Electrical

Vehicle(EV)

Modelling for

Smart Grid

Prepared By:

Srikanth Reddy K

Renewable Energy-NIT Jaipur

(srikanthkonda.eee@gmail.com)

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Vehicle Architectures HEV

EV

PHEV

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General Nature and Engg. Fields of HEV[1]

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System level diagram of HEV[1]The HEV’s can be of two types:

1.HEV with battery systems

2.HEV without battery systems

In HEV the ICE will drive the electric generator which in turn supplies the electric motor. The advantage is that

the ICE can be run at an optimal speed to achieve the best possible efficiency.

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HEV Architectures[1]Series HEV Parallel HEV

Series-Parallel

HEV

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System level diagram of EV[1]WHY EV?

High overall efficiency: The ICE itself has an efficiency of 30-37% and by the time the power arrives at wheels it

will become 5-10% where as in EV the efficiency of motor , inverter& battery are above 90% individually, by the

time power arrives at wheels it would be in the order of 70%.

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System level architecture of PHEV[1]This allows the battery to be charged from external utility grid and also discharge back to it.

Since the battery is charged from utility ,vehicle can have a larger battery than that of HEV which is fuel economic.

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Marketed models of HEV’s[1]Toyota Pirus HEV Honda Civic Hybrid

Ford escape

hybrid

The chrisler

Aspen Hybrid

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Battery Equivalent electric circuit models

There are many electrical equivalent models that were developed for different types

of batteries, some of them were are discussed here:

This is the simplest model for battery in which a single voltage source and an

internal resistance is considered.

The drawback is that the internal resistance is different for charging and

discharging conditions. Therefore the model is modified.

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Larmine and lowry model equations[1]1)Terminal voltage is given by

𝑽𝒕 = 𝑽𝒐𝒄 − 𝑰𝒃 𝑹𝒊𝒏𝒕Where,

𝑉𝑡 = terminal voltage

𝑉𝑜𝑐 =open circuit voltage which is a function of SOC and temperature

𝐼𝑏 = battery discharge current

𝑅𝑖𝑛𝑡 =Internal resistance

2)The open circuit voltage is given by

𝑽𝒐𝒄 = 𝑬𝒐 +𝑹 𝑻

𝑭𝒍𝒏

𝑺𝑶𝑪

𝟏 − 𝑺𝑶𝑪Where,

𝐸𝑜 = standard (nominal voltage) potential of battery

𝑅 = Ideal gas constant

T= absolute temperature

F = Faraday constant

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Modified battery models[1]: This model includes separate charge and discharge resistances and two diodes associated with them

such that either of them comes into picture in charging and discharging conditions.

For a required amount of power(Preq) the battery current is given by:

𝑰𝒃 =𝑽𝒐𝒄 − (𝑽𝒐𝒄𝟐− 𝟒(𝑹 × 𝑷𝒓𝒆𝒒))

𝟐𝑹Where,

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Models with capacitance[1] Again a capacitance is added to indicate the diffusion of electrolyte and its resultant transients

RC model

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Factors effecting Battery performance1. Discharge Rate/C-rate:

The C rate is given by discharge current(A) divided by capacity of the battery(Ah).

For example if a 100Ah battery is discharged at 10A then Cr=0.1,if discharged at 5A then Cr=0.05.

The discharge rate effects the battery life(Number of cycles of use),the available energy for discharge and

voltage.

The lower the discharge rate, more the available energy is. This is called as Rate Capacity Effect and the

estimation of the effect can be calculated by Peukert’s Law[1].

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Peukert’s law The peukert’s equation relates the available capacity of the battery to the discharge rate for a constant discharge

current.

Since the discharge current is variable in most of the cases the peukert’s method is modified to adapt it to

variable discharge current.

Ibatt*t = C

If capacity(C1) at any discharge rate(Ibatt1) is given then the capacity(C2) at any discharge rate(Ibatt2) can be

found by the equation given by:

𝑪𝟐 = 𝑪𝟏(𝑰𝒃𝒂𝒕𝒕𝟏/𝑰𝒃𝒂𝒕𝒕𝟐)𝒏−𝟏

If the discharge current is varying consider constant current for a particular time interval(∆𝑡) then change in

SOC is given by:

∆𝑺𝑶𝑪 =𝑰𝒃𝒂𝒕𝒌

𝑪𝟏

𝑰𝒃𝒂𝒕𝒕𝒌

𝑰𝒃𝒂𝒕𝒕𝟏

𝒏−𝟏∆𝒕

𝑺𝑶𝑪 𝒕𝒌 = 𝑺𝑶𝑪(𝒕𝒌−𝟏) ± ∆𝑺𝑶𝑪

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2. Temperature:

Temperature effects the batteries chemical reactions and there by the energy available in the battery.

The battery’s available energy is lower at lower temperatures due to high portion of the activation

polarisation losses and available capacity will increase as the temperature increases however the

battery life may degrade under high temperatures.

The empirical relation of the temperature effect for the given battery can be estimated by using the

equation derived from curve fitting method.

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SOC determination:

Coulomb counting method[2]:

Where,

θ= SOC remaining

θ o=Initial SOC

δ (I)=Current loss coefficient (typically 0.9 to 1)

Ibatt =Battery discharge current

CN= Nominal battery capacity

There are many other models/ Algorithms proposed to estimate the SOC[2],[3],[4].

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Battery charging control

The charging control is very important as per the efficiency and life of battery is concerned.

Some of the battery charging control methods are given as follows:

1.Passive charging: In this method the battery is directly connected to DC link. It is the worst method

and may cause serious damage to battery with the current spikes and voltage fluctuations.

2.Constant Voltage(CV) charging: In this the charge voltage is maintained slightly above the battery

voltage irrespective of SOC. This suffers from disadvantage of Current spike when battery charged at

low SOC.

3.Constant Current(CC) charging: In this the charging current is kept constant. The advantage is that

the charging current remains constant and below the safe limit of battery which will improve battery

performance and life. Disadvantage is that towards the end of charge deposits may form at the

electrodes and cause to shorting of battery.

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CC-CV charging control method:

CC-CV charging method is the widely used method of charging.

This method eliminates the problems such as current spike and short circuiting associated with CV

and CC methods respectively.

Compared to CC charging the charging time as well as is more.

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Pulsed charging method: It is the most advance and fast charging method.

The charging current is applied in pulses. So this is often called as PWM charging.

When the SOC is low the pulse duration is high.

As the SOC tends towards 100% the pulse width reduces and becomes zero at 100% SOC.

This method has an advantage of charge normalization during the rest/relaxation period between two pulses

which improves the efficiency(by reducing concentration polarization losses) and life of battery.

[3]

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Regenerative charging In this we recover kinetic energy at time of breaking

For this the torque is reversed thus reversing the power. It is done by revering the

voltage of drive.

Recovery power depend on the how and where you drive.

Factors to be taken care of :

Safety

Performance

Limitations

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V/F and Voltage control of Induction drives

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V2G

MODELING

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Requirements for V2G Storage element

Semiconductor devices

Inverter

Chopper

Control circuitry

Communication system

Internal

External

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One type of Circuitry

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Control strategy of V2G[1]

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Applicable standard for V2G IEEE for Power and Energy

P2030 for smart grid infrastructure

P1547 physical and electrical interconnection b/w utility and distribution

Society of Automotive and Engineers(SAE)

J2293 communications b/w PEV and EV supply equipment for DC energy

J1772 electrical connection b/w PEV and EV supply equipment

J2847 communications for PEV interactions

J2836 use cases for PEV interactions

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Underwriters Laboratories (UL)

2202 Electrical vehicle charging system

2231-1and-2 Personal protection system for EV supply system

2251 Plugs, Receptacles and couplers for EV

2580 batteries for use in EV

458A power converters/Inverters for Electric Land Vehicle

2594 EV supply equipment

Applicable standard for V2G (Cntd.)

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References 1. Hybrid Electric Vehicles: Chris Mi, Abul Masrur, Weily publications.

2. http://www.teslamotors.com/blog/magic-tesla-roadster-regenerative-braking

3. Design of Duty-Varied Voltage Pulse Charger for Improving Li-Ion Battery-Charging Response, Liang-Rui

Chen, Member, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 56, NO. 2, FEBRUARY

2009.

4. A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and

lithium-ion batteries Dennis Doerffel , Suleiman Abu Sharkh, science direct.

5. A New Online State-of-Charge Estimation and Monitoring System for Sealed Lead–Acid Batteries in

Telecommunication Power Supplies Koray Kutluay, Yigit Çadırcı, Yakup S. Özkazanç, Member, IEEE, and

Isik Çadırcı, Member, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 52, NO. 5,

OCTOBER 2005.

6. State-of-Charge Determination From EMF Voltage Estimation: Using Impedance, Terminal Voltage, and

Current for Lead-Acid and Lithium-Ion Batteries Martin Coleman, Chi Kwan Lee, Chunbo Zhu, and William

Gerard Hurley, Fellow, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 54, NO. 5,

OCTOBER 2007.

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THANK YOU

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