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 15-11 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 2.2 Hz, which is about 3 RPM higher than commanded by the speed reference. For a 4-pole pair motor, this frequency results in a speed of 30 ± 3 RPM once it has stabilized.
The challenge we run into when using hysteresis dynamometers is that the torque production and the detent torque present in the dynamometer shaft produce an instantaneous torque higher than the commanded torque, causing the motor to be stalled from time to time. This is the main reason why we increased the torque command of the dynamometer at a lower rate compared to the previous example, to avoid the dynamometer to produce more torque than commanded when the motor is stalled temporarily.
Figure 15-12, Figure 15-13, Figure 15-14, and Figure 15-15 show the behavior of the FAST algorithm. FAST stands for Flux, Angle, Speed and Torque, and this is how the torque step command affects those variables. The first variable is the flux linkage of the motor.
Figure 15-13, Figure 15-14, and Figure 15-15 show the flux angle provided by FAST. As was seen with the previous test, the angle is tracked through the increase of motor load, and also the decrease of motor load.
Zooming in the angle plot, we can see transients when the motor is being loaded, and when the load is removed. As we get lower in speed, the quality of the signals, combined with the torque pulsations of the hysteresis dynamometer, makes the angle not look like a perfect saw tooth. Even then, the angle information provides good enough information to run a full FOC control at 2 Hz and a full load transient.
Zooming in when the load is removed from the shaft, we can see an instantaneous angle tracking.
The speed plot is shown in Figure 15-16. The target speed is 30 RPM, and we can see higher ripple on the estimated speed compared to 60 RPM. This is due to the pulsating torque present in the hysteresis dynamometer and also, the estimated speed output is instantaneous as opposed to every electrical cycle. So any distortion on the angle ramp will be reflected in a speed oscillation.
FAST variables consistently enable FOC system to apply full torque even with a 100% step-load at low speeds.
Also, when the load is completely removed, which is done by turning off the dynamometer controller, the speed estimation follows the real speed even when there is rapid acceleration, as shown in Figure 15-11.
The torque signal is shown in Figure 15-17. Oscillations are due to the low frequency of the estimator, as well as the torque pulsations present in the hysteresis dynamometer at low speeds.
The current controller follows the curve of the commanded torque as can be seen in Figure 15-18, taking the current to the rated 4 A in Iq.