Battery Electric Modelling Using Model-Based Design

Electric vehicles (EV) has been received progressively attention in research and development over universities, companies and research institutes. For one hand, it is addressed as the cutting-edge solution for greenhouse gases, global climate changes and city pollution and efficiency on power demand, in another hand it is necessary more studies in the impact the integration with the power grids and grid-tied applications of the charging stations.

Despite being divided into: BEV (Battery Electric Vehicle), HEV (Hybrid Electric Vehicle), FCEV (Fuel Cell Electric Vehicle) and PHEV (Plug-in Hybrid Electric Vehicle), this article addresses only aspects of modelling for BEV, in order to analyze electrical interaction and specifications and integration with the electrical grid for hereafter articles coming.

By using Model-Based Design (MBD), it is possible to overcome traditional development process of electric vehicles issues, such as specification comprehension by the engineering team, algorithm redesign and foresee detect the problem before testing step. In other words, it can be stated as cost and time saving once it mitigates design errors.

This development process model using MBD can be summarized into five steps as:

• Determination use and specifications;

• Modelling of components (subsystems);

• Building the models, tests and implementation of the subsystems;

• Running the application and evaluation the prototype.

These steps can be evolved into those ones illustrated on the Figure 1, as known as the V-model (development cycle).


Figure 1. Steps of model-based design of generic system.

In the requirements step it is planned the using goals and targets for the prototype as well as the specification. In the model-based design of the system it is modelled all the components (subsystems) of the system and assumptions, parameters of the vehicles and equations for each component are taken. In the subsystem and implementation, each component is built. For the subsystem integration and model-in-the loop tests, it is performed simulation and hardware tests for each subsystem and for the resulting integration of them. Finally, the prototype is ready for the complete system final test and evaluation.

The MBD of systems is well-known in aeronautics and automotive industries mainly used for communication, control, signal processing systems. Therefore, in this article it is applied in one elementary concept of electric vehicle regarding the basic electric components. 

The concept of EV in the electric subsystem aspects is shown on Figure 2.


Figure 2. Concept of system for EV.

Using MBD the system modelling (according to Figure 2) would be: 

• Step 1: Determination of vehicle specification (e.g. torque, speed and control) and driving cycles. As output parameters: driving range, charge/discharge of battery, EV performance and power flow;

• Step 2: Get the equations for controllers, motor, traction and the road speed and torque behavior (in which could be used look-up table method as subjective user behavior). 

• Step 3: Build the subsystems through MIL both using drive-by-wire and ECU (Electronic Control Unit) functions and/or softwares MDB-driven such as Simulink, Labview or Xcos. 

• Step 4: Put all the parameters and models together in order to get the power flow and dynamic load from the system.

Thus, the using MBD can be useful for fast and efficient analysis of EV environment of complex systems once, during the development of the system, each subsystem can be analyzed separated, and the modelling can be refined. 

In addition, for the next studies, the system can be built using simulation softwares and it can be applied AWGN (Additive White Gaussian Noise) as source of noise on the electric models to get the overall system response and analysis of the integration between the systems.

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