SPRUHJ1I January 2013 – October 2021 TMS320F2802-Q1 , TMS320F28026-Q1 , TMS320F28026F , TMS320F28027-Q1 , TMS320F28027F , TMS320F28027F-Q1 , TMS320F28052-Q1 , TMS320F28052F , TMS320F28052F-Q1 , TMS320F28052M , TMS320F28052M-Q1 , TMS320F28054-Q1 , TMS320F28054F , TMS320F28054F-Q1 , TMS320F28054M , TMS320F28054M-Q1 , TMS320F2806-Q1 , TMS320F28062-Q1 , TMS320F28062F , TMS320F28062F-Q1 , TMS320F28068F , TMS320F28068M , TMS320F28069-Q1 , TMS320F28069F , TMS320F28069F-Q1 , TMS320F28069M , TMS320F28069M-Q1
In this example the load is increased 30% above the rated torque of the motor (Figure 15-64). The dynamometer is set to a torque command of 2.5 N·m. Keep in mind that the rated torque capability of this motor is about 1.9 N·m, so in fact we are putting about 130% load to the motor shaft. This will cause the motor to overheat, hence the need for the Rs Online feature to keep an accurate resistance while the motor is running.
In Figure 15-64, where a slow rotating angle, which is due to the Rs Online feature can be seen superimposed on the 5 A amplitude current. To learn more about the Rs Online feature, see Section 16.
Zooming into the current (Figure 15-65), we can clearly see the frequency to be 13.33 Hz, which is exactly what we command for the speed reference, which in this case is 200 RPM. The conversion is well known, which depends on the number of pole pairs. Speed (RPM) = Speed (Hz) * 60 / Pole Pairs = 13.33 Hz * 60 / 4 = 200 RPM.
The stator resistance is captured for a period of 5 minutes (300 seconds) and it is shown in Figure 15-66. It can be seen that the value we start with is 2.8 Ohms, and during a period of about 200 seconds it reaches about 3.45 Ohms, stabilizing at this value.
With this increase, we have a difference in resistance of (3.45-2.8)/2.8 * 100% = 23% increase. Applying the equations we use in Section 16, this difference in resistance represents a motor temperature of:
The following estimated values were taken after 10 minutes of working, where the resistance measures about 3.5 Ohms. The estimated flux (Figure 15-67) measures a value very close to the rated flux of 0.5 V/Hz.
We plot the angle (Figure 15-68) when the motor is 30% overloaded.
Zooming into the angle (Figure 15-69), expanding one second of information, we see a clean and continuous ramp. Keep in mind that the data here was taken every 200 samples, so there is a discontinuity at the end of every cycle.
The estimated speed is around 200 RPM, as shown in Figure 15-70.
The estimated torque is around 2.5 Nm. Estimated torque, when overloading the motor, is also accurate and fairly constant as can be seen in Figure 15-71.
The current in this example is about 5.2 A or so (Figure 15-72), due to the 30% of overloading for a long period of time, the current must be higher for higher stator resistance value in order to produce the commanded torque.