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The continued electrification of aircraft is required such that ambitious decarbonisation targets can be met. A significant challenge presented with this trend is the increased reliance on electrical systems to perform flight-critical operations in a manner that has not been seen in previous generations of aircraft. The power electronic converter is a key enabling technology in aircraft electrification. Its prevalence is such that the failure rate of flight critical-loads is closely linked with that of the associated power electronic converters. As such, there is a clear need to better understand the impact of improvements in both the reliability and failure estimation of novel power electronic converters at a systems level in future aerospace applications. Accordingly, this paper presents key highlights from literature on power converter research, summarising advances in reliability-enhancing features and more accurate Physics-of-Failure modelling methods.

Contemporary trends are leading towards the electrification of aircraft for urban mobility applications. Accordingly, there is a high demand for advancements in light-weight, high voltage technologies to realize these new aircraft types. Driven by recent developments in the automotive industry, hybrid Pyrofuse protection devices have emerged as one such new candidate technology. Pyrofuses offer rapid clearance of fault currents, reduced cost and weight when compared to conventional mechanical breakers. In addition, Pyrofuses have the ability to tune the time-current curve to fit the application’s fault response characteristics. However, Pyrofuses are non-resettable devices whose exclusive use for electrical protection could present potential operational hazards and certification challenges in aerospace applications. Model-based analysis will be critical in supporting this evaluation.

Direct current (DC) for primary power distribution is a promising solution that is being explored by aircraft system integrators for MEA applications to enable the paralleling of non-synchronized engine off-take generators, and to enable the reduction of energy conversion stages required to supply electronically actuated loads. However, a significant challenge in the use of DC systems is the reliable detection of arc faults. Arcing presents a significant fire risk to aircraft and their presence can result in critical system damage and potentially fatal conditions. Series arc faults in DC systems are particularly challenging to detect as the associated reduction in system current eliminates the use of conventional overcurrent and current differential methods for fault detection. This paper provides an overview of series arc faults in DC systems and presents both simulation and hardware results to illustrate key trends, characteristics and discriminating features.

The aviation industry has witnessed a technological shift towards the More Electric Aircraft (MEA) concept. This shift has been driven by a number of perceived benefits including performance optimization and reduced life-cycle costs. Increased electrification within MEA has made aircraft electrical networks larger and more complex and this necessitates an increased electrical power offtake from the engine. The paralleling of multiple generation sources across the aircraft is one potential design approach which could help improve engine operability and fuel efficiency within more-electric aircraft platforms. Accordingly, this paper will investigate options for the realization of paralleled generation systems within the context of current design and certification rules. The paper first illustrates, through simulation, that MIL-STD-704F voltage envelopes may be breached for some interconnected electrical architectures under fault conditions.

The increasing electrical demand in commercial and military aircraft justifies a growing need for higher voltage DC primary distribution systems. A DC system offers reduced power losses and space savings, which is of major importance for aircraft manufacturers. At present, challenges associated with DC systems include reliable fast acting short circuit protection. Solid State Contactors (SSC) have gained wide acceptance in traditional 28 VDC secondary systems for DC fault interruption. However, the reliable operation at higher operating voltages and currents requires further technology maturation. This paper examines a supporting method to SSC for more reliable fault mitigation by investigating bidirectional AC/DC converter topology with DC fault current blocking capability. Replacement of semiconductor switches with full bridge cells allows instant reversal of voltage polarities to limit rapid capacitor discharge and machine inductive currents.

A number of concepts have been proposed to meet future aircraft performance goals. One such concept under consideration is Turboelectric Distributed Propulsion (TeDP) featuring a large number of superconducting motors powered by two superconducting generators placed on each wingtip and connected through a DC distribution network. A key aspect in any design concept is the ability to prove that the system will exhibit a satisfactory reliability for all intended operating conditions. A common tool to support the calculation of failure rates and reliability is Fault Tree Analysis (FTA), and this will be utilized within this paper. The paper undertakes an architectural level FTA on a NASA proposed TeDP architecture to identify any significant factors contributing to the failure rate of key functionalities within the network.

The Turboelectric Distributed Propulsion (TeDP) concept uses gas turbine engines as prime movers for generators whose electrical power is used to drive motors and propulsors. For this NASA N3-X study, the motors, generators, and DC transmission lines are superconducting, and the power electronics and circuit breakers are cryogenic to maximize efficiency and increase power density of all associated components. Some of the protection challenges of a superconducting DC network are discussed such as low natural damping, superconducting and quenched states, and fast fault response time. For a given TeDP electrical system architecture with fixed power ratings, solid-state circuit breakers combined with superconducting fault-current limiters are examined with current-source control to limit and interrupt the fault current.

In addition to providing thrust, the engines on conventional civil jet airliners generate power for on-board systems and ancillary loads in the form of pneumatic, hydraulic and electrical power. Reduced fuel-burn and efficiency targets have driven the move towards More Electric Aircraft (MEA) technology which seeks to replace hydraulic and pneumatic loads with electrical equivalents. This technological shift, in conjunction with a growing electrical power load per passenger in general, has greatly increased the electrical power demands of aircraft in recent years - over 1 MVA for the Boeing 787 for example. With increasing fuel prices, there is a growing need to optimise efficiency of power extraction from the aircraft engines for the electrical system and loads. In particular, the utilisation of multi-shaft power off-takes, interconnected generation and power sharing between shafts is thought to offer potentially significant engine operability and fuel efficiency benefits.

Within aircraft electrical network designs, energy storage systems (ESS) provide a means of decoupling the electrical-mechanical interactions between the aircraft electrical power system and the aircraft engine, meeting peak load demand and maintaining power quality during network disturbances and variable load conditions. Within the literature to date, control and management strategies of ESSs for such applications has primarily focused on normal network operation with only limited coverage on the behavior of such technologies under abnormal conditions and the subsequent impact on the operation of the wider power system. Through modeling and simulation of a generic aircraft electrical system, this paper will highlight the potential risks of the inherent, sub-optimal operation of certain existing control strategies during fault conditions.

NASA has compiled a set of research goals for five year periods starting 2015, 2020 and 2025 for three classes of future subsonic aircraft, N+1 (2015), N+2 (2020) and N+3 (2025). With the intention of progressively making reductions in noise emissions, greenhouse gas emissions, fuel burn and energy consumption at each of these points to achieve Technology Readiness Levels (TRL's) of between 4 and 6. In the last few years much progress has been made towards achieving these goals through the development of new technologies and designs. This paper assesses how the current More Electric Aircraft (MEA) design concepts are advancing to allow the near term, N+1 goals of reducing 32 dB of noise emissions, 60% of the landing and take-off (LTO) NOx emissions, 55% of cruise emissions and 33% saving of fuel burn and energy consumption, relative to single aisle B737-800, could be met and eventually surpassed.

This paper analyses the behaviour of a highly-capacitive DC UAV network under fault conditions. Through simulation, the nature of overvoltage transients caused by the redistribution of stored energy following the clearance of a fault is illustrated. It is found that clearance of fault currents at or around their peak magnitude can result in substantial quantities of inductive energy being redirected into the smaller load capacitors, causing severe overvoltages across these loads. Recommendations for a protection strategy are given on the basis of the results presented, with consideration given to the use of surge arrestors to provide additional overvoltage protection to sensitive loads.

Increasingly complex and challenging mission requirements for Unmanned Aerial Vehicles (UAVs) may in the future place demands on the vehicle electrical system. Direct current and high-frequency alternating current have been proposed as alternatives to conventional AC approaches in manned aircraft which may contribute to meeting these requirements. The paper reviews the advantages and disadvantages a number of power distribution options across a range of metrics likely to be of interest to UAV designers and operators including factors such as weight, fault management and electrical losses. Important technical challenges in the application of these technologies are identified.