Capacitors in Electric Drive application
DC Link Capacitors for Hybrid and Electric Vehicles + Filter Capacitors
Applications
DC-Link
To support a DC network by supplying periodically high currents
AC/DC
Converter
DC/AC
Converter
Typical rated voltages for film DC-Link 450VDC and 1100 VDC Demanded Life Expectancy: ~20khours for >10 years (100k hours)
Typically the DC-Link capacitors must withstand higher operating temperatures than the AC Filters due to the proximity to the IGBTs 3
DC Link Capacitors for Hybrid and Electric Vehicles
Essential questions for a DC Link capacitor are :
What is the Capacitance and Voltage profile What is the AC Spectrum Frequency and Ripple Current What is the Ambient Temperature and possible Cooling What is the Inductance requirement What are the Mechanical Stresses / Vibration and Shock What is the Mechanical Shape/Dimensions/Connections
Hybrid Vehicles will due to the presence of the Combustion Engine require in general Higher Temperature capacitors than Full Electric vehicles
Electrical Parameters
- Capacities up to several thousand F - Nominal voltage up to 2800V - Ripple current up to 280A - Operating temperature up to 125C - Very low dissipation factor - Customized design - Power dissipation depending on design
Total serial resistance: terminal s + busbar s + welding + spayed metal + film metallisation resistance + dielectric losses
DC Link - comparison Film / Lytic
Parameter
Life
Film
Up to 100,000 hours
Electrolytic
2,000 to 50,000 hours
(with high C derating)
Voltage
Up to 1,100Vdc
(C44U series)
450Vdc
ESR
Low
High
Ripple Current
High
Low
Capacitance
Low
High
Energy Density
0.16 J/cm3
(C44U series)
0.8 J/cm3
DC Link circuit
PROJECT EXAMPLE 3 phase AC Motor
Output V Vdc Link V ripple max Frequency Capacitance Ripple Current Freq DcLink Temp 690Vac 1000Vdc 100V 50Hz 500uF 30A 300Hz 75C
Electrolytic Solution
C uF V dc DxL mm Volume cm3 I ripple (A) Series Nr. Branches Nr. Irp/Branch Capacitor Nr. Tot. Vol. Tot. C uF Actual V rp 1500 400 63x105 0.327 12.2 3 3 10 9 2.95 1500 33
Film (C44U)
250 1100 85x140 0.794 30 1 2 15 2 1.58 500 100
DC Link circuit
PROJECT EXAMPLE
ELECTROLYTIC Total Volume 30A Total Volume
FILM
2.95 Liters
1.58 Liters
30A
10A
10A
10A
15A
15A
1100 Vdc
1500 uF 3 times Capacitance Project But not stable through years
500 uF (stable over years)
DC Link circuit - Comparison of capacitor designs
Description
Capacitance Rated Voltage Individual capacitor Individual part number Capacitors in parallel Assembly dimensions B x H x L Assembly volume ( dm ) Irms @ 10 KHz Tcase=70C Theorical stray inductance Power dissipation Cooling / Cold plate Bus bar Life expectancy @ Un, In, Tcase=70C Cost factor without assembly operations, bus bar, printed circuit board 360 F 900 Vdc C4AE 40F / 900V C4AEOBW5400A3NJ 9 115 x 50 x 182 (*) 1,0 180 A 4 nH Excellent Air ventilation To be defined 100000 h 100 330 F 900 Vdc C44U 110uF / 900Vdc C44UOGT6110A7TK 3 76 x 76 x 238 (*) 1,4 100 A 13 nH Good Forced cooling To be defined 100000 h 170 350 F 900 Vdc C4E 350uF / 900Vdc C4EEOMX6350AASK 1 90 x 70 x 180 1,1 90 A 10 nH Mild Cold plate Integrated 100000 h 280
(*) = capacitors set in parallel with distance of 5 mm from each other to easen the power dissipation
MINIMAL INDUCTANCE of the DC-Link Capacitors
Why is Inductance (ESL) a concern?
Stray inductance on the source-return path of the DC bus from the DC capacitor bank to the inverter devices can cause: - Reduced switching frequency. Parasitic oscillations may get out of control and cause the inverter to exceed its safe operating area. - Excessive transient overshoots in conventional hard switching converters resulting in increased device heating, which eventually exceeds the device's safe operating area causing device failure.
basics
C = capacitance K = material constante / Dielectrizittsconstante A = Area: Foilwidth * perimeter_of_spindel * number_of_turn t = thickness of foil
Material properties of film
properties PPS Polyphenylen Sulfit 285 160-190 3.0 1.35 PEN Polyethylen Naphthalat 266 150-170 3.05 1.36 260 PET Polyethylen Terephthalat 254 125-150 3.25 1.36 240 PP Polypropylen
Melting temperatur (C) Operating temperatur (C) Dielectric constante density (g/cm) Withstanding voltage raw foil @ 25C (V/m) Tan Delta (1kHz/10kHz) cost/ kg Thinnest foil (m) voltage E-density (nF * V/ mm)
160-170 105-125(135) 2.2 0.91 300-400
0.002 / 0.0025 750%
0.004 / 0.01 371% 1,2
0.005 / 0.015 100% 0,9 180
0.0005 / 0.0007 114% 3(2.7) 2800 50
140
250
400
ESR create heat
PET DF
DF = Dissipationfactor = tan
PP
0.0005 / 0.0007
0.005 / 0.015
Hot Spot Definition
C
IRMS
PD [W] = ESR(f i ) * I i2
i =1
A
Harm Curr
m
ESR
THS
Hot Spot
TAmb-HS
TCase kHz
freq
TAmb
TAmb-HS Rth * PD
The hot spot is the internal point of the capacitor where the temperature reaches its maximum value. The hot spot temperature is always depending on the ambient temperature and on the internal overheating generated by the Irms
14
ESR
Temperature gradient between upper and lower side
AMBIENT = 125C CAPACITOR COOLING = 70C
Equivalent Circuit of Thermal Model
Heat generator Thermal capacitance of element
Thermal capacitance Thermal resistance of can element-can Thermal resistance can-ambient
17
Thermal Model Duty cycle
(hot spot)
Duty cycle 100%
Duty cycle 25%
18
Ambient temperature
T<=15C
Cooling with Thermopads
Ambient = 125C
Cooling =70C
Lifetime
8 LE = LN x (VN/V)
LE = Life expectancy at operating V LN = Life expectancy at nominal voltage VN = Nominal voltage Un (V) V = Operating voltage (V)
LE = LTd x 2
(TD - Ths) / 7
LE = Life expectancy at operational Hot Spot temperature Ths LTd = Designed Life expectancy at Ths = TD TD = Design Hot Spot temperature Ths = Operational Hot Spot 7 = Arrhenius coefficient
22
ESL = Equivavlent Series Inductance
Defined as electrical field around an area Rule of thumb U_induced = -7V/nH Line or plates in parallel reduce in inductance
Additional temperature rise
DC current across the busbar add additional temperature to the hotspot
Thermocycling requires specual busbar design for a compensation of the CTEs
CTE[ppm/K]
CTE=Coefficientofthermalexpansion
Cu PP PET PPS 16 160 60 50
Automotive : Hybrid Vehicles
C=1000uF/650Vdc/100Arms
Winding Technologies
We have two technologies: Winding and Stacked Winding: Wide voltage range
Up to 2800VDC possible
Natural for high capacitance values with less elements in parallel than in Stacked Wider films possible than in Stacked
Stacked: In todays technology nominal voltage limitation in ca. 500 VDC
Possible to improve if necessary
Basic building blocks typically 100 F each, up to 10 connected in parallel In both technologies PET (< ca. 300 VDC) and PP possible Customized mechanical construction possible in both technologies
case
Plastic is the prefeerd solution for automotive In rigid enviromenet metal case is more robust Plastic cases has to have inlays for bolts and/or nuts Aluminium is weight is an issue Black cases have a lower thermal resistance Metal is better in humidity protection
Automotive DC-Link Capacitors Toroidal Type
DC-Link for Hybrid cars : 200uF/600Vdc/150Arms
Toroidal capacitor with external diameter 250mm.
INVERTER IGBT
Electric Motor
Not for mass production
Automotive DC-Link Capacitors Toroidal Type
250mm film
Example of minimal Inductance TOROIDAL TYPE
We tested different solutions of the bus-bur in order to reduce the ESL at the same level of the brick type :
150uF in Brick type ESL = 20nH
200uF with Internal and external bus-bur ESL = 37nH
NO
200uF with Internal bus-bur ESL = 20nH With side-by-side layout
OK
Fraunhofer
Sum up
Electrical values are fixed very fast Mechanical is the driving factor DC Link design is thermal management Do not cross the busbars with battery current All terminals on one side Cost can be optimized by early involvement of the supplier Collect datas as much as possible ( mission profile, frequency spectrum )
Questions ?
The End
Thank you for your attention
What about MLCC in 1000uF/450V
450V/ 6,3V = 72 Kondensatoren in Reihe Kapazitt einer Reihe C_row = 1/72 * C_nom = 100uF/72 = 1,4uF Anzahl der Reihen = 1000uF / 1,4uF = 715 Reihen Gesamtzahl der Kondensatoren = 715 * 72 = 51480 Annahme 1210/100uF/6,3V MLCC Preis 17,50EUR/100 Film MLCC ______________________________ Anzahl 1 51480 Vol 0,6l 0,08l / ohne PCB ohne DC-Bias Verluste Gewicht 940g 2200g Preis 100EUR 9009EUR
Kontakt
Axel Schmidt Field Application Engineer +49 172 89 25 284 AxelSchmidt@kemet.com KEMET Electronics GmbH Rudolf-Diesel-Strae 21 86899 Landsberg 08191 33500 www.kemet.com
