Design and Optimization of an ESU for hybrid light vehicles with the use of Supercapacitors

1
Design and Optimization of an ESU for hybrid
light vehicles with the use of Supercapacitors
Supervisor Stefano Carabelli Marcello Chiaberge

• Students
• Aniello Valentino
• Francesco Villella

2
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

3
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

4
Introduction

• Context

• Motivations

• Objectives

5
Contex
Introduction?Context
ESU with add-on Supercapacitors
The Supercapacitors are an addition to batteries
they can be inserted or excluded depending on the
needs.
TTW Three Tilting Wheels
6
Motivations
Introduction?Motivations

• 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.
7
Objectives
Introduction?Objectives
8

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

9
Battery vs Supercap
Supercapacitor
Type Energy/ weight Wh/kg Power/ Size W/kg Nom, Cell V Cycles Durability cicli Charge time h
Lead (Pb)? 2030 1300 2 200300 816
Ni-Cd 3055 10900 1.25 1500 1
Ni-MH 5080 20 1000 1.25 30 500 24
Li-ion 110 160 1800 3.7 500 1000 24
Li-ion VHP Saft 74 6900 3.6 500000 20m
Nanosafe 90 4000 13.8 15000 lt10m
Supercap 3.95.7 470 13800 2.5 2.7 1000000 030s
The non conventional batteries have High Power
density but the charging time is high for this
application.
10
Supercapacitor
Supercapacitor

• ADVANTAGES
• 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

11
Equalization net
Supercapacitor
In power applications, supercapacitors are used
in stacks where many cells are connected in
series or in parallel to obtain acceptable
voltages and energy.

• 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.

12
Possible Solution
Supercapacitor
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
• High efficency
• User friendly
• DRAWBACK
• Expensive 40

• ADVANTAGES
• Simplest Solution
• DRAWBACK
• Power loss

13
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

14
ESU with Supercapacitors
ESU with Supercapacitor
ACTUAL SYSTEM
PROPOSED SOLUTION

• 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

15
Specifications
ESU with Supercapacitor

• 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

16
Sizing supercapacitor bank
ESU with Supercapacitor

• 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

17
Supercapacitor working voltage
ESU with Supercapacitor
The 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.
18
Supercapacitor working voltage
ESU with Supercapacitor
1,3V (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
Then the Energy of Supercapacitor bank is given
by the following equation
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.
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Restriction of the DC/DC converter
ESU with Supercapacitor
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.
20
Procedure
21
Compromise Weight-Energy
ESU with Supercapacitor
Result 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
• 45,591 V
• Weight 11,19 kg
• Energy 133087J
• 36,96Wh
• Power26.62kW for 5s
• Volume 9000 cm3
• ModelBCAP 1500

22
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

23
DC/DC Bidirectional Converter
DC/DC Converter
It is necessary because the supercapacitors
voltage (91V) is different in comparison to the
DC BUS voltage (200V).
Principle of Operation
Constraints
Step-down Phase Step-up Phase
VinV 200 45.5-91
VoutV 91 200
IoutA 100 110
PoutkW 9.1 22
Max time phase s 10 5
Constraint of application
Weight application less possible
24
Comparison isolated-non isolated
DC/DC Converter

• Two main categories of bidirectional DC/DC
  converters can be envisaged for this task
• Isolated converters
• Full Bridge
• Tapped Boost
• Non isolated converters
• BuckBoost
• Multiphase

BuckBoost Multiphase Full Bridge Tapped 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
25
Non isolated converters
DC/DC Converter
A variant of the BuckBoost solution is the
Multiphase Converter.

• ADVANTAGES
• Simplest topology of
• the DC/DC converter
• DRAWBACKS
• 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.

26
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

27
Modeling
Modeling

• The modeling is needed to allow you to enter the
  ESU designed in the system.

Virtual Prototype Longitudinal dynamics model
of the vehicle
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Supercap
Modeling
Simulink Model
Laboratory Test
Analysis of results
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DC/DC Converter Supercap
Modeling

• FIRST APPROXIMATION
• Assumptions
• Linearity
• No losses (DC/DC)
• Equations
• Buck eq.
• Boost eq.

• SECOND APPROXIMATION
• Assumptions
• No Linearity,
• Losses (DC/DC)
• Equations
• State Equations(L,C)

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Models Comparison
Modeling

• Comparison Parameters
• Assumptions for the buck phase (braking)
• Static Simulations (fixed duty cycle)
• Iniatial SC Voltage60V
• D duty cycle 40 T Period 20 us
• Simulation time 40s

• 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'

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First vs Second approximation
Modeling
Speed Simulation Accurancy
First Approx Very fast low
Second Approx Very slow high

• 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.

32
Dynamic Simulation
Modeling

• Real operating assumptions
• Dynamic Simulations (First approximation model
  with control)
• Iniatial SC Voltage 0V
• D duty cycle variable T Period 20 us
• Simulation time 100s
• C/!D Charge/!Discharge '1', after 40 s '0'

• In the figure you can
• see 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

33
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conlusions

34
Results
Results

• The choices made concerning the following four
  points
• Topology
• DC/DC Converter
• SC Bank
• Modeling

35
Topology
Results?Topology
DC/DC converter with high voltage battery pack

• 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.

36
Bidirectional DC/DC Converter
Results?DC/DC Converter

• The components are
• commercially available
• more easily
• It is a direct converter
• then avoids losses related
• to the transformer

37
Results Supercapacitor bank
Results?SC Bank

• Number of Scap 35
• Type of Scap BCAP1500
• Resulting Capacitance 42,85F
• Resulting ESR 16,45m?
• Energy storage133087 J 36,97Wh
• Volume 9000cm3
• Cost Scaps 2750 dollars
• Weight Scaps 11,19 Kg
• Estimated weight DC/DC converter 22 Kg
• Max weight battery 20 Kg
• Estimated weight ESU 53Kg
• Estimated operating temperature -25 70 C

38
ESU Model
Results?Modeling

• 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.

39
Index

• Introduction
• Supercapacitor
• ESU with Supercapacitors
• DC/DC Converter
• Modeling
• Results
• Conclusions

40
Conclusions

• Very high cost (Supercap DC/DC Conv.)
• High weight and volume (Supercap DC/DC Conv.)

41
Conclusions
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.
42
Thanks

• Aniello Valentino Francesco Villella

43
Analisys of discharge transient
ESU with Supercapacitor
Dynamic simulation used to verify the power
variation during charge and discharge equations
The figure shows that in 5 s the bank of
supercaps can provide the power required 22kW
(violet line).