Service-Learning Model: An Example

This article is a follow-up of the previous "A Service Learning Model" post. The model suggests interdisciplinary engineering students working on real-life projects that benefit the communities.

Earlier we talked about how this model is useful in three ways:
1. BITSians learn to work on real-life projects that have customer requirements, deadlines and the most essential aspect of engineering: design, build and test.
2. The needy communities benefit from the delivered products, so BITSians help the society around them.
3. BITSians make industry connections so that they share a great relationship at the time of internships, placements.

As an added advantage, such project provides a great platform to strengthen students' skills and resumes. This model, truly has an enormous potential to become one-of-its-kind in India to be implemented exclusively by BITS, just like our renowned Practice School program.

Now, let's consider an example of such a project:
   
Primary/High school children learn basics of physics, biology and solar system roughly in their 1st to 7th standard. It'll be an interesting exercise to create models to teach them basic concepts through interactive mechanical models with which they can play around. To take an example, one project can be to demonstrate operations of a biological cell with the help of a workshop-fabricated model with microcontroller-based sound system, LCD displays and rotation mechanism. This model can be an excellent exhibit in a local science museum. This will benefit the children around BITS campus.
  
 Let's break it down to see what the project components are. Firstly, this project has a great interdisciplinary aspect to it. BITSians from various engineering and science major can contribute. The mechanical subteam can handle: the choice of material, fabrication of the model, fitting various parts to it and mechanical movement capabilities. The electrical subteam can take up microcontroller programming, motor and LCD interfacing and power management. The biology subteam can help with the biological processes within a cell and help draw a skeleton of the model and its intended functionalities. Folks interested in project management can work on the plan, timeline, keeping everyone on track and community/industry communication. They can also apply for industry grants and gather support from local administration.

----There are tons of exciting tasks with each project and each task cultivates a skill that is very useful in post-graduation (industry) life.

More on this model with some more examples in future posts.... Stay tuned!


 

The Electric Motor

Hey Guys,

The third most important part of an electric vehicle is the electric motor. There are tons of books and online material on electric motors and hence I will not go into the mathematical details of it. You guys will learn the basics of electric machines in your ES2 (Electrical Sciences 2) course and I urge you to do that sincerely (even if you do not like the text book! :))

Today I will try to give you some pointers on electric motors so that we can  directly jump into modeling of all these components

You may want to be conversant with the following if you want to excel in this field

1. AC Induction Motors (3ph, Single phase)
2. Brushed DC motors and Brushless DC motors
3. Permanent magnet motors
4. Differences between the above three
5. Theory of Induction (stator/ rotor construction, importance of air gap, winding patterns etc)
6. Equivalent circuits of induction motors (very important)
7. Finite Element analysis of Motors (to calculate fundamental parameters like resistances and inductance which are used in motor control)
8. Motor Control Basics

A few of the good resources that I know are:

1. MIT Open course ware for Electric machines:
2. NPTEL: Electrical Machines 1, 2,3courses: 

     Books:

1. Electric Motors and Drives by Austin Hughes
2. Induction Motor Control Design by Riccardo Marino et al. (advanced book)
3. Motors and Drives (A practical Technology Guide) by Dave Polka  

I would say this should get you started on electric motors. Your aim should not be memorizing equations and solving problems, but to understand the induction concept and modeling a motor in MATLAB. I will briefly go over MATLAB modeling later

The Motor Controller

Before we looked why electric vehicles are important, the architecture of an electric vehicle and started looking at the components of the electric powertrain. Last time we saw the battery management controller and its functions. Today we will glance over the motor controller.

Similar to the BMS (Battery management system) which manages the interaction of the battery with various other components of the powertrain, the motor controller manages the interaction of the motor with the battery and rest of the vehicle. In most of the electric vehicles the motor used is 3ph AC induction motor. You should be studying this in your ES2 (Electric sciences 2) course in second year. AC motor is used because it has many advantages, the most important being high efficiency and low maintenance. Now this being a “3ph-AC” motor, it requires 3ph AC current whereas the battery outputs DC current. Hence there is a need of an “Inverter” in between the battery and the motor which converts DC current into AC current and the role of the motor controller is to control the functionality of this inverter.

The control action

The most important function of the motor controller is the 3ph AC current generation. Without going into detail mathematics, I would say that this is achieved by transforming the  current vector by a series of transformations, controlling their magnitudes by tuned controller gains and feeding them to the IGBTs of the inverter to convert them in 3ph-AC. 

So to be more specific the motor controller does the following things

1. It measures the fed back current and the speed (RPM) of the motor via appropriate sensors. 
2. It takes in these values and applies a few transformations transform these quantities into quantities that are easy to control. The controller uses Clarke and Park transformations.
3. The PI (proportional-Integral) controller compares these values with the ideal values which are generated from the pedal position. (More the pedal is pressed, more velocity/ power is requested and hence more magnitude of AC current is needed). 
4. This controller outputs corresponding voltages that would be required to generate appropriate PWMs for the 3 phases. 
5. These voltages are then passed in a SVPWM (Space vector PWM) algorithm coded inside this controller which gives out the 3 ph PWM signals, which are in turn fed to the IGBTs with the DC current from the battery to generate the correct 3ph AC currents. This current is then fed to the motor windings to generate torque.

Hence the motor controller is a closed loop controller which ensures the correct 3ph currents are generated to achieve the requested torque and power levels.

If you guys want to go deeper into the design of motor controller you should be aware of the following things

1. Clarke/ Park transformations
2. Feedback controller design (PI, LQR)
3. Space Vector PWM techniques
4. Inverter (IGBT) Electronics
5. Field Weakening algorithms etc.

I will try to give you brief information on these to give you a head start for the intereseted. Tons of information is available on motor control techniques online. This is a very well developed area and it should not be difficult to find research papers on this. I think Texas A&M university in the US has a good research lab on motor controls.