Power electronics Solution to examination 2007-12-13 Industrial Electrical Engineering and Automation Lund University, Sweden
Examination 20071213 1a © Namn Namn Föredragstitel
Examination 20071213 1b Maximum dc voltage Average dc voltage Maximum allowed voltage for the IGBT is 1700 V. The margin is sufficient © Namn Namn Föredragstitel
Examination 20071213 1c © Namn Namn Föredragstitel
Examination 20071213 1c cont’d © Namn Namn Föredragstitel
Examination 20071213 1d Threshold voltage 0.9 V Differential resistance 2.5 mohm Irms 115 A Average rectifier diode current: Rectifier diode power loss © Namn Namn Föredragstitel
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) 85+15/2=92.5% Conduction percentage of IGBT diode (when freewheeling) 15/2=7.5% © Namn Namn Föredragstitel
Examination 20071213 1e cont’d IGBT transistor On state voltage at 149 A 3.5 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 2.5 V Turn on energy= Turn off energy 0 mJ Switching frequency 3 kHz Power loss © Namn Namn Föredragstitel
Examination 20071213 1f Max temp for both transistor and diode is 150 deg Rectifier diode (6) Loss each 71 W Rth diode 0.13 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 0.069 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 150-48-42=60 deg Total loss 6*71+2*695+2*28=1872 W Required Rth_heatsink 60/1872=0.032 C/W © Namn Namn Föredragstitel
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 0.00167 s Average dc current: 127.5 A Current in recifier pulse 255 A Current between pulses 0 A © Namn Namn Föredragstitel