Comparative Analysis of Hybrid vs. Conventional Electric Powertrains Efficiency

Thesis Abstract

The study addresses the efficiency performance gap between hybrid and conventional electric powertrains in light-duty vehicles, with particular emphasis on real-world operating conditions, component-level energy flows, and system-level recycling of regenerative energy. The aim is to quantify and compare energy conversion efficiency,peak electric propulsion efficiency, and overall vehicle energy use across representative driving regimes, while isolating the influence of control strategies and auxiliary energy consumption. Specific objectives include (i) to evaluate average and peak propulsion efficiencies for hybrid and conventional powertrains under standardized drive cycles (WLTC and FTP-75) and diverse ambient temperatures (-10°C to 40°C); (ii) to assess the contribution of regenerative braking, thermal management, and energy storage subsystem losses to overall efficiency; (iii) to analyze the sensitivity of efficiency to controller strategies, such as torque-split optimization for hybrids and motor-thermal coupling in both configurations; (iv) to develop a comparative life-cycle efficiency framework incorporating manufacturing and end-of-life considerations; and (v) to provide design and control recommendations to maximize efficiency while maintaining performance and emissions targets. The methodology adopts a comparative, mixed-methods design combining experimental measurement with simulation-based analysis. The population comprises passenger vehicle powertrains deployed in mass-market markets, with a stratified sample of 20 hybrid and 20 conventional electric powertrains sourced from two manufacturers. Data collection relies on bench- and chassis-dlevel instrumentation high-precision dynamometers for propulsion efficiency, torque and speed sensors, battery state-of-charge and internal resistance monitoring, thermal cameras for thermal losses, and data loggers capturing drive-cycle, ambient conditions, and energy flow. For hybrids, additional instrumentation captures the power-split control signals and regenerative braking activity. The instruments’ validity is established via calibration against standard reference units and cross-validated with manufacturer data sheets. Reliability is ensured through repeated trials on each drive cycle (n=3 per cycle per vehicle type), with randomization of cycle order to mitigate sequence effects. Analytical approaches include (i) regression analyses (multivariate and hierarchical) to quantify the relationships between efficiency and operating variables (speed, torque, temperature, state of charge, and cycle type); (ii) ANOVA and post-hoc tests to compare mean propulsion and system-level efficiencies between powertrain types across drive cycles and temperatures; (iii) energy balance modeling to decompose losses into drivetrain, electrical, and thermal components, supplemented by Monte Carlo simulations to assess uncertainty; (iv) sensitivity analyses on control strategies, using a reduced-order model to simulate torque-split optimization in hybrids and motor-thermal coupling in both configurations; and (v) a life-cycle efficiency framework applying a simplified cradle-to-grave assessment to contextualize energy use. The theoretical framework draws on the Theory of Constraints for identifying bottlenecks in energy flow and the Energy Management Theory for optimizing control allocation between modes. A conceptual model integrates drive-cycle energy demand, powertrain losses, and environmental conditions to yield a comparative efficiency index. Expected findings indicate that hybrids exhibit superior overall efficiency in urban and mixed-drive cycles due to higher regenerative braking efficiency and optimized torque sharing, while conventional electric powertrains perform more efficiently at sustained high-speed cruising where regenerative opportunities are limited. Thermal management losses are anticipated to be more pronounced in hybrids due to auxiliary subsystems, but partially mitigated by optimized energy recovery. The analysis is expected to reveal statistically significant differences in both propulsion and system-level efficiencies across cycles and ambient temperatures, with the magnitude of advantage for hybrids diminishing at higher speeds where friction and electrical losses dominate. The study contributes to knowledge by delivering a comprehensive experimental-computational benchmark of hybrid versus conventional electric powertrains, outlining specific design and control strategies that maximize efficiency without compromising performance or reliability, and by presenting a standardized methodology for cross-sectional efficiency evaluation applicable to future drivetrain innovations. The conclusion will highlight practical recommendations for vehicle manufacturers, policymakers, and standards bodies, including calibrated torque-split strategies, enhanced thermal management approaches, and cycle-specific efficiency targets to guide technology roadmaps and regulatory metrics.