The test circuit is used for application oriented type-tests of IGBT modules. Also the calculation ... Temperature- and load-cycling tests are other important issues for traction ..... TULIP has proved to be a very powerful tool for easy and fast ...
EVALUATION OF HIGH POWER IGBTs FOR TRACTION APPLICATIONS M. A. Hollander, G. E. Zetterberg ABB Daimler Benz Transportation (Sweden) Ltd, Sweden
Trondheim
Abstract. This paper describes a test circuit for high power IGBTs, aimed for traction applications . A typical application for the IGBTs is Metro cars with 750 V or 1500 V DC supply. The test circuit is used for application oriented type-tests of IGBT modules. Also the calculation program TULIP, which calculates power losses and junction temperatures of semiconductors in a three-phase inverter is described. Keywords. Traction, Inverter, IGBT, Module
To ensure good quality of traction converters using IGBTs, a test equipment for high power IGBT-modules with maximum ratings 3.3 kV and 2 kA has been designed, built and tested.
The evaluation also includes the calculation program TULIP which calculates the power losses and junction temperature of semiconductor switches used in a three phase inverter. Comparison can be made between semiconductor switches from different suppliers, different driving conditions, different cooling conditions, different operation points and so on.
Two electrical circuits are used for the type-testing of IGBTs: the Phase-Leg and the Full-Bridge. In both cases two IGBT-modules forming a single-phase switching leg are tested simultaneously; one acting as an IGBT-transistor, the other as an inverse diode. In the Phase-Leg the switching behaviour of the IGBTs can be studied by single switchings and the switching losses can be measured. In the Full-Bridge the IGBTs are stressed thermally. The power losses can be measured . by comparing measured temperatures with the ones of an earlier made calibration with pure DC-current. Furthermore an application test can be made with the Full-Bridge, in which the IGBTs are exposed to the same conditions as in the real application. The test equipment has been tested successfully and measurements have been made on many different types of IGBT-modules, the largest up to now is with ratings 3.3 kV and 1.2 kA .
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Temperature- and load-cycling tests are other important issues for traction applications. However, this is not considered here because this asks for a different circuit.
IGBT TEST CIRCUIT The main requirement of the test circuit is to type test IGBT-modules with maximum ratings of 3.3 kV and 2 kA. In a type-test, one or a few samples are tested and identified in order to be able to compare the properties of that type with another type. One key parameter to be measured is the switching energy.
Temperature control
Control panel
Measuring equipment
-'Auxiliary : phase
380V
3-
I I I I I
50Hz
Protection system
Control electronics
Figure 1. Principle circuit diagram of the test circuit
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The mechanical construction of the test circuit is designed to test IGBTs in different kinds and sizes of housing. Besides the IGBT itself, surrounding components like clamping circuits and driver circuits can be tested with the test circuit. This requirement was met by building the test circuit in a modular way.
4411f
DC·link
capacitor
The scope of the test circuit described in this paper is shown in the principle circuit diagram in Figure 1. The power supply transforms and rectifies the three-phase voltage from the mains and feeds the DC-link. With the control panel the power supply is switched on and off and the DC-link voltage can be controlled between 0 and 2000 V .
4.7mF
Figure 2. Arrangement for measuring switching energy The switching energy is measured in the well-known way [1] by measuring the voltage across, and the current through, the IGBT. The time integral of the product of this voltage and current is the switching energy. An example of the switching waveforms and switching energy for a 3.3 kV / 1.2 kA device is shown in Figure 3.
In case of component or system failure, the protection system switches off the power supply and discharges the DC-link capacitors. Two phases are connected to the DC-link: one Test phase with two IGBTs under test and an Auxiliary phase which is part of the test equipment. With switch S 1 in Figure 1, the selection between the Phase-Leg and the Full-Bridge is made. In the Phase-Leg, only the Test phase is active and single switchings can be made; in the Full-Bridge both phases are active and the IGBTs in the Test phase are stressed thermally.
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1200 A
1650VI
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Uee
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The control electronics generate suitable gate pulses for the tests in the Phase-Leg and the Full-Bridge.
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The temperature control has a dual function . In the Phase-Leg the IGBTs are warmed up to the desired temperature. In the Full-Bridge the IGBTs have to be cooled and the power losses are measured with the help of this system.
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1':::clL=
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vertical :
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300 V/div. 200 Aldiv. p olf lOOOkW/div. Eon 500 mJ/div.
The measuring equipment measures the voltage across and the current through the IGBTs.
Figure 3 Tum-off at Ude PHASE-LEG
horizontal: time 2 jlS/div.
=1650 Y, Ie =1200 A, Tj =115°C
The switching energy is measured at different currents, temperatures, DC-link voltages and driving conditions. Figure 4 shows the turn-off energy at Ddc = 1650 V as a function of collector current and junction temperature.
The switching waveforms are studied by single switchings in the Phase-Leg (Figure 2). In this PhaseLeg, a step down chopper with inductive load, the dynamic parameters of IGBTs can be measured. For converter design, the switching energy is an important parameter to be measured. The switching energy should be known, in order to be able to predict the power loss of the IGBTs in the converter and to dimension the cooling system for the IGBTs. Furthermore, switching speed is important to know when designing lowinductive intermediate links, gate-driver circuits and clamping circuits.
Turn-ofT energy at Udc
=1650 V
1800 1600 1400 _ 1200
-0-115 "C
!
~75 " C
1000 I:: 800 0 ~ 600
--tr- 25 "C
400 200 0
In Figure 2 it can be seen that a clamping-capacitor is used close to the IGBTs in order to minimise the equivalent stray inductance.
0
300
600
900
1200
Ie (A)
Figure 4 Tum-off energy of an 3.3 kY / 1.2 kA IGBT
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fundamental frequency is considered), type of modulation, modulation index and temperature, This kind of test should be seen as an "overall type-test" on the IGBTmodules before they are put into a prototype inverter.
Figure 5 shows the voltage across and the current through the IGBT, the switching power and the switching energy at transistor turn-on at Ude = 1650 V and 1.: = 1200 A. I
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A problem is that both an IGBT-transistor and an inverse diode are present in the same housing, both warming up the module, Because of this, AC-current is applied to the two IGBT-modules in one phase of a full-bridge .
1200 A
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measurements.
is the frequency of the fundamental wave
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(3)
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T
=aI IC BT ,... + bIicBT.mIJ + d· f i;GRT (t) d(t) o
The total power dissipation in the IGBT-transistor is :
where, P,CBT ,IOIUJ
(4)
1
(4
IT llCBT .3 () () 3 .J2 - + m-cosqJ 3n ) t d t = l loud"", To' 2n 3 8
ndrc:h .(J\'t.
The conducting and reverse recovery losses of the diode are calculated in a similar way as for the IGBTtransistor. The heatsink and junction temperature of the IGBT-transistor and the diode are determined for the stationary state from the calculated power losses with the thermal model in Figure 10.
(5)
-
(10)
= ~GBT.cofld .(J\'t + P'CBT ..
(6)
Now, the IGBT conduction loss is written as a function of known parameters. Please note that this is valid for only one given junction temperature. In order to take the temperature into consideration, this calculation is made with the data at three different junction temperatures. Because the junction temperature is dependent on the losses and the losses are dependent on the junction temperature, TULIP calculates the junction temperature in an iterative way.
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