A Single-Phase Low Cost, Compact/High Power Density Portable EV Charger for High Voltage EV Battery Packs with Weak/Strong Grid Operation Capability

Abstract

This paper presents a grid interactive portable single phase EV charger for EVs with high voltage battery packs, especially terminal voltage lies between 280–500 V range. Furthermore, the EV charger is capable to work under both strong/weak grid scenarios while maintaining total harmonic distortion (THD) of grid current as per the IEEE 519–2014 and IEC-61000-3-2 standards during complete charging profile. It incorporates single phase Vienna rectifier as an active power factor correction (APFC) stage, and full bridge LLC converter (FB-LLC) as isolation stage. The control of APFC stage allows the front-end converter operation without any reflection in grid angle under weak grid conditions due to presence of harmonics, DC offset and frequency/phase drift in grid voltage. It is because of grid faults, non-linearities of power electronics interfaces in distributed power generation and sensor anomalies. For this, frequency fixed second order generalized integrator (FF-SOGI) based synchronous reference frame-based phase locked loop (SRF-PLL) is utilized. Along with that a low pass filter (LPF) is used in SOGI to eliminate the DC offset in grid voltage. The intermediate split DC link voltage is actively regulated in conjunction with the variation in battery terminal voltage, which provides active tracking of zero voltage switching (ZVS) operating region over variation in battery terminal voltage while charging. A detailed design procedure of tank circuit parameters of FB-LLC converter is shown to ensure the converter operation within safe operating region with ZVS ON, limited turn-off losses and lower di/dt at secondary side diodes, over complete charging profile. For this, a 3.3 kW system is designed and simulated to validate the effectiveness of the claimed benefits.