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Design and Optimization of Design and Optimization of an ESU for hybrid light an ESU for hybrid light vehicles with the use of vehicles with the use of
SupercapacitorsSupercapacitors
Students:Aniello ValentinoFrancesco Villella
Supervisor:Stefano CarabelliMarcello Chiaberge
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IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions
3
IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions
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ContexContexESU with add-on Supercapacitors
TTW Three Tilting Wheels
IntroductionContext
The Supercapacitors are an addition to batteries they can be inserted or excluded depending on the needs.
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MotivationsMotivations Use supercapacitors in parallel with the battery to improve
acceleration and energy recovery during braking Designed for peak power requirements to increase the
efficency and the life cycle of the ESU system Feasibility study of an ESU
Why Supercapacitors?The purpose is to allow higher accelerations and deceleration of the vehicle with minimal loss of energy, and conservation of the main battery pack.
IntroductionMotivations
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ObjectivesObjectives
IntroductionObjectives
Analysis and design of supercapacitor pack
Analysis and design of supercap equalization net Analysis and design of DC/DC converter Definition of a dynamic model for supercap and
DC/DC converter with several degrees of approximation
Design procedure definition for supercaps
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Battery vs SupercapBattery vs SupercapType
Energy/ weight [Wh/kg]
Power/Size
[W/kg]
Nom,Cell [V]
CyclesDurabilit
y[#cicli]
Charge time [h]
Lead (Pb) 20÷30 1÷300 2 200÷300 8÷16
Ni-Cd 30÷55 10÷900 1.25 1500 1
Ni-MH 50÷8020÷1000
1.2530÷500
2÷4
Li-ion110÷160
1800 3.7500÷1000
2÷4
Li-ion VHP Saft
74 6900 3.6 500000 20m
Nanosafe 90 4000 13.8 15000 <10m
Supercap 3.9÷5.7470÷13800
2.5÷2.7
1000000 0÷30s
The non conventional batteries have High Power density but the charging time is high for this application.
Supercapacitor
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SupercapacitorSupercapacitorADVANTAGES
High Capacitance and ultra low ESR
High Density of Power Fast charging /
discharging High Available Current High number of life
cycles
DRAWBACKS Low voltage for each
cell High Weight and
Volume Very expensive
Supercapacitor
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Equalization netEqualization net
The disparities among the cell's parameters won't exhibit the same charging dynamic and, at end of charge transient, some cells may present over-voltage while some others are insufficiently charged.
The tolerance of the supercaps is 20%, but presumably if you buy supercaps from the same stock the tolerance reduces itself.
This involves the introduction of a control.
In power applications, supercapacitors are used in stacks where many cells are connected in series or in parallel to obtain acceptable voltages and energy.
Supercapacitor
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Possible SolutionPossible Solution
DC/DC active solution Switched Resistor Integration Kit
ADVANTAGES : High efficency
DRAWBACKS : Several DC/DC converter The implementation of the hardware and its control is very costly.
ADVANTAGES : Simplest Solution
DRAWBACK : Power loss
ADVANTAGES : High efficency User friendly
DRAWBACK : Expensive 40$
Supercapacitor
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IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions
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ESU with SupercapacitorsESU with Supercapacitors
ADVANTAGES In case of failure is always guaranteed connection between the battery and the inverter. During braking, the controller decides which energy source recharge. This power system allows acceleration and deceleration of the vehicle with minimal loss of energy and minimizes the stress of the batteries.
DRAWBACK We need to design a Bidirectional DC/DC converter.
ADVANTAGES Simple realization
DRAWBACKS Great stress for battery No longer battery life with high absorbed currents Long charging time Few charge-discharge cycles
ACTUAL SYSTEM PROPOSED SOLUTION
ESU with Supercapacitor
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SpecificationsSpecifications Ptraction = 22kW
Phase of Traction = 5 s
Phase of Braking = 10 s
Supercapacitor Add-on
ESU must be fault tolerant
Weight of ESU : less possible
Other important elements
Vbattery = 200V
Restriction of DC/DC converter
ESU with Supercapacitor
Specifications
Matlab Algorithm
Results SC bank
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Sizing supercapacitor bankSizing supercapacitor bank
To respect the energy constraints, the physical limits of supercapacitors and the restrictions imposed by the DC/DC converter must be considered.
In our analysis the following issues have been taken into account:
Supercapacitor working voltage
Restriction of the DC/DC converter
ESU with Supercapacitor
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Supercapacitor working voltageThe working voltage of the supercaps must be lower than nominal voltage in order to lengthen life expectation.
The aging processes of supercapacitors are mostly driven by temperature and cell voltage, which have an influence on the calendar life of the devices.
2,6V (96% of continuous voltage rating) was chosen because it is a voltage that ensures a sufficent life expectancy.
ESU with Supercapacitor
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Supercapacitor working voltage1,3V (50% of continuous voltage rating) was chosen because it is a voltage that ensures a sufficient input voltage to the DC/DC converter and keeps the ratio max-input / min-input near 2.The discharge voltage ratio d (in %) of the supercapacitors bank is defined as:
The DOD “Depth of Discharge” (in %) is then equal to:
This equation shows that, for a 50% DOD, the useful energy represents 75% of the maximun energy. Is inefficent to discharge the bank below 50% of its max voltage.
Then the Energy of Supercapacitor bank is given by the following equation:
ESU with Supercapacitor
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Restriction of the DC/DC converterRestriction of the DC/DC converter
The converter imposes constraints on the ratio between maximum input voltage and minimum input voltage, also between output voltage and input voltage.The restrictions refer to a non-isolated converter.
ESU with Supercapacitor
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ProcedureProcedure
specifications
datasheet
VinMAX
Vinmin
Constraints DC/DC
# SC in series=N
Initial condition
N=1
Needed
Energy
Repeat this procedure for all models and for 1<N<100 and Research the SC bank with minimum weight.
Add Module
Does the number of SC
in series respect the
costraint 5:1 ?
Add SC
Choose a model
Calculate the energy
of a module
NeededEnergy
>E_module ?
save data
processing
NO
YES
YES
NO
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Compromise Weight-EnergyCompromise Weight-EnergyResult:The best compromise between weight and energy considering all the constraints on supercap and DC / DC converter has been found through a Matlab algorithm.
# cell in series (module): 35 # module: 1 # total of supercap : 35 Input voltage range: 45,5÷91 V Weight : 11,19 kg Energy: 133087J 36,96Wh Power:26.62kW for 5s Volume : 9000 cm3
Model:BCAP 1500
ESU with Supercapacitor
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IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions
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DC/DC Bidirectional ConverterDC/DC Bidirectional ConverterIt is necessary because the supercapacitors voltage (91V) is different in comparison to the DC BUS voltage (200V).
Weight application : less possible
Principle of Operation
Step-downPhase
Step-upPhase
Vin[V] 200 45.5-91
Vout[V] 91 200
Iout[A] 100 110
Pout[kW] 9.1 22
Max time phase [s]
10 5
Constraint of application
Constraints
DC/DC Converter
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Comparison isolated-non isolatedComparison isolated-non isolatedTwo main categories of bidirectional DC/DC converters can be envisaged for this task:
Isolated converters Full Bridge Tapped Boost
Non isolated converters Buck+Boost Multiphase
Buck+Boost Multiphase Full BridgeTapped Boost
Inductor Very heavy N but light heavy heavy
Trasformator none none yes Yes L couple
Diff.Control Middle(2sw) Hard(Nsw) Hard(8sw) Middle(2sw)
Efficiency high high low middle
DC/DC Converter
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Non isolated convertersNon isolated converters
ADVANTAGES: Simplest topology of the DC/DC converterDRAWBACKS: Excessive weight Complicated Inductor costruction
ADVANTAGES: The key principle of these converters is the output current sharing among several parallel channels.DRAWBACK: Interleaved strategy is very difficult.
A variant of the Buck+Boost solution is the Multiphase Converter.
DC/DC Converter
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IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions
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ModelingModelingThe modeling is needed to allow you to enter the ESU designed in the system.
Virtual Prototype : Longitudinal dynamics model of the vehicle
Modeling
ESU ModelingPlant
ACU
Host
ICE
Electric motor
Power Module
ECU System
Battery
Supercap
DC/DC Converter
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DC/DC Converter + SupercapDC/DC Converter + Supercap
FIRST APPROXIMATIONAssumptions:
Linearity
No losses (DC/DC)
Equations :
Buck eq.
Boost eq.
SECOND APPROXIMATIONAssumptions:
No Linearity,
Losses (DC/DC)
Equations :
State Equations(L,C)
Modeling
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Models ComparisonModels Comparison
In the first approx are visible only the mean values. Very fast time simulation. Simulation Time(40s) : 0,001s In the second approx are visible the instantaneous values and you can see the voltage/current ripple. Very long time simulation Simulation Time(40s) : 30'
Comparison ParametersAssumptions for the buck phase (braking):
Static Simulations (fixed duty cycle) Iniatial SC Voltage:60V D = duty cycle = 40% T = Period = 20 us Simulation time : 40s
Modeling
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First vs Second approximationFirst vs Second approximation
If you need a fast simulation, and you do not want to see the transient then you can use the first approximation model. If you want to see the current and voltage ripples you can use the second approximation model, this model is the most similar to the electric model. For a more accurate comparison should have circuital simulations.
Speed Simulation
Accurancy
First Approx Very fast low
Second Approx Very slow high
Modeling
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Dynamic SimulationDynamic Simulation
In the figure you cansee the possible real behaviour of the first approximation model. Are visible the correct functioning of the system. Very fast time simulation. Simulation Time(100s): 0,001s
Real operating assumptions :Dynamic Simulations (First approximation model with control) Iniatial SC Voltage : 0VD = duty cycle = variable T = Period = 20 usSimulation time : 100sC/!D = Charge/!Discharge = '1', after 40 s '0'
Modeling
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IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conlusions
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ResultsResults
The choices made concerning the following four points:
Topology DC/DC Converter SC Bank Modeling
Results
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TopologyTopology
In this solution we need to design only one bidirectional DC/DC converter. Inserting an electronic switch in the converter it is possible to guarantee the safeness of the application. The number of the supercap bank is not extreme. The supercap bank is an add-on of the existing system.
DC/DC converter with high voltage battery pack
ResultsTopology
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Bidirectional DC/DC ConverterBidirectional DC/DC Converter
The components are commercially available more easily It is a direct converter then avoids losses related to the transformer
ResultsDC/DC Converter
Multiphase
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Results Supercapacitor bankResults Supercapacitor bank
Number of Scap = 35Type of Scap = BCAP1500Resulting Capacitance = 42,85FResulting ESR = 16,45mΩEnergy storage=133087 J 36,97WhVolume = 9000cm3
Cost Scaps = 2750 dollarsWeight Scaps = 11,19 KgEstimated weight DC/DC converter 22 KgMax weight battery = 20 KgEstimated weight ESU 53KgEstimated operating temperature -25 ÷ 70 °C
ResultsSC Bank
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ESU ModelESU Model
The first approximation model is a simple solution and has a short time simulation, in the future it will be placed in the Virtual Prototype.
It will be used to evaluate the performance of the vehicle with and without the use of the supercapacitors.
ResultsModeling
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IndexIndex
Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions
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ConclusionsConclusions Very high cost (Supercap + DC/DC Conv.) High weight and volume (Supercap + DC/DC
Conv.)
In conclusion, for the requested application, the resulting data are excessive in terms of weight and volume occupied.However, to confirm these conclusions, it would be interesting being able to perform tests, using the simulator. They will produce curves that may highlight the performance gap with and without the ESU.
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ConclusionsConclusions
The supercaps are suitable to be used either in buses, trains, trolley buses...
...or in high performance vehicles, such as sport cars and competition motorcycles.