Final Project: Electric Rickshaw modelling

OBJECTIVE : To create a Electric Rickshaw matlab model

CONDITIONS : The follwing are the different conditions given for modelling of Electric Rickshaw

i. Rear wheels should be driven by PM brushed type motor

ii. Assume efficiency points of motor controller and motor

iii. Make an excel sheet of all input and assumed data 

• Results should be shown for any three standard driving cycles show energy consumption, temperature rise of motor and controller for 100 km constant speed driving at 45 kmph.

 

THEORY :

Electric rickshaw have been becoming more popular in some cities since 2008 as an alternative to Auto rickshaw and Pulled rickshawas because of their low fuel cost, and less human effort compared to pulled rickshaws. They are being widely accepted as an alternative to petrol/diesel/CNG auto rickshaws. They are three-wheelers powered by an electric motor ranging from 650 to 1400 Watts. They are mostly manufactured in India and China, only a few other countries manufacture these vehicles. Battery-run rickshaws could be a low-emitter complementary transport for the low-income people, who suffer most from a lack of transport facility.

The body weight of the E- rickshaw is extremely light and because of that durability of the battery does not get decreased. The main elements that actually drive the electric rickshaw are a motor, controller, harness and most importantly its throttle. To get the best service and to increase the benefits from this vehicle these elements are essential.

The motor of the battery generally varies from 650w to 1250 while according to the rules the unit should not increase 650 W. The power supplies at the rate of 48 V which can also be controlled by a specific controller. It is essential that manufacturers use the superior quality battery to get the best performance and takes care that the batteries don’t get overheated very fast.

The best part of this rickshaw is that they need minimal maintenance. Although it is important that at regular intervals the vehicle must be taken to the service centres. Any misuse with the vehicle might affect the entire system. Also, wrong adjustments with the brakes might also affect the motor and other essential elements. If this happens then not only it will severely affect the vehicle but also decrease the mileage.

Benefits : The following are different benefits we can get from an Electric rickshaw

No need of fuel – A traditional rickshaw which runs on human effort needs fuel to operate. This fuel may be diesel or petrol. The owner has to spend a lot of money for it to function. The amount of money which is generated as his earnings never improves his economical condition because of the fuel expenses he needs to make. On the other hand, an e-rickshaw operates on batteries which can be effectively charged whenever, wherever required. Thus, fuel need is totally eliminated which minimizes the functioning expense for its owner. The money saved becomes valuable addition to his monthly income.

Cheaper to purchase - An e rickshaw costs remarkably lesser than traditional rickshaws. At the same time, it offers more advantages as compared to manually functioned rickshaws. This ensures a lot greater value for investment. These rickshaws operating on batteries are more affordable for people who belong to lower class category or for people residing in remote regions.

Environment-friendly – An e rickshaw causes no environmental pollution and thus it is completely safe to use. No smoke is emitted because the vehicle does not operate on any type of fuel. Environmental pollution is one of the most threatening national problems of India. So use of e rickshaws will greatly check environmental pollution caused by vehicles or automobiles used for short distance communication.

Long functioning life – A rickshaw which runs on batteries effectively functions for a lot longer span of time if compared to traditional rickshaws. They need minimum repair which greatly saves maintenance cost for the owner. This greatly adds to the income of the owner and accordingly assures the owner about his judicious purchase.

Greater passenger accommodation – This type of rickshaw can accommodate much greater number of passengers in comparison to traditional rickshaws which ensures greater income for the owner.

Maintenance  

Vehicle tyres are responsible for your safety and comfort. The better the quality, the better your experience you have while driving. Tyres are pretty expensive and they require replacement every 4-5 years. However, within this 4-5 years we have to encounter that tyres are prone to be torn down to shreds or have essentially lost the durability it requires. It is important to take care of the tyres. To ensure riders safety and prolong the life of tyres, E rickshaw tyre maintenance should be on top of the list when servicing the vehicle. 

Tyre maintenance tips to follow:

i. Inspect Visually - 

The first thing is a simple but useful step. We need to check vehicles’ tyres once a week or at least every fortnight. See if there are any problems or not. Deep treads are crucial for keeping your car safe on wet roads, so do keep in mind that they are legally compliant. 

ii. Check Tyre pressure - 

We need to know the correct pressure for tyres by seeing the vehicle user manual so that we can refill the correct pressure of air in tyres every month as required. If you overfill your tyres it may crack under pressure and burst. However, a slight excess will not cause any problem and it can reduce the chances of flatspot. This is another maintenance tip that will help you to maintain the long life of your vehicle.

iii. Rotate Tyres - 

In order to reduce uneven wear and tear, rotating your tyres is a must. While onboarding passengers you will probably not want to stop in between due to any kind of disruption caused by your tyres. Thus, checking whether the tyres rotate properly or not will ensure a safer, smooth, and convenient drive. 

iv. Avoid Rash and Erratic driving - 

Though it is a known fact that battery-operated vehicles are a safe option but reckless driving can always be dangerous. Also in the case of e rickshaws when there is only a single passenger, there are high chances of mishaps as the vehicle is light-weighted it can overturn if driven carelessly or at too high speed. Sudden braking can reduce the shelf life of tyres additionally. 

The 3 wheeler E- rickshaw is definitely the best substitute for fuel driven vehicles and efficient when comes to battery power. Also, there is no emission of harmful pollutants from this vehicle so it helps to increase the durability and strengthens the vehicle. The materials which are used in constructing the vehicle such as fibreglass help it to make the vehicle more efficient. Also, this vehicle is absolutely perfect to cover the short distance as well as carry small loads.

Battery: Battery is the main part to store energy for running the vehicle. Following are the two different batteries used mostly and their concerns.

 Attributes of Lead Acetate Batteries:

• Lead is carcinogenic and hence is not a safe option.
• The construction of a lead acetate battery makes it extremely bulkier than any other variant. With five 100 ah batteries, the weight of the e rickshaws would add up to 120 kg weight.
• The shelf life of the batteries is only three years
• The minimum charging time is about 6-8 hours which means its needs to be plugged in overnight

Attributes Of Lithium (Li) Ion Batteries:

• These batteries are often termed green batteries due to their eco-friendliness
• The design of Li batteries are very compact and does not use too much space
• Charging time is also lower and you will only need 2-3 hours to charge it completely. 
• It is lighter and five 100ah batteries will cost around 40 kgs
• The batteries have a warranty for a year and the shelf life is nearly 6 years. 

Thus, the use of Li batteries are increasing due to better features, low cost, and extended shelf life. 

The following is the block diagram for an Electric Rickshaw:

SOLUTION :

The simulink model for E Rickshaw is as below:

 

Model description :

Drive cycle - 

A driving cycle is a series of data points representing the speed of a vehicle versus time. Driving cycles are produced by different countries and organizations to assess the performance of vehicles in various ways, as for instance fuel consumption, electric vehicle autonomy and polluting emissions.

Another use for driving cycles is in vehicle simulations. More specifically, they are used in propulsion system simulations to predict performance of internal combustion engines, transmissions, electric drive systems, batteries, fuel cell systems, and similar components.

Drive cycle block generates the standard longitudinal drive cycle which can be used for simulation. It is used to predict engine torque and fuel consumption that a vehicle requires to achieve desired speed and acceleration for a given gear shift reference. It gives braking commands for vehicle models. 

There are several duty cycles used as per the requirement. We can change the drive cycle input

Three drive cycles are used :

i. FTP75

The following plot represents the FTP75 drive cycle plot

 

Maximum velocity obtained from the drive cycle is 25m/s

 

ii. Wide Open Throttle 

We have to create the drive cycle for 100 km of constant speed of 45kmph

Time = Distance / speed = (100/(45/3600)) 

Then time is 8000 seconds, so the plot is shown above.

 

Longitudinal Driver - 

A parametric longitudinal speed tracking controller for generating normalized acceleration and braking commands based on reference and feedback velocities.

Drive cycle is connected to this block which has various ports like velocity reference, velocity feedback, grade, acceleration, deceleration. Referece velocity from drive cycle is compared with Feedback velocity from motor and result is given to the motor controller.

It has PI controller which matches the actual drive cycle with reference drive cycles

Motor and Controller - 

Whole Controller and Motor is created in the subsystem as below:

The following decription gives clear idea about all the parts inside the subsystem.

i. Motor: Permanent Magent Brushed type motor should be used. 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. 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 flows 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.

To sense the motor temperature rise we have to use thermal port. Motor parameters are as follows:

Armature Inductance  = 12e-6

No-load speed            = 3000 RPM

Rated speed               = 1500 RPM

Thermal mass             = 20 KJ/K

Initial temperature      = 25 degrees celcius

From longitudinal driver output is given as input to motor controller. So motor controller controls the speed of motor, torque as we required from input. It has various blocks like PWM, Hbridge to get the desired output.

H-Bridge:

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.

Controlled Voltage (PWM):

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.

Controlled voltage source and Current sensor:

Controlled Voltage Source 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.

The Current Sensor block represents an ideal current sensor, that is, a device that converts current measured in any electrical branch into a physical signal proportional to the current.

Temperature sensor - 

We have to measure the temperature of H-bridge and motor as per the problem. Temperature sensor is used as below:

This block measures temperature is a thermal network. There is no heat flow through the sensor. The physical signal port T reports the temperature difference across the sensor. The measurement is positive when the temperature at port A is greater than the temperature at port B.

Battery

This block models a battery. If you select Infinite for the Battery charge capacity parameter, the block models the battery as a series internal resistance and a constant voltage source. If you select Finite for the Battery charge capacity parameter, the block models the battery as a series internal resistance plus a charge-dependent voltage source defined by:

V = Vnom*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]

Lithiumion battery is used in this problem, and the parameters are:

 

Energy consumption calculation is also provided here. Using the bus selector block, three signals such as SOC%, Voltage, Current are brought out from the battery. 

For Energy consumption calculation Voltage and Current are necessary. 

Energy consumed = Workdone / Time

Time is taken as 3600seconds

Work done is product of voltage and current.

So this formula is implemented using the product block, divide block and integrator is used to denote the total work done for a given period of time. Result is displayed in Display block

For the given ratings, the battery characteristics are as below:

 

Vehicle Body

 The whole vehicle body parts are in subsystem as below:

The following explanation is for all parts of vehicle body

Tyre

Tire 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.

The following are the different parameter values we can fix as we need for tire block

Vehicle Body:

Represents a two-axle vehicle body in longitudinal motion. The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. The vehicle can have the same or a different number of wheels on each axle. Optionally include pitch and suspension dynamics or additional variable mass and inertia. The vehicle does not move vertically relative to the ground.

Connection H is the mechanical translational conserving port associated with the horizontal motion of the vehicle body. The resulting traction motion developed by tires should be connected to this port. Connections V, NF, and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces, respectively. Wheel forces are considered positive if acting downwards. Connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively. If variable mass is modeled, the physical signal input ports CG and M are exposed. CG accepts a two- element vector representing the x and y distance offsets from vehicle CG to additional load mass CG. M represents the additional mass. If both variable mass and pitch dynamics are included, the physical signal port J accepts the inertia of the additional mass about its own CG.

 

Inertia:

As the motor is rotating part we have to represent the inertia for rotating shaft. The block represents an ideal mechanical rotational inertia. The block has one mechanical rotational conserving port. The block positive direction is from its port to the reference point. This means that the inertia torque is positive if the inertia is accelerated in the positive direction.

Simple Gear:

Represents a fixed-ratio gear or gear box. No inertia or compliance is modeled in this block. You can optionally include gear meshing and viscous bearing losses.

Connections B (base) and F (follower) are mechanical rotational conserving ports. Specify the relation between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and expose thermal conserving port H by right-clicking on the block and selecting Simscape block choices to switch between variants.

SIMULATION RESULTS:

i. FTP75 drive cycle: 

The output plots obtained are as below:

Input drive cycle and output velocity are in sync

The maximum output velocity obtained is 13-14 m/sec.

SOC is falls to 99.2 from 100 at the end of drive cycle

 

Temperature of motor is about 306K at the end of drive cycle

Temperature of motor controller is around 300k at the end of drive cycle.

 

ii. WOT (100km for a constant speed of 45kmph)

The output velocity Vs Input speed plot is 

Output velocity is maximum 13-14 V at the end of drive cycle

Motor temperature is 310K at the end of drive cycle

Motor controller temperature is around 300k at the end of drive cycle

The SOC of battery decreased to 90 at the end of drive cycle.

 

CONCLUSION :

From the given conditions an Electric Rickshaw is modelled in Simulink Matlab. Using different drive cycles the outputs are plotted.