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

© 2020 IEEE. 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

Design and losses analysis of a high power density machine for flooded pump applications

This paper describes the design process of a 10 kW 19000 rpm high power density surface mounted permanent magnet synchronous machine for a directly coupled pump application. In order to meet the required specifications, a compact machine, with cooling channels inside the slots and flooded airgap, has been designed through finite element optimization. For high power density, high speed machines, an accurate evaluation of the power losses and the electromechanical performance is always extremely challenging. In this case, the completely flooded application adds to the general complexity. Therefore this paper deals with a detailed losses analysis (copper, core, eddy current and mechanical losses) considering several operating conditions. The experimental measurements of AC copper losses as well as the material properties (BH curve and specific core losses), including the manufacturing process effect on the stator core, are presented. Accurate 3D finite element models and computational fluid dynamics analysis have been used to determine the eddy current losses in the rotor and windage losses respectively. Based on these detailed analysis, the no load and full load performance are evaluated. The experimental results, on the manufactured prototype, are finally presented to validate the machine design

Thermal overload and insulation aging of short duty cycle, aerospace motors

Electrical machines for transportation applications need to be highly reliable, particularly if they drive safety-critical systems. At the same time, another main requirement is represented by the significant torque density, especially for aerospace, where weight constraints are extremely stringent. For achieving high peak torque, an effective strategy consists in supplying the windings with a current greater than the rated value; thus, thermally overloading the machine for limited time periods. However, if the insulation is overheated, the machine lifetime is shortened and reliability issues can arise. This paper experimentally investigates the influence of short-time thermal overload on the insulation lifetime for low voltage, random wound electrical machines. The analysis is performed on round enamelled magnet wire coils, which are aged by accelerated thermal cycles. The obtained results are statistically processed through a two parameter Weibull distribution. According to the findings of the experimental data post processing, a lifetime prediction model is built. This model is employed for predicting the lifetime consumption of a motor embedded into an electromechanical actuator for aerospace application

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

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. The 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

Prognostics of aerospace electromechanical actuators: Comparison between model-based metaheuristic methods

Electro-Mechanical Actuators (EMAs) deployment as aircraft flight control actuators is an imperative step towards more electric concepts, which propose an increased electrification in aircraft subsystems at the expense of the hydraulic system. Despite the strong benefits linked to EMAs adoption, their deployment is slowed down due to the lack of statistical data and analyses concerning their often-critical failure modes. Prognostics and Health Management (PHM) techniques can support their adoption in safety critical domains. A very promising approach involves the development of model-driven prognostics methodologies based on metaheuristic bio-inspired algorithms. Evolutionary (Differential Evolution (DE)) and swarm intelligence (particle swarm (PSO), grey wolf (GWO)) methods are approached for PMSM based EMAs. Furthermore, two models were developed: a reference, high fidelity model and a monitoring, low fidelity counterpart. Several failure modes have implemented: dry friction, backlash, short circuit, eccentricity and proportional gain. The results show that these algorithms could be employed in pre-flight checks or during the flight at specific time intervals. Therefore, EMA actual state can be assessed and PHM strategies can provide technicians with the right information to monitor the system and to plan and act accordingly (e.g. estimating components Remaining Useful Life (RUL)), thus enhancing the system availability, reliability and safety

Design and Development of a Planetary Gearbox for Electromechanical Actuator Test Bench through Additive Manufacturing

The development and validation of prognostic algorithms and digital twins for Electromechanical Actuators (EMAs) requires datasets of operating parameters that are not commonly available. In this context, we are assembling a test bench able to simulate different operating scenarios and environmental conditions for an EMA in order to collect the operating parameters of the actuator both in nominal conditions and under the effect of incipient progressive faults. This paper presents the design and manufacturing of a planetary gearbox for the EMA test bench. Mechanical components were conceived making extensive use of Fused Deposition Modelling (FDM) additive manufacturing and off-the-shelf hardware in order to limit the costs and time involved in prototyping. Given the poor mechanical properties of the materials commonly employed for FDM, the gears were not sized for the maximum torque of the electric motor, and a secondary torque path was placed in parallel of the planetary gearbox to load the motor through a disc brake. The architecture of the gearbox allowed a high gear ratio within a small form factor, and a bearingless construction with a very low number of moving parts

A matrix converter drive system for an aircraft rudder electro-mechanical actuator

The matrix converter is an attractive topology of power converter for the Aerospace Industry where factors such as the absence of electrolytic capacitors, the potentiality of increasing power density, reducing size and weight and good input power quality are fundamental. The matrix converter potential advantages offers the possibility to achieve the aim of the More Electric Aircraft research which intends to gradually re- place, from the aircraft architecture, the hydraulic power source and its infrastructure with electric power generation and a more flexible power distribution system. The purpose of this work is to investigate the design and implementation of a 40kVA matrix converter for an Electro Mechanical Actuator (EMA) drive system. A SABER simulation analysis of the candidate matrix converter drive systems, for this application, is provided. The design and implementation of the matrix converter is described, with particular attention to the strict requirements of the given aerospace application. Finally, the matrix converter PMSM drive system and the EMA drive system are respectively assembled, tested and commissioned

Fractional slot concentrated winding PM synchronous motors for transport electrification applications

Moving towards electrification of transport including electric vehicles (EV), more electric aircraft (MEA), and electric ships offers a crucial way in dealing with global carbon emissions and climate change. Electric motors are a key enabling technique in these applications, but their increased use is associated with requirements of extreme power/torque density, excellent fault-tolerance, high efficiency, and good manufacturability. The main goal of this thesis is to study permanent magnet electric machine winding theory to determine the suitable electric machine winding topologies for different applications. Two separate vehicle transport applications are investigated, including an EV traction motor and a novel modular electromechanical actuator (EMA) for MEA. The study of the EV traction motor involves the investigation of methods for reducing the significant stator MMF harmonics in fractional slot concentrated winding (FSCW) electric machines, and the development of novel FSCW topologies while keeping the benefits of easy manufacturing and the non-overlapping characteristic of concentrated windings. The novel FSCW topologies can be extended to multi-phase FSCW motors. A traction motor equipped with a novel 24 slots, 14 poles FSCW topology and interior PM (IPM) rotor is developed for evaluation. The performance under normal and fault conditions is fully explored and validated with simulation and experimental results, which demonstrates the applicability and strong potential of the proposed 24 slots, 14 poles IPM motor in fault-tolerant traction motor applications. The second topic focuses on modular fault-tolerant EMAs for aircraft actuation systems which can meet a diverse range of requirements. The architecture and design considerations of the actuator system are firstly determined considering reliability, fault-tolerance, and weight. The modular EMA scheme consisting of a direct-drive rotary motor and mechanical screw is identified. A dual 3-phase 24 slots, 22 poles FSCW motor with a surface-mounted permanent magnet (SPM) rotor is developed and evaluated in terms of electromagnetics, thermal management, and fault-tolerance. Experimental results of the modular EMA motor prototypes agree well with predicted results. All this confirms the applicability and satisfactory implementation of the modular EMA motor for aircraft actuation system applications