Final Project: Design of an Electric Vehicle

AIM OF THE PROJECT: Modelling an Electric Vehicle in MATLAB using a Battery and a DC Motor.

OBJECTIVES: To create a Matlab-Simulink model for analysing the behaviour of an Electric Vehicle which includes the following purpose:

• System Level Configurations
• Model Parameters
• Results
• Conclusion

INTRODUCTION:

 Just as there are a variety of technologies available in conventional vehicles, Electric Vehicles(EVs) have different unique capabilities that can effectively serve the needs of the drivers. A major feature of the EV's is that drivers can plug them in so as to get charge from an off-board electric power source. This distinguishes them from the Hybrid EVs(HEV) which consists of an internal combustion engine along with the battery power but cannot be plugged in. Fueling with electricity offers some advantages which are not present in conventional internal combustion engine vehicles and it is due to the fact that as Electric Motors react quickly, so EVs are very responsive and can able to provide a good torque along with higher efficiency. There are two basic types of EV's which are as follows:

• All-Electric Vhicles(AEV)
• Plug-in Hybrid Electric Vehicles(PHEV)

AEVs most generally includes Battery Electric Vehicles(BEVs) and Fuel Cell Electric Vehicles(FCEVs). In addition to charging from the electric grid, both types are charged in part by Regenerative Braking which basically generates electricity from some of the energy normally lost due to the Braking phenomena. AEVs are gradually runs only on eletricity, most of them have an all-electric ranges of 80-100 miles while a few luxury vehicles have ranges upto 250 miles. When the battery is depleted, it can take from 30 minutes(with fast charging) upto nearly a full day(with Level 1 charging) to get recharge depending on the type of charger and the battery.  

Whereas PHEVs runs on electricity for shorter ranges(6-40 miles) but has the ability to switch over to an internal combustion engine which runs on gasoline when the Battery is depleted. This flexibilty of PHEVs allows drivers to use electricity as per requirements while also being able to fuel up with gasoline if needed. Thus, powering the vehicle with electricity from the grid reduces fuel costs, cut petroleum consumption and reduces emissions to a greater extent than other conventional vehicles.

In India, the first concrete decision to incentivise electric vehicles was taken in 2010. According to a 95 crore sceme approved by the Ministry of New and Renewable Energy(MNRE), the governments announced a financial incentive for manufacturers of electric vehicles to be sold in India. In 2013, India unveiled the 'National Electric Mobility Mission Plan(NEMMP) 2020' to make a major shift to electric vehicles and to address the issues of national energy security, vehicular pollution and growth of domestic manufacturing capabilites. This plan was mostly remained on papers but while presenting the Union Budget for 2015-16 in Parliament, then finance minister Arun Jaitley announced faster adoption and manufacturing of electric vehicles(FAME) with an initial outlay of Rs 75 crore. In 2017, Transport Minister Nitin Gadkari made a statement showing India's intent to move to 100 percent electric cars by 2030, which later diluted to 30 percent from 100 percent.

Various Components of Electric Vehicles:

The Schematic Diagram of an Electric Vehicle is shown in the figure below:

and the corresponding Block Diagram of the entire Electric Vehicle setup is shown below:

• Battery Pack: The function of the Battery in an Electric Car is as an electric storage system in the from of Direct -Current Electricity. If it gets a signal from the controller, the battery will flow DC electrical energy to the Inverter which is then be utilised to drive the motor. The type of battery used is a rechargable battery that is arranged in a stack fashion so as to from what is called a Traction Battery Pack. There are various types of Electric Car Batteries and the most widely used is the Lithium-Ion batteries becuse of its capabilty of having very high power to weight ratio. This type of electric car battery posseses high energy efficiency along with high performance at higher temperatures. This type of battery has a greater energy ratio per weight- a parameter that is very important for electric car batteries.

                    

                                                                    Battery Pack of Audi E-tron.

                              

                                                     Advatages of Lithium-Ion Battery Pack.

 

• Power Inverter: The DC supplied by the Battery Pack is then converted to AC and supplied to the Electric Motor. This power transfer is managed by a sophisticated motor control mechanism(also referred to as Powertrain Electronic Control Unit) that controls the frequency and magnitude of the voltage supply to the Electric Motor in order to manage the speed and the acceleration as per Driver's instructions communicated via acceleration/brakes. In addition, the inverter on an electric car also has a function to change the AC current when Regenrative Braking is taking place to DC current and then used to recharge the battery.

                       

                                                       Pules Controlled Power Inverter of Audi Q5 quattro(Hybrid)

 

• Controllers: As the control tower of all electric power control systems of the vehicle, the controller and its unit aslo known as VCU(Vehicle Control Unit) is arguably the most important component of the EPCU(Electric Power Control Unit). EPCU is an efficient integration of nearly all devices that control the flow of electric power in the vehicle. It consists of the Inverter, Low Voltage DC-DC Converter(LDC) and the VCU. Whereas, the VCU oversees nearly all the vehicles power control mechanisms including the motor control, regenerative braking control, A/C load management and power supply for the electronic system. This controller gets the main input from the car pedal(which is set by the driver). This pedal setting will determine the frequency variation that will enter the Motor and at the same time determine the car's speed.

                  

                                                 The Controller Unit of Hyundai IONIQ.

 

• Electric Traction Motor: The Traction motor of EVs is responsible for converting electrical energy to mechanical energy in such a way that the vehicle is propelled to overcome the aerodynamic drag, rolling resistance drag, and kinetic resistance. Traction motors usually required frequent start/stop, high rate of acceleration/deacceleration, high torque low speed hill climbing, low-torque high speed cruising, and very wide speed range of operation. The Electric traction motors will work turning the Transmission and the wheels. Some hybrid cars use a type of generator-motor combination that performs the function of propulsion and regeneration. In general, the type of electric motors used is the Brushless DC Motor(BLDC).

                 

                                                         Traction Motor Drive Unit of Chevrolet Bolt EV.

 

• Charger: It is the battery charging device. Chargers get electricity from outside sourcessuch as the utility grid or the solar power plants. The general type of electric car charger is the On-Board Charger(OBC) which is used to convert alternating current(AC) from slow chargers or portable chargers used on home outlets into Direct Current(DC). This may make the OBC similar to the Inverter but they differ crucially in function where the OBC is for charging and the Inverter is for acceleration/deacceleration. And the other type of charger is the Off-Board Charger which is not located or installed within the car.

               

                                                          Typical Battery Charger

 

• Transmission: Transmissions can be simply defined as the transfer of power generated from the source to the wheels of the vehicles. Transmission can be either Manual type or Automatic Type. In Electric Vehicle only automatic transmission is used as the speed variations is electric vehicle is less and also automatic transmission gives comfort to driving the vehicle. The key factors affecting on Transmission are fuel efficiency, motor efficiency, speed-torque variation, power, cost, weight, etc. 

                                

                                         Typical 3-Speed Transmission System

 

• DC-DC Converter: A Battery pack delivers a fixed voltage, but the requirement of different accessory systems(e.g., wipers, lights, infotainment system, mirror control) in the EV would vary. The DC-DC converter helps to distribute power to different systems by converting the output power from the battery pack to the expected levels. After conversion, power is delivered to respective smaller ECUs via wiring harness.

                  

                                  DC-DC Converter for Electric Vehicle

 

• Thermal System-Cooling: Responsible for maintaining optimum operating temperature range for powertrain components such as the engine, electric motor, power electronics and other auxilliary components.

                         

                                                                 Thermal Management System of Nissan Leaf.

 

• Charger Port: The Charger port allows the vehicle to connect to an external power supply in order to change the traction battery pack.

                

                                                                      Charger Port on various countries.

 

• Body-Control Module(BCM): The BCM is responsible for supervising and controlling the functions of electronic accessories such as power windows, mirrors, security, and vehicle access control.

                          

                                                                      Schematic Diagram of BCM Unit.

 

MODEL REPRESENTATION OF THE ELECTRIC VEHICLE(EV) IN MATLAB-SIMULINK: 

a) Summary Of The Model Build-Up:

 Building up of the entire electric vehicle model in Matlab is divided into some procedures which is discussed briefly below:

• Creation of the Sub-System for corresponding vehicle block which represents the setup of the block like for example vehicle dynamics subsystem constitute the connection setup of the vehicle body with the tires and the gears. Each of these subsyetms is then connected to form the main model.
• Analysing the vehicle performance of the model by comparing the velocity of the Driving Cycle Source to that of the Vehicle, so as to mitigate the error(corresponding to the deflection between the two velocities) as much as possible by changing the values of all the possible parameters ranging from the DC Motor and its Controller Subsystem, Battery Management System to that of the Vehicle Dynamics Subsystem, Longitudinal Driver block.
• To monitor and examine various performance charateristics like the current drawn by the Motor, SOC(State of Charge) estimation after the cycle ends, calculation of the Total Distance travelled by the vehicle after each driving cycle and calculation of the corresponding energy usage by the vehicle. Besides these a comparison of the velocities discussed above is also shown w.r.to the deviation between them.
• Finally, observing the results and providing a detailed discussion so as to realize the Model in the practical scenario.

 b) Circuit Diagram of the Matlab EV Model:

The Circuit Diagram is basically divided into three parts: where one is the Main Model which gives the main performance charateristics of the vehicle and the other two diagram is concerned with the Distance Calculation and the Energy Calculation respectively. The discussion of all the components and subsystem used is given in detail in the next section.

 

c) Subsystem and Component Level Analysis with Interpretation:

1. Drive Cycle Source:

The Drive Cycle Source block generates a standard or user specified drive cycle. It generally constitute a curve between the vehicle speed(longitudinal) w.r.to time which can be used for the following purpose:

• Predict the engine torque and the amount of fuel required by the vehicle in order to achieve desired speed and acceleration for a given gear shift reference.
• Can effectively produce velocity curve for a practical scenario with shift references for closed loop acceleration and braking commands for vehicle control and plant models.
• Examine, tune and optimize vehicle control, system performance and system robustness over mutiple drive cycles.
• Identification of the faults within the tolerence specified by the standardized tests including:

                         - EPA dynamometer driving schedules. 

                         - Worldwide Harmonised Light Vehicles Test Procedures(WLTP) labratory tests.   

For the Dirve cycles these are the options from whcih we can choose as given below:

                                                                                

In this project the Drive Cycle FTP75 is choosen which is corresponds to EPA Federal Test Procedure for testing and emission purpose defined by the US Environmental Protection Agency. For this Drive Cycle it takes 2474 seconds to complete the entire setup and so that's why the entire model is also run for 2474 seconds.

 

2. Longitudinal Driver:

The study of driver behaviour is an important part of the vehicle dynamics and control research. Additionally, it is also an important basis for the closed loop evaluation of the vehicle control stability and the development of a vehicle assisted driving system. When manipulating the vehicle, the driver's behaviour is a process consisting of simultaneously adjusting the drection and the speed of the vehicle. This enables the vehicle to proceed safely in accordance with the Driver's intention. Driving behaviour mainly includes two aspects, namely, vehicle direction control and vehicle speed control.

This block represents a parametric longitudinal speed tracking controller for generating normalized acceleration and braking commands based on the reference and the feedback velocities.The use of the external actions in order to input signals that can disable, hold or override the closed-loop commands determined by the block.The block uses this priority for the input commnads: Disable, Hold or Override.

In this project, the controller type choosen is a simple PI controller with tracking wind-up and feed forward gains. The PI controller is commonly used method to correct for error between the command set point which in this case is the reference speed and the actual speed through a feedback loop. By controling the Proportional Gain(Kp) and the Integral Gain(Ki) of the PI controller we can able to mitigate the error to a large extent and correspondingly the performance charecteristics of the vehicle gets improved. The governing equation for achieving the Speed control output using PI controller is shown below:

The parameters that are required to be controlled for optimizing the performance charecteristics of the vehicle is shown below:

Here the comparison of the Speed performance of the Vehicle is done by changing the Kp, Ki and the vnom between two values of [15, 3 and 5000] and [40,8 and 500].

 

3. Motor And Its Controller Subsystem:

The Subsystem Configuration is shown below:

i) Controlled PWM Voltage:

This block creates a Pulse-Width Modulation(PWM) voltage across the PWM and REF ports. The output voltage is zero when the pulse is low, and on the other hand it is equal to the Output voltage amplitude parameter when high. The Duty cycle is set by the Input value. Here the user have to specify the Input value by connecting any voltage source between electrical +ref/-ref. At time zero, the pulse is initialized as high unless the duty cycle is set to zero or the Pulse Delay time is more than zero. In this project, the Simulation mode is selected to Averaged mode where the ouput signal will be constant with value equal to the averaged PWM signal.

In this project, the PWM frequency is choosen as 6k Hz with an output voltage ampitude of 300V respectively, as shown below:

ii) H-Bridge:

H-Bridge is a very effective circuitry for driving motors and its find a lot of applications in many industrial or commercial applications like electric vehicle. It consists of Four switches with Four Diodes connected in anti-parallal w.r.to the switches. The Diodes provide a safer path for the Back emf from the motor to dissipate and thus it protects the corresponding switches from damage. So at a particular moment of time only two switches will operate thereby providing the source voltage across the Motor.

In Matlab, the H-Bridge block performs the same function discussed above which is ultimately driven by the Controlled PWM Voltage block in Average Mode as per the project requirement. In Average Mode, the PWM port Voltage divided by the PWM signal amplitude parameter defines the ratio of the on-time to the PWM period. Using this ratio and assumptions about the load, the block applies the average voltage to the load that acheives the correct average load current. The Simulation mode parameter value must be same for the Controlled PWM Voltage and the H-Bridge block. If the REV port voltage is greater than the Reverse Threshold Voltage, then the output voltage polarity is reversed. If the BRK port voltage is greater than the Braking Threshold Voltage, then the output terminals are short circuited via one bridge arm in series with the parallal combination of the second bridge arm and the freewheeling diode. For Average Simulation Mode, the load current charateristics is set to Smoothed rather than Discontinuous.

The choice of the corresponding value of the H-Bridge parameters along with the Simulation mode is shown in the figure below:

iii) DC Motor:

This block represents the Electrical and Torque Characteristics of the DC Motor. The assumption of this block is that no electromagnetic energy is lost, and hence the back emf and the torque constants have the same numerical value as in SI Units. The parameters of the Motor used is choosen either directly or derived from the no-load speed and the stall torque. When the positive current flows from the electrical positive to negative 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. The type of the Motor choosen is the Permanent Magnet Type so that it resemblance the BLDC type of Motor which is most commonly used in the Electric Vehicle.

Here the 'C' port represents the casing of the Motor which needs to be grounded using the Mechanical Rotational Reference frame whereas the 'R' ports constitutes the Rotor of the Motor which is connected to the Gear system of the Vehicle Dynamics. The value of the parameters choosen for the DC Motor is shown in the figure below:

iv) Controlled Voltage Source:

The block represents an Ideal Voltage Source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V=Vs, where Vs is the numerical value presented at the physical signal port. 

Two quantity of this Voltage Source Block is required., one is to drive the Controlled PWM voltage source and another is to drive the Braking command of the H-Bridge. The respective voltage of this block is controlled as per the acceleration command(to control the PWM voltage source) and the Deacceleration command(to control the Braking voltage of the H-Bridge) of the Longitudinal Driver. The positive terminal of the first Controlled voltage source is connected to the ref+ of the PWM voltage source and the negative terminal is grounded, whereas the positive terminal of the second Controlled Voltage source is connected to the BRK port of the H-Bridge block and the negative terminal is gorunded.

V) Current Sensor:

This block represents an idea current sensor, which is a device that converts current measured in any electrical branch into a physical signal proportional to the current. Connections positive(+) and negative(-) are conserving electrical ports through which the sensor is inserted into the circuit. Connections 'I' is a physical signal port that outputs current value.

 The positive and the negative part of this block is connected between the H-Bridge and the DC Motor whereas the physical port 'I is connected to the Controlled Current Source of the Battery management system from where it can track the current flowing in the Battery system.

vi) Solver Configuration:

The Solver Configuraion block specifies the Solver parameters that the model needs before one can begin the simulation. Each topologically distinct Simscape block diagram requires exactly one Solver Configuration block to be connected to it. In this project, only the option 'Filtering at 1-D/3-D connections when needed' is required which is used for models that connects blocks from Simscape Multibody Second Generation library to Simscape blocks, or blocks from other add-on products.

The options required for the Solver Configuration specifically for this project is shown in the figure below:

 

4. Vehicle Dynamics Subsystem:

The Sub-system configuration is shown below:

 

i) Vehicle Body:

This block represents a two-axle vehicle body in longitudinal motion. The block accounts for body mass, aerodynamic drag, road inclination, weight distribution between axles due to acceleration, rolling resistance criteria and road profile. This block gives the option of having same or different number of wheels on each axle along with optional inclusion of pitch and suspension dynamics or additional variable mass and inertia. The mass, inertia and center of gravity of the vehicle body can vary over the course of simulation in response to the system changes.

In this block there are all total 6 connection port out of which:  'H' is the mechanical translational conserving port associated with the horizontal motion of the vehicle body and it is connected to the 'H' of the wheel hub of the tire through which the resulting traction motion of the tires will get generated, 'V' is the physical output port through which we can examine and monitor the vehicle velocity curve, 'NF' and 'NR' are also physical ouput ports but they represents front and rear normal wheel forces and that's why they are connected to the 'N' of the tires through the forces will get act on the wheel for rotation, 'W' and 'beta' are physical signal input ports corresponding to headwind speed and road inclination angle and whose values are assigned from the PS-Constant Block as '4' and '0' respectively.

The value of the parameters assigned to the Vehicle Body is shown in the figure below:

ii) Tire(Magic Formula):

It represents the longitudinal behaviour of a highway tire characterized by the tire magic formula. The block is built from Tire-Road interaction(Magic Formula) and Simscape foundation library wheel and axle blocks. Additionally, the effects of the tire inertia, stiffness and damping can be included as per requirements. To increase the fidelity of the tire models, you can specify properties such as tire compliance, inertia and Rolling resistance. However, these properties will increase the complexity of the tire models and can increase the simulation time. One has to ignore the tire compliance and the inertia if simulating the model in real time or if preparing the model in hardware-in-loop(HIL) simulation.

In this block there are all total 4 connection port out of which: 'A' is the mechanical rotational conserving port for the wheel axle and it is connected to the Gear arrangement of the vehicle, 'H' is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tires is applied to the vehicle and it is connected to the 'H' port of the vehicle body for initiation of the horizontal motion, 'N' is the physical signal input port that applies the normal force acting on the tire and it is connected to the 'NR' and 'NF' port of the vehicle body which provides the force required, 'S' is the physical signal output port that reports the tire slip and in this model it is made inactive by connecting to the PS-Terminator block as it is not required.

The value of the parameters assigned to the tire is shown in the figure below:

iii) Simple Gear:

It represents a fixed-ratio gear or gear box. It does not include any options regarding Inertia or Compliance. This block gives the options for including gear meshing and viscious bearing losses.

Connection Port 'B'(Base) and 'F'(Follower) are mechanical rotational conserving ports which are connected to the Shaft Input of the DC Motor and 'A' port of the wheel and axle respectively. The relation between the Base and the Follower rotation can be specify with the Output shaft rotates parameter. Additionally, the thermal effects can be included through the thermal conserving port 'H' which is optional. If the block rotates in the same direction, then the angular velocity of the follower and the angular velocity of the base posseses the same sign. If they rotate in the opposite direction then they will have opposite sign.

The value of the parameters assigned to the Simple Gear is as follows:

 

iv) Inertia:

This block represents an Ideal Mechanical Rotational Inertia which consists of one rotational conserving port. The block positive direction is from its port to the reference point which means that the inertia torque is positive if the inertia is accelerated in the positive direction.

The value of the Inertia is chhosen to be 4 kg/m2 which is shown as follows:

 

5. Battery Management Subsystem:

The configuration of the Subsystem is shown below:

i) Battery:

This block represents a Battery. As per the requirement of the project, the Battery charged capacity is needed to be finite so according to it the block models the battery as a series internal resistance plus a charge dependent voltage source defined by the equation:

where;

SOC(State of Charge) is the ratio of current charge to rated battery capacity.

`Vunderset(0)` is the voltage when the battery is fully charged at no load condition as defined by the Nominal Voltage,Vnom

`beta`is the constant that is calculated so that the battery voltage is V1 when the charge is AH1. AH1 is the charge when the no-load (open circuit) voltage is V1, and V1 is less than the nominal voltage.

The equation defines an approximate relationship between voltage and the remaining charge. This approximation replicates the increasing rate of voltage drop at low charge values, and ensures that the battery voltage becomes zero when the charge is zero. The advantage of this model is that it requires very few parameters for approximation which are readily available in most datasheets.

The magnitude of the battery as well as other parameters is shown in the figure as follows:

ii) Controlled Current Source:

It is the representation of an Ideal Current Source that is powerful enough to maintain the specified current through it regardless of the voltage across it. The output current is I=Is, where Is 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 the electrical terminals.

The electrical terminals of the block is connected across the battery and the physical signal port 'I' is connected to the physical output port 'I' of the Current Sensor of the DC Motor Subsystem. It is arranged in a fashion that the current drawn by the DC Motor is coming from the Battery.

 

6. SOC Estimation Subsystem:

The Block used in the Subsystem is shown in the figure below:

i) Rate Transition:

 

This block transfers data from the output of a block operating at one rate to the input of a block operating at a different rate. This block is used to trade data integrity and deterministic transfer for faster response or lower memory requirements. The behaviour of the Rate Transition block depends on the following criteria:

• Sample Time of the port which is connected to a block.
• Priorities of the tasks for the source and the destination sample times.
• Whether the model used a fixed or variable step solver
• Setting of the Model configuration parameters.

As per for the project, the Initial Conditions of the output is kept at zero and the output port sample time is specified with a magnitude of -1.

The parameters window of the Rate Transition block is shown in the figure below:

ii) Discrete Time Integrator:

The Discrete Time Integrator block is used to create a purely discrete model of the Integrator Block. This block helps to define- the Initial Conditions on the block dialog box or as input to the block, the input gain(K) value, Upper and Lower limits of the Integral, Reset value of the state with an additional reset input.

As per the project, the Integrator method is choosen as Forward Euler Method with a Gain value of 1.0 with no initial conditions and with a Sample Time of -1.

The parameters choosen for the Discrete Time Integrator block is also shown as a figure below:

iii) Gain:

 

This block is used to multiply any value as per the user with the Input signal. The input and the gain can each be a scalar, vector or a matrix. The value of the Gain is specified in the Gain parameter section of the block. The multiplication parameters gives the option to specify element wise or matrix wise multiplication. Gain is converted from doubles to the data type specified in the block mask offline using round to nearest and saturation. The input and the gain are then multiplied, and the result is converted to the output data type using the specified rounding and overflow modes.

The Gain value is shown in the figure below:

In this project, the value of the Gain parameter determines the rate of discharge of the battery for a particular driving cycle.

iv) Add/Subtract:

This block performs addition or subtraction of the Input Signal. The Add, Subtract, Sum of elements and Sum Blocks are indentical in operation. The main intention of these blocks is to add or subtract scalar, vector or matrix inputs. It can also collapse the elements of a signal and perform summation. As per the project requirement, this block is set to the subtract form so as to examine the amount of charge get left after every driving cycle.

 

7. Distance Calculation Subsystem:

The Subsystem configuration is shown as follows:

i) Zero-Order Hold:

This block is used to hold the magnitude of the input for the sample period specified by the user. If the input constitutes a vector then it will hold all the elements of the vector for a given sample period. The user have to specify the sample time parameter which is by default set to -1. The Zero-Order hold block is a bus capable block which means that the input can be either virtual or non-virtual. All signals in a non-virtual bus input to a Zero-Order hold block must have the same sample time, even if the elements of the associated bus object specify inherited sample times.

This block is connected in between the 'Gain' and the 'Divide' block so as to convert the input signal with a continuous sample time to an output signal with a discrete sample time.

ii) Divide/Multiply:

The divide block gives the output by dividing the first one(first input) with the second. The inputs can be a scalar, scalars, a non-scalar or two non-scalars that have the same dimension. Setting the non-default values for either of those parameters can change the Divide Block to be functionally equivalent to a Product Block. This block is set to Divide mode so as to change the unit of time from 'sec' to 'hr'.

iii)Integrator:

The Integrator block represents the continuous time integration of the Input signal. The Integrator Block saves its output at the current time step for use by the solver to compute its output at the next time step. The block also provides the option of introducing an initial condition to the solver for the usage of computing the block's initial state at the beginning of the simulation.

The parameters that can be define using this block are as follows:

• Upper and Lower limits of the intergral
• Input that can reset the block's output(state) to its initial state depending on how the input changes.

 

8. Energy Calculation Subsystem:

The configuration of the blocks used in the subsystem is shown below:

In this subsystem the amount of energy usage by the vehicle is calculated and monitored. The Energy is derived from the following forces:

• Rolling Resistance Force(`Funderset(rr)`): This force is responsible for resisting the motion of the body when it is in motion. In broad sense, the rolling resistance is defined as the force per unit vehicle weight required to move the vehicle on the level ground at a constant slow speed where aerodynamic drag is useless and where there are no traction forces or brakes are applied.

        The governing equation of the Rolling Resistance Force is given by:

        `Funderset(rr)`= `muunderset(rr)`*m*g

          where; `muunderset(rr)` is the Rolling Resistance Coefficient(Dimensionless)

                       'm' is the Mass of the vehicle

                       'g' is the acceleration due to gravity.

         In this project, `muunderset(rr)`is taken as 0.015, Mass of the vehicle is taken as 1500kg and gravitational acceleration is by default 9.81m/sec2.

• Aerodynamic Drag Force(`Funderset(ad)`): It is the force offered by the resistance of the oncoming air to the movement of the body. Technically, it is the friction offered by the air to the vehicle which affects it's speed and performance. It always has a negative effect on the vehicle's overall performance and efficiency.

        The governing equation of the Aerodynamic Drag Force is given by:

         `Funderset(ad)`= 0.5*`rho`*`Cunderset(d)`*`v^2`*A

           where; `rho`is the air density

                      `Cunderset(d)` stands for the drag coefficient(Dimensionless) that is used to quantify the resistance offered to an object in the environment such as air.

                      'v' velocity of the vehicle

                      'A' is the frontal area of the vehicle.

          As per the project requirement, `rho`is taken as 1.18kg/m3, `Cunderset(d)`is taken as 0.4, 'v' is taken from the ultimate output of the Vehicle Dynamics subsystem, A is taken as 3m2.         

In this model, the vehicle is assumed to be moving on a level ground i.e., Grade=0 so the Hill Climbing Force will also be equal to zero and that's why this force is neglected.

After computing the Forces we can find out the respective Power by multiplying the Force with the respective Velocity points of the vehicle which is coming as an output from the Vehicle Dynamics Subsystem. Now, the Integration of this Power w.r.to Time will ultimately give the Energy usage of the vehicle at every driving cycle. 

The Energy Calculation is very important from the perspective of the size of the Battery required to be implemented for a particular Electric Vehicle. The Dynamic performance and the Charging time of the battery can be optimtise by knowing the average energy consumption and the range of the Vehicle.

 

RESULTS AND DISCUSSIONS:

In this model, a comparison of the velocity of the vehicle with that of its driving cycle source is made. Initially it was found that there is a considerable amount of deflection persists between the two velocities which resulting in some amount of deviation in the Distance calculation of the vehicle and that of the Driving Cycle Source. To mitigate this error an optimization technique is used by fine tunning the values of the Proportional Gain(Kp) and the Integral Gain(Ki) of the Longitudinal Driver system. So in this section both the situation i.e before fine tunning and after fine tunning is discussed in detail along with the respective results.

Case 1: Before Fine Tunning: 

 Initially the values of the Proportional Gain(Kp) and Integral Gain(Ki) is taken as 15 and 3 respectively. In this scenario, the nominal speed vnom is taken as 5000.

The respective velocity curve of the vehicle along with the Driving Cycle Source and the Distance of the two is given as follows:

If we zoom the above figure we can clearly see the deviation between the two which is as follows:

The corresponding deviation is distance is coming as follows:

                             This is the Distance Covered by the Vehicle in km.

                         This is the actual distance corresponds to the Driving Cycle Source.

The difference between the two distances can also be visualised from the corresponding distance curve shown below:

From the above curve it is clearly visible that some amount of deviation is present between the two curves. If this get persists then it will become a problem for the vehicle as it will unable to track any other driving cycle precisely.

The corresponding energy consumption by the vehicle is given as :

                        This is the amount of energy consumed by the EV in kWhr.

 

Case 2: After Fine Tunning:

After Tunning the values of the Proportional Gain(Kp) and the Integral Gain(Ki) changes to 40 and 8 respectively. In this scenario, the nominal speed is reduced to 500.

 The respective velocity curve of the vehicle along with the Driving Cycle Source and the Distance of the two is given as follows:

Here the velocity of the vehicle is clearly gets coincide with that of the Driving Cycle source but there is a some amount of deflection occurs during braking situation as shown below:

This occurs due to the fact that the vehicle can't able to deaccelerate to follow the sharp edge of the driving cycle because of some limitations in the dynamics of the tires or the vehicle body but it is within the tolerable limit. 

Due to this deflection, there will also be some difference present(which is much less than the 'Before Tunning Case') in the Distance magnitude corresponding to the two velocities which is shown in the below figure:

                           This is the actual distance corresponds to the Driving Cycle Source.

                                  Total Distance Covered by the vehicle in km.

The overall deviation between the two distance curve get minimised which can clearly get visible from the below distance curves:

From the above curve it is quite visible that the Vehicle Distance and the Corresponding distance of the Driving Cycle Source get coincide to a great extent. Thus we can say that After Tunning the Electric Vehicle is now tracking the Driving Cycle with very less amount of error and high amount of precision and accuracy.

After tunning the corresponding energy consumption by the vehicle is also get less to some extent which is shown as follows:

                       Amount of Energy consumed by the EV after tunning in kWhr.

 

Other Output Results from the Model:

 i) Energy Consumption Curve of the Vehicle:

The figure shown below is the Energy Consumption curve of the vehicle w.r.to the Driving Cycle:

 The energy curve shown above is more or less similar to the distance curve of the vehicle but the difference lies on the region where the rate of change of velocity is high. On those region shown by the 'blue circle' the energy consumption rises steeply as more power is required by the vehicle to accelerate in order to acheive the given speed in a very small amount of time. So to cover a total distance of 17.82km the vehicle consumed 1.988kWhr of energy and this will increase whenever the distance covered by the vehicle is increased or the rate of change of velocity is increased over the Driving Cycle.

ii) SOC Estimation Curve:

The rate at which the battery will get discharge over the entire Driving Cycle is shown in the figure below:

This curve shows the amount of charge left in the Battery after the end of the Driving Cycle which is around 0.63 or 63%. Those small upward spikes in the curve is due to the phenomenon of Regenerative Braking which is taking place when the vehicle is deaccelerating as the power is feding back to the battery due to the reverse rotation of the DC Motor. From the above data we can predict that the vehicle can able to cover a total distance of around 50km before the battery get fully discharge.

iii) Current Curve:

The nature of the current drawn by the DC Motor in accordance with the Driving Cycle is shown below:

The above curve shows the current profile of the DC Motor which switches between the negative and the positive half according to the switching frequency assigned to the PWM controlled voltage source block. The negative part of current is due to the Regenerative Braking phenomena as the direction of the current flow gets altered. When the speed of the vehicle is increasing then the current drawn by the Motor is also increasing and which can be visible from the huge spike in the curve. During acceleration of the vehicle the current is moving to a maximum value of 320A and during braking the current is having a maximum value of 175A but in the opposite direction.

 

CONCLUSION:

Thus from the above output charateristics of the vehicle it is clearly visible the possible error that can take place while following the Driving Cycle. In this project, the analysis of this error is done and an optimization technique is found out to mitigate the error by fine tunning some vehicle parameters and a comparison has been showned before and after fine tunning. From the comparison it is very much clear that the vehicle is clear following the Driving Cycle without any deviation after the successful implementation of the tunning method by analysing the Distance Curve along with the velocity profile of the two. The Energy Estiamtion of the vehicle after each Driving Cycle is also chalked out in this project by creating a different subsystem and by providing a detailed description of the parameters under consideration, thereby ultimately showing the energy consumption profile of the vehicle which is a very important discussion from the Battery point of view. Along with this, SOC Estimation and the Current drawn by the Motor is also presented with detailed interpretation. 

In the early stage of this project, a brief introduction of the various MATLAB components used for bulding the Model is also discussed along with the various parts present in a Electric Vehicle. Thus the EV design model is successfully implemented with detailed discussion and implementation of the given objectives related to the project.

 

REFERENCES:

1] https://www.business-standard.com/about/what-is-electric-vehicle

2] https://www.energy.gov/eere/electricvehicles/electric-vehicle-benefits

3] https://www.energy.gov/eere/electricvehicles/electric-vehicle-basics

4] https://www.omazaki.co.id/en/electric-vehicle-components/

5] https://news.hyundaimotorgroup.com/Article/Understanding-EV-Components#:~:text=As%20such%2C%20EVs%20have%20no,Power%20Control%20Unit(EPCU).

6] https://evreporter.com/ev-powertrain-components/

7] https://www.hindawi.com/journals/sv/2018/7487295/

8] https://in.mathworks.com/help/autoblks/ref

9] https://in.mathworks.com/help/physmod/sps/index.html?searchHighlight=simscape&s_tid=srchtitle

10] https://www.youtube.com/watch?v=tM9Akdo8QeA&t=6s

 

The Model file is attached :

https://drive.google.com/drive/folders/11hAX_uopyidb4A6HPQcTMGWTTFhciR52?usp=sharing