Design, Modelling and Verification of Distributed Electric Drivetrain

The electric drivetrain in a battery electric vehicle (BEVs) consists of an electric machine, an inverter, and a transmission. The drivetrain topology of available BEVs, e.g., Nissan Leaf, is centralized with a single electric drivetrain used to propel the vehicle. However, the drivetrain components can be integrated mechanically, resulting in a more compact solution. Furthermore, multiple drivetrain units can propel the vehicle resulting in a distributed drive architecture, e.g., Tesla Model S. Such drivetrains provide an additional degree of control and topology optimization leading to cheaper and more efficient solutions. To reduce the cost, the drivetrain unit in a distributed drivetrain can be standardized. However, to standardize the drivetrain, the drivetrain needs to be dimensioned such that the performance of a range of different vehicles can be satisfied. This work investigates a method for dimensioning the torque and power of an electric drivetrain that could be standardized across different passenger and light-duty vehicles. A system modeling approach is used to verify the proposed method using drive cycle simulations. The laboratory verification of such drivetrain components using a conventional dyno test bench can be expensive. Therefore, alternative methods such as power-hardware-in-the-loop (PHIL) and mechanical-hardware-in-the-loop (MHIL) are investigated. The PHIL test method for verifying inverters can be inexpensive as it eliminates the need for rotating electric machines. In this method, the inverter is tested using a machine emulator consisting of a voltage source converter and a coupling network, e.g., inductors and transformer. The emulator is controlled so that currents and voltages at the terminals resemble a machine connected to a mechanical load. In this work, a 60-kW machine emulator is designed and experimentally verified. In the MHIL method, the real-time simulation of the system is combined with a dyno test bench. One drivetrain is implemented in the dyno test bench, while the remaining are simulated using a real-time simulator to utilize this method for distributed drivetrain systems. Including the remaining drivetrains in the real-time simulation eliminates the need for a full-scale dyno test bench, providing a less expensive method for laboratory verification. An MHIL test bench for verification of distributed drivetrain control and components is also designed and experimentally verified

Multiple electrical machines applied for high drive train efficiency

Conventionally, electric powertrain in battery electric vehicles are designed and optimized for a particular vehicle category and performance requirements. In this paper the design of an electric powertrain using two different type of machines is proposed with a focus on the design of electricmachines. The powertrain is dimensioned by analyzing vehicle specifications, both combustion based and electric, vehicle performance requirements and wheel load analysis performed on simplified vehicle models using standard drive cycles. Two different vehicle models representing a small and medium size vehicle are used. To compare the distributed drive topology with two different machines, a third machine is designed to represent conventional electric powertrain. The proposed drive system is observed to achieve similar peak torque and power as the centralized drive using single machine. However, the proposed design of the powertrain resulted in slightly higher operating efficiency while providing a scalability of performance

Acceleration-based wheel slip control realized with decentralised electric drivetrain systems

Traction control is one of the most important functions in vehicle drivetrain systems. When a vehicle is driven on a low-friction road surface, loss of traction force can cause the driven wheels to spin. This reduces vehicle acceleration performance and can even cause the driver to lose control of the vehicle. The high bandwidth of electric machine control in electric vehicles gives more possibilities to regulate driving torque on wheels and prevent wheel spin. An acceleration-based wheel slip control is designed and investigated. Compared to traditional slip-based traction control, the proposed method does not depend on the estimation of the vehicle speed and only relies on the driven wheel rotational acceleration. The control method is verified using the simulation of an electric vehicle with a decentralised electric drivetrain system. The vehicle and the electric drive are modelled in CarMaker and PLECS, respectively. The simulation results show that the proposed method is able to prevent the driven wheel from spinning when the vehicle is accelerated on an ice road. In addition, the control is fast enough and requires only half a second to reduce the wheel acceleration to a normal range

Real-Time FPGA/CPU-Based Simulation of a Full-Electric Vehicle Integrated with a High-Fidelity Electric Drive Model

Real-time simulations refer to the simulations of a physical system where model equations for one time-step are solved within the same time period as in reality. An FPGA/CPU-based real-time simulation platform is presented in this paper, with a full-electric vehicle model implemented in a central processing unit (CPU) board and an electric drive model implemented in a field programmable gate arrays (FPGA) board. It has been a challenge to interface two models solved with two different processors. In this paper, one open-loop and three closed-loop interfaces are proposed. Real-time simulation results show that the best method is to transmit electric machine speed from the vehicle model to the electric derive model, with feedback electric machine torque calculated in FPGA. In addition, a virtual vehicle testing tool (CarMaker) is used when building the vehicle model, achieving more accurate modeling of vehicle subsystems. The presented platform can be used to verify advanced vehicle control functions during hardware-in-the-loop (HIL) testing. Vehicle anti-slip control is used as an example here. Finally, experiments were performed by connecting the real-time platform with a back-to-back electric machine test bench. Results of torque, rotor speed, and d&q axis currents are all in good agreement between simulations and experiments

Multidisciplinary Cooling Design Tool for Electric Vehicle SiC Inverters Utilizing Transient 3D-CFD Computations

This paper proposes a new design tool that can be used for the development of a proper cooling component for high-power three-phase SiC module-packs for electric vehicles. Specifically, a multidisciplinary approach of the design process is presented that is based on the accurate electrical, thermal and fluid-mechanics modeling as well as computational testing of a high-power three-phase SiC modulepack under transient-load conditions, so that it can effectively meet the highly-demanding cooling requirements of an electric vehicle inverter. The cooling plate is initially designed by using steady-statebased 3D-computational-fluid-dynamic (CFD) tool, as in a conventional method. Then, the proposed design algorithm fine-tunes it through transient 3D-CFD computations by following a specific iterative improvement procedure considering the heat dissipation requirements for the SiC power switchesduring the official driving cycles for passenger vehicles and during abrupt acceleration tests under several ambient environments. Therefore, not only overheating at all operating conditions is avoided, but also, accurate thermal modeling of the individual inverter modules is provided that can be used forlifetime estimations and for calculating the overload capability of the inverter. The design improvement attained with the proposed procedure against the conventional steady-state approach is validated on a traction 450 A SiC inverter with the model of a real passenger vehicle

Modeling and Experimental Verification of High-Frequency Inductive Brushless Exciter for Electrically Excited Synchronous Machines

Electrically excited synchronous machines have shown potential to be an alternative to permanent magnet synchronous machines in electromobility and wind power applications. High frequency wireless power transferring technology enables a compact design of brushless exciters for the machine. In this paper, a dynamic model of high frequency brushless exciters is proposed for the purposes of operating condition monitoring and excitation control. The modeling is done by using arithmetic and differential equations, as well as considering different operation modes of the system. The operation modes are defined based on the physical behaviors of the excitation circuit. The model is verified by experiments with variations of different circuit parameters. With the proposed model, further studies, including parameter sensitivity study, component parameter selection and loss analysis are conducted to demonstrate the effectiveness of the model. These studies can be used to assist design and optimization of the brushless excitation system

Designing Thermally Uniform Heatsink with Rectangular Pins for High-Power Automotive SiC Inverters

This paper presents the design of a high-performance liquid-cooled heatsink for three-phase automotive inverters that attains uniform thermal distribution at the surface of the three power modules. Power modules with SiC-MOSFETs are used in this study and a uniform thermal distribution on the heatsink guarantees equal thermal loading of the semiconductor devices. A comparative study of various cooling plate geometries is made and their effectiveness in meeting the design objectives of low sink-temperature and coolant pressure drop and the highest possible temperature uniformity along the surface of the plate is presented. Plates with straight and wavy fins are compared with designs accommodating rectangular pins and the advantages of each case is shown with the corresponding simulation results. Key design parameters of the cooling plate geometries are optimized with an iterative process, which is presented with selective simulation results of 3D Conjugate Heat Transfer computations for coolant flow rates up to 10~l/min. The final heatsink design accommodates multiple rectangular pins and attains temperature difference of less than 2oC among the three SiC power modules

Zero-Sequence Current Reduction Technique for Electrical Machine Emulators With DC Coupling by Regulating the SVM Zero States

In this article, a new zero-sequence current suppression technique for electrical machine emulators with reduced component count is proposed. The proposed control scheme is implemented by properly regulating the zero states in space vector modulation (SVM). It is well known that a machine emulator allows fast experimental validation of the control and design of a drive system without having a physical electrical machine, since the machine is replaced by another voltage-source converter and a three-phase inductor. However, in emulators with a coupled dc link, circulating zero-sequence current is freely developed creating additional load for the power switches. The currently available control methods require additional hardware common-mode filters to effectively reduce this current. Contrarily, the proposed SVM algorithm suppresses the zero-sequence current more effectively via direct compensation of common-mode voltage, and thus, no additional hardware filters are needed. Thus, an electrical machine emulator with less hardware requirements can be developed with the proposed control technique for being utilized in several laboratory test-bench applications. Experimental results on a 60-kW system validate the effectiveness of the proposed SVM algorithm, since the zero-sequence current amplitude has been measured to be 3.7% of the phase current or even less than this

Design of a power hardware-in-the-loop test bench for a traction permanent magnet synchronous machine drive

The challenges in inverter development for traction applications are low cost, better performance, optimized design and faster time to market. A solution is to use machine emulators whose phase currents and voltages at the terminal resembles a machine connected to a mechanical load for testing. Testing of an inverter for traction applications using permanent magnet synchronous machine (PMSM) emulator is presented. The emulator test bench consists of two identical front-to-front connected 2-level voltage source converters connected via an auxiliary inductor. Verification of the emulator is carried out in MATLAB/PLECS by comparing simulated phase currents, torque and rotor speeds to an equivalent PMSM drive. A common dc-link is used between the emulator and the inverter under test resulting into circulating common-mode currents. A common-mode choke and controller is used to eliminating common-mode currents. It is shown that the emulator can effectively emulate the PMSM drive with reasonable accuracy