Battery/Supercapacitor Energy Management system for Electric Vehicle

Electric vehicles (EVs) require appropriate design and sizing of their energy sources and proper management. The solution will be an energy efficient with cost-effective, increased lifespan, and an increase in the vehicle’s range. As per theory of evolution the model and rating calculations are discussed. Also this paper addresses the distribution of power within two energy sources, adopting a converter. Only one energy element unable to meet each preferred parameters. In addition to assisting electric vehicles in acceleration, the Hybrid Energy Storage System captures regenerative braking energy. By controlling the current of battery as consistent as viable at the time of picks, power management is primarily concerned with reducing battery stress and merging supercapacitors to supply instantaneous current at the time of pick and to recover power during deceleration. According to the results of HESS and experimental setup, current of battery is controlled as consistent as at the time of acceleration when the power management algorithm is implemented. In other words, only normal current is provided by the battery at the time of picks, while transitory current is provided via the ultracapacitor during acceleration.


Introduction
Since electric energy could be obtained from a variety of sources, it was highly flexible and it did not emit any harmful air pollutants.Currently, conventional systems need to be replaced with more fuelefficient and pollution-free ones.Innovative vehicles along with electric power are mostly restricted in their fuel efficiency and performance of Energy Storage Systems (ESSs).In order to be successful in these applications, energy storage systems must meet a number of parameters including high power and energy densities, long life cycles, fast charging times, rate, size etc.However, it is difficult to achieve all desired characteristics with a single element (Battery).The midway is the use of different heterogeneous energy sources, which combines low power battery for normal power and a supercapacitor for transient power during picks and deceleration.With hybridization, two elements can be combined to form an efficient storage system, one having huge energy density, such as a super capacitor, and the other having large power density, such as a battery [1][2][3][4][5].

Power Estimation
For a particular scooter, the speed between two successive steps can be determined by analysing the drive pattern during different speed conditions.The power required for an electric scooter can be estimated by calculating required power as given in [11].Assume vehicle parameters as mass (m), velocity (v) and angle (θ).
Eq. ( 1) gives between tractive effort, is the result of rolling resistance force F RR , aerodynamic drag force   and Hill climbing force   .In eq. ( 3) drag coefficient is Cd.All quantities of electric scooter are expressed in Table 1.Force and speed can be multiplied to determine power.Estimated Power for scooter at constant speed is 414.4Watt.
Total energy for 3600 seconds is 1.49 Mega Jul, and accordingly the covered distance is 36 kilometres.
During acceleration, constant speed, and variable speed the power required is different and it is much greater during hill climbing and acceleration.The power required for different speed is summarized as:

Battery sizing
The size of the battery must precisely match the vehicle's range for electric cars that run only on batteries.Voltages and Ah rating of Battery module are two factors that must be established for battery sizing.
When power delivery is required, battery module as well as supercapacitor module provide only nominal voltages that are close to the specified values.For required voltage and energy numbers of cells are in series and parallel respectively. _ battery series cell can be estimated as Where Vbus is voltage of bus and Vcelbat is nominal battery cell voltage.The distance that an electric vehicle can go on a single charge is referred to as the range of Zero Emission.On ground level zero-emission range for normal vehicle is 60 miles.Considered electric vehicle have a nominal DC voltage of 48 volts, which calls for a total of 13 series cells to be wired in series to create the battery pack.Battery pack current rating is estimated as follows: 2 Supercapacitor sizing 2.7 is the highest voltage of an supercapacitor cell, Equivalent capacitance diminishes if such cells are connected in series, As a result, a supercapacitor needs to connect in series and parallel [13].For desired voltage no. of supercapacitors in series estimated as follows and capacitance will be (5) (7) (6) (8) Where Vbus is desired bus voltage, VSC supercapacitor nominal cell voltag and Cseries series equivalent capacitance of a supercapacitor The necessary number of parallel supercapacitors is provided by Where the necessary capacitance for energy storage is Cdefined Supercapacitor power and stored energy can be calculated as ESR is Equivalent Series Resistance of supercapacitor.Above estimated quantities are summarized in Table 4.Where 13S10P stands for 10 parallel-connected cells and 13 Li-ion cells connected in series, and the same for an supercapacitor pack.

Experimental Result
A test configuration based on a DC-motor is going to be used to verify the experiment based results, as depicted in Figure 1.In laboratory, prototype with a reduced power level is created to validate the findings.Power control flow chart between battery and supercapacitor is shown in Figure 3.The power control has 3 modes: constant speed, acceleration and deceleration.Depending on the mode, a certain energy storage element will supply power Mode I: Only battery mode: Since the discharge battery voltage in this situation is becomes larger than the DC bus voltage, so the switch of supercapacitor is disabled, preventing supercapacitor from charging or discharging.Voltage of DC bus is 12 Volt so higher voltage is required.Figure 4 displays the experimentally determined input voltage of a fully charged lithium-ion battery, Vin = 8.4 Volt (blue), which is then increased to Vout = 19 Volt (black) by a DC/DC boost converter then given to the motor.Mode II: Combination of battery and supercapacitor.In this mode, the vehicle's high power requirements cause current spikes on the DC side.The ultra-capacitor sends current to the motor along with the battery so as to lower battery's increased current demand.Since the current required to load is higher than the discharge battery current, the battery is supplying an average current.In other words, if the voltage of battery drops to 12 Volt, the switch S4 of supercapacitor activates.At that point, the input voltage of the supercapacitor is increased to 12 Volt by a DC/DC boost converter, which then powers the motor.
Figure 5 shows that the battery current and peak load current are not drastically different from one another.The outcome demonstrates that when there is change of load current the super capacitor may react right away, at that time, load current will gradually supplied by battery.Battery current is kept as steady as possible because the load current applied to the battery changes very slowly.So life of battery is enhanced reduction in stress.Figures 5 and 6 illustrate how the battery's current is nearly constant while the supercapacitor's current fluctuates in response to changes in load.Mode III: Regenerative Mode: The motor starts regenerating when the vehicle decelerates.So, the supercapacitor is able to recover and store the vehicle's kinetic energy that is generated during deceleration.Figure 8 shows the charging of supercapacitor during deceleration.From it, it can be deduced that peak energy and peak power return to energy source are, respectively, 1.474 Watt-hour and 0.7371 Watt, while average energy and average power return to energy source are 5.303 Watthour and 0.055245 Watt. Figure 10 shows mode three voltage profile

Conclusion
The conclusion drawn from the practical and theoretical study of the HESS is that while constructing the battery-powered electric vehicle in real life, consideration should be given to the number battery and supercapacitor cell to be connected in series and parallel with the required power and energy.The power control algorithm discussed above can satisfy both the load profile and the power demand.
Because transient current is provided by an extra energy source, such as a supercapacitor, the battery current is kept as steady as possible, resulting in a much longer battery life.
power in Watt Vvehicle = Velocity of Vehicle in m/s ZEV Range = Zero emission vehicle range in m η DT = Efficiency of Drivetrain VN ominal = Nominal Battery Voltage in Volt E = Energy in Watt-hour 3.

Figure 1 .
Figure 1.Block diagram of Energy Storage

Figure 2 .
Figure 2. Flow Chart of power management

Figure 6 .
Figure 6.Battery current discussed in the section II, Section III gives rating of Energy elements.Research based results and conclusion summarized in the Sections IV, and V respectively.

Table 3 .
Power Calculation

Table 4 .
Specifications of Scooter