Coordinated charging of electric vehicles (EVs) is critical to provide safe and cost effective operation of distribution systems where household single phase charging of EV could contribute to imbalance of the distribution system. To date, reported researches on optimization methods for coordinated charging aiming at minimizing power losses have the disadvantages of low calculation efficiency when applied to large systems or have not taken the voltage constraints into account. The phase component and polar coordinates power flow equations of an unbalanced distribution system are derived. Primal dual interior point dynamic programming is introduced for coordinated charging of EVs to minimize distribution system losses where charging demand, voltage and current constraints have been taken into account. The proposed optimization is evaluated using an actual 423-bus case as the test system. Results are promising with the proposed method having good convergence under time-efficient calculations while providing optimization of power losses, lower load variance, and improvement of voltage profile versus uncoordinated scenarios.