After completing the following series of exercises, the student will understand the characterization and control of a DC motor.
Real-time simulation results are shown in the laboratory panel.

Parameters Identification

back-emf Constant

• Open the model with the default settings.
• Gradually apply a field voltage of 460 V for the DC machine.
• Gradually apply a field voltage of 460 V for the DC motor under test.
• Connect K1 as shown in figure 10.

Figure 10: DC Machine Armature Connected to the Inverter

•  Apply different voltage values and fill out table 10 below.

Table 10: Speed and Voltage Values for the Determination of Back-emf Constant

• Plot the speed values (x-axis) vs armature voltage (y-axis).
  • Show your graph.
  • Find the slope of the plotted line.
  • What is the value of the back-emf constant in V/rpm?
  • What is the value of the back-emf constant in V.s/rad?
  • Compare the estimated back-emf constant with the value of table 6.
    What do you observe?

Armature Resistance

• Disconnect K1, then set the applied voltage to 0 V.
• Connect K2 as shown in figure 11.

Figure 11: MUT Armature Connected to the Inverter

• Connect K3 as shown in figure 12.

Figure 12: Connection of the DCM Resistive Load

• Apply different voltage values and fill out table 11.
  The values of V_a, I_a, and N can be directly taken from the displays under the Tab “Parameters Identification Ra”.

Table 11: Speed, Voltage, and Current Values for the Determination of R_a

• From table 11, compute the average value of the armature resistance.
• Compare the obtained result for armature resistance with the value of table 6.
• How accurate is the estimation?
  Explain.
  Hint: Use equation (4) with the back-emf constant [V/rpm] found earlier to compute R_a.

Armature Inductance 

• Disconnect K3, then slowly decrease the applied voltage to 0 V.
• Block the rotor as shown in figure 13.

Figure 13: Activation of Blocked Rotor Test

• Apply a voltage source value of 40 V.
  • What is the armature voltage of the DC machine?
  • What is the armature voltage of the MUT?
• Observe the waveform under the “Parameters Identification L_a” tab.
• Use the zoom-in capability of the graph and the available cursors to measure two values of armature current at the linear part of the graph.
  • Compute L_a using equation (6).
  • Compare the obtained result of armature inductance to the value of table 6.
  • How accurate is the estimation?
    Explain.

Friction Parameters

• Decrease the applied voltage to 0 V.
• Deactivate the “Block Rotor” button. If a fault occurs, click on the “Reset” button.
• Go to the “Parameters Identification Tf & B” tab.
• Fill out table 12 by varying the applied voltage.

Table 12: Speed, Current, and Torque Values for Friction Parameters’ Determination

• Based on table 12, plot the speed (x-axis) vs T_em (y-axis).
  • Show your graph.
  • Find the slope of the line and the y-intercept.
  • What is the value of the friction torque T_f?
  • What is the value of the friction coefficient B?
  • Compare the obtained T_f to the total friction of table 9.
• Based on table 12, plot the current (x-axis) vs T_em (y-axis).
  • Show your graph.
  • What is the slope of the line?
  • Explain your result based on equation (9).

Moment of Inertia

• Slowly decrease the applied voltage to 0 V.
• Go to the “Parameters Identification J” tab.
• Apply a voltage source value of 100 V.
  • What is the armature current of the MUT?
    This value corresponds to i_a (0^-) in equation (12).
• Increase the Trigger Level to 340 rpm, then activate the Apply Trigger for Acquisition, as presented in figure 14 below.

Figure 14: Activation of Trigger Level

• Disconnect K2 and observe the waveform of the decreasing speed.
• Use the zoom-in capability of the graph and the available cursors to measure two speed values at the very beginning of the decreasing slope.
  • Compute the slope of the line.
  • Compute the inertia using equation (12).
  • Compare the obtained inertia with the value of table 9.

Current control

• Deactivate the Apply Trigger for Acquisition
• Bring the voltage source to 0 V, then connect K2.
• Activate K3, the “Connect Load” button. Then reduce the load resistance to 15 ohms.
• Go to “Current Control” tab and activate the current control as shown in figure 15.

Figure 15: Activation of Current Control

• Apply a reference current of 10 A.
  • Does the measured current follow the reference?
  • What is the speed of the DC motor under test?
  • What is the armature voltage of the MUT?
• Increase the reference current to 15 A.
  • Does the measured current follow the reference?
  • What is the speed of the DC motor under test?
  • What is the armature voltage of the MUT?
• Increase the reference current to 20 A.
  • Does the measured current follow the reference?
  • What is the speed of the DC motor under test?
  • What is the armature voltage of the MUT?
• Increase the reference current to 25 A.
  • Does the measured current follow the reference?
  • What is the speed of the DC motor under test?
  • What is the armature voltage of the MUT?
  • How do the speed and voltage of the MUT change with increase of reference current?
    Explain your observation.

Speed control

• Decrease the reference current to 0 A.
• Go to the “Speed Control” tab and activate the speed control as shown in figure 16.

Figure 16: Activation of Speed Control

•  Apply a reference speed of 200 rpm.
  • Does the measured speed follow the reference?
  • Does the measured current follow the reference?
  • What is the armature voltage of the MUT?
  • What is the armature voltage of the DCM?
• Increase the reference speed to 400 rpm.
  • Does the measured speed follow the reference?
  • Does the measured current follow the reference?
  • What is the armature voltage of the MUT?
  • What is the armature voltage of the DCM?
• Increase the reference speed to 600 rpm.
  • Does the measured speed follow the reference?
  • Does the measured current follow the reference?
  • What is the armature voltage of the MUT?
  • What is the armature voltage of the DCM?
• Increase the reference speed to 800 rpm.
  • Does the measured speed follow the reference?
  • Does the measured current follow the reference?
  • What is the armature voltage of the MUT?
  • What is the armature voltage of the DCM?
• Increase the reference speed to 1000 rpm.
  • Does the measured speed follow the reference?
  • Does the measured current follow the reference?
  • What is the armature voltage of the MUT?
  • What is the armature voltage of the DCM?
  • How do the armature voltages of the MUT and the DCM change with increase of reference speed? Explain your observation.