Electric Aircraft Applications Research Articles

Improved dynamic performance of triple active bridge DC-DC converter using differential flatness control for more electric aircraft applications

The triple active bridge (TAB) converter has been proposed to improve power density and availability in more electric aircraft applications. However, the conventional proportional-integral (PI) controller used for TAB voltage control often exhibits slow response and significant overshoot, which can impact dynamic performance. Moreover, achieving decoupling control among ports introduces computational complexity in controller design. To address these issues, this paper introduces an effective diagonal matrix decoupling strategy based on differential flatness control with single-phase shift modulation applied to a TAB converter. The proposed differential flatness control offers superior transient performance, control flexibility, and precision, ensuring compliance with DC voltage regulations while achieving optimal decoupling among ports. The comparative analysis assesses various criteria, including steady-state and dynamic performance, control complexity, and regulation and tracking properties, against PI control, unit matrix decoupling control, and the proposed differential flatness control. Hardware-in-loop (HIL) experimentation verifies the performance, confirming faster dynamic characteristics and robust port power decoupling. The results show a significant improvement in efficiency, reaching a maximum of 95.5 %, indicating reduced switching losses and enhanced overall system performance. The study concludes with a discussion on the implications of these findings and potential future research directions, such as integrating advanced optimization algorithms further to enhance the control strategy's robustness and adaptability.

Performance enhancements of HTS power cables by minimizing the electric field enhancements for electric transport applications

Abstract Design innovations to manage the electric field enhancements and successful use of cryogenic epoxy EP37 as electrical insulation for high temperature superconducting (HTS) cables for electric aircraft applications are reported. Detailed finite element analysis (FEA) of the electric field distribution shows that the highest electric field is at the interface of the ground and electrical insulation layers. The FEA led to the design, fabrication, and experimental characterization of four model cables with stress cones and a direct bond of the ground and insulation layers. Enhanced partial discharge inception voltage (PDIV) was achieved in the model cables by minimizing the electric field enhancements at the ground layer interface. Using a helium gas mixture with 4 mol% H2, with higher intrinsic dielectric strength than pure helium, further enhanced the PDIV. The results warrant further studies on long HTS cables with EP37 as electrical insulation with a direct bond between the insulation and ground layers.

A Modified 72-Pulse Rectifier for Harmonic Suppression in More Electric Aircraft Applications

A Modified 72-Pulse Rectifier for Harmonic Suppression in More Electric Aircraft Applications

Multilevel Inverters for Electric Aircraft Applications: Current Status and Future Trends

Multilevel Inverters for Electric Aircraft Applications: Current Status and Future Trends

Optimal Droop Control Design Using Artificial Intelligent Techniques for Electric Power Systems of More-Electric Aircraft

The design of the droop coefficient is one of the challenges for the droop control of converters, as it plays a key role in enhancing the performance of the droop control method. This paper proposes an artificial neural network (ANN) based technique for the design of optimal droop control of parallel-connected converters in a fast and accurate manner, without imposing an additional computational burden on the system. The developed ANN-based design strategy of droop coefficients is used for load sharing and DC bus voltage regulation for the more electric aircraft application. In the design process, the optimal droop coefficient setting is obtained by evaluating a user-defined fitness function with the aid of a trained ANN-based surrogate model. It is observed that the system performance metrics predicted by the surrogate model matched very well with that obtained from the simulation model. The experimental results show that the selected optimal droop coefficient setting can enhance the performance of the traditional droop control method in both steady and transient conditions.

Cosmic Radiation Reliability Analysis for Aircraft Power Electronics

Cosmic Ray induced failures are a major concern for the electronic system reliability of airborne and space systems. Power system voltages on aerospace platforms are on a steady upward trend. High voltage power converters suffer from Single Event Burnout failures caused by cosmic rays. The established standards propose a scaling factor based on measured background galactic cosmic rays intensity at operating altitude to apply de-rating factors. The radiation environment in the atmosphere can be increased due to the cascading of primary solar energetic particles during solar eruptions. In this work, the altitude profile of the radiation environment is simulated using a GEANT4 Monte-Carlo code. The failure rates due to both background Galactic Cosmic Rays and Solar Energetic Particles are quantitatively evaluated. Further to the known influence of geomagnetic shielding of cosmic rays, the geographical distribution of cosmic rays at flight altitudes of 10 km are also presented. The estimated cosmic ray intensity can then be combined with experimentally measured failure rate data to predict the impact on the reliability of power converters, giving a new level of accuracy in the modeling of such failure mode in more electric aircraft applications. It is shown for the first time in the scientific literature by using experimental data and state-of-the-art models, that the solar energetic particles storms fluxes vastly exceed the recommended standard and constitute a risk for the power electronics reliability.

Derivation of Ambient Enhancement Factors of Impregnated Twisted Pairs for Partial Discharge Risk Evaluation

Partial discharge (PD) is the main issue challenging the electrical machine (EM) insulation system for more electric aircraft (MEA) applications. Indeed, the trend of adopting higher DC link voltage and fast switching device further boost the risk of PD. Partial discharge inception voltage (PDIV) is mostly dominated by ambient conditions (i.e., temperature, pressure, and humidity), and their influence is accounted for through experimentally determined ambient enhancement factors. For non-impregnated windings, ambient enhancement factors are suggested by both IEC 60034-18-41 and recent literature. However, in many applications, EMs’ windings are often impregnated with resin to improve thermal performance, mechanical resistance, and electrical insulation. In this case, no indications of the enhancement factors for PD risk assessment are given. The ambient enhancement factors are experimentally determined in this paper to enable the PD risk evaluation for impregnated windings. These factors are obtained relying on an extensive PD investigation, where PDIV and partial discharge extinction voltage are measured under variable temperature, pressure, and humidity conditions. Finally, the tests are performed on different wire types and motorette samples to validate the applicability of the derived factors.

Design and Flight Qualification of a Flying Capacitor Multilevel Converter for Electric Aircraft Applications

Multilevel switched-capacitor converters, such as the flying capacitor multilevel (FCML) converter, offer high energy density and efficiency, over a wide voltage range, making them suitable for applications in electrified aircraft. However, concerns of reliability due to the increased number of active and passive components have limited the use of high-level count converters in aircraft applications. This work addresses the challenges of designing a high-level count converter with the goal of extremely high efficiency and power density, with maintained reliability and flight readiness. We present detailed component selection and design techniques to achieve this goal, along with a high-performance 28.2 kW/kg, 99.52% efficient high-voltage dc-dc step-up power converter for experimental validation. Finally, we demonstrate successful completion of critical flight qualification testing of the hardware prototype, including thermal, shock and vibration.

An ejector-assisted integrated thermal management of electric vehicles switchable between heating and cooling (reversible AC/HP)

Electric vehicles have become increasingly widespread in recent years due to environmental issues and limited natural resources, and the related thermal management strategies are receiving growing notice. A heat pump air conditioning system for cabin and battery pack thermal regulation (both heating and cooling) is proposed and studied under different operating conditions. The attention of the present study is more directed towards the heating mode of operation; cabin air conditioning in winter and electric aircraft application. Due to environmental considerations and restrictive laws, environmentally friendly refrigerants are also considered as alternatives for R134a. To improve the system's performance, an ejector is placed before the compressor and the refrigerant temperatures in the evaporator and chiller are set to be different. The performance of the proposed system is studied for both heating and cooling modes to compare with the basic system (without ejector). An exergy analysis is also carried out to further analyze the thermodynamic characteristics of the system. The results indicate that the proposed system's COP is improved for both cooling and heating modes under all operating conditions. For the heating mode, the highest COP was equal to 4.36 for R600a, and the COP improvement was between 8 and 47 % based on the different operating conditions. For the cooling mode, the highest COPs were equal to 5.20 and 5.17 for R600a and R1234ze(E) atTevap=Tchil=5°C respectively. The COP improvement for R600a was equal to 14 % atTevap=Tchil=−25°C, and it increases as the chiller temperature is raised. The exergy analysis also indicate that the highest exergy destruction occurs in the compressor and throttling valves. Moreover, R600a and R1234ze(E) show a better overall performance compared to other refrigerants. R600a and R1234ze(E) resulted in the least total exergy destruction of approximately 41 kW for the cooling mode and 51 kW for the heating mode. The exergy efficiency for R600a and R1234ze(E) was equal to 64 and 63 % respectively for both the cooling and heating modes.

A Double Rotor Flux Switching Machine With HTS Field Coils for All Electric Aircraft Applications

The increasing demand for high-power density motors in electric transport industries opens a new research opportunity to develop motor topologies with less weight and high efficiency. In particular, all-electric aircraft applications require very high power density motors. This paper shows the design of a new 1 MW 20-pole/15-slot double rotor flux switching machine with high-temperature superconducting field coils and thermal management system. The proposed motor features an air-core stator. Aluminum Litz wire is used for the armature conductors, and the YBCO- high-temperature superconducting material is used for the field coils. The armature winding and field coils operate at 95K and 65K, respectively. The active part power density including rotors, armature windings and field coils obtained with the proposed design is 29.3kW/kg. The specific power density of proposed motor considering mechanical, support structure and TMS is about 18.5 kW/kg. The efficiency can be higher than 98.7% which satisfies the requirement of electric aviation.

Performance Analysis of Resistive Superconducting Fault Current Limiter Using LN2and GHe Cooling

Large-scale electric aircraft is a disruptive technology to address the environmental impact of air travel. Fault current limitation is crucial to realise the safety and reliability of the electric aircraft, in particular for large-scale electric aircraft using DC distribution network. This paper investigates the behavior of the resistive SFCL under different cryogenic cooling systems including liquid nitrogen and helium gas circulation cooling systems for the electric aircraft DC distribution network. Electromagnetic and thermoelectric models were used to predict the characteristics of resistive SFCL. The simulation results demonstrate that it is promising to design resistive SFCL using liquid nitrogen cooling as well as helium gas circulation cooling systems, which offer flexibility for SFCL cryogenic cooling system for electric aircraft applications.

Design and Experimental Testing of a Magnetic Gear for an Electric Aircraft Drivetrain

This paper presents the magnetic, thermal and mechanical design details as well as testing result for a high mass torque density coaxial magnetic gear (MG). The MG was designed for use in an electric aircraft application and has a 12.4:1 gear ratio. The MG was designed to be competitive with a mechanical equivalent aircraft gear and had a calculated total mass torque density of 53 Nm/kg with a rated torque of 229 Nm. The proof-of-principle MG used Garolite support parts, rather than carbon fiber and due to dimensional differences, the tested MG was shown to achieve a 23.5 Nm/kg torque density. The importance of using laminated magnets and the importance of accounting for both parallel and in-plane eddy current losses within the MG is highlighted.

Experimental Investigation of Decoupled Discontinuous PWM Strategies in Open-End Winding Induction Motor Supplied by a Common DC-Link

Currently open-end winding induction motors fed by a dual inverter (OEWIM-DI) present an innovative approach to enhance the performance of modern electric drive systems; such as electrical vehicles and electric aircraft applications. However, the dual inverter topology requires a proper switching control strategy to enable the OEWIM drive to fully achieve its performance. This work aims to investigate experimentally the impact of different Decoupled Discontinuous Pulse Width Modulation (DDPWM) control strategies on the performance of the OEWIM-DI supplied by a common DC-link. The criteria performance adopted in this study are: (i) the Total Harmonic Distortion (THD) of the current and voltage, (ii) the Zero Sequence Voltage (ZSV), (iii) the Common Mode Voltage (CMV), and (iv) the dual inverters losses. The various DDPWM control schemes for the 1.5 kW OEWIM-DI motor drive are implemented on a dSPACE 1104 board and the results are compared with the popular and widely used Space-Vector PWM (SVPWM) strategy. From the results, it can be concluded that the optimised DDPWM technique gives the best performance. This technique has reduced the CMV by one level and reduce the losses by 50% while having the same THD and ZSV obtained with the SVPWM technique.

Adaptive droop control design with overcurrent protection for onboard DC microgrids in hybrid electric aircrafts

In this paper, an adaptive nonlinear droop-based control approach is proposed for converter-based self-contained electrical power systems (EPS) designed for electric aircraft applications to ensure tight voltage regulation and accurate load power distribution among parallel sources. By taking into account the accurate nonlinear dynamic models of the power converters, we mathematically prove an upper bound for the input current of each converter separately by means of Lyapunov methods and ultimate boundedness theory. In particular, the adopted nonlinear droop-based controller introduces a virtual voltage and a virtual resistance in series with the inductance and parasitic resistance of each DC/DC boost converter. To verify the proposed controller performance and its underlying developed theory, simulation results of the low-voltage bus dynamics have been presented for an onboard aicraft DC microgrid (MG).

A Dual Inverter Topology With Quasi-Isolated Power Supplies for More Electric Aircraft Applications

Open-end load system fed by the dual inverter (DI) is a promising technique for more electric aircraft (MEA) applications. Yet, two isolated power supplies preferred by the DI are hardly available in most MEAs. To address this issue, a novel DI topology with quasi-isolated power supplies is proposed in this letter. A simple nonisolated H-bridge boost converter is adopted to generate the second power supply and, moreover, to compensate for the load zero-sequence voltage generated by the DI. The operating principle and the applicability of the proposed DI topology are presented. Besides, a simple decoupled system control strategy is proposed. It is revealed that the proposed DI topology can generate a very high output voltage from the single power supply, while the load control performance is hardly affected by the zero-sequence current. This is a prominent advantage for MEA applications. The experimental results have verified the validity of the proposed topology.

An Optimized Asymmetric Modulation Scheme for Three-Phase Buck Rectifier Without Input Current Distortion at the Sector Boundaries

Space vector pulsewidth modulation (SVPWM) is usually utilized in a three-phase buck rectifier to obtain low total harmonic distortion (THD) and low switching losses. When the conventional SVPWM scheme is applied, the input currents of the three-phase buck rectifier are distorted during the transition from even sector to odd sector, which will deteriorate the harmonics of input currents. In this letter, an asymmetric modulation scheme is proposed to eliminate the distortion of input currents of the three-phase buck rectifier during the transition from even sector to odd sector. The proposed modulation scheme combines two kinds of traditional asymmetric modulations in different sectors. A 1.5 kW experimental prototype of the three-phase buck rectifier with an ac input voltage of 115 V/400 Hz is built for more electric aircraft applications. The experimental results show that the THD of 1.3% can be achieved for the three-phase buck rectifier.

Speed/Torque Ripple Reduction of High-Speed Permanent Magnet Starters/Generators With Low Inductance for More Electric Aircraft Applications

With the electrification trend of future aircraft, high-speed permanent magnet starters/generators (PMSs/Gs) will potentially be widely used in onboard generation systems due to their high power density and high efficiency. However, the per-unit reactance of such high-speed machines is normally designed to be very low due to limited onboard power supply voltage and large electrical power demand, which can result in large current ripples in the machine and thus large torque ripples especially when the machine is fed with a semiconductor-based inverter of a lower switching frequency. The torque ripples may further lead to speed oscillation and generate severe vibrations and noises that are harmful to the mechanical system and human beings around. In this article, a speed/torque ripple reduction method for high-speed PMS/Gs with a low inductance is proposed to improve their performance within a wide speed range. An active damping technique is applied to the speed loop to increase the anti-disturbance capability and generate a smoother reference for the current loop, whereas an adaptive output voltage saturation limit is utilized for the current loop to limit the peak value of current to prevent overcurrent and torque spikes. The parameter tuning criteria are derived through a thorough analysis. Finally, the proposed method is validated on a high-speed PMS/G with an inductance of 99 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{H}$ </tex-math></inline-formula> . The results show that the speed ripples and torque ripples are reduced by over 50% within a speed range of 2–14 krpm.

An All Silicon Carbide 3 kV/540 V Series-Resonant Converter for Electric Aircraft Systems

In this work, an all silicon carbide (SiC) series-resonant converter (SRC) design is proposed and demonstrate to achieve a single stage dc-to-dc conversion from 3 kV to 540 V (±270 V) for future electric aircraft applications. The proposed SRC consists of a neutral-point-clamped converter using 3.3-kV SiC MOSFETs on the primary side, an H-bridge converter using 900-V SiC MOSFET on the secondary side and a high-frequency (HF) transformer. The detailed design methods for the SRC power stage and the HF transformer are presented. Especially, a tradeoff between the complexity for the cooling system and the need for high power density and voltage insulation is addressed in the transformer design, leading to a novel multilayer winding structure design to enhance the insulation capability and also the mechanical robustness. The proposed bobbin design is realized using additive manufacturing. The detailed analysis and modeling of the parasitic capacitance between sections introduced by fringe electrical field are presented. To validate the effectiveness of the proposed SRC design, a 25-kW converter prototype using 3.3-kV SiC discrete devices has been developed with a peak efficiency of 99.08% achieved in experimental studies.

Electromagnetic Design Characterization of a Dual Rotor Axial Flux Motor for Electric Aircraft

This article presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain-oriented electrical steel, Halbach arrays, and wires with rectangular cross sections, are used to improve torque density and efficiency. A novel winding arrangement is used to mitigate interturn short-circuit faults. Rather than simply optimizing the motor by itself, this article evaluates the tradeoffs between motor performance and its interfaces with the drive, thermal management system (TMS), and mechanical structure. This information can be used along with similar analyses of these subsystems to select the design with the system-level optimal performance. This article uses finite-element simulations to characterize tradeoffs among active mass, efficiency, fundamental frequency, power factor, axial forces on the rotors, and cooling surface area. Several designs exceed 95% efficiency at takeoff with less than 8 kg of active mass. While high pole counts, a large outer radius, and short stator teeth tend to optimize the magnetic performance at takeoff, this can reduce cruise efficiency, reduce the surface area through which the TMS can extract heat, increase the fundamental frequency the drive must supply, increase the structural mass required to support the rotors, and introduce complexity to the manufacturing process. Further analysis for a selected design reveals that the power factor can be significantly improved with a minimal torque penalty via field weakening due to significant saturation in the stator teeth.

Using DC–DC Converters as Active Harmonic Suppression Device for More Electric Aircraft Applications

Harmonics generated from power electronic converters will impose significant power quality challenges to the electric grid onboard future aircraft. In this article, we propose an innovative modulation scheme that enables using a buck–boost dc–dc converter as a harmonic absorber. To demonstrate the effectiveness of the proposed method, a hybrid power generation system involving a high-speed electrical generator and a high voltage battery is introduced. The electrical generator is connected to a dc bus through an ac–dc converter and the battery to the dc bus with a dc–dc converter. For the studied hybrid power generation system, it is identified that the first carrier frequency side-band harmonic ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f_c</i> -3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f₀</i> ) from the ac–dc converter is most relevant and is targeted for cancellation. For the control of the dc–dc converter, a new modulation technique, called equal-gate-width modulation is proposed. It allows active control of the magnitude and phase angle of some specific harmonic components from a dc–dc converter. By properly tuning the phase angle and amplitude, the controlled harmonics can thus be used to cancel harmonics from other converters on a common dc bus. Without losing generality, this article focuses on the development of this specific harmonic cancellation scheme and the effectiveness of our proposed methods has been demonstrated using experimental results.