ferromagnetic material on the rotor part that affects the flux through any cross section of rotor magnetic circuit. The value of
This variation in the magnet in this investigation is classified to be of the DSIPM with thin pole shoe and DSIPM with thick pole shoe. The resultant magnetic circuit reluctance value is as shown in
The features of the double stator thin pole shoe configurations with series magnetic circuit topology include the influence on the magnetic energy in the air gap that is affected by the permanent magnet area. The magnetic energy in the air gap can be improvised by having thinner pole shoe to reduce the reluctance torque value (Figure
Magnetic circuit analysis of the DSIPM with thin pole shoe. (a) Magnetic flux flow path; (b) equivalent magnetic circuit flow.
In this configuration with the series magnetic circuit, the permanent magnet width and height values are interchanged with fixed magnet volume to increase the effective area between permanent magnet and pole shoe. The magnetic energy improvement in the airgap can be achieved with the introduction of thinner magnet and increasing the pole shoe contact area (Figure
Magnetic circuit analysis of the DSIPM with thick pole shoe. (a) Magnetic flux flow path; (b) equivalent magnetic circuit flow.
The additional air gap reluctance between the stator and rotor influence the improvement in the torque density values. However the design has to be optimized in order to minimize the effect of radial pull. Also the construction of this type of structures using the double stator topology is quite challenging. The analysis of the proposed magnetic circuit by the variations in the various mechanical parameters is essential to have a comprehensive analysis of the results. The parameters used in this investigations include the width of outer stator (
In order to facilitate the torque characteristics of single phase DC permanent magnet motor based on the magnetic circuit design finite element analysis (FEA) is employed to predict the magnetic distribution. Finite element analysis (FEA) is used to compute the magnetic characteristics, but this necessitates a package and more time for modeling the motor and is used extensively by researchers in machine design. Most of them use computational tools to demonstrate the first hand information on the property of the machine [
The nodal force
Figure
Mesh setting inside the FEA. (a) Mesh of the design; (b) six layers of mesh in the air gap set for FEA.
Magnetic circuit analysis using FEA.
The torque characteristic of interior permanent magnet motor is compared through values of maximum torque (
Methodology in the magnetic circuit evaluation strategy.
Table
Parameters varied in this investigation.
SSIPM | DSIPM | DSIPM with thin pole shoe | DSIPM with thick pole shoe |
---|---|---|---|
|
|
|
|
Values of taper parameters used in the simulation.
Single stator topology (SSIPM) | Double stator topology (DSIPM) | ||
---|---|---|---|
Parameter | Range of values | Parameter | Range of values |
|
54°, 52°, 50°, 48°, 46° |
|
46°, 48°, 50°, 52°, 54° |
|
54°, 52°, 50°, 48°, 46° |
|
46°, 48°, 50°, 52°, 54° |
|
0.5, 1.0, 1.5, 2.0, 2.5 |
|
46°, 48°, 50°, 52°, 54° |
|
2.5 |
|
46°, 48°, 50°, 52°, 54° |
|
0.5, 1.0, 1.5 |
|
0.5, 1.0, 1.5 |
— | — |
|
0.5, 1.0, 1.5 |
— | — |
|
0.5, 1.0, 1.5 |
— | — |
|
0.5, 1.0, 1.5 |
The double stator topology involves two taper parameters, namely, outer stator taper (
For each of the combinations from Table
Selection of min. THD, max.
|
|
|
THD | |
---|---|---|---|---|
SSIPM |
|
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DSIPM |
|
|
|
|
|
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DSIPM with thin pole shoe |
|
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DSIPM with thick pole shoe |
|
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Values of
Evaluation type | SSIPM | DSIPM | DSIPM with thin pole shoe | DSIPM with thick pole shoe | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
|
THD % |
|
|
|
THD % |
|
|
|
THD % |
|
|
|
THD % | |
Min THD | 0.97 | 0.008 | 0.566 | 57.88 | 1.308 | 0.0120 | 0.648 | 91.77 | 1.045 | 0.041 | 0.852 | 30.71 | 2.01 | 0.2325 | 1.60 | 42.56 |
Max |
1.13 | 0.016 | 0.699 | 70.09 | 1.306 | 0.0195 | 0.809 | 101.12 | 1.583 | 0.072 | 1.169 | 39.99 | 2.08 | 0.2303 | 1.65 | 43.37 |
Max |
1.58 | 0.016 | 0.671 | 92.74 | 2.322 | 0.0335 | 0.661 | 148.14 | 2.352 | 0.064 | 1.1563 | 67.54 | 2.94 | 0.3512 | 1.58 | 61.19 |
Min |
0.909 | 0.002 | 0.413 | 86.46 | 1.397 | 0.0084 | 0.711 | 107.72 | 1.224 | 0.004 | 0.8086 | 51.06 | 1.36 | 0.0731 | 1.07 | 48.53 |
Figure
Choice on the best fit value of
The fabricated best fit DSIPM with thick pole shoe for the same size and volume as that of the fabricated SSIPM is as shown in Figure
Fabricated best fit DSIPM with thick pole shoe motor. (a) Inner coil; (b) rotor; (c) assembled structure.
The equipment arrangement for static torque measurement setup is shown in Figure
Equipment setup for torque measurement. (a) Block representation; (b) experimental setup.
Figure
Measurement characteristics of the fabricated motor (a) SSIPM with thick pole shoe. (b) DSIPM with thick pole shoe.
For final comparison, motor constant square density
Comparative evaluation of various structures of the IPM.
Parameters | SSIPM | DSIPM | DSIPM with thin pole shoe | DSIPM with thick pole shoe | Reference [ | ||
---|---|---|---|---|---|---|---|
Numerical | Measurement | Numerical | Numerical | Numerical | Measurement | Numerical | |
|
6 | 6 | 6 | 6 | 6 | 6 | 4 |
|
3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 6.25 |
|
4.75 | 4.75 | 4.75 | 4.75 | 4.75 | 4.75 | 4.75 |
|
0.65 | 0.6 | 0.64 | 0.852 | 1.60 | 1.68 | 0.8 |
|
0.108 | 0.1 | 0.106 | 0.142 | 0.267 | 0.28 | 0.2 |
|
2.28 | 2.1 | 2.23 | 2.98 | 5.62 | 5.89 | 16.84 |
|
10.8 | 10 | 10.6 | 14.2 | 26.7 | 28 | 0.02 |
|
2.45 | 2.1 | 2.36 | 4.24 |
|
|
8.42 |
Interior permanent magnet single phase motor based on improvement of magnetic circuit is comprehensively investigated. The torque components for the various proposed magnetic topology are designed and compared to derive the best structure. The optimal parameters value is derived based on analysis using FEA. The fundamental torque for the best fit DSIPM with thick pole shoe exhibits double the torque value compared to conventional magnetic circuit due to the series magnetic circuit. The motor constant square density shows a performance improvement of 85.5% for the best fit DSIPM with thick pole shoe better compared to the conventional magnetic circuit of the SSIPM. The proposed magnetic circuit structure is fabricated and experimentally evaluated.
The authors declare that there is no conflict of interests regarding the publishing of this paper.