The PTV system was invented by engineers Porsche AG and was first installed on the Porsche 911 Turbo (code 997) which works using basic physics principles to reduce understeer. It works by directing the rear wheel brake on the inside of the curve (red disc brake in the picture) to reduce the rotation of the wheels, which results in the inner rear wheel arching as a momentary pivot point to distribute power to the weight of the tank and pull the front of the car back into place.

This system was later upgraded to PTVPlus which differs from the previous system by installing Limited-Slip Differential (LSD) at the rear differential gear to distribute the power to create a balance between the left and right wheels. This also improves the power transmission efficiency on wet, slippery road surfaces. It also allows for a more perfect transmission of propulsion while the car is in a curve.

Source: Porsche AG