Week-6 Challenge: EV Drivetrain
4. Explain in brief the author’s perspective.
In that odious world of gas-powered vehicles, engines are not all alike. There are flat-heads, Hemis, straight, opposed, and V configurations. And on and on. One would have thought that, years ago, someone would have figured out which was best. That would have ended all the choices and thereafter, only the best engine type would be in production. Not so. There is no one best engine type; rather, there are different types of engines to suit personal requirements, such as price and performance. This is also true for electric vehicles.
Back when I had hair on my head and carried a slide rule, there were lead-acid batteries, DC brush motors, and contactor controllers. Today, none of these remain (including my hair). Lead has been replaced by lithium and DC by either DC brushless or induction. Contactors, meanwhile, have given way to modulating inverters. So, will each of these elements also become obsolete in the near future or is it possible that some “stability” may be at hand? Without a good crystal ball, it is hard to predict the future. My guess, however, is that we will see both induction and brushless machines “duke it out” for many years to come. Each will have its loyal proponents and religious detractors.
A Closer Look
So what are these two technologies? How do they work? What differentiates them? And what do they have in common? Let’s start with DC brushless drives.Let’s move on to induction motor drives. A forerunner of the 3-phase induction motor was invented by Nikola Tesla sometime before 1889. Curiously, the stators for the 3-phase induction motor and the DC brushless motor are virtually identical. Both have three sets of “distributed windings” that are inserted within the stator core. The essential difference between the two machines is with the rotor.When a 3-phase induction motor is connected to utility-type 3-phase power, torque is produced at the outset; the motor has the ability to start under load. No inverter is needed. (Were an inverter needed, Tesla’s invention would have been useless until sometime in the 1960s.) The fact that induction motors are directly compatible with conventional utility power is the main reason for their success. In contrast, a brushless DC motor produces no starting torque when directly connected to fixed-frequency utility power. They really need the aid of an inverter whose “phase” is maintained in step with the angular position of the rotor.
While 3-phase induction motors have great utility, they also have some severe limitations. They cannot operate from DC; AC is a must. Shaft speed is proportionate to line frequency. Hence, when used with utility power, they are constant-speed machines. Finally, when operated from utility power, they have limited starting torque and somewhat limited running peak torque capabilities when compared to DC-type machines.
1. Which types of power converter circuits are employed in electric and hybrid electric vehicles?
Electric and hybrid electric vehicles (EVs and HEVs) utilize various types of power converter circuits to manage the flow of electrical energy between the battery, motor, and other components. The main types of power converter circuits used in these vehicles are:
1. DC-DC Converters:
**Step-Down (Buck) Converters**: These converters reduce the voltage from the high-voltage battery pack to lower voltages needed for various vehicle subsystems, such as the 12V battery used for lighting, infotainment, and other accessories.
Step-Up (Boost) Converters: These converters increase the voltage when necessary, for instance, to supply high voltage to the motor from a lower voltage source.
Buck-Boost Converters: These can either increase or decrease the voltage, providing flexibility for different operational needs.
2. DC-AC Inverters:
These inverters convert DC power from the battery to AC power to drive the electric motor. In EVs, the motor typically operates on AC power, so inverters are crucial for propulsion.
There are different types of inverters used, such as voltage source inverters (VSIs) and current source inverters (CSIs), with VSIs being more common due to their efficiency and control characteristics.
3. AC-DC Converters:
These converters, also known as rectifiers, are used to convert AC power from the grid to DC power for charging the vehicle's battery. They are integral to the onboard charger in EVs and HEVs.
4. Bidirectional Converters:
These converters can operate in both directions, allowing for the transfer of energy to and from the battery. They are used in regenerative braking systems, where the kinetic energy of the vehicle is converted back into electrical energy and stored in the battery.
5. **Onboard Chargers**:
Onboard chargers are specialized AC-DC converters that manage the battery charging process from external AC power sources. They include power factor correction (PFC) circuits to ensure efficient energy use and compliance with power quality standards.
6. Motor Controllers:
Motor controllers, which include inverters, manage the delivery of power to the electric motor based on driving conditions and driver input. They handle functions such as torque control, speed control, and regenerative braking.
### Key Functions of Power Converter Circuits:
**Voltage Regulation**: Ensuring the correct voltage levels are supplied to various components.
Power Management: Efficiently managing the distribution and flow of electrical power within the vehicle.
Energy Conversion: Converting electrical energy between different forms (DC to AC, AC to DC) as required by different components.
**Regenerative Braking**: Capturing and converting kinetic energy back into electrical energy to recharge the battery.
**Charging Management**: Safely and efficiently charging the vehicle’s battery from external power sources.
These power converter circuits are critical for the efficient and reliable operation of electric and hybrid electric vehicles, enabling them to meet performance requirements while optimizing energy use.
3. Develop a mathematical model of a DC motor for the below equation using Simulink.
`omega`= V/K`phi` -Ra/K`phi`^2 .T
To develop a mathematical model of a DC motor using Simulink based on the given equation:
\[ \omega = \frac{V}{K\phi} - \frac{R_a}{K\phi^2} \cdot T \]
where:
- \(\omega\) is the angular speed of the motor,
- \(V\) is the input voltage,
- \(K\) is the motor constant,
- \(\phi\) is the magnetic flux,
- \(R_a\) is the armature resistance,
- \(T\) is the torque,
we can proceed as follows:
1. **Rearrange the equation** to simplify the model representation:
\[ \omega = \frac{V}{K\phi} - \frac{R_a T}{K \phi^2} \]
2. **Simulink Model Components**:
- **Input voltage (V)**
- **Torque (T)**
- **Constants \(K\), \(\phi\), and \(R_a\)**
- **Blocks for mathematical operations** to perform division, multiplication, and subtraction.
### Steps to Create the Simulink Model:
1. **Open Simulink and Create a New Model**:
- Open MATLAB and type `simulink` in the Command Window.
- Click on "Blank Model" to create a new Simulink model.
2. **Add Input Blocks**:
- Drag and drop two "Constant" blocks from the Simulink library. These will represent the input voltage \(V\) and the torque \(T\).
3. **Add Gain Blocks**:
- Drag and drop two "Gain" blocks. These will be used to implement the constants \(\frac{1}{K\phi}\) and \(\frac{R_a}{K\phi^2}\).
4. **Add Mathematical Operation Blocks**:
- Add two "Product" blocks to perform the multiplication operations.
- Add one "Sum" block to perform the subtraction.
5. **Configure the Blocks**:
- Set the first "Constant" block value to \(V\) and label it as "Input Voltage".
- Set the second "Constant" block value to \(T\) and label it as "Torque".
- Set the first "Gain" block value to \(\frac{1}{K\phi}\).
- Set the second "Gain" block value to \(\frac{R_a}{K\phi^2}\).
6. **Connect the Blocks**:
- Connect the "Input Voltage" block to the first "Gain" block.
- Connect the output of the first "Gain" block to the first input of the "Sum" block.
- Connect the "Torque" block to the second "Gain" block.
- Connect the output of the second "Gain" block to the second input of the "Product" block.
- Connect the output of the "Product" block to the second input of the "Sum" block.
7. **Add Output Block**:
- Add a "Scope" block or a "Display" block to visualize the output angular speed \(\omega\).
8. **Arrange and Label the Blocks**:
- Arrange the blocks neatly and label them appropriately for better readability.
### Simulink Model Diagram
The resulting Simulink model will look something like this:
```
[Input Voltage] --- [Gain (1/Kϕ)] ---+
|
[Sum] --- [Output (ω)]
|
[Torque] --- [Gain (Ra/Kϕ^2)] --- [Product]
```
### Configuring Blocks in Detail:
- **First Gain Block**:
- Set the gain value to \(\frac{1}{K\phi}\).
- **Second Gain Block**:
- Set the gain value to \(\frac{R_a}{K\phi^2}\).
### Running the Simulation:
1. **Set Simulation Parameters**:
- Go to `Simulation` -> `Model Configuration Parameters` and set the appropriate solver and simulation time.
2. **Run the Simulation**:
- Click on the "Run" button in the Simulink toolbar to execute the simulation.
3. **Observe Results**:
- Use the "Scope" block or "Display" block to observe the angular speed \(\omega\) of the motor.
This model represents the given equation in Simulink, allowing you to simulate the behavior of the DC motor under various input conditions.