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Development of Optical Fibre based High Voltage compatible IGBT driver with status
acknowledge and protection
Y.Kelkar#, Y.P. singh, A.C.Thakurta
Power Supply and Industrial Accelerator Division, Centre for Advanced Technology, P.O. CAT,
Indore -452 013
Abstract
IGBT is one of the preferred switch in many power
application. With the availability of wide range of HV
IGBTs the need to drive them reliably with protection is
a challenging task. Some of the important requirements to
drive the IGBT is to have galvanic isolation, appropriate
output power, detection of fault condition and subsequent
protection. An IGBT driver was developed for driving
two IGBT’s in series via Optical fibre interface and with
the capability of status acknowledge and protection.
INTRODUCTION
IGBT is a minority carrier device with high input
impedance and large current carrying capability. It can be
viewed as a functional integration of MOSFET and BJT.
The main advantages of IGBT are- low on state voltage
drop, low drive power, excellent forward and reverse
blocking capabilities. The drawbacks are slow turn off
speed due to current tailing and possibility of current latch
up. Typical features of the assembled OFC IGBT driver
are- a. Providing requisite On and Off gate drive voltages
that are independent of Collector emitter voltage b.
Capable of isolating system high voltages and switching
noise
c. Providing requisite drive power d. Short
circuit detection and protection f. Over Voltage protection
g. Status acknowledge (health of driver and also the
acknowledge path) h. Providing isolated DC power
supply to floating circuit . The details of above mentioned
features is discussed furtherA. Providing requisite On and Off gate drive voltages
that are independent of Collector emitter voltage- The
driver circuit must be capable of providing stable On and
Off gate drive voltages which are independent of
Collector emitter voltage and system duty cycle. Secondly
enough power must be provided by the drive circuit so as
to charge and discharge IGBT gate capacitances and
device stays fully saturated and maintaining short circuit
capability. In the assembled circuit IGBT driver Powerex
make M57962CL-01 in conjunction with Powerex make
DC to Dc converter VLA 106-15242 was used which
provides +15V and ~ – 8V . Negative bias provides
additional noise immunity B. Capable of isolating system
high voltages and switching noise- As the IGBT switch is
floating in many configurations, the gate drive control
interface must be designed for high common mode
voltage and high transient noise immunity. A pulse
transformer with low inter winding capacitance or a
optocoupler / optical fibre interface with high common
mode transient noise immunity may be used for this
purpose. Width of the gate drive pulse and required
isolation voltage will limit the use of pulse transformer.
Minimising gate drive length will reduce noise coupling
as the developed driver can be placed very near to driven
IGBT c. Providing requisite power level in the driveDuring each turn On and Turn Off the driver must charge/
discharge the effective gate capacitance. The driving
power required is
P(W)= Ceff X (ΔV gate)2 X Fswitching
The Ceff is more than the input capacitance value due to
miller effect.
D. Short circuit detection and protection-The short
circuit protection was provided by desaturation detection,
i.e. Collector emitter voltage sense. The desaturation
detection feature and subsequent withdrawal of gate drive
is the inherent feature of Powerex make M57962CL-01
IGBT gate driver. As the desaturation is detected the
IGBT driver will start soft shut down of IGBT which
helps to combat large transient voltages which may be
generated due to large fault current interruption. f. Over
Voltage protection- In the series operation of devices, one
of the devices may be burdened by over voltage due of
a. failure of one of the series devices b. unequal off stage
voltages c. delay in turn On of any device will lead to
unequal voltage sharing d. failure of any device to turn
ON will lead to over voltage across that device. In the
assembled system a voltage sense from resistive divider
across each series connected is compared with reference
voltage and decision is taken. The output of the
comparator is gated with other faults to generate healthy/
fault condition g. Status acknowledge (health of driver
and also the acknowledge path)- The rising and falling
edge of the gate drive gives as indication of health of
IGBT. This signal is gated with over voltage comparator
signal and overall information is transmitted back to
control card via OFC. Power failure at the driver section
or break in OFC transmission path is also taken care
while generating trip signal in control card. h. Providing
isolated DC power supply to floating circuit – The
floating power supply was needed for driver section
which has voltage comparator, pulse width generator
monostable IC’s, DC to DC converter, OFC transmitter
and receiver and gating. This supply was provided by
multi winding 5kV isolation transformer.
OPERATION
The driver system was designed to trigger two series
connected IGBT’s(IXGR32N170AH1,1700V) driving a
resistive load to generate a voltage pulse of ~11us
duration across the load at a repetition rate of 1 Hz. The
block diagram of power circuit is shown in figure 1 and
voltage pulse across load is shown in figure 6. The input
DC is obtained from single phase HV step up transformer,
rectification and subsequent filtration. The number of
series connected switched can be increased if needed and
also the output pulse width can be adjusted according to
need.
standard plastic OFC with 1mm diameter and attenuation
0.22 db/m was to link the control and trigger cards.
The function of trigger card is to receive trigger pulse
width information via Agilent make OFC receiver HFBR
1521. The block diagram of the trigger card is shown in
figure 3.
High Voltage
Rectifier
High Voltage
AC
mains
OFC receiver
Driver Card#1
Step up
Driver Card#2
OFC
IGBT Driver
OFC
OFC
Control Card
Transformer
HFBR 2521
VLA 106-15242
.
Figure 1
Isolated DC
Power suply
The assembled driver system has two cards- namely
Control card and Trigger card. The block diagram of
control card is shown in figure 2. The function of the
control card is to generate 1Hz master clock using timer
IC NE555 in astable configuration. The falling edge of
the master clock acts as reference for events to follow.
The requisite Pulse width from master clock falling edge
is obtained from monostable multivibrator CD 4538. The
pulse repetition rate and High Voltage output pulse width
can be adjusted according to load requirement. The
healthy/fault condition from the series connected IGBT is
received using Agilent make OFC receiver HFBR 2521.
The received pulses during normal and desaturation
detection are shown in figure 4 and Figure 5.
Astable
Multivibrator
1 Hz
Source
NE555
OFC receiver
OFC
Monostable
Multivibrator
Pusle width
generator
CD 4538
M57962CL-01
DC-Dc
converter
To other
Driver
Hardware
Monostable
Multivibrator
Rising and
falling edge
pulse
generator
CD 4538
-
OFC
+
Trip Set Point
Figure 3
The output of the receiver is used to drive Powerex make
IGBT driver M57962CL-01. The requirement of +Vcc
and -VEE of IGBT driver is catered by Powerex make DC
to Dc converter VLA 106-15242. This card also contains
floating DC power supply for monostable multivibrator ,
comparator and gating IC’s. The monostable
multivibrator will generate two pulses, one from the rising
edge and another from falling edge of the IGBT gate
drive.
OFC Transmitter
Monostable
Output
during fault
OFC
OFC Transmitter
CD 4538
S S/R Flip Flop
OFC receiver
OFC
HFBR 2521
CD4044
OFC break
detect
OFC
HFBR 1521
R
.
Figure 2
The received pulses from respective IGBT driver cards
and the master width are gated together to identify
healthy/ desaturation detect/ OFC break/ power supply
unavailability at the trigger card. The fault condition will
trigger a set/reset flip flop and will generate a trip signal
and will also inhibit further transmission of pulses to
trigger card. A reset is also provided to again resume the
operation. The output of the set/reset flip flop can be used
to trip the incomer of High voltage transformer so as to
inhibit generation of High voltage. The pulse width
generated is optically transmitted after amplification
using Agilent make OFC transmitter HFBR 1521 if the
healthy condition prevails. In the assembled system
Figure 4
The voltage across the IGBT device also compared by a
reference value based on attenuation ratio of resistive
attenuators and safe limit voltage the IGBT can handle.
The output of multivibrator mentioned earlier and output
of voltage comparator were gated together and the overall
bundled information transmitted by Agilent make OFC
transmitter HFBR 1521. Each series connected IGBT
will have their own trigger card. The information received
from all the trigger cards will be processed on a single
control card.
Figure 8
Figure 5
EXPERIMENTAL RESULTS
The voltage across the load measured by Tektronix
make P5100, 100X probe is shown in figure 6. The delay
between the falling edge of the 1 Hz generator which acts
as the master edge, and the IGBT gate voltage is 980ns as
shown in figure 7. All the measurements were taken ob
Tektronix make TPS2024B DSO.
Across load
Acknowledgement
We are grateful to Shri U.Karandikar, Shri R.Barothiya
and Shri Y. Raikwar who helped us in the development of
charger. Authors wish to thank Shri Yunus Khan ,Shri
S.D. Yadav and M.D.Jha for technical assistance for
wiring and fabricating various parts of assembly.
Conclusion
A setup to drive two series connected high voltage
IGBT’s were developed using OFC interconnect with
acknowledge and protection. The developed scheme can
be extended to drive more numbers of IGBT keeping their
drive requirement in consideration.
References
[1] Heinz Ruedi, Peter Kohli,” Driver Solutions for High
Voltage IGBT’s”, Power Electronics Magazine, April
2002
[2] ICT power application notes, NTAN-06
[3] IXYS application notes, AN-401
[4] Datasheet of Powerex make DC-DC converter M
57145L-01 and IGBT driver M57962CL-01
[5] Datasheet of Agilent make Fibre Optic Versatile link
series
555 o/p
Figure 6
Figure 7
The jitter between the falling edge of the 1 Hz
generator and the voltage across the load was measured
to be ± 1.8ns as shown in figure 8.