Thrust PM ring

Radial PM

Iron disk

C-shapedstator core

Windings

Magnetizeddirection

Rotor

Stator

0

10

20

30

40

50

0 0.5 1 1.5 2

Eff

icie

ncy

[%]

Torque current iq[A]

1000rpm 2000rpm 3000rpm

Powder core Bulk core

+25％

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5 3 3.5 4

Torq

ue[m

Nm

]

Torque current iq[A]

1000rpm 2000rpm 3000rpm

Powder coreBulk core

Powder

core

Bulk

core1000 20.1 20.8

2000 19.4 17.6

3000 18.6 13.1

Rotational

speed[rpm]

kT[mNm/A]

0

5

10

15

1000 1500 2000 2500 3000

Pow

er co

nsu

mption[W

]

Total Copper loss Iron loss

回転速度[rpm]

圧粉

回転速度[rpm]

Suspension

Rotational speed[rpm]

Motor Total

0

5

10

15

Pow

er co

nsu

mption[W

]

Copper lossIron loss

Rotational speed[rpm]

Powdercore

Bulk core

1000 30002000 4000

-85％

0

5

10

15

Pow

er co

nsu

mption[W

]

Suspension Motor

回転速度[rpm]Rotatinal speed[rpm]

1000 2000 3000 4000

Bulk core

Powder core

-74％

Efficiency improvement of a bearingless motor with powder iron core D. Kanehara*, J. Asama*, T. Oiwa, A. Chiba** (*Shizuoka University, Japan **Tokyo Institute of Technology, Japan)

Introduction

□A motor which combines magnetic bearing function

and rotation in the same unit

□Application：Chemical pumps, Blood pumps, etc

□Proposed a compact bearingless motor (fig.1)

□Succeeded in stable suspension and rotation

□Problem：Motor loss is large ⇒ Low efficiency (fig.3)

Proposed bearingless motor

□Improvement of efficiency with powder iron core

Fig.1 Proposed structure

□Radial direction：Suspension force is generated by

superposition of PM flux and suspension flux

□Radial position (suspension force) is actively regulated

□Axial/tilting direction：Passively stable with magnetic

attractive force

fig.2 Suspension principle (b) Tilting direction (c) Axial direction

Iron loss reduction

□Powder iron core is material which compresses

insulated iron powder

□ High electrical resistance ⇒ Reduced eddy current

⇒ Reduced iron loss

□Use powder iron core for stator core of proposed

bearingless motor

□Stator core is molded with epoxy resin

⇐ Because powder iron core is very brittle

□Rotor motion range in radial direction is ±0.25mm

fig.5 Fabricated test machine

fig.4 Powder iron core

Iron powder (φ 100μm)

Resin binder

Insulating layer

Conclusion □It is effective to use powder iron core for proposed

bearingless motor to improve efficiency

◎ No wear particles, Lubricant-free

PM flux

Suspension flux Suspension force

(a) Radial direction Restoring torque Restoring force

Test machine loss (with bulk core)

fig.3 Power consumption

□Motor loss is 70% or more of total loss

□Iron loss is 60% of motor loss ⇐ Eddy current

Powder iron core performance

□Total：74％ reduction (Motor loss reduction is large)

□Iron loss：85％ reduction ⇒ Eddy current is reduced

fig.6 Measured power consumption

x

z

y

Stator Rotor

φ 45

Stator core (Powder iron)

Epoxy resin

Gap sensor

Thrust PM ring

Sensor target

Radial PM

Iron disk

Frame

(a) Real view (b) Schematic view

10

×Low permeability than bulk

⇒ Torque and force are reduced?

⇒ Investigation of motor

performance with powder iron core

(b) Only motor (a) Total

□Torque (kT[mNm/A]) at 3000rpm ： Powder ＞ Bulk

⇐ Eddy current works as brakes

□Efficiency：25％ improvement (at 3000rpm)

fig.7 Measured torque fig.8 Efficiency

□Rotor：Two iron disks (with PM) and a PM ring

□Stator：C-shape ⇒ Reduction motor height

□Two kind of windings

：Suspension and motor are combined

Ptotal = Poutput+ Pmech+ Pcopper+ Piron

Piron = Physteresis+ Peddy current

No load Frictionless

Increase

Y. Yamamoto1, J. Asama1,

BACKGROUND AND OBJECTIVE

1 Shizuoka University, Japan.

FINAL GOAL OF RESEARCH

Realization of precise positioning bearingless motor

PRINCIPLE OF RADIAL SUSPENSION FORCE AND DIRECTION ERROR

OBJECTIVE OF THIS PRESENTATION

Investigation of the optimal two-pole suspension winding configuration for miniaturization of an error angle (Fig.3).

Application possibility: Micro endmilll cutting Z,θZ

X,θX Y,θY

Rotor

Stator

Work

Problem of conventional cutting axial runout

Heterogeneous cutting force

Fig.1 Concept of application

PROPOSED STRUCTURE

Bearingless motor

5 DOF control BelM_Unit1 and BelM_Unit2: X, Y, θX, θY

Thrust control bearing(TMB): Z

8-pole homo-polar bearingless motor Permanent magnet-free (on rotor)

Realization of Robust rotor

Fig.3 Principle of radial suspension force

(a) Symmetrical (b) Asymmetrical

Undersirable Force Interference (Fig.3)

Affects the control system

(a) At a symmetrical position

Suspension force Fx

Suspension force Fx and Fyx

(b) At an asymmetrical position

)(tan 1

x

yx

eF

F

Distributed winding

24 slots

Error angle

Position of endmill Cutting force

Measurement and control Realization of Precision cutting

Sine wave MMF

X

YRotor Suspension flux

Radial control

stator

Bias flux

DenseSparse

Suspension

forceF

θe

Fx

Fyx

X

YError angle Suspension force

BelM_Unit1 BelM_Unit2Thrust magnetic bearing

Motor and radial control stator

Thrust permanent magnet

Thrust control stator

Shaft4-pole rotor core

Thrust rotor core

x

y

z

Fig.2 Proposed structure of homo-polar bearingless motor

00.2

0.40.6

0.81

0

0.01

0.02

00.2

0.40.6

0.81

L -

RM

S va

lue

of

err

or

angl

e °

K -

Minimum value (K-0.4, L=0.1)

INVESTIGATION OF OPTIMAL SUSPENSION WINDING CONFIGURATION

CONCLUSIONS

Suspension winding configuration of Model 2 is optimal.

3D-FEM analysis results agree well with theoretical calculated results.

Production test model in near future.

Fig.4 Single-layer winding (Model 1)

THEORETICAL CALCULATION

dA

g

RlFx )cos()(

2

2

2

0

0

dA

g

RlFyx )sin()(

2

2

2

0

0

Calculated error angle θe

Calculated magnetomotive force distribution A(φ) Fx, Fyx ,θe

μ0: the permeability of free space

g0: the air gap length R: the mean air-gap radius l : the stack length

Single-layer winding model

Double-layer winding model (Model 2)

U-phase 1 A V-phase -0.5 A W-phase -0.5 A

Slot No.2,3: 1 turn

Slot No.1,4: M turn (M=0, 0.1, 0.2, …, 0.9, 1)

Fig.5 RMS value of error angle

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

RM

S v

alu

e o

f err

or

angle

°

Winding ratio M -

Optimal winding ratio (M=1)

U-phase 1 A V-phase -0.5 A W-phase -0.5 A

U

WV

1

1

2

2

3

3

4

4

V

U

W

1

1

2

2

3

3

4

4

1

1

2

2

3

3

4

4

1 turn1 turn

5 6 87

5867

5

6

7

8

57

8 6

8

5

6

75

6

7

8

K turn

L turn

Fig.7 RMS value of error angle

Fig.6 Double-layer winding (Model 2)

Slot No.1~4: 1 turn

Slot No.5,6: K turn

(K,L=0, 0.1, 0.2, …, 0.9, 1) Slot No.7,8: L turn

Fig.8 Comparison of Model 1 and Model 2

U

W

W V

V

U

1

1

2

2

3

3

4

4

V

U

W1

1

2

2

3

3

4

4

1

1

2

2

3

3

4

4

M turn1 turn

M turn

1 turn

M turn

1 turn

RMS value of Model 2: 95.5% decreased against RMS value of Model 1

-2

-1

0

1

2

0 15 30 45 60 75 90

Err

or angle

°

Rotation angle °

Model 1 (M=1)

Model 2(K=0.4, L=0.1)

99.5%

RMS 1.11°

RMS 0.005°

3D-FEM ANALYSIS

-4

-2

0

2

4

6

0 15 30 45 60 75 90

Err

or angle

°

Rotation angle °

Model 1(theoretical calculation)

Model 1(FEM analysis)

Model 2(theoretical calculation)

Model 2(FEM analysis)

Fig.9 Comparison of theoretical

calculation and FEM analysis

Analyze error angle θe

Table.1 RMS value of Theoretical calculation

and FEM analysis

Calculation FEM

Model 1 1.11° 2.22°

Model 2 0.005° 0.300°

Certified validity of theoretical calculation

Design and Test Results

of a One-DOF Actively Positioned Bearingless Motor

Introduction

D.Watanabe*, J.Asama*, T.Oiwa*, A.Chiba** *Shizuoka University, Japan **Tokyo Institute of Technology, Japan

Configuration ＆ Drive Principle

Conclusions

Electromagnetic Analysis

・One three-phase inverter

・Position control(Z) ：d-axis current (id)

・Rotation(θz) ：q-axis current (iq)

q

d

w

v

u

i

i

θcosθsin

θsinθcos

2321

2321

01

3

2

i

i

i

・Radial direction(X,Y) ，Tilting direction(θX,θY)

Test Model

Stator

Rotor

Passive Magnetic Bearing

(PMB)

Motor

Coreless

Coil

Permanent

Magnet (PM)

Z

Y X

Yoke

Fig.2 Proposed model

N

S

N

S

S N N ○Small size

0

5

10

15

0 15 30 45 60

Torq

ue

(mN

m)

Rotation angle (˚)

0.0

0.5

1.0

1.5

0 15 30 45 60

Susp

enti

on

forc

e (N

)

Rotation angle (˚)

・Rated current ：0.25A

・Rated suspension force ：0.9N (Fig.6)

・Rated torque ：10mNm (Fig.7)

Y

X Z

U V

W

U

V

V

W

U

W

《Coreless coil》 《Motor PM》

Current

direction

Magnetization

direction

Y

X Z

《Coreless coil》 《Motor PM》

Z

Y X

《Motor U-phase》

Lorenz force

Magnetic flux Current

Suspension force

N

S

N

S

N

S

N

S

N

S

《Radial direction》 《Tilting direction》

Restoring

force

Restoring

torque

PMB

0θ

0i

1i

q

d

If , then

61i

61i

32i

w

v

u

0θ

1i

0i

q

d

If , then

21i

21i

0i

w

v

u

Transformation formula

Position control

Rotation

・Realize of one-DOF actively positioned bearingless motor

only one three-phase inverter.

PMB

(Fig.1)

(Fig.2)

・6-pole, 9-slot

・Coreless motor

《Proposed model》

Ave. 0.9N Ave. 10mNm

Displacement sensor

(Position Control)

70mm

55

mm

Displacement sensor

(Vibration measurement)

26

mm

Rotor

Fig.8 Prototype

Coreless

coil

PMB

Magnet

43.8mm

21

.5m

m

Fig.10 Stator

PM

49mm

PMB

Magnet

Frame

Fig.9 Rotor (Reverse)

・Axial length ：26mm (Fig.8)

・Rotor diameter ：49mm (Fig.9)

・Magnetic gap ：1.0mm

Drive test (No load)

Fig.3 Principle of position control

Fig.4 Principle of rotation

Fig.5 Principle of passive suspension

(Fig.3,4)

(Fig.5)

・2250rpm ： Resonance of radial direction

・3000rpm ： Axial 4μm Tilting 4.9mrad

Radial 0.07mm

(Fig.11,12)

Fig.6 Analysis result of suspension force Fig.7 Analysis result of torque

・2250rpm

Increase of oscillation

Friction loss

Copper loss

・3000rpm：0.14W

0.0

0.2

0.4

0.6

0.8

0 1000 2000 3000

振動振幅

3σ

mm

回転速度 rpm

Oscill

ation

am

plit

ud

e

3σ

(m

m)

0 1000 2000 3000

0

0.8

0.2

0.4

0.6 Radial direction (Y)

Axial direction (Z)

Resonance

Fig.11 Radial and axial oscillation

Rotation speed (rpm)

0

10

20

30

40

0 1000 2000 3000

振動振幅

3σ

mra

d

回転速度 rpm

0

40

10

20

30

Oscill

ation

am

plit

ud

e

3σ

(m

rad

)

0 1000 2000 3000

Tilting direction (θX)

Fig.12 Tilting oscillation

Rotation speed (rpm)

×Large size

(Fig.13)

Increase

0.0

0.5

1.0

1.5

2.0

0 500 1000 1500 2000 2500 3000

消費電力

W

回転速度 rpm

0

2.0

0.5

1.0

1.5

Pow

er

Consum

ptio

n (

W)

0 1000 2000 3000

Total

Copper loss

Fig.13 Power consumption

Rotation speed (rpm)

0.14W

《Motor W-phase》

Lorenz force Current Magnetic flux

Torque

《Motor V-phase》

・One-DOF actively positioned bearingless motor for cooling fan

is proposed.

・Rated suspension force is 0.9N, and rated torque is 10mNm.

・Axial, radial and tilting oscillation amplitude at 3000rpm are

4μm, 0.07mm, and 4.9mrad.

Coil

PM

Yoke

Cooling fan Application

・Required number of inverter

・One single-phase inverter

for magnetic bearing

・One three-phase inverter

for motor

・Position control : Z direction

One-DOF actively positioned

Motor Magnetic bearing +

Magnetic Bearing Motor

Coil Permanent

Magnet (PM)

Z

Y X Stator

Rotor

(Reference:Tokyo Institute of Technology)

Fig.1 One-DOF actively positioned magnetic bearing motor

U V

W

U

V

V

W

U

W

Torque

Z

Y X

Z θZ

r

Fabrication of a three-phase votage source inverter and its drive Y. Fujii, J. Asama

(Shizuoka University, Japan)

Outline of Inverter

Principle of Drive Circuit

Inverter control by PWM(pulse width modulation) control

Introduction

Fabrication of three-phase voltage source inverter and its drive circuit

Goal of Research

Conclusion

Amplitude of modulation wave

Control circuit: low electric system Drive circuit: high electric system 15V or-15V output by DC-DC converter

PWM(Pulse width modulation) Control

Fig.5. small amplitude of modulation wave

Interior of TLP250

1

2

3

4

CCV

0V

0V

GND 5

6

7

8

AMP

Fig.9. Fabricated Drive Circuit Fig.10. Confirmed Three Phase Wave

Fabrication of inverter and its drive circuit Confirmed Three-phase wave

Fig.2.Variable Load voltage by switching

Conventional AC motor control

Supply of AC by commercial power ×Variable frequency , ×Variable voltage

Solution

Variable voltage Variable frequency(VVVF) control Performance of inverter Important fabrication of drive circuit

Forward Convert Circuit: rectifier from AC to DC

Reverse Convert Circuit：from DC to AC

Control Circuit :transmission of PWM signal Drive Circuit：switching semiconductor device

Principle of behavior

Fig.1. Outline of Inverter

Forward convert circuitAC→DC

Inverter Main Circuit

Reverse convert circuitDC→AC

1Tr

2Tr

3Tr

4Tr

5Tr

6Tr

viui

wi

PWM Signal

Drive CircuitControl Circuit

<Example> focus on U-phase Tr1=ON Vu=E/2 Tr2=ON Vu=-E/2

viui

wi

6Tr

1Tr 3Tr5Tr

4Tr2Tr

2/E

2/E

Vu

Vv Vw

t

E/2

0

Tr1ON

Vu

Tr2ON Tr1ON Tr2ON Tr1ON

-E/2

Approximation sinusoidal wave by PWM

Comparison of carrier wave and modulation wave in control circuit In case of Modulation wave =Sinusoidal modulation wave Output of approximation sinusoidal wave

Fig.4. Principle of PWM control

es>ec→Vu=E/2 es<ec→Vu=-E/2

Fig.3. Carrier wave comparison

＋

－

PWM signal

Sinusoidal wave es

Carrier wave ec

ComparatorCarrier wave ecSinusoidal modulation wave es

Approximation sinusoidal wave

E/2

－E/20

Vu

EcES

t

t

tEc

ES

t

E/2

－E/2

0

Vu

Smaller amplitude of modulation wave than Fig.4. Amplitude of approximation sinusoidal wave Proportion to amplitude of modulation wave

Fig.6. Principle of drive circuit

ⅰ. PWM ON signal ⅱ. 6 and 7 pin Vo=15V ⅲ. VGE=15V→IGBT ON ⅳ. Start ICE

IGBT ON

Isolation by photocoupler

ⅰ. PWM OFF signal ⅱ. 6 and 7 pin Vo=-15V ⅲ. VGE=-15V→IGBT OFF ⅳ. Stop ICE

IGBT OFF

Control Circuit

V0

PWM SignalV5

390

GND2

1

2

3

4

CCV

0V

0V

GND 5

6

7

8

PhotocouplerTLP250

V5DC-DC

ConverterOut In Stabilizaion

power

C

E

CEi

GEV

F. 10

k10

V15

G

V15GND1

ON Voltage

OFF Voltage

Gate resistance

IGBT

Isolation

Experiment of chopper circuit

-20

-14

-8

-2

4

10

16

-0.15 -0.1 -0.05 0 0.05 0.1

Voltage

V

Time ms

VGEVL

Fig.7. Experiment of chopper circuit Fig.8. Response of VL

Confirmed response of VL(Fig.8) Optimization of Surge voltage and switch speed

RG=15.6Ω,Shorter length of LS,Insertion of capacitance

Fabrication of Drive circuit

Control Circuit

V0

PWM SignalV5

390

GND2

V5DC-DC

ConverterOut In Stabilizaion

power

F. 10

k10

V15

V15GND1

ON Voltage

OFF Voltage

Gate resistance

1

2

3

4

CCV

0V

0V

GND 5

6

7

8

PhotocouplerTLP250

Isolation

CCEi

GEV

off

Load

SL

V6

Wiring inductance

F10G

E

StabilizationPower

LV

Li

GR

Fabrication of drive circuit by optimized value of chopper experiment(Fig.9) Check of fabricated inverter

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0 0.01 0.02 0.03 0.04

Load c

urr

ent

A

Time s