To understand SVC, you first have to understand "regular" output from a VFD, called "Scalar" or "V/Hz" output. At this basic level, the VFD puts out a voltage and frequency commensurate with what the motor is designed for, which determines the torque it produces. So a 460V 60Hz designed motor requires 7.67V/Hz (460 divided by 60) to produce rated torque, ergo a scalar VFD spits out 7.67V/Hz. So at 30Hz the voltage is 230V, at 10Hz the voltage is 76.7 etc. etc. This output from the VFD has to provide the excitation (flux) current to the motor as well as the "torque producing" current all at once. So when something in the load changes, the VFD can only respond by giving more current to produce more torque, but at the same time more flux current, even though the currents are flowing at different portions of the size wave; the flux current goes first, followed by the torque current. Because they are increasing together, the excess flux saturates the windings magnetically. So when the load changes (a "step change" in load) with scalar control, the motor slows, the slip increases, that causes the motor to draw more current, which increases torque (AND flux) and eventually the load speeds up again. How long that all takes is a function of the size of the step change in load and the torque capability of the motor. It might take seconds, it might take minutes, it might cause the motor to overload if it takes too long because that excess flux is turning into waste heat.
With Vector Control, the reaction that the motor has to the change in load is monitored by the VFD and the output wave form is altered sub-cycle to "tweak" that V/Hz pattern such that the torque producing current is increased WITHOUT needlessly increasing the flux producing current, each of them measured as vectors of the total current. So more of the energy going to the motor is doing useful work and that allows the motor to respond to that change in load more rapidly. To accomplish vector control, something must tell the mP in the VFD exactly where the rotor is at any given moment so that it can crunch the numbers to know precisely how much torque to apply to affect the desired change. That rotor position measurement was originally accomplished with shaft encoders that fed that data back into a motion control positioning loop in the drive. By making the motor react more precisely and quickly, the "drift" of error in speed (or torque) is corrected much faster; measurable in radians rather than seconds. That allows for more precise control of whatever you need control of.
Vector control has several variants and sub-variants. SVC, so called "sensorless" vector control, is a later development that eliminated the need for an external shaft encoder by looking at subtle changes in the current waveform and comparing that to a mathematical "model" of the motor that is created in the VFD's memory (via tuning to the motor). So SVC is not looking at rotor position with EXTERNAL sensors (shaft encoders), but neither is it really "sensorless" because there are still sensors, they are just current sensors INSIDE of the VFD itself. In addition, the rotor position is not absolute, it is only relational; compared to a previous moment in time and the model. It's far more accurate than basic V/Hz control, but not exactly high precision. So it has limitations, especially at very very low speeds where the signals become too weak to detect. Because of this relational positioning, it's not really possible to totally separate the flux producing current from the torque producing current. It's better at it, and for a vast many applications it's good enough.
If you need more precision, you go with Flux Vector Control (FVC) or another sub-set called Field Oriented Control (FOC). Then even within FVC, there are two sub variants; Velocity Vector Control and Torque Vector Control, based on what you want to accomplish; speed or torque control. Basically, each requires a separate regulator loop within the mP (or DSP). Simple low-cost drives, like the PF525 or PF40, are only capable of Velocity Vector Control when using the encoder feedback, but do not have the mP power to add the Torque Regulator Loop algorithm; that requires a more powerful (and expensive) mP (and/or dual processors), which is what you get with a more advanced drive such as the PowerFlex 70/700/750 series.
So how does that relate? If what you are really after is the equivalent of an "Electronic Shear Pin" protection functionality, you may find that the PF525 functions that provide that (A455-458) are good enough, it will be as good or better than any COTS Electronic Shear Pin relay you can buy. But that's not the same as "separating flux current and torque current", which the PF525 is not totally capable of like the PF755. However, you don't really need that capability just to enable an Electronic Shear Pin, that's more applicable to torque control applications such as winders.
After all, it's the root of the vector calculation.
