Bidirectional Three-Phase 3L-SNPC Converter for EV Charging Stations

Abstract

This paper presents a bidirectional three-phase, three-level stacked neutral-point-clamped (3L-SNPC) converter for electric vehicle charging stations. The proposed architecture employs two distinct power sources i.e. photovoltaic (PV) modules and the ac utility grid. If rated power is required by the loads i.e. batteries, both sources are responsible for supplying them. Otherwise, if the demanded power is less than that generated by the PV source, the 3LSNPC inverter is responsible for injecting the exceeding amount into the grid. The following advantages can be addressed to the proposed topology: a three-level voltage waveform exists across each leg and the neutral point, while filtering requirements are reduced; the voltage stresses on all semiconductors are equal to half of the total dc-link voltage; power factor is nearly unity in any operation mode; and the voltages across the dc-link capacitors are balanced. However, it aggregates regarding the existence of 18 switches, while the peak input voltage must be less than or equal to half of the total output voltage so that high power factor is obtained. In order to verify the operating principle of the converter, the current and voltage control loops are properly designed according with the following specifications: rms input voltage of 220 V; total output voltage of 800 V, power processed of 15 kW; and grid frequency of 60 Hz. Simulation results on a 15kW converter are also presented and thoroughly discussed.