Abstract: This paper presented a DC charging spot system suitable for large parking lots. Its first stage is electrolytic capacitor-less uncontrolled rectifier. The second stage is Superbuck converter acting as the charging interface. The DC charging spot has many advantages, such as high reliability, high efficiency, simple structure, easy control and low cost. However, its input voltage becomes a DC six-pulse wave. Hence, the right half plane zero（RHPZ） existence of the charging interface converter will change constantly with the variation of operation voltages. Furthermore, the pulsating input voltage will generate serious low frequency ripple（LFR） into the output side and adversely affect the battery lifetime. To ensure that the charger operates stably and LFR meets requirements throughout the whole operating range, this paper proposed a robust stability controller design method—globally scanning method—for variable structure system. The transfer admittance-based design criterion of the LFR robust suppression controller was also proposed. Firstly, the stability conditions of the charging system in constant current（CC） mode and constant voltage（CV） mode were given, separately. Secondly, the LFR transmission mechanism and its basic suppression strategy were analyzed. Then, the design criteriaand methods for the input voltage feed-forward controller and the robust PI controllers were given. Finally, the correctness of theoretical analysis had been verified by a 1.8 kW/80 kHz prototype.