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Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Supercapacitors: Summary
• Generalities on Supercapacitors– Principle– Model of a supercapacitor– Series connection of supercapacitors
• Sizing of a supercapacitive tank– Sizing method– Energy efficiency and power availability
• Applications and converters– Voltage drop compensation for weak distribution networks– Energy buffers for elevators– Uninterruptible power supplies
• Conclusion
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Generalities on Supercapacitors
• Principle
– Supercapacitors: electrochemical double layer capacitor
– High energy density, together with a high power density
– Energy stored by charge transfer at the boundary between electrodes and electrolyte
– Amount of stored energy is a function of :• Electrode surface,• size of ions,• level of electrolyte decomposition voltage
Separator Electrolyte
Electrodes Currentcollector
+ -
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Generalities on Supercapacitors
• Principle : technology– Electrodes: activated carbon
• High surface area part• Define the energy density
– Current collectors• High conducting part
– Membrane• Avoids electronic contacts between the
electrodes• Allows the mobility of the charged ions
– Electrolyte• Supplies and conducts ions• Dissociation voltage of organic electrolytes
less than 3V• Organic electrolytes have a lower ionic
conductivity (reduced power capability)
Separator Electrolyte
Electrodes Currentcollector
+ -
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+-+-+-+-+-+-+-+
-+-+-+-+-+
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Generalities on Supercapacitors
• Model of supercapacitors
Rs
Co
ic
ucCuu
r1 r2 rn
c1 c2 cn
Rl
– Voltage dependant capacitance– Series resistor
– Leakage resistor– rc sub-circuits (relaxation phenomena)
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Generalities on Supercapacitors
• Series connection of supercapacitors– Voltage sharing solution, using power electronics solutions to offer a high efficiency.
C1
C2
C3
D2
D3
D1
Ns1
Ns2
Ns3
Np
I
i1
i2
i3
T
C1
C2
C3
L1
L2
T1 D1
T2 D2T'2 D'2
T'3 D'3
I
i1
i2il1
il2
i'2
i3C1
C2
C3
T1
T2
T3
D2
D3
D1
Np1
Np2
Np3
Df
Nf
I
i1
i2
i3
forward dc-dc converterwith distributed primary
association of buck-boostdc-dc converters
Centralized flyback dc-dcconverter with distributed
secondary
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Sizing of a supercapacitive tank
• Sizing method– Energy stored in a supercapacitor
2M M
1W CU2
=
– Voltage discharge ratio: the minimum voltage during the discharge has to be limited for efficiency reasons
m
M
Ud 100U
=
– The usable energy is then only part of the maximum stored energy2
u MdW W 1
100⎛ ⎞⎛ ⎞= −⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠⎝ ⎠
– Number of supercapacitors for a given usable energy
us 2
2M
2WNdCU 1
100
=⎡ ⎤⎛ ⎞−⎢ ⎥⎜ ⎟
⎝ ⎠⎢ ⎥⎣ ⎦
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Sizing of a supercapacitive tank
• Sizing method– Example
Wu=0.55MJ (5.7kW.h) C=1800F, UM=2.5V, IM=200A
Ns d (%) Volume (m3) Weight (kg) E (kw.h)4872 50 1.46 1948 7.6 5709 60 1.71 2283 8.92 7164 70 2.15 2865 11.2
The needed energy isEu=20.55MJ(5.7kWh)
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Sizing of a supercapacitive tank
• Energy efficiency and power availability– Due to the series resistor, energy efficiency of supercapacitors has to be taken into
account during the sizing of the supercapacitive tank– Energy efficiency has also an influence on the power availability– Two cases have to be investigated:
• Energy efficiency for a constant current charge/discharge• Energy efficiency for a constant power charge/discharge
Ue
L Rs
C ucic
Rs
Cuc
ic
Iu
u
IP=Cte
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Sizing of a supercapacitive tank
• Energy efficiency and power availability : Example of a 2600F/2.5V/0.7mΩ ScapCharge Discharge
– Time for loading energy has to be kept up to 10s for a 90% energy efficiency (Ic<320A or P<700W)
– Time for unloading energy has to be kept up to 10s for a 90% energy efficiency (Ic<320A or P<400W)
– Taking into account the necessity of 90% of energy efficiency, the current or the power for charging/discharging have to be limited: the power density is only 806W/kg (instead of 4300W/kg)
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
• Voltage drop compensation for weak distribution networks– Using supercapacitors to provide/absorb the energy needed to maintain at a constant level
the end-of-line voltage.
TL
675Vdc
SupplyStation
3 kmVal-VertStation
BellefontaineStation
DC
DC
End of lineSupercapacitive
Tank
Val-VertStation
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
• Voltage drop compensation for weak distribution networks– Typical waveforms on the line No7 (Lausanne, CH)
Power ProfileAt the “Bellefontaine” station
Voltage at the end of line“Val-Vert” Station
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
• Voltage drop compensation for weak distribution networks– It is necessary to use a double stage power converter to interface the supercapacitive tank
to the end of the line.
SupercapacitiveTank
End ofLine
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
• Voltage drop compensation for weak distribution networks– Special control algorithm have to be implemented
Voline
Cinter Cscaps
PWM PWM
Vscaps_max
DOUBLE-STAGE DC/DC CONVERTER CONTROL
+
-
G1
-1
Vinter_ref
Iref_charge_scaps_max
+
+
+
-+
-
+
-
+
-
RECTIFIERSUBSTATION SUPERCAPACITORS-BASED SUBSTATIONLINE
(CATENARY)
R_Vendline
R_Vinter
R_Iinject R_Iscaps
R_Vscaps
Vendline Iinject Iscaps VscapsVinter
Vendline_ref-
+Itransfer
ymaxIline_r G2RlineDeltaVline
L2 RL2L1 RL1
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
• Voltage drop compensation for weak distribution networks– Simulation results
0 200 400 600 800 1000 1200 1400 1600 1800-800
-600
-400
-200
0
200
400
600
800
t (s)
U end-of-line (V)
U Scaps (V)
I Scaps (A)
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
Principle of operationMG M
RECUPERATION
Diesel
Scap
ConvertisseurAC - DC
unidirectionnel
ConvertisseurDC - AC
bidirectionnel
ConvertisseurDC - DC
bidirectionnel
Elémertsstockeursd’énergie
• Application in transportation : reduction of emissions and energy savings– Diesel-electric trains: reduction of emissions and energy savings– Partner : Stadler Rail/ ABB
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
The track
Instantanous value of power
0 2000 4000 6000 8000 10000 12000 14000 16000 180001000
1200
1400
1600
1800Altitude trajet COMPLET
temps (s)
Alti
tude
(m)
0 2000 4000 6000 8000 10000 12000 14000 16000 18000-2
-1.5
-1
-0.5
0
0.5
1x 106
Puissance des moteurs de traction trajet COMPLET
temps (s)
Puis
sanc
e (W
)
P netteP moyPmoy = 42.46 kW
Altitude
• Application in transportation : reduction of emissions and energy savings
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
0 100 200 300 400 500 6000
100
200
300
400
500
600
700Réduction de la puissance max des moteurs diesel en fonction de la quantité d`énergie stockée
Energie stockée (MJ)
Réd
ucio
n de
la p
uisa
nce
des
mot
eurs
die
sel (
kW)
• Application in transportation : reduction of emissions and energy savings– Reduction of the maximal delivered power of diesel motors in dependency of the amount
of stored energy
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
• Energy buffers for elevators
I D1I s
Us
Ud
Uc
Id
3
I D2
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
Speed, Position for a 10-floors up/down run Power and Energy for a 10-floors up/down run
The needed energy is 220kJ (61Wh)
• Energy buffers for elevators : – simulations regarding a real system
⇒car weight : 720kg, counter weight : 1440kg, load : 1400kg
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Applications and converters
Scaps voltage/current (10-floors up/down run) Powers for a 10-floors up/down run
• Energy buffers for elevators– Simulations regarding a real system
• The power provided by the network has only to compensate the losses of the lift drive
Energy storage and applications with supercapacitorsDr. P. Barrade/A. Rufer
Conclusion
• Supercapacitors are new components for energy storage– High energy density (even if lower than batteries)– High power density
• Model of supercapacitors have to take into account– The voltage dependence of the capacitance– The series/leakage resistors– Relaxation phenomenon
• Energy efficiency– Power availability of supercapacitors is affected by their energy efficiency
• Applications– Main applications use supercapacitors as energy buffers– In applications where supercapacitors are used as main energy source (UPS), the reduced
energy density is compensate by their high power density, combined with an increased lifetime compared to batteries.
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