Overview of Sensitivity Analysis Methods Capabilities for Traction AC Machines in Electrified Vehicles

© 2021 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/.A robust design in electrified powertrains substantially helps to enhance the vehicle's overall efficiency. Robustness analyses come with complexity and computational costs at the vehicle level. The use of sensitivity analysis (SA) methods in the design phase has gained popularity in recent years to improve the performance of road vehicles while optimizing the resources, reducing the costs, and shortening the development time. Designers have started to utilize the SA methods to explore: i) how the component and vehicle level design options affect the main outputs i.e. energy efficiency and energy consumption; ii) observing sub-dependent parameters, which might be influenced by the variation of the targeted controllable (i.e. magnet thickness) and uncontrollable (i.e. magnet temperature) variables, in nonlinear dynamic systems; and iii) evaluating the interactions, of both dependent, and sub-dependent controllable/uncontrollable variables, under transient conditions. Hence the aim of this study is to succinctly review recent utilization of SA methods in the design of AC electric machines (EM)s used in vehicle powertrains, to evaluate and discuss the findings presented in recent research papers while summarizing the current state of knowledge. By systematically reviewing the literature on applied SAs in electrified powertrains, we offer a bibliometric analysis of the trends of application-oriented SA studies in the last and next decades. Finally, a numerical-based case study on a third-generation TOYOTA Prius EM will be given, to verify the SA-related findings of this article, alongside future works recommendations.Peer reviewe

Modeling, Analysis and Testing of a Novel Spoke-Type Interior Permanent Magnet Motor with Improved Flux Weakening Capability

Spoke-type interior permanent magnet (IPM) machines are an attractive topology for high performance electric motors, especially designed for vehicle traction applications. In this paper, a special design for a spoke-type IPM motor is presented to enhance motor flux-weakening capability in the operation over a wide speed range. The proposed design consists of a simple and robust mechanical device that includes radially-displaceable rotor yokes, connected to the shaft by means of springs. At high speed, the centrifugal force prevails over the elastic one due to springs, causing the mobile yokes to displace radially and to establish a partial magnetic short circuit between permanent magnets. This increases permanent magnet leakage flux and consequently reduces the air-gap field. As a result, a mechanical flux weakening effect is achieved at high speed, which helps significantly reduce the demagnetizing d-axis current to be injected by the inverter, along with the related copper losses and demagnetization issues. The proposed design is investigated in the paper using an analytical model whose parameters are computed by finite-element analysis (FEA). The effectiveness of the solution being set forth is successfully proven by some testing on a laboratory prototype. Experimental results are compared to analytical predictions showing a satisfactory accordance

Traction motors for electric vehicles: Maximization of mechanical efficiency – A review

With the accelerating electrification revolution, new challenges and opportunities are yet emerging, despite range anxiety is still one of the biggest obstacles. Battery has been in the spotlight for resolving this problem, but other critical vehicle components such as traction motors are the key to efficient propulsion. Traction motor design involves a multidisciplinary approach, with still significant room for improvement in terms of efficiency. Therefore, this paper provides a comprehensive review of scientific literature looking at various aspects of traction motors to maximize mechanical efficiency for the application to high-performance Battery Electric Vehicles. At first, and overview on the mechanical design of electric motors is presented, focusing on topology selection, efficiency, transmission systems, and vehicle layouts; Special attention is then paid to the thermal management, as it is one of the main aspects that affects the global efficiency of such machines; thirdly, the paper presents a discussion on possible future trends to tackle ongoing challenges and to further enhance the performance of traction motors

Critical Aspects of Electric Motor Drive Controllers and Mitigation of Torque Ripple - Review

Electric vehicles (EVs) are playing a vital role in sustainable transportation. It is estimated that by 2030, Battery EVs will become mainstream for passenger car transportation. Even though EVs are gaining interest in sustainable transportation, the future of EV power transmission is facing vital concerns and open research challenges. Considering the case of torque ripple mitigation and improved reliability control techniques in motors, many motor drive control algorithms fail to provide efficient control. To efficiently address this issue, control techniques such as Field Orientation Control (FOC), Direct Torque Control (DTC), Model Predictive Control (MPC), Sliding Mode Control (SMC), and Intelligent Control (IC) techniques are used in the motor drive control algorithms. This literature survey exclusively compares the various advanced control techniques for conventionally used EV motors such as Permanent Magnet Synchronous Motor (PMSM), Brushless Direct Current Motor (BLDC), Switched Reluctance Motor (SRM), and Induction Motors (IM). Furthermore, this paper discusses the EV-motors history, types of EVmotors, EV-motor drives powertrain mathematical modelling, and design procedure of EV-motors. The hardware results have also been compared with different control techniques for BLDC and SRM hub motors. Future direction towards the design of EV by critical selection of motors and their control techniques to minimize the torque ripple and other research opportunities to enhance the performance of EVs are also presented.publishedVersio

Study of innovative electric machines for high efficiency vehicular traction applications

This thesis collects some of the work accomplished during the PhD research activity focused on the study of special electric machines for vehicle traction applications. The work is divided into due parts. The rst part is mainly technological and covers some studies and experimental activities concerning new technical solutions to solve some common issues in operation of electric motors for automotive use, namely ux weakening and cogging torque. The second part has a more theoretical nature and focuses on some methods for electric machine modeling and analysis which has been developed to facilitate the study and design optimizations carried out during the PhD research work. The chapters in the rst part address the following topics: 1. Development and testing of an interior-permanent-magnet motor prototype fully conceived, designed and manufactured at the University of Trieste to implement a new concept of flux weakening system at high speeds. The concept has been also protected through a pending patent. 2. Multi-objective design optimization of an interior permanent magnet reluctance-assisted synchronous motor for the automotive industry. The design optimization was meant to support an industrial development project which is still in progress so no prototype has been built yet. 3. Study of a new optimized magnetic wedge design capable of reducing cogging torque in automotive propulsion motors having open stator slots. The second part proposes some analytical and numerical results that have been worked out to approach the modeling and optimization of various kinds of permanent magnet synchronous motors. The main problem to which these chapters try to answer is to nd suciently fast but accurate methods for permanent magnet analysis without time-consuming finite-element transient analysis. The proposed methods have been successfully integrated into design optimization programs used in the industrial environment in the development of innovative electric machines not only for the automotive industry

Urban and extra-urban hybrid vehicles: a technological review

Pollution derived from transportation systems is a worldwide, timelier issue than ever. The abatement actions of harmful substances in the air are on the agenda and they are necessary today to safeguard our welfare and that of the planet. Environmental pollution in large cities is approximately 20% due to the transportation system. In addition, private traffic contributes greatly to city pollution. Further, “vehicle operating life” is most often exceeded and vehicle emissions do not comply with European antipollution standards. It becomes mandatory to find a solution that respects the environment and, realize an appropriate transportation service to the customers. New technologies related to hybrid –electric engines are making great strides in reducing emissions, and the funds allocated by public authorities should be addressed. In addition, the use (implementation) of new technologies is also convenient from an economic point of view. In fact, by implementing the use of hybrid vehicles, fuel consumption can be reduced. The different hybrid configurations presented refer to such a series architecture, developed by the researchers and Research and Development groups. Regarding energy flows, different strategy logic or vehicle management units have been illustrated. Various configurations and vehicles were studied by simulating different driving cycles, both European approval and homologation and customer ones (typically municipal and university). The simulations have provided guidance on the optimal proposed configuration and information on the component to be used

Advancements in Flux Switching Machine Optimization : Applications and Future Prospects

This work was supported by the Commonwealth Scholarship Commission, U. K., under Grant Number: NGCN-180-2021Peer reviewe

Multi-phase Starter-Generator for 48 V Mild-Hybrid Powertrains

Transportation electrification has experienced a significant growth in recent years, and the electrification of the powertrain – namely hybridization – is considered the most viable solution seen by car manufacturers to achieve the challenging emission targets. Among the hybrid electrical powertrain topologies, the mild-hybrid configuration with the 48 V battery system offers the best ratio cost versus CO2 improvements. In particular, the 48 V technology does not require electrical shock protection whilst allows to leverage a variety of fuel saving functions such as electrical boost and regenerative braking. The thesis is focused on the electromagnetic and thermal design of a Belt-driven Starter Generator, BSG, for 48 V mild-hybrid powertrains. In the BSG layout, the starter-generator replaces the conventional alternator with a low impact on the engine compartment layout, even if a redesign of the belt tensioner is required. It is noteworthy to keep in mind that the electrical machine shall provide high starting torque and wide constant power speed range, both in motor and generator mode. Furthermore, the application imposes the adoption of low cost materials and the electrical machine is located in a harsh environment. As a consequence, the design is challenging from the electromagnetic, thermal and mechanical point of view. The novelties of the research lie in the 48 V automotive applications, by describing the practical difficulties to fulfill the design specifications through a suitable material selection, the identification of the cooling system and the available technological solutions. The first section of the thesis reports results from a literature review on electrical machine for mild-hybrid application aiming to highlight different criteria for the selection of the electrical machine. In this context the advantages in terms of fault tolerance and stator current splitting of multiphase drives are investigated. Furthermore, in this section the required performances and the constraints imposed by the specific application are analyzed. Among the different motor technologies, a dual three-phase induction machine having two stator winding sets shifted by 60 electrical degrees is selected as a suitable candidate. The second part of the thesis reports electromagnetic and mechanical issues addressed during the design stage, with special focus on stator winding layout, pole number and rotor slot. The adopted six-phase machine uses a four-layer bar stator winding that has been demonstrated as a good solution to improve the slot fill factor and thermal behavior. In addition, the thesis reports a comparison supported by experimental tests between open and closed rotor slots solutions; the focus is to maximize the machine electromagnetic performance according to the mechanical limits imposed by the rotating speed. Finally, predicted and measured performance of the prototypes are reported and discussed for validation purposes. The third part of the thesis deals with the thermal assessment of the BSG with particular emphasis on accurate winding temperature prediction as well as the cooling system selection. Since the stator-winding region is very sensitive to thermal issues and is usually attributed as being the main heat source within the machine body, its thermal modeling is of major importance. In these regards, a simplified stator winding thermal model was developed for the temperature prediction during transient condition. Moreover, considering that the driving cycle is characterized by time variable loss distribution, an effective cooling system must be mandatorily adopted together with high temperature class insulation material. In this context, the development of heat extraction through forced convection is experimentally investigated on the BSG prototype. As a main outcome of this research activity, it has been demonstrated the feasibility of the proposed design solution with respect to electromagnetic and thermal requirements

In-wheel motors for electric vehicles

PhD ThesisThe in-wheel motor technology as the source of traction for electric vehicles has been researched recently because it is compact and ease-to-integrate. The motor is housed in the wheel. Since the room for the motor is tightly defined by the size of the wheel and there is no gearing system, the motor must have a high torque density to drive the vehicle directly and a high efficiency to keep cool. The existing motor uses a surface-mounted magnet topology. To make it more cost-competitive, the magnet material needs to be reduced while maintaining the torque performance at the rated operating condition. It is the motive of this Ph.D. research. The thesis starts with a brief introduction on the background of the electric vehicle. Then the major challenges of the in-wheel motor technology are summarised. With the derived specifications, an induction machine and a switched reluctance machine are then simulated and analysed. Still, the permanent magnet synchronous machine is proved to have the highest torque density. Change from surface-mounted to interior topology, six new magnet topologies are investigated. The V-shaped interior magnet topology shows superior torque-to-magnet-mass ratio and is easy-to-manufacture. It gives 96% torque while using 56% of the magnet mass compared to the existing motor due to the assist from the additional reluctance torque and the lower magnetic circuit reluctance. The key to use less magnet mass while avoiding the demagnetisation is the front iron shielding effect. The analytical explanation on the better resistance to demagnetisation in the V-shaped motor is provided. The magnet loss mechanism is discussed for proper segmentation. Detailed design adjustments are made to compromise between the torque-to-magnet-mass ratio and the manufactural practicality. Issues regarding to lower mechanical rigidity occurred in initial assembly of the prototype and solutions are proposed. Followed by successful assembly, experimental tests were conducted and results show good agreement with the simulation. A specific form of torque ripple is found in the V-shaped motor and occurs generally in all fractional-slot concentrated-winding machines with saliency. It is explained by an analytical model. This model is also extended to explain the generally lower reluctance torque in vi fractional-slot concentrated-winding machines. Potential design improvements are suggested and simulated for future versions.Protean Electri