Catherine E. Jones

A new control method for the power interface in power hardware-in-the-loop simulation to compensate for the time delay

In an attempt to create a new control method for the power interface in PHIL simulations, a simulated PHIL simulation is carried out where the simulation and hardware part are modelled in MATLAB/Simulink along with the new control method. This power interface control is proposed to achieve high accuracy in PHIL simulation with closed-loop control for aerospace, marine or micro grid applications. Rather than analyzing the Real Time Simulator (RTS) data and controlling the interface using time-domain resonant controllers, the RTS data will be analyzed and controlled at the interface in the frequency domain, on a harmonic-by-harmonic and phase-by-phase basis. This should allow the RTS time delay to be compensated accurately, and removes the requirement to include additional components to compensate for the simulation delay into the simulated power system as it is not appropriate for power systems which have short transmission lines. This is extremely relevant for marine and micro grid scenarios where such inductive components may not be present.

Comparison of candidate architectures for future distributed propulsion aircraft

Turbine-engine-driven distributed electrical aircraft power systems [also referred to as turboelectric distributed propulsion (TeDP)] are proposed for providing thrust for future aircraft with superconducting components operating at 77 K, in order for performance and emission targets to be met. The proposal of such systems presents a radical change from current state-of-the-art aeroelectrical power systems. Central to the development of such power systems are architecture design trades which must consider system functionality and performance, system robustness, and fault ridethrough capability, in addition to the balance between mass and efficiency. This paper presents a quantitative comparison of the three potential candidate architectures for TeDP electrical networks. This analysis provides the foundations for establishing the feasibility of these different architectures subject to design and operational constraints. The findings of this paper conclude that a purely ac synchronous network performs best in terms of mass and efficiency, but similar levels of functionality and controllability to an architecture with electrical decoupling via dc cannot readily be achieved. If power electronic converters with cryocoolers are found to be necessary for functionality and controllability purposes, then studies show that a significant increase in the efficiency of solid-state switching components is necessary to achieve specified aircraft performance targets.

Turboelectric Distributed Propulsion Protection System Design Trades

The NASA N3-X blended-wing body with turboelectric distributed propulsion concept is being studied to achieve N+3 goals such as reduced noise, emissions, and improved energy efficiency. The electrical distribution system is cryogenic in order to maximize its efficiency and increase the power density of all associated components, while the motors, generators, and transmission lines are superconducting. The protection of a superconducting DC network poses unique electrical and thermal challenges due to the low impedance of the superconductor and operation in the superconducting or quenched states. For a given TeDP electrical system architecture with fixed power ratings, conventional and solid-state circuit breakers combined with superconducting fault-current limiters are examined with both voltage and current source control to limit and interrupt the fault current. To estimate the protection system weight and losses, scalable models of cryogenic bidirectional current-source converters, cryogenic bidirectional IGBT solid-state circuit breakers, and resistive-type superconducting fault current limiters are developed to assess how the weight and losses of these components vary as a function of nominal voltage and current and fault current ratings. The scalable models are used to assess the protection system weight for several trade-offs. System studies include the trade-off in fault-current limiting capability of SFCL on CB mass, alongside the fault-current limiting capability of the converter and its impact on CB fault-current interruption ratings and weight.

Fault behaviour of a superconducting turboelectric distributed propulsion aircraft network: A comprehensive sensitivity study

Variations in the network architecture and component choices of superconducting DC networks proposed for future aircraft propulsion systems could have a significant impact on their fault response. Understanding these potential variations is key to developing effective protection solutions for these aircraft applications. To this end, this paper presents the results of sensitivity studies conducted using a representative model of a faulted superconducting DC network in which key system parameters are varied. Of the parameters considered, network voltage and the cable dimensions are shown to have the greatest impact on fault current profile whilst the rate of change of fault current is shown to be sensitive to network voltage and cable length. The paper concludes by exploring the implications of these findings on the prospective protection strategy for future aircraft propulsion systems.

A pre-design sensitivity analysis tool for consideration of full-electric aircraft propulsion electrical power system architectures

Turbo-electric distributed power (TeDP) systems proposed for hybrid wing body (HWB) N3-X aircraft are complex, superconducting electrical networks, which must be developed to meet challenging weight, efficiency and propulsor power requirements. An integrated system sensitivity analysis tool is presented, which can be used to support rapid appraisal studies of architectures, protection systems and redundancy requirements for TeDP systems. The use of this tool can help direct future research on TeDP systems towards the key challenges relevant to meeting the stringent weight and efficiency targets set out for N+3 aircraft concepts.

Protection system considerations for DC distributed electrical propulsion systems

Distributed electrical propulsion for aircraft, also known as turbo-electric distributed propulsion (TeDP), will require a complex electrical power system which can deliver power to multiple propulsor motors from gas turbine driven generators. To ensure that high enough power densities are reached, it has been proposed that such power systems are superconducting. Key to the development of these systems is the understanding of how faults propagate in the network, which enables possible protection strategies to be considered and following that, the development of an appropriate protection strategy to enable a robust electrical power system with fault ride-through capability. This paper investigates possible DC protection strategies for a radial DC architecture for a TeDP power system, in terms of their ability to respond appropriately to a DC fault and their impact on overall system weight and efficiency. This latter aspect has already been shown to be critical to shaping the overall TeDP concept competitiveness.

Impact of key design constraints on fault management strategies for distributed electrical propulsion aircraft

Electrically driven distributed propulsion has been presented as a possible solution to reduce aircraft noise and emissions, despite increasing global levels of air travel. In order to realise electrical propulsion, novel aircraft electrical systems are required. Since the electrical system must maintain security of power supply to the motors during flight, the protection devices employed on an electrical propulsion aircraft will form a crucial part of system design. However, electrical protection for complex aircraft electrical systems poses a number of challenges, particularly with regard to the weight, volume and efficiency constraints specific to aerospace applications. Furthermore, electrical systems will need to operate at higher power levels and incorporate new technologies, many of which are unproven at altitude and in the harsh aircraft environment. Therefore, today’s commercially available aerospace protection technologies are likely to require significant development before they can be considered as part of a fault management strategy for a next generation aircraft. By mapping the protection device trade space based on published literature to date, the discrepancy between the current status of protection devices and the target specifications can be identified for a given time frame. This paper will describe a process of electrical network design that is driven by the protection system requirements, incorporates key technology constraints and analyses the protection device trade space to derive feasible fault management strategies.

Understanding the impact of failure modes of cables for the design of turbo-electric distributed propulsion electrical power systems

The turbo-electric distributed propulsion (TeDP) concept has been proposed to enable future aircraft to meet ambitious, environmental targets as demand for air travel increases. In order to maximize the benefits of TeDP, the use of high temperature superconductors (HTS) has been proposed. Despite being an enabling technology for many future concepts, the use of superconductors in electrical power systems is still in the early stages of development. Hence their impact on system performance, in particular system transients, such as electrical faults or load changes, is poorly understood. Such an understanding is critical for the development of an appropriate electrical protection system for TeDP. Therefore, in order to enable appropriate protection strategies to be developed for TeDP electrical networks an understanding of how electrical faults will propagate in superconducting materials is required. An understanding of how technologies that utilize these materials may experience failure modes in ways that are uncharacteristic of their conventional counterparts is also needed. This paper presents a dynamic electrical — thermal model of a superconducting cable, at an appropriate level of fidelity for electrical power system studies, which enables the investigation of failure modes of cables. This includes the impact of designing fault tolerant cables on the electrical power system as a whole to be considered.

Fault management strategies and architecture design for turboelectric distributed propulsion

The TeDP concept has been presented as a possible solution to reduce aircraft emissions despite the continuing trend for increased air traffic. However, much of the benefit of this concept hinges on the reliable transfer of electrical power from the generators to the electrical motor driven propulsors. Protection and fault management of the electrical transmission and distribution network is crucial to ensure flight safety and to maintain the integrity of the electrical components on board. Therefore a robust fault management strategy is required. With consideration of the aerospace-specific application, the fault management strategy must be efficient, of minimal weight and be capable of a quick response to off-nominal conditions. This paper investigates how the TeDP architecture designs are likely to be driven by the development of appropriate fault management strategies.

Electrical and Thermal Effects of Fault Currents in Aircraft Electrical Power Systems With Composite Aerostructures

The upward trend for the use of electrical power on state-of-the-art aircraft is resulting in significant change to the design of power system architectures and protection systems for these platforms. There is a pull from the aerospace industry to integrate the electrical power system with the aircraft’s structural materials to form an embedded system, reducing the need for bulky cable harnesses. This directly impacts the fault response for ground faults and ultimately the development of appropriate protection systems. Such structural materials include composites such as carbon fiber reinforced polymer (CFRP). This paper presents the experimental capture and analysis of the response of CFRP to electrical fault current, which indicates the need for two distinct sets of electrical ground fault detection criteria for low and high resistance faults and identifies the threshold resistance for this distinction. By extrapolating these results to develop models of CFRP for use in transient simulation studies, the key electrical fault detection thresholds for speed, selectivity, and sensitivity for a dc system rail to ground fault through CFRP are identified. This provides the first set of key factors for electrical fault detection through CFRP, providing a platform for the design of fully integrated structural and electrical power systems, with appropriate electrical protection systems.