IIT Madras Thesis

Hybrid Powertrain Modelling & Control for a Two Wheeler Application

This was my thesis at IIT Madras that contributed towards my Mechanical Engineering undergrad degree. I worked on this with Prof. A. Ramesh and Dr. M. Mittal at the IC Engines Lab at IIT Madras. Here is a brief overview of what I worked on. If you are interested in any of the details don't hesitate to drop me a mail/message!

Keywords: Physics based modelling, Dynamic Programming, Optimal Control, Hybrid powertrains

Engine Modeling

The first part of the project was modelling the engine and it's peripheral systems using a first principles approach. I wanted to predict the performance and emissions over each cycle of the engine. I coded up the whole simulation in MATLAB, the important part was that the simulation provides crank angle resolved data.

Although the final simulation was zero dimensional (no spatial resolution), I did generate some cool animations while calculating a few areas!

I was pleasantly surprised by how nicely this animation came out from a MATLAB figure window.

After putting the whole simulation together, running tests, debugging it, and finally tuning (& retuning) it based on experimental data, I was ready to move to the next part of the powertrain, the three way catalytic converter.

I also found that it would be useful if this MATLAB based simulation of the engine was available as a custom Simulink block, so after a few modifications I had a Simulink simulation of the engine (and catalytic converter).

At the end I had a simulation that looked pretty much like this.

Three Way Catalyst Modeling

The next module of the hybrid powertrain that I modelled was the three way catalytic converter. Incorporating the Langmuir Hinshelwood reaction mechanism for the surface reactions was important to get the sensitivity on the catalyst temperature and also model the light-off characteristics. With the model, I know I got some pretty plots!

Dynamic Programming for Torque Split

In parallel hybrid topologies, i.e. both the combustion engine and electric motor can directly drive the vehicle. This means, that to provide the same acceleration (that the driver commands), there are multiple solutions for how the torque can be split between the engine and the motor.

For example, a 50-50 split or a 35-65 split can both provide the commanded acceleration. The question now arises, "How should the optimal split be chosen?" and then subsequently, "What exactly does optimal mean?"

Dynamic programming is used as a discrete acausal controller for the optimal torque split over a finite horizon. The DP controller pics the optimal split and can be used to make design decisions on the topology.

Topology Comparison

Using the dynamic programming torque split controller with a chosen metric for the meaning of "optimal" - a combination of fuel efficiency and tailpipe emissions, I compared two proposed topologies for a P2 hybrid vehicle.

I also analyzed 3 different modes of operation of this hybrid vehicle,

Conserve Mode: The IC engine and electric motor work together to propel the vehicle in the optimal trajectory.
Charge Mode: The IC engine generates more power than needed to move the vehicle, the excess power is used to charge the battery to a target setpoint.
Combustion Only Mode: Only the IC engine propels the vehicle.
Electric Only Mode: Only the electric motor propels the vehicle.

The final simulation of the whole hybrid powertrain had this layout, with those inputs and outputs finally used to determine the better topology.

All figures are mine.

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