More Electric Aircraft Research Articles

Field Prediction and Validation of a Slotless Segmented-Halbach Permanent Magnet Synchronous Machine for More Electric Aircraft

High-performance propulsion motors for more electric aircraft (MEA) are highly appreciated in transportation electrification. For the widely adopted permanent magnet synchronous machines (PMSMs) for MEA propulsion, the segmented Halbach magnetization has distinct merit that it contributes to sinusoidal air-gap magnetic fields for smooth operation. However, it is hard to fast predict the field distribution and machine performance due to the model complexity. Based on the subdomain method, this article first proposes an exact analytical model for slotless PMSM with the segmented Halbach PMs. Then, the model is applied in the fast computation of the magnetic field and performance prediction. Subsequently, the analytical results are compared with the finite element method (FEM), including the flux density, flux linkage, induced voltage, and steady-state torque at different loads. Also, the computation burden and prediction error are included to validate the model’s rapidity and accuracy. Finally, by prototype fabrication and unique field measurement methods, the flux density distribution is originally validated.

Reliability and sensitivity analysis of more‐electric aircraft based on cross‐entropy

The traditional Monte Carlo sampling method has several deficiencies in evaluating the reliability of more-electric aircraft (MEA), such as more sampling times and longer simulation time, due to the complex topology and low probability of failure of the aircraft. In this Letter, the optimal probability distribution of multi-component systems is introduced by cross-entropy, which theoretically makes the variance of reliability evaluation zero. Based on this, an evaluation method for the power-supply reliability of MEA is presented. For further analysis of the system vulnerabilities, the sensitivity of MEA is modelled based on reliability calculation. Finally, the hybrid MEA and high-voltage direct current MEA power systems are used as application scenarios to calculate the reliability and sensitivity. The results show that the proposed method has advantages in evaluating small probability events, and it is useful for the optimisation of MEA's power-supply system structure.

Optimisation of power electronics for regulated transformer rectifier units

This study presents a comprehensive approach for the design optimisation of passive components and heatsinks in power electronic converters. The design and selection of passive components are posed as a multi-objective optimisation problem, which can be simplified to a single-objective optimisation based on preferences and weights assigned by the designer. The mathematical equations describing the efficiency, volume, and reliability are laid out to describe the feasible space for optimisation in this study. In addition to the proposed optimisation, a substantial amount of passive component comparison data has been consolidated and presented in this study. The results from the optimisation are demonstrated on the target power electronic circuit of a regulated transformer rectifier unit for more-electric aircrafts. The optimisation framework is developed in a generic manner that would lend itself to the optimisation of any choice of converter topology, circuit components, or objective functions.

DSP-Based SiC-MOSFET SAPF With 100-kHz Sampling and Switching Frequency for Wideband Harmonic Suppression

In this article, 100-kHz sampling and switching frequency shunt active power filter (SAPF), which is based on a dual-core DSP TMS320F28377D, is designed for the potential market of high-frequency harmonic suppression in more electric aircraft (MEA) or high-speed train (HST). By utilizing the multithreading and multiprocessing method, different computation segments, such as analog-to-digital conversion, recursive discrete Fourier transform (RDFT), and inner loop current and outer loop voltage control, can be rearranged as several parallel operation groups. Compared with the traditional single pipeline structure of the mostly 10–20 kHz switching frequency commercial SAPF, this parallel execution speeds up the signal processing so that the highly increased sampling frequency makes the current control loop reaches wider bandwidth even with simple proportional integral (PI) regulator. Meanwhile, for wideband harmonic suppression, a multiresolution RDFT strategy is proposed to extend the range of the selected harmonic without sacrificing its extraction accuracy. After raising the sampling frequency to 100 kHz, the proposed SAPF with much easier current controller could suppress wider frequency harmonics than other 10–20 kHz SAPF. A 10- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {kV}\cdot \text {A}$ </tex-math></inline-formula> prototype with CREE SiC power module CCS050M12CM2 is set up to verify its effectiveness. The result complies with the IEEE standard 519-2014.

Challenges and Opportunities for Wound Field Synchronous Generators in Future More Electric Aircraft

Electrical machines and drives keep moving away from traditional technologies such as brushed machines and wound field machines toward lighter, “easier to maintain” machines. A very interesting aspect is that certain transport applications, especially the aerospace industry, still favor the classical wound field machine for its main generating system such as Boeing 787. This article focuses on investigating this particular trend by presenting a detailed overview of the historical power-generation systems on aircraft. This article compares the current state of the art of wound field machines with other generator families. The results of this analysis are then projected into the needs of the electrical power generation and distribution system on aircraft. Although power density is a major objective for any aerospace application, however, the extra benefits associated with wound field systems are still essential in modern aircraft. This article then focuses on the main challenges for improving the power density of wound field machines. Recommendations, opportunities, and improvements related to wound field machines are discussed. In conclusion, if robust designs for higher speed wound field generators were consolidated, it would be very probable that these classical machines might still be implemented on future More Electric Aircraft (MEA) platforms.

Reliability Evaluation for Aviation Electric Power System in Consideration of Uncertainty

With the rapid development of more electric aircraft (MEA) in recent years, the aviation electric power system (AEPS) has played an increasingly important role in safe flight. However, as a highly reliable system, because of its complicated flight conditions and architecture, it often proves significant uncertainty in its failure occurrence and consequence. Thus, more and more stakeholders, e.g., passengers, aviation administration departments, are dissatisfied with the traditional system reliability analysis, in which failure uncertainty is not considered and system reliability probability is a constant value at a given time. To overcome this disadvantage, we propose a new methodology in the AEPS reliability evaluation. First, we perform a random sampling from the probability distributions of components’ failure rates and compute the system reliability at each sample point; after that, we use variance, confidence interval, and probability density function to quantify the uncertainty of system reliability. Finally, we perform the new method on a series–parallel system and an AEPS. The results show that the power supply reliability of AEPS is uncertain and the uncertainty varies with system time even though the uncertainty of each component’s failure is quite small; therefore it is necessary to quantify system uncertainty for safer flight, and our proposed method could be an effective way to accomplish this quantization task.

Nanoelectromechanical relay without pull-in instability for high-temperature non-volatile memory

Emerging applications such as the Internet-of-Things and more-electric aircraft require electronics with integrated data storage that can operate in extreme temperatures with high energy efficiency. As transistor leakage current increases with temperature, nanoelectromechanical relays have emerged as a promising alternative. However, a reliable and scalable non-volatile relay that retains its state when powered off has not been demonstrated. Part of the challenge is electromechanical pull-in instability, causing the beam to snap in after traversing a section of the airgap. Here we demonstrate an electrostatically actuated nanoelectromechanical relay that eliminates electromechanical pull-in instability without restricting the dynamic range of motion. It has several advantages over conventional electrostatic relays, including low actuation voltages without extreme reduction in critical dimensions and near constant actuation airgap while the device moves, for improved electrostatic control. With this nanoelectromechanical relay we demonstrate the first high-temperature non-volatile relay operation, with over 40 non-volatile cycles at 200 ∘C.

Detection of DC series arc in more electric aircraft power system based on optical spectrometry

Series arcing faults have been recognised as a hazardous phenomenon in the power system of more electric aircraft (MEA), especially with the increasing voltage level and power supply. Instead of the electrical method, the optical method can be used as an approach to detect arc fault with the advantages of fast response and immunity to electromagnetic interference. It is the basis of optical arc detection to determine the distribution spectrum range of direct current (DC) arc fault. Aiming at series arc optical detection in the MEA DC system, a DC series arc test platform was established to measure the series arc spectrum. The spectrum was disassembled though empirical mode decomposition to extract characteristic wavelengths of arc light and de-noised by means of wavelet decomposition and reconstruction (wavelet transformation) to reduce equipment noise. To resolve the baseline drift, the baseline of the arc spectrum measured was calculated and corrected based on Savitzky−Golay. The experimental results indicate that there are several series arc characteristic spectra of the MEA DC system, including 309.3 and 324.5 nm in the ultraviolet range. Moreover, the arc spectrum with different metals, copper and aluminium, were contrasted, indicating the arc spectral behaviour is related to the melting/boiling point and chemical properties of the anode material. The measurement of the series arc spectrum makes it more effective to apply optical detection in the MEA discharging faults diagnosis.

Power Management Problem for Civil Aircraft under More Electric Environment

The civil aviation industry is moving toward the more electric aircraft (MEA) which is to use electrical power to meet the load demands on multiple aircraft subsystems which are conventionally driven by other power resources. Thus, there will be introduced a large amount of new electrical power demands which are safety-critical for aircraft’s flight and this may lead the challenge for a reliable and efficient power management problem (PMP): the balance between the aircraft power supply and demands while minimizing the operation costs. To cope with the PMP for civil aircraft under more electric environment, in this paper, we explicitly give a detailed and complete modeling of all power supply resources (fuel and battery) and safety-critical electrical loads and cast the PMP as a mixed-integer nonlinear programming problem; we develop a practical solution methodology for the application on the real civil MEA. The proposed formulation and solution algorithm can give an efficient power schedule result with the minimal fuel and battery operation cost through a smart codispatch between the gas turbine generator, storage devices, and all electrical loads of MEA. Numerical testing results based on one real civil aircraft case demonstrate the economic and operational effectiveness.

A Composite Finite-Time Controller for Decentralized Power Sharing and Stabilization of Hybrid Fuel Cell/Supercapacitor System With Constant Power Load

The hybrid fuel cell/supercapacitor (FC/SC) system is a promising onboard power supply system for more electric aircraft (MEA), where system stability is a critical issue due to the high penetration of constant power loads (CPLs) in MEA. This article proposes a composite finite-time controller for decentralized power sharing and stabilization of the hybrid FC/SC system with CPLs. It consists of an integral droop (ID) + finite-time controller for the SC converter and a proportional droop (PD) + finite-time controller for the FC converter. First, the coordination of PD and ID achieves decentralized power sharing between FC and SC such that SC only compensates fast fluctuations and FC provides smooth power at the steady state. Then, a finite-time observer is designed to provide feedforward compensation for the disturbances and enables accurate tracking with fast dynamics. Finally, a composite finite-time controller is constructed following a nonrecursive synthesis procedure with a rigorous large signal stability analysis. The proposed controller guarantees finite-time convergence even under large signal variations and can be easily implemented with a practical gain tuning procedure. Simulations and experiments are conducted to verify the proposed technique.

Power Scheduling in More Electric Aircraft Based on an Optimal Adaptive Control Strategy

In this article, an optimal control problem (OCP) for the power management system is proposed for the more electric aircraft (MEA) with consideration of the dynamics in the generators and the energy storage systems. Electrical power components included in the electrical power system (EPS) of MEA such as the generator, the bus, the rectifier, and the battery system are modeled in this OCP. Based on this formulation, a three-stage optimization architecture is introduced to obtain the optimal power references and the optimal control policies. In the first stage, an optimization problem for the power scheduling and allocation is solved as a mixed integer quadratic programming problem and the optimal power allocation schemes (power references) are obtained. In the second stage, an OCP to minimize the fluctuations in power generation systems is proposed and solved via an off-policy integral reinforcement learning approach. In the third stage, the voltage restoration is applied to maintain the main-bus voltage in the onboard high voltage dc system. Extensive case studies are carried out to illustrate the effectiveness of our proposed methodology. Simulations show that the optimal power references are obtained based on various requirements, and the optimal power control policy is achieved based on off-policy iterations.

High-Power Machines and Starter-Generator Topologies for More Electric Aircraft: A Technology Outlook

More electric aircraft (MEA) architectures consist of several subsystems, which must all comply with the settled safety requirements of aerospace applications. Thus, achieving reliability and fault-tolerance represents the main cornerstone when classifying different solutions. Hybrid electric aircraft (HEA) extends the MEA concept by electrifying the propulsive power as well as the auxiliary power, and thereby pushing the limits of electrification. This paper gives an overview of the high-power electrical machine families and their associated power electronic converter (PEC) interfaces that are currently competing for aircraft power conversion systems. Various functionalities and starter-generator (S/G) solutions are also covered. In order to highlight the latest advancements, the efficiency of the world’s most powerful aerospace generator (Mark 1) developed within the E-Fan X HEA project is graphically represented and assessed against other rivaling solutions. Motivated by the strict requirements on efficiency, power density, trustworthiness, as well as starting functionalities, supplementary considerations on the system-level design are paramount. In order to highlight the MEA goals and take advantage of all potential benefits, all subsystems must be treated as a whole. It is then shown that the combination of PECs, aircraft grid and electrical machines can be better adapted to benefit the overall system. This survey outlines the influence of these concerns and offers a view of the future technology outlook, as well as covering the present challenges and opportunities.

Uncertainty Sources in the Estimation of the Partial Discharge Inception Voltage in Turn-to-Turn Insulation Systems

Partial discharges (PD) are one of the main causes of premature failure in low-voltage motors driven by variable-speed drives. The use of these control systems are being quite extended due to new applications, such as the more electric aircraft (MEA) or hybrid and electric vehicles, and this has pushed research towards appropriate designs of electric motors to avoid, as much as possible, the presence of PD within their windings. This article presents a model to predict the partial discharge inception voltage (PDIV) in the insulation of low-voltage machines. A value for the secondary ionization coefficient based on a statistical study is also proposed. The deviations of the model are also studied by obtaining the uncertainty of the value of that coeficient and the predicted values of the PDIV for a set of wires. This uncertainty will be compared with other error sources such as generator harmonics and humidity. Finally, the tests are done for different temperatures extend the model applicability.

Machine Learning Building Blocks for Real-Time Emulation of Advanced Transport Power Systems

The revolution of artificial intelligence (AI) is transforming major industries worldwide. With accurate inferencing, AI has caught the attention of many engineers and scientists. Promisingly, hardware-in-the-loop (HIL) emulation can adopt this type of modeling method as one of the alternatives after comprehensive investigation. This paper proposes an approach for emulating power electronic motor drive transients for advanced transportation applications (ATAs) using machine learning building blocks (MLBBs) without any traditional circuit-oriented transient solver. The more electric aircraft (MEA) power system is chosen as a case study to validate the real-time emulation performance of MLBBs. Inside MLBBs, neural networks (NNs) have been applied to build component-level, device-level, and system-level models for various equipment. These models are well trained in a cluster and transplanted into the field-programmable gate array (FPGA) based hardware platform. Finally, MLBB emulation results are compared with PSCAD/EMTDC for system-level and SaberRD for device-level, which showed high consistency for model accuracy and high speed-up for hardware execution.

Electric Power Systems in More and All Electric Aircraft: A Review

Narrow body and wide body aircraft are responsible for more than 75% of aviation greenhouse gas (GHG) emission and aviation, itself, was responsible for about 2.5% of all GHG emissions in the United States in 2018. This situation becomes worse when considering a 4-5% annual growth in air travel. Electrified aircraft is clearly a promising solution to combat the GHG challenge; thus, the trend is to eliminate all but electrical forms of energy in aircraft power distribution systems. However, electrification adds tremendously to the complexity of aircraft electric power systems (EPS), which is dramatically changing in our journey from conventional aircraft to more electric aircraft (MEA) and all electric aircraft (AEA). In this article, we provide an in-depth discussion on MEA/AEA EPS: electric propulsion, distributed propulsion systems (DPS), EPS voltage levels, power supplies, and EPS architectures are discussed. Publications on power flow (PF) analysis and management of EPS are reviewed, and an initial schematic of a potential aircraft EPS with electric propulsion is proposed. In this regard, we also briefly review the components required for MEA/AEA EPS, including power electronics (PE) converters, electric machines, electrochemical energy units, circuit breakers (CBs), and wiring harness. A comprehensive review of each of the components mentioned above or other topics except for those related to steady state power flow in MEA/AEA EPS is out of this article's scope and should be found somewhere else. At the close of the paper, some challenges in the path towards AEA are presented. Unless the discussed challenges are satisfactorily addressed and solved, arriving at an AEA that can properly operate over commercial missions will not be possible.

Harmonic Control for Variable-Frequency Aviation Power System Based on Three-Level NPC Converter

At present, three-phase 115V/360-800Hz variable frequency AC power system is mostly used in the main power system of More-Electric Aircraft. With the increase of EMA (Electro-Mechanical Actuator), EHA (Electro-Hydrostatic Actuator), DC/DC power supply and power electronic devices in More-Electric Aircraft, harmonic and reactive power problems are brought, which seriously affect the power supply quality of variable frequency power supply for aircraft. According to the characteristics of high frequency and wide range of aviation variable frequency power supply, this paper studies a three-level active filter which can effectively improve the power quality of aviation variable frequency power supply system. This paper analyzes the working principle of the diode clamped three-level topology active filter, and deduces its mathematical model; proposes the frequency detection of the aviation variable frequency power supply based on the improved Rife method; the ip-iq method based on the instantaneous reactive power theory, accurately detects the harmonic current of the aviation variable frequency power supply system; uses the quasi PR controller to track the current, and improves the harmonic suppression effect. Finally, the experimental hardware platform is built to verify the feasibility of the proposed control strategy.

Energy Optimization Analysis of Turbofan Engine for More-Electric Civil Aircraft

The civil aviation industry is moving into the more-electric environment where the civil aircraft uses electricity to meet the multiple energy demands of the associated aircraft subsystems. The civil aircraft’s turbofan engine, which is the largest energy supply system of civil aircraft, will thus utilize more fuel resource to provide increased electric energy besides of its conventional responsibility of maintaining the fundamental thrust requirements by aircraft. This will introduce new challenge for the energy optimization analysis of aircraft turbofan engine: it was nearly a simple optimal setting of engine’s component parameters for keeping required thrust, but under the more-electric environment it will become an optimization problem in order to minimize the fuel consumption while obeying the multiple constraints by thermodynamic limits of turbofan engine and by varying electric power demands associated with the flight profile of aircraft. We present a complete modeling in this paper for the energy optimization analysis of turbofan engine for more-electric civil aircraft and formulate it as a nonlinear programming form. We propose an algorithm based on Benders decomposition method to solve this problem; the numerical results demonstrate the economic effectiveness of the proposed modeling and algorithm.

Analysis of 6-Pulse and 12-Pulse in Conversion of the 115VAC/400Hz to 270 VDC for Application on Fighter

The development of aircraft secondary power technology is moving from mechanical power, pneumatic power and hydraulic power to electric power. The trend toward electric power is known as More Electric Aircraft (MEA). Modern military aircraft are designed using 270VDC for electric power system. Today, some military aircraft still use 115VAC/400Hz for their electrical power system. If this type of aircraft need provides 270VDC electrical power, then they require Multi-Pulse Transformer Rectifier Unit (TRU). The development of this type TRU has not been aimed to comply with aircraft military standards. This research investigates the variation of the number of pulses (p) and firing angle (α) to the amplitude ripple voltage, output voltage, and distortion factor in order to comply with the MIL-STD-704F standards. The multi-pulse transformer rectifier unit being analyzed consists of 6-Pulse and 12-Pulse. The research shows that the amplitude ripple voltage and distortion factor of the 6-Pulse TRU do not comply MIL-STD-704F. The amplitude ripple voltage and distortion factor of 12-Pulse comply MIL-STD-704F with firing angle (α) ≤4°.Keywords: Transformer Rectifier Unit, thyristor, ripple voltage, distortion factor, firing angle

Performance Comparison of Active Rectifier Control Schemes in More Electric Aircraft Applications

In a more electric aircraft (MEA) design, the onboard electric generators are mechanically coupled directly to the jet engines, thus producing a variable-frequency constant magnitude voltage. This wild-frequency characteristic imposes a new design challenge on the onboard power converters. In this article, an experimental performance comparison between the model predictive and the proportional–integral (PI)-based control schemes for active rectifiers in MEA applications is presented. The comparison of the aforementioned controllers is executed under the MEA variable input frequency perspective for the first time and, therefore, constitutes the main contribution of this article. This comparison mainly addresses the dynamic response of the controllers in terms of dc-bus voltage regulation and unity power factor operation under frequency ramping, frequency step changes, and load step variations. Furthermore, the robustness of the controllers is analyzed in terms of their performance degradation in the presence of parameter mismatch. Both the model predictive and PI-based controllers are experimentally tested using a 1-kW SiC-MOSFET two-level voltage-source-converter topology.

Design of a High-Efficiency, High Specific-Power Three-Level T-Type Power Electronics Building Block for Aircraft Electric-Propulsion Drives

The electric propulsion drives for the more-electric aircraft need lightweight and high-efficiency power converters. Moreover, a modular approach to the construction of the drive ensures reduced costs, reliability, and ease of maintenance. In this article, the design and fabrication procedure of a modular dc-ac three-level t-type single phase-leg power electronics building block (PEBB) rated for 100-kW, 1-kV dc-link is reported for the first time. A hybrid switch (HyS) consisting of a silicon insulatedgate bipolar junction transistor (IGBT) and silicon carbide metal-oxide-semiconductor field-effect transistor (MOSFET) was used as an active device to enable high switching frequencies at high power. The topology and semiconductor selection were based on a model-based design tool for achieving high conversion efficiency and lightweight. Due to the unavailability of commercial three-level t-type power modules, a printed circuit board (PCB) and off-the-shelf discrete semiconductor-based highpower switch was designed for the neutral-point clamping. Also, a nontrivial aluminum-based multilayer laminated bus bar was designed to facilitate the low-inductance interconnection of the selected active devices and the capacitor bank. The measured inductance indicated symmetry of both current commutation loops in the bus bar and value in the range of 28-29 nH. The specific power and volumetric power density of the block were estimated to be 27.7 kW/kg and 308.61 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively. The continuous operation of the block was demonstrated at 48 kVA. The efficiency of the block was measured to be 98.2%.