FIELD OF THE INVENTION
The present invention relates to IGBT based inverter module for locomotive
applications.
BACKGROUND OF THE INVENTION
IGBT is power switching device for medium to high power application. IGBT is
suitable for high frequency application, high di/dt capacity and its simple gate
driver and low consumption of gate power and accordingly provides very high
power gain during turn on as well as turn off. For DC to AC application, IGBT is
replacing the known GTO which has frequency limitation, a complex gate driver
circuit and low turn of power gain.
GTO is thyristor type current control device which can be turned on and off
through its Gate and cathode. For switching of the GTO, particularly during
turning off, the GTO gate require very high negative current peak which is
dependent on main circuit load current. Being a current control device, the GTO
needs high current spike or pulses of specific profile during ON and OFF period.
Therefore, the GTO based inverter requires quite a complex gate driver card for
turning on and off of the GTO's. Further, power consumptions in its driver card is
very high. In contrast thereto, the IGBT is a voltage control device like MOSFET

and so it's driver circuit is simpler and consumes very less power. GTO
application is limited with low frequency whereas IGBT can work with frequency
as high as 50Khz. Additionally, higher di/dt capability makes the IGBT more
suitable in traction application for its reliability. Therefore it is common practice
to use IGBT in place of GTO.
GTO modules are mainly capsule type with contact points at both sides. (One
called +ve or Anode and another -ve or cathode). For connections, it needs bus
burs at both sides for clamping under certain pressure with one or more spring
column. Less pressure may lead to loose contact resulting in localized over
temperature and eventually destroying the device, whereas more pressure may
crack and destroy the device. Generally, one side of the devices is directly
mounted on at least one heat sink with bus bars and a freewheeling diode
connected across the GTO's for inverter application. Therefore an isolation base
is essential to mount multiple devices on a heat sink and it is also essential to
isolate the base heat sink from the electrical Circuit.
Whereas in case of IGBT, the IGBT's are having isolated base for mounting with
a heat sink. This enables one or more IGBT modules to mount on a single heat
without any additional requirement of isolation. And there is no need of spring
column and clamping arrangement in IGBT, like the GTO.
Presently in 6000HP 3-phase electric loco, GTO based inverter module is used in
Aux. converter. This inverter module communicates with an electronic Rack of
the converter for protection, measurement and firing signal for the GTO's.

OBJECTS OF THE INVENTION
To overcome the drawbacks of the prior art, the innovative remedial actions are
under-taken and as such objects of the invention are summarized below:
The primary object is to propose an IGBT based Inverter module which can be
used for ac output 415V, 150Amp replacing a GTO based inverter module of
WAG9/WAP5/WAP7 locomotives of Indian Railways.
Another object is to propose an IGBT based Inverter module for
WAG9/WAP5/WAP7 locomotive which can be used safely at a distance from DC
link capacitor bank.
Further objective is to propose an IGBT based Inverter module for
WAG9/WAP5/WAP7 locomotive which produce controlled rate of rise of output
voltage (dv/dt).
Further objective is to propose an IGBT based Inverter module for
WAG9/WAP5/WAP7 locomotive which can be operated with pulse width
modulation (PWM) technique for improved total harmonics distortion (THD).
Another objective is to propose an IGBT based Inverter module for
WAG9/WAP5/WAP7 locomotive which enable to use a sine filter at output for
improved output power quality.

Another objective is to propose an IGBT based Inverter module for
WAG9/WAP5/WAP7 locomotive which is capable of handling short circuit current
up to 10KA for up to 10 micro second.
SUMMARY OF THE INVENTION
Accordingly, there is provided an IGBT based inverter module with dedicated
communication protocol for locomotive applications, comprising a power circuit
block having one or two H-bridge IGBT module. In case of two H-bridge IGBT
modules, they are connected in parallel; and a dv/dt limiting L-C filter circuit; and
a control module circuit block having a gate interface card, a gate control circuit,
and a current sensing transducer, wherein each IGBT module comprises one
upper IGBT and lower IGBT connected in series making the inverter module with
three power terminals configured; gate -emitter as well as collector terminals of
each IGBT are connected with driver card for controlling, monitoring &
protecting the IGBTs. The L-C filter reduces dv/dt at the motor terminal; and a
damping resistor connected in series with capacitor of the L-C filter to reduce
high frequency oscillation at output voltage. The series resistance also
dissipates un-useful power as well as limits the peak IGBT current while
discharging the capacitor with turn on of IGBT.
According to the present invention, a new gate driver card for IGBT and a power
module with IGBT have been developed to replace a GTO based inverter module.
Mechanical fittings and other electrical interfacing are kept same as those of the
existing GTO based inverter module to maintain interface compatibility.

Unlike the prior art, the stray inductance of cable from the capacitor bank to the
inverter modules is compensated with an input capacitor in the module and
voltage spikes are controlled within a safe limit.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a circuit diagram of the modified GTO-based module according
to the invention.
Figure 2 - describes an outline of an IGBT module.
Figure 3 - illustrates the power circuit schematic of a modified GTO-based
module; its gate driver, gate circuit connection, input capacitor and
output filter circuit.
Figure 4 - illustrates the modified Inverter module isometric views with
Identification of all components.
Figure 5 - illustrates the switching voltage pulse during overcurrent situation.

DETAIL DESCRIPTION OF THE INVENTION
IGBT based module for WAG9/WAP5/WAP7 locomotive has two main distinct
functional block, one is a power circuit and another is control circuit. The power
circuits comprise input filter capacitor, power connectors, snubber capacitor and
dv/dt control filter circuit. And the control circuit comprises a gate interface card,
a gate control circuit, and at least one current sensing transducer.
SPECIFICATION
• Input voltage : 560V(DC)
• Output voltage: 415V(+/_5%),AC
• Output current 195A(nominal),AC
• KVA: 140KVA(nominal) at 0.8Pf
• Short time rating : 280KVA for 5 sec
• Output Frequency : 5Hz to 50Hz
• Switching frequency : 50Hz / 2Khz
IGBT based Inverter module for WAG9/WAP5/WAP7 locomotive comprises two
H-bridge IGBT module connecting in parallel. Each IGBT based module is having
2 IGBT's connecting in series (Ref. Figure 1 and Figure 2), one is known as upper
IGBT and the other is Lower IGBT. Therefore a total of four discrete IGBT's are

connected in series with parallel combination (2S-2P) in the modified Inverter
module. Thus, there are 3 power terminals in each IGBT based module for
WAG9/WAP5/WAP7 locomotive .
Terminals 4, 5 and 6, 7 are respective gate-emitter connector points of upper
and lower IGBT and turn on/off control pulses are applied across these. For
monitoring the voltage fall pattern across each IGBT, the collectors (C1 and C2)
are also connected with the driver card.
One capacitor CT2 is connected across the input side of the inverter to
compensate stray inductance of cable.
The IGBT module output feeds one or more Motors in the locomotive auxiliary.
There is a possibility of ringing at every turn off pulse due to inherent
characteristics of the IGBT. Since the module is to work in existing system
without any sine filter (although a sine filter is recommended), a high rate of rise
of voltage (dV/dT) may have detrimental effects on the motor. An L-C filter is
used to reduce dV/dt at the motor terminal which is provided in the IGBT
module. However, a simple LC circuit, driven by high dV/dt, would generate
oscillations with a resultant output voltage much higher than the DC link; thus, a
damping resistor, R1 is used in series of C1 capacitor. The series resistance also
dissipates the un-useful power as well as limits the peak IGBT current while
discharging the capacitor with turn on of the IGBT.

As shown in Figure 4, IGBT based Inverter module for WAG9/WAP5/WAP7
locomotive comprises:
IGBTS (1),
an input capacitor (2),
a gate circuit (3),
a gate drive (4),
a gate Interface card (5),
at least three Power connecting terminals (2, 3, 4)
an Earth terminal,
a Heat sink (6),
a Current transducer (9),
a dv/dt filter capacitor (CP1) 10,
an Inductor core (L1) (11),
a damping resistor (12); and
IGBT gate connectors (13)
The gate driver (4) is having two parts
1) Gate Interface card: It is having the electronics circuit to signal interface with
existing electronics Rack. It is energized with + 24 V supply from the Rack,
and generates + 15 V and + 5 V for control electronics of the gate interface
card. It processes inverter enable signal, phase signal and system monitoring

signals and sends the unified inverter output current signal to electronics Rack.
The phase signal (R/Y/B) is splinted into two 180° phase shifted pulses and
transmitted through open collector to the isolated gate circuit for onward
transmission to IGBT's. The gate interface card is having 2nd level of protection
of the IGBT's and the inverter module. It monitors and checks all the connector
integrity; receive OK signals from IGBT gate driver circuit which is having 1st
level of protection in-built.
The output phase current is also monitored in the interface card. In case of
overcurrent situation i.e. whenever inverter output current exceeds a set value,
the firing pulses duty cycle to the IGBT is reduced for short time before blocking
permanently and sending an error message to main control electronics. This
feature has improved the reliability of the module as sudden overcurrent
situation is well taken care of electronically and excessive current stress through
IGBT is avoidable. Figure 5 shows the effect of over current limit circuit on the
IGBT gate pulse.
2) Isolated gate circuit: the main features of this dedicated care are as follows:

• Dual channel IGBT Driver
• Suitable for IGBT of 600V, 1200 V and 1700V.
• VCE sat monitoring: This monitors voltage fall pattern across collector and
emitter at every instance of switching. In case of any abnormality it
generates error signal and stop switching.
• Soft shut down: This helps in turning off IGBT softly to reduce excessive
voltage spike during short circuit.
• Isolation voltage: 5000 VAC.
• Integrated DC-DC SMPS.
• High peak output current (+/-30A) to operate with large size IGBT'S are in
parallel operation, which can enhance peak power handling capacity of
Inverter module.
• 15 V secondary drive voltage.

ADVANTAGES OF THE INVENTION
Comparison between a modified GTO based inverter module acting as an IGBT
module, and a GTO based Inverter module for locomotive is tabulated herein
below:


WE CLAIM:
1. An IGBT based inverter module for locomotive applications,
comprising:
a power circuit block having H-bridge IGBT module; and
a control circuit block having a gate interface card, a gate control
circuit, and current sensing transducer,
wherein each IGBT module comprises one each upper IGBT and lower
IGBT connected with three power terminals;
- at least one electric motor in the locomotive auxiliary receiving the
output from the IGBT module via an L-C filter to reduce dv/dt at the
motor terminal; and
a damping resistor connected in series with output to damp the
generated oscillation due to IGBT switching.

2. The inverter module as claimed in claim 1, wherein the gate interface
card comprises electronic circuit to signal interface with the electronics
rack, and enabled to process inverter activation signal, phase signal,
system monitoring signals and transmit an unified output current
signal of the inverter to the electronics rack.
3. The inverter module as claimed in claim 1 or 2, wherein the gate
interface card is capable of splitting the phase signal into two 180°
phase shifted pulses and transmit through the open collector to the
isolated gate circuit for onward transmission to the IGBTS.
4. The inverter module as claimed in any of claims 1 to 3, wherein the
gate interface card is enabled monitor the output phase current and
temporarily reduce firing pulses duty cycle to the IGBT whenever the
output phase current exceeds a pre-set value.
5. The inverter module as claimed in claim 1, wherein the gate control
circuit comprises an integrated DC-DC SMPS with isolated pulse
transmission circuit an acting as a dual channel IGBT driver.

6. The inverter module as claimed in claim 1 or 5, wherein the gate
control circuit is enabled to monitor voltage fall pattern across the
collector and generate error signal and stop switching in case of
abnormality in data.