(SEM VI) THEORY EXAMINATION 2024-25 ELECTRICAL AND HYBRID VEHICLES

BEE064 – ELECTRICAL AND HYBRID VEHICLES

Section-Wise Solved Answers (2024–25)

SECTION A

(Attempt all questions) – 2 × 7 = 14 marks

(a) Define the term State of Charge (SoC) in battery systems.

State of Charge (SoC) represents the amount of electrical energy remaining in a battery compared to its maximum capacity. It is expressed as a percentage. An SoC of 100% indicates a fully charged battery, while 0% indicates a completely discharged battery. SoC is a key parameter for energy management and range estimation in electric vehicles.

(b) Mention any two differences between DC motor and Switched Reluctance Motor in EVs.

A DC motor uses brushes and a commutator for operation, whereas a Switched Reluctance Motor (SRM) is brushless and electronically controlled. DC motors require more maintenance due to brushes, while SRMs are rugged, have lower maintenance, and are more suitable for harsh EV operating conditions.

(c) List any four environmental benefits of electric vehicles.

Electric vehicles reduce air pollution by producing zero tailpipe emissions. They lower greenhouse gas emissions when powered by clean energy. EVs reduce noise pollution and help decrease dependence on fossil fuels, contributing to a cleaner and sustainable environment.

(d) Define State of Health (SoH) in battery performance monitoring.

State of Health (SoH) indicates the overall condition of a battery compared to its original performance when new. It reflects capacity degradation, internal resistance increase, and aging effects. SoH helps predict battery life and replacement needs.

(e) Give two examples of energy management strategies used in HEVs.

Two common energy management strategies in Hybrid Electric Vehicles are rule-based control strategies and optimization-based strategies. These methods decide how power is shared between the engine and electric motor to improve efficiency and reduce emissions.

(f) Name two driving cycles commonly used for EV performance evaluation.

Two commonly used driving cycles are the WLTP (Worldwide Harmonized Light Vehicles Test Procedure) and NEDC (New European Driving Cycle). These cycles simulate real-world driving conditions to evaluate EV range and efficiency.

(g) What is power split hybrid architecture?

Power split hybrid architecture is a hybrid vehicle configuration in which engine power is divided between mechanical and electrical paths using a power-splitting device. This allows flexible operation of the engine and motor for improved fuel efficiency.

SECTION B

(Attempt any three) – 7 × 3 = 21 marks

(a) Explain flywheel-based energy storage and its analysis.

Flywheel energy storage stores energy in the form of rotational kinetic energy. A rotating mass is accelerated during charging and decelerated during discharge. Flywheels offer high power density, fast response, and long life, making them suitable for regenerative braking in EVs. However, energy losses due to friction and safety concerns limit their widespread use.

(b) Comparison of Lithium-ion and Lead-acid batteries for EV use.

Lithium-ion batteries have higher energy density, longer life, and faster charging compared to lead-acid batteries. Lead-acid batteries are cheaper but heavier, have lower efficiency, and shorter cycle life. Hence, lithium-ion batteries are preferred in modern EVs.

(c) Explain the basic configuration of a Battery Electric Vehicle (BEV).

A Battery Electric Vehicle consists of a battery pack, power electronic converter, electric motor, transmission system, and control unit. Energy stored in the battery is converted into mechanical energy by the motor to drive the wheels. BEVs do not use internal combustion engines.

(d) Challenges in implementing energy management strategies.

Major challenges include battery aging, varying driving conditions, computational complexity, and accurate prediction of driver behavior. These factors make real-time energy optimization difficult in hybrid vehicles.

(e) Working and control scheme of Induction Motor in EVs.

Induction motors in EVs are controlled using vector control or field-oriented control techniques. These methods independently control torque and flux, ensuring high efficiency and smooth speed control over a wide operating range.

SECTION C

Q3. Attempt any one

(a) Mathematical modeling of vehicle performance considering tractive forces.

Vehicle performance modeling considers forces such as rolling resistance, aerodynamic drag, gradient force, and acceleration force. The total tractive force required at the wheels is the sum of these forces. This model helps estimate power requirements and energy consumption of EVs.

(b) Environmental and societal importance of electric vehicles.

Electric vehicles play a vital role in reducing air pollution and greenhouse gas emissions. They improve urban air quality, reduce noise pollution, and decrease reliance on fossil fuels. Societally, EVs support sustainable development and energy security.

Q4. Attempt any one

(a) Electric drive-train topologies and their efficiency.

Different drive-train topologies include series, parallel, and series-parallel configurations. Series systems offer simple control, parallel systems provide higher efficiency, and series-parallel systems combine advantages of both for optimal performance.

(b) Configuration and control of PMSM drives in EVs.

Permanent Magnet Synchronous Motors use permanent magnets on the rotor and are controlled using vector control techniques. They offer high efficiency, high power density, and are widely used in EV propulsion systems.

Q5. Attempt any one

(a) Hybrid energy storage using battery and ultra-capacitor.

Hybrid energy storage systems combine batteries and ultra-capacitors. Batteries provide high energy density, while ultra-capacitors handle peak power demands. This improves battery life and overall system efficiency.

(b) Function and structure of Battery Management System (BMS).

A Battery Management System monitors battery voltage, current, temperature, SoC, and SoH. It ensures safe operation, balances cells, protects against over-charging and over-discharging, and enhances battery life.

Q6. Attempt any one

(a) Classification of energy management strategies in hybrid EVs.

Energy management strategies are classified as rule-based strategies, optimization-based strategies, and intelligent strategies. Each method aims to optimize fuel efficiency and battery usage.

(b) Rule-based vs optimization-based EMS in HEVs.

Rule-based EMS is simple and easy to implement but less efficient. Optimization-based EMS provides better fuel economy but requires high computational power and accurate models.

Q7. Attempt any one

(a) Configuration and working of DC motor drive in electric propulsion.

DC motor drives use power converters to control speed and torque. The controller adjusts voltage and current supplied to the motor, enabling smooth acceleration and regenerative braking.

(b) Role of communication protocols in vehicle power-train control.

Communication protocols like CAN and LIN enable data exchange between sensors, controllers, and actuators. They ensure coordinated control, safety, and efficient operation of the vehicle power-train.