Off board EV Charger with SEPIC Converter

Abstract

Charging an EV using external infrastructure (off-board charging) involves dedicated stations featuring AC/DC power conversion stages and control mechanisms to manage the charging process safely and efficiently. The fundamental architecture of these converters (unidirectional or bidirectional AC-DC and DC-DC) is a primary determinant of the system\'s cost, physical footprint, efficiency, and functional capabilities. Fast charging via high-power converters not only benefits users but also provides grid ancillary services. A significant challenge emerges; however, as expanding EV fleets and renewable energy penetration into distribution networks generate harmonics. This harmonic pollution deteriorates power quality, potentially compromising grid operation, safety, and dependability. Therefore, advancing power converter technology, refining charging methodologies, and improving grid interconnection strategies are essential to fully realize the potential of electric vehicles. In this paper a SEPIC converter for charging of electric vehicle in an off boards charging technique. The system is proposed to integrate a PV source and energy storage system. The converter is controlled through a fuzzy logic controller with a view to improve dynamic response of the charging system.

Introduction

Off-board EV chargers are external charging units that convert grid AC power into battery-compatible DC using power converters such as rectifiers and DC–DC converters. Their selection depends on compatibility, charging speed, installation needs, and cost. Among DC–DC converter topologies, conventional boost, Cuk, and buck–boost converters face issues like high ripple, low efficiency under disturbances, lack of isolation, and slow transient response. To address these limitations, the SEPIC converter has gained prominence because it provides non-inverted output, low ripple, inherent isolation, high efficiency, and true shutdown capability.

Integrating photovoltaic (PV) arrays into EV charging systems enables sustainable off-board charging. A typical PV-EV charger consists of PV panels, DC–DC converters with MPPT, an energy storage system, and a controller. MPPT techniques such as perturb-and-observe optimize PV efficiency under varying irradiance. However, traditional boost converters draw large inrush currents and lack fail-safe behavior, motivating the adoption of SEPIC converters for voltage boosting in EV charging.

This paper presents a SEPIC-converter-based off-board EV charging system supported by a bidirectional DC–DC converter and an auxiliary battery. The SEPIC converter operates in buck or boost mode depending on the duty cycle and provides stable, low-ripple DC output. Its operating principle involves two intervals—switch ON and switch OFF—during which inductors and capacitors exchange energy to produce a regulated output.

A MATLAB/Simulink model integrates a 400 W PV panel, SEPIC converter, EV battery, auxiliary battery, and a fuzzy logic controller (FLC). The FLC generates PWM signals using voltage error and change in error through a 7×7 rule base. A three-stage bidirectional converter manages power flow between PV, auxiliary storage, and the EV battery. When PV power exceeds 300 W, both main and auxiliary batteries charge; when power drops below 200 W, the auxiliary battery discharges to support the EV battery. The SEPIC converter maintains a stable 28 V DC link under varying solar irradiance levels (1000, 200, and 750 W/m² in simulations).

Conclusion

An off-board EV charger with a SEPIC converter offers an efficient and flexible solution for charging of EVs. The SEPIC converter provides several advantages in this context, such as the ability to step up or step down the input voltage, making it well-suited for applications where the charger needs to handle variable grid or renewable energy sources. Additionally, SEPIC converters ensure continuous current input, leading to less stress on the components and improved reliability.

References

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Copyright

Copyright © 2025 Kiran Ravindra Shivasharan, Dr. Seema Diwan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.