2013 Flux Conference
Investigation of electromagnetic and
thermal behaviour during frequent
fast transients in a PMSM: Flux 2D/3D
and MotorCAD simulation
Liviu I. Iepure, A. Munteanu
AVL Trimerics GmbH
Date: 17 October 2013
Outline
 AVL Trimerics at a glance
 Introduction
 From Theory to Flux simulation
 Flux simulation model
 Exploring the loss computation
 MotorCAD thermal analysis
 Conclusions
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
2
AVL Trimerics
Company Overview
Businesspark Stuttgart
Am Zettachring 2
70567 Stuttgart
 AVL Trimerics founded in 1993 in
Filderstadt since 2004 part of AVL
 AVL Trimerics
Experienced engineers in:
 E-Machine
concept and series development
 EMC
design EMC into products
 AVL Trimerics
meanwhile more than 28 employees
with close to 200 man-years of
experience in automotive
development
 AVL Trimerics
fully embedded in AVL worldwide
development network
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
3
E-Machine
System Design
Battery
System Simulation
AVL BOOST
MATLAB
Thermodynamic
Cycle Calculation
Control Systems and
Model Design
AVL CRUISE
Vehicle Simulation
Platform
FLOWMASTER
1D Fluid Cycle
Calculation
Power Electronic
Electronics
C, FORTRAN
C, FORTRAN
User written
Components
AVL E-MOBILITY
System Development Capabilities
Battery Management
Typical Battery Pack System
+ HV bus
+HV Contactor
+HV
Safety Disconnect
(1- pole of 2)
Pre-Charge
+HV bus current measurement
+HV bus voltage measurement
C1
Cell
Equalizer
CAN
2.0b
Cell voltage and current
measurements
C2
Battery Pack ECU
(BCU)
Cell Charge
Controller Board
#1
C3
Battery Module Temperature
Measurements
Battery
Management
System
Cx2
Cell
Equalizer
Cx3
Cell voltage and current
measurements
Cell Charge
Controller Board
#n
Cxn
- HV bus voltage measurement
CAN 2.0b
Cn
Cx1
CAN 2.0b
To other test/
vehicle
controllers
+12Vdc
Power
Other control
and safety I/O
- pack cooling
- pack heating
- leak fault det.
- HVIL
Battery Module Temperature
Measurements
- HV bus
-HV
- HV Contactor
Safety Disconnect
(1- pole of 2)
Vehicle Controls
E-Motor Controls
HMI
Requested torque
Vehicle coordinator
Components
Battery
E-Motor
Heating
DCDC
Torque Management
EMC
Transmission Control
Transmission
POWER-Electronic /
Charger
Torque limit at wheel
Transversal control / ESP
Energy Management
Thermo Management
Range Extender
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
ACCompressor
4
Introduction
 The simulation of specific driving cycles in an electric drive presents a growing
interest in the nowadays increasing integration of electric machines in
variable speed drives. It helps having a better insight into the electromagnetic
and thermal stresses an electric machine has to withstand.
 Specific aspects related to the application where the electric machine will be
integrated can be investigated through dedicated simulation scenarios.
 Coupled multi-domain simulations are often used to predict the electric
machine behaviour in specific working conditions.
 The possibility to create customized and dedicated simulation scenarios is one
of the biggest advantages that comes with the use of a finite element
software like Flux.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
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Motivation
 An electric machine efficiency is usually evaluated in steady state operating
points and then the cooling system is designed in order to evacuate the
estimated losses.
 It may happen that such an approach is not enough and more detailed
analysis is required.
 The simulation of frequent torque transients at imposed constant rotational
speed was assumed to be one of those situations. Such a driving cycle can
cause excessive rotor heating.
 One application can be encountered in automotive dynamometers designed
to test drive shaft components like transmissions/differentials. It has to
emulate the shaft torque pulsations given by individual piston firing torques.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
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Abstract
 A special driving cycle, consisting in frequent electromagnetic torque
transients at imposed constant speed, is investigated with FLUX. No coupled
or linked simulation with Simulink or Portunus is implied.
 A simple and yet comprehensive method to simulate in Flux2D the situation of
such frequent torque reversals in a PMSM is detailed.
 The electric machine power loss components are calculated for both a steady
state operating point (constant speed and torque) and for the above
described operation cycle ( constant speed, variable torque).
 A MotorCAD thermal analysis is done in order to highlight the thermal
behaviour as a consequence of the previous calculated power losses.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
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PMSM main characteristics

24 slots

4 poles

M270-35 stator and rotor laminations

STEEL-1010-XC10 solid shaft

Stator OD :
320 mm

Rotor OD:
140 mm

Stack Length:
450 mm

Rated Torque:
750 Nm

Rated Speed:
4500 rpm

DC link voltage:
800V
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
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From Theory to Flux simulation
 The principle of a PMSM control is based on field orientation
 For a surface PMSM this means having the PM flux linkage aligned with the daxis and the stator current vector aligned with the q-axis.
 With 𝑖𝑑 = 0 , the electromagnetic torque is proportional with the phase
currents amplitude.
 𝑇𝑒 = 1.5𝑝Ψ𝑃𝑀 𝑖𝑞
 𝐼𝑚𝑎𝑥 =
𝑖𝑞 2 + 𝑖𝑑 2
 Thus, imposing different electromagnetic torque profiles reduces to the
control of the phase current amplitude.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
9
Physical Properties
 Transient Magnetic Application
 The induced eddy currents in all rotor conductive parts and also the Eddy
currents reaction field are considered
 Rotational motion: constant rotor speed
 Electromagnetic torque : sinusoidal
 The torque dynamic is dictated by the current slope.
 In a drive system the current response is given by the PI current controller
and it is limited by the available voltage.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
10
Flux Simulation Model
 Laminated stator and rotor modeled as magnetic non-conducting regions.
 PMs segments modeled as individual solid conductor regions
 The solid shaft modeled as a solid conductor region with a defined
magnetization curve and electrical resistivity (𝞺𝑒𝑙 = 5 ∙ 10−6 [Ωm])
 Sinusoidal current sources
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
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Flux Simulation Model
 Motor/generator reversals at constant speed (4500 rpm)
 Sinusoidal waveform for the current amplitude
 𝐼𝑚 = 𝐼𝑚𝑎𝑥 𝑉𝑎𝑙𝑖𝑑 𝑡𝑖𝑚𝑒, 0, 0.01125 + 𝐼𝑚𝑎𝑥 sin⁡(2π𝑓𝑡 𝑡)𝑉𝑎𝑙𝑖𝑑 𝑡𝑖𝑚𝑒, 0.01125, 0.06
 Current sources :
 𝑖𝑎 = 𝐼𝑚 sin⁡(2π𝑓𝑡)
 𝑖𝑏 = 𝐼𝑚 sin⁡(2π𝑓𝑡 − 2π/3)
 𝑖𝑐 = 𝐼𝑚 sin⁡(2π𝑓𝑡 + 2π/3)
where⁡𝑓𝑡 - reference torque reversals frequency, 𝑓-fundamental electrical frequency
 The amplitude current reference was set as in the figure above, sinusoidal
oscillating between +1350A and -1350A with a frequency of 200 Hz.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
12
Flux Simulation Model

Phase Currents


Electromagnetic Torque


Distorted waveforms caused
by repeated transients
Transients between motor and
generator
Phase Voltages:

Notice higher values required
during transients
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
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Exploring the loss computation
 The main reasons for heating are the Joule and iron losses.
 An accurate calculation of power losses leads to a properly sized cooling
solution and a good thermal rating.
 The calculation of power loss components is described further for the case of
frequent torque transients at imposed constant speed.
 The main calculated losses are :
 rotor losses
 Solid steel shaft and PM Joule losses : calculated as the active power induced in these
regions defined as solid conductors
 Rotor yoke iron losses: postprocesor calculation with Loss Surface Method
 stator losses
 Copper losses (stray losses given by skin and proximity effect are neglected)
 Stator yoke and teeth iron losses: LS method
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
14
Rotor losses: Joule and Iron losses
 Rotor losses are separated in iron losses and eddy current losses
 PMSM are usually considered to have negligible rotor losses, since the rotor
rotates in synchronism with the fundamental stator magnetomotive-force
(MMF).
 Only the MMF harmonics move asynchronously with the rotor and they
induce losses in all its conductive parts.
 Major causes of the rotor losses are:
 no-load rotor losses caused by the existence of slots
 load rotor losses caused by the slot winding distribution (space harmonics)
 load rotor losses induced by the time harmonics of the phase currents (time
harmonics)
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
15
Rotor Joule losses
 The induced Joule losses in all
conductive parts of the rotor
are increased
 PM Joule losses (Flux 3D)
 Average value during torque
transients : 920 W (whole
machine)
 Solid shaft Joule losses
 Average value when the
steady state is reached: 397 W
(whole machine)
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
16
Rotor PM Joule losses (Flux 3D)
 To consider the PM axial segmentattion, PM losses were computed with
Flux3D Transient Magnetic Application.
 The 3D model axial length (30 mm) considers only one PM axial segment. Final
results are multiplied with the number of axial segments (15).
Flux 3D Model description
Computed current density in PMs
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
17
Rotor Iron losses
 Because of the extra time harmonics in the currents during repetitive torque
transients, Loss Surface method is used for iron losses computation.
 The magnetic field strength is reconstructed based on experimentally
determined H(B,dB/dt) curve for the used material.
 Iron losses are obtained through integration of hysteresis loop area in each
node.
0.9
Radial components
1.5
Tangential components
1
0.8
B [T]
B [T]
0.5
0.7
0
-0.5
0.6
-1
0.5
-500
0
H [A/m]
500
1000 -1.5
-500
0
H [A/m]
500
1000
Reconstructed hysteresis loops from LS method for a point in the rotor yoke
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
18
Rotor Iron losses
 The additional time harmonics in the phase currents are
producing additional asynchronous rotational fields in the
rotor laminations.
 Radial and tangential magnetic flux
density components in the rotor yoke.
 Rotor iron losses
 Average value during torque
transients: 140 W (whole machine)
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
19
Stator losses: Copper and Iron losses
 Copper losses:
 𝑃𝑐𝑜 = (𝑖1 2 + 𝑖2 2 + 𝑖3 2 )R 𝑝ℎ = 2828 W
 Iron losses are calculated with the same
LS method
 Stator yoke
 Average value during torque
transients : 824 W (whole machine)
 Stator teeth
 Average value during torque
transients : 728 W (whole machine)
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
20
Summarizing loss calculation results
 All power loss components are summarized bellow.
 The two considered cases are :
 steady state, :
 constant rotational speed (4500 rpm)
 constant torque (750 Nm)
 torque transient:
 constant rotational speed (4500 rpm)
 sinus torque variation ( ±750 Nm)
Losses [W]
PFe_st_yoke PFe_st_tooth
PFe_rotor
Pshaft
PPM
PCo
Steady state
860
740
0
0
518
5656
Transient
824
728
140
397
920
2828
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
21
MotorCAD Thermal Analysis Scenario 1.
 The machine is characterized by a high thermal loading (~55·1010 A2/m3),
therefore a spiral water jacket cooling was considered appropriate
 The water circulates with a flow rate of 8 [l/min]
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
22
Shaft losses consideration
 The magneto-transient simulation has showed that additional loses are to be
expected in the shaft, while performing frequent motoring/generating driving
cycles; in order to consider this aspect, a power source is added to the shaft
center node.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
23
Thermal transient simulation –water jacket cooling
200
180
 Simple temperature transient simulation is performed
160
T [ °C ]
140
120
Winding max
Winding avg
PM
Rotor
Shaft
Const. Torque
212
170
154
152
142
Torque Transients
155
123
183
182
178
Temperature during torque transients
Temperatures during constant torque
60
40
Temperature [C]
80
220
220
200
200
180
180
Temperature [C]
100
160
140
120
100
2,000
60
40
140
120
100
80
80
0
160
0
2,000
4,000
4,000
6,000
8,000
6,000
60
8,000
Time
[secs]
40
10,000
0
2,000
4,000
b
c
d
e
f
g
6,000
8,000
Rotor Back Iron
b [Active] Rotor Back Iron Magnet
c
d
e
f
g
b
c
d
e
f
g
Rotor Back Iron
Shaft
Magnet
Shaft
[Active]
Winding (Average)
Winding
(Hotspot)
Winding (Hotspot)
b
c
d
e
f
g
Winding (Average)
Winding (Hotspot)
b
c
d
e
f
g
g
b
c
d
e
f
Magnet
Winding (Average) gfedcb
b
c
d
e
f
g
10,000
Time [secs]
Time [secs]
b
c
d
e
f
g
10,000
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
Shaft [Active]
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
24
MotorCAD Thermal Analysis Scenario 2.
 Even though the water jacket cooling protects the motor at steady state,
during the considered transients it is not sufficient.
 A through ventilation solution was considered as good alternative
 Ambient air (0.175m3/s) and the same loss data were used for simulation
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
25
Thermal transient simulation – through ventilation
200
180
 Simple temperature transient simulation is performed
160
T [ °C ]
140
120
Winding max
Winding avg
PM
Rotor
Shaft
Const. Torque
211
170
132
130
125
Torque transients
150
124
150
150
147
Temperature during torque transients
Temperatures during constant torque
Temperature [C]
80
60
40
220
220
200
200
180
180
Temperature [C]
100
160
140
120
100
140
120
100
80
80
0
160
2,000
60
40
0
2,000
4,000
4,000
6,000
8,000
60
6,000
40
Time
[secs]
0
10,000
8,000
2,000
4,000
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
Magnet
Winding (Average) gfedcb
Magnet
b
c
d
e
f
g
Rotor Back Iron
b
c
d
e
f
g
Shaft [Active]
b
c
d
e
f
g
6,000
8,000
10,000
Time [secs]
Time [secs]
b
c
d
e
f
g
10,000
Winding (Average) g
b
c
d
e
f
Winding (Hotspot)
Rotor Back Iron
Winding (Hotspot)
b
c
d
e
f
g
b
c
d
e
f
g
Magnet
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
Winding (Average) g
b
c
d
e
f
Shaft [Active]
Rotor Back Iron
Shaft [Active]
Winding (Hotspot)
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
26
Summary
 A procedure to simulate high frequency torque transients at constant speed in
Flux was described.
 No coupled simulation was required (with Portunus, Simulink or similar
software), resulting in quick implementation.
 The simulation scenario assumes sinusoidal current sources and the torque
profile is obtained through maximum phase current control.
 The torque transients are limited by the available voltage.
 An analysis of power losses was done for the simulated scenario.
 The influence of loss calculation on the thermal behaviour was investigated.
 The need to have an interconnected electromagnetic and thermal design was
outlined.
 The advantage of considering the real driving cycle in the design was
emphasized through associated thermal effects.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
27
Conclusions
 Because of the extra time harmonics in the currents during the simulated
torque transients, the LS method has to be used for iron loss computation.
 Increased rotor iron loss and Joule loss are obtained for the simulated driving
cycle.
 Frequent transients can cause temperature problems in an electric machine if
the cooling system is designed based on only a continuous operation thermal
loading.
 In case of a real time thermal monitoring, depending on the cooling solution,
the winding temperature measurement might not be sufficient.
Investigation of electromagnetic and thermal behavior during frequent fast transients in a PMSM: Flux 2D/3D and MotorCAD simulation
2013 Flux Conference - Aix-les-Bains
28