(SEM VIII) THEORY EXAMINATION 2024-25 ELECTRIC VEHICLES

SECTION A – Short Answers (2 Marks Each)

(Paragraph style, brief but complete)

a) A modern EV has a battery pack of 50 kWh. Calculate the charger capacity to charge it in 10 hours.

To fully charge a 50 kWh battery in 10 hours, the charger capacity is calculated by dividing energy by time. Charger power equals 50 kWh divided by 10 hours, which gives 5 kW. Therefore, a 5 kW home charger is required to completely charge the battery in 10 hours.

b) Write the full form of FAME and EMPS schemes.

FAME stands for Faster Adoption and Manufacturing of Electric Vehicles, which is a Government of India scheme aimed at promoting electric mobility. EMPS stands for Electric Mobility Promotion Scheme, introduced to further encourage EV adoption through incentives and infrastructure support.

c) Which type of motors are predominantly used in electric three-wheelers in India?

Electric three-wheelers in India predominantly use Brushless DC (BLDC) motors due to their simple control, high efficiency, low maintenance requirements, and cost-effectiveness, making them suitable for commercial applications.

d) Enlist the motors used in modern electric cars.

Modern electric cars mainly use Brushless DC motors, Permanent Magnet Synchronous Motors, and Induction Motors. These motors are selected based on efficiency, torque characteristics, cost, and vehicle performance requirements.

e) Explain the objectives of Battery Management System (BMS).

The primary objective of a Battery Management System is to ensure safe and efficient operation of the battery. It monitors voltage, current, temperature, and state of charge, protects the battery from over-charging and over-discharging, balances cells, and enhances battery life.

f) Define SoC and C-rating of a battery.

State of Charge (SoC) indicates the available charge in a battery expressed as a percentage of its total capacity. C-rating defines the rate at which a battery can be charged or discharged relative to its capacity, such as C50 indicating a discharge over 50 hours.

g) Explain billing systems for EV charging.

EV charging billing systems can be based on energy consumed (per kWh), time of charging, or a combination of both. Advanced billing systems also include subscription-based and dynamic pricing models integrated with smart meters and digital payment platforms.

h) Mention major power quality problems in fast EV chargers.

Fast EV chargers introduce power quality issues such as harmonic distortion, voltage fluctuations, poor power factor, and increased stress on the electrical grid, which must be addressed during charger design.

i) What is a fuel cell? Comment on its efficiency.

A fuel cell is an electrochemical device that converts chemical energy directly into electrical energy using hydrogen and oxygen. Fuel cells are highly efficient, typically achieving efficiencies of 40–60%, which is higher than conventional internal combustion engines.

j) Define Depth of Discharge (DoD).

Depth of Discharge refers to the percentage of battery capacity that has been used relative to its total capacity. A higher DoD indicates deeper battery usage and directly affects battery life and performance.

SECTION B – Descriptive Answers (10 Marks Each)

a) Compare electric vehicles with IC engine vehicles and comment on source-to-wheel efficiency.

Electric vehicles differ significantly from internal combustion engine vehicles in terms of energy source, efficiency, and environmental impact. EVs use electricity stored in batteries, whereas IC engines rely on fossil fuels. From source-to-wheel perspective, EVs achieve much higher efficiency because electric motors convert a large portion of electrical energy into motion with minimal losses. In contrast, IC engines lose a major portion of energy as heat. As a result, EVs typically achieve source-to-wheel efficiency of around 70–80%, whereas IC vehicles operate at only about 20–30%.

b) Critically compare BLDC, PMSM, and Induction motors used in EVs.

BLDC motors are efficient, easy to control, and suitable for low-cost EVs but have limited high-speed performance. PMSMs offer high efficiency, high power density, and excellent torque characteristics, making them ideal for premium EVs, though they are costly due to rare-earth magnets. Induction motors are robust, magnet-free, and cost-effective but slightly less efficient compared to PMSMs. The choice depends on cost, performance, and vehicle application.

c) Short note on Cell Balancing and UN38 Regulations.

Cell balancing ensures uniform voltage across battery cells, preventing over-charging or under-charging of individual cells and improving battery life. UN38 regulations are international safety standards that lithium batteries must comply with during transportation, ensuring resistance to vibration, shock, thermal stress, and short circuits.

d) Discuss on-board and off-board chargers and the need for charging systems.

On-board chargers are installed inside the vehicle and are used mainly for slow or moderate charging using AC supply. Off-board chargers are external units that provide fast DC charging. Charging systems are required to ensure safe, efficient, and standardized energy transfer between the grid and EV while protecting both the vehicle and infrastructure.

e) Explain V2V and V2G technology.

Vehicle-to-Vehicle (V2V) technology allows energy transfer between electric vehicles, while Vehicle-to-Grid (V2G) enables EVs to supply power back to the grid. These technologies help in load balancing, grid stabilization, and effective utilization of renewable energy sources.

SECTION C – Long Answer (10 Marks)

a) Explain the architecture of an Electric Vehicle.

The architecture of an electric vehicle consists of key components such as the battery pack, electric motor, power electronics, controller, transmission system, and charging unit. The battery stores electrical energy, which is supplied to the motor through an inverter. The motor converts electrical energy into mechanical energy to drive the wheels. Power electronics manage energy flow, while the controller ensures optimal vehicle performance. This integrated architecture results in high efficiency, low emissions, and smooth operation.

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b) Explain the historical development of electric vehicles.

Electric vehicles evolved through multiple generations. Early EVs appeared in the late 19th century but declined due to the rise of IC engines. The second generation emerged with hybrid vehicles to improve fuel efficiency. Modern EVs represent the latest generation, driven by advancements in battery technology, power electronics, and environmental concerns, leading to widespread adoption today.