Lang, Xiaoyu
(2021)
Advanced integrated power generation centre for future More-Electric Aircraft.
PhD thesis, University of Nottingham.
Abstract
The More-Electric Aircraft (MEA) concept is a major trend in aircraft electrical power system engineering and results in an increase in onboard electrical loads and electrical power demand. On an aircraft the jet engine acts as the prime power source, providing to the onboard systems pneumatic power, hydraulic power, mechanical power and electrical power. As the aerospace industry is moving towards the MEA paradigm, many functions which are conventionally driven by pneumatic, hydraulic and mechanical power systems are being replaced by their electrical counterparts. However, due to the power off-take limit from the high-pressure (HP) spool, extra power is considered to be extracted from the low-pressure (LP) spool of an engine through the coupled generators. Increased number of generators and power electronic penetration renders a higher requirement to the power generation centre (PGC) in a more electric engine in terms of controllability, stability, fault tolerance, and power flow flexibility.
In recent years, a dual-channel single DC bus PGC was developed for the MEA application. Two electrical machines are coupled to the HP and LP spools of the engine respectively, and each of them is independently regulated by an AC/DC power converter. The DC outputs of the converters are parallel connected to supply a common DC bus. Theoretical analysis and experimental results of relevant research confirm the superiority of the PGC in efficiency and power sharing between sources. However, the PGC suffers from three critical drawbacks: 1) poor fault tolerance to the main rectifier failure; 2) power losses caused by the significant de-fluxing current in the HP generator at high-speed settings, and 3) the incapability to achieve engine and HVDC grid stability optimization in the high-power settings of the engine.
To address these drawbacks, an advanced power generation centre (APGC) with an AC/AC bridging converter is proposed in this Thesis. The bridging converter is introduced to make the APGC much more flexible than the PGC in terms of managing the power flow and the generators control. Compared with the PGC, the APGC allows post-fault operation and supplies uninterruptible power to the downstream loads in the case of main rectifier failure. It also allows the permanent magnet synchronous machine-based HP generator to operate at a high speed without field-weakening operation, which significantly reduces the stator currents and power losses in the HP generator and power converters. Moreover, due to establishing a power exchange path between the HP and LP power generation channels, the stability of the onboard HVDC grid and the engine can be enhanced simultaneously in the high-power settings of the engine.
System configuration, control schemes in normal and post-fault operation modes, power losses and stability with different power sharing ratios between sources of the APGC have been thoroughly analysed in this Thesis. Theoretical findings of the APGC support the above-mentioned improvements over the PGC. The technical results and simulations are supported by Matlab/Simulink based models and validated by experimental work on an engine emulator system and a downscaled lab prototype of the APGC.
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