Architecture and Working of Electric Vehicles (EVs)

Hindi 

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🔋 Lesson: Architecture and Working of Electric Vehicles (EVs)

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1. Introduction

Electric Vehicles (EVs) are automobiles powered entirely or partially by electric power. Fully electric vehicles (BEVs – Battery Electric Vehicles) operate solely on electricity stored in batteries and do not have internal combustion engines.

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2. Architecture of Electric Vehicle

Block Diagram:

Battery Pack → Power Electronics (Inverter/DC-DC) → Electric Motor → Transmission → Wheels
                           ↓
                   Auxiliary Loads (Lights, AC, etc.)

Main Subsystems:

• Energy Source: Battery Pack (Li-ion)

• Energy Conversion: Inverter + Motor

• Transmission System: Fixed or single-speed gear

• Control Unit: Motor Controller + Vehicle Control Unit (VCU)

• Auxiliary System: HVAC, lighting, infotainment, etc.

• Charging System: On-board charger, external EVSE

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3. Working Principle of a Fully Electric Vehicle

1. Power Supply: Energy stored in the battery is DC (Direct Current).

2. Inverter: Converts DC to AC (for AC motors) or controls switching (for DC motors).

3. Electric Motor: Converts electrical energy to mechanical torque.

4. Transmission: Transfers torque to wheels.

5. Regenerative Braking: Converts kinetic energy back into electrical energy during braking and stores it in the battery.

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4. Major Components of an Electric Vehicle

Component	Function
Battery Pack	Stores electrical energy
Inverter	Converts DC to AC and controls motor speed
Electric Motor	Converts electric energy to mechanical power
Transmission	Transfers torque to wheels
Vehicle Control Unit	Coordinates all subsystems
DC-DC Converter	Steps down voltage for auxiliary systems
On-board Charger	Manages power intake from charging stations

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5. Performance Parameters of an EV

• Range (km): Total distance the vehicle can travel on full charge.

• Efficiency (km/kWh): Distance covered per unit of energy.

• Top Speed (km/h): Maximum achievable speed.

• Acceleration (0–100 km/h): How fast the car reaches a certain speed.

• Gradeability: Ability to climb slopes.

• Regeneration Efficiency: Energy recovered during braking.

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6. Basics of Electric Motors in EVs

Motor Types:

• DC Motors: Simple, but low efficiency and maintenance-heavy.

• BLDC (Brushless DC): High efficiency, low maintenance.

• Induction Motors (AC): Rugged, used in Tesla (Model S/X).

• Permanent Magnet Synchronous Motors (PMSM): High torque, efficient, common in high-performance EVs.

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7. Motor Selection for EV

Factors to Consider:

• Required torque and speed

• Vehicle mass and payload

• Driving cycle (urban vs highway)

• Cost and availability

• Cooling system constraints

Motor Sizing Parameters:

• Rated Power (kW)

• Peak Torque (Nm)

• Rated Voltage (V)

• Maximum RPM

• Thermal limits

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8. Motor Characteristics

Parameter	Description
Torque-Speed Curve	Indicates how torque varies with speed
Efficiency Map	Shows motor efficiency at various loads
Power Density	Power output per unit volume or weight
Thermal Profile	Heat generated vs. time or load

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9. Motor Effort Calculation (Tractive Force)

To size the motor, we calculate the total tractive effort (Ftotal) required to move the vehicle:

Formula:

$$F_{\text{total}} = F_{\text{rolling}} + F_{\text{aero}} + F_{\text{grade}} + F_{\text{acceleration}}$$

Where:

• $F_{\text{rolling}} = m \cdot g \cdot C_r$

• $F_{\text{aero}} = \frac{1}{2} \cdot \rho \cdot A \cdot C_d \cdot v^2$

• $F_{\text{grade}} = m \cdot g \cdot \sin(\theta)$

• $F_{\text{accel}} = m \cdot a$

Then, Motor Power:

$$P = \frac{F_{\text{total}} \cdot v}{\eta}$$

Where:

• $m$: mass (kg)

• $g$: gravity (9.81 m/s²)

• $C_r$: rolling resistance coefficient

• $C_d$: drag coefficient

• $A$: frontal area (m²)

• $\rho$: air density

• $\theta$: road slope angle

• $\eta$: motor + drivetrain efficiency

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10. Electric Transmission in EVs

Unlike ICE vehicles, EVs often have simplified transmission systems, often with:

• Single-speed gearboxes

• Direct drive options

• Reduction gear sets

Advantages:

• High torque at low speeds → no need for multi-gear systems

• Lower mechanical losses

• Lighter and more compact

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✅ Conclusion

Understanding the architecture, components, and operation of EVs is crucial for modern automotive engineering. A well-matched electric motor based on vehicle dynamics ensures optimal performance and efficiency.

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🧮 Optional Homework or Exercise:

1. Calculate the required motor power for a 1500 kg EV to accelerate from 0 to 100 km/h in 10 seconds on a level road.

2. Compare the torque-speed characteristics of BLDC and Induction motors.

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