1. Design and Optimization of an ESU for hybrid light vehicles with the use of Supercapacitors Students: Aniello Valentino Francesco Villella Supervisor: Stefano Carabelli Marcello Chiaberge

2. 2 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

3. 3 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

4. 4 Introduction  Context  Motivations  Objectives

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

6. 6 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. Introduction  Motivations

7. 7 Objectives Introduction  Objectives  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

8. 8  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

9. 9 Battery vs Supercap Type Energy/ weight [Wh/kg ] Power/ Size [W/kg] Nom, Cell [V] Cycles Durabilit y [#cicli] Charge time [h] Lead (Pb) ‏ 20÷301÷3002200÷3008÷16 Ni-Cd30÷5510÷9001.2515001 Ni-MH50÷80 20÷ 1000 1.25 30÷ 500 2÷4 Li-ion 110÷ 160 18003.7 500÷ 1000 2÷4 Li-ion VHP Saft 7469003.650000020m Nanosafe90400013.815000<10m Supercap3.9÷5.7 470÷ 13800 2.5÷ 2.7 10000000÷30s The non conventional batteries have High Power density but the charging time is high for this application. Supercapacitor

10. 10 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 Supercapacitor

11. 11 Equalization 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

12. 12 Possible Solution DC/DC active solutionSwitched ResistorIntegration 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

13. 13 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

14. 14 ESU 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 SYSTEMPROPOSED SOLUTION ESU with Supercapacitor

15. 15 Specifications  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

16. 16 Sizing 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

17. 17 Supercapacitor working voltage 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. ESU with Supercapacitor

18. 18 Supercapacitor working voltage 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: 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

19. 19 Restriction 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

20. 20Procedure specifications datasheet Vin MAX Vin min 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 Needed Energy > E_module ? save data processing NO YES NO

21. 21 Compromise Weight-Energy 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: 45,5÷91 V  Weight : 11,19 kg  Energy: 133087J 36,96Wh  Power:26.62kW for 5s  Volume : 9000 cm 3  Model:BCAP 1500 ESU with Supercapacitor

22. 22 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

23. 23 DC/DC Bidirectional Converter It 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-down Phase Step-up Phase Vin[V]20045.5-91 Vout[V]91200 Iout[A]100110 Pout[kW]9.122 Max time phase [s] 105 Constraint of application Constraints DC/DC Converter

24. 24 Comparison isolated-non isolated Two 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+BoostMultiphaseFull Bridge Tapped Boost InductorVery heavyN but lightheavy Trasformatornone yesYes L couple Diff.ControlMiddle(2sw)Hard(Nsw)Hard(8sw)Middle(2sw) Efficiencyhigh lowmiddle DC/DC Converter

25. 25 Non isolated converters 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. A variant of the Buck+Boost solution is the Multiphase Converter. DC/DC Converter

26. 26 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

27. 27 Modeling The modeling is needed to allow you to enter the ESU designed in the system. Virtual Prototype : Longitudinal dynamics model of the vehicle Modeling ESU Modeling Plant ACU Host ICE Electric motor Power Module ECU System Battery Supercap DC/DC Converter

28. 28 Supercap Laboratory Test Simulink Model Analysis of results Modeling

29. 29 DC/DC Converter + Supercap 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) Modeling

30. 30 Models 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 Parameters Assumptions 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

31. 31 First 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 ApproxVery fastlow Second ApproxVery slowhigh Modeling

32. 32 Dynamic Simulation 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 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' Modeling

33. 33 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conlusions

34. 34 Results The choices made concerning the following four points:  Topology  DC/DC Converter  SC Bank  Modeling Results

35. 35 Topology  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 Results  Topology

36. 36 Bidirectional DC/DC Converter  The components are commercially available more easily  It is a direct converter then avoids losses related to the transformer Results  DC/DC Converter Multiphase

37. 37 Results Supercapacitor bank  Number of Scap = 35  Type of Scap = BCAP1500  Resulting Capacitance = 42,85F  Resulting ESR = 16,45mΩ  Energy storage=133087 J 36,97Wh  Volume = 9000cm 3  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 Results  SC Bank

38. 38 ESU 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. Results  Modeling

39. 39 Index  Introduction  Supercapacitor  ESU with Supercapacitors  DC/DC Converter  Modeling  Results  Conclusions

40. 40 Conclusions  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.

41. 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. 43 Analisys of discharge transient The figure shows that in 5 s the bank of supercaps can provide the power required 22kW (violet line). Dynamic simulation used to verify the power variation during charge and discharge equations: ESU with Supercapacitor