removal of decaying dc and harmonics from current and voltage signals for exact estimation of fundamental frequency complex phasor and quick convergence for distance relay

The current and voltage signals contain serious harmonics and decaying dc during the fault period. Moreover, the time constant and amplitude of decaying dc are unknown and associated with the fault resistance, fault position and fault beginning time. How to develop the matlab code that takes the voltage and current signals from three-phase VI measurement and remove the decaying dc and harmonics which added during different faults conditions and further to estimate the exact phasors of voltage and current signals.?