(18)Module 2: Final Project-2 ---> Design of an Electric Vehicle

                                                            Module 2: Final Project ----> Design of an Electric Vehicle

 

Problem Statement: 

Create a MATLAB model of an electric car that uses a battery and a DC motor. Choose suitable blocks from the Powertrain block set. Prepare a report about your model including the following:

Objectives: 

       1. System-level configurations

       2. Model parameters

       3. Results

       4. Conclusion

 

Answer: 

An electric car is a car that is propelled by one or more electric motors, using energy stored in rechargeable batteries. Compared to internal combustion engine (ICE) vehicles, electric cars are quieter, have no exhaust emissions, and lower emissions overall. In the United States, as of 2020, the total cost of ownership of recent EVs is cheaper than that of equivalent ICE cars, due to lower fueling and maintenance costs. Charging an electric car can be done at a variety of charging stations; these charging stations can be installed in both houses and public areas.

Several countries have established government incentives for plug-in electric vehicles, tax credits, subsidies, and other non-monetary incentives. Several countries have established a phase-out of fossil fuel vehicles, and California, which is one of the largest vehicle markets, has an executive order to ban sales of new gasoline-powered vehicles by 2035.

The Tesla Model 3, which has a maximum range of 570 km (353 miles) according to the Environmental Protection Agency EPA, has been the world's best-selling electric vehicle (EV) on an annual basis since 2018 and became the world's all-time best-selling electric car in early 2020.

As of December 2019, the global stock of pure electric passenger cars totalled 4.8 million units, representing two-thirds of all plug-in passenger cars in use. In 2019, over half (54%) of the world’s all-electric car fleet was in China. Despite rapid growth, the global stock of fully electric and plug-in hybrid cars represented about 1 out of every 200 vehicles (0.48%) on the world's roads by the end of 2019, of which pure electrics comprised 0.32%. 

India is also picking up pace with the west worlds as the market is becoming is very competitive, more car manufacturers are shifting their focus on EVs, to make them more cost-effective to their customers. Some of the existing EVs in the market are Tata Neoxon EV, MG ZS EV, Hyundai Kona EV, etc. Here, I have tried to match the vehicle dynamics of the Tata Nexon EV in my project, up to a certain extent like giving it the same kerb weight, Motor design, Battery capacity, etc. Although, it is to be noted that this model does not resemble that closely to the said EV car, but just a practical approximation of how a practical car of random but near-realistic parameter values would behave. 

Now, in this project, to satisfy the objectives I have presented the same by giving all the necessary ideas about every important component of an EV, and also their representation and all the needed plots and data are given. The key representations can be narrowed down to some handful of points:

• A simple and low run time model of an electric car using SIMULINK is developed.
• To examine the various performance characteristics such as Speed Comparison between the Drive cycle and the Vehicle, State of Charge, Current, and so on.
• To manipulate certain design parameters such as Motor Power, Vehicle Body Design Constraints including Gear-box, Battery Capacity, etc, and to explore the results of the change in these parameters.
• Finally, to construct the EV model in such a way that it behaves similarly to an actual model, which can be realized in a practical set-up also.

 

Brief Discussions about EV components: 

            

 

Basic Block Diagram:        

 

 

Traction Battery Pack: The function of the battery in an electric car is as an electrical energy storage system in the form of direct-current electricity (DC). If it gets a signal from the controller, the battery will flow DC electrical energy to the inverter to then be used to drive the motor. The type of battery used is a rechargeable battery that is arranged in such a way as to form what is called a traction battery pack. There are various types of electric car batteries. The most widely used is the type of lithium-ion batteries.

 

                               Typical EV Battery pack

 

TATA Nexon EV Battery pack 

 

Power Inverter: The inverter functions to change the direct current (DC) on the battery into an alternating current (AC) and then this alternating current is used by an electric motor. Also, the inverter on an electric car has a function to change the AC when regenerative braking to DC and then used to recharge the battery. The type of inverter used in some electric car models is the bi-directional inverter category.

                    Typical EV Power-Inverter  

 

Controller: The main function of the controller is as a regulator of electrical energy from batteries and inverters that will be distributed to electric motors. While the controller itself gets the main input from the car pedal (which is set by the driver). This pedal setting will determine the frequency variation or voltage variation that will enter the motor, and at the same time determine the car’s speed. In brief, this unit manages the flow of electrical energy delivered by the traction battery, controlling the speed of the electric traction motor and the torque it produces. This component will determine how electric cars work.

       Typical EV Motor Controller  

 

TATA Nexon EV Power Electronics Hub

 

Electric Traction Motor: Since the controller provides electrical power from the traction battery, the electric traction motors will work turning the transmission and wheels. Some hybrid electric cars use a type of generator-motor that performs the functions of propulsion and regeneration. In general, the type of electric motor used is the BLDC (brushless DC) motor.

Typical EV Traction Motor 

 

 

TATA Nexon EV Traction Motor 

 

 

                                    Working of a brushed DC Motor 

Other Secondary Electric Car Components: 

Charger: It is a battery charging device. Chargers get electricity from outside sources, such as the utility grid or solar power plants. AC electricity is converted into DC electricity and then stored in the battery. There are 2 types of electric car chargers:

• On-board charger: the charger is located and installed in the car
• Off-board charger: the charger is not located or not installed in the car.

               Nexon EV Charger 

 

Transmission: The transmission transfers mechanical power from the electric traction motor to drive the wheels. All-electric vehicles have an automatic gearbox or automatic transmission. Some also provide different driving modes which are tuned with the gearbox.

 

DC/DC Converter: This one of the electric car parts that convert higher-voltage DC power from the traction battery pack to the lower-voltage DC power needed to run vehicle accessories and recharge the auxiliary battery.

                           EV DC-DC Converter 

Battery: In an electric drive vehicle, the auxiliary battery provides electricity to power vehicle accessories.

 

Thermal System for Cooling: This system maintains a proper operating temperature range of the engine, electric motor, power electronics, and other components.

 

Thermal Cooling System 

 

Charge Port: The charge port allows the vehicle to connect to an external power supply to charge the traction battery pack. It comes with a standard 230 V/ 50 Hz rating and also has an option for DC fast charging.

                     Nexon EV Charging Port 

 

 

Representation Of The EV Model In MATLAB Simulink: 

 

 

 

Final EV Model Unmasked 

 

 

 

Final EV Model Masked 

 

Individual Subsystems & Blocks:  

 

Drive Cycle Source: 

This block generates a standard or user-specified longitudinal drive cycle. The block output is the specified vehicle longitudinal speed, which you can use to:

                  

 

Longitudinal Driver:  

          

This block implements a longitudinal speed-tracking controller. Based on reference and feedback velocities, the block generates normalized acceleration and braking commands that can vary from 0 through 1. You can use the block to model the dynamic response of a driver or to generate the commands necessary to track a longitudinal drive cycle.

External Actions parameters can be used to create input ports for signals that can disable, hold, or override the closed-loop acceleration or deceleration commands. The block uses this priority order for the input commands: disable (highest), hold, override.

However, in this model, we have not considered any external actions to simplify the model.

The controller type is set to Proportional-integral (PI) control with tracking windup and feed-forward gains. To compare how the tuning parameters affect the output results two different sets of values are given two them and they are compared to each other and the best one is considered. Proportional Gain (Kp) is set to 5 & 13, whereas the Integral Gain (Ki) is set to 1 & 8. This tuning of the controller is done to help the vehicle follow the Drive Cycle to the greatest possible extent.

The shift type is set to none which represents 'No transmission'. Block outputs a constant gear of 1.This setting is used to minimize the number of parameters we need to generate acceleration and braking commands to track forward vehicle motion. This setting does not allow reverse vehicle motion.

                   

 

Electric Motor Drive: 

 

Controlled Voltage Source: This block represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current flowing through the source. The output voltage is V = Vs, where Vs is the numerical value presented at the physical signal port. The block has one physical signal input port and two electrical conserving ports associated with its electrical terminals.

We have used two Controlled Voltage Source blocks. The outputs associated with the Longitudinal Driver are fed as input to each of the two Controlled Voltage Source blocks, through the physical signal input port. The Controlled Voltage Source blocks generate an output voltage proportional to the Acceleration and Deceleration signals provided by the Longitudinal Driver.

The positive terminal of the Controlled Voltage Source block provided with the Acceleration input signal is connected to the positive reference of the Controlled PWM Voltage block, whereas the negative terminal is grounded to an Electrical Reference block.

The negative terminal of the Controlled Voltage Source block provided with the Deceleration input signal is connected to the Brake port of the H-Bridge block, whereas the negative terminal is grounded to an Electrical Reference block.

 

Controlled PWM Voltage: This block represents a pulse-width modulated (PWM) voltage source. It creates a Pulse-Width Modulated (PWM) voltage across the PWM and REF ports. The block calculates the duty cycle based on the reference voltage across its ref+ and ref- ports. The output voltage is zero when the pulse is low and is equal to the Output voltage amplitude parameter when high.

We have set the simulation mode to 'Average' to speed up simulations. This applies the average of the demanded PWM voltage to the motor. The Averaged mode assumes that the impedance of the motor inductive term is small at the PWM frequency. The averaged model also helps in linearising the model. We can only linearize the block for inputs corresponding to a duty cycle greater than zero and less than 100 per cent. The PWM frequency was 5KHz. 

            

 

H-Bridge: The H-Bridge block represents an H-bridge motor driver. The block has the following two Simulation mode options:

1. PWM — The H-Bridge block output is a controlled voltage that depends on the input signal at the PWM port. If the input signal has a value greater than the Enable threshold voltage parameter value, the H-Bridge block output is on and has a value equal to the value of the Output voltage amplitude parameter. If it has a value less than the Enable threshold voltage parameter value, the block maintains the load circuit using one of the following three Freewheeling mode options:

 

Simulation Solver:  The simulation solver was chosen the same as the default setting it has i.e variable step and it automatically selects the solver which fits best regarding the Simulink model being simulated. The EV model was simulated for 1400 seconds for a better understanding of its behaviour.

          

 

The Simulink model for the EV can be accessed from the following link: Final EV Model

Output Results:  

Comparison Between Drive Cycle Data and Vehicle Data: 

This is the most important verification tool by which it can be determined if the model is being successfully simulated or not. Also, to witness the effect and importance of tuning the PI controller in the Longitudinal Driver block are given two separate values at two different times. 

*PI: KC=5 & KI=1---> 

Fig-1 

 

      Fig-2 

 

     Fig-3 

 

 

                                       &  Fig-4 

From Fig-1, we can see that the vehicle tries to replicate the same as the drive cycle input and it does its job well most of the times but fails at the times when the vehicle is at rest. If you look closely at Fig-2 then it can be found that it comes to rest at the very last moment and from Fig-3 it is easily seen that the vehicle did not even come to rest and later tries to catch the up speed of the drive cycle. Also, from Fig-4 we can clearly see that vehicle travels more distance than the given drive cycle as the input. We can clearly state that because this vehicle not coming to rest properly and not so good tuning parameters are to blame for this. 

 

 

**PI: KC=13 & KI=8---> 

 Fig-5  

 

Fig-6 

 

 

 Fig-7 

 

                                 & Fig-8  

 

 

 From Fig-5, we can see that tuning is quite good that is why the vehicle's speed data line coincides with the drive cycle data and because the latter one is overlapping the former one; only one data line can be seen. But if we zoom in as we did in Fig-6, we can see the tuning is surely improved with the changed values that is why the vehicle is coming to rest very quickly most of the times as expected from its side. Now, the zoomed-in output Fig-7 can be compared with the previous Fig-3 and by doing so it can be easily found out that the vehicle is following the drive cycle quite well. Finally, from Fig-8 we can clearly see that the covered distances are the same for both the drive cycle and vehicle. So, we can say that with the second set of PI values the Objective is completed, by developing an EV model in Simulink.

 

Other Outputs for the best performing model: 

SOC Status: 

Fig-9 

The State Of Charge(SOC) of the vehicle's battery after the approximately 12Kms travelling is down to 97.2% from its initial 100% charge. This gives us a rough idea that the vehicle will go 400Kms approximately at one single charge i.e from 100% to 0%.

Distance Travelled Graph: 

    Fig-10 

This graph shows at what point of time the vehicle is travelled how much distance altogether. This helps to understand the vehicle's speed behaviour over time.

 

Battery Current: 

Fig-11 

 

The above figure shows the battery currents reading of the vehicle over time. By taking a look at the current reading we can tell if the vehicle is speeding up or slowing down. The current varies from +115 Amps to - 108 Amps. Here. negative current means regenerative braking.

 

Conclusions: The Output results proclaims that the vehicle design parameters related to the Electric Motor Drive, Vehicle Body and Battery Module have to be tweaked appropriately to ensure that the vehicle follows the drive cycle as efficiently as possible. This Model is Developed by taking some bits of information from TATA Nexon EV and the focus is concentrated on making the EV model as much practical as it can be. Two types of tuning are given here to understand the tuning effect and the best tuning parameters are chosen arbitrarily by using the trial and error method. Hence, The EV model is successfully simulated and the given objectives have been addressed in this project analysis. 

References: 

1. https://en.wikipedia.org/wiki/Electric_car#:~:text=An%20electric%20car%20is%20a,emissions%2C%20and%20lower%20emissions%20overall.
2. Tata builds a Nexon EV. EDIT: Launched at ₹13.99 lakhs - Page 23 - Team-BHP
3. https://en.wikipedia.org/wiki/FTP-75
4. https://www.treehugger.com/how-inverters-and-converters-work-85612
5. http://media3.ev-tv.me/gevcumanual6.pdf
6. https://en.wikipedia.org/wiki/Electric_motor
7. https://in.mathworks.com/help/vdynblks/ref/longitudinaldriver.html#:~:text=The%20Longitudinal%20Driver%20block%20implements,vary%20from%200%20through%201.
8. https://in.mathworks.com/help/physmod/sps/ref/battery.html
9. https://books.google.co.in/books?id=T2PRDwAAQBAJ&pg=PA387&lpg=PA387&dq=This+block+represents+the+electrical+and+torque+characteristics+of+a+DC+motor.+The+block+assumes+that+no+electromagnetic+energy+is+lost,+and+hence+the+back-emf+and+torque+constants+have+the+same+numerical+value+when+in+SI+units.+When+a+positive+current+flows+from+the+electrical+%2B+to+-+ports,+a+positive+torque+acts+from+the+mechanical+C+to+R+ports.+Motor+torque+direction+can+be+changed+by+altering+the+sign+of+the+back-emf+or+torque+constants.&source=bl&ots=zeli3CzrzL&sig=ACfU3U2hxcEVgf7I69vHO_Z_LVT0GXu-fA&hl=en&sa=X&ved=2ahUKEwjCvuqj_pPwAhX2zDgGHSlqCdcQ6AEwBXoECBQQAw#v=onepage&q=This%20block%20represents%20the%20electrical%20and%20torque%20characteristics%20of%20a%20DC%20motor.%20The%20block%20assumes%20that%20no%20electromagnetic%20energy%20is%20lost%2C%20and%20hence%20the%20back-emf%20and%20torque%20constants%20have%20the%20same%20numerical%20value%20when%20in%20SI%20units.%20When%20a%20positive%20current%20flows%20from%20the%20electrical%20%2B%20to%20-%20ports%2C%20a%20positive%20torque%20acts%20from%20the%20mechanical%20C%20to%20R%20ports.%20Motor%20torque%20direction%20can%20be%20changed%20by%20altering%20the%20sign%20of%20the%20back-emf%20or%20torque%20constants.&f=false
10. https://in.mathworks.com/help/physmod/sdl/ref/tiremagicformula.html
11. https://in.mathworks.com/help/physmod/sdl/ref/vehiclebody.html#:~:text=The%20Vehicle%20Body%20block%20represents,of%20wheels%20on%20each%20axle.&text=The%20block%20accounts%20for%20body,to%20acceleration%20and%20road%20profile.
12. (1) Modeling of Electric Vehicles using MATLAB & Simulink - (Part-2) - YouTube