electric machine design toolkit -...

© 2012 ANSYS, Inc. June 19, 2013 1

Electric Machine Design Toolkit Efficiency and Loss Maps for IPM Motors

Emad Dlala, Mark Solveson, and Zed Tang, ANSYS, Inc.

Raymond Ong, Magna Electronics

© 2012 ANSYS, Inc. June 19, 2013 2

User Defined Outputs of Electric Machines

Average & RMS Solutions

Transient D-Q Solutions

Solutions for Special Machines

Design Toolkits of Electric Machines

Torque-Speed Curve

Efficiency Map

Comparison of Efficiency Map with Measurements

Magna IPM Motor

Reduction of Magnet Size Application

Outline

© 2012 ANSYS, Inc. June 19, 2013 3

Motivation

Reduce weight, size, cost

Reduce magnet size

Improve efficiency

Reduce torque ripple

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00Time [ms]

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

Mo

vin

g1

.To

rqu

e [N

ew

ton

Me

ter]

Design_BH_right_1_Current_Gamma_Sweep1XY Plot 2Curve Info

Moving1.TorqueSetup1 : Transient

© 2012 ANSYS, Inc. June 19, 2013 4

Electrical Machines Design Flow

RMXprt

Maxwell2D

Maxwell3D

Toolkit

UDOs &Toolkit

Initial Design FE Design Optimal Design

© 2012 ANSYS, Inc. June 19, 2013 5

User Defined Outputs (UDOs)

© 2012 ANSYS, Inc. June 19, 2013 6

D-Q Solution Calculation Method (1/3)

Phase diagram

d-axis

q-a

xis

E

Vq

Vs

Is

-Id -Vd

Iq

we Lq Iq

-we Ld Id

g

d

j

Ypm

Phasor diagram illustrating the operation of a PM machine based on the D-Q axis theory where 𝛿 is the torque angle, 𝜑 is the power factor angle, 𝐸 is the induced voltage, 𝜔𝑒 is the operating fundamental frequency

𝐼𝑠 = 𝐼𝑑2 + 𝐼𝑞

2 ≤ 𝐼max

𝑉𝑠 = 𝑉𝑑2 + 𝑉𝑞

2 ≤ 𝑉max

© 2012 ANSYS, Inc. June 19, 2013 7

-

--

-

-

3

2sin

3

2cos

3

2sin

3

2cos

sincos

3

2C

CLCL ABC

T

QD **

θ = 0[deg]

C

B

A

T

q

d

i

i

i

Ci

i

CCCBCA

BCBBBA

ACABAA

ABC

LLL

LLL

LLL

L

w

v

u

T

q

dC

where is in electrical degrees

D-Q Solution Calculation Method (2/3)

© 2012 ANSYS, Inc. June 19, 2013 8

D-Q Solution Results

-200

0

200

-300

-200

-100

0

100

200

300-400

-200

0

200

400

Id [A]I

q [A]

To

rque [

N.m

]

-300

-200

-100

0

100

200

300

-300

-200

-100

0

100

200

300-0.4

-0.2

0

0.2

Id [A]I

q [A]

Flu

xL

inag

e(q

-axis

) [W

b]

-300

-200

-100

0

100

200

300

-300

-200

-100

0

100

200

300-0.4

-0.2

0

0.2

Id [A]I

q [A]

Flu

xL

inag

e(d

-axis

) [W

b]

© 2012 ANSYS, Inc. June 19, 2013 9

D-Q ECE Model vs. Finite-Element Analysis

dqqd IIpT -2

3

The validation shows that the ECE model of DQ solution is accurate

0 100 200 300 400-300

-200

-100

0

100

200

300

Current angle [degree]

To

rque [

N.m

]

FEA

DQ-solution

0 100 200 300 40020

40

60

80

100

120

Current angle [degree]

Vo

ltag

e [V

]

FEA

DQ-solution

qeqsq

dedsd

IRv

IRv

w

w

22

qds vvV

© 2012 ANSYS, Inc. June 19, 2013 10

Electric Machines Design Toolkit

© 2012 ANSYS, Inc. June 19, 2013 11

• Maximum-Torque Per Ampere unit (MTPA) control strategy applied

Efficiency Mapping: Method of Computation

• At a given operating condition, the trajectory of the current is crucial for the

optimal efficiency operation of PM machines • By varying the input voltage, there can be an infinite number of Id and Iq

combinations that can produce the required torque at a given speed

• MTPA strategy is applied. The scheme results in minimizing the stator current and thus maximizing the efficiency below base speed assuming that the winding loss is dominant

• In flux-weakening region, output power is maximized & apparent power is minimized to improve power factor

© 2012 ANSYS, Inc. June 19, 2013 12

• Time-domain (2D or 3D) FEA is used with current source

• Simulate a parametric sweep of transient simulations for different current magnitudes and angles, g, at a constant speed.

• Apply the MTPA algorithm using multi-objective optimization to calculate the operation points (Id and Iq) for the torque-speed range

• Run the final time-stepping simulations at the operating speed range using the calculated operation points found by the MTPA

• Compute the efficiency from the output power and total losses

Efficiency Mapping: Method of Computation

Tlossshaft

shaft

PP

P

shaft

Tlossshaft

P

PP -

Motor Generator

TlossP = Copper Loss + Core Loss + Magnet Loss + Mechanical Loss

© 2012 ANSYS, Inc. June 19, 2013 13

End –Winding Inductance

The toolkit also considers the effect of end winding inductance manifested in the torque speed curve

dt

td

dt

tdiLtiRtv es

)()()()(

2D approach 3D approach

Base speed

© 2012 ANSYS, Inc. June 19, 2013 14

• Script integrates vital effects on loss & efficiency mapping:

Efficiency Map Computations

AC Resistance of Stator Windings

Effect of Temperature

© 2012 ANSYS, Inc. June 19, 2013 15

Effect of Rotor Segmented Skewing

Skewing influences the torque and back emf voltage

0.00 12.50 25.00 37.50 50.00 62.50 75.00 87.50Gamma_TSC [deg]

-12.50

7.50

27.50

47.50

67.50

87.50

100.00

Y1

[N

ew

ton

Me

ter]

Design_BH_right_Current_Gamma_Sweep1Torque vs Gamma

Skewed

No skew

© 2012 ANSYS, Inc. June 19, 2013 16

Skewing Effect – Maxwell2D

Skewing angle

Segment

Skewing angle

Segment

Single-sided staircase

Double-sided staircase

© 2012 ANSYS, Inc. June 19, 2013 17

Skewing Effect – Maxwell2D

Example double-sided staircase:

Skew angle = 3.75 Poles = 8 Segments = 4

-20 0 20 40 60 80 100 120-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Gamma

To

rque

Center

Positive

Negative

Skew angle (electrical) = 3.75*8/2 = 15 degrees

0 10 20 30 40 50 60 70 80 900

0.2

0.4

0.6

0.8

1

Gamma

To

rqu

e

Unskewed

Skewed

© 2012 ANSYS, Inc. June 19, 2013 18

Frequency-Dependent Core Loss Coefficients Kh, Kc, Ke

𝑝 = 𝐾ℎ 𝑓 𝐵2𝑓 + 𝐾𝑐 𝑓 (𝐵 𝑓)2+𝐾𝑒 𝑓 (𝐵 𝑓)1.5

© 2012 ANSYS, Inc. June 19, 2013 19

• Script offers an intuitive UI to display:

Efficiency Map Displayer: List of Maps

© 2012 ANSYS, Inc. June 19, 2013 20

Script Compresses Simulation Data in txt Files

© 2012 ANSYS, Inc. June 19, 2013 21

• 2D Prius Motor:

2D Simulations of Efficiency Map

© 2012 ANSYS, Inc. June 19, 2013 22

• 3D Prius Motor:

3D Simulations of Efficiency Map

© 2012 ANSYS, Inc. June 19, 2013 23

• Motor specifications:

Imax = 300 A (peak value)

Vdc = 200 V

Rdc = 8 mohm @ 20 C (per-phase stator resistance)

Le = 30 uH (per-phase end-turn inductance)

P = 8

Max. speed = 9000 rpm

Magna Electronics IPM Motor – Test Case

© 2012 ANSYS, Inc. June 19, 2013 24

Experimental vs. Simulation

Experimental 2D Simulation

© 2012 ANSYS, Inc. June 19, 2013 25

Magna Electronics IPM Motor – MTPA Simulation Results

0 1000 2000 3000 4000 5000 6000 7000 8000 90000

50

100

150

200

250

300

Speed, rpm

sta

tor

cu

rren

t , A

Each line represents a constant torque level

© 2012 ANSYS, Inc. June 19, 2013 26

Magna Electronics IPM Motor - Simulation

Torque Ripple

Current Voltage

Power Factor

© 2012 ANSYS, Inc. June 19, 2013 27

Magna Electronics IPM Motor - Simulation Total loss

Copper loss

Core loss

Magnet loss

© 2012 ANSYS, Inc. June 19, 2013 29

Investigation on Magnet Size Reduction

Our goal is to reduce

magnet size by 20%

V-angle is varied in

parametric analysis to

maintain the

maximum torque

Same current and

voltage

Original Design

V-angle

Magnet

Length

Modified Design

© 2012 ANSYS, Inc. June 19, 2013 30

Investigation on Magnet Size Reduction

FEA results of 𝐿𝑑 and 𝐿𝑞 of the original and modified designs.

𝑇𝑒 =3

2𝑝 ψ𝑃𝑀𝐼𝑞 − 𝐿𝑞 − 𝐿𝑑 𝐼𝑑𝐼𝑞

The increase in the saliency of the modified design is illustrated by the slight increase of 𝐿𝑞, and the

decrease of 𝐿𝑑 which is due to the magnet reduction.

© 2012 ANSYS, Inc. June 19, 2013 31

Investigation on Magnet Size Reduction – Efficiency

• Percentage difference

of efficiency between

the original and

modified designs

• The positive scale

means that an increase

of the efficiency is

gained in the modified

design.

© 2012 ANSYS, Inc. June 19, 2013 32

Investigation on Magnet Size Reduction - Harmonics

Instantaneous flux densities at a point in a tooth tip of the stator simulated at 𝐼𝑑 = −42 A, 𝐼𝑞 = 56 A, 𝑆𝑝𝑒𝑒𝑑 = 8500 rpm. Higher harmonics cause an increase in

losses with an increase of speed.

© 2012 ANSYS, Inc. June 19, 2013 33

Investigation on Magnet Size Reduction – Torque Ripple

• Absolute difference in the torque ripple in N∙m between the modified & original designs.

© 2012 ANSYS, Inc. June 19, 2013 34

• Simulations run on Distributed Solve Option (DSO):

Speed-up Improvements

0 20 40 60 80 1000

20

40

60

80

100

Number of cores

Sp

eed-u

p f

acto

r

Total CPU time ~3 hours on a laptop with 6 cores

© 2012 ANSYS, Inc. June 19, 2013 35

Summary • User Defined Outputs and Toolkit Scripts were created by ANSYS for

computing Torque Speed Curve as well as Efficiency and Loss Maps • Script is generic, fully automated, extendable, efficient and robust • Method integrates most vital effects on losses such as end-turn inductance,

ac resistance, skewing, and frequency-dependent core loss coefficients • Optimal operation points are calculated by the toolkit for the whole torque

and speed range • Efficiency map simulations for a Magna Interior PM Motor with

experimental comparison showed that the method is accurate • An investigation of reducing the permanent magnet size where 20% of

magnet size reduction was achieved while maintaining the desired efficiency over the operating range

© 2012 ANSYS, Inc. June 19, 2013 36

Click to edit Master text styles

Coming Soon: User Defined Core Loss

Solve Time Step

Solver

Read User.Ctl

Call

Solution.ctl

A, B, J, w

Last Time Step

MyCoreLoss.exe

CoreLoss.txt Hysteresis.txt Excess.txt Eddy.txt

© 2012 ANSYS, Inc. June 19, 2013 39



0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

2

4

6

8

10

12

14

16

18

time, s

Co

re l

oss

, W

User Defined

Maxwell

© 2012 ANSYS, Inc. June 19, 2013 40


Separation of Core Loss

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

2

4

6

8

10

12

14

16

18

time, s

Co

re l

oss

, W

Total loss

Hysteresis loss

Eddy loss

Excess loss

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