Flux braking is a term that applies to VFDs that have an option for true "Flux Vector Control" (as opposed to the simpler and cheaper "Sensorless Vector Control") In FVC in it's any forms, the VFD control algorithm is capable of, within EACH sine wave going to the motor, separate the flux current vector from the torque current vector. This is part and parcel to why FVC is better, because it can totally separate these values and avoid putting more of the available energy into making the motor into a motor (flux current) vs creating rotation (torque current). BECAUSE of that capability, when a motor is decelerating and regenerating BACK into the DC bus, the FVC capability can force the excess energy BACK into the motor by over-fluxing it, essentially "wasting" that energy back into the motor where it becomes heat. So it's basically the same as Dynamic Braking, but uses the MOTOR as the "resistor" for a place to put that converted kinetic energy. It then of course suffers from the same limitations as DC Injection Braking in that you are thermally stressing the motor. If your braking cycles are few and far between, this is often not too bad of a problem. But you should NEVER use Flux Braking on any high duty cycle application.