Study on the Design Process of the Spoke Type Permanent ......M ag n etiz oY k Rotor Core...
1
Sung Gu Lee 1 , Jaenam Bae 2 Kwangsoo Kim 3 and Won-Ho Kim 4 1 Department of Electrical Engineering, Dong-A University, Busan, Korea 2 Department of Electrical Engineering, Dongyang mirae University, Seoul, Korea 3 Department of Mechatronics Engineering, Halla University, Wonju, Korea 4 Department of Energy IT, Gachon University, Seongnam, Korea Study on the Design Process of the Spoke Type Permanent Magnet Synchronous Motor Considering Magnetization Performance Demagnetization of PMs directly leads to deterioration of the performance characteristics of PMSM. Therefore, it is common for the design process of PMSM to include consideration of demagnetization of PMs. In this paper, we propose the design process of spoke type PMSM considering not only the demagnetization performance of PM but also magnetization performance directly related to mass production. Unlike other motors, spoke type PMSM is difficult to obtain magnetization performance suitable for mass production unless magnetization performance is considered in the design stage. Therefore, the design process proposed in this paper will be a good guide for engineers designing spoke type PMSM in real industry. Finally, in order to verify the validity of the proposed design process, a real motor was fabricated and its performance was evaluated by experiments. Abstract 1. Introduction An important index in determining the performance of a permanent magnet synchronous motor (PMSM) is the maximization of using the permanent magnet (PM) inserted in its rotor. Thus, a process that verifies the demagnetization of PM is generally included in a design process of PMSM. However, the magnetization, which is also one of the important indexes in the design process, has not been much considered. It is due to the fact that most of the mass produced motors are categorized as surface permanent magnet synchronous motors (SPMSMs) and interior permanent magnet synchronous motors (IPMSMs) and the whole magnetization of these motors can be performed using properly designed magnetization yokes without any major trouble. The spoke type PMSM is a shape that maximizes the surface area of PM vertically inserted in a rotor core. Also, studies on SPMSM have been actively performed because of increasing more power density than that of IPMSM. However, it plays disadvantage to the magnetization performance in a rotor structure for improving motor performances. Consequently, the whole magnetization could not possibly be performed depending on models of the spoke type PMSM and it requires a new process that has not been considered in the conventional design process of PMSM. Thus, a new design process of the spoke type PMSM that considers the magnetization performance is proposed in this study. 2. General Magnetization Methods of PMSM As illustrated in Fig. 1, the magnetization method of PMSM is usually divided into three different types. First, it is a single supply magnetization method that magnetizes PM and assembles it as a single product. Second, it is a yoke magnetization method that first assembles un-magnetized PM on a rotor and magnetizes it in an exclusive yoke. Third, it is an in-situ magnetization method that applies the magnetization through applying magnetization currents to the stator coil after assembling the rotor with un- magnetized PM on the stator. 3. Decreasing Factors of the Magnetization Performance in the Spoke type PMSM 4-1. Indicator of the magnetic saturation caused by the magnetization flux 4-2. Design process with the magnetizing performance In this paper, we proposed a new design process considering magnetization performance of spoke type PMSM. For this purpose, we have defined an indicator that can consider the level of magnetic saturation of the rotor core by the magnetization flux, which is the biggest cause of the deterioration of the magnetization performance. Through the design process using the defined indicator, we were able to design a spoke type PMSM with high magnetization performance and excellent motor performance. 9. Conclusion Mon-Mo-Po1.07-08 [83] Explanation Single Magnetization Yoke Magnetization In-situ Magnetization Conceptual diagram of flowchart Magnetization Performance Very High High Low (It is very difficult to be fully magnetized) Mass production Very low (The assembly process becomes complicated due to the magnetic force between magnetized magnets and the magnetic force between the magnet and the core.) High Very High Rotor Assembly Coil Magnetization Current Magnet Motor Assembly Rotor Assembly Motor Assembly Magnetization Yoke Rotor Assembly Motor Assembly Stator Core Item ① Separation of magnetization flux ② Magnetic saturation of the rotor core due to length of PM ③ Leakage magnetization flux according to rotor shapes Cause of degradation Solution Magnet Magnetization Yoke Rotor Core Magnetization Yoke Rotor Core 100% 50% Magnet Magnetic Flux Magnetic Flux 50% Magnet (a) Conventional SPMSM (b) Spoke type PMSM Magnetization Coil Magnetization Yoke Magnetization Flux Magnetized PM Non-magnetized PM (a) Magnetic flux density in magnetization (b) Magnetic air gap length according to permanent magnet position Bridge Magnet Rotor Core Position locking projection Bridge Position locking projection Magnetization Non-magnetization Magnet Rotor Core (a) Rotor core shapes of the spoke type PMSM (b) Magnetization analysis result with bridge and projection Magnetization Un-magnetization Magnetization analysis result without bridge and projection Magnetization Yoke Coil Magnet Rotor Core 10 8 6 4 2 B [tesla] Rotor Core 2π P Magnet Magnetization Yoke ① ② L 2 L 1 Magnetization Non-magnetization L 1 L 2 > Magnetization Yoke Rotor Core π P Magnet W c T m 2 π P Fig.1 Analysis model for the magnetic saturation The magnetic saturation of the rotor core caused by the magnetic flux is increased according to increases in the length of the inserted PM. The magnetic saturation of the rotor core can be influenced by the design parameter of the spoke type PMSM. In order to investigate the major factors that affect the magnetic saturation, the analysis model presented in Fig. 1 was used. where P is the number of poles, T m is the thickness of PM, and R is the radius of the rotor core. Here, the scale of the magnetic flux density required for the magnetization of PM is assumed as B m . As shown in Fig. 1, it is assumed that all magnetization fluxes, which pass through PM, are passing through the upper section of the rotor core. In the condition that all sections of PM are to be magnetized, the average value of the magnetic flux density at the upper section of the rotor core is determined as Eq. (2). = = 2 2− where L m is the length of PM, B c is the average magnetic flux density in the upper section of rotor core during the magnetization process. = = 2 2− The parameter, k, defined in Eq. (3) is a magnetic saturation indicator in the rotor core that determines the level of magnetic saturation caused by the magnetization flux in the spoke type PMSM. ······················(2) ······················(3) Design parameters that affect the magnetization performance of the spoke type PMSM also influence the motor performance such as a torque constant. Fig. 2 shows the analysis results of the magnetization and motor performances according to the values of the indicator, k. The relationship between the magnetization performance and the motor performance of the spoke type PMSM represents an inverse proportion. As a result, the spoke type PMSM that is designed by considering the motor performance only without considering the magnetization performance becomes a meaningless design in terms of mass production. = 1− 2 = 2 2− ······················(1) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.5 2 2.5 3 3.5 4 4.5 5 Magnetization Ratio [%] Torque Constant [Nm/A] Indicator k Motor Performance Magnetization Performation Fig.2 Comparison between the motor and magnetiz ation performances according to the indicator, k Start Motor Sizing Design Select number of poles & slots Design of detailed shape of rotor and stator core Was the motor performance satisfied? Was the demagnetization performance satisfied? END Target Performance Design of PM size by using Eq.(3) Was the magnetization performance satisfied? Yes No Yes Yes No No No Yes Try ≤ 10 Try ≤ 10 No Yes No Try ≤ 10 Yes The proposed design process makes possible to design spoke type PMSMs that allow the high productivity in mass production and represent excellent motor performances. The design targets of the proposed design process are to highly achieve magnetization performance, motor performance, such as torque constant and efficiency, and demagnetization performance. In addition, it makes possible to add cost as one of the design targets. In the design process, whether or not the selected specification achieves the design target is confirmed using FEA analysis. Here, the magnetization performance is to be verified first using the magnetization analysis after design of detailed shape of core. As the magnetization performance is satisfied, the demagnetization performance is also verified using the demagnetization analysis. If the target is not achieved in each stage, the design process should be returned to the stage of the PM size. Then, the target performance is to be verified again. If the target evaluation is failed by about 10 times repeatedly, the design process should be returned to the stage of determining the number of poles rather than the stage of the PM size in order to redefine the number of poles. It is due to the fact that the number of poles largely affects the motor and magnetization performances. Fig.3 Proposed design process of the spoke type PMSM Fig. 4 Rotor core of fabricated spoke PMSM Parameter Unit Spec. Number of poles - 8 Number of slot - 12 Diameter of stator mm 104 Diameter of rotor mm 67.2 Air gap length mm 0.4 Length of PM mm 18.5 Thickness of PM mm 8.5 Width of bridge mm 0.75 Stack length mm 23 Table 1. Specifications of Fabricated motor 2) Experimental Test 1) Fabricated motor and yoke specifications and pictures Table 2. Specifications of Magnetization yoke Parameter Unit Spec. Number of slot - 8 Air gap length mm 0.7 Diameter of yoke core mm 150 Turns of magnetization coil mm 11 Stack length mm 43 Rotor Core Magnet Insulating paper Yoke Core Upper & Lower Cover Coil Tub for cooling water Terminal box Rotor Assay Magnetization Yoke 90% 92% 94% 96% 98% 100% 8 8.5 9 9.5 10 10.5 11 Magnetization Ratio Magnetization Current [kA] Fig. 5 Fabricated magnetization yoke (b) Details of the yoke (a) Magnetization test Fig. 6 Analysis result of 3D FEA (99.2%@10kA) Fig. 7 Magnetization experiment results 3D FEA result (99.2%@10kA) Magnetization Non-magnetization Magnetization Yoke Magnet Coil Rotor Core 5. Verification
Transcript of Study on the Design Process of the Spoke Type Permanent ......M ag n etiz oY k Rotor Core...
Sung Gu Lee1, Jaenam Bae2 Kwangsoo Kim3 and Won-Ho Kim4
1Department of Electrical Engineering, Dong-A University, Busan, Korea2Department of Electrical Engineering, Dongyang mirae University, Seoul, Korea
3Department of Mechatronics Engineering, Halla University, Wonju, Korea4Department of Energy IT, Gachon University, Seongnam, Korea
Study on the Design Process of the Spoke Type Permanent Magnet
Synchronous Motor Considering Magnetization Performance
Demagnetization of PMs directly leads to deterioration of the performance characteristics of PMSM. Therefore, it is common for the design
process of PMSM to include consideration of demagnetization of PMs. In this paper, we propose the design process of spoke type PMSM
considering not only the demagnetization performance of PM but also magnetization performance directly related to mass production. Unlike
other motors, spoke type PMSM is difficult to obtain magnetization performance suitable for mass production unless magnetization
performance is considered in the design stage. Therefore, the design process proposed in this paper will be a good guide for engineers
designing spoke type PMSM in real industry. Finally, in order to verify the validity of the proposed design process, a real motor was fabricated
and its performance was evaluated by experiments.
Abstract
1. Introduction
An important index in determining the performance of a permanent magnet synchronous motor (PMSM) is the maximization of using the permanent magnet (PM) inserted in its
rotor. Thus, a process that verifies the demagnetization of PM is generally included in a design process of PMSM. However, the magnetization, which is also one of the important
indexes in the design process, has not been much considered. It is due to the fact that most of the mass produced motors are categorized as surface permanent magnet
synchronous motors (SPMSMs) and interior permanent magnet synchronous motors (IPMSMs) and the whole magnetization of these motors can be performed using properly
designed magnetization yokes without any major trouble.
The spoke type PMSM is a shape that maximizes the surface area of PM vertically inserted in a rotor core. Also, studies on SPMSM have been actively performed because of
increasing more power density than that of IPMSM. However, it plays disadvantage to the magnetization performance in a rotor structure for improving motor performances.
Consequently, the whole magnetization could not possibly be performed depending on models of the spoke type PMSM and it requires a new process that has not been
considered in the conventional design process of PMSM. Thus, a new design process of the spoke type PMSM that considers the magnetization performance is proposed in this
study.
2. General Magnetization Methods of PMSM
As illustrated in Fig. 1, the magnetization
method of PMSM is usually divided into three
different types. First, it is a single supply
magnetization method that magnetizes PM
and assembles it as a single product.
Second, it is a yoke magnetization method
that first assembles un-magnetized PM on a
rotor and magnetizes it in an exclusive yoke.
Third, it is an in-situ magnetization method
that applies the magnetization through
applying magnetization currents to the stator
coil after assembling the rotor with un-
magnetized PM on the stator.
3. Decreasing Factors of the Magnetization Performance in the Spoke type PMSM
4-1. Indicator of the magnetic saturation caused by the magnetization flux
4-2. Design process with the magnetizing performance
In this paper, we proposed a new design process considering magnetization performance of spoke type PMSM. For this purpose, we have defined an indicator
that can consider the level of magnetic saturation of the rotor core by the magnetization flux, which is the biggest cause of the deterioration of the
magnetization performance. Through the design process using the defined indicator, we were able to design a spoke type PMSM with high magnetization
performance and excellent motor performance.
9. Conclusion
Mon-Mo-Po1.07-08 [83]
Explanation Single Magnetization Yoke Magnetization In-situ Magnetization
Conceptual
diagram of
flowchart
Magnetization
PerformanceVery High High Low
(It is very difficult to be fully magnetized)
Mass productionVery low
(The assembly process becomes complicated due to the
magnetic force between magnetized magnets and the
magnetic force between the magnet and the core.)
High Very High
Rotor Assembly
CoilMagnetization
Current
Magnet
Motor Assembly
Rotor Assembly
Motor Assembly
Magnetization Yoke
Rotor Assembly
Motor Assembly
Stator Core
Item ① Separation of magnetization flux②Magnetic saturation of the rotor core
due to length of PM
③ Leakage magnetization flux according
to rotor shapes
Cause of
degradation
Solution
Magn
et
Magnetization Yoke
Rotor Core
Magnetization Yoke
Rotor Core100% 50%
Magnet
Magnetic
Flux
Magnetic
Flux
50%
Magn
et
(a) Conventional SPMSM (b) Spoke type PMSM
Magnetization
Coil
Magnetization
Yoke
Magnetization
Flux
Magnetized PMNon-magnetized PM
(a) Magnetic flux density in
magnetization
(b) Magnetic air gap length according
to permanent magnet position
Bridge
Magnet
Rotor
Core
Position locking
projection
BridgePosition locking
projection
Magnetization
Non-magnetization
Magn
et
Rotor
Core
(a) Rotor core shapes of the
spoke type PMSM(b) Magnetization analysis result
with bridge and projection
Magnetization
Un-magnetization
Magnetization analysis result without bridge and projection
Magnetization
Yoke
Coil
Magn
et
Rotor
Core
10
8
6
4
2
B [tesla]
Rotor Core
2πP
Magn
et
Magnetization
Yoke
①
②
L2L1
Magnetization
Non-magnetization
L1 L2>
Magnetization
Yoke
Rotor Core
πP
Ma
gn
et
Wc
Tm
2
πP
Fig.1 Analysis model for the
magnetic saturation
The magnetic saturation of the rotor core caused by the magnetic flux is increased according to increases in the length of the inserted
PM. The magnetic saturation of the rotor core can be influenced by the design parameter of the spoke type PMSM. In order to
investigate the major factors that affect the magnetic saturation, the analysis model presented in Fig. 1 was used.
where P is the number of poles, Tm is the thickness of PM, and R is the radius of the rotor core.
Here, the scale of the magnetic flux density required for the magnetization of PM is assumed as Bm. As shown in Fig. 1, it is assumed that all
magnetization fluxes, which pass through PM, are passing through the upper section of the rotor core. In the condition that all sections of PM
are to be magnetized, the average value of the magnetic flux density at the upper section of the rotor core is determined as Eq. (2).
𝐵𝑐 =𝐵𝑚𝐿𝑚𝐿𝑠𝑊𝑐𝐿𝑠
=2𝑃𝐵𝑚𝐿𝑚𝑅𝜋 2 − 𝑇𝑚
where Lm is the length of PM, Bc is the average magnetic flux density in the upper section of rotor core during the magnetization process.
𝑘 =𝐵𝑐𝐵𝑚
=2𝑃𝐿𝑚
𝑅𝜋 2 − 𝑇𝑚
The parameter, k, defined in Eq. (3) is a magnetic saturation indicator in the rotor core that determines the level of magnetic
saturation caused by the magnetization flux in the spoke type PMSM.
······················(2)
······················(3)
Design parameters that affect the magnetization performance of the spoke type PMSM also influence the motor performance
such as a torque constant. Fig. 2 shows the analysis results of the magnetization and motor performances according to the
values of the indicator, k. The relationship between the magnetization performance and the motor performance of the spoke
type PMSM represents an inverse proportion. As a result, the spoke type PMSM that is designed by considering the motor
performance only without considering the magnetization performance becomes a meaningless design in terms of mass
production.
𝑊𝑐 = 𝑅𝜋
𝑃1 −
𝑇𝑚2
= 𝑅𝜋
2𝑃2 − 𝑇𝑚 ······················(1)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.5 2 2.5 3 3.5 4 4.5 5
Ma
gn
eti
za
tio
n R
ati
o [
%]
To
rqu
e C
on
sta
nt
[Nm
/A]
Indicator k
Motor Performance
Magnetization Performation
Fig.2 Comparison between the motor and magnetiz
ation performances according to the indicator, k
Start
Motor Sizing Design
Select number of poles &
slots
Design of detailed shape
of rotor and stator core
Was the motor performance
satisfied?
Was the demagnetization
performance satisfied?
END
Target Performance
Design of PM size
by using Eq.(3)
Was the magnetization
performance satisfied?
Yes
No
Yes
Yes
No
No
No
Yes
Try ≤ 10
Try ≤ 10
No
Yes
No
Try ≤ 10
Yes
The proposed design process makes possible to
design spoke type PMSMs that allow the high
productivity in mass production and represent
excellent motor performances. The design targets of
the proposed design process are to highly achieve
magnetization performance, motor performance, such
a s t o r q u e c o n s t a n t a n d e f f i c i e n c y, a n d
demagnetization performance. In addition, it makes
possible to add cost as one of the design targets. In
the design process, whether or not the selected
specification achieves the design target is confirmed
using FEA analysis. Here, the magnetization
performance is to be verified first using the
magnetization analysis after design of detailed shape
of core. As the magnetization performance is satisfied,
the demagnetization performance is also verified
using the demagnetization analysis. If the target is not
achieved in each stage, the design process should be
returned to the stage of the PM size. Then, the target
performance is to be verified again. If the target
evaluation is failed by about 10 times repeatedly, the
design process should be returned to the stage of
determining the number of poles rather than the stage
of the PM size in order to redefine the number of
poles. It is due to the fact that the number of poles
largely affects the motor and magnetization
performances.
Fig.3 Proposed design process of the spoke
type PMSM
Fig. 4 Rotor core of
fabricated spoke PMSM
Parameter Unit Spec.
Number of poles - 8
Number of slot - 12
Diameter of stator mm 104
Diameter of rotor mm 67.2
Air gap length mm 0.4
Length of PM mm 18.5
Thickness of PM mm 8.5
Width of bridge mm 0.75
Stack length mm 23
Table 1. Specifications of Fabricated motor
2) Experimental Test
1) Fabricated motor and yoke specifications and pictures
Table 2. Specifications of Magnetization yoke
Parameter Unit Spec.
Number of slot - 8
Air gap length mm 0.7
Diameter of yoke core mm 150
Turns of magnetization coil mm 11
Stack length mm 43
Rotor
Core
Magnet
Insulating
paper
Yoke CoreUpper & Lower
Cover
Coil
Tub for cooling waterTerminal box
Rotor AssayMagnetization
Yoke
90%
92%
94%
96%
98%
100%
8 8.5 9 9.5 10 10.5 11
Magn
etiz
ati
on
Rati
o
Magnetization Current [kA]
Fig. 5 Fabricated magnetization yoke
(b) Details of the yoke(a) Magnetization test
Fig. 6 Analysis result of 3D FEA (99.2%@10kA) Fig. 7 Magnetization experiment results
3D FEA result
(99.2%@10kA)
Magnetization
Non-magnetizationMagnetization
Yoke
Magnet
CoilRotor
Core
5. Verification
