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
Figure 15-3 shows the current waveform under these conditions:
A torque transient of the motor's rated torque of 1.9 N·m is applied to the motor shaft, resulting in a current of 4 A. The electrical frequency as seen in the oscilloscope plot is 4 Hz. For a 4-pole pair motor, this frequency results in a speed of 60 ± 1 RPM once it has stabilized. Notice that the time where the load is applied might be different compared with the time of the capture variables. However the conditions of applied torque shown in the scope plot compared to captured variables is identical. The difference in time is due to the fact that the capture current was captured in a different test although having the same parameters.
FAST stands for Flux, Angle, Speed and Torque. Figure 15-4, Figure 15-5, Figure 15-6, and Figure 15-7 show the behavior of the FAST algorithm and how the torque step command affects the FAST output variables.
FAST variables are consistent even with a 100% step- load.
Figure 15-4 is the estimated flux of the motor. It is actually the flux linkage provided by FAST, and it is shown to be fairly constant. The variation of this flux is a result of different aspects such as motor parameter accuracy as well as how well the magnetic circuit of the motor is designed for a particular load.
Figure 15-5, Figure 15-6, and Figure 15-7 show the flux angle provided by FAST. As can be seen, the angle is tracked through the increase of motor load, and also the decrease of motor load.
If the angle is zoomed in where the motor is loaded, it can be seen how the rate of change of the angle changes to a very low rate of change, and once the speed controller corrects for this, the rate of change is picked back up to the commanded speed.
The same behavior can be seen when the load is removed from the motor shaft. The speed is increased due to the torque command provided by the speed controller, and after some time, the speed controller regulates the speed down to the 4 Hz (60 RPM) command.
It is worth mentioning that the purpose of showing the speed variation is not to show the performance of the speed controller. In fact, the speed controller has nothing to do with the FAST estimator. Figure 15-8 shows how the estimator tracks the speed of the motor even when the torque demand stalls the motor for a small period of time.
Figure 15-9 shows the torque signal produced by FAST. This torque signal is useful to know the instantaneous torque on the motor shaft, and calculate motor loading without a torque sensor. This high bandwidth signal shows tracking of the torque even when steps are commanded.
Also, we plot the Iq current waveform to show the field oriented control performance that FAST allows when torque steps are commanded. As can be seen in the current plot for Iq (Figure 15-10), the response to the current demand can follow a step as in the example, where a step load is applied to the shaft. The angle tracking capability of the estimator allows this step response in the Iq controller. You might also notice that the torque curve is not as flat as the current curve. This is due to the variation of the flux linkage seen in the previous flux plot, possibly due to a mismatch on the motor model compared to what the reality of the model is.
In the previous example it can be seen that when the load changes so drastically, the speed of the motor can fall all the way to zero. This response can be improved with the speed controller loop itself, but the point of the test is to show how the variables provided by FAST are consistent and valid even with a 100% step on the load command.