Today’s popular commercial power system dynamics simulation (PSDS) software use explicit integration to handle the time-increment response of power system controls. The basis of this goes back to as early as 1960, when an integration technique known as the Fortran Analog Computer Equivalent, or FACE, was proposed. Explicit integration allows for simpler programming by assuming the response to stimulus can be represented in the next time step, thus avoiding iteration.  However, explicit integration leads to a slight numerical error that is cumulative.  This error leads to phenomena such as the “lie” and “drift” (illustrated in a case study below) encountered during dynamic simulation.