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Y. Liang

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Doctoral thesis (2026) - Y. Liang, P. Bauer, G.R. Chandra Mouli
Electric aircraft (EA) are an important pathway toward zero-emission transportation. Their deployment is constrained by technological and regulatory challenges, including standards and certification, battery development, powertrain hardware, and grid integration. Among these, the battery is the most critical, as it serves as the primary energy source in all-electric aircraft (AEA). Across flight profiles and propulsion configurations, AEA batteries require significant improvements in specific energy, specific power, and cycle life. This thesis defines the performance requirements of battery systems for AEA and develops methods to address them from two perspectives: battery pack design and power electronics interfaces connecting the pack to the powertrain.

This thesis begins with an overview of current EA development, including AEA, hybrid-electric aircraft (HEA), and electric vertical takeoff and landing (eVTOL) aircraft. Key battery performance metrics for aviation are examined, including specific energy, specific power, cycle life, safety, and pack design. Future trends, challenges, and suitable battery chemistries for different stages of EA deployment are also discussed.

To determine battery pack size, a methodology is proposed to map EA performance requirements to the corresponding energy and power demands across mission phases. These include takeoff, climb, cruise, and descent for all-electric conventional takeoff and landing (eCTOL) aircraft, and hover, climb, cruise, descent, and landing for eVTOL aircraft. Since existing cell chemistries typically involve a trade-off between specific energy and specific power, battery packs based on a single cell type may be oversized to satisfy either energy or peak power demands, increasing mass unnecessarily. To address this limitation, a hybrid battery pack is developed. High-specific-energy cells form the primary pack for energy-intensive cruise operation, while high-specific-power cells in a secondary pack support power-intensive phases such as takeoff and climb. The design is formulated as an optimization problem that minimizes pack mass under energy and power constraints.

Powertrain integration of the hybrid battery pack is then investigated. In conventional hybrid energy storage systems (HESS), a semi-active topology is commonly used, where a DC/DC converter regulates power flow from the secondary pack. This requires the converter to handle peak secondary-pack power, increasing system mass and reducing efficiency. To overcome these limitations, a partial power processing (PPP) architecture is adopted. In this structure, only part of the total power is processed by the converter, while the remainder follows a direct path to the bus. This reduces converter rating, losses, and thermal stress, improving overall efficiency.

To further improve efficiency, a partition variable-frequency triple-phase-shift (TPS) modulation strategy is developed for the dual-active-bridge (DAB) converter in the PPP architecture. This enables zero-voltage switching (ZVS) across all switches and reduces inductor current stress. In addition, the optimal secondary battery pack voltage is determined using a detailed converter loss model to minimize total integration mass, including converter mass and additional battery mass required to compensate for conversion losses.

Finally, battery thermal management is optimized at the pack level. Since pack-level energy density is lower than cell-level energy density due to packaging and the battery thermal management system (BTMS), improving pack design is essential. An electrical-thermal-aging (ETA) model is developed for a liquid-cooled battery pack, accounting for cell C-rate, state of charge, temperature, aging state, electrical topology, and BTMS design parameters. This model enables prediction and optimization of pack performance under EA operating conditions, resulting in improved energy density while maintaining favorable thermal and aging performance. ...
Conference paper (2025) - Y. Liang, G. R. C. Mouli, P. Bauer
Electric aircraft represent a promising lowemission alternative to conventional fuel-powered aviation. This study proposes a battery sizing method for small all-electric aircraft using an electro-thermal battery cell model, considering different flight segments based on a reference commercial aircraft. The experiment is conducted to verify the proposed electro-thermal battery cell model. It considers varying battery efficiency throughout the flight mission, highlighting the importance of battery efficieny in the design process. ...
Electric aircraft represent a promising low-emission alternative to fuel-powered aviation. As the energy source, the battery pack must guarantee key performance metrics such as energy density, power density, lifetime, and safety. Among these, energy density is particularly critical as it directly impacts the range and payload capacity. Additionally, the battery thermal management system (BTMS) of the battery pack is essential to maintain safety, efficiency, and lifetime. Hence, to design a battery pack with improved energy density and optimized thermal and aging performance, a complete electro-thermal-aging (ETA) model at both cell and pack levels is developed to predict pack behavior under operational conditions. Simulations demonstrate that the proposed model achieves an accurate thermal prediction accuracy within 0.87°C during an example all-electric aircraft (AEA) mission profile. Optimization based on the proposed model is conducted, focusing on geometric configurations of the battery pack and coolant flow parameters, including channel wall thickness (LAl), inlet width (Wcl), cell spacing (Dcell), package wall thickness (Lenc), inlet flow temperature (Tcl,in), and flow velocity (Ucl,in). An optimized liquid-cooled battery module using Samsung 18650-35E cells is designed with [LAl, Wcl, Dcell, Lenc] = [0.4, 1.6, 20, 0.5]mm, Tcl,in =35°C, and Ucl,in = 0.05ms-1 during cruise and 0.02ms-1 during takeoff, climb, and descent. This configuration achieves a maximum temperature of 41.76°C and a maximum cell-to-cell temperature difference of 3.11°C, improving thermal uniformity. The lifetime performance also demonstrates a 5.51% improvement in state-of-health (SOH) after 180 cycles. Based on the module-to-pack structure analysis, the battery pack exhibits energy densities of 227.01Wh kg-1 gravimetrically and 353.67Wh L-1 volumetrically. This study facilitates the guideline for compact and lightweight liquid-cooled battery pack design with improved thermal and aging performance for AEA applications. ...
Electric aircraft (EA) is a promising alternative to conventional fuel-based aircraft, offering reduced greenhouse gas emissions and enhanced operational efficiency. To ensure seamless operations and optimize energy management, accurate EA charging demand prediction becomes imperative. This article presents a study on forecasting the charging demand for future small- and short-range EA. First, battery sizes are determined for various types of small all-EA (AEA) and electric vertical takeoff and landing (eVTOL) aircraft. Utilizing the electrical circuit model (ECM) for lithium-ion batteries (LIBs), this study derives the charging power curve of EA under the constant current-constant voltage (CC-CV) charging strategy. Subsequently, the charging demand prediction is conducted using the flight schedule of a selected airport, allowing for a realistic assessment of the power requirements for charging EA. Finally, case studies exploring charging demand under different scenarios are conducted. The results highlight the substantial power demand associated with the charging process, emphasizing the essential infrastructure needs and potential approaches for managing charging power in electric flight. ...

Synergizing High-Specific-Energy and Power Battery Types

The aviation industry, responsible for over 2% of energy-related CO2 emissions in 2022, aims for Net Zero Emissions by 2050. Despite electric aircraft's environmental benefits and improved operational efficiency, the current battery technology limits their range and size. Based on the optimal system voltage and power profile of the reference all-electric aircraft, this paper presents the design of a hybrid reconfigurable battery pack. The design incorporates a combination of high-specific-energy (263 W h kg-1 at cell level) and high-specific-power (1800 W kg-1 at cell level) battery types and its performance is compared with that of a fixed configuration battery pack comprising a single battery type. Simulation results suggest a potential 900 kg (18% lighter than fixed configuration) weight savings with reconfigurable pack, translating into enhanced payload, energy savings, or range extension for 9 PAX Eviation Alice electric aircraft at just 0.4% more energy capacity loss in 500 cycles. ...

State of the Art, Trends, and Challenges

Electric aircraft technology has gained considerable attention and is rapidly developing to mitigate the environmental impact of air transportation and move toward more sustainable modes. Nevertheless, the unique characteristics of electric aircraft pose significant challenges for the charging infrastructure, which must be effectively addressed to facilitate the growth of electric aircraft. This article provides a comprehensive review of the latest developments and future trends in electric aviation, which covers electric aircraft, battery technology, and electric aircraft charging systems. This article also surveys the possible charging system architectures that can be employed for electric aircraft charging. Various power electronic converter topologies that are suitable for future electric aircraft dc fast chargers are presented. This article concludes by identifying future challenges in the path toward charging electric aircraft and discusses potential solutions to these challenges. ...
Conference paper (2022) - Yawen Liang, Lu Wang, Zian Qin, Pavol Bauer
In emerging fast-charging stations, DC fast chargers (DCFCs) are employed which rely on power electronics and control to achieve the required performance. Harmonic emission induced by the complex system behavior is of great concern in the DCFC system. This paper proposes a harmonic emission model for the typical electric vehicle charger design, i.e., two-level active front end. The technique is based on the Fourier series method and the impedance model which is able to reveal the harmonic current emission of DCFCs under different grid conditions. Time-domain simulations are presented subsequently to validate the proposed model. ...