Project-1: Modelling an electric Car with Li-ion battery

Create a MATLAB model of electric car which uses lithium ion battery and suitable motor. Choose suitable blocks from Simscape or Powertrain block set. Implement the vehicle speed control using PI controller and generate brake and accelerator commands. Avoid using readymade driver block for speed control.

Prepare a report about your model including following:

Objectives, System level configurations, Model parameters, Results, Conclusion.

(Note- The simulink model file should be compulsorily attached)

Answers

AIM:

To design a matlab model of an electric car with Li-ion battery

OBJECTIVES:

• Modelling of electri car with Li-ion battery.
• Avoid using of a readmate blocks for speed control
• Use PI controller for brake and acceleration commmands.

EXPLANATION AND MODELLING:

Electric car

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

Electric cars are a type of electric vehicle (EV). The term "electric vehicle" refers to any vehicle that uses electric motors for propulsion, while "electric car" generally refers to highway-capable automobiles. Low-speed electric vehicles, classified as Neighborhood Electric Vehicles (NEVs) in the United States, and as electric motorised quadricycles in Europe,are plug-in electric-powered microcars or city cars with limitations in terms of weight, power and maximum speed that are allowed to travel on public roads and city streets up to a certain posted speed limit, which varies by country.

While an electric car's power source is not explicitly an on-board battery, electric cars with motors powered by other energy sources are typically referred to by a different name. An electric car using solar panels as a power source is a solar car, and an electric car powered by a gasoline generator is a form of hybrid car. Thus, an electric car that derives its power from an on-board battery pack is a form of battery electric vehicle (BEV). Most often, the term "electric car" is used to refer to battery electric vehicles, but may also refer to plug-in hybrid electric vehicles (PHEV).

Block diagram

In the designed Electric Rickshaw main blocks are

• Battery
• drive cycle
• controller
• DC Motor
• Vehicle body &amp
• Transmission system.

Drive cycle is the input data like how a human drive his actual vehicle here FTP75, WOT & Excel (Manually Prepared in Excel sheet) drive cycles are used to make the designed vehicle to give the output how it reacts to the drive cycle. The main objective is to obtain the speed by the driver, to estimate the temperature of Motor and Controller, to estimate the sates of charge (SOC), distance travelled by the vehicle. There is a SOC block that will estimate the state of charge of a battery, distance is calculated by speed and time parameters for all the three Drive cycles.

MATLAB SIMULINK MODEL

Initially the current flows to DC Motor from the battery through the DC-DC power converter to drive the motor. The required voltage will be controlled in the controller. The Controller will follow the given drive cycle reference and run the motor in the required rpm. Then the motor power is transmitted to the wheels of a vehicle through the gear box. and the controller will take the vehicle speed and compare and controlled.

MODEL PARAMETERS

DRIVE CYCLE

Drive cycle is assumed as the driver's input of a vehicle, it replaced how a driver will drive a vehicle. Here I have used three drive cycles which is used to test the vehicle performances. These drive cycle will have high speed, low speed, braking conditions in it. There are different drive cycles like WOT, FTP75 etc., Here in this model I have used FTP 75, WOT & Manually prepared in excel Drive Cycle source.

Generates a standard or user-specified longitudinal drive cycle. The block output is the vehicle longitudinal speed. You can import drive cycles from:

• Predefined sources
• Work space
• .mat,xlsx,slx and text files

DRIVE CONTROLLER

PID controller

PID control respectively stands for proportional, integral and derivative control, and is the most commonly used control technique in industry

PID control involves several tasks that include:

• Selecting an appropriate PID algorithm (P, PI, or PID)
• Tuning controller gains
• Simulating the controller against a plant model
• Implementing the controller on a target processo

Controller

Motor & controller

Motor type

DC motor ( PM brushed type motor)

This block represents the electrical and torque characteristics of a DC motor includes Thermal port to sence the temperature of 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. Motor parameters can either be specified directly, or derived from no-load speed and stall torque. If no information is available on armature inductance, this parameter can be set to some small non-zero value.

When a positive current flow from the electrical + 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.

Motor parameters

• Armature inductance 12e-6
• No-load speed 3000rpm
• Rated speed 1500rpm
• Rated load 1 kW
• Rated DC supply voltage 48V
• Rotor inertia 0.01
• Thermal mass 20 kJ/K
• Initial temperature 25 degrees

TheMotor controller will get input from the longitudinal driver. Its tasks are to control the speed of the motor and drive according to the input of the driver. Majorly motor controlled we designed had two main parts named PWM voltage generator and H-Bridge.

Input1 is getting from the accelmd of a longitudinal driver and it is given to a controlled voltage source block where it is input to the controlled PWM voltage. Controlled PWM voltage will generate a PWM signal in such a way that H-bridge will generate the required voltage to operate the DC motor for the given driver input. PWM voltage block negative reference and REF are grounded and REF of H-bridge respectively. H-bridge is a motor controller that has IGBT components aligned in the shape of H and will operate only two at a time respectively to the input of the signal from the PWM block. When deceleration occur this H-bridge will give an output from the positive and negative terminals of it. These negative & positive terminals are later connected to the DC motor and battery. All these components are the simscape electrical components so they need a connection to the solver configuration block which helps to solve the simulation.

Controlled PWM voltage source.

This block creates a Pulse-Width Modulated (PWM) voltage across the PWM and REF ports. The output voltage is zero when the pulse is low, and is equal to the Output voltage amplitude parameter when high. Duty cycle is set by the input value. Right-click the block and select Simscape->Block choices to switch between electrical +ref/-ref ports and PS input u to specify the input value.

At time zero, the pulse is initialized as high unless the duty cycle is set to zero or the Pulse delay time is greater than zero.

The Simulation mode can be set to PWM or Averaged. In PWM mode, the output is a PWM signal. In Averaged mode, the output is constant with value equal to the averaged PWM signal.

Power Converter

H-bridge

It is used as a DC_DC converter

This block represents an H-bridge motor drive. The block can be driven by the Controlled PWM Voltage block in PWM or Averaged mode. In PWM mode, the motor is powered if the PWM port voltage is above the Enable threshold voltage. In Averaged 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 an average voltage to the load that achieves the correct average load current. The Simulation mode parameter value must be the same for the Controlled PWM Voltage and H-Bridge blocks.

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 parallel combination of a second bridge arm and a freewheeling diode. Voltages at ports PWM, REV and BRK are defined relative to the REF port.

If exposing the power supply connections, the block only supports PWM mode.

Motor controller parameters

Threshold voltage 2.5 V

PWM amplitude 5V

Reserve threshold 2.5VB

Braking voltage 2.5 V

Output voltage 200V

Solver configuration

Defines the solver settings to use for simulation

References

1. Electrical reference: It act as a ground . All the electrical parameters connected to it.
2. Mechanical reference: All the mechanical parameters are connected to it.

Battery

Battery parameters

Battery type Li-ion type

Nominal voltage 330V

Rated capacity 75 Ah

Initial SOC% 100

Internal resistance 0.0012 ohms

The battery is required to power the controller and motor. The controller uses the battery power according to produce the input given by the motor to obtain maximum speed. The battery is also used to power every electrical component in the vehicle. The battery has two stage one is charging and another one is discharging state. The battery is of 75Ah capacity.

The battery as a series internal resistance plus a charge-dependent voltage source defined by:

`V=(V_n.SoC)/((1-beta).(1-SoC)`

where SoC is the state of charge and Vnom is the nominal voltage. Coefficient beta is calculated to satisfy a user-defined data point [AH1,V1].

The battery has a positive and negative terminal which is given the voltage-controlled source where the battery consumption is controlled by the motor controller and then it is given to the SOC block.

State of charge

SoC is the percentage or level of battery presents after certain travel or consumption of battery charge by the vehicle. In the designed vehicle battery charge or SOC is calculated by the giving it to the rate transition and then to gain where 1/(nominal battery capacity) then to a discrete-time integrator and it will get minus from the 1 as it is considered a 100% of battery and it is multiplied with 100 to get percentage of battery.

The majority of blocks are simscape blocks where physical to simulink converter is used to convert the physical signal from simscape block to simulink signal.

Vehicle body and transmission

Motor will produce the rotational output which will give to the vehicle body and transmission system. The rotational output is taken by the gear system here to maintain the constant speed throughout the transmission without any loss in speed from the motor to tires. Below is a diagram that is how it is how it inside the vehicle body and transmission system and in the main design, it is referred just only as a transmission system.

The gear output is given to axels of Rear tires, in the circuit it is shown that gear is connected to Rear wheels and front tire is free to rotational motion, thus vehicle moves forward. N is the normal force caused by the tires and it is given to the vehicle body normal force port. The vehicle body has an H-Hub, S- Tire slip, N- Normal force, A- axel connection, wind velocity, inclination angle. The tires hub is connected as a common node to the vehicle body. The vehicle body wind velocity is connected to a constant block and the beta-inclination angle is connected to another constant block where we can assign wind velocity and inclination angle as per requirement. Velocity is the output port where we can get at which speed the vehicle is moving. The velocity is taken out to the get the distance travelled and state of charge.

Vehicle body

Parameters

Mass 615kgs

No. of wheels per axle 2

Frontal area 1.48 m^2

Drag coefficient 0.5

Air density 1.18 kg/m^3

Wheels

Represents the longitudinal behavior 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. Optionally, the effects of tire inertia, stiffness, and damping can be included.

Connection A is the mechanical rotational conserving port for the wheel axle. Connection H is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Connection N is a physical signal input port that applies the normal force acting on the tire. The force is considered positive if it acts downwards. Connection S is a physical signal output port that reports the tire slip. Optionally expose physical signal port M by setting Parameterize by to Physical signal Magic Formula coefficients. Physical signal port M accepts a four element vector corresponding to the B, C, D, and E Magic Formula coefficients.

Parameters of wheels

• Wheel radius 0.305m
• Vertical load 3000N
• Peak longitudinal force at rated load 3500 N
• slip 10

Results

Energy consumption of electric car for FTP 75 drive cycle is 30 kWh

SOC of the battery of th electric car is reduced from 100 % to 75% .

Using PID controller after tuning , reference speed and car speed are almost equal. All the above points are observed in below graph.

CONCLUSION

Hence the modelling of electric car with Li-ion battery is done.Implement the vehicle speed control using PI controller and generate brake and accelerator commands. Avoid using readymade driver block for speed control.