Final Project: Electric Rickshaw modelling

AIM

To create a detailed MATLAB model of an electric rickshaw (three wheel passenger vehicle). 

 

OBJECTIVES

Electric rickshaw model with following details,

1. Rear wheels driven by PM brushed type motor.
2. Assume efficiency points of motor controller and motor.
3. To create an excel sheet with all input and assumed data.
4. Energy consumption values for three standard driving cycles.
5. Temperature rise of motor and controller for 100Km constant driving at 45Kmph.

 

THEORY

An electric rickshaw or e-rickshaws is a vehicle that has 3 wheels, with two in the rear and one in the front powered by one electric motor. These are eco-friendly and has low fuel cost. They are mostly manufactured in India and China. The most common types of motor used are Permanent Magnet Synchronous Motor (PMSM).

one of the popular E-rickshaw model in India , the Mahindra Treo is shown below,

The batteries used are commonly of 48V and the power of motor ranging from 1kW to around 8kW. The battery type used is lead acid type. And they are designed to carry loads upto 500-1000Kg.

BLOCK DIAGRAM

The block diagram for an Electric rickshaw which uses a battery and a PMDC brushed type motor is shown below,

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.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 3 different drive cycles.

The first drive cycle source and its parameters are shown below,

The second drive cycle used is Wide Open Throttle . this particular drive cycle is used to run the vehicle for 100Km at constant 45Kmph.

The parameters for this block is calculated as follows,

Time taken to cover `100Km` at constant `45Kmph` can be found as shown below,

`Time = "distance"/(speed)`

`Time = 100/(45/3600)` , to convert `45Kmph` to `"Km"/s` we have divided it by`3600`.

     `=8000s`

Now the block parameters for this block is given as shown below,

The last drive cycle given is custom made using excel sheets and added by clicking the ‘select file’ button in the Drive cycle source block as shown below,

The drive cycle plot is shown below,

Now to select the required drive cycle , we have used a multi-port switch block. To which we can connect all three drive cycles. And this block has a control signal input port , to which we connect a constant block. So by entering the position at which the required drive cycle is connected we can select any of them. This block and its parameters are shown below,

Here we can see number 2 in the constant block , this will select the second drive cycle connected to it.

 

• 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,

 

 

• Power control unit subsystem

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, a current sensor , temperature sensor and a Goto block..

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.

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. Also we have added thermal port to this block to measure the temperature. This port is added by right clicking on the block , which will open the window shown below, where we can select the thermal port,

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,

Temperature sensor

This block and its parameters are shown below,

This block is used to measure the temperature of the controller in Kelvin(K). This block is connected to a Goto block with tag ‘control_temp’ as shown below,

Goto block is used to pass values to the ‘From block’ so that this value can be accessed from anywhere in the Simulink diagram. This input can be a real or complex valued signal or vector of any data type. This ‘From block’ and ‘Goto block’ allows us to pass a signal from one block to another without actually connecting them.

 

• DC motor

To convert the electrical energy to mechanical energy we use motors. In this electric vehicle model we have used PMDC brushed type motor. This motor can act as a generator also in case of regenerative braking. Also thermal port is added to this block by right-clicking on the model , and selecting simscape -> block choices -> show thermal port. This port will output the temperature of the motor. This port is connected to the temperature sensor block and it is connected to the Goto block with tag ‘motor_temp’ as shown below,

The motor block parameters are shown below,

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

 

• Battery subsystem

In this subsystem we have a Li-ion battery block , a controlled current source block ,a goto block , and a bus selector which is connected to the m port of the battery block.

Li-ion Battery block

This battery block implements a generic battery model for most popular battery types. In this case we have selected Li-ion battery type as shown below,

All other parameter sections are kept at default values.

Now from the m port of the battery block , we get SOC,ampere and voltage values. These values are extracted using bus selector , which when connected to the m port , will show those values as shown below,

The SOC output is connected to a Goto block with tag ‘SOC’.

The ampere and voltage output is connected to a product block and multiplied to get the energy value in Watts. This output is connected to a integrator block which will add those Watts over the simulation time and gives us Watt second value. This Watt second value is converted to Watt hour by dividing by 3600. And the output is connected to a Goto block with tag ‘Energy’.

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,

 

Then a Goto block is connected to this current source block with tag 'current'.

 

• Vehicle body subsystem

This subsystem represents the body of the electric rickshaw with three wheels . 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 7 . 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 the rear two wheels , representing a rear 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 three tires. One at NF and two at NR ports. This represents the front 1 tire 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 m/s. This m/s is converted to Km/h by multiplying by 3.6.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.

 

RESULT

The results section of this e-rickshaw model is shown below,

Here we can see a scope which shows us the input vs output velocity graph. This scope has two inputs , one is the drive cycle and the other one is the velocity feedback. This two is combined using a bus and connected to a Goto block with tag ‘result’ and the corresponding ‘From block’ is connected to the scope to get this graph.

The resulting graph for this scope is shown below ,

For FTP 75 drive cycle,

For 100Km at constant 45Kmph ,

For custom made drive cycle,

 

The next scope is used to get the change in SOC value with respect to time. The input for this scope is the SOC output of the Li-ion battery block’.

The resulting graph is shown below,

For FTP 75 drive cycle,

For 100Km at constant 45Kmph ,

For custom made drive cycle,

Then another 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,

For FTP 75 drive cycle,

For 100Km at constant 45Kmph ,

For custom made drive cycle,

Then we have two other scopes , which has input connected to ‘From block’ with tags ‘motor_temp’ and ‘control_temp’ respectively.These graphs shows us the variation of temperature with respect to time. These two ‘From blocks’ are also connected to two displays , which displays the temperature value in degree Celsius.

The motor temperature graph for FTP 75 drive cycle is shown below,

The controller temperature for FTP 75 drive cycle is shown below,

The motor temperature graph for 100Km at constant 45Kmph drive cycle is shown below,

The Controller temperature graph for 100Km at constant 45Kmph drive cycle is shown below,

The motor temperature graph for Custom made drive cycle is shown below,

The Controller temperature graph for Custom made drive cycle is shown below,

Then we have the display which displays the distance covered by the vehicle in Km. It is calculated by integrating the velocity feedback value and dividing it by 3600 to convert it to Km.

Also there is another display , which is connected to the ‘From block’ with tag ‘Energy’. This display shows us the energy consumed to complete the drive cycle.

The temperature of the motor and controller , energy consumed , distance covered  and SOC values for the three drive cycles are shown in the table below,

CONCLUSION

The MATLAB model of an electric rickshaw which uses PMDC motor and has rear wheel drive have been successfully made by choosing suitable blocks from the Powertrain block set and following conclusions has been drawn from the results.

 

For FTP 75 Drive Cycle

From the input vs output velocity graph we can see that the e-rickshaw model that we designed have traced the FTP 75 drive cycle quite accurately till the maximum speed it can achieve which is 70 Kmph.  

Now looking at the SOC graph we can see that almost 84% of the battery capacity is remaining after 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 230A and during regenerative braking the maximum current value reached is near to 200A.

The energy consumed for completing this drive cycle is 890Wh. And the motor temperature reached 80 °C and the controlled temperature reached 73 °C , these temperature values are within the operating temperature range and hence no issues. And from the graph for the two temperature values we can see that it is increasing as the distance covered increases , so if have to travel more distance than this drive cycle , then we should implement proper thermal system management.

 

For 100 Km at constant 45 Kmph drive cycle

From the input vs output velocity graph for this drive cycle we can see that it follows the drive cycle and stays at 45 Kmph throughout the simulation time. At the beginning it took few seconds to reach 45 Kmph but after reaching it remained constant.

The SOC graph for this drive cycle is pretty straight forward because there is no braking or deceleration taking place . So the SOC value decreased proportional to the distance covered. Only 29% of the battery capacity was remaining after completing this drive cycle.

Looking at the current variation graph we can see that at the start of the simulation , the current reached very high value of 590A to attain the 45Kmph mark in an instant but after that the current drastically decreased and reached 33A after 110 seconds. It stayed at this value till the end of the simulation.

The energy consumed to complete this drive cycle is 3837Wh. And the motor and controller temperature reached 104 °C and 75 °C respectively. Here the motor temperature is quite high and its beyond the optimum working temperature range of 70-100 °C. So for this drive cycle we need very high power cooling mechanism so as to maintain the motor temperature at a optimum value.

 

For custom made drive cycle

This drive cycle is very small and it covers only a distance of 1.296Km. From the input vs output graph of this drive cycle we can see that our model tracks the reference velocity almost perfectly. And since the top speed of this rickshaw is 70Kmph , it was able to reach the highest velocity point of this drive cycle which was around 65Kmph.

The SOC graph didn’t had much change and the battery percentage remaining was 99%. But from this SOC graph we can clearly see the point at which regenerative braking takes place , these are the points where the graph increases.

From the current variation graph we can see that the maximum current drawn is around 700A and during regenerative braking it reached around 400A. These current values are quite high and the reason for that is , in this drive cycle the time taken for  change in speed is very low.

The energy consumed for completing this drive cycle is 53Wh.And the motor and controller temperature reached 34 °C and 33 °C respectively. These are very low values , and this is because the vehicle hasn’t travelled for long distance.