Assignment 3: Part 2:

Use the Matlab/Simulink and develop models of the PM and Series DC motors.

The small motors are similar and they have the following parameters:

PM Motor

Va = 6 V (rater – nominal voltage); La = 120e-3 H; Ra = 7 Ohms;

J = 2.12e-6; Dm = 6.04e-6 N*m*s; Kv = 1.41e-2  V*s/rad;

Nominal load torque: Tm = 3.53e-3 N*m;

Series Motor

Va = 6 V (rater – nominal voltage); combined inductance of both windings La+Lf = 120e-3 H; combined resistance of both windings Ra + Rf = 7 Ohms;  

(you may assume La = 80e-3 H, Lf = 40e-3 H, Ra = 6 Ohms, Rf = 1 Ohms)

J = 2.12e-6; Dm = 6.04e-6 N*m*s; Laf = 39.5e-3 H;

Nominal load torque: Tm = 3.53e-3 N*m;

Hint: Open Matlab and start the Simulink by clicking on  button, or by typing Simulink on the Matlab command line. Then, create a new model and build the motor model using the appropriate Library Blocks (summers, gains, integrators, transfer-functions, etc.).  In your model window, go under Simulation => Simulation Parameters: For better accuracy set the both error tolerances to 1e-4 and limit maximum time step to 1e-3; Also, set your model stop time to 1 sec. The easiest way to view the results is to use the Scopes that can be found under the Sinks. Otherwise, you can output the variables into Matlab workspace for future plotting.

You may type in all the values in each block, or you may create a script file which will contain the parameters. When you execute the script file on Matlab command line all the variables will be loaded into the workspace. You can then use these variables (names) in each block instead of numerical values. 

a) Implement the following transient study:

Start both motors with zero initial conditions. At time t = 0.5 sec, apply the constant nominal torque to each of the motor. Use the step function Step that can be found under the Sources in the Simulink Library. Plot and compare the armature current Ia, rotor speed wr, and electromagnetic torque Te.

You should observe the start-up transient followed by the response to the applied load.

b) Steady state analysis:

Calculate the starting current Istart and starting torque Te_start for each motor. Compare these values with the peak values observed during the start-up transient. How and why are these values different?

For this part, turn in the following:

Plot and comparing Ia, wr, Te, as required in a) transient study

Calculations/answers as required in b) steady state analysis

Page showing your Simulink model  

To help you to get started, here are two example Simulink models of a 5-hp Separately Excited DC motor:

Model file (use save as) (model1) and (model2), and the parameter script file (dc_par.m)

Run the parameter file first. It will load the variables into the Matlab workspace.

Then, you can run the models and observe the results using the Scope.

Play with the model and get familiar with the Simulink interface.

You can modify these models to make the models of the two motors that you have to compare.

Good Luck !