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.

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

This paper proposes a capacitor voltage regulation method for the dual converter with a floating bridge for aerospace applications. This topology has previously been reported, but with a constrained voltage utilization factor due to the need for capacitor voltage regulations. In this paper, the effect of switching states on the voltage variation of capacitor is quantitatively modeled and an enhanced space vector modulation scheme with current feedback is proposed to achieve an active control of the floating capacitor voltages. This proposed method also allows further exploitation and utilization of converter voltage. The relationship between the allowed modulation index of dual converter and load power factor is obtained and expressed using a fitted polynomial equation. The advantages of the proposed method include boosted voltage utilization and superior performance in term of capacitor voltage balance. These advantages have been proven through simulation and experimental results on RL loads as well as with an open-end winding induction motor. The proposed modulation scheme can boost the converter voltage utilization by at least 10% while achieving full four-level operation. More importantly, the higher available voltage allows extending the constant torque region of the motor, the further beginning of field weakening operation could be postponed.

/pdf/an-active-modulation-scheme-to-boost-voltage-utilization-of-24djp65jng.pdf

An Active Modulation Scheme to Boost Voltage Utilization of the Dual Converter With a Floating Bridge

The ever-increasing demand for passenger air traffic results in larger airline fleets every year. The aircraft market forecast reveals an unprecedented growth for the coming decades, leading to serious environmental and economic concerns among airlines and regulatory bodies. Different approaches, for both airborne and ground operations, have been proposed to reduce and control emissions without compromising profit margin. For on-ground activities, the electric taxiing (ET) methodology is one of the suggested solutions for reducing the emissions and the acoustic noise in the airport, and for lowering the fuel consumption and operating costs. This article, thus, aims to review and collate the more important literature related to ET systems, in order to draw an inclusive picture regarding the current state-of-the-art of a moving and growing sector that just started its first steps toward an ambitious target. After introducing the general concept of ET, elaborations on the benefits and challenges of available technologies are done with a detailed comparison of the different systems. Finally, recommendations for future research and outlook on ET are presented.

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Review, Challenges, and Future Developments of Electric Taxiing Systems

The more electric aircraft concept aims to improve the fuel consumption, the weight, and both the maintenance and operating costs of the aircraft, by promoting the use of electric power in actuation systems. According to this scenario, electromechanical actuators for flight control systems represent an important technology in next generation aircraft. This paper presents a linear-geared electromechanical actuator for secondary flight control systems, where the safety and availability requirements are fulfilled by replicating the electric drive acting on the drivetrain. Indeed, the architecture considered consists of two power converters feeding as many electrical machines coupled to the same mechanical system. The design of both the permanent magnet synchronous machine and the power converter are addressed. Preliminary results on the electric drive prototype are also provided and compared to the design requirements. Finally, the electromechanical actuator performance at system-level is evaluated in Dymola environment, analyzing different operating modes.

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Considerations on the Development of an Electric Drive for a Secondary Flight Control Electromechanical Actuator

Electrical machines (EMs) are required to consistently perform their intended mission over a specified timeframe. The move toward transportation electrification made the EMs’ reliability an even stringent and predominant requirement, since a failure might cause severe economic losses, as well as endanger human lives. Traditionally, the design procedure of motors conceived for safety-critical applications mainly relies on over-engineering approaches. However, a paradigm shift is recently taking place and physics of failure approaches/methodologies are employed to meet the reliability figures, while delivering an optimal design. This article proposes and outlines a reliability-oriented design for low-voltage EMs. Thermal accelerated aging tests are preliminarily carried out on custom-built specimens. Once the aging trend of the turn-to-turn insulation system is assessed, the thermal endurance graph at several percentile values is determined and lifetime models are developed, for both constant and variable temperature operations. Finally, these models are used to predict the turn-to-turn insulation lifetime of motors meant for aerospace and automotive applications.

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Moving Toward a Reliability-Oriented Design Approach of Low-Voltage Electrical Machines by Including Insulation Thermal Aging Considerations

Electric drives are an essential part of more electric aircraft (MEA) applications with ever-growing demands for high power density, high performance, and high fault-tolerant capability. High-speed motor drives can fulfil those needs, but their speeds are subject to the relatively low DC-link voltage adopted by MEA. The power inverters are thus expected to efficiently and effectively manage that limited voltage. A recently popular topology is represented by the dual inverters. They are featured by inherited fault tolerance, a high DC-link voltage utilization and an excellent output power profile. This paper aims to present a comprehensive review of different structures based on the dual inverter. To meet the stringent requirements of MEA applications, three performance aspects, including the voltage utilization, the inverter output quality and the fault-tolerant capability, are selected. Based on the chosen performance metrics, the key features of adopting dual inverter topologies against other converter selections are explicitly demonstrated. Finally, a practical guideline for choosing suitable dual inverters for different MEA applications is provided.

Technical Review of Dual Inverter Topologies for More Electric Aircraft Applications

This article studies a dual inverter supplied by a dc-link and a floating capacitor (FC), emerged as a promising inverter topology for motor drive applications. For this type of inverter, the voltage ratio between the dc-link and the FC can be actively controlled. This ratio design is crucial as it essentially defines both the dc-link voltage utilization and the inverter output quality. Several voltage ratios have previously been discussed to enhance the dual inverter performance, but only one aspect, either the voltage utilization or the output quality, is investigated. As a result, although one performance aspect can be improved, the other aspect has been adversely affected. In this article, a comparative study considering both aspects is carried out for all the possible voltage ratios. Based on this analysis, the optimal ratios for different inverter modulation indices are identified. This is followed by proposing a ratio selection strategy to double the voltage utilization without degrading the output quality. This strategy enables an electric drive to work at a higher maximum speed without flux weakening for a given dc-link voltage. The claimed advantages have been proved by experimental tests on an open-end windings induction motor drive.

Enhanced Performance of Dual Inverter With a Floating Capacitor for Motor Drive Applications

This study proposes a modified modulated model predictive control (MMPC) scheme to control an open-end winding induction motor drive using an asymmetric source dual inverter with one floating bridge. The control algorithm uses a modulation algorithm within the cost function optimisation scheme to avoid variable switching frequency. The voltage of the floating capacitor is regulated utilising predefined redundant switching sequences as well as the voltage vector location is identified to improve calculation time. The proposed MMPC scheme enhances the output performance with comparison to the model predictive control scheme. Experimental results are presented to verify theory and simulation results.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2018.5395

Fixed switching frequency predictive control of an asymmetric source dual inverter system with a floating bridge for multilevel operation

Solid-state power controllers (SSPCs) have been received increasing attention as they can configure the electrical system and protect the system by fast tripping mechanism at the same time. Although the high-voltage direct current (HVDC) electrical system can bring sustainable savings on the cables’ weight and losses, the protection can be considerably challenging. SSPCs have been successfully utilized for 28V DC aircraft onboard network. However, high-voltage ones are impeded by the vast over-voltage and the excessive losses generated from SSPC switching. This paper tries to fill this gap and presents the development of high-power SSPCs for a ±270VDC network of a future turboprop aircraft. Comprehensive designs of proper over-voltage suppression along with SSPC thermal management are presented in this paper. Besides, a comparative study on the SSPC device is carried out. Two prototypes, including a single MOSFET module and paralleling several discrete MOSFET devices, are built and then tested in the experiment. It has been validated that the proposed voltage clamping design cannot only effectively suppress the over-voltage, but also limit the SSPC temperature increase during switching for both candidates. After comparing the conduction losses, maximum junction temperature, power density, weight and volume, the single device solution is recommended as a preferable SSPC option for future aircraft.

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Zhen Huang

Papers

An Active Modulation Scheme to Boost Voltage Utilization of the Dual Converter With a Floating Bridge

Technical Review of Dual Inverter Topologies for More Electric Aircraft Applications

Enhanced Performance of Dual Inverter With a Floating Capacitor for Motor Drive Applications

Fixed switching frequency predictive control of an asymmetric source dual inverter system with a floating bridge for multilevel operation

Development of High-Current Solid-State Power Controllers for Aircraft High-Voltage DC Network Applications