Post on 11-Aug-2015
IEEE Houston SectionC ti i Ed ti O D dContinuing Education On Demand
Seminar
Presentation Code: 620
April 3-4, 2007
Motor StartingEquivalent Circuits, Starter Types, Load
Types, and Dynamics
Review of induction and synchronous motor design,equivalent circuits for start and operation; starting,
operating and breaking operating characteristics, loadtypes. Review starting techniques, calculations, and
comparison.
Agenda
Induction MotorInduction Motor Synchronous MotorSynchronous Motoryy Mechanical Train SystemMechanical Train System Starting, Operation and Breaking MethodsStarting, Operation and Breaking Methodsg, p gg, p g Special ConsiderationSpecial Consideration Calculations, Simulation, ApplicationsCalculations, Simulation, ApplicationsCalculations, Simulation, ApplicationsCalculations, Simulation, Applications
Agenda
Induction MotorInduction Motor Basics, characteristics, and modeling
Synchronous MotorSynchronous Motor Basics, characteristics, and modeling
M h i l T i S tM h i l T i S tMechanical Train SystemMechanical Train System Load characteristics Inertia Torque Consideration Train Acceleration Time
St ti O ti d B ki M th dSt ti O ti d B ki M th dStarting, Operation and Breaking MethodsStarting, Operation and Breaking Methods Induction and Synchronous Motor Synchronous Motor Onlyy y
Agenda
Special ConsiderationSpecial Consideration Harmonic Torques
H i Fl Harmonic Flux Rotor Slots Design
Calculations Simulation ApplicationsCalculations Simulation ApplicationsCalculations, Simulation, ApplicationsCalculations, Simulation, Applications Software Methodology
Induction Motor
Basics, type characteristics, load characteristics, and modeling • Induction motor - General data, principle of
operation and nameplate information describing motormotor
• Motor types and characteristics, application consideration
• Load types and characteristics, application consideration
• Motor model• Motor model• Equivalent motor parameters• Other considerationOther consideration
Induction Motor
General data Motor electro-mechanical characteristics are described
bby:• Nominal Voltage• Nominal frequency• Nominal Current• Number of phases• Number of poles• Number of poles• Design class• Code letter
M f i i• Moment of inertia• All others (rated power factor, efficiency, excitation current etc.)
Induction Motor
Type of TorquesCurrent Curve
Break-
Motor Torque CurvePull-up Torque
Down/Critical Torque
Locked Rotor/ Breakaway
Torque
Full Load Operating
Full Load Operating Current
Load Torque Curve
p gTorque
Full Load Operating Critical Load Torque CurveSpeed/SlipSpeed/Slip
Induction MotorType of Torques Locked Rotor or Starting or Breakaway Torque
• The Locked Rotor Torque or Starting Torque is the torque the electrical motor develop when its starts at rest or zero speed.
• A high Starting Torque is more important for application or machines hard to start - as positive displacement pumps, cranes etc. A lower Starting Torque can be accepted in applications as centrifugal fans or pumps where the start load is low or close to zero.
Pull-up Torque• The Pull-up Torque is the minimum torque developed by the electrical motor when it runs from zero to full-
load speed (before it reaches the break-down torque point)• When the motor starts and begins to accelerate the torque in general decrease until it reach a low point at a
certain speed - the pull-up torque - before the torque increases until it reach the highest torque at a higher speed - the break-down torque - point.
• The pull-up torque may be critical for applications that needs power to go through some temporary barriers hi i h ki di iachieving the working conditions.
Break-down Torque• The Break-down Torque is the highest torque available before the torque decreases when the machine
continues to accelerate to the working conditions.
Full-load Torque or Braking Torque• The Full-load Torque is the torque required to produce the rated power of the electrical motor at full-load
speed.
Induction Motor
Code letters• In general it is accepted that small motors requires higher
starting KVA than larger motors Standard 3 phase motors oftenstarting KVA than larger motors. Standard 3 phase motors often have these locked rotor codes:
o less than 1 hp: Locked Rotor Code L, 9.0-9.99 KVAo 1 1/2 to 2 hp: Locked Rotor Code L or M 9 0 11 19o 1 1/2 to 2 hp: Locked Rotor Code L or M, 9.0-11.19o 3 hp : Locked Rotor Code K, 8.0-8.99o 5 hp : Locked Rotor Code J, 7.1-7.99o 7.5 to 10 hp : Locked Rotor Code H, 6.3-7.09o more than 15 hp : Locked Rotor Code G, 5.6-6.29
Induction Motor Design Type
Different motors of the same nominal horsepower can have varying starting current torquevarying starting current, torque curves, speeds, and other variables. Selection of a particular motor for an intended task must take all engineering parameters i t tinto account.The four NEMA designs have unique speed-torque-slip relationships making them suitable to different type of applications:to different type of applications:
• NEMA design A
• NEMA design B
• NEMA design C
• NEMA design D
Induction MotorDesign Type
• NEMA design Ao maximum 5% slipo high to medium starting current o normal starting torque (150-170% of rated)o normal locked rotor torqueo normal locked rotor torqueo high breakdown torqueo suited for a broad variety of applications - as fans and pumps
• NEMA design Bo maximum 5% slipo low starting currento high locked rotor torqueo high locked rotor torqueo normal breakdown torqueo suited for a broad variety of applications, normal starting torque -
common in HVAC application with fans, blowers and pumps
Induction MotorDesign Type
• NEMA design Co maximum 5% slipo low starting currento high locked rotor torqueo normal breakdown torqueo normal breakdown torqueo can’t sustain overload as design A or Bo suited for equipment with high inertia starts - as positive
displacement pumps
• NEMA design Do maximum 5-13% slipo low starting currentgo very high locked rotor torqueo Usually special ordero suited for equipment with very high inertia starts - as cranes, hoists
etc.etc.
Synchronous Synchronous Motor
General data Motor electro-mechanical characteristics are described
bby:• Nominal Voltage• Nominal frequency• Nominal Current• Number of phases• Number of poles• Number of poles• Design class• Code letter
M f i i• Moment of inertia• All others (rated power factor, efficiency, excitation current etc.)
Load Load Types
Breakaway Accelerating Peak Running
Blowers centrifugal:
Load Torque as a Minimum Percent Drive TorqueApplication
Blowers, centrifugal:Valve closed 30 50 40Valve open 40 110 100
Blowers, positive displacement, rotary, bypass 40 40 100Centrifuges 40 60 125Compressors, axial-vane, loaded 40 100 100Compressors, reciprocating, start unloaded 100 50 100Conveyors belt (loaded) 150 130 100Conveyors, belt (loaded) 150 130 100Conveyors, screw (loaded) 175 100 100Conveyors, shaker-type (vibrating) 150 150 75Fans, centrifugal, ambient:
Valve closed 25 60 50Valve open 25 110 100
Fans, centrifugal, hot:Valve closed 25 60 100Valve closed 25 60 100Valve open 25 200 175
Fans, propeller, axial-flow 40 110 100Mixers, chemical 175 75 100Mixers, slurry 150 125 100Pumps, adjustable-blade, vertical 150 200 200Pumps, centrifugal, discharge open 40 150 150Pumps oil field flywheel 40 150 150Pumps, oil-field, flywheel 40 150 150Pumps, oil, lubricating 40 150 150Pumps, oil, fuel 40 150 150Pumps, propeller 40 100 100Pumps, reciprocating, positive displacement 175 30 175Pumps, screw-type, primed, discharge open 150 100 100Pumps, slurry-handling, discharge open 150 100 100P t bi t if l d ll 50 100 100Pumps, turbine, centrifugal, deep-well 50 100 100Pumps, vacuum (paper mill service) 60 100 150Pumps, vacuum (other applications) 40 60 100Pumps, vane-type positive displacement 150 150 175
Inertia Inertia
Jz
wJi
nin1
2
p
miVin1
2
1i
n1 1i
n1
w - numer rotating elementsb li i lp - number linera motion elements
Inertia
Torque, Speed, Inertia
TTL
JL I N2
nd
n BL B N2
N - gear ratioJ - inertia
Tm NJL Im N t
nmd
nm BL Bm N
B - dumping
Mechanical Train Acceleration
S1 - scale of speed acceleration
S2 - scale of torque acceleration
S3 - scale of time required to accelerate train with acceleration torque from one speed toS3 - scale of time required to accelerate train with acceleration torque from one speed to another
S4 - scale of dynamic energy needed for acceleration
S2 S4S1 S3
S1 100RPMdiv1
S 20N·m
S2 20div2
S30.1secdiv3
S4S2 S3
k S4 0.04S4 S1k S4 0.04
Jtrain 0.431 kg m2
OA Jtrain
30 S4 OA 1.128m2 kg
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Software ETAP, SKM/PTW
• Sufficient for DOL starting and reduce voltage discrete calculations; not applicable for RVSS starters analysis
SPICE, MATLAB, EMTP-ATPSPICE, MATLAB, EMTP ATP• Applicable for motor starting analysis with control loops
considerations, can predict waveforms and effect on power systemsystem
Custom Software• Write own software utilizing Compilers or high level language
(i M tl b Vi Si )(i.e. Matlab or VisSim)
Hand Calculations• Utilize MathCad or other mathematical analysis package; must y p g ;
understand electrometrical theory
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – CalculationsMotor Data
Pn 1200 Hp fn 60 Hz fs fn p 2
Pn 895 2kWPn 895.2kW
Un 4kV mkr 1.8
PF 0 87 n 1789 RPMPFn 0.87 nn 1789 RPM
n 0.9595
ir 5.0
mr 0.7
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – CalculationsNominal Parameters
InPn
n 3 Un PFn In 154.79A
PTn
Pn
nn
30
Tn 4778.38N m Tn 3524.36ft·lbf
2 fs 60 fs -1s
s
p ns
s
p s 188.5s 1
ns 1800RPM
snns nn
sn 0.0061n nnn
ZzUn
3 ir In Zz 2.98
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – Calculations
rr XaX 2' SXSR aII r
2' SI
'R
rR'
XR1V
oI
FeI mISRa
SR rr
2'OR
)1( SS
R r mXFeR
21 aEE
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Iteration starting parameters:
Equivalent Schematic Parameters – Calculations
Rz 0.001 Xz 0.2
Given { From motor equivalent diagram }
Zz Rz2 Xz
2z z z
mr Tn3s
Un
3
2
Rz
2
Rz2 Xz
2
Rz
Xz
Find Rz Xz Rz 0.7 Xz 2.9
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – CalculationsRs Rz
510
Rs 0.35
5Xs Xz
510
Xs 1.45
R'r Rs X'r Xs
1 nPn Pn
n
n Pn 37.79kW
Pun32
In2 Rz Pun 25.22kW
Pm 0.01Pn Pm 8.952kW
Pfen Pn Pun Pm Pfen 3.61kW
RfeUn
2
Pfen Rfe 4426.97
UIfe
Un
3 Rfe Ife 0.52A
I0 20% In I0 30.96A
I I 2 I 2 I 30 95AIm I0 Ife Im 30.95A
XmUn
3 Im Xm 74.61
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – CalculationsZs f( ) Rs
ff
j Xs Change "f" only when analysis with VSDfn
Z'r s f( )R'rs
ffn
j X'r
ZmRfe Xm j
R X j Zm f( )
ffn
0.7Rfe
ffn
Xm j
m Rfe Xm jm( )
ffn
0.7Rfe
ffn
Xm j
Z s f( ) Zs f( )Z'r s f( ) Zm f( )
Z'r s f( ) Zm f( )
fU f( ) Un
ffn
n s f( )60 f
p1 s( )
Is s f( )U f( )
3 Z s f( ) I'r s f( ) Is s f( )
Zm f( )
Z'r s f( ) Zm f( )
T s f( )3 p
I' s f( ) 2 Re Z' s f( ) Te s f( )2 f
I r s f( ) Re Z r s f( )
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – CalculationsNominal Slip Calcs
s 0.0100
Given
Te s fn n s fn
30 Pn Pm
30sn Find s( ) sn 0.0228
In Is sn fn In 147.59A
T T f T 4908 38NTn Te sn fn Tn 4908.38N m
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters –IEEE 112
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – Sensitivity Calculations
Basis for ETAP Motor Estimating Calcs
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – Sensitivity Calculations
EMTP ATP G S ftEMTP-ATP Group Software
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Equivalent Schematic Parameters – Sensitivity Calculations
EMTP ATP G S ftEMTP-ATP Group Software
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
U1Isc 3P 150.0 MVAIsc SLG 36.0 MVA
B113800 V
S
P TR1Size 3250.00 kVAPri Delta Sec Wye-Ground yPriTap -2.50 %%Z 5.7500 %X/R 11.0
B24160 V
CB-001
CBL-00012- #4/0 MV EPR 150.0 MetersAmpacity 560.0 A
B34160 V
M12500.000 hpLoad Factor 1.00 X"d 0.17 pu
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
U1Isc 3P 150.0 MVAIsc SLG 36.0 MVA
G18750 kVAX"d 0.2 pu
B113800 V
S
P TR1Size 3250.00 kVAPri Delta Sec Wye-GroundSec Wye Ground PriTap -2.50 %%Z 5.7500 %X/R 11.0
B24160 V
CB-001
CBL-00012- #4/0 MV EPR 150.0 MetersAmpacity 560.0 A
B34160 V
M12500.000 hpLoad Factor 1.00 X"d 0.17 pu
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
1.1
Ub 1Gen KCR
0.9
1
Ub_1Gen_KCRUb 2Gen KCR 0 9
1
Ub_1Gen_KCR
Ub_2Gen_KCR
Ub_1Gen_DECS
Ub_2Gen_DECS
0 5 10 15 200.8
0.9 Ub_2Gen_KCRUb_1Gen_DECSUb_2Gen_DECS
0.9
Time
2000 1 2
1500
2000
1800
RPM 0 9
1
1.1
1.2Ub [pu]
1.0
0 9
500
1000
Mot RPMMot Amp
Amp
0.6
0.7
0.8
0.9 0.9Ub
0 10 20 30 400
Mot Amp
Time0 20 40 60
0.5
Time
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
1
1.2
1Ub 1Gen KCR
0.8
1
Ub_1Gen_KCRUb 2Gen KCR
0.9
1Ub_1Gen_KCR
Ub_2Gen_KCR
Ub_1Gen_DECS
Ub_2Gen_DECS
0 5 10 15 200.6
Ub_2Gen_KCRUb_1Gen_DECSUb_2Gen_DECS
Time
2000
1500
2000
1800
RPM 0 9
1
1.1
1.2Ub [pu]
1.0
0 9
500
1000
Mot RPMMot Amp
RPM
Amp
0 6
0.7
0.8
0.9 0.9Ub
0 10 20 30 400
Mot Amp
Time0 20 40 60
0.5
0.6
Time
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
3500
5000
Pfpso
2000
3500fpso
Q fpso
Ptlp
Q tlp
0 20 40 601000
500p
Time
1500
2000Mot RPMMot Amp
1.1
1.2Ub_fpso [pu]Ub_tlp [pu]
500
1000RPM
Amp
0.9
1
0.9
1
Ubfpso
Ubtlp
0 10 20 30 400
Time
0 20 40 600.8
Time
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
PARKs equations for this machnie:
Motor Simulation
ps s r j s s vspr r s j s m r
T Tpm n
Te Tr
J
State variable assigment: x0 = s (stator) , x1 = r (rotor), x2 = m (angular speed)
32
Veff x0 x1 j x0
f x t( ) x1 x0 j x2 x1
n MLk L Im x0 x1
k
x2n
2
Lk Lr n J
n
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Coeficients for Runge-Kutta (R-K) interation 4th degree:
Motor Simulationg ( ) g
k1 x t( ) h f x t( ) k2 x t( ) h f x k1 x t( )2
t h2
k3 x t( ) h f x k2 x t( )
2 t h
2
k4 x t( ) h f x k3 x t( ) t h( )( )2 2
k4 x t( ) h f x k3 x t( ) t h( )
Final equation for R-K calcualtions:
x i 1 x i 1 k1 x i i h 2 k2 x i i h 2 k3 x i i h k4 x i i h x x6
k1 x i h 2 k2 x i h 2 k3 x i h k4 x i h
is
i
1L L
Lr
M
M
L
s
Equations for current in stator:
ir Lk Lr M Ls r
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Conversion Park reference frame to phase domain:Motor Simulation
i( ) h i
cos i( ) cos i( ) 23
cos i( ) 43
TP i( ) 23
( )
sin i( )
( )3
sin i( ) 23
( )3
sin i( ) 43
12
12
12
if i( ) TP i( ) 1
isdi
isq
Pase currentsif i( ) TP i( ) isqi
0
Pase currents
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
100
Angular Speed vs. time
125
Motor Simulation
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
50
0
i
0.80 h i
100
600
Torque vs. time
700
400
T.ei
550
Average, dynamical and load torques
T
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7400
400
0.80 h i
450
50
Tei
Tci
Tri
0 20 40 60 80 100 120450
i
Calculations, Simulation, ApplicationsCalculations, Simulation, Applications
Phase A, B, C Current
Motor Simulation
150
50
250350
350
i.f i( )0
i.f i( )1
i.f i( )2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7350
350
0.80 h i
50
250
Phase A, B, C Current
350
i.f i( )0
i.f i( )1
i i( )
0 0.05 0.1 0.15 0.2 0.25350
150
350
i.f i( )2
0.30 h i
Testing/ProtectionTesting/Protection
6000
7000
8000
70
80
90
100
Avg Phase Current (A) Ground Current (A)
3000
4000
5000
30
40
50
60 Avg Line Volt (V) kW Power (kW) kvar Power (kvar) T. C. Used (%) Hottest Stator RTD (° C)
0
1000
2000
0 200 400 600 800 1000 12000
10
20 Motor Load (x FLA)
Testing/ProtectionTesting/Protection
6000
7000
8000
80
100
120
Avg Phase Current (A) Avg Line Volt (V)
3000
4000
5000
40
60
80 Current U/b (%) kW Power (kW) kvar Power (kvar) Hottest Stator RTD (° C) T. C. Used (%)
0
1000
2000
0 200 400 600 800 1000 1200 14000
20 Ground Current (A)
Testing/ProtectionTesting/Protection
120
9
10
80
100
7
8
60
4
5
6
Hottest Stator RTD (° C)
T. C. Used (%)
Motor Load (x FLA)
20
40
2
3
00 1000 2000 3000 4000 5000 6000 7000
0
1
Testing/ProtectionTesting/ProtectionLAST "BLOW" - Phase A Current (Amps)
2000
3000
4000
LAST "BLOW" Phase B Current (Amps)
2000
3000
4000
-2000
-1000
0
1000
Tim
e
-47.
91
22.9
1
93.7
3
164.
56
235.
38
306.
2
377.
02
447.
84
518.
66
589.
49
660.
31
731.
13
801.
95
872.
77
943.
59
1014
.41
1085
.24
1156
.06
1226
.88
1297
.7
1368
.52
1439
.34
1510
.17
1580
.99
1651
.81
1722
.63
1793
.45
1864
.27
1935
.09
2005
.92
CU
RR
ENT
( A
Phase A Current (Amps)
-2000
-1000
0
1000
Tim
e
-47.
91
22.9
1
93.7
3
164.
56
235.
38
306.
2
377.
02
447.
84
518.
66
589.
49
660.
31
731.
13
801.
95
872.
77
943.
59
1014
.41
1085
.24
1156
.06
1226
.88
1297
.7
1368
.52
1439
.34
1510
.17
1580
.99
1651
.81
1722
.63
1793
.45
1864
.27
1935
.09
2005
.92
CU
RR
ENT
( A
Phase B Current (Amps)
-4000
-3000
TIME (ms)
-4000
-3000
TIME (ms)
LAST "BLOW" Phase C Current (Amps) LAST "BLOW" AN(AB) Voltage (V)
1000
2000
3000
4000
ENT
(A
2000
4000
6000
8000
GE
(V)
-4000
-3000
-2000
-1000
0
Tim
e
-47.
91
22.9
1
93.7
3
164.
56
235.
38
306.
2
377.
02
447.
84
518.
66
589.
49
660.
31
731.
13
801.
95
872.
77
943.
59
1014
.41
1085
.24
1156
.06
1226
.88
1297
.7
1368
.52
1439
.34
1510
.17
1580
.99
1651
.81
1722
.63
1793
.45
1864
.27
1935
.09
2005
.92
CU
RR
E Phase C Current (Amps)
-8000
-6000
-4000
-2000
0Ti
me
-49.
99
18.7
5
87.4
9
156.
22
224.
96
293.
7
362.
44
431.
18
499.
92
568.
66
637.
39
706.
13
774.
87
843.
61
912.
35
981.
09
1049
.83
1118
.56
1187
.3
1256
.04
1324
.78
1393
.52
1462
.26
1530
.99
1599
.73
1668
.47
1737
.21
1805
.95
1874
.69
1943
.43
2012
.16
VOLT
AG AN(AB) Voltage (V)
TIME (ms) TIME (ms)
Testing/ProtectionTesting/Protection
2.5
3
3.5
0.5
1
1.5
2
LINE
2 5
3
3.5
-0.5
00 100 200 300 400 500 600
0 5
1
1.5
2
2.5
Series1Series2
3.5
-0.5
0
0.5
0 100 200 300 400 500 600
1.5
2
2.5
3
3.5
Series1
-0.5
0
0.5
1
1.5
0 100 200 300 400 500 600
Series2
ReferencesReferences
• Fitzgerald & Kingsley, Electric Machinery, McGraw-Hill, 1961• Liwschitz-Garik, Whipple, A-C Machines, Van Nostrand, 1961• Say, M.G., Alternating Current Machines, John Wiley & Sons, 1976
Gra Electrical Machines and Dri e S stems John Wile & Sons 1989• Gray, Electrical Machines and Drive Systems, John Wiley & Sons, 1989• Leonhard, Control of Electrical Drives, Spinger-Verlag, 1985• Maxwell, James Clerk, A Treatise on Electricity and Magnetism, third edition, 1891• IEEE Standard 519-1992 “IEEE Recommended Practices and Requirements
for Harmonic Control in Electrical Power Systems”, IEEE Press SH15453, New York, 1993• Hammond, P. Power Factor Correction of Current Source Inverter Drives with Pump
Load 1980 IEEE/IAS Conference Record pp 520-529.• Osman R A Novel Medium Voltage drive Topology with Superior Input and• Osman, R., A Novel Medium-Voltage drive Topology with Superior Input and
Output Power Quality, VI Seminario de Electronica de Potencia, 1996.• Hammond, P., A New Approach to Enhance Power Quality for Medium Voltage Drives,
1995 IEEE/PCIC Conference Record pp231-235.• Ferrier, R., McClear, P. Developments and Applications in High-Power Drives Proceedings,
Advanced Adjustable Speed Drive R&D Planning Forum, EPRI-CU-6279 NC, USA, Nov 87.• Bin Wu, DeWinter, F. Voltage stress on induction motors in medium voltage (2300 to 6900V)
PWM GTO CSI drives PESC 95 Record 26th Annual IEEE Power Electronics SpecialistsPWM GTO CSI drives, PESC 95 Record. 26th Annual IEEE Power Electronics Specialists Conference (Cat. No. 95CH35818) Part vol.2 p.1128-32 vol.2; IEEE, New York, NY, USA, 1995.