Electric Drivetrain Research Articles

Robust Design Optimization of Mechatronics Systems: Parallel Electric Drivetrain Application

AbstractThis paper addresses the problem of finding a robust optimal design when uncertain parameters in the form of crisp or interval sets are present in the optimization. Furthermore, in order to make the approach as general as possible, direct search methods with the help of sensitivity analysis techniques are employed to optimize the design. Consequently, the presented approach is suitable for black box models for which no, or very little, information of the equations governing the model is available. The design of an electric drivetrain is used to illustrate the benefits of the proposed method.

Bidirectional Nonisolated Fast Charger Integrated in the Electric Vehicle Traction Drivetrain

Integrated chargers, where the traction inverter is used as the primary charging interface, have emerged as a solution for reducing the cost and footprint of electric vehicle (EV) charging. This article proposes a bidirectional nonisolated integrated charger topology that also provides benefits to motor lifetime and reliability through a reduction in bearing currents and voltages. This is achieved by adding to an EV drive: an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter per phase with a common-mode (CM) voltage control; a CM inductor for additional leakage current filtering; contactors to switch between traction and charging modes; and a residual current device to satisfy standards for transformerless charging. To obtain high efficiency and make the filter small for traction applications, variable frequency critical soft switching is leveraged. Traction mode experimental validation demonstrates torque and speed steps with no degradation compared to a standard drive, a decrease in leakage currents and shaft voltages of more than 90%, and an increase in motor drive efficiency of 0.6% at 5-kW output power. Charging mode validation shows active and reactive power steps and peak efficiency of 99.4% and 98.4% at a rated power of 11 kW. Charging mode leakage current is measured to be 22 mA, which satisfies standards permitting the transformerless operation.

The Potential of a Separated Electric Compound Spark-Ignition Engine for Hybrid Vehicle Application

Abstract In-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be completely brought down to ambient pressure, causing a 20% theoretical energy loss. Several systems have been implemented to recover and use this energy such as turbocharging, turbomechanical and turbo-electrical compounding, or the implementation of Miller cycles. In all these cases however, the amount of energy recovered is limited allowing the engine to reach an overall efficiency incremental improvement between 4% and 9%. Implementing an adequately designed expander–generator unit could efficiently recover the unexpanded exhaust gas energy and improve efficiency. In this work, the application of the expander–generator unit to a hybrid propulsion vehicle is considered, where the onboard energy storage receives power produced by an expander–generator, which could hence be employed for vehicle propulsion through an electric drivetrain. Starting from these considerations, a simple but effective modeling approach is used to evaluate the energetic potential of a spark-ignition (SI) engine electrically supercharged and equipped with an exhaust gas expander connected to an electric generator. The overall efficiency was compared to a reference turbocharged engine within a hybrid vehicle architecture. It was found that, if adequately recovered, the unexpanded gas energy could reduce engine fuel consumption and related pollutant emissions by 4–12%, depending on overall power output.

Improvement of Steerability and Driving Safety of an Electric Three-Wheeled Vehicle by a Design Modification of its Steering Mechanism

Abstract Three-wheeled vehicles are transport means which generally combine properties of two-wheeled vehicles (principal motorcycles) and four-wheeled vehicles (standards cars). Three-wheeled vehicles have been designed and manufactured as units which are made up of one front wheel and two rear wheels, powered by an electric drive-train, and referred to in some countries under a non-English term as E-3kolka. These vehicles also comprise a special steering mechanism which improves their overturning stability when driving around curves. However, several tests have revealed certain deficiencies of the steering mechanism, where the main issue included unreliable self-restraining effect of steering wheel straightening after driving around a curve. This may even lead to unacceptable properties of the vehicle. Therefore, the authors of this paper suggest particular technical solutions to eliminate or completely avoid the described negative effects during driving. Proposed designs are mutually compared and a final decision is presented.

Quantitative Reliability Evaluation of Silicon Carbide-Based Inverters for Multiphase Electric Drives for Electric Vehicles

Abstract Reliability of power converter in the electric drivetrain of a vehicle can be a criterion for the comparison of various converter topologies, cooling system designs and control strategies. Therefore, reliability prediction is important for the design and control of vehicles. This paper presents an approach for quantitative evaluation of the reliability of converters for multiphase motor drives for electric vehicles (EVs) after considering the driving cycle. This paper provides a good background of reliability quantification so that it is easy to extend the presented approach to other applications. The models of subsystems have been selected to have excellent computational efficiency with good accuracy which is necessary for simulating long driving cycles. A simple vehicle model is used to obtain the traction motor torque demand for various points of the driving cycle. A multiphase interior permanent magnet synchronous motor has been used for traction motor. The operating voltage and currents of the motor are found using maximum torque per ampere (MTPA) control of IPMSM. The analytical loss calculation has been used to find the losses of switching devices of the converter. A thermal model of silicon carbide (SiC) MOSFET has been used to calculate junction temperature from the losses. The model developed here gives the failure rate and mean time between failures (MTBF) of switching devices of the inverter, which can be used to determine the failure rate. The model has been used to find the transition probabilities of a Markov model which can be used to quantify the reliability of converters of multiphase electric drives.

Selection of Magnet Wire Topologies With Reduced AC Losses for the Windings of Electric Drivetrains

In high speed electrical machines, one of the main challenges that can be faced is the high frequency losses in the machine windings due to both skin and proximity effects. This paper studies the effect of using different types of magnet wires on the AC losses in the winding of high speed electric machines. Using finite element modelling (FEM), the conductors are subdivided into multiple strands to calculate the losses in each conductor and in each layer. Aiming at loss minimization, different arrangements are introduced and compared at a wide range of frequencies. Further, four coil designs are prototyped using different magnet wires or arrangements. Moreover, the design and performance are compared with highlighting the pros and cons of each case. Eventually, recommendations are provided based on the obtained results for a better selection of magnet wire.

Exploring the Potential for Electric Retrofit Regulations and an Accreditation Scheme for the UK

Electric vehicles have zero tailpipe emissions and can reduce greenhouse gas emissions by up to 90% compared to internal combustion engine (ICE) vehicles. Electric retrofits involve converting an ICE vehicle to an electric drivetrain, aiding the transition to zero emission vehicles by adapting current vehicles and, thus, reducing the transport sector emissions. Other benefits include charge exemptions in major cities, reduced driving costs, and lower maintenance. The UK has a considerable retrofit market, with a large price range of services offered. There is a varying level of practice undertaken and current regulations may not adequately cover these retrofits. Industrial engagement has highlighted the varying levels and common themes of practice, such as restoration work, computer-aided design, and finite element analysis. Converting the registered fuel type of a vehicle to electricity, post-retrofit, appears to be a limited process, with few steps. Therefore, a regulatory framework, such as an accreditation scheme, could be introduced to ensure high levels of safety and good practice. Future work suggestions include further meetings with the DVLA and DVSA, and meeting the Motor Insurers’ Bureau.

Impact of Ultra-Low Viscosity Fluids on Drivetrain Functionality and Durability

Increasing automotive powertrain electrification is impacting drivetrain complexity and the profiles of the fluids needed. Since the millennium, drivetrain fluid viscosities have been reduced for better efficiency, but this new challenge is driving them to unprecedented low levels. This paper assesses some of the potential implications of ultra-low viscosity fluids on drivetrain functionality and durability. Model formulations have been prepared from a variety of base fluids combined with additive packages. These have been evaluated in typical automotive drivetrain rig tests, as well as with some selected functional tests. In addition, the thermo-oxidative stability and electrical and thermal properties of the fluids were compared. Based on the results, the impact of low viscosity fluids on drivetrain functionality and durability varies depending on the performance parameter evaluated. For example, gear scuffing and bearing wear is highly dependent on additives, whilst gear and bearing fatigue is mainly affected by fluid viscosity. However, by carefully balancing base fluids and additives, acceptable component and fluid durability can be achieved. With respect to new electric drivetrain performance needs, the thermal properties of the finished fluid are essentially dependent on the base fluid composition, whilst its electrical properties are more influenced by additive chemistry, with some secondary impact from base fluid composition.

E-Drive into the Future

The development of a next-generation electric vehicle drivetrain platform builds upon the success of previous technology to deliver a flexible, powerful, and secure solution for vehicle manufacturers

Conversion of Two-Stroke Vehicle to an Electric Vehicle

Amid the global pandemic of covid-19, fuel prices have soared a record high, crossing the Rs. 100 landmark for petrol and diesel. This leads to an increase in prices across all products, which cuts in deeper into the already thin bottom lines of ordinary citizens. Public outcry aside, the rise in fuel prices indicates an accelerating trend, which emphasizes the need to find alternative sources of fuel for transport; the ever growing sector. In recent years, reports of possible banning two-stroke engines, coupled with the emergence of a new emission standard in India, have re-ignited questions about how two-stroke vehicles, can be powered from alternative sources of energy. This project intends to address the above question, by assessing the feasibility of a different alternative, by designing an electric drivetrain for a twowheeler, while aiming to be practical and economical for the ordinary man riding it. This project intends to be a cost-feasibility study, whose aim, to realize a full EV conversion of a twowheeler, less than 50% of current market price of base level, original EV’s, thereby proving to be a feasible alternative to people who cannot afford the alternative; and also solving the logistical and environmental problems arising from a large number of abandoned or suboptimal use of such vehicles, when the shift happens.

(Invited) Development of Vertical Gallium Nitride Power Devices for Use in Electric Vehicle Drivetrains

The rapid acceleration of vehicle drivetrain electrification is expected to be a major driver for the widespread adoption of silicon carbide (SiC) power devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and junction-barrier-Schottky (JBS) diodes (the latter needed as the freewheeling diode in parallel with the MOSFET switch), due to their ability to increase the efficiency and reduce the volume of the power electronic inverter that ties the vehicle’s battery to the electric motor(s). The move from traditional silicon-based power electronics to SiC-based power electronics is necessary to achieve the U.S. Department of Energy (DOE) power electronics density target of 100 kW/L. However, gallium nitride (GaN)-based inverters may offer additional benefits beyond what can be achieved with SiC. For example, genetic-algorithm-based system-level simulations of the Pareto front trade-off between power density and efficiency of the inverter indicate that GaN power devices offer solutions superior to those achievable with SiC. However, given that the drivetrain DC bus voltage in future electric vehicles is expected to be 800 V or higher, commercially-available GaN power switching high electron mobility transistors (HEMTs), which typically have voltage ratings of 650 V or less, are unsuitable for a two-level inverter design, which is preferred by automotive system designers due to its simplicity and associated reliability. As such, vertical GaN power devices with voltage ratings of 1.2 kV or greater are necessary. This talk will describe our team’s efforts to develop both vertical GaN MOSFETs and JBS diodes. Designs for both trench MOSFETs and double-well MOSFETs (DMOSFETs) will be discussed. Experimental work has focused on trench MOSFETs, chiefly due to the need for selective-area doping in the DMOSFET, which is generally challenging in GaN and is particularly so in this structure due to the double well. The trench MOSFET presents significant challenges as well, including the need for a high-quality gate dielectric on the etched sidewall of the trench as well as mitigation of high electric fields at the bottom of the trench. Vertical GaN trench MOSFETs utilizing drift layers grown by metal-organic chemical vapor deposition (MOCVD) on native GaN substrates have been fabricated. Devices with an atomic-layer-deposited SiO2 gate dielectric have demonstrated a positive threshold voltage of ~8 V, an on/off ratio of ~108, and a current density of ~400 mA/mm. Additionally, GaN JBS diodes are being developed concurrently, and in this case selective-area doping cannot be avoided as alternating regions of p- and n-doped material are inherent to the operation of the device. Our team has utilized an etch-and-regrowth approach to demonstrate vertical GaN JBS diodes with reverse hold-off voltage >1.5 kV and forward turn-on voltage <1 V, consistent with JBS operation, although the reverse leakage current is higher than is typically observed for a continuously-grown GaN PN junction. Prospects to further improve device performance will be discussed, including reducing the reverse leakage current though advances in the selective-area p-GaN regrowth process. This work was supported by the Electric Drivetrain Consortium managed by Susan Rogers of DOE’s Vehicle Technologies Office and by the ARPA-E PNDIODES program directed by Isik Kizilyalli. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Prognostics and Health Management Features for Large Circuit Boards to Be Implemented Into Electric Drivetrain Applications

Abstract Canary structures being used as early warning indicators represent an important tool for condition and health monitoring of electronic components and systems. In this paper, printed circuit boards (PCBs) with canary structures based on surface mounted device (SMD)-2512 ceramic chip resistors with reduced solder pad sizes were studied. Focus of these investigations was set on thermomechanical and mechanical stresses caused by passive thermal cycling as well as by vibrational loads. For this purpose, experimental methods such as deformation analysis and accelerated aging tests as well as finite element (FE) based methods were applied. In addition, an outlook on the implementation of these canary structures into dual inverter electronic control boards for electrical powertrain applications will be given.

Electromechanical modeling of a motor–gearbox system for local gear tooth faults detection

Many of today’s industrial applications are powered by electromechanical drives. Wind turbines, fuel based and hydroelectric generators or electric drivetrains are examples of these applications. Developing accurate models of these systems has attracted a significant interest in recent years, because it can help enormously to enhance their reliability and develop efficient maintenance strategies to avoid prominent failure modes. In this paper, motor–gearbox systems are investigated in their both mechanical and electrical aspects. An electrical model of an induction machine is coupled with a lumped parameter model of a two-stage gear system to build an integrated model of these systems. The coupling between these sub-models is realized in a way that allows to consider transient regimes. Furthermore, an improved potential energy method is used to determine the mesh stiffness of gear pairs considering actual gear shapes and an original method is proposed to refine stiffness curves based on the correlation measure with experimental measurements. The developed model is validated under varying operating conditions using vibration and electrical measurements and simulation results were in good agreement with experiment. Moreover, the model was investigated for the detection of gear tooth faults using both vibration and motor current signature analysis in time and frequency domains, the model response under faulty condition was satisfactory compared with the observed response.

Electric Vehicle Modelling and Simulation of a Light Commercial Vehicle Using PMSM Propulsion

Even though the Internal Combustion Engine (ICE) used in conventional vehicles is one of the major causes of global warming and air pollution, the emission of toxic gases is also harmful to living organisms. Electric propulsion has been developed in modern electric vehicles to replace the ICE.The aim of this research is to use both the Simulink and Simscape toolboxes in MATLAB to model the dynamics of a light commercial vehicle powered by electric propulsion. This research focuses on a Volkswagen Crafter with a diesel propulsion engine manufactured in 2020. A rear-wheel driven electric powertrain based on a Permanent Magnet Synchronous Motor was designed to replace its front-wheel driven diesel engine in an urban environment at low average speeds.In this research, a Nissan Leaf battery with a nominal voltage of 360 V and a capacity of 24 kWh was modelled to serve as the energy source of the electric drivetrain. The New European Driving Cycle was used in this research to evaluate the electric propulsion. Another test input such as a speed ramp was also used to test the vehicle under different road conditions. A Proportional Integral controller was applied to control the speed of both the vehicle and synchronous motor. Different driving cycles were used to test the vehicle. The vehicle demonstrated a good tracking capability in each type of test. In addition, this research determined that the fuel economy of electric vehicles is approximately 19% better than that of conventional vehicles.

Hybrid drivetrain systems 48 V in rally cars

The International Automobile Federation (FIA) over the last few years consistently implements the strategy of introducing hybrid and electric drivetrains to all motorsport competitions. The article discusses the implementation of a hybrid drivetrain system powered by 48V for such FIA rally cars groups like Rally2, Rally3 and Rally4 based on current discussions held at the FIA Technical Working Groups. The implementation of hybrid drive systems in rally cars was analysed in terms of their advantages and disadvantages. In the case of this application the important aspect is the assumption regarding an increase in performance, while keeping a high level of safety and reasonable costs. Additionally, the assumption is to reduce the emissions of harmful substances produced by rally cars. The article concludes selection of elements of the above-mentioned system for further reasearch were presented. An analysis and calculations of the energy recoverable from regenerative braking using the BISG on a given section of the rally were carried out. Conclusions were also drawn regarding further work that will be carried out to successfully implement the above-mentioned systems for rally cars.

Design, Simulation and Optimization of an Electrical Drive-Train

Today, design engineers engaged in the development of a high-performance electrical drive-train are challenged by the multitude of possible topological choices and numerous mutually interconnected physical phenomena. Development teams around the globe struggle with this challenge; usually they employ several tools for simulation and topology optimization and transfer multiple versions of their product models in a mainly manual process. The research presented in this paper aims to explore a holistic possibility to realize a sensible analysis-synthesis cycle that takes into consideration current developments in design, simulation and optimization processes. This kind of process can enhance the transparency of design decisions, can reduce the risk of design and process flaws and can support the approach toward a holistic optimum. The investigation starts with the development of the topological concept of the drive-train and continues over the interconnected simulation of several decisive properties of the drive-train. Obviously, these properties concern several domains (mechanical, electrical, thermal and the control domain). The optimization of the drive-train takes into consideration the main requirement—in the investigated example, which is a formula student drive-train—the lap time. The result is a holistic concept for a design, simulation and optimization approach that considers topological variety, interconnected multi-domain simulation and a continuous connection to the decisive requirements.

Comparison of Electrified Aircraft Propulsion Drive Systems with Different Electric Motor Topologies

Electric aircraft propulsion is a growing research area that looks into achieving propulsion through fully electric or hybrid electric systems while achieving low emissions. The system-level benefit gained by different electric and hybrid-electric propulsion schemes depends heavily on the performance of system-level components in the electric drive-train, including the electric motor, gear box, motor drive, protection systems, as well as the thermal management system. When comparing motor topologies, it is important to understand performance measures such as efficiency and specific power on a drive system level. Many different motor types have been qualitatively compared and can be found in the literature. To guide appropriate component selection, this paper presents details of a quantitative study for a given electric propulsion drive system. A Pareto optimal front for a notional drive system of a 1.5 MW electrical propulsor with different motor types is generated and compared. An optimization algorithm coupled with an electromagnetic finite element analysis software tool was used to optimize the induction motor, switched reluctance motor, wound rotor synchronous motor, permanent magnet synchronous motor (PMSM), slotless PMSM, permanent-magnet-assisted synchronous reluctance motor, brushless DC motor, and brushless doubly fed reluctance motor types for efficiency and specific power. Overall advantages considering system-level efficiency, specific power, and a few other key metrics such as origin of losses, cooling complexity, manufacturing tolerance, and fault tolerance are discussed. This gives an indication of the relative performance of different motor types and confirms the overall advantage of PM motor topologies in aircraft propulsion.

A Review of Electric Aircraft Drivetrain Motor Technology

This article reviews the power density and torque density of permanent magnet (PM) motor technology that is currently commercially developed for use in electric aircraft. The review shows that in order to meet the ambitious electrical motor power density goals recently set forth, the power density of a motor needs to more than double. The requirements imposed by the maximum propeller rotor tip speed, as well as the diameter constraints set by the aerodynamic requirements, will further limit the practical electric motor design sizing options. This article advocates for considering using magnetic gearing (MG) and using an integrated contra-rotating motor propeller co-design approach as a way of both increasing propulsive thrust performance and thereby increasing the aircraft’s overall power density.

Electric Drivetrain Optimization for a Commercial Fleet with Different Degrees of Electrical Machine Commonality

At present, the prevalence of electric vehicles is increasing continuously. In particular, there are promising applications for commercial vehicles transferring from conventional to full electric, due to lower operating costs and stricter emission regulations. Thus, cost analysis from the fleet perspective becomes important. The study of cost competitiveness of different drivetrain designs is necessary to evaluate the fleet cost variance for different degrees of electrical machine commonality. This paper presents a methodology to find a preliminary powertrain design that minimizes the Total Cost of Ownership (TCO) for an entire fleet of electric commercial vehicles while fulfilling the performance requirements of each vehicle type. This methodology is based on scalable electric machine models, and particle swarm is used as the main optimization algorithm. The results show that the total cost penalty incurred when sharing the same electrical machine is small, therefore, there is a cost saving potential in higher degrees of electrical machine commonality.

Quantifying the Fleet Composition at Full Adoption of Shared Autonomous Electric Vehicles: An Agent-based Approach

Aims: Exploring the impact of full adoption of fit-for-demand shared and autonomous electric vehicles on the passenger vehicle fleet of a society. Background: Shared Eutonomous Electric Vehicles (SAEVs) are expected to have a disruptive impact on the mobility sector. Reduced cost for mobility and increased accessibility will induce new mobility demand and the vehicles that provide it will be fit-for-demand vehicles. Both these aspects have been qualitatively covered in recent research, but there have not yet been attempts to quantify fleet compositions in scenarios where passenger transport is dominated by fit-for-demand, one-person autonomous vehicles. Objective: To quantify the composition of the future vehicle fleet when all passenger vehicles are autonomous, shared and fit-for-demand and where cheap and accessible mobility has significantly increased the mobility demand. Methods: An agent-based model is developed to model detailed travel dynamics of a large population. Numerical data is used to mimic actual driving motions in the Netherlands. Next, passenger vehicle trips are changed to trips with fit-for-demand vehicles, and new mobility demand is added in the form of longer tips, more frequent trips, modal shifts from public transport, redistribution of shared vehicles, and new user groups. Two scenarios are defined for the induced mobility demand from SAEVs, one scenario with limited increased mobility demand, and one scenario with more than double the current mobility demand. Three categories of fit-for-demand vehicles are stochastically mapped to all vehicle trips based on each trip's characteristics. The vehicle categories contain two one-person vehicle types and one multi-person vehicle type. Results: The simulations show that at full adoption of SAEVs, the maximum daily number of passenger vehicles on the road increases by 60% to 180%. However, the total fleet size could shrink by up to 90% if the increase in mobility demand is limited. An 80% reduction in fleet size is possible at more than doubling the current mobility demand. Additionally, about three-quarters of the SAEVs can be small one-person vehicles. Conclusion: Full adoption of fit-for-demand SAEVs is expected to induce new mobility demand. However, the results of this research indicate that there would be 80% to 90% less vehicles required in such a situation, and the vast majority would be one-person vehicles. Such vehicles are less resource-intense and, because of their size and electric drivetrains, are significantly more energy-efficient than the average current-day vehicle. This research indicates the massive potential of SAEVs to lower both the cost and the environmental impact of the mobility sector. Quantification of these environmental benefits and reduced mobility costs are proposed for further research.