More Electric Aircraft Power System Research Articles

Dual‐port network‐based impedance modelling and AC‐port characteristic analysis of wound rotor synchronous machine for more electric aircraft

AbstractDue to the increasing variety of converters in more electric aircraft (MEA), the stability of the MEA power system has become a critical issue that receives wide concerns. As the primary power source for MEA, the wound rotor synchronous machine (WRSM) greatly affects the stability of the whole power system, and therefore accurate modelling of the WRSM serves as the basis for the analysis of system characteristics and even stability. Nevertheless, the complex structure and coupling of WRSM bring great challenges to small‐signal modelling methods. This paper introduces a novel method to model the WRSM in a modular and cascaded manner. Instead of deriving the complex transfer function, the proposed method uses a dual port to model each component. By connecting the dual port of each component from the rear stage to the front stage in a cascaded way, a dual‐port network can be built to describe the external impedance characteristics of the WRSM. Kirchhoff law can be applied to calculate the impedance by circumventing the complicated decoupling process. The proposed dual‐port network model has been validated on a hardware‐in‐loop platform. Furthermore, the output impedance characteristics of the AC port has also been analysed with the proposed model.

A review on insulation challenges towards electrification of aircraft

AbstractCompared to the traditional aircraft, electrification of power system in aircraft has potential to revolutionise the aviation industry. Typically, more‐electric aircraft (MEA), even all‐electric aircraft has been developed and delivered to decrease the greenhouse gas emission and increase the energy efficiency. The next generation of MEA will operate at high voltage to facilitate the transfer of significant levels of electrical power in an electrified aircraft. However, the higher voltage inevitably leads to an increased risk to the insulation of the electrical components and power system. This study aims to provide a critical overview of the insulation challenges from the perspective of electrified aircraft, typically MEA application. The development of MEA and the special working conditions are explained at the beginning. Then the insulation challenges of power modules, electric machines, aeronautical cables etc. are discussed in detail. Finally, the existing technical barriers and future prospects of insulation for electrified aircraft are summarised. It provides a reference for the future design and test in power system of next generation MEA and related electrified air transportations.

A two-stage bidirectional DC-DC converter system and its control strategy

With the development of more-electric aircrafts, bidirectional DC-DC converter has been widely used in this field. In order to improve the voltage regulation range and stability of the bidirectional DC-DC converter system, a two-stage bidirectional DC-DC converter with some operation modes is used and analyzed in this paper. The converter is composed of a four-switch buck-boost circuit and an isolated CLLC resonant circuit, where all MOSFETs can realize soft switching action. The four-switch buck-boost circuit regulates the output voltage in a certain range through the duty cycle control, and the CLLC resonant circuit can control the output voltage by changing its switching frequency, where the two-stage bidirectional DC-DC converter adopts voltage closed-loop control strategy to realize the stable voltage output. Due to the existence of the intermediate part conversion voltage, the converter has three-port network characteristics, which makes it applicable to the working occasions with multiple voltage levels. The feasibility of this two-stage bidirectional DC-DC converter system combined with control strategy and its three-port operation used for more-electric aircraft power system are verified by simulation analysis.

Adaptive state of energy evaluation for supercapacitor in emergency power system of more-electric aircraft

This paper presents an adaptive state of energy (SOE) evaluation method for a supercapacitor in the emergency power system of a more-electric aircraft. The adaptive SOE evaluation is realized based on a dynamic first-order RC equivalent circuit and its self-adaptive updated parameters. First, a dynamic first-order RC equivalent circuit with three parameters (i.e., the charge/discharge resistance R0, the dynamic self-discharge resistance R1, and the dynamic capacity C1) and a state-space model are introduced for modeling the supercapacitor. Then, an adaptive sliding mode observer is designed for tracking the dynamic change of the three state-space model parameters (i.e., R0, (R0+R1)/R1C1, and 1/R1C1). With this design, the three parameters of the dynamic first-order RC equivalent circuit can be updated adaptively along with the derivation of the three state-space model parameters. Moreover, the adaptive sliding mode observer is redesigned with a sign function, which can enhance the convergence rate of the three self-adaptive updated parameters. Finally, the accurate SOE evaluation would be achieved based on the three self-adaptive updated parameters. Various simulations and experiments are conducted to validate the adaptive SOE evaluation method. It is shown that the adaptive SOE evaluation method can achieve 0.5% of the maximum relative error of the estimated SOE. Compared with the commonly used method, the adaptive SOE evaluation method has over 1% improvement for the SOE estimation accuracy.

Hybrid Deep Reinforcement Learning Considering Discrete-Continuous Action Spaces for Real-Time Energy Management in More Electric Aircraft

The increasing number and functional complexity of power electronics in more electric aircraft (MEA) power systems have led to a high degree of complexity in modelling and computation, making real-time energy management a formidable challenge, and the discrete-continuous action space of the MEA system under consideration also poses a challenge to existing DRL algorithms. Therefore, this paper proposes an optimisation strategy for real-time energy management based on hybrid deep reinforcement learning (HDRL). An energy management model of the MEA power system is constructed for the analysis of generators, buses, loads and energy storage system (ESS) characteristics, and the problem is described as a multi-objective optimisation problem with integer and continuous variables. The problem is solved by combining a duelling double deep Q network (D3QN) algorithm with a deep deterministic policy gradient (DDPG) algorithm, where the D3QN algorithm deals with the discrete action space and the DDPG algorithm with the continuous action space. These two algorithms are alternately trained and interact with each other to maximize the long-term payoff of MEA. Finally, the simulation results show that the effectiveness of the method is verified under different generator operating conditions. For different time lengths T, the method always obtains smaller objective function values compared to previous DRL algorithms, is several orders of magnitude faster than commercial solvers, and is always less than 0.2 s, despite a slight shortfall in solution accuracy. In addition, the method has been validated on a hardware-in-the-loop simulation platform.

A Novel More Electric Aircraft Power System Rectifier Based on a Low-Rating Autotransformer

From a theoretical and practical point of view, to increase rating and decrease the cost and complexity of a multi-pulse rectifier (MPR), its pulse number has to be increased. In many industrial applications, a 20-pulse rectifier is suggested as the practical solution considering its simple structure and low weight. But the 20-pulse rectifiers, suggested in different studies, must use filters to satisfy the DO-160G requirements for 21st and 39th harmonics for ac–dc more electric aircraft (MEA) power systems. To overcome this problem, this article proposes a novel 20-pulse rectifier for the ac–dc MEA power system based on a low-rating autotransformer (LRA). Also, a passive harmonic reduction circuit (PHRC) is used on the dc side of the 20-pulse rectifier to suppress the harmonics up to the 40th order according to DO-160G without using any filter. In this article, simulations are provided to show the merits of this new rectifier over other proposed solutions. Then, an experimental prototype is implemented for evaluating and verifying the simulation results. By investigating the captured outcomes, this article concludes that the introduced design is practical and can simultaneously consider the trade-off among autotransformer structure, pulse number, complexity, rating, and cost.

Autonomous energy management strategy for a hybrid power system of more-electric aircraft based on composite droop schemes

In this paper, an autonomous energy management strategy is proposed for multiple batteries, photovoltaic (PV) generators and fuel-cells (FCs) s in a promising future power system of more-electric aircraft (MEA). This provides a more comprehensive and generalized approach to coordinate those three types of power sources. The operation of each power source is autonomously coordinated to maintain the balance between power generation and consumption, while ensuring controlled charging/discharging of the batteries in the hybrid power system. To achieve this objective, the dc bus voltage are configured to follow the specifically designed multi-segment V/P characteristic curves. First, a state-of-charge (SoC) based droop control strategy is applied to batteries to support dc bus voltage and balance their SoCs. Second, a novel adaptive power control strategy with a simple algorithm is designed for PV generators, which can seamlessly and rapidly regulate the output power off or return maximum power point tracking (MPPT) mode in accordance with the actual dc bus voltage. Third, the proposed control system releases the stress of batteries, which can extend these lifetime due to the reduced charging/discharging cycles. Furthermore, the stability of the whole hybrid system with the proposed control strategy is analyzed. The effectiveness of the proposed control strategy is validated by the real-time controller hardware-in-loop (HIL) platform.

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.

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.

Configuration method of hybrid energy storage system for high power density in More Electric Aircraft

For the safe flight of More Electric Aircraft (MEA), the hybrid energy storage system (HESS), which includes battery (Bat) and super-capacitor (SC), are used to smooth the pulse power and feedback energy in electrical power system of MEA. This paper addresses the combination of HESS by taking into account their characteristics to realize high power density in this particular application. The proposed configuration method can decrease the weight of HESS by selecting the type of energy storage system, energy storage cells and appropriate combination. Moreover, the discrete wavelet transform (DWT), which has great capability for analyzing signals, is chosen as a frequency approach to allocate the load power to Bat and SC in HESS. A simple theory proposed in this paper can solve two critical parameters, wavelet basis and decomposition level, in DWT. The case studies and results validate the feasibility and advantages of the configuration method.

A Global Convergence Estimator of Grid Voltage Parameters for More Electric Aircraft

Phase-locked loops (PLLs) are widely popular in applications of grid synchronization for single- and three-phase utility power systems. However, these PLL-based methods are usually designed for constant frequency grids and these schemes only have fast dynamics and good accuracy in a small local region (i.e., phase-locked region). When applying these PLLs in the grids of more electric aircraft (MEA), in which the grid frequency varies in a wide range (360–800 Hz), both the dynamic response and the steady-state accuracy of PLLs reduce significantly. In light of this, this article presents a global convergence method to estimate the frequency, positive- and negative-sequence components of grid voltage in MEA power systems. By analyzing the relationship between the DC-offset component, the grid voltage, and their derivatives, a mathematic model with the unknown parameters, which are the DC-offset component and the grid frequency, is established. Accordingly, a global estimator is proposed to estimate the grid voltage parameters accurately. A Lyaponov-based argument ensures that the proposed estimator is global convergent and it has the capability to eliminate the DC offset effect completely. The experimental results are provided to verify the effectiveness of the proposed estimator.

Systematic Reliability Modeling and Evaluation for On-Board Power Systems of More Electric Aircrafts

Modern aircrafts are evolving toward more electric aircraft (MEA), resulting in greater reliance on the electrical system for safe flight. On-board power system of MEA integrates a large number of power electronic converters, and it is reported that semiconductor devices and electrolytic capacitors in power converters are the most vulnerable links impacted by loading conditions; thus, reliability becomes a critical concern in an MEA power system. This paper proposes a hierarchical approach for systematic reliability modeling and evaluation for the on-board power system of MEAs. It consists of three hierarchical levels (HLs): component level (HL1), subsystem level (HL2), and system level (HL3). In HL1, failure rates of power electronic components are modeled considering relevant inner structure and loading conditions; in HL2, the reliability of individual subsystems such as converters are constructed; in HL3, the system reliability is quantified based on the network architecture and reliability of the subsystems. The impacts of different parts (components/subsystems) on the overall system are assessed effectively with the identification of the vulnerable parts. This also provides a guideline for reliability enhancement by using thermal control techniques, adding redundancies or performing maintenance on the vulnerable parts to ensure the satisfactory of system reliability requirements. The proposed method is demonstrated on the future MEA power system architectures (hybrid ac-dc architecture and HVdc architecture).

Electrical and Electronic Technologies in More-Electric Aircraft: A Review

This paper presents a review of the electrical and electronic technologies investigated in more-electric aircraft (MEA). In order to change the current situation of low power efficiency, serious pollution, and high operating cost in conventional aircraft, the concept of MEA is proposed. By converting some hydraulic, mechanical, and pneumatic power sources into electrical ones, the overall power efficiency is greatly increased, and more flexible power regulation is achieved. The main components in an MEA power system are electrical machines and power electronics devices. The design and control methods for electrical machines and various topologies and control strategies for power electronic converters have been widely researched. Besides, several studies are carried out regarding energy management strategies that intend to optimize the operation of MEA power distribution systems. Furthermore, it is necessary to investigate the system stability and reliability issues in an MEA, since they are directly related to the safety of passengers. In terms of machine technologies, power electronics techniques, energy management strategies, and the system stability and reliability, a review is carried out for the contributions in the literature to MEA.

Minimal Cut Sets-Based Reliability Evaluation of the More Electric Aircraft Power System

The More Electric Aircraft (MEA) stands for the direction of aviation development in the new era, and the reliability of power systems on the MEA has attracted widespread attention. Based on the characteristics of MEA power systems, an equivalent method of electrical topology structure is presented in this article, and evaluation method is proposed which shows the reliability of the overall system with the reliability of specific nodes. Firstly, electrical topology structure of a MEA power system is converted into a network node diagram according to the proposed equivalent method. Then, the minimal path sets of specific nodes are obtained by the adjacent matrix algorithm, and the low-order minimal cut sets of disjointed are obtained. After that, the actual failure rate of components is converted to node failure rate, and the reliability of the overall system is evaluated by operational reliability indexes of specific nodes. Finally, taking the MEA A380 as an example, this paper compares and analyzes the reliability of AC loads, DC loads, and key loads to verify the validity and feasibility of the proposed evaluation method. This evaluation system can predict the weak points existing in the MEA power system, as well as providing theoretical support for maintenance schedule.

Modeling and Integration of a Lithium-Ion Battery Energy Storage System With the More Electric Aircraft 270 V DC Power Distribution Architecture

With an aim to decrease pollution level due to aviation transportation sector, aircraft industries are focusing on more electric aircraft (MEA). The design of MEA is made with an aim to reduce the CO2 emission, noise pollution, increased comfort level for the passengers, and so on. In this paper, a detailed study of the evolution of the MEA along with the load profile for electrical load is presented. Based on the requirements of the electrical load, a high-energy-density lithium-ion “Li iron phosphate” battery is selected, designed, and modeled. The modeling is based on the modified Shepherd curve-fitting model with the addition of the voltage polarization term to have a lower complexity and more proximity with the real battery profile. The phase shifted high power bidirectional dc–dc (PSHPBD) converter is used in the battery energy storage system (BESS) as a battery charger. The modeled Li-ion battery is integrated to the 270- $\text{V}_{dc}$ MEA power distribution bus using the optimal harmonic number-based harmonic model of the PSHPBD converter. Since BESS has to provide the transient loads, the fast dynamic response is required for the PSHPBD converter working as the charger in the BESS. A predicted peak current-based fast response control technique is proposed in this paper for the integration of the BESS with an MEA power system architecture. The proposed control structure provides a maximum limit on the coupled inductor current to the predicted peak current value as well as it gives fast transient response desired in the MEA system.

Decoupled TAB converter with energy storage system for HVDC power system of more electric aircraft

It is an important trend to develop the more electric aircraft (MEA) ±270 V high-voltage direct current (HVDC) power system because of its better reliability, power quality and power density. However, there also exists the low-voltage 28 V DC system in HVDC power system, for the aviation battery and some equipment still rely on it. In traditional MEA power systems, battery is only used as a backup power supply, hardly participating in the adjustment of the power system. On the other hand, the function of turbine engine is unidirectional. Hence, it's necessary to add an energy storage port. In this research, the authors put forward the problems of power coupling and strong non-linearity in traditional three-port triple active bridge (TAB) converters, and propose a decoupled TAB topology, which has the feature of decoupled power flow. The topology is compatible with ±270 V DC, 28 V DC and energy storage system with high-power density and efficiency. In addition, the authors unify the efficiency optimisation problem of dual active bridge topology mathematically and provide an optimal parameter design approach for inductance and turns ratio. Simulation results show the power flow control strategy is appropriate for the topology.

A Module-Based Approach for Stability Analysis of Complex More-Electric Aircraft Power System

Moving toward more-electric aircraft (MEA) architecture, future aircraft power system will consist of a large number of power converters and motor drive loads which behave as constant power load and may cause stability issues. It is essential to ensure stable operation of the MEA power system, even though the complexity of the system hinders the comprehensive analysis of system stability. This paper presents a framework for stability analysis of a complex MEA power system. A module-based approach is proposed to provide a general and flexible solution for modeling and integrating complex systems, even under situations of system extension and reconfiguration. Using the proposed technique, a complex system model is conveniently formulated and overall system stability can be evaluated. Then, the critical stability points can be investigated. Impacts of parameters and their damping effects are identified by eigenvalue analysis and sensitivity analysis. The hybrid ac/dc MEA power system adopted by Boeing 787 is analyzed using the proposed technique. Simulations in MATLAB/Simulink are conducted to validate the effectiveness of the proposed modeling technique and the analytical results.

A Comparative Study of Energy Management Schemes for a Fuel-Cell Hybrid Emergency Power System of More-Electric Aircraft

This paper presents a comparative analysis of different energy management schemes for a fuel-cell-based emergency power system of a more-electric aircraft. The fuel-cell hybrid system considered in this paper consists of fuel cells, lithium-ion batteries, and supercapacitors, along with associated dc/dc and dc/ac converters. The energy management schemes addressed are state of the art and are most commonly used energy management techniques in fuel-cell vehicle applications, and they include the following: the state machine control strategy, the rule-based fuzzy logic strategy, the classical proportional–integral control strategy, the frequency decoupling/fuzzy logic control strategy, and the equivalent consumption minimization strategy. The main criteria for performance comparison are the hydrogen consumption, the state of charges of the batteries/supercapacitors, and the overall system efficiency. Moreover, the stresses on each energy source, which impact their life cycle, are measured using a new approach based on the wavelet transform of their instantaneous power. A simulation model and an experimental test bench are developed to validate all analysis and performances.

Design of Star-Connected Autotransformer Based 24-Pulse Rectifier and Its Application in the More Electric Aircraft

Power quality is one of the challenging issues toward future more electric aircraft (MEA). In this paper, the authors presented a solution based on the application of a star-connected autotransformer based 24-pulse rectifier. Analysis and development of the proposed 24-pulse rectifier and the simplified MEA power system structure have been done in MAT-LAB/SIMULINK prior to the experimental implementation. Both simulation and experimental results are presented to validate the developed design procedure and the simulation models. The proposed autotransformer-based rectifier has resulted in elimination of less than 23rd harmonic in the supply current. As a result, the supply current is near sinusoidal in shape with low total harmonic distortion (THD). Moreover, the power factor is also improved to nearly unity in the wide operating range of permanent magnet motor loads in MEA. Thus the proposed 24-pulse rectifier is ideally suited for retrofitting with existing motor drives in MEA.

Input Impedance Modeling and Analysis of Line-Commutated Rectifiers

This paper presents the modeling and analysis of small-signal input impedance for line-commutated rectifiers. The recently developed impedance mapping method, which has been applied to single-phase rectifiers with sinusoidal line inputs, is generalized to single-phase rectifiers with distorted lines as well as three-phase rectifiers. The modeling method assumes known impedance of the circuit on the dc side of the rectifier bridge (including its output filter and the load), and determines the corresponding ac input impedance by using a current and voltage mapping function that describes the operation of the rectifier bridge in the frequency domain. In this approach, closed-form analytical expressions are derived for the ac input impedance as functions of the dc circuit impedance. The resulting models are intended for stability analysis and design of large ac power systems involving significant number of rectification loads, such as more-electric aircraft power systems and microgrids. Detailed derivation of the models is presented in this paper. Numerical simulation and experimental measurement results are also presented to validate the developed models.