Final Project: Design of an Electric Vehicle

AIM : Create a MATLAB model of an electric car which uses a battery and a DC motor.

OBJECTIVES : 

• To create a simple and low run time model of an electric car using SIMULINK.
• To examine the various performance characteristics such as Speed, State of Charge, Current and so on.
• To manipulate certain design parameters such as Motor Power, Vehicle Body Design Constraints, Battery Capacity etc and to explore the results pertaining to the change in these parameters.
• Finally, to construct the EV model in such a way that it behaves similarly to an actual model.

INTRODUCTION : 

An electric car is a car which 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 fuelling 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%.

Electric Car Components

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.

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. In addition, the inverter on an electric car also has a function to change the AC current when regenerative braking to DC current and then used to recharge the battery. The type of inverter used in some electric car models is the bi-directional inverter category.

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 car work.

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.

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.

Transmission : The transmission transfers mechanical power from the electric traction motor to drive the wheels.

DC/DC Converter : This one of electric car parts that to converts 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.

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

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

Charge Port : The charge port allows the vehicle to connect to an external power supply in order to charge the traction battery pack.

MATLAB SIMULINK MODEL OF PURE ELECTRIC VEHICLE

INDIVIDUAL SUB-SYSTEMS

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.

With reference to 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.The Proportional Gain (Kp) is set to 150, whereas the Integral Gain (Ki) is set to 100.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.

With reference to this model :

We have used two Controlled Voltage Source blocks.The outputs associated with the Longitudinal Driver is 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 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 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.

With reference to this model :

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.Averaged mode 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 percent.

H-Bridge : The H-Bridge block represents a 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: