Dynamic Gate Controller (DGC) - A New IGBT Gate Unit for High Current / High Voltage IGBT Modules

Dynamic Gate Controller (DGC) - A New IGBT Gate Unit for High
Current / High Voltage IGBT Modules
The “Dynamic Gate Controller” (DGC) represents the forth generation of intelligent IGBT
driver concepts. The DGC is especially designed to drive and to protect high-power IGBTs as
well as to simplify the construction of complete IGBT power stages.
The DGC concept is suitable for applications characterised by the following criteria:
• A perfect protection of the IGBTs with very short delay and switching times
• High PWM carrier frequencies at minimised dynamic power losses of the IGBT
• Low EMI/RFI emissions at a high switching speed (high dv/dt and di/dt slopes)
• A perfect driver and protection circuit for high-voltage IGBTs (Vces > 1600 V)
In contrast to high-power inverters using a SCR or GTO as power switch, IGBT inverters are
mainly meant to work at higher PWM frequencies. To operate the power stage at high PWM
frequencies, the IGBT has to be switched as fast as possible to reduce the overall power
loss and to increase the efficiency of the system. Especially as far as high-power inverters
are concerned, high PWM frequencies cannot easily be realised because of the large
mechanical set-up and the resulting stray inductance of the wiring. This stray-inductance
limits the switching speed of the IGBT due to several well-known effects. Nevertheless, to
increase the PWM frequency, snubber networks which are connected to the IGBTs should
reduce the max. collector voltage and should keep the dv/dt and di/dt slopes within an
acceptable value. In IGBT inverters those snubber networks show only disadvantages. They
generate power losses even in no-load operation of the inverter and the snubber has to be
mounted on a heatsink. The construction of the power stage becomes more expensive and
the snubbers enlarge the total mechanical set-up. Furthermore the snubber components
themselves are quite expensive.
To make high-power IGBT inverters competitive to SCR and GTO inverters one has to:
• simplify the mechanical construction, leave out all components which are not necessary to
achieve the basic function.
• take full advantage of the current and voltage capability of the IGBTs. This is important in
order to compensate the higher component prices for IGBTs as compared to SCRs
or GTOs.
In spite of using state-of-the-art power semiconductors, today’s new high-power IGBT
inverters show only slight improvements concerning working frequency, efficiency and costs
compared to standard SCR- or GTO inverters.
The basic ideas of the DGC are:
• to take full advantage of fast switching IGBT chips in high-power applications.
• to use the “intelligence” of the DGC to get rid of all snubber networks which have so far
been necessary to ensure a secure operation of the IGBT.
Semiconductor Group
IGBT Application Hints
The use of the DGC in high-power IGBT inverters makes it possible to realise a power stage
consisting of only 5 different components:
1. The IGBT modules
2. The Dynamic Gate Controller
3. The power capacitors
4. The low inductive interconnection
5. The heatsink
The DGC fully controls the dynamic parameters of the IGBTs such as dv/dt and di/dt slopes,
delay times and diode reverse recovery. All the parameters are independent of each other
and are controlled in such a way that the predetermined values which are programmed by
the user of the DGC will be achieved under all load conditions either in no-load operation or
in full-load respectively over-load/short-circuit operation.
Semiconductor Group
IGBT Application Hints
General Description
The block diagram Figure 1 shows the basic set-up of the DGC. The test circuit for all
measurements is shown in Figure 2. The DGC test circuit was build up as a standard
chopper configuration. The high-side IGBT was blocked by a negative gate voltage and the
build in diode was used as free-wheeling diode to get the real reverse recovery behaviour.
The DGC was connected to the Kelvin collector, the Kelvin emitter, the main emitter and to
the gate terminal of the FZ800R16KF1 IGBT module which was used as chopper IGBT.
short circuit detection
Vce monitoring
Power supply
Power supply
Return interface
Gate driver
Gate monitoring
CONCEPT Dynamic Gate Controller (DGC)
Figure 1
Block Diagram of the DGC
V+ DC link
Figure 2
DGC Test Circuit
Semiconductor Group
IGBT Application Hints
Control Inputs
The control inputs consist of a standard fiber optic transceiver and receiver. In normal
operation (e.g. inverter power stage) the IGBT is turned on as long as light is turned on. For
other applications like crow-bar or DC-link voltage limiter (security relevant applications)
“light = on” indicates that the IGBT is turned off. If the supply voltage to the system controller
fails, the light signal will disappear and the IGBT will turn on.
Gate Driver
The driver output stage of the DGC is able to deliver ± 15 A peak gate current together with
± 15 V gate voltage. Due to the modular concept of the DGC the output power can easily be
adapted to meet the requirements of future high-power IGBT modules.
The switching performance of the IGBT (as well as the gate currents) are no longer
determined by gate resistors which have so far been used in standard straightforward
In order to operate the IGBT in the desired safe operating area the dynamic turn-on and turnoff controller determines the necessary gate current.
Dynamic Turn-off Control
To minimise the turn-off power loss of a semiconductor the turn-off transition time has to be
as short as possible. Therefore an ideal power switch must turn-off in an infinite short time.
But unfortunately this cannot be put into practice with real semiconductors. A lot of parasitic
effects limit the possible switching speed:
• High gate capacitances have to be charged and discharged. This results in high peak gate
currents which can be handled by a powerful gate driver.
• Additional capacitive currents due to the MILLER-effect of the power chip can dramatically
influence its switching performance.
• Stray-inductances of the mechanical set-up and the power module itself create
overvoltage spikes during turn-off. To keep these voltage spikes within a certain limit
under all working conditions is one of the basic problems in high-power IGBT inverters.
• Turn-on delay time of the free wheeling diode leads to high VFR values, especially with very
high di/dt slopes.
• The dv/dt of the motor supply voltage is limited by the windings of the motor. No partial
discharge should occur under all working conditions from overload down to no-load
• Electro-magnetic interferences
For standard driver concepts using discrete gate resistors to limit the di/dt and dv/dt slopes it
is not possible to operate the IGBT with the optimum switching speed for all load conditions.
The gate resistors have to be chosen in such a way that the IGBT stays in the SOA under
worst case conditions, normally dedicated to a short-circuit turn-off. The switching
characteristic then depends on the load condition and is no longer ideal for nominal or
no-load condition.
Semiconductor Group
IGBT Application Hints
Using the DGC all dynamic parameters like:
• maximum gate current
• turn-off dv/dt of the IGBT
• diF/dt of the free-wheeling diode
• maximum IGBT collector voltage
can now be adjusted almost independently of each other and are controlled in such a way
that they are independent of the load current. That means that the IGBT works under all load
conditions from no-load to overcurrent/short-circuit turn-off with the same di/dt and dv/dt
slopes which are predetermined by the manufacturer of the inverter.
Figure 3 shows the turn-off behaviour of a 1600 V IGBT carrying a small load current and
Figure 4 shows the overcurrent turn-off of the same power stage.
FZ 8 0 0 R1 6 K F1 w ith DGC at 4 0 0 A Load
FZ 8 0 0 R 1 6 K F1 w ith DGC at 1 6 0 0 A Load
I L = 1600A (200A/Div)
Input Signal (2V/Div)
IL = 400A (200A/Div)
Input Signal (2V/Div)
In 0V
In 0V
I L 0A
I L 0A
---- Overshoot = 320V
---- Overshoot = 200V
Vce= 800V (200V/Div)
t = 0,5us/Div
Vce= 800V (200V/Div)
Vce 0V
t = 0,5us/Div
Vce 0V
Figure 3
Figure 4
Turn-off Behaviour (low Collector Current) Turn-off Behaviour (Overcurrent)
As depicted, the dv/dt and di/dt slopes are almost the same. So we can for the first time
control the dynamic parameters of the IGBT and make them independent of the load current
and DC-bus voltage.
Semiconductor Group
IGBT Application Hints
Dynamic Turn-on Control
The DGC controls not only the turn-off but also the turn-on parameters of an IGBT. Apart
from the above mentioned problems of gate capacitance, MILLER effect and strayinductance, another power chip influences the turn-on behaviour of an IGBT: the freewheeling diode. The reverse recovery characteristic of this device limits the turn-on speed of
the IGBT. Especially fast switching high voltage diodes (VRRM > 1600 V) show a worse
reverse recovery behaviour than those diodes with a lower VRRM. Higher recovery currents
and a fast (snappy) turn-off of the diode lead to high dv/dt ratings and increase the EFI/RFI
The DGC will now control and limit the:
• -diF/dt of the free wheeling diode
• the turn-on dv/dt of the IGBT
and therefore enables the direct control of the reverse recovery behaviour of the free
wheeling diode.
Electromagnetic / Radio Frequency Emissions
The dynamic turn-on and turn-off control of the DGC dramatically reduces the EMI/RFI
emissions of a power stage due to the continuous control of the voltage and current slopes.
The dimensions of filter networks can be reduced and the power stages get more cost
efficient. The most efficient way to reduce EMI/RFI is to avoid them from the beginning. The
switching losses of the IGBT will be a little higher but the total power loss of the whole
inverter stage are lower compared to a standard straightforward driver where a snubber
circuit is connected to the IGBTs and a large output filter is necessary (Figure 3 and
Figure 4).
FZ 8 0 0 R 1 6 K F1 w ith gate r esistor at 1 6 0 0 A Load
FZ 8 0 0 R 1 6 K F1 w ith DGC at 1 6 0 0 A Load
I L = 1600A (200A/Div)
I L = 1600A (200A/Div)
Input Signal (2V/Div)
Input Signal (2V/Div)
In 0V
In 0V
I L 0A
I L 0A
Overshoot = 590V ------- Overshoot = 320V
Vce= 800V
t = 0,5us/Div
Vce= 800V (200V/Div)
Vce 0V
Figure 5
Turn-off with Gate Resistors
Semiconductor Group
Figure 6
Turn-off with DGC
t = 0,5us/Div
Vce 0V
IGBT Application Hints
Short-circuit and Overcurrent Protection
A new short-circuit detection concept enables a very short reaction time of the DGC to detect
a short-circuit. In case of a short-circuit the DGC turns off the IGBT within a few
microseconds, much faster than most of the conventional protection systems will do. The
advantages of the new system are:
• The short-circuit detection is independent from the overcurrent monitoring and therefore
optimised for very fast detection.
• An immediate short-circuit cut-off reduces the thermal stress of the silicon and of the bond
wire contact which result in an increased reliability of the power stage or in a much higher
number of allowed short-circuit turn-offs.
• The DGC minimises the overvoltage spike during turn off of the high short-circuit current.
FZ 8 0 0 R1 6 K F1 w ith gate r esistor at shor t cir cuit
FZ 8 0 0 R1 6 K F1 w ith DGC at shor t cir cuit
ISC= 5800A (1000A/Div)
ISC= 5800A (1000A/Div)
Overshoot = 730V ----
Overshoot = 270V ---Vce= 800V (200V/Div)
Vce= 800V (200V/Div)
t = 1us/Div
t = 1us/Div
Vce 0V
Figure 7
Short-circuit Turn-off with Gate Resistors
Vce 0V
Figure 8
Short-circuit Turn-off with DGC
The overcurrent protection is realised via a VCE monitoring. The VCE trip level can be adjusted
in such a way that the DGC turns off at 2 to 3 times nominal current. The actual trip level
depends on the forward characteristic of the IGBT itself and can easily be adjusted to meet
the requirements of the actual application (Figure 9).
Semiconductor Group
IGBT Application Hints
DGC over cur r ent-detection w ith FZ 8 0 0 R 1 6 K F1
Input Signal (2V/Div)
In 0V
overcurrent-treshold 3 x IN ---------------------I L = 2400A (500A/Div)
IGBT was turned off due to overcurrent
I L 0A
Vce= 800V (200V/Div)
t = 10us/Div
Vce 0V
Figure 9
Overcurrent Detection and Turn-off
Carrier-Frequency Monitoring
A carrier frequency monitoring is implemented in the control logic of the DGC. This feature
protects the IGBT from unacceptable carrier frequencies due to a faulty PWM controller or
disturbances of the fiber-optic link between controller and DGC (Figure 10).
D G C ca r r ie r f r e q u e n cy m o n ito r in g
Input Signal (1V/ Div)
In 0 V
IGBT turned off due too
high carrier frequency
Vge 0V
Vge= +/ -15V (5V/ Div)
O SC1 3 4 9
t = 50us/ Div
Figure 10
Turn-off Due to Carrier Frequency Failure
Semiconductor Group
IGBT Application Hints
IGBT Status- and Diagnostic System (ISDS)
The control logic of the DGC enables a variety of feedback information from the DGC to the
Microcontroller or host system. The simplest information is a “fault” signal as it is standard for
most straightforward drivers. It indicates that the DGC has turned off due to some kind of
failure. In advanced mode the DGC transmits a digital code to the controller which can
indicate one or more of the following information:
• DGC has no supply voltage (fatal system breakdown)
• IGBT is turned-off (real-time information if IGBT is really in blocking mode)
• IGBT is turned-on (real-time information if IGBT is really in conduction mode)
• IGBT was turned-off due to overcurrent
• IGBT was turned-off due to short-circuit
• IGBT was turned-off due to too high carrier frequency
Using the ISDS the host controller exactly knows whether the IGBT has turned-on or off.
Therefore the dead time between high and low-side switch can be reduced in such a way
that, for example, the high-side switch will turn on if the DGC indicates that the low side
switch has really turned off. The reduction of the dead time results in:
• a higher degree of modulation. In inverters the RMS value of the output voltage will be
higher and in SMPS it allows a more detailed design of the transformer.
• The dynamic of the total system will be improved. This is important for 4Q-inverters
because the magnetic flux of the motor will remain almost the same either for driving the
motor or for regenerative braking.
• Oscillation of the IGBT collector voltage is minimised due to minimised dead time.
Figure 11 shows the set-up of a complete 3-phase inverter power stage suitable for traction
applications or other high-power inverters (e.g. inductive heating). Together with a custom
specific control chip (Multi-Phase Controller, MPC) the complete power stage can
communicate directly with a microprocessor system via a standard µP bus architecture.
V+ DC link
ISDS Interface
Phase L1
Phase L2
V- DC link
Figure 11
Complete µP Compatible High-power Inverter with DGC and MPC
Semiconductor Group
Phase L3
IGBT Application Hints
Power Supply and Isolation
The DGC is supplied via a 16 kHz AC bus as it is usual for e.g. GTO driver units. The AC
source may be supplied by the user of the DGC or is available as accessory. The galvanic
isolation between AC bus and DGC is achieved by a transformer already implemented in the
As described the Dynamic Gate Controller is the perfect driver for available high power
IGBTs with blocking voltages up to 1700 V and current ratings from 400 to 1200 A and
above. The dynamic turn-on and turn-off control improves the overall system behaviour and
allows the design of snubberless high-power IGBT inverters combined with reduced RFI/EMI
emissions. The programmable interface to the host-system and the various protection
systems enables the use of the DGC in almost every high-power IGBT power stage from DC
choppers to AC inverters.
Future Trends
The new “open concept” of the DGC will allow the perfect adaptation of the DGC to future
high-power IGBTs. If the new IGBT generation with blocking voltages up to 4500 V is
available for the market the DGC will be ready for those devices. Special options will allow
the perfect paralleling of IGBTs as well as the series connection without any dynamic
snubber network.
A Copyright 1994, 1995 by CT-Concept Technlogie AG, CH-2533 Leubringen/Evilard
Semiconductor Group