Abubakar, Abdullahi
(2025)
Advanced design of hybrid energy storage system to achieve low weight for aircraft applications.
PhD thesis, University of Nottingham.
Abstract
The growing demand to reduce carbon emissions poses a significant challenge for the aviation industry, particularly due to its contribution to greenhouse gas emissions, which are a major factor in climate change. The transportation sector is responsible for emitting high amount of CO_2 annually, along with other harmful pollutants, which have been linked to deaths.
In response to these, the Advisory Council for Aviation Research and Innovation (ACARE) introduced a mandate aiming for cleaner and quitter aircraft. This directive has spurred the aviation industry to develop aircraft that are not only lighter but also have lower maintenance and operating costs. Traditionally, the electrical grid in aircraft operates at 115V AC with a variable frequency range of 360Hz to 800Hz for high-power loads, alongside a 28V DC system used for avionics. These has caused an increased system inefficiency and maintenance cost with heavier weight thus, leading to increased fuel consumption. The More Electric Aircraft (MEA) is introduced to overcome this issue, and a new system architecture is introduced to provide a reduced operating cost and fuel consumption, increase system efficiency and reliability, simplifies electrical wirings and reduce the weight. However, the MEA still retains the use of fuel-based engines for engine propulsion, the goal is to achieve a zero-flight emission All Electric Aircraft (AEA) by relying entirely on electric propulsion.
Various energy storage systems are explored in powering the AEA which Lithium-ion batteries becoming a widely employed in electric vehicles due to their high energy density. However, despite the battery capabilities, implementing peak power demands during the aircraft take-off phase results in rapid discharge and subsequent accelerated degradation of the batteries. Therefore, investigation of hybridization the battery and supercapacitor energy storage are considered to provide with the aircraft’s energetic requirement with reducing the weight of the energy storage system.
Various DC/DC converters for interfacing with the energy storage systems and the aircraft DC bus are explored. The DC/DC non-isolated bidirectional converter is considered owing to its simple structure and wide applicability in interfacing with energy storage systems. The high-power DC/DC converter with coupled inductors are implemented owing to its improved power density with improved efficiency compared to the interleaved DC/DC converter with non-coupling. The interleaved non-isolated DC/DC converter is employed to interface with the supercapacitor energy storage system, while a single-channel DC/DC converter is utilized to interface with the battery energy storage system. The supercapacitor converter is specifically designed to supply the peak power demands, whereas the battery converter is responsible for providing lower power requirements during various phases of the aircraft mission.
This thesis further proposed the control of interleaved converter within saturation of coupled inductor. Two different control structures are considered using two channel interleaved DC/DC converter to control the magnetizing current. The control structure 1 consists of two independent current controller plants with each acting separately and independently. The control structure 2 is a decoupled control structure involving two different current control plants each acting independently and separately. The output of the coupled inductor is the common mode component while the differential mode components of the interleaved channels. This involves using coupled inductor in a single core, to use the concept of controlling the magnetizing currents. Therefore, by controlling the magnetizing current, the decoupled converter control structure allows the operation of the coupled inductor within its saturation limit with discrepancies in the channel currents.
The research further investigates on advanced cooling techniques for power electronic components, aimed at reducing heat dissipation by lowering junction temperatures using thermoelectric module. This is setup by the interfacing a thermoelectric module between the semiconductor power device with heatsink and cooling fan. This helps in reducing the thermal stress with enhancing the operational lifespan of the converter system.
The sizing of the battery only and hybrid battery and supercapacitor energy storage systems are investigated, and their simulation models are developed and analysed using the PLECS simulation. Also, the performance of the interleaved DC/DC converters, hybrid DC/DC converter, the DC/DC converter thermal cooling and the proposed converter decoupled converter control are evaluated through simulation using PLECS software with the different cases considered. A laboratory scaled prototype is built and is used experimentally to validate the operation of the converters.
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