Final Project: Electric Rickshaw modelling

Aim:

To Create a detailed MATLAB model of an electric rickshaw.

Objective:

To Create a detailed MATLAB model of an electric rickshaw for the following condition:

1.Rear wheels driven by PM brushed type motor.

2.Assume efficiency points of motor controller and motor.

3.For any three standard driving cycles show energy consumption, temperature rise of motor and controller for 100 km constant speed driving at 45 kmph.

Introduction:

In India, Rikshaw is mainly used for public transport. A typical rikshaw is three-wheeler vehicle with driver+3 passenger arrangement. In this project, we are designing a Rear wheel driven electric rickshaw using permanent magnet brushed type motor with payload of 300 kg.

Important result to be obtained is the rise in temperature of motor and controller when the vehicle has travelled 100km distance at 45kmph constant speed throughout. For this a separate drive cycle is created. In this drive cycle the speed is 12.5m/s constant for 8000 seconds. With speed of 12.5m/s for 8000 seconds, the vehicle should complete 100km.

Procedure:

An electric autorickshaw should have the following components to simulate in virtual environment:

1.Drive cycle

2.Battery

3.Driver Configuration

4.Power Controller

5.Motor and Gear system

6.Vehicle Dynamics

An electric rikshaw is combination of above-mentioned subsystems.

Block diagram of electric rikshaw is as follows:

FTP(2474sec) Drive cycle:

Model for Constant speed drive cycle:

Model for WOT(60sec) drive cycle:

Model for WOT(60sec) drive cycle:

Drive cycle:

A driving cycle is a series of data points representing the speed of a vehicle versus time. 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. Here we are using two standard drive cycle:

A.FTP75 (2474 cycle):

The Federal Test Procedure (FTP) is composed of the UDDS followed by the first 505 seconds of the UDDS. Though it was originally created as a reference point for fossil fuelled vehicles, the UDDS and thus the FTP-75, are also used to estimate the range in distance travelled by an electric vehicle in a single charge.

B.Wide Open Throttle (WOT) (60 Seconds):

Generates a standard or user-specified longitudinal drive cycle. The block output is the vehicle longitudinal speed. Vehicle speed is 0 for first 5 second, 60kmph for 5 to 30 seconds and zero from 30 to 60 seconds.

C.User defined cycle(constant speed driving cycle):

This cycle has a constant speed of 45kmph or 12.5m/s for 8000 seconds. The reason of the time being 8000 seconds is that the vehicle will take 8000 seconds for completing 100km ride at 45kmph speed.

Battery Package:

The battery used is a lithium-ion battery of 60V and 630Ah capacity. The output of the battery is its current, SOC, and voltage. A controlled current source drives the battery to charge and discharge. The input for this controlled current source is the current from the Power controller block.

Driver:

This subsystem compares the input speed and the vehicle speed. If the output is positive speed accelerating command is given from the controller. If the output is negative, deceleration command is given from the controller output.

The PID controller is tuned and is a continuous time based.

Power Controller:

Power controller block has prime significance in the electric powertrains. It consists of controlled PWM voltage block, H-bridge block, two controlled voltage source, current sensor and temperature sensor.

Controlled acceleration from driver subsystem is provided to controlled voltage source, the controlled voltage source converts the input of controlled acceleration signal to the equivalent voltage signal and output of controlled voltage source is provided to controlled PWM voltage block. Similarly, controlled braking signal is provided to another controlled voltage source and output of controlled voltage source is provided to H-bridge block.

Controlled PWM Voltage:

The Controlled PWM Voltage block represents a pulse-width modulated (PWM) voltage source. The block calculates the duty cycle based on the reference voltage across its ref+ and ref- ports.

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 portvoltage 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 signal at the REV port determines the polarity of the output. If the value of the signal at the REV port is less than the value of the Reverse Threshold Voltage parameter, the output has positive polarity; otherwise, it has negative polarity.

Motor and Gear system:

+ and – terminal output from power controller block is connected to respective terminals of DC motor

DC motor:

The block assumes that no electromagnetic energy is lost, and hence the back-emf and torque constants have the same numerical value Motor parameters can either be specified directly, or derived from no-load speed and stall torque. H port output from DC motor is provided to temperature sensor and shown on scope as motor Temp. Mechanical rotational reference block is used to connect mechanical rotational ports that are rigidly affixed to ground.

Gear Box:

The gear box is characterized by its Gear ratio. The gear ratio is determined as the ratio of the input shaft angular velocity to that of the output shaft. Here Gear ratio is 5.

Vehicle Dynamics:

Vehicle dynamics subsystem is simply the vehicle body with 3 wheels working to the given task. It has wheels road conditions, surrounding conditions, load on the vehicle etc.

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. 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 modelled, 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.

Tyres:

Tyre block Represents the longitudinal behaviour of a highway tire characterized by the tire Magic Formula. 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 right-clicking on the block and selecting Simscape block choices to switch between variants. Physical signal port M accepts a four-element vector corresponding to the B, C, D, and E Magic Formula coefficients.

Drive Input :

The block is capable of taking feedback velocity of the ehicle and changing the speed by giving output signal, it can decide when the vehicle needs to be accelerated and when the break need to be applied.

1. Drive Cycle Source

The Drive cycle source block is used to provide the refernence Speed of the simulation.

The following image shows the Drive Cycle Source block from Powertrain blockset.

There are many Drive cycle sources as well as we can generate our own signal by using signal builder. So I used the FTP75 Drive Cycle Source block to create the Drive input.

4. Testing and simulation

After designing the circuit, all thet is left is testing the circuit. We usually need to put scope at any point in the circuit to measure the desired parameters. The scope module looks like the one shown below.

The scope can have multiple inputs, and the real time output is displayed when the simulation.

RESULT:

Drive Cycles:

The model is made to run at drive cycles: FTP75.

FTP75

First, with the aid of the Drive Cycle source FTP75. Each drive cycle has its own time duration.So the Drive Cycle source FTP75 has time duration is 2474 seconds.

1. Distance travelled

The distance travelled by the vehicle is 17.77km

SOC

The graph of the SOC percentage.

The SOC of vehicle after running for 2474 seconds the battery has changed intermittently from 100% to (appro.) 83.63%. During this vehicle has travelled for 18.24Km. Trend is decreasing but during some time it is increasing. The SOC increases because of Regenerative braking.

The SOC is dropped from 100% to (approxi.) 83.63%.

• The designed Electric Vehicle model for a suitable FTP75 drive cycle travels for a distance of 17.81 Km for the simulation time of 2474 secs.
• The designed Electric Vehicle has a SOC of about 83.51% after a successful run of 17.81 Km.

• For Constant speed driving cycle:
  • This cycle has a constant speed of 45kmph or 12.5m/s for 8000 seconds. The reason of the time being 8000 seconds is that the vehicle will take 8000 seconds for completing 100km ride at 45kmph speed.
  • The designed Electric Vehicle has a SOC of about 37.98% after a successful run of 99.95 Km.
  • The SOC is dropped from 100% to (approxi.) 37.98%.
    • 
  • 

• The designed Electric Vehicle model for WOT drive cycle travels for a distance of 0.74 Km for the simulation time of 60 secs.
• The designed Electric Vehicle has a SOC of about 99.3% after a successful run of 0.74 Km.

After 30 seconds the vehicle speed is reduced immediately to zero through sudden braking so there is a sharp current generated due to regenerative braking back to the battery(the negative current).

For analyzing the thermal behaviour of power converter & motor we need to add thermal port to H-Bridge & Motor simscape block by right click on H-bridge/DC motor -> click on simscape-> Block choices -> show thermal port.

This thermal port is connected to temperature sensor .

Now we analyze the temperature change for the power converter & motor for the 3 driving cycles considered:

1. For FTP(2474 seconds) driving cycle:

in above scope, the first plot is for converter temp., the second one for motor temperature & the third for the driving cycle FTP75 in this case.

-> the converter temperature remains almost constant at 300K during first 1000sec of the driving cycle, with negligible change as there as very frequent brakings as there are accelerations & during these 1000sec the motor temperature steadily increases from 298K to 301K.

-> From 1000sec to 1375sec of driving cycle, the converter temperature rises from 300K to 400K & motor temperature rises from 301K to 302.2K.

->the converter & motor temperature remain constant at 400K & 302.2K respectively when the vehicle is not running between 1375sec & 2000sec of the driving cycle.

-> from 2000sec to 2474sec the temperature of power converter rises from 400K to 1650K & at the same time the motor temperature rises from 302.3K to 303.8K.

In this case the power converter shows abnormal temperature change between 1000-1375 sec when it rises by 100K & again between 2000-2474 sec when it rises by 1250K but motor's temperature change is very steady & normal.

So a very efficient thermal response from the cooling system is needed in this type of driving scenario.

2. For WOT(60 seconds) driving cycle:

-> In this driving cycle where the vehicle is in rest for first 5sec the temperature of both Motor & power converter is same (~298K)

-> at the 5th second the vehicle is suddenly accelerated to 60kmph but the temperature change for power converter & motor is negligible.

-> During coasting mode/constant speed mode for 25sec the temperature of power converter & motor remains constant at around same value of 298.5K(again negligible change in temperature).

-> Sharp brake is applied at 30th second bringing vehicle at rest & again the temperature change is negligible for both power converter & motor.

In this case the thermal response of cooling system is excellent.

3. For Constant speed driving cycle:

when driven at 45km/hr for 100km for 2.2.hrs, the temperature change for power converter is from 298K-330K & for motor its from 298.4K to 301.4K, which is again very acceptable.

-> So as per our inference the power converter shows good thermal response in situations like full throttle & sudden braking modes but shows erratic/poor thermal response during dynamic/real life drive cycle/FTP75 case.

For deciding which drive cycle is most energy efficient

-> In the FTP75 drive cycle, the final battery SOC at the end of journey is 83.51% after running for 17.81km.If vehicle is driven under same conditions till full battery charge is used the vehicle would run for estimated 107.9km

-> In WOT(60 sec) drive cycle, the final battery SOC at the end of journey is 99.58% after running for 0.4350km.If vehicle is driven under same conditions till full battery charge is used the vehicle would run for 87km.

-> In constant speed drive cycle, the final battery SOC is 37.98 % after running for 100km.If vehicle is driven under same conditions till full battery charge is used the vehicle would run for 161.2km.

So the most efficient drive cycle from the above is the constant speed drive cycle where the vehicle is driven at constant 45km/h for 100km for 2.2 hrs runs for 161.2 kms at full battery usage,then comes the FTP75 drive cycle & finally the WOT(60sec).