JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ELECTRICAL AND HYBRID VEHICLES Previous Question Paper (July/August - 2022 - R18)

A conventional vehicle relies solely on an internal combustion engine (ICE) for propulsion, converting chemical energy from fuel into mechanical energy. It typically uses a transmission to manage torque and speed, with efficiency limited by the engine's operating map and idling losses. In contrast, a hybrid electric vehicle (HEV) integrates an ICE with an electric motor and a battery pack. The design allows for load leveling, where the electric motor assists during high-demand periods like acceleration, and regenerative braking, which captures kinetic energy that would otherwise be lost as heat. The working comparison shows that HEVs achieve higher fuel efficiency and lower emissions by operating the ICE in its optimal efficiency range and utilizing electric-only propulsion during low-speed or stop-and-go driving conditions.

Power source characterization in HEVs involves evaluating the performance, efficiency, and limitations of both the ICE and the electric drive system. The characterization process focuses on several key parameters:

• Energy Density and Power Density: The battery must be characterized by its specific energy (range capability) and power density (acceleration capability). High power density is critical for regenerative braking and rapid acceleration, while energy density dictates the electric-only range.
• Efficiency Maps: Both the ICE and the electric motor are characterized by efficiency maps, which plot efficiency against torque and speed. The control strategy uses these maps to determine the optimal power split between sources.
• State of Charge (SoC) and Depth of Discharge (DoD): The battery's performance is highly dependent on its SoC. Characterization includes defining the usable SoC window to ensure battery longevity and consistent power delivery.
• Thermal Constraints: Both the battery and the electric motor require characterization under various temperature conditions, as thermal management significantly impacts internal resistance, power output, and safety.
• Transient Response: The ability of the power sources to respond to rapid changes in load demand is measured to ensure stable vehicle dynamics during mode transitions between electric-only, engine-only, and combined operation.