Using the Predictive Time-Frequency Analysis, several different pulse width modulation (PWM) techniques are studied with naturally and regular sampled PWM. This study observes a dynamic trajectory modelling an electric drive chain with a constant acceleration of the machine to its nominal speed. This global method allows to observe different phenomena at the same time (resonance, sub-harmonics, and harmonic distortion) specific to the trajectory. The Predictive Time-Frequency Analysis applied to Electric Drive Systems (PreTiFEDS) highlights the reasons why a naturally sampled PWM is not necessarily the most appropriate when it comes to using other PWM strategies for high-speed applications.
Increasing the knowledge about components used to assemble an electric drive becomes more and more crucial. Especially for efficient electrical drives, that are produced in large volumes, it becomes necessary to know, how build in components like electrical steel stacks of stator and rotor perform. For the latter, their magnetic behavior is primarily responsible for an electric drive's overall performance. Hence, a magnetic measurement device has been designed and built to further investigate net shape parts regarding production-related magnetic property variations. Within this paper, a detailed insight in the design of a net shape part measuring setup for segmented stator teeth is given. The measurement system is validated concerning its ability to perform repeatable measurements of the same part geometry. The small measurement deviation allows to further investigate variations in testing conditions like the applied mounting pressure. To give an outlook on the future field of application of such measurement systems in large volume production lines, an investigation of parts produced from different batches indicates the range in which magnetic properties of final parts vary.
With the development of modern electric drive train systems, an effective cooling strategy is becoming a critical issue. Among various cooling methods, direct oil cooling is becoming more popular since it enables it to remove the heat directly from the heat source and subsequently improves the cooling performance. Aside from the cooling performance with direct cooling, the material compatibility of the coolant with machine components, particularly the electrical insulation system, is currently getting more attention. However, practical work regarding this issue is rare. Importantly, there still need to be widely recognised standards or instructions for compatibility evaluation. In the present work, the feasibility of conventional diagnostic approaches of insulation systems for compatibility evaluation is discussed. Particularly, a method to estimate the lifetime of the insulation system considering the compatibility issue is provided, and the role of mechanical stress during the compatibility study is analysed.
Refurbishment of hydro-generators promises an increased lifespan and improved efficiency. Old generators are not only less efficient but also less reliable; their fault occurrence is more common. The economic impact of out-service time can be astronomical. Thus, refurbishment is a critical task; but it is challenging too. Most of the conducted works focus on the material update, enhancing the cooling network, and obtaining better efficiencies. Modifying winding type, i.e. conversion from lap winding to wave winding is rare since it often requires a change in the slot number. Such a move can be laborious, size change can become mandatory. In this study, a refurbishment design strategy is proposed which includes a winding type conversion. The task is to implement a wave winding since it has less out-service time and is easily replaced by field workers. In this paper, an old generator that started operation in 1956 is used for a refurbishment. This study promises a guideline to hydro-generator designers who work on a refurbishment study on old hydro-generators that have diamond coils.
This article presents a MATLAB-based iterative design strategy, aimed at the investigation of axially asymmetric design possibilities for electrical machines. The developed tool for this strategy has modifiable individual portions and the capability of selecting various design criteria. The current study showcases the interdependence of various design parameters on the output performance parameters of a synchronous reluctance machine, for a selected set of design constraints. A brief analysis of the interrelated variables is presented and an approach to study and establish better control over compromising parameters is proposed for future work.
This paper presents a design methodology for a high power rotary transformer solution for novel offshore X-rotor wind turbine. The design methodology is studied for both in 2D and 3D finite element method for a 100KW system. The results of current, voltage, output power and magnetic field in 2D model is the same as 3D model. The results verify the design methodology, and that efficiency is high enough to present the rotary transformer solution as an alternative for slip rings in the novel X-rotor wind turbine design. Also, the sensitivity analysis has been performed to show the effect of some important parameters.
This paper presents a study of permanent magnet machines for automotive applications, comparing different slot, pole and phase number combinations in terms of torque and power output and NVH performance under constraint of the same active volume. FEM simulations are used to estimate electromagnetic performance and an analytical model to evaluate noise emissions for each configuration. In this analysis, a novel two-phase machine with mildly overlapped windings emerges as the best combination between NVH and electromagnetic performance, at the expense of a 4-leg power converter instead of a standard 3-phase 2-level inverter.
Frequency Response Analysis (FRA) technique has been widely used for many years to diagnose winding transformers. However, more recently, there has been a concerted effort to apply this technique to other types of windings, including large salient poles. This paper presents two new FRA diagnostic techniques that have been specifically developed and proven to work effectively on large salient poles. These two techniques - the FRA ungrounded test and the fault diagram method - are combined to provide a novel approach for predictive and corrective diagnosis of inter-turn faults on large salient poles. The fault diagram is constructed using the ungrounded technique test results, and an analysis is carried out to identify new properties and enhance the diagnostic sensitivity. The laboratory tests are described in detail, and a comparison with on-site tests is provided to validate the effectiveness of the new techniques.This paper presents a new and innovative approach to diagnose inter-turn faults on large salient poles using FRA techniques. The FRA ungrounded test and the fault diagram method have been specifically developed for this purpose and provide a reliable and cost-effective diagnosis compared to traditional methods. The comprehensive laboratory tests and comparison with on-site tests demonstrate the effectiveness and practicality of the proposed techniques.
This paper presents experimental measurement and analysis of both stray and air gap magnetic fluxes performed on various large hydro generators. The study shows the similarity and the differences of these two types of measurements when it comes to develop diagnosis method and remedial strategies. The radial and tangential components of the stray flux are also shown at different measurement points around the electrical machine. The study shows the usefulness of this measurement approach to detect electrical and mechanical faults found in large hydrogenerators such as rotor eccentricity (static or dynamic), rotor ellipticity and interturn short circuit in the rotor windings.
To minimise AC losses in power dense electrical machines, multistrand stator windings are routinely employed. However, the magnitude of AC losses can be highly sensitive to the strand transposition achieved in the as-manufactured winding, which can differ significantly from that assumed during design. This paper employs X-ray Computed Tomography (XCT) to verify the twisted strand transposition in a compressed aluminium coil, through the construction of 3D models for each of the strands within the coil. These models enable the strand transposition to be verified by qualitative and quantitative means, providing initial insight into the actual strand transposition achieved at the mid-point of the coil active length.
This paper investigates the magnetic flux leakage across the slots of the distributed windings in a yokeless, dual-rotor axial flux machine. The unique feature of the axial flux design presented is that distributed windings are used in a yokeless stator, where the conductors are in slots which are fully open at both ends and are thus subject to a greater effect of flux leakage across the slots. The slot leakage inductance is predicted with the analytical model and validated using a Finite Element (FE) model in this novel arrangement. An analytical model is developed to capture the skin and proximity effects of the conductors. Also, an analytical AC copper resistance model is developed, and the results are compared with those from FE analysis.
This paper presents the experimental investigation of how the E-Drive efficiency is impacted by system voltage. To evaluate the impact on a system level for automotive application, an 800 V E-Drive is evaluated in a test rig. A 385 kW electric motor is used together with an 800 V Silicone-Carbide inverter. Two different tests are conducted, the first bring high accuracy efficiency measurements of the motor and inverter at a number of fixed operation points. The second test is the WLTC cycle in which the total E-Drive efficiency and on a component-level is measured over the total drive cycle. The results are presented and discussed where significant voltage dependency can be noted for the efficiency, both for the motor and inverter. Hence this paper highlights one of the challenges as automotive OEMs move towards higher voltages. Future studies to be conducted are mentioned in the discussion to further investigate how the inverter conditions will influence the total system efficiency and to show possible solutions to reduce the impact of the system voltage level.
The state-of-the-art for high-speed rotors in induction machines and permanent magnet synchronous machines is discussed. The rotors for permanent magnet synchronous machines are distinguished between rotors with surface permanent magnets and rotors with buried permanent magnets. For induction machines, the conventional laminated rotor is compared to solid rotor designs. Based on the equivalent ring method, analytical models to calculate mechanical stresses within the presented rotor topologies are developed. Thereby a morphological comparison of the rotor topologies with regard to achievable circumferential velocity is possible.
Multiphase machines are becoming a potential solution for several high-power applications since they provide intrinsic fault-tolerance capability. Due to the various stator phase arrangements, standard fault detection techniques are unfeasible and cannot be considered to diagnose faults in the various configurations of multiphase machines, especially those employing closed-loop control strategies and under Fault Tolerant Operating (FTO) conditions. This paper evaluates two distinctive indicators for diagnosing both inter-turn short-circuit faults (ITSCFs) and open- circuit faults (OCFs), resorting to the Short Time Least Square Prony's algorithm (STLSP). The indicators are employed in an asymmetrical six-phase induction motor (ASPIM), controlled by a model predictive control (MPC) algorithm. MPC is selected since it offers an attractive control scheme for the regulation of multiphase electric drives, exploiting their inherent advantages. A variety of operating scenarios confirm the excellent generalization capability of the proposed indicators, high accuracy and robustness, along with the ability to distinguish between the occurrence of motor ITSCFs and converter faults (OCFs), under FTO conditions.
Given a generic product, which satisfies customer requirements, cost competitiveness is generally what makes it appealing and successful on the market. Such an aspect, whilst being evident and well known, seems to be often overlooked when designing or proposing 'novel' or 'exotic' electrical machine designs. Indeed, very often, designers strive for the best power density, without giving proper consideration to cost-sustainability and mass-manufacturability. This paper investigates how material cost fluctuations can affect the total manufacturing cost of three different machine topologies, for an automotive traction use-case. It is demonstrated that the cost of permanent magnet-based motors is essentially driven by (and tied to) rare-earth magnets. This indicates that, in the current market and geopolitical scenario, only rare-earth-free machine topologies can offer a fair cost sustainability perspective.
The trend towards higher onboard DC link voltage keeps increasing the partial discharge (PD) risk of electrical machines (EMs) for more electric aircraft (MEA) applications. Compared to the traditional Type I insulation, the corona-resistant (CR) wire with an additional inorganic layer boosts the lifetime of EMs under the PD regime and enables the design of EMs capable of safely operating at higher DC bus voltage. In this paper, the lifetime of CR wires operating under the PD regime is estimated. A starter/generator meant for more electric aircraft applications is selected as the study case, whose windings employ CR wire. The partial discharge inception voltage and electrical endurance are experimentally determined, and the lifetime model is built based on the collected results. Then, the starter/generator lifetime is estimated by considering both operating conditions and electric drive parameters.
The global decarbonization targets require increasingly higher levels of efficiency, torque and power density, reliability, etc. of electrical machines intended for transport applications. Recently, hairpin windings are receiving more and more interest from both industry and academia, as they are a promising solution to achieve the above requirements altogether. However, a number of challenges still need to be addressed, including electromagnetic, thermal and manufacturing aspects. One of these is the reliability of the welding process, where the solution could be adopting continuous hairpin windings. However, these result in open slot designs or special stator arrangements, which can produce undesirable effects in motors, such as ripple torque, increased permanent magnet losses, etc. This paper aims at comparing the main electromagnetic performance metrics for a conventional hairpin winding, wound onto a benchmark stator with a semi-closed slot opening design, and a continuous hairpin winding, where the slot opening is open. Finally, the adoption of semi-magnetic slot wedges is investigated and aimed at improving overall motor performance.
Nowadays, one of the key challenges in the design of electric drives' components is the reduction of high losses at high-frequency operations. The aim of this work is to investigate the AC losses in hairpin windings (HWs) triggered by a space vector pulse width modulation (SVPWM) during both maximum torque per Ampère (MTPA) and flux-weakening (F-W) operations of an interior permanent magnet synchronous motor (PMSM). The ensuing additional losses are evaluated and a fast methodology for the conductor sizing is illustrated. Subsequently, after evaluating the harmonic content of the current feeding the electric motor, estimated considering a standardized highway driving cycle, the losses are assessed using analytical and finite element methods (FEM) and then compared with an HW layout taken as benchmark. The results demonstrate that HWs, when appropriately sized, can significantly reduce AC losses compared to conductors optimised for low-speed extra-urban conditions.
Wound-field synchronous machines are widely used as generators to cover the electric energy demands in various low-speed applications. The main advantages over their rare earth permanent magnet counterpart are the ease of control, the inherent fault tolerance, the low cost, the use of more sustainable materials, etc. However, permanent magnet machines are well known to provide higher power density and efficiency values, which make them the usually preferred choice as generator on board of aircraft. This is also enabled by the more robust structure of the rotor which allows operations at relatively high speeds. Contrarily, the rotor of the wound-field machine comprises salient poles, making it unsuitable for high-speed operations. This paper aims at investigating the structural and thermal performance of a high-speed wound-field generator for aircraft applications. The electromagnetic aspects, extensively dealt with in a previous publication of the authors, are not discussed in this paper. On the other hand, 2D and 3D finite-element structural analyses, as well as computational fluid dynamics evaluations, are carried out. From a structural point of view, the centrifugal forces acting on the end windings were managed by adding a layer of non-magnetic material at the periphery of the rotor. From a thermal point of view, removing the rotor cage previously designed as a retaining system allowed the enabled axial flow to cool down the rotor. The results revealed the designed motor to be suitable for the application at hand.
In the power electronics and machine drives area, recent advancements in power electronics devices are paving a more sustainable future. The importance of improved power devices is beneficial within the growing industry, for example, Electric Vehicles. New power devices are continuously researched to combat drawbacks like loss and switching time. The electrical engineering curriculum should be supported by market-oriented knowledge and industry skills based on the market leaders' vision and recruiting plans. Our ultimate objective is to modify the power electronics modules' curriculum and reskill our graduates to satisfy the industry's needs. This paper introduces one of the topics in power electronics which was identified as an industry requirement: the Double Pulse Test (DPT), to be highlighted in future curriculums. This test will be used as a comparison tool for two power electronic devices: Silicon MOSFET (Si-MOSFET) and Silicon Carbide MOSFET (SiC-MOSFET).
