Presented by Youngkook Lee, December 04, 2006
A STATOR TURN FAULT TOLERENT STRATEGY FOR INTERIOR PM SYNCHRONOUS MOTOR DRIVES in SAFETY CRITICAL APPLICATIONS
Youngkook LeeProfessor Thomas G. Habetler
School of Electrical and Computer EngineeringGeorgia Institute of Technology
Atlanta Georgia
Presented by Youngkook Lee, December 04, 2006 2
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
Presented by Youngkook Lee, December 04, 2006 3
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
Presented by Youngkook Lee, December 04, 2006 4
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
Presented by Youngkook Lee, December 04, 2006 5
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
Presented by Youngkook Lee, December 04, 2006 6
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
Presented by Youngkook Lee, December 04, 2006 7
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
Presented by Youngkook Lee, December 04, 2006 8
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
Presented by Youngkook Lee, December 04, 2006 9
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
Presented by Youngkook Lee, December 04, 2006 10
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
Presented by Youngkook Lee, December 04, 2006 11
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
Presented by Youngkook Lee, December 04, 2006 12
Fault Tolerant Machines
Converter Topologies for Conventional 3-phase motors and SRMs
(a) Conventional 3-phase Motors (b) SRMs
2
Presented by Youngkook Lee, December 04, 2006 13
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
Presented by Youngkook Lee, December 04, 2006 14
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
Presented by Youngkook Lee, December 04, 2006 15
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
Presented by Youngkook Lee, December 04, 2006 16
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
Presented by Youngkook Lee, December 04, 2006 17
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
Presented by Youngkook Lee, December 04, 2006 18
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
Presented by Youngkook Lee, December 04, 2006 19
Q1 Q3 Q5
Q4 Q6 Q2
D1 D3 D5
D4 D6 D2
the number of the shorted turnsthe 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
Presented by Youngkook Lee, December 04, 2006 20
Machine Equations under Fault-Free Conditions
Stator Line-Neutral Voltages
Developed Torque
r rrd d ddt dt dt
s s PMs s s s s
i Lv r i L + i ︵ ︶ ︵ ︶︵ ︶
(1)
1= +2 2
r re
r r
d dPTd 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 LL L LL 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
Presented by Youngkook Lee, December 04, 2006 21
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 ( )]321( ) ( ) cos[2 ( )]21( ) ( ) 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
Presented by Youngkook Lee, December 04, 2006 22
Machine Equations under Turn Fault Conditions
Stator Line-Neutral Voltages
Developed Torque
r rrd d ddt dt dt
' ' '
' ' ' ' 's s PMs s s s s
i Lv r i L + i ︵ ︶ ︵ ︶︵ ︶
1= +2 2
r re
r r
d dPTd d
' ''T ' 'Ts PMs s s
Li i i ︵ ︶ ︵ ︶
where,
(1 ) 0 0 00 0 00 0 00 0 0
s
s
s
s
rr
rr
'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 LL L L L LL L L L LL L L L L
'SL
1 2T
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
Presented by Youngkook Lee, December 04, 2006 23
Machine Equations under Turn Fault Conditions
* Rearranging (3) and (4) yields
Stator Line-Neutral Voltages
Developed Torque
( ) ( ) ( ) ( ) ( )12
( ) ( )12
T 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 +idθ dθ dθ d
d θ d θ+dθ dθPT =
2θ 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 idt dθL θ
d d θ d θω ωdt dθ dθ
L θ
i L λv r i L i
2
Presented by Youngkook Lee, December 04, 2006 24
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 id d d
r idt d d
di dLr i L L i
dt d
i LL i
+ fan bn cn s f ls
div v v r i L
dt
(9)
3
Presented by Youngkook Lee, December 04, 2006 25
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 voltagegenerator IPMSM
sv eT*sov
*eT
r
*r
, ,, ,r e a b ci , ,,e a b ci
Load
Pole to phase
Presented by Youngkook Lee, December 04, 2006 26
Key Parameters for Specifying the Model
Class Item Unit Values
Motor
Pole Number [ - ] 8Rated /Max. Torque [Nm] 40 / 80
Rated Current [A] 114 / 250Rated 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
InverterNominal dc-Link Voltage [Vdc] 216
Switching Frequency [kHz] 7Current Control Rate [kHz] 7
Presented by Youngkook Lee, December 04, 2006 27
Simulation under Various Rotating Speeds
Simulation Conditions and Summary of the Results
Items Unit ValuesLoad Torque [Nm] 20
Rotating Speed [rpm] 1500 2450 3500Fault 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 82.26Negative 1.2 1.93 2.72
Zero 0.12 0.19 0.27
Sequence components in line currents
Positive[A]
62.30 61.95 61.85Negative 2.18 4.77 6.8
TorqueFund.
[Nm]20 20 20
2nd order 1.77 1.40 1.37
Presented by Youngkook Lee, December 04, 2006 28
Simulation Conditions and Summary of the Results
Items Unit ValuesLoad Torque [Nm] 0 40 80
Rotating Speed [rpm] 1500Fault 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 48.67Negative 1.11 1.33 1.61
Zero 0.11 0.13 0.16
Sequence components in line currents
Positive[A]
2.57 117.09 211.20Negative 1.24 3.04 3.75
TorqueFund.
[Nm]0 40 80
2nd order 1.63 2.27 3.61
Simulation under Various Loads
Presented by Youngkook Lee, December 04, 2006 29
Simulation Conditions and Summary of the Results
Simulation under Various Fault Fractions
Items Unit ValuesLoad Torque [Nm] 40
Rotating Speed [rpm] 1500Fault 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 36.83Negative 0 1.33 3.61 5.52
Zero 0 0.13 0.35 0.55
Sequence components in line currents
Positive[A]
113.07 117.09 124.72 131.84Negative 0 3.04 8.32 12.76
TorqueFund.
[Nm]40 40 40 40
2nd order 0 2.27 6.38 9.99
Presented by Youngkook Lee, December 04, 2006 30
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
Presented by Youngkook Lee, December 04, 2006 31
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
Presented by Youngkook Lee, December 04, 2006 32
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
Presented by Youngkook Lee, December 04, 2006 33
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 rf s f ls am r e f as
r
R di dLi r i L L i vdt d
where, represents the instantaneous value of the line-neutralvoltage 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)
Presented by Youngkook Lee, December 04, 2006 34
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)
Presented by Youngkook Lee, December 04, 2006 35
Machine Equations in the qd-variables in a steady State Condition under Fault-Free Condition Stator Voltage
Developed Torque
32 2
e e ee 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)
Presented by Youngkook Lee, December 04, 2006 36
Theoretical Foundations 4
Representation in Circle Diagram
di
qiConstant torque hyperbola, 0
eT
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
qiConstant torque hyperbola, 0
eT
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
Presented by Youngkook Lee, December 04, 2006 37
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 qC Cv r L i r i L
C i C i
e* e*
s ds dse* e*ds ds
2
0vi
se*ds
(16)
(17)
(18)
sv
Presented by Youngkook Lee, December 04, 2006 38
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 CL i i
e* e*ds ds
2 * 2 * 21 2 2 12 2[ ( ) ] [ ( ) ]
( ) ( )s m s s m sC C C Cv r L i r i Li i i i
e* e*s ds dse* e* e* e*
ds ds ds ds
(21)
2
0vi
se*ds
(22)
Presented by Youngkook Lee, December 04, 2006 39
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
Presented by Youngkook Lee, December 04, 2006 40
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
Presented by Youngkook Lee, December 04, 2006 41
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
Nor
mal
ized
Tor
que
Normalized speed
fi
3
Presented by Youngkook Lee, December 04, 2006 42
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 eee sym s PM d q
s e q d s e q d
LPT r L Lr L L r L L
( )00
e ees qs e d ds PMqs
e ees ds e q qsds
r i L ivr i L iv
Simulation for Comparing with Symmetrical Short-Circuit Operation
1
(23)
(24)
(25)
Presented by Youngkook Lee, December 04, 2006 43
Comparison of
Time (sec)
Circulating current in the shorted turns
In the case of the proposed
strategy
Cur
rent
(A)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
fi
2
Presented by Youngkook Lee, December 04, 2006 44
Comparison of the a-phase Currents
Time (sec)
a-phase current
In the case of the proposed
strategy
Cur
rent
(A)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
3
Presented by Youngkook Lee, December 04, 2006 45
Comparison of the a-phase Line-Neutral Voltages
Time (sec)
a-line to neutral voltage
In the case of the proposed
strategy
Volta
ge (V
)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
4
Presented by Youngkook Lee, December 04, 2006 46
Comparison of the Developed Torque
Time (sec)
Developed torque
In the case of the proposed
strategy
Torq
ue (N
m)
In the case of symmetrical short circuit operation
Simulation for Comparing with Symmetrical Short-Circuit Operation
5
Presented by Youngkook Lee, December 04, 2006 47
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
Presented by Youngkook Lee, December 04, 2006 48
Effects of the Machine Specifications
Torq
ue (N
m)
Speed (rpm)
Blue solid line : #1Red dotted line : #2Black dashed line : #3
Torque-Speed Characteristic Curves
2
Presented by Youngkook Lee, December 04, 2006 49
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
Presented by Youngkook Lee, December 04, 2006 50
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
Presented by Youngkook Lee, December 04, 2006 51
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
Presented by Youngkook Lee, December 04, 2006 52
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
Presented by Youngkook Lee, December 04, 2006 53
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)e
dsi eqsi
fiai
2
Presented by Youngkook Lee, December 04, 2006 54
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
Presented by Youngkook Lee, December 04, 2006 55
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
Presented by Youngkook Lee, December 04, 2006 56
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
Presented by Youngkook Lee, December 04, 2006 57
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
Presented by Youngkook Lee, December 04, 2006 58
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
Presented by Youngkook Lee, December 04, 2006 59
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
36
( )dq qdM MM
Presented by Youngkook Lee, December 04, 2006 60
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
1 cos 2 sin 22
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 21 cos 2 sin 22
( )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
Presented by Youngkook Lee, December 04, 2006 61
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
LL
L Li
Presented by Youngkook Lee, December 04, 2006 62
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
12 e
Presented by Youngkook Lee, December 04, 2006 63
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
Presented by Youngkook Lee, December 04, 2006 64
A STATOR TURN FAULT TOLERENT STRATEGY FOR INTERIOR PM SYNCHRONOUS MOTOR DRIVES in SAFETY CRITICAL APPLICATIONS
Presented by Youngkook Lee, December 04, 2006 65
Appendices
Further Simulated Waveforms Simulation under various rotating speeds
Simulation under various fault fractions
Simulation under various loads
Presented by Youngkook Lee, December 04, 2006 66
Spee
d (r
pm)
Torq
ue (N
m)
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
Presented by Youngkook Lee, December 04, 2006 67
Waveforms : Phase Voltage, Line Current, and Fault Current
Time (sec)
Volta
ge (V
)C
urre
nt (A
)C
urre
nt (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
Presented by Youngkook Lee, December 04, 2006 68
Waveforms : Circulating Currents C
urre
nt (A
)
Time (sec)
Circulating current in the shorted turns
1 %
3 %
5 %
Simulation under Various Fault Fractions 1
Presented by Youngkook Lee, December 04, 2006 69
Torq
ue (N
m)
Time (sec)
Waveforms : Developed Torques
Developed torque
No fault
1 %
3 %
5 %
Simulation under Various Fault Fractions 2
Presented by Youngkook Lee, December 04, 2006 70
Waveforms : Rotating Speeds
Time (sec)Rotating speed
No fault
1 %
3 %
5 %
Spee
d (r
pm)
Simulation under Various Fault Fractions 3
Presented by Youngkook Lee, December 04, 2006 71
Waveforms : Circulating Currents
Time (sec)
Circulating current in the shorted turns
No load
40 Nm
80 Nm
Cur
rent
(A)
Simulation under Various Loads 1
Presented by Youngkook Lee, December 04, 2006 72
Torq
ue (N
m)
Waveforms : Developed Torques
Time (sec)
Developed torque
No load
40 Nm
80 Nm
Simulation under Various Loads 2
Presented by Youngkook Lee, December 04, 2006 73
Waveforms : Rotating Speeds
Time (sec)
Rotating speed
No load
40 Nm
80 Nm
Spee
d (r
pm)
Simulation under Various Loads 3