1. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Istvan Szenasy Szechenyi University, Dept. of Automation Hungary

2. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Our approach uses modeling and simulation to evaluate the potential of capacitive energy storage, an emerging technology for renewable energy. Supercapacitors and other battery technologies can contribute to rapid energy recovery. Fast energy recovery is especially important in electric vehicles, in which powerful batteries enable regenerative braking.

3. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG Renewing braking energy can significantly reduce the total energy consumed in short-distance passenger traffic using electrified lines or urban vehicles. Using Matlab-Simulink to model an urban-metro railcar of the Budapest Metro Railway, we have demonstrated that reducing the minimal capacitance value needed can make supercapacitor-based energy storage more viable. NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR

4. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Mass without load 34 t, fully loaded 44 t. The total rated motor power is 200 kW, the nominal speed is 75 km/h, the maximum acceleration is greater than 1 m/s 2, the average distances are approximately 800 m between stations, the overhead line voltage is 750V DC nominally. The weakening of the DC motor fields begins over the speed of 36 km/h. Charging-discharging of the SCAP ( abbreviated C) is executed by its bidirectional DC-DC converter.

5. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Figure 2. Aim and direction of simulations and calculations in modelling Our objective was to determine the lowest necessary capacitance value for a supercapacitor (C) for the storage of all regenerative braking energy under different conditions (mass, speeds, grades, stopping distances.) We set the optimum initial supercapacitor voltage to 840 V DC before starting the railcar. The lowest voltage of C was 400 V at the end of driving/start of braking. We achieved this under all conditions by: - tuning the variation of C, the capacitance value, - applying the ‘beforehand charged energy to C’ ECo applying the ‘constant charging power Pct’ from the overhead line, through execution of a Matlab-Simulink simulation.

6. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The benefits of applying a constant charging-power Pct are: a system operating in a cycle in which capacitance charging is adequate, more equal grid, lower grid losses in the motoring operation mode. In this investigation, the value of the factor d d=(Ucmin /Ucmax) (1) is about 48 % if the Ucmin is 400 V. In a real-world application, this value of d is acceptable. Our simulation considered the two distances between stations.

7. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR When varying the mass for a railcar from 30 to 55 t, the maximum motor current is a function of mass to achieve similar acceleration and speed Figure 7. The speed, the covered distance, the motor currents and powers between two stations 800 m apart

8. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Energety characteristics (for the same case in figure 7) Figure 8. Mass, m is varied from 35-55 t. Energy consumption of motors Emot, energy of C Ec, voltage of C Uc and current of overhead line I line v. time. Due to constantly charging power, line current remains constant.

9. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Improving the charging method If the charging power is not only a constant value but is varied by some function of the total motor current or motor power over the time of traction, then Line energy consumed is higher, energy derived from C is lower, and the necessary value of C will be less. Consequently, the charging power has two components, - one as a function of motor power adjusted by a “correction factor” - another a much lower “constant charging power”, Pct. (In investigating other functions as well, the correction factor consistently performed best, proportional to motor power.)

10. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Varied the set of energy management by a range of correction factor values, from 0 to 0.4 Figure 9 The energy consumption Eused does not depend on the correction factor. An increase in the current from the line decreases the needed value of C.

11. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Calculating the actual energy Ech to charge into C by charging power Pch may be realized with two components: At correction factor 0.4 the energy by motors flows in rate of 60 % from the C, and 40 % from overhead line. These task is solvable by the adequate voltage-control of DC-DC converters. Energy management is executable with the controller, measuring - motor current and voltage, - speed, - and line voltage and calculating the motor power.

12. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Application of the correction factor Figure 11. Overhead line current is NOT constant, varying in proportion to the grade at corrfact=0.4

13. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The decrease of the needed capacitance by applied correct factor 0.4 Figure 14. The decreasing of the possible need minimum values of the capacitance between cases corrfact=0 and corrfact=0.4. (In the case of corrfact=0, C increases by 5.5 F)

14. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The energy saving vs. the speed and the distance Figure12. The rated energy saving vs. the speed (km/h) and the distance (m) between stations. (The value of 0.55 is 55 %.) Energy saved does not depend on the correction factor.

15. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The actually needed minimum capacitance vs. the speed and mass Figure 13. The actually needed minimum values of the capacitance C needed vs. the speed (km/h) and mass (t) at corrfact=0.4, by its two-varied function

16. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Hybrid energy storage by Li-ion batteries and by supercapacitor Fig. 10: The model of hybrid energy storage system on a railcar: the battery is parallel switched with scap and both controlled by energy-management through own DC-DC converter. We sold a separately variable method for handle the control of capacitive energy storage and one of the battery.

17. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Fig..The curves of the Li-ion battery. If the discharge current is low as like 40 A the discharging time is 2,25 hour and this time decreases to 8,2 minutes if the current set to 180 A. The curves of the Matlab’2009-modelled Li-ion battery (750 V, 30 Ah)

18. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Searching of a suitable control method We set a model according to Fig. 11, and we solved the separately variable method for handle the control of capacitive energy storage and one of the battery. For managing all these tasks we investigated the behaviour of two control for the two energy-storage. In this model we applicate a current-limit method instead of a current control: we had searched and set the suitable upper and lower current values of the battery. We could show that the values of battery current are suitable all operation cycle.

19. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The limitations of battery current are suitable all operation cycle. When the limitation operates the need current flows to or from capacitor only. These peaks of current are proved by the capacitor in both direction. In this solution achived an aime that the energy storage is firstly proved by battery, but for giving or receiving the peak- current there is a little supercapacitor.

20. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR Figure 14: Speed, distance, motor current, motor power and line current. Grade = + 40%o. Figure 15: Battery voltage, S.O.C., current battery, current SCAP, voltage SCAP according to Fig. 14. PCt=124 kW, cf=0.271, SOCo=66 %, current limits +172, - 180 A. The system features in grade + 40 %o in 5 distances :

21. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The system features in grade - 30 %o : Fig. 26. The grade is - 30 %o. The speed of energy consumption (‘dch’) is high, and under regenerativ braking at charging (‘ch’) is longer and moderate. PCt=0 kW, cf=0, SOCo=66 %, current limits +180, - 217 A

22. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR The needed capacitance: 1 to 1.6 F, the decreasing is very significant ( for a hybrid energy storage, with cooperation a Li-ion battery 750V, 30 Ah)

23. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG The available decreasing ratio of the needed hybrid energy storage system at case SCAP is 30 % to 60 % - with this improved hybrid energy control method. These are significant values as decreasing in volume, mass and price. This novel process and its results are practically independent of the type of the traction motor. For these tasks the mass of SCAP is about 1500 kg. The mass of 800 kg about with presented Li-ion battery + SCAP hybrid storage-system, without converters. Mass reduction of this hybrid storage system is significant, about 50 % rated to supercapacitor type energy storage. NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR

24. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG The correction factor must be varied, 0.1 to 0.4, instead of a constant value 0.4 NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR

25. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG The change of Pct, constant power from line is larger: NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR

26. GREAT MINDS THINK ELECTRIC / WWW.EVS26.ORG Thanks for your attantion NEW ENERGY MANAGEMENT AND HYBRID ENERGY STORAGE IN METRO RAILCAR