Abstract
Title of the project:Multi-phase fault tolerant MW range generation systems for hybrid-electric aircrafts Electrifying transportation is one of the European Union’s strategic objectives. In the aviation sector, this is driving the development of hybrid-electric propulsion systems aimed at reducing emissions while enhancing reliability and lowering maintenance costs. These systems typically feature a gas turbine powering an electric generator, which supplies energy to electric motors connected to the aircraft’s propellers. This configuration enables distributed propulsion, optimizing thrust efficiency and reducing aerodynamic drag. In such aircraft, the electrical system must be designed to incorporate fault-tolerant features and handle high current levels, given the relatively low voltage available on board. Multi-phase generation systems offer an integrated solution for applications requiring high current and a high level of safety. Their inherent redundancy supports compliance with stringent reliability standards and operational demands. By distributing power across multiple phases, it becomes possible to utilize faster semiconductor devices, thereby enhancing both power quality and efficiency. Architectures built from independent single-phase or three-phase modules exhibit superior fault tolerance, as the failure of a single converter module can be mitigated by isolating it, enabling continued operation, albeit with reduced performance. Nonetheless, ensuring safe operation in the event of a machine-level fault remains a significant challenge. Additionally, control algorithms must be capable of identifying faults within the converter or machine and implementing appropriate countermeasures to limit the impact on drive performance. The goal of this project is to advance both theoretical understanding and practical solutions for fault-tolerant generation systems in hybrid-electric aircraft. The research will focus specifically on the development of multi-phase generator architectures capable of maintaining functionality even in the presence of one or more faults. In particular, the Bologna university unit will develop control algorithms for detection and management of fault conditions within the generating system. The research methodology will follow established investigative practices in the field of industrial engineering, integrating both theoretical analysis and experimental validation. The process will begin with a review of the current state of the art, followed by the identification of recent advancements and promising approaches found in literature. Selected solutions will then be designed, modeled, and subjected to experimental validation. Moreover, insights gained from the experimental phase will not only guide refinement of the design decisions, but also inspire new avenues for further investigation. The project includes dedicated experimental work to validate both the design process, and the simulation techniques employed. Objectives The first goal of the Research Project is to establish a cohesive research team and foster a coordinated national effort aimed at advancing both theoretical and practical expertise in the design, simulation, and control methodologies of electrical components in hybrid-electric propulsion systems for aircraft. Specifically, the project primarily aims to develop design and modeling methodologies for high-power multi-phase electric generators and power converters equipped with fault-tolerant capabilities, tailored for hybrid-electric aircraft applications. This objective will be validated through dedicated experimental test setups. Passenger and cargo air transport demand exceptionally high standards of reliability and safety. The design of modular multiphase power generators and converters will achieve the redundancy levels required to meet these stringent specifications. Developing a design methodology for fault-tolerant generating systems, along with the associated control and diagnostic systems, will have short- to medium-term impacts on avionic applications and transport sectors. The More Electric Aircraft approach, currently applied in civil aviation, will benefit from these advancements. Numerous on-board actuators that require fault tolerance, such as flight controls, cabin pressurization and conditioning systems, fuel pumps, and engine lubrication equipment, can leverage the advantages of multiphase architectures. The availability of electric technology that meets the stringent safety and reliability requirements of aircraft is crucial, as manufacturers strive to anticipate the factors influencing future purchase decisions by transport operators. Additionally, a network of knowledge, skills, and design methodologies for innovative electric drives in hybrid-electric aircraft will support the industry and facilitate its transition. The topics explored, with necessary variations, can be applied to hybrid/electric systems for road and naval transport, high-power generation units (such as diesel-electric), renewable energy generation systems like wind and wave motion, and various industrial applications within the megawatt power range. Results The research carried out by the Bologna unit focused on advancing the theoretical understanding of multiphase multilevel generation systems operating under fault conditions, where redundancy and reconfiguration capabilities play a central role in ensuring reliability and continuity of operation. A major outcome of the project was the development of comprehensive mathematical modelling frameworks for six-phase permanent magnet synchronous machines and five-level E-Type converters under both healthy and faulty operating conditions. These models enabled a systematic analysis of fault-induced asymmetries, electromagnetic coupling effects and performance degradation mechanisms. Two complementary models were developed: a time-domain model, including air-gap magnetic field harmonics up to the 11th order and all the major faults (open-phase, open-switch, high-resistance connections, inter-turn short circuits and balancing-circuit faults), and a frequency-domain model incorporating proportional–integral current regulators to analyse the steady-state behaviour of the complete controlled system. To fully exploit the intrinsic fault tolerance of the multiphase generating system, a two-step approach was adopted. First, advanced diagnostic techniques were developed to rapidly detect, classify and localise faults. Second, dedicated fault-tolerant control strategies were designed to prevent fault propagation and minimise performance degradation by exploiting the structural redundancy provided by the dual three-phase stator windings and the additional converter legs, which enable independent control of each three-phase set. Passive fault-tolerant techniques were also investigated to limit the effects of faults even before diagnosis and controller reconfiguration, thus improving system robustness. Based on the developed models, a new extended field-oriented control scheme was proposed, introducing additional regulators in selected reference frames to better exploit multiphase redundancy. A machine-learning-based multi-stage diagnostic framework was also developed to detect, classify and localise high-resistance connection and inter-turn short-circuit faults using only variables available within the control system. Regarding fault-tolerant operation, the proposed eight-leg converter architecture demonstrated superior performance under open-phase faults without reducing DC-bus utilisation. Properly designed passive control strategies achieved steady-state performance comparable to active approaches while avoiding fault detection and reference reconfiguration. For open-switch faults, five auxiliary current-injection strategies were proposed and compared, evaluating their effects on torque ripple, copper losses and DC-bus voltage oscillations. Another important contribution concerned the multilevel E-type converter. To overcome the reliability limitations associated with auxiliary balancing circuits, a novel PWM strategy was developed to ensure continuous DC-link capacitor voltage balancing without additional hardware, significantly improving converter fault tolerance. The diagnostic algorithms and fault-tolerant control strategies were implemented using real-time rapid-prototyping platforms and successfully validated through both machine emulation and dedicated experimental test benches assembled using cost-effective components while remaining representative of the target application. Machine parameters were identified experimentally and through finite-element analysis, and fault conditions were reproduced by introducing additional phase resistance, electrically connecting winding turns or disconnecting supply conductors. During the initial project phase, a representative five-phase setup was temporarily adopted because of procurement delays affecting the planned six-phase system, without compromising the planned experimental investigations or the resulting scientific publications. Overall, the project significantly advanced the state of the art in fault-tolerant multiphase multilevel generating systems. The scientific results provide a solid theoretical and experimental basis for future developments in reliable electromechanical energy conversion systems and are expected to have a long-term impact extending well beyond the specific aeronautical application considered.
Project details
Unibo Team Leader: Angelo Tani
Unibo involved Department/s:
Dipartimento di Ingegneria dell'Energia Elettrica e dell'Informazione "Guglielmo Marconi"
Coordinator:
Politecnico di TORINO(Italy)
Total Unibo Contribution: Euro (EUR) 49.120,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
28/02/2026
