MODEL BASED DESIGN FOR EV AND HEV
Model-Based Design (MBD) is a mathematical and visual method of addressing problems associated with designing complex control, signal processing and communication systems. It is used in many motion control, industrial equipment, aerospace, and automotive applications. Model-based design is a methodology applied in designing embedded software.
How does Model Based Design Work?
• Model-Based Design is transforming the way engineers and scientists work by moving design tasks from the lab and field to the desktop.
• Model-Based Design allows designers to create virtual assemblies to understand whether product parts/algorithms will work together before even being manufactured.
• Developers can automatically generate embedded code from simulation models.
Basic steps of MBD
In Model-Based Design of control systems, development is manifested in these four steps:
- Modelling a plant
- Analysing and synthesizing a controller for the plant
- Simulating the plant and controller
- Integrating all these phases by deploying the controller
Using MBD provides a lot of benefits to the companies by
- Achieving product quality that the competition cannot match
- Creating products that could not have been developed otherwise
- Minimizing the number of physical prototypes
- Reusing models and adapting designs for upgrades and for derivative systems with expanded capabilities
- Using smaller teams
While coming to the topic of how Model Based Design is useful in the automotive industry and especially for Electric and Hybrid Vehicles. Model based design provides a single environment for managing a multi-domain complex system. It facilitates iterative modelling and elaborate designing of the system. Also with MBD there is Continuous verification and Validation done throughout the development process which not only reduces errors but also reduces the development time. Model can be developed for the following systems in EV and HEV
- Component performance
- Battery pack sizing
- Range and Power estimation
- Vehicle performance
- BMS and Motor Controllers
STEPS TO MODEL BASED DESIGNING AND IMPLEMENTATION
When it comes to System level implementation of MBD number of factors are to be considered :
- Mathematical complexity: How detailed or how simple your model needs to be. Suppose if you are to test only a certain important parameters of the system you can develop a simple model with less complexity and which can provide you the expected results. The more real world like your model is the more complex it gets.For example: The DC motor control is simpler compared to an AC motor control. Hence reducing computation time.
- Requirements: The user needs to decide what are the inputs and outputs in the system. The user must consider the factors on which the system reacts and also which all factors to neglect.
- System-level realization: Another important factor to keep in mind that most of the models developed are not stand-alone and are depended on other systems as well. For example: A battery doesn’t only drive the motor but also powers other peripherals such as Headlights,
- System integration : The next step would be to integrate various systems either by creating a test setup or an experimental rig.
- Power management strategy: A challenge in hardware implementation is the Power management and wiring. For example if a system consists of various inputs(Sensors) and outputs (actuator) then it must be ensured that each component has the required power supply and that no two wires are short.
- Controller design:One needs to not only select the right peripherals of the system but also ensure that the controller being used i compatible with all the subsystems. Other factors to be considered are processing speed, I/O ports, Communication protocol, etc. Once the algorithm is developed it is tested on a target hardware. Various iterations are performed and the bugs are removed.
- Verification and validation: Verification and validation is to be done at every step. The system needs to be checked multiple times and at various stages to reduce errors and minimize the development time.
Since we have talked a lot about what MBD is and how it works next we would look into some examples which can give a better insight to Model Based Design. The below diagram shows the concept of switching logic in a Hybrid electric vehicle and how it can be implemented in Simulink.
Given below is another example of how a complete vehicle system can be modeled.
- Saurabh Mahapatra, Tom Egel, Raahul Hassan, Rohit Shenoy, Michael
Carone “Model-Based Design for Hybrid Electric Vehicle Systems “
Mathworks Inc , 2008