Detachment control based on ion saturation current Isat measurements from Langmuir probes (LPs) is implemented in the KSTAR tokamak and shown to be capable of following dynamic and constant target trajectories with good accuracy, in H-mode, by moderating the flow rate of nitrogen or deuterium. Isat controllers normalize Isat in order to form attachment fraction (Afrac) as their control parameter. The KSTAR implementation of Afrac control differs from previous work in that it continuously calculates a model for attached Isat and uses that as the denominator in Afrac, whereas prior implementations either record peak Isat at rollover as they pass it or take estimated as a manual input prior to the shot. The KSTAR controller therefore does not need to keep track of rollover status and keep separate targets for pre- and post-rollover states, and it can automatically adapt to changes in scenario at any time. It is also less vulnerable to noise as it will not lock in an outlier as a rollover point.