A Bidirectional NPC-based Level 3 EV Charging System with Added Active Filter Functionality in Smart Grid Applications

Abstract

This paper proposes a bidirectional Level 3 (fast) power level Electric Vehicle (EV) charging system where the control strategy consist of two cascaded stages. At first stage, the control strategy allows the control structure to utilize a Three- Level (TL) Neutral Point Clamped (NPC) multilevel converter ensuring a unity power factor correction (PFC) by absorbing/injecting a sinusoidal current from/to the grid with low current harmonics. At second stage, two dc-side capacitors of the TL NPC on the dc-bus voltage are connected to two Dual Active Bridge (DAB) DC/DC converters paralleled at the battery. This stage regulates the current that is delivered to or from the battery according to its State of Charge (SOC) and matches the difference between the dc-link and battery voltages. The purpose of the proposed strategy is to deal with higher power levels with reduced stress on components. In addition to bidirectional power exchange, active power filter capability is also added to the control strategy for enhancing power quality in presence of reactive, non-linear and/or unbalanced loads at point of common coupling (PCC) based on the Conservative Power Theory (CPT). Simulation results are presented to demonstrate the validity of the proposed charger system offering very flexible, and selective functionalities.