A Thermal Management Approach to Fault-Resilient Design of Three-Level IGCT-Based NPC Converters

1. A Thermal Management Approach to
Fault-Resilient Design of Three-Level
IGCT-Based NPC Converters
Presented by
Shambhu R
11739
Seminar date 16/09/2014
Guided by
Ms.Mareena Francis
Asst. Professor
Electrical and Electronics Engg. Dept.

2. Variable Frequency Drive
Block diagram of a typical IGCT based NPC VFD
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3. OVERVIEW
1. IGCT
1.INTRODUCTION
2.KEY FEATURES
3. APPLICATIONS
2. NPC Converter
1.THEORY
2.SWITCHING STATES
3. Case Study
1.INTRODUCTION
2.OVERCURRENT PROTECTION
3.POWER DEVICE THERMAL STRESSES
4.JUNCTION TEMPERATURE
5. MANAGING THE POWER DEVICES THERMAL STRESS
6. IMPROVEMENTS IN THE THERMAL STRESS OF IGCTS
7. CONCLUSION
4. Reference
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4. Integrated Gate
Commutated Thyristor
(IGCT)
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5. Introduction
• Introduced by ABB and Mitsubishi in the year
1997.
• Basically a high voltage, high power, hard driven
device.
• Similar to GTO, it is a fully controllable power
switch.
IGCT
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6. IGCT Symbol
IGCT
10 KV IGCT
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7. Features
• Improved GTO switching characteristics
for operation without dv/dt snubbering
at high current density
• Reduced on-state and turn-off losses
through minimization of the silicon
thickness
• Reduced gate-drive requirements, especially
during conduction
• High-frequency operation for continuous
and dynamic conditions
• Reliability Improvement per MVA by reduction of
complexity and components
IGCT
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8. IGCT
(µs)
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IGCT Turnoff Characteristics

9. Applications
• Variable Frequency Drives (VFD)
• Static VAR Compensators (SVC)
• Traction
• Industrial Drives
IGCT
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10. NPC CONVERTER
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11. Theory
• Better waveform quality.
• One of the multilevel converter
topologies.
• Contains 4 Power Switches in
each phase.
• 2 Clamping Diodes.
• Capacitors are used for realizing
voltage divider circuits.
NPC CONVERTER
Names
Neutral point clamped
converter
3 Level converter
Diode clamped
converter
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12. 3 Level Inverter
NPC CONVERTER
• Symbolic representation
of 3 level inverter.
• A TPST switch is used.
• At each position, different
voltage levels.
VOLTAGE LEVELS
Sa0 -Vdc/2 V
Sa1 0V
Sa2 Vdc/2 V
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13. Switching States
NPC CONVERTER
Switching
State
Device Switching Status
(Phase A)
Inverter Terminal
Voltage
Q1 Q2 Q3 Q4
P On On Off Off Vdc/2
O Off On On Off 0
N Off Off On On -Vdc/2
Vdc/2
O
t
V
Q1 and Q4 are called as Main devices
Q2 and Q3 are called as Auxiliary devices
Diodes Cd1 and Cd2 are the Clamping diodes
P
N
Vdc/2
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14. Circuit Diagram
NPC CONVERTER
E
E
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15. CASE STUDY
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16. Introduction
• Availability of the converters are mandatory, as
maintenance or replacement needs large downtimes
incompatible with the requirements of production
process.
• Main goal of the paper –if there is a malfunction of the
breaker element in the case of an over current, then
reduce the damage extension and to restrict the
damage to the free wheeling power diodes, thus
protecting the IGCTs.
CASE STUDY
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17. Overcurrent Protection
• Has vital importance in VFDs
• When fault condition occur in commercial drives with
AFE(Active Front End) Rectifier
 Protection is given by firing all the IGCTs
 To limit the thermal stress on each devices
 This mode of protection is called firing mode protection scheme
 In such a case the faulty converter should be quickly disconnected from
the mains
 Malfunction of the breaker device result in the damage of AFE
CASE STUDY
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18. Short Circuit Current Distribution
CASE STUDY
• If firing mode protection scheme
is activated, then there is chance
of short circuit paths as shown in
fig .
• Shaded (through clamp diodes),
dotted and dashed paths
(through freewheeling diodes)
• The internal IGCTs share most
of the current(Q2C,Q3B)
• Similarly in other phases also
 As an inference we get the idea that
internal IGCTs of all phases will get
affect by the thermal stress
NPC regenerative rectifier short-circuit paths during
shoot-through firing protection (phases B and C)
VBN > VCN
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19. Power Device Thermal Stresses
• Subjected to sequence of two
different types of thermal
stresses
 Transient Thermal Stress due to dc
link capacitor
 Short circuit Thermal Stress due to
short circuit current from power grid
• DC Link capacitor discharge
 Shown in figure.
 With a frequency
Where
Leq –Equivalent inductance in the bridge.
Ceq- Equivalent series capacitance in
the bridge
CASE STUDY
Equivalent dc bus discharging network on the
shoot-through firing mode protection
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Fo=1/(2*¶*(Leq *Ceq )^1/2)

20. Junction Temperature
• Consequence of keeping the
converter in the shoot through
mode for more time is shown in
fig.
• Shows the thermal stress in
the freewheeling diodes is less
than the other power devices.
• Result s in the permanent
damage of the internal IGCTs.
CASE STUDY
Junction temperature rises on shoot-through mode
Phase A devices.
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21. Managing the Power Devices Thermal
Stress• To protect the internal IGCTs,
the current through the
clamping diode must be
reduced.
IQ-short circuit current through internal
IGCT
IFW-short circuit current through
freewheeling diodes
Reduce IQ /IFW , for this the
resistance clamp diode circuit
should be increased Rc-
resistance of the clamp
Rf - resistance of the freewheeling
diode branch
Rc /Rf should be increased.
• So , add an additional
resistance Zr (“resilience
impedance”) is added to the
clamp diode branch.
CASE STUDY
Insertion of the resilience impedances (Zr) in the
Clamping Diode branches of the 3L NPC IGCT-based
converter.
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22. Improvements in the Thermal stress
of IGCTS
• Redesigned the path of current
flow in shoot through mode by
addition of “resilience
impedance” .
• To restrict the damage to the
power diodes(free wheeling) as
much as possible
.
• So that IGCTs can be protected
in the converters shoot through
mode even if the breaker fails to
work properly.
Junction temperature rises on shoot-through
mode Phase A devices of the resilient converter
CASE STUDY
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23. Conclusion
• In this paper, the short-circuit behavior of the IGCT-based
high-power 3L NPC topology has been addressed by the
damage pattern resulting from a shoot-through mode followed
by a protection scheme malfunction.
• To make minimum repair cost and minimum repair time,
damage should be restricted to the diodes, keeping IGCTs
safe.
• By proper design of the converter bus bars and management
of the thermal stresses, it is possible for the IGCTs to survive
the converter shoot-through mode even in the event that the
circuit breaker fails to operate.
CASE STUDY
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24.  Anderson Vagner Rocha, Hélder de Paula, Manoel Eustáquio dos Santos, Braz J.
Cardoso Filho,” A Thermal Management Approach to Fault-Resilient
Design of Three-Level IGCT-Based NPC Converters” IEEE Trans. Ind. Appl., VOL.
49, NO. 6, november/december 2013
 P. K. Steimer, H. E. Gruening, J. Werninger, E. Carroll, S. Klaka, and S. Linder,
“IGCT—A new emerging technology for high power, low cost inverters,” IEEE Ind.
Appl. Mag., vol. 5, no. 4, pp. 12–18, Jul./Aug. 1999.
 A. Nabae, I. Takahasai, and H. Akagi, “A new neutral-point-clamped PWM inverter,”
IEEE Trans. Ind. Appl., vol. IA-17, no. 5, pp. 518–523,Sep. 1981.
 D. Floricau, E. Floricau, and G. Gateau, “Three-level active NPC converter: PWM
strategies and loss distribution,” in Proc. IEEE IECON,Nov. 2008, pp. 3333–3338.
 Muhammad H.Rashid ” Power Electronics” ,2012
Reference
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