High Voltage Capacitors Webinar

1. HV Capacitors in Automotive & Industry
Application

2. Agenda
• High voltage > 250V
• Dielectric must withstand the voltage at elevated
temperature
• Electrodes carry high ripple current - low ohmic resistance
• Reliable - 24/7 operation over years
• Design most often for long life operation

3. End of Life
• No standard
• Capacitor is out of specified parameters
• In general : Capacitance and/or ESR
• Limits are supplier specific
• 20% or 30% capacitance drop
• 2x or 3x ESR increase
• AND / OR relation

4. DC-Link Aspects

5. DC-Link Application
Film Lytic MLCC
Capacitance 130/27µF 11.000µF 220/33nF
Voltage 450/1100V 500V/(600V) 500/1700V
Temperatur 125°C/(170°C) 85°C/105°C/150°C 150°C
Switching Frequ
ency
60kHz 10kHz 1MHz/(9MHz)
FIT (½ Un,40°C) 2 12 3

6. How much capacitance we need?
10kHz 100kHz 1MHz
1kW 14µF 1,4µF 140nF
15kW 210µF 21µF 2,1µF
50kW 700µF 70µF 7µF
Assume U_max = 360V and U_max = 440V

7. PV equation
Stress for capacitors
1. n = voltage stress
2. Ea = activation energy
Inverse Power law : Electrical field apply a force on a charged atom
Arrhenius : accelerated move of particles
T1, T2 in [°K] and k in [eV]

8. Live in Space …
• The stretch is 20% in voltage, temperature and lifetime
• BUT T_max need to be considered

9. Lifetime calculation - C4AE
• Vr = 900V → V_upper = 1,3*Vr = 1170V
• Lifetime is equal for 1170V@70°C and 900V@90°C
900V
30kHrs

10. Lifetime calculation - C4AE / 900Vr
• Lifetime is equal for 1170V@70°C and 900V@90°C
30kHrs
900V * 1,3 = 1170V

11. C4AE Main product parameters
• T_hotspot = T_ambient + T_selfheating
• ESR is frequency dependent, lower for higher frequencies
• Rth depends on surface-area, construction and material

12. Electrolytic Lifetime Calculator(1)
• ALS40/41 - 9000h/105°C

13. Electrolytic Lifetime Calculator(1)

14. Electrolytic Lifetime Calculator(2)
3 harmonics

15. Electrolytic Lifetime Calculator(3)
5 harmonics

16. Impact of the harmonics
• Determine harmonics for non-sinusoidal waveforms
• Nominal Lifetime is 9000h@105°C and Vr = 900V
• Result doesn’t change much after 3rd harmonics
NoOfHarmonics LOP/h Change / %
1 15770 100 %
3 11190 71,0 %
5 11150 70,7 %

17. Dynamic thermal model
17

18. Dynamic thermal model,Thermal simulation
Calculation of operational life (Lop)

19. 2000V / 4 capacitors à 500V

20. Worst case
• C1 = Cnom -20%
• C2 = C3 = C4 = C-nom +20%
Nominal Worstcase
500 667
500 444
500 444
500 444

21. Worst case calculation
• in general
• Example 2000V / 4 capacitors each 500V 20% tolerance
• Approximately 25% overvoltage

22. how many chips needed?
22

23. Chips
23

24. WITY = what Is important to you(customer)
24

25. on the first view - standard conditions
• 1000V rated voltage / Working frequency = 140kHz @RT
• X7R offers 4x capacitance of C0G
C0G X7R
5,5nF 20,45nF

26. second view - @ 840V DC-Bias
• 840V application and 1000V rated voltage
• C0G has a similar capacitance - X7R drops by 75%
C0G X7R
5,5nF 5,6nF

27. Impedance and ESR
• ½ the ESR
C0G X7R
373mΩ 706mΩ

28. 10x ripple current
• Same cap, size and VR leads to more layers for C0G
• more Ni electrode layers leads to better cooling
C0G X7R
1,53A 0,11A

29. Ripple current over frequency
29

30. Vertical vs. Horizontal: convection
Heat dissipation in Air
Heat dissipation
to the Cu board.
12ARMS@140kHz

31. Summary
• The application somehow determine the technology
(traditional 10kHz or WideBand Gap 100kHz)
• Ceramic is suitable for WBG due high SRF
• Higher application voltage need:
• Filter or ceramic
• Aluminium capacitor bank
• Film - Lifetime can be adjusted around 20% voltage and T
• Ceramics C0G perform better than X7R
• Upright ceramic chips improve thermal behavior
• For non sinusoidal waveforms 3 harmonics are sufficient

32. Thank You!
Axel Schmidt
Field application Engineer
Cell +49 172 89 25 284
email: AxelSchmidt@kemet.com
Hermann-Köhl-Str. 2
86899 Landsberg am Lech
Germany
www.kemet.com