1. Power electronics Solution to examination 2007-12-13
Industrial Electrical Engineering and Automation
Lund University, Sweden

2. Examination a
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3. Examination 20071213 1b Maximum dc voltage Average dc voltage
Maximum allowed voltage for the IGBT is 1700 V. The margin is sufficient
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4. Examination c
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5. Examination c cont’d
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6. Examination d
Threshold voltage 0.9 V Differential resistance 2.5 mohm Irms A Average rectifier diode current:
Rectifier diode power loss
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7. Examination 20071213 1e Dc current to the dc link and to the 4QC
Duty cycle 85% IGBT and diode on state current 127/0.85=149 A Conduction percentage of IGBT transistor (incl freewheeling) /2=92.5% Conduction percentage of IGBT diode (when freewheeling) 15/2=7.5%
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8. Examination e cont’d
IGBT transistor On state voltage at 149 A V Turn on energy at 900 V and 180 A 65 mJ Turn off energy at 900 V and 180 A 80 mJ IGBT diode On state voltage at 149 A V Turn on energy= Turn off energy 0 mJ Switching frequency kHz Power loss
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9. Examination f
Max temp for both transistor and diode is 150 deg
Rectifier diode (6) Loss each 71 W Rth diode C/W Temp diff 9.2 deg
IGBT diode (2) Loss each 28 W Rth diode 0.25 C/W Temp diff 7 deg
IGBT transistor (2) Loss each 695 W Rth trans C/W Temp diff 48 deg
Heatsink Contribution fron 6 rectifier diodes and from two IGBT. Use the IGBT transistor temp diff 48 deg Ambient temperature 42 deg Maximum component temperature 150 deg Temp diff over heatsink =60 deg Total loss 6*71+2*695+2*28=1872 W Required Rth_heatsink 60/1872=0.032 C/W
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10. Examination 20071213 1g Capacitance and voltage ripple
The rectifier is the source of ripple. The switching frequency of the 4QC is 3 kHz and will thus not contribute. Max voltage ripple 40 V time for a pulse s Average dc current: A Current in recifier pulse 255 A Current between pulses 0 A
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