how can i set the load condition to 20% of full load

i have to design a simulink model for a shunt DC motor under the given load condition

where I am asked to

set the simulation time to 10 sec

set the load condition to 20% of full load

what is meant by 20% of full load?

please help me out with this

TIA

Answer 1

[Pratyush Roy]

Hi Ayesha,

Every DC Machine block in Simulink comes with several preset models. Each of these models specify certain values for rated armature voltage, output power, rotational velocity and field voltage. Consider the image below:

This configuration suggests a DC Motor with output power of 5 HP and rotational velocity of 1750 rpm. It also considers armature voltage of 240 V and field voltage of 300 V. From these rated values we can calculate the rated load torque using the following script:

Nrpm = 1750;
w = 2*pi*Nrpm/60; %w = velocity in rad/s
P = 5;
P_watts = 746*5; %P_watt = power in watts
T_L = P_watts/w;

This is the full load torque. When we say that 20% of full load is available, this means the external load torque is 20% of the the calculated rated load torque T_L. We can introduce this torque to the Simulink model through a step block as illustrated below:

Here we can change the final value of the step function to the 20% of load torque and then run the simulation.

The attached Simulink(.slx) file might be helpful to understand the working of the DC shunt motor.

Hope this helps!

[Ayesha Faizun Kalame]

hi

thanks for your help

i do not why, when i open th file it is blank. can you send it again

i want to what i have to write(or the value i have to put) in the step function for 20%

[Pratyush Roy]

Hi,

I have attached the code to this comment. For the step function, calculate the load torque using the code snippet

Nrpm = 1750;
w = 2*pi*Nrpm/60; %w = velocity in rad/s
P = 5;
P_watts = 746*5; %P_watt = power in watts
T_L = P_watts/w;

Then calculate 20% of the T_L magnitude and put it inside the step function.

Hope this helps!

[Pratyush Roy]

Yes, I got the same value, i,e, 8.15 N-m. I think your design values are proper.

[Ayesha Faizun Kalame]

thank you.

is the set up for the model is alright? i have attach the file with the previous reply.

[Pratyush Roy]

According to the preset model values, the armature voltage is 240 V and field voltage is 300 V. So you might consider separate voltage sources instead of a common voltage source, one connected across armature with value of 240 V and the other conencted across field with value of 300 V. Rest is correct.

Hope this helps!

[Ayesha Faizun Kalame]

thank you