Electric Vehicle Modeling Considerations
In order to model any electric vehicle, three major parts should be taken into consideration: vehicle dynamics, transmission performance, and battery.
The vision of electrified transportation is the perfect combination of renewable energy sources and battery electric vehicles. It promises zero greenhouse gas emissions without using petroleum or other fossil fuels. High efficiencies can be accomplished with a possible 80% grid-to-wheel [1]. The adoption of electric vehicles is expanding across consumers, commercial, industrial and public sectors which represent opportunities for electric utilities. One crucial point for the electric vehicle market to succeed is to focus on research and development to model and develop the battery technology, motor efficiency, vehicle dynamics and transmission performance. Read on to learn more about the modeling and challenges of traction power electronics in electrified transportation.
Overview
The paths to electrified transportation include the implementation of hybrid electric vehicles (HEVs), plug-in HEVs (PHEVs), all electric vehicles (AEVs) and hydrogen with fuel cell electric vehicles (FCV). Modeling of electric vehicles helps in the design, analysis and implementation phases. The aspects that need to be modeled include vehicle dynamics, transmission performance and battery of the electric vehicles to acquire the power requirements of the storage system [2]. This also helps in identifying the right types of hardware like choice of specific battery for an application in hand. The simulations are typically performed by integrating the Matlab code along with the Simulink blocks. The velocity of the vehicle and the distance travelled correspond to actual driving cycles and torque variations of an electric vehicle. It is also important to consider modeling of factors like aerodynamic drag, linear acceleration and rolling resistance forces. A sample top-level EV model is as shown in Figure 1 [3].
Figure 1. Top-level EV model [3]
Modeling of Transportation Electrification
In order to model any electric vehicle, three major parts should be taken into consideration: vehicle dynamics, transmission performance, and battery. A major input to the electric vehicle model is the acceleration of the vehicle which helps yield the driving cycle of an EV. The first step towards modeling an EV is studying vehicle dynamics. It is important to represent the net forces acting on a vehicle during its driving cycle and the effect of multiple parameters in its velocity and performance. These include aerodynamic drag, acceleration, rolling resistance and hill-climbing forces. The complete system modeling in case of transportation electrification involves the integration of several subsystem models that together form a complete vehicle model. Further, system evaluation and design considerations need to be accounted for.
The design of system architecture in the case of an electric vehicle involves multiple aspects including vehicle dynamics and MATLAB/Simulink-based modeling of the same. Also, different electric vehicle architectures need to be considered based on the application in hand like plug-in hybrid (PHEV) or hybrid (HEV). The rating and sizing of drivetrain components need to be accounted for. The model of the electric vehicle in turn is formed using multiple power electronic components and electric machines along with the energy storage piece. These are integrated and adequately modeled to function together by means of control and automation software. The modeling and simulation of a sample electrical model view of an electric vehicle is as shown in Figure 2 [3].
Figure 2. Modeling and simulation of a sample electrical model view of an electric vehicle [3]
Challenges for Transportation Electrification
In general, the challenges with respect to electrified transportation are the engineering of electric drivetrain components including efficient, high-density, reliable power electronics along with charging infrastructure with batteries. Power converters that are vital for any EV are made up of several components that possess different sizes and mechanical properties. They vary from small and fragile electronic chips to extremely bulky magnetic components and cold plates. The interactions between the components and their operating conditions are so tight that an improvement at any level can yield an overall enhancement of the entire design. This could be one of the several parameters like switching frequency, cooling, current density or magnetic flux density. The key challenge for traction power electronics is to have a semiconductor technology that offers high power density while being cost effective.
The other aspects to consider include adequate cooling and thermal limitations of power switches. In general, it is observed that the recent wide-band gap-based technologies offer higher switching frequency operation while reducing the cooling requirements. However, the biggest challenge for the next generation of automotive power electronic systems is to reduce the cost in order to provide more affordable solutions. This can possibly be accomplished by improvements in the manufacturing process, design scalability, and development of more integrated components and systems such as smart power modules [4].
Key references:
- Philip Jones et. al., The Future of Transportation Electrification: Utility, Industry and Consumer Perspectives, 2018.
- Marah et. al., Modeling of Electric Vehicles using Matlab/Simulink, 2020.
- Dragan Maksimovic et. al., Power Electronics for Electric Drive Vehicles, 2013.
- Berker et. al., Making the Case for Electrified Transportation, 2015.
