Simulink model of an Electric Vehicle

AIM

To create a MATLAB model of  an electric car which uses a battery and a DC motor, by choosing suitable blocks from Powertrain block set.

THEORY

An electric car is a vehicle that is propelled by one or more electric motors, using energy stored in rechargeable battery packs. These are eco-friendly and has higher efficiency compared to ICE cars. An electric vehicle is 69-72% efficient when counted against stored chemical energy and around 59-62% efficient when counted against required energy to recharge. They use electric motors for propulsion. The most common types of motors used are Permanent Magnet Synchronous Motor (PMSM) and three phase induction motor.

Motor comparison,

The battery packs are recharged using AC/DC charging technologies. AC charging is slow as it has to be converted to DC. Hence for fast charging DC chargers are used. The charging sockets has different standards as shown below,

BLOCK DIAGRAM

The block diagram for an Electric vehicle which uses a battery and a DC motor is shown below,

Vehicle Body Subsystem Block,

Now let us look at each of the blocks used to create this MATLAB model.

• Drive cycle data

For this we have used Drive cycle source block.

The block parameters for this block is as shown below,

This block will help us in inputting the drive cycle data , whether it is built in or custom made by the user. That is we can use custom made drive cycle data in excel sheet using this block.

For this model we have used FTP 75 drive cycle , which is built-in in this block.

• Longitudinal driver

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

The block parameters is as shown below,

Here the unit for the Velocity is considered to be in Km/hr.

• Power control unit

This subsystem has the blocks which are used to create the voltage signals to control the motor speed as per the input drive cycle data.

This subsystem is connected to the longitudinal driver block output ports namely acceleration command and deceleration command.

This subsystem will convert this acceleration and deceleration command into voltage signals using two controlled voltage source block, controlled PWM voltage block, a H-bridge and a current sensor.

• Controlled voltage source block

The block parameters is shown below,

This block is used to maintain the specified voltage at its output regardless of the current flowing through the source.

• Controlled PWM voltage block

The block and its parameters is as shown below,

This block is used to create the pulse-width modulated (PWM) voltage.

Electrical input ports :- The block calculates the duty cycle based on the reference voltage across its ref+ and ref- ports. This modeling variant is the default.

The value of the Output voltage amplitude parameter determines amplitude of the output voltage. Amplitude value is taken as 100 HZ.

• H-bridge block

This block is used to change the polarity of the voltage applied across the DC motor so as to run the motor in forward and reverse direction as per the input command.

The block and its parameters are shown below,

• Current sensor block

This is used to measure the current flowing through the H-bridge.

The block and its parameters is shown below,

• DC motor

To convert the electrical energy to mechanical energy we use motors. In this electric vehicle model we have used DC motor. This motor can act as a generator also in case of regenerative braking.

The motor block and its parameters are shown below,

This block represents the electrical and torque characteristics of a DC motor.

• Battery System
• In this subsystem we have a battery block , a controlled current source block and a goto block.

• Battery block

This battery block represents a simple battery model. The block models the battery as a series internal resistance and a constant voltage source.

The block and its parameters are shown below,

 All other parameter sections are kept at default values.

• Controlled current source block

This block gives a constant current output regardless of the voltage across it.

The block and its parameters are shown below,

• Vehicle body subsystem

This subsystem represents the body of a vehicle. The block diagram for this subsystem is shown below,

The input to this subsystem is the mechanical rotational conserving port of the DC motor block.

This is connected to the single speed gear box of gear ratio 6. This block and its parameters are shown below,

The inertia acting on the shafts is given using a Inertia block. This block and its parameters are shown below,

Now the simple gear is connected to all four wheels , representing an All wheel Drive vehicle. The tires are represented using tire (magic formula) block. This block and its parameters are shown below,

The simple gear is connected to the axle port of the tire block.

Now to represent the vehicle body we have used the vehicle body block . This block and its parameters are shown below,

Now to the front and rear normal forces ports represented by NF & NR respectively of the vehicle body we have connected the four tire. Two at NF and two at NR ports. This represents the front 2 tires and the rear 2 tires.

Also the mechanical translational conserving port for the wheel hub represented by ‘H’ in tire block is connected to the port ‘H’ in the vehicle body block which represents the mechanical translational conserving port associated with the horizontal motion of the vehicle body.

To the gradient and wind speed ports of the vehicle body block , we have connected physical signal constant block.

The output from the vehicle body is the velocity of the vehicle in Km/hr. This output is connected to the Goto block with tag ‘vfd’.

Now coming back to the longitudinal driver block, the VelFdbk input to this block is given using the ‘From block ‘ with tag ‘vfd’. This is the output from the vehicle body block.

Wind Velocity-

The wind velocity is known using the PS-Constant block. Here we have considered  the wind velocity to be  5m/sec.

Inclination Angle-

Since we have not taken any inclination angle it is considered to be zero.

Result and Conclusion-

The block diagram shows the simulation done for 1000 sec and the final results achieved in terms of Average Vehicle Velocity, State of Charge of Battery,TOtal distance Tarvelled by the vehicle in given time.

The resulting graph for this scope is shown below ,

From the graph it is understood that the Total distance achieved by the vehicle is 10.14 Km

The Average Speed achieved is 37.85 Km/hr 

The top speed achieved by the vehicle is 90 Km/hr

The next scope is used to get the change in SOC value with respect to time. The input for this scope is ‘From block’ with tag ‘SOC’.

The resulting graph is shown below,

from the graph we can say that SOC of the battery has changed intermittently from 95% to 84%. During this the vehicle has travelled for 10.14 Kms with an average speed of 37.8 Km/hr.

The third scope is used to get the current value with respect to time. Its input is ‘From block’ with tag ‘current’.the resulting graph is shown below,

The current rating shows 181.1 Amps.

CONCLUSION

The MATLAB model of an electric car which uses a battery and a DC motor has been successfully made by choosing suitable blocks from Powertrain block set and following conclusions has been drawn from the results.

From the input vs output velocity graph we can see that the EV model that we designed have traced the FTP 75 drive cycle very closely. Only when the speed suddenly drops to 0 in the FTP 75 drive cycle , the model takes time to catch up. On all other occasions the model traced the drive cycle closely.

Now looking at the SOC graph we can see that only 10% of the battery capacity is used for completing this drive cycle. And also we can see sudden spikes in that graph , these spikes represents the regenerative braking region. During which the SOC value increases.

And from the Current variation graph , we can see that the maximum current value during normal driving is around 300A and during regenerative braking the maximum current value reached is near to 181.1 A

The distance covered is 10.14 Km which is higher than the drive cycle data. For FTP 75 the total distance is 10.14 Km. But still the value is closer to that FTP 75 value , showing that the model is quite accurate in following the drive cycle data.

The link to the above Simulink model  -

https://drive.google.com/file/d/1lSL0KyWO9t1tX37izQ4EjJN_uXeJ-qPf/view?usp=sharing