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Presented by Youngkook Lee, December 04, 2006
A STATOR TURN FAULT TOLERENT STRATEGY
FOR INTERIOR PM SYNCHRONOUS MOTOR
DRIVES in SAFETY CRITICAL APPLICATIONS
Youngkook Lee
Professor Thomas G. Habetler
School of Electrical and Computer EngineeringGeorgia Institute of Technology
Atlanta Georgia
2Presented by Youngkook Lee, December 04, 2006
Outline
Part 1. Introduction
Background of the Research
Problem Statement and Research Objective
Survey on Previous Work
Part 2. Proposed Work
Modeling of an IPMSM with Stator Turn Faults
Turn Fault Tolerant Strategy
Part 3. Conclusions and Future Work
3Presented by Youngkook Lee, December 04, 2006
Interior PM Synchronous Motors (IPMSMs)
Features Having large power (torque) density, wide constant power-speed ratio, and high
efficiency
Creating special challenges under any fault condition due to the presence of
permanent magnets that cannot be turned off at will
Requiring special care in safety critical applications where any failure can result in
serious accidents
Permanent Magnet
Rotor
Stator
Cross-Sectional View
4Presented by Youngkook Lee, December 04, 2006
Fault Tolerance
Defined as a performance characteristic that a fault in a component or sub-system does not cause the overall systems to malfunction
Quantified in terms of “reliability and availability”
Increased conventionally by “conservative design and
redundancy”; however, these approaches increase the
cost and complexity of the system
Recently, increased via “fault diagnosis and tolerant
strategies”; however, focusing on how to detect a fault,
while the research on how to increase the availability
remains uncharted area
5Presented by Youngkook Lee, December 04, 2006
Stator Turn Faults
Referring to the insulation failures in several turns of a stator coil within one phase
Generating excessive heat in the shorted turns due to a large circulating current
Developing rapidly into the catastrophic failures
Initiating a large portion of stator winding-related failures
that attribute to about 35~37% of induction machine
failures
6Presented by Youngkook Lee, December 04, 2006
Outline
Part 1. Introduction
Background of the Research
Problem Statement and Research Objective
Survey on Previous Work
Part 2. Proposed Work
Modeling of an IPMSM with Stator Turn Faults
Turn Fault Tolerant Strategy
Part 3. Conclusions and Future Work
7Presented by Youngkook Lee, December 04, 2006
Problem Statement and Objective Research
The primary objective of this research is to develop a stator turn fault tolerant strategy in IPMSM drives satisfying the following requirements:
The ultimate goal of this research is to develop a complete solution for high turn fault tolerance of IPMSM drives in safety critical applications including modeling, detection method, and tolerant strategy
Preventing a turn fault from developing into the destructive phase
Not resulting in the complete loss of the availability of the drive
under a turn fault condition
Not requiring any change in the standard IPMSM drive
configuration
8Presented by Youngkook Lee, December 04, 2006
Outline
Part 1. Introduction
Background of the Research
Problem Statement and Research Objective
Survey on Previous Work
Part 2. Proposed Work
Modeling of an IPMSM with Stator Turn Faults
Turn Fault Tolerant Strategy
Part 3. Conclusions and Future Work
9Presented by Youngkook Lee, December 04, 2006
Approaches in Previous Work
Since it is generally accepted that there is no way to prevent turn faults from developing destructive phase except for stopping the machine completely, a small amount of work has been done in the following three ways:
Redundancy
Development of fault tolerant machines
Post-fault operations for stopping the faulty machine without further damage
10Presented by Youngkook Lee, December 04, 2006
Redundancy Approach
LoadMotor 1 Motor 2
Position sensor 2
Position sensor 1
Inverter 1 Inverter 2
DC source 1
DC source 2
Controller 1 Controller 2
Gate signal Gate signal
Back up Controller
11Presented by Youngkook Lee, December 04, 2006
Fault Tolerant Machines
Requirements for Fault Tolerant Machines Complete electrical isolation between phases
Implicit limiting of fault currents
Magnetic isolation between phases
Physical isolation between phases
More than 3-phases
Switched Reluctance Motors (SRMs) Coming close to achieving the requirements
Having inherently large acoustic noise and vibration, and low
efficiency
Requiring a different converter topology from the standard 6-
switch full bridge inverter
1
12Presented by Youngkook Lee, December 04, 2006
Fault Tolerant Machines
Converter Topologies for Conventional 3-phase motors and SRMs
(a) Conventional 3-phase Motors (b) SRMs
2
13Presented by Youngkook Lee, December 04, 2006
Fault Tolerant Machines
Modular Fault Tolerant PM Motors
Combining the advantages of PM motors and SRMs
Being subjected to stator turn faults due to the presences of the permanent magnets
Requiring the same converter topology as SRMs
3
14Presented by Youngkook Lee, December 04, 2006
Post-Fault Operations
Free-Running Mode
Not being an appropriate post-fault operation for IPMSMs
Possibly being subjected to a critical damage on the dc-link due to unregulated generating power in high speed ranges
Resulting in the loss of the control over the speed and torque
ia
ea
VDC A B C
D4 D6 D2
ib ic
eb ec
O
n
D3 D5D1
1
15Presented by Youngkook Lee, December 04, 2006
Post-Fault Operations
Symmetrical Short-Circuit Operation
Being a good choice for post-fault operation for IPMSMs
Resulting in the loss of the control over the speed and torque
ia
ea
VDC A B C
D4 D6 D2
ib ic
eb ec
O
n
2
16Presented by Youngkook Lee, December 04, 2006
Outline
Part 1. Introduction
Background of the Research
Problem Statement and Research Objective
Survey on Previous Work
Part 2. Proposed Work
Modeling of an IPMSM with Stator Turn Faults
Turn Fault Tolerant Strategy
Part 3. Conclusions and Future Work
17Presented by Youngkook Lee, December 04, 2006
Demands for Modeling An accurate model is required to develop an effective detection
method or tolerant strategy
A test-bench for confirming any fault detection scheme or tolerant
strategy is required since even a minor deficiency can result in a
serious damage to the drives
Modeling of an IPMSM with Stator Turn Faults
Approaches in Modeling of Electric Machines Finite element analysis (FEA) based models
Accurate, but take long time for simulation and require detail
specification of the machine
Equivalent circuit-oriented models
Simple, but less accurate and difficult to consider non-linearity in
the magnetic system
1
18Presented by Youngkook Lee, December 04, 2006
A Circuit-Oriented Model of IPMSMs with Turn Faults Being derived in phase-variables
Being integrated with a vector-controlled drive model since almost
IPMSM applications utilize current-controlled inverters
Being used to investigate the behaviors of a stator turn fault in an
IPMSM drive
Modeling of an IPMSM with Stator Turn Faults
Basic assumptions for the henceforth analysis Each phase winding consists of turns connected in series, and the
3-phase windings are Y-connected with a floating neutral
A stator turn fault occurs on the a-phase winding
2
19Presented by Youngkook Lee, December 04, 2006
Q1 Q3 Q5
Q4 Q6 Q2
D1 D3 D5
D4 D6 D2
the number of the shorted turns
the number of turns per phase
Schematic Diagram of an IPMSM drive with a turn Fault
ia
ib ic
a
bc
as1
as2 if
ia
ib ic
a
bc
Rfia- if
20Presented by Youngkook Lee, December 04, 2006
Machine Equations under Fault-Free Conditions
Stator Line-Neutral Voltages
Developed Torque
r rr
d d d
dt dt dt
s s PMs s s s s
i Lv r i L + i
( ) ( )( )
(1)
1= +
2 2r r
er r
d dPT
d d
T Ts PMs s s
Li i i
( ) ( )
where, , , [ ]a b cdiag r r rsr
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
aa r ab r ac r
r ba r bb r bc r
ca r cb r cc r
L L L
L L L
L L L
sL( ) _ _ _[ ( ) ( ) ( )]Tr a PM r b PM r c PM r PM ( )=
P is the number of poles, r represents the rotor position in electrical radians.
(2)
[ ]Tan bn cnv v vsv [ ]Ta b ci i isi
1
21Presented by Youngkook Lee, December 04, 2006
Machine Equations under Fault-Free Conditions
Stator Self- and Mutual Inductances
Flux Linkages Contributed by Permanent Magnets
1 21
1 21
1 21
( ) cos(2 ) ( )
2( ) cos[2 ( )] ( )3
4( ) cos[2 ( )] ( )3
aa r l k r l am rk
bb r l k r l bm rk
cc r l k r l cm rk
L L L L k L L
L L L L k L L
L L L L k L L
1 21
1 21
1 21
1( ) ( ) cos[2 ( )]32
1( ) ( ) cos[2 ( )]
2
1( ) ( ) cos[2 ( )]32
ab r ba r k rk
bc r cb r k rk
ca r ac r k rk
L L L L k
L L L L k
L L L L k
(a) Self inductances (b) Mutual inductances
2 11
sin[(2 1) ]
2sin[(2 1)( )]32sin[(2 1)( )]3
r
r k rk
r
k
k
k
PM( )=
2
22Presented by Youngkook Lee, December 04, 2006
Machine Equations under Turn Fault Conditions
Stator Line-Neutral Voltages
Developed Torque
r rr
d d d
dt dt dt
' ' '
' ' ' ' 's s PMs s s s s
i Lv r i L + i
( ) ( )( )
1= +
2 2r r
er r
d dPT
d d
' ''T ' 'Ts PMs s s
Li i i
( ) ( )
where,
(1 ) 0 0 0
0 0 0
0 0 0
0 0 0
s
s
s
s
r
r
r
r
'sr
2
2
(1 ) (1 ) ( ) (1 ) ( ) (1 ) ( ) (1 ) ( )
(1 ) ( ) ( ) ( ) ( )( )
(1 ) ( ) ( ) ( ) ( )
(1 ) ( ) ( ) ( ) ( )
l am r am r ab r ac r
am r l am r ab r ac rr
ab r ab r l bm r bc r
ac r ac r bc r l cm r
L L L L L
L L L L L
L L L L L
L L L L L
'SL
1 2
T
as as bn cnv v v v'sv
T
a a f b ci i i i i 'si
_ _ _ _(1 ) ( ) ( ) ( ) ( )T
r a PM r a PM r b PM r c PM r 'PM( )=
(3)
(4)
1
23Presented by Youngkook Lee, December 04, 2006
Machine Equations under Turn Fault Conditions
* Rearranging (3) and (4) yields
Stator Line-Neutral Voltages
Developed Torque
( ) ( ) ( ) ( ) ( )1
2
( ) ( )1
2T TS r sr r
2 2aa r ar r aa r ab r ac r
s s sr
f f f a b cr r r r
e
r
r
dL θ dλ θ dL θ dL θ dL θ+ μ i - μi - μi i +i +i
dθ dθ dθ d
d θ d θ+
dθ dθPT =
2
θ dθ
L λi i i
(5)
(6)
( ) ( )0 ( )
( ) ( )
( )0 ( ) ( )
s aa r aa rff ab r e ab r f
rac r a
s s r sr rs s s s e s e
r
r r
c
r L θ L θdi dμ i L θ +ω L θ i
dt dθL θ
d d θ d θω ω
dt dθ dθ
L θ
i L λ
v r i L i
2
24Presented by Youngkook Lee, December 04, 2006
Machine Equations under Turn Fault Conditions
Voltage Equation at the Healthy Turns
Voltage Equation at the Shorted Turns
Summation of the Line-Neutral Voltages
(7)
(8)
( ) ( )( )
( )( )
( )
s a r a rs a a r e s e
r ras1
f am ram r e f
r
d d θ dλ θr i + θ +ω +ω
dt dθ dθv = 1 μ
di dL θμ L θ +ω i
dt dθ
i LL i
2
e e
e
( ) ( )+ + +
= ( )
( )
as f f
s a r ar rs a a s
r r
f am rs f ls am r f
r
v R i
d d dr i
dt d ddi dL
r i L L idt d
i LL i
+ fan bn cn s f ls
div v v r i L
dt
(9)
3
25Presented by Youngkook Lee, December 04, 2006
Implementation of a simulation model
Block Diagram of the Simulation model
Discrete PI
controller
S-function(anti-windupPI with feed-
forwardcontroller)
Phase-variableModel
MotionEquation
Speed controller
Currentcontroller
Phase voltage generator IPMSM
sv eT*sov*
eT
r
*r
, ,, ,r e a b ci , ,,e a b ci
Load
Pole to phase
26Presented by Youngkook Lee, December 04, 2006
Key Parameters for Specifying the Model
Class Item Unit Values
Motor
Pole Number [ - ] 8
Rated /Max. Torque [Nm] 40 / 80
Rated Current [A] 114 / 250
Rated Speed [rpm] 2450
Stator Resistance [mohm] 4.85
Stator Leakage Inductance [uH] 18.9
Stator Magnetizing Inductance [uH] L1 : 167.4, L2: -33
PM Flux Linkage [Wb] 0.0543
Inverter
Nominal dc-Link Voltage [Vdc] 216
Switching Frequency [kHz] 7
Current Control Rate [kHz] 7
27Presented by Youngkook Lee, December 04, 2006
Simulation under Various Rotating Speeds
Simulation Conditions and Summary of the Results
Items Unit Values
Load Torque [Nm] 20
Rotating Speed [rpm] 1500 2450 3500
Fault Fraction [%] 1
Fault Impedance [ohm] 0 ( a bolted fault)
Circulating current [A] 1621 1650 1678
Sequence components in line-neutral voltages
Positive
[V]
35.58 57.67 82.26
Negative 1.2 1.93 2.72
Zero 0.12 0.19 0.27
Sequence components in line currents
Positive[A]
62.30 61.95 61.85
Negative 2.18 4.77 6.8
TorqueFund.
[Nm]20 20 20
2nd order 1.77 1.40 1.37
28Presented by Youngkook Lee, December 04, 2006
Simulation Conditions and Summary of the Results
Items Unit Values
Load Torque [Nm] 0 40 80
Rotating Speed [rpm] 1500
Fault Fraction [%] 1
Fault Impedance [ohm] 0 ( a bolted fault)
Circulating current [A] 1532 1813 2218
Sequence components in line-neutral voltages
Positive
[V]
33.41 39.85 48.67
Negative 1.11 1.33 1.61
Zero 0.11 0.13 0.16
Sequence components in line currents
Positive[A]
2.57 117.09 211.20
Negative 1.24 3.04 3.75
TorqueFund.
[Nm]0 40 80
2nd order 1.63 2.27 3.61
Simulation under Various Loads
29Presented by Youngkook Lee, December 04, 2006
Simulation Conditions and Summary of the Results
Simulation under Various Fault Fractions
Items Unit Values
Load Torque [Nm] 40
Rotating Speed [rpm] 1500
Fault Fraction [%] 0 1 3 5
Fault Impedance [ohm] 0 ( a bolted fault)
Circulating current [A] 0 1813 1630 1483
Sequence components in line-neutral voltages
Positive
[V]
40.82 39.55 38.20 36.83
Negative 0 1.33 3.61 5.52
Zero 0 0.13 0.35 0.55
Sequence components in line currents
Positive[A]
113.07 117.09 124.72 131.84
Negative 0 3.04 8.32 12.76
TorqueFund.
[Nm]40 40 40 40
2nd order 0 2.27 6.38 9.99
30Presented by Youngkook Lee, December 04, 2006
Characteristics of Turn Faults in Current-Controlled Inverter-Driven Applications
A Stator turn fault induces a large circulating current in the shorted turns that has the following characteristics :
1
The fundamental frequency is the same as the synchronous
frequency
The current generates magnetic flux that acts against the main air-
gap flux. In the case of a stator turn fault where a large number of
turns are shorted, the additional flux can be large enough to
demagnetize the permanent magnets
The amplitude is strongly related to the amplitude of the stator
line-neutral voltages, while fault fraction has very little effect
The current is mainly limited by the stator resistance and leakage
inductance
31Presented by Youngkook Lee, December 04, 2006
Characteristics of Turn Faults in Current-Controlled Inverter-Driven Applications
A Stator turn fault in current-controlled inverter-driven applications induces …
2
Decreased positive sequence and increased negative sequence
voltages since the inverter tries to control the currents so as to
follow their references by reducing positive sequence voltage and
compensating negative sequence voltage
Reduced positive sequence impedance, and increased negative sequence
and coupling impedances as the same as those in line-fed applications
A circulating current that decreases as fault fraction increases,
because the amplitude of current is nearly proportional to the
amplitude of the stator line-neutral voltage and negative sequence
voltage is much smaller than positive sequence voltage
32Presented by Youngkook Lee, December 04, 2006
Outline
Part 1. Introduction
Background of the Research
Problem Statement and Research Objective
Survey on Previous Work
Part 2. Proposed Work
Modeling of an IPMSM with Stator Turn Faults
Turn Fault Tolerant Strategy
Part 3. Conclusions and Future Work
33Presented by Youngkook Lee, December 04, 2006
Theoretical Foundations
Relation between and (Stator Voltage)
Rearranging the voltage equation (8) at the shorted turns yields
Generally, the asymmetry introduced in the stator voltages due to
a stator turn fault has a small effect on the overall stator voltage;
thus
0( )( ) f f am r
f s f ls am r e f asr
R di dLi r i L L i v
dt d
where, represents the instantaneous value of the line-neutral
voltage at the faulty winding.
0asv
fi sv
where, represents the stator voltage vector. sv
1 2( 3 )ff s e ls s
Ri r j L L L v
1
1
(11)
(12)
34Presented by Youngkook Lee, December 04, 2006
Theoretical Foundations
Relation between and (Stator Voltage)
The amplitude of the circulating current in the shorted turns is
Three Options for
(1) Increasing the fault impedance
(2) Increasing the resistance and leakage inductance of the stator
winding
(3) Reducing the stator voltage vector
fi sv
1 2[ ( 3 )]
sf
fs e ls
vi
Rr j L L L
2
2
(13)
35Presented by Youngkook Lee, December 04, 2006
Machine Equations in the qd-variables in a steady State Condition under Fault-Free Condition
Stator Voltage
Developed Torque
3
2 2e e e
e PM qs d q ds qs
PT i L L i i
( ) ( )
e es qs ds
e e e es qs ds e q qs e d ds PM
v v jv
r i ji j L i L i
Theoretical Foundations 3
(14)
(15)
36Presented by Youngkook Lee, December 04, 2006
Theoretical Foundations 4
Representation in Circle Diagram
di
qi
Constant torque hyperbola, 0eT
Voltage Ellipse, in the case that
Maximum Torque-per-Amp Trajectory
(Motoring)
PM
dL
Current circle, in the case that 0 0 and e e e e
ds ds qs qsi i i i A
0 0 and e e e eds ds qs qsi i i i
di
qi
Constant torque hyperbola, 0eT
Voltage Ellipse, in the case that
Maximum Torque-per-Amp Trajectory
(Motoring)
PM
dL
Current circle, in the case that 0 0 and e e e e
ds ds qs qsi i i i A
B
Current circle, in the case that * * and e e e e
ds ds qs qsi i i i
0 0 and e e e eds ds qs qsi i i i
Voltage Ellipse, in the case that* * and e e e e
ds ds qs qsi i i i
37Presented by Youngkook Lee, December 04, 2006
Development of the Proposed Strategy
From the torque equation, the q-axis current is expressed as a function of the d-axis current under a given torque condition as,
Inserting into the stator voltage vector equation yields,
The specific combination of the d- and q-axis currents minimizing , consequently, minimizing the circulating currents can be determined by solving
0* 1
** 2
3[ ( ) ]
2 2
e eqs e
e dsPM d q ds
T Ci
P C iL L i
2 21 1
2 2
[ ( )] [ ]s e d PM s e q
C Cv r L i r i L
C i C i
e* e*
s ds dse* e*ds ds
2
0v
i
s
e*ds
(16)
(17)
(18)
sv
38Presented by Youngkook Lee, December 04, 2006
Extension to Induction Motor Drives
From the induction motor torque and slip equations,
By inserting (19) and (20) into voltage equation,
By solving the following equation,
(19)
(20)
01
3(1 )
4
e
s
T Ci
P iL i
e*qs e*
e* dsds
** * * * 2
2( )
eqsr
e m sl m mr
ir C
L i i
e* e*ds ds
2 * 2 * 21 2 2 12 2
[ ( ) ] [ ( ) ]( ) ( )s m s s m s
C C C Cv r L i r i L
i i i i e* e*
s ds dse* e* e* e*ds ds ds ds
(21)
2
0v
i
s
e*ds
(22)
39Presented by Youngkook Lee, December 04, 2006
Simulation for Comparing with MTPA Operation
Simulation Conditions : Optimal d- and q-axis Current trajectories for reducing the
stator voltage
(a) d-axis current (b) q-axis current
1[%], and 0 (a bolted fault)fR
1
40Presented by Youngkook Lee, December 04, 2006
Simulation for Comparing with MTPA Operation
Comparison of
(a) In the case of MTPA operation (b) In the case of
the proposed strategy
fi
2
41Presented by Youngkook Lee, December 04, 2006
Simulation for Comparing with MTPA Operation
Comparison of Available Operating Areas with Limiting within 3 Times the Rated Current
MPTA operation : red circle markedProposed strategy : blue x marked
No
rmal
ized
T
orq
ue
Normalized speed
fi
3
42Presented by Youngkook Lee, December 04, 2006
Machine Equations in the qd-Variables under Symmetrical Short-Circuit Operation
Stator Voltages
Stator Currents
Developed Torque
22 2
1es e PMqs
ee q PMs e q dds
riLr L Li
32
_ 2 2 2 2 2
3[ ( ) ]
2 2 ( )q ee
e sym s PM d qs e q d s e q d
LPT r L L
r L L r L L
( )0
0
e ees qs e d ds PMqs
e ees ds e q qsds
r i L iv
r i L iv
Simulation for Comparing with Symmetrical Short-Circuit Operation
1
(23)
(24)
(25)
43Presented by Youngkook Lee, December 04, 2006
Comparison of
Time (sec)
Circulating current in the shorted turns
In the case of the proposed
strategy
Cu
rren
t (A
)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
fi
2
44Presented by Youngkook Lee, December 04, 2006
Comparison of the a-phase Currents
Time (sec)
a-phase current
In the case of the proposed
strategy
Cu
rren
t (A
)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
3
45Presented by Youngkook Lee, December 04, 2006
Comparison of the a-phase Line-Neutral Voltages
Time (sec)
a-line to neutral voltage
In the case of the proposed
strategy
Vo
ltag
e (V
)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
4
46Presented by Youngkook Lee, December 04, 2006
Comparison of the Developed Torque
Time (sec)
Developed torque
In the case of the proposed
strategy
To
rqu
e (N
m)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
5
47Presented by Youngkook Lee, December 04, 2006
Effects of the Machine Specifications
Items Unit #1 #2 #3 Remark
Pole Number [ - ] 8
Max. Current [A] 300 Inverter Max. Current
Rated Speed [rpm] 2450
DC-link Voltage [Vdc] 216
Stator Resistance [mΩ] 4.85
Leakage Inductance [uH] 33
d-axis Inductance [uH] 220 311 127
q-axis Inductance [uH] 440 622 287
Saliency Ratio [ - ] 2 2 2.26
PM Flux Linkage [Wb] 0.0543 0.0384 0.0543
Char. Current [A] 247 123 428
Parameter Lists of Different Machine Designs
1
48Presented by Youngkook Lee, December 04, 2006
Effects of the Machine Specifications
To
rqu
e (N
m)
Speed (rpm)
Blue solid line : #1Red dotted line : #2Black dashed line : #3
Torque-Speed Characteristic Curves
2
49Presented by Youngkook Lee, December 04, 2006
Effects of the Machine Specifications
Comparison of under MTPA Operationfi
(a) In the case of Design #1 (b) In the case of Design #2
(c) In the case of Design #3
3
50Presented by Youngkook Lee, December 04, 2006
Effects of the Machine Specifications
Comparison of under the Proposed Strategy Operationfi
(a) In the case of Design #1(b) In the case of Design #2
(c) In the case of Design #3
4
51Presented by Youngkook Lee, December 04, 2006
Effects of the Machine Specifications
Comparison of under the Proposed Strategy Operationsi
(a) In the case of Design #1(b) In the case of Design #2
(c) In the case of Design #3
5
52Presented by Youngkook Lee, December 04, 2006
Experimental Results-Preliminary
Experimental Conditions Motor : 5HP Induction Motor
Rotating Speed and Load : 800 rpm, 5 Nm (0.25 rated torque) Fault Conditions : 1.03[%], and 0 (a bolted fault)fR
(a) Specially rewound induction motor (b) Diagram of test bench
1
53Presented by Youngkook Lee, December 04, 2006
Experimental Results-Preliminary
Transition of Operating Modes
(a) Ch. 4: Rotating speed (400 rpm/V),
Ch. 3: (5 A/V), Ch. 1: (5 A/V), Time (500 ms/div)
(b) Ch.1: (50A/10mV),
Ch. 2: (10 A/10mV), Time (200 ms/div)edsi
eqsi
fi
ai
2
54Presented by Youngkook Lee, December 04, 2006
Experimental Results-Preliminary
Steady-State Conditions
Ch.1: (50A/10mV), Ch. 2: (10 A/10mV), Time (200 ms/div)fiai
(a) before activating the proposed Strategy (b) after activating the proposed Strategy
3
55Presented by Youngkook Lee, December 04, 2006
Outline
Part 1. Introduction
Background of the Research
Problem Statement and Research Objective
Survey on Previous Work
Part 2. Proposed Work
Modeling of an IPMSM with Stator Turn Faults
Turn Fault Tolerant Strategy
Part 3. Conclusions and Future Work
56Presented by Youngkook Lee, December 04, 2006
Conclusions
A stator turn fault in an IPMSM is one of the dangerous failure mode that can result in serious accidents in safety critical applications
The amplitude of the circulating current due to a stator turn fault has a close relationship with the amplitude of the machine terminal voltages
A proper adjustment of the machine terminal voltage can reduce the circulating current significantly; consequently can prevent the complete loss of the faulty machine
The proposed strategy is very effective in safety critical applications, especially in applications where a limp-operation can prevent serious accidents due to an abrupt interruption of an electric motor drive
57Presented by Youngkook Lee, December 04, 2006
Future Work
Validation of the Proposed Strategy via Experiments Enhancing the Proposed Strategy by
Considering non-linearity in the magnetic system
Providing machine design guideline for maximizing the
effectiveness of the proposed strategy
Developing a Turn Fault Detection Scheme for IPMSM Drives
Investigation of the Thermal Behaviors of Stator Turn Fault with a Thermal Model
58Presented by Youngkook Lee, December 04, 2006
Consideration on Non-Linearity of the Magnetic System
Two main sources of non-linearity : Magnetic saturation and Cross-coupling effects
Approaches for Including Non-linearity in a Machine Model : FEA and
Physical Experiments
Flux Equations with considering cross-coupling effects
,
,
e e eq q q qd d
e e ed d d dq q PM
L i M i
L i M i
Determination of the self- and coupling qd-inductances from the measured qd-flux under various operating conditions by
, ,
, ,
e eq q
q ls mq qde eq d
e ed d
d ls md dqe ed q
L L L Mi i
L L L Mi i
1
59Presented by Youngkook Lee, December 04, 2006
By applying the inverse transform from the qd-synchronous rotating reference frame to the abc-stationary reference frame, the phase inductances can be obtained as
Consideration on Non-Linearity of the Magnetic System
2
1 2 1
1 2 1
1 2 1
cos 2 sin 2
4 4cos 2 sin 23 3
2 2cos 2 sin 23 3
( )
( )
( )
aa r ls r r
bb r ls r r
cc r ls r r
L L L L M
L L L L M
L L L L M
Where , , , 1 3md mqL L
L
2 3md mqL L
L
1 3dq qdM M
M
2
3
6
( )dq qdM MM
60Presented by Youngkook Lee, December 04, 2006
1 2 1 2
1 2 1 2
1 2 1 2
1 2 1 2
1 2 1
1 2 2cos 2 sin 23 32
1 2 2cos 2 sin 23 32
1 2 2cos 2 sin 23 32
1cos 2 sin 2
2
1 2 2cos 2 sin 23 32
( )
( )
( )
( )
( )
ab r r r
ac r r r
ba r r r
bc r r r
ca r r r
M L L M M
M L L M M
M L L M M
M L L M M
M L L M
2
1 2 1 2
1cos 2 sin 2
2( )cb r r r
M
M L L M M
Consideration on Non-Linearity of the Magnetic System
3
By applying the inverse transform from the qd-synchronous rotating reference frame to the abc-stationary reference frame, the phase inductances can be obtained as
61Presented by Youngkook Lee, December 04, 2006
Consideration on Non-Linearity of the Magnetic System Simplified Flux Model from General Profiles of the qd-inductances of
an IPMSM
4
[ ]L H
qL
[ ]Current A
dL
As the negative d-axis current decreases
As the q-axis current increases
,
,
e eq q q
e ed d d PM
L i
L i
0
0
constant,
,
d
qq q
qs
L
LL L
i
62Presented by Youngkook Lee, December 04, 2006
In the voltage references, positive- and negative-sequence components will appear
Observation of Voltage References in the Synchronous Rotating Reference Frame
Stator Turn Fault Detection Method
• Blue solid line : Stator voltage vector under fault-free condition• Red dashed line : Positive sequence voltage with stator turn faults• Red long-dashed line: Negative sequence voltage with stator turn faults
qsv_
eqds nomv
dsv
ee
e
_eqds posv
_eqds negv
qdsv_
eqds nomv
_eqds posv
_eqds negv
Time
1
2 e
63Presented by Youngkook Lee, December 04, 2006
A stator turn fault generates a hot-spot spreading very fast; therefore, modification of conventional lumped parameter thermal model is required
Thermal Model with Stator Turn Faults
'sP rP
3R
'1R 2R'
1C 2C
S r
a
P RC
RC
SR
P
R
RotorShorted turns Adjacent turns Other healthy turns
64Presented by Youngkook Lee, December 04, 2006
A STATOR TURN FAULT TOLERENT STRATEGY
FOR INTERIOR PM SYNCHRONOUS MOTOR
DRIVES in SAFETY CRITICAL APPLICATIONS
65Presented by Youngkook Lee, December 04, 2006
Appendices
Further Simulated Waveforms
Simulation under various rotating speeds
Simulation under various fault fractions
Simulation under various loads
66Presented by Youngkook Lee, December 04, 2006
Sp
eed
(r
pm
)T
orq
ue
(Nm
)
Waveforms : Rotating Speeds and Developed Torque
(a) Speed reference (dashed red-line) and actual Speed (solid blue-line)
Time (sec)
(b) Torque reference (dashed red-line) and actual torque (solid blue-line)
Time (sec)
Simulation under Various Rotating Speeds 1
67Presented by Youngkook Lee, December 04, 2006
Waveforms : Phase Voltage, Line Current, and Fault Current
Time (sec)
Vo
ltag
e (V
)C
urr
ent
(A)
Cu
rren
t (A
)
(a) a-phase line-neutral voltage
(c) Circulating Current in the shorted Turns
(b) a-phase current Time (sec)
Time (sec)
Simulation under Various Rotating Speeds 2
68Presented by Youngkook Lee, December 04, 2006
Waveforms : Circulating Currents C
urr
ent
(A)
Time (sec)
Circulating current in the shorted turns
1 %
3 %
5 %
Simulation under Various Fault Fractions 1
69Presented by Youngkook Lee, December 04, 2006
To
rqu
e (N
m)
Time (sec)
Waveforms : Developed Torques
Developed torque
No fault
1 %
3 %
5 %
Simulation under Various Fault Fractions 2
70Presented by Youngkook Lee, December 04, 2006
Waveforms : Rotating Speeds
Time (sec)
Rotating speed
No fault
1 %
3 %
5 %
Sp
eed
(r
pm
)
Simulation under Various Fault Fractions 3
71Presented by Youngkook Lee, December 04, 2006
Waveforms : Circulating Currents
Time (sec)
Circulating current in the shorted turns
No load
40 Nm
80 Nm
Cu
rren
t (A
)
Simulation under Various Loads 1
72Presented by Youngkook Lee, December 04, 2006
To
rqu
e (N
m)
Waveforms : Developed Torques
Time (sec)
Developed torque
No load
40 Nm
80 Nm
Simulation under Various Loads 2
73Presented by Youngkook Lee, December 04, 2006
Waveforms : Rotating Speeds
Time (sec)
Rotating speed
No load
40 Nm
80 Nm
Sp
eed
(r
pm
)
Simulation under Various Loads 3