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Title: Discriminative Acquisition of Power IGBT Low Rate Transients
Author(s): Ermel, V; Meisner, J; Kurrat, M; Kahmann, M
Journal: 2012 IEEE International Workshop on Applied Measurements for Power Systems (AMPS
2012)
Year: 2012
Event name: 2012 IEEE International Workshop on Applied Measurements for Power Systems
(AMPS 2012), place: Aachen, Germany, date: 26 to 28 September 2012
DOI: 10.1109/AMPS.2012.6343990
Funding programme: EMRP A169: Call 2009 Energy
Project title: ENG07: HVDC: Metrology for High Voltage Direct Current
Copyright note: This is an author-created, un-copyedited version of an article accepted for
publication in the 2012 IEEE International Workshop on Applied Measurements for Power
Systems (AMPS 2012). THe publisher is not responsible for any errors or omissions in this
version of the manuscript or any version derived from it. The definitive publisher-authenticated
version is available online at http://dx.doi.org/10.1109/AMPS.2012.6343990.?
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Discriminative Acquisition of Power IGBT Low Rate
Transients
V. Ermel
J. Meisner
Institute for High Voltage Technology and Electrical Power
Systems
Technische Universität Braunschweig
Braunschweig, Germany
v.ermel@tu-bs.de
Electrical Energy Measuring Techniques
Physikalisch-Technische Bundesanstalt
Braunschweig, Germany
johann.meisner@ptb.de
M. Kurrat
M. Kahmann
Institute for High Voltage Technology and Electrical Power
Systems
Technische Universität Braunschweig
Braunschweig, Germany
m.kurrat@tu-bs.de
Electrical Energy Measuring Techniques
Physikalisch-Technische Bundesanstalt
Braunschweig, Germany
martin.kahmann@ptb.de
Abstract— The frequency spectrum of the power IGBT circuit
originates mostly from high gradient switching and low rate
conduction components. A chopper circuit is introduced for the
acquisition of the IGBT low rate transients in conductive stage of
operation. A Zener discriminator enhances the measurement
accurateness by two orders of magnitude. The experimental
results are presented for a half-bridge converter. Measurement
uncertainties are acquired with DC and impulse calibration
apparatus.
Measurement;
discriminator
IGBT;
I.
converters;
voltage
the stray field that impress transversion of the voltage transient.
The introduction of the Pockel cell to the voltage acquisition
channel [4] enhances the response time up to some
nanoseconds [5] due to the negligible loading on the output of
the divider and application of high frequency opto-electronic
converter.
transients;
INTRODUCTION
Power IGBT circuits exhibit voltage/current transients in a
broad range of gradients and magnitudes. The switching of the
semiconductor proceeds with voltage gradients of over 109
volts per second. The overall uncertainty of the measurement is
calculated as a result of partial uncertainties originating from
the probes and data acquisition system. The probes are
designed for operation in the full range of the voltage/current
transients. To the contrary, the conduction stage of IGBT
operation is characterized by low gradient voltage transients
caused by the development of the commutated current (see
fig.1). The dynamic range of the IGBT voltage lies from
kilovolts of the applied voltage to several volts of the collectoremitter potential fall in the conduction stage of the operation.
The conventional method of high voltage measurement
regards an application of the resistive, capacitive or
compensated dividers [1-3] that measurement uncertainty is
mostly affected by tolerance and temperature shift of the used
parts. As well a design of the assembly affects distribution of
The research leading to these results has received funding from the
European Union on the basis of Decision No 912/2009/EC
Figure 1. IGBT switching and conduction voltage dynamic range.
Development of the precise high voltage measurement units
emerges through all-round test of the metrology centers
accomplishing comparative measurements against a reference
measuring system [6-8]. The measurement uncertainty of the
HV dividers amounts to 5x10-3-1x10-2.
Due to broad dynamic range of the IGBT voltage, it is
preferable to introduce a two channels data acquisition system.
The first high sampling rate (HR) channel acquires high
gradient voltage/current transients during IGBT switching. The
probes of the first channel are designed for on-level
measurement of quantities in the whole range of transients. The
second low sampling rate (LR) channel is supplied with a
discriminator allowing a chopping of the high voltage portion
of the transient. On this way the slowly developing low voltage
transient of the IGBT potential fall in conduction stage is
acquired within the required accurateness.
The voltage discrimination is effectively realized in the
circuit based on Zener diode. High nonlinear characteristics of
the Zener diode and its high stability allow an introduction of
the voltage standard in metrology [9, 10]. The Zener diode
circuit is widely used as a voltage discrimination part as well is
applicable for circuit protection [11, 12].
II.
ZENER DISCRIMINATOR
The transients in the discriminator circuit are modeled with
MATLAB software. The model includes a series connected
resistor of 10 kΩ and a behavioral model of the Zener diode
(see fig. 2).
U=A(tg(103t-1.5))α+∆U
where A=0.6364E-6, α=8, ∆U=5. The approximation curve
simulates an abrupt fall of the IGBT collector-emitter voltage
from 1000 V to 5 V in the conductive state followed by the
growth back to 1000 V during switch-off. The pulse length
amounts to 3 ms. The discriminator chops during the voltage
drop the transients that exceed the Zener level (dotted curve in
fig. 3). The following run of the discriminator response shows
voltage drop up to tail magnitude of 5 V. The discriminator
exhibits a response delay to the applied voltage attributed to the
RC constant of the circuit.
The response of the discriminator is investigated with regard
to the variation of the tail voltage. The magnitude of the tail
voltage amounts to 2 V (curve a. in fig. 4), 4 V (b.), 6 V (c.)
and 8 V (d.). The discriminator output exhibits similar behavior
during the voltage drop up to the tail value. The magnitude of
the response agrees with the tail value.
Figure 2. Zener discriminator.
The capacitance of 900 pF of the diode G08-045 delivered by
co. Reichelt Elektronik and the input impedance of 1 MΩ of
the digital converter are included. The Zener voltage amounts
to 10 V. The model of the Zener diode is constructed based on
the static current versus voltage relationship.
.
Figure 4. Response of Zener discriminator to HV falling impulse at tail
voltage of 2 V (a), 4 V (b), 6 V (c) and 8 V (d).
Fig. 5 shows an approximation curve of the resistance of the
Zener diode as dependent upon the voltage. The curve is placed
in the first quadrant of a Cartesian coordinate system.
Figure 3. Input and ouput voltage of the Zener discriminator.
Measurement points are approximated with following
equation for Zener conductance:
σzen=(B.exp(C(Uzen-D)β1)+D.Uzenβ2)-1
where Uzen - Zener diode voltage, B=3E+9, C=-5E-11, D=6.3,
β1=20, β2=-14.
Applied voltage is shaped according to the following
equation:
Figure 5. Zener resistance.
The discriminator response to the voltage Ua under the
Zener level remains constant up to the voltage Us1 (phase A in
fig. 5) and equals:
Udisc=Ua.RM/(RM+RL),
where RM is the input impedance of the digital converter, and
RL is the input resistance. The tail to Zener voltage ratio affects
mostly a deviation of the discriminator response from the
magnitude of the tail voltage. Voltage growth up to Us2 causes
a drop of the diode resistance being comparable with the
converter impedance affecting the circuit response (phase B) in
this way. The voltage development to Zener level (phase C)
causes an attenuation of the input signal.
III.
MEASUREMENT UNCERTAINTY OF THE DISCRIMINATOR
The linearity and stability of the discriminator are
investigated at DC voltage step-up test. The multifunction
gauge Fluke 5700A was used for the calibration. The
uncertainty of the calibrator in the DC voltage mode is less
than 10 ppm.
are accomplished by variation of the applied step voltage that
exhibit similar transients. To investigate an influence upon the
discriminator output, the RG-58 cables of different length are
inserted in the circuit. Due to the strict dependence of the
output rise pulse time upon the cable length, the investigations
are accomplished with a direct connection of the Zener
discriminator to the measurement device. Figure 8 shows the
discriminator response to an impulse of 60 V. In the first phase
of the operation, the applied impulse is chopped up to the
Zener level of 10 V. The input voltage fall causes an
exponential drop of the discriminator output, this depicts a
discharge of the Zener capacitance. The transition time
amounted to 2-3 µs.
Figure 6. Response of Zener discriminator with step up DC input.
DC voltages from 200 mV up to 12 V are applied in 50 mV
steps. It is noticeable that the Zener diode closes the circuit at a
voltage of approximately 9.8 V (see fig. 6).
Figure 8. Discriminator output by impulse excitation.
IV.
IGBT VOLTAGE TRANSIENTS IN CONDUCTIVE PHASE
The test circuit is constructed assuming an inductive mode
of operation. The circuit includes a high voltage DC power unit
connected to the large capacitor bank C1 (see fig. 9). IGBT1
and IGBT2 are connected in series. The power IGBT modules
CM1200HC-66H made by co. Mitsubishi are used for this
investigation. Inductor L1 is connected in parallel to IGBT1 and
determines the current gradient during the conduction. The coil
inductance amounts to 4.4 mH at its resistance of 0.6
Ω. Voltage divider VD and current shunt RS deliver signals to
the digital recorder. Current shunt ISM100 made by co. HILOTEST with its resistance of 1 mΩ is used for current
measurement.
Figure 7. Deviation of Zener discriminator output.
Measurement of the discriminator output is accomplished
with a traced-back precision digital voltmeter (DVM) of the
Physikalisch-Technische Bundesanstalt (PTB). The uncertainty
of this DVM in the range of DC voltage measurements is less
than 5 ppm.
The transition characteristic exhibits a high linearity slope in
the whole measurement range up to the Zener level (see fig. 6).
The absolute deviation of the discriminator output amounts
below 20 µV (see fig. 7).
The impulse calibration is accomplished with a high
gradient generator of PTB. The generator consists of mercury
relays with a rise time of ca. 5 ns and a high voltage source.
The step response of the discriminator is acquired with an
oscilloscope at a sampling rate of 5 GS/s. The investigations
Figure 9. Half-bridge converter with data acquisition system.
Figure 10 shows the development of the IGBT collectoremitter voltage during commutation of the inductive current.
The switch-on of the IGBT causes an abrupt fall of the voltage
across the semiconductor to ca. 1 V. The subsequent voltage
growth is attributed to development of the inductive current.
gradient. Increasing the commutation time from 1 ms to 2 ms
(see fig. 10b), the curves exhibit an enlargement of the voltage
to over 2 V. The first stage of the voltage development agrees
with commutation transients of the impulse of 1 ms duration.
The enlargement of the commutation time to 3 ms (see fig.
10c) exhibits an adequate growth of the voltage up to 3 V.
The voltage and current transients which are shown in Fig.
11 are presented for converter voltage of 400V. The curves
exhibit continuable runs for voltage over the Zener crossing
point as well for pulse region of the low collector-emitter
voltages in IGBT conductive state (see fig. 11a). The current
transients exhibit a nearly linear growth (see fig. 11b).
.
Figure 12. Collector current and conduction energy loss by commutation of
the impulse of 3 ms duration.
Figure 10. IGBT emitter-collector voltage by variation of the applied voltage
and conduction time.
Increasing the applied voltage from 200 V (a1 in fig. 12) to
400 V (a2) causes a proportional growth of the collector
current. The following growth up to 600 V (a3) and 800 V (a4)
brings about an adequate increase of the current.
The variation of the applied voltage from 200 V to 800 V
Figure 11. Voltage and current transients by 1ms, 2ms and 3 ms timing.
brings about a displacement of the curve to a higher magnitude
of the collector-emitter voltage due to growth of the current
Figure 13. Power and energy loss by variation of the conduction time, a. 1ms,
b. 2ms, c. 3ms.
The commutation current matrix was multiplied with the
matrix of the IGBT voltage after that the result was integrated
to acquire the conduction energy loss. These curves exhibit a
quasi-quadratic growth (see b1, b2, b3 and b4 in fig. 12) in the
concordance to the applied voltage settings of 200 V, 400 V,
600 V and 800 V, respectively.
Figure 13 presents the calculated power and energy losses
by variation of the conduction time. Calculations were
completed for converter run by voltage of 400V that voltage
and current transients are shown in Fig. 11. Power loss curves
show continuable course by variation of the conduction time
and exhibiting some nonlinear growth due to increase of the
collector-emitter potential fall by development of the collector
current. Accordingly the development of the energy loss curve
exhibits quasi unary quadratic form.
Dynamic tests on the circuit by variable gradient of the
output power of the converter were conducted. For this purpose
the converter run by voltage of 600V and pulse time of 1ms is
compared with data obtained during converter run by voltage
of 200V and pulse time of 3ms. Figure 14 presents the
discriminator output voltage (a.), IGBT collector current (b.) as
Figure 14. a. dicriminator output voltage, b. IGBT collector current, c.
conduction power loss, d. energy loss.
well calculated conduction power loss (c.) and energy loss (d.).
Discriminator output exhibits some drive of the crossover by
increased converter voltage comparable with presented in Fig.
10. Displace of the crossover is exhibited during switch-on as
well switch-off state of the converter. Collector-emitter voltage
curves show similar values at the end of the conduction.
Collector current exhibits the same behaviour. Conduction
energy (see fig. 14d.) growth is contributed to enlargement of
the conduction time.
V.
CONCLUSION
The acquisition of IGBT low rate transients based on Zener
discrimination circuit allows for considerable reduction of the
voltage measurement range. Introduction of the circuit in the
data acquisition channel decreases the upper voltage level from
some kilovolts of the IGBT collector voltage up to below the
chopping voltage of 10 V. DC calibrations of the circuit exhibit
a high linearity slope in the whole measurement range up to the
Zener level. The IGBT transients are investigated with a high
voltage half-bridge converter. The measurement uncertainty of
the data channel equipped with the chopper amounts ca. 1% of
the Zener voltage.
The time constant of the introduced circuit amounts to 2-3
µs approaching the switching time of the power IGBT. The
voltage transient in conductive state of the power IGBT
operation is acquired in the whole range of timing that lies
typically in sub milliseconds range. The investigations are
intended to enhance the reaction time of the circuit.
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