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
Rs Online recalibration is added to InstaSPIN-FOC to provide an accurate stator resistance while the motor is operating in closed loop. The updates of the resistance are done in real time, and the motor's model is updated according to the new resistance, providing the best performance results when the motor is running in the entire operating range, from no load, up to full load capability of the motor.
Taking a closer look to the InstaSPIN-FOC block diagram, Rs Online is enabled by setting a flag. Stator resistance is measured while the motor is running through a current injection on the direct component of the current, also known as D-axis current. Figure 16-2 highlights the areas used for Rs Online recalibration.
As can be seen from the block diagram, the online resistance recalibration is done by adding an additional component to Irated. This addition is performed within the FAST estimator, and Irated that comes out of FAST already contains the current needed for Rs Online recalibration. This Irated can be zero for permanent magnet motors, or the magnetizing current for induction motors. In the case of field weakening or field boosting, another current can be added as User_IdRef and this additional current does not interfere with Rs Online recalibration.
An important point to notice is that the Rs Online recalibration is calculated from the alternating value of the additional Id injected by the FAST module. These currents are alternating between positive and negative to allow the internal algorithm to function. In addition to that, the user can still command a user's Id reference on top of the value coming from FAST. A typical scenario would be for example to have a negative Id reference to operate in field weakening, and at the same time, have FAST provide a new Irated to compute the online resistance recalibration. This is expected to be a typical use case and it would work giving expected results from both field weakening and online resistance recalibration.
Due to the current injection done, the phase current waveform going to the motor loses it sinusoidal shape depending on the ratio between the injected current and the mechanical load present on the shaft. For light loads, the sinusoidal shape is greatly affected, and for partial to full load the current shape change is barely perceivable. A few plots are shown below, with a motor running at 500 RPM and Rs Online enabled and disabled at various mechanical loads. It can be seen that in some cases the shape of the phase currents lose their sinusoidal shape.
Figure 16-3 shows that currents are sinusoidal at light loads when Rs Online is disabled.
Under the same mechanical loading conditions, when Rs Online is enabled it can be seen in Figure 16-4 how the currents shape is a distorted sinusoidal waveform.
On the other hand, a motor mechanically loaded, with and without Rs Online, the shape change is difficult to perceive. Figure 16-5 shows when Rs Online is disabled and there is a mechanical load present.
And these are the currents under mechanical load and Rs Online enabled, as shown in Figure 16-6.
As can be seen on the last plot, even though Rs Online is enabled, at medium to high loads the distortion is much less, and as the load increases, the distortion is no longer perceivable. In the following sections of this document, it will be shown how low the additional current is to allow Rs Online recalibration.