Loss analysis of three-level flying capacitor converter-based EV chargers using hybrid WBG-Si devices

Abstract

Electric Vehicles (EVs) are vital for reducing greenhouse gas emissions and promoting sustainable transportation. Advancements in EV charging technology focus on developing power converters with higher DC-link voltages (800V-1000V) and multilevel topologies. This paper explores a full-bridge five-level Flying Capacitor (FC) converter using hybrid silicon and Wide Bandgap (WBG) devices for EV charger grid connections. A key challenge in FC converters is maintaining floating capacitor voltage balance while minimizing power losses. Although higher switching frequencies reduce voltage fluctuations, they increase switching losses. WBG devices, with their high band gaps and low switching losses, address this issue effectively. Thermal analysis of the converter is conducted using PLECS software, comparing Si-IGBT, SiC MOSFET, and GaN MOSFET. The paper proposes a novel multilevel PWM scheme that combines Phase-Disposition (PD) PWM and Phase-Shift (PS) PWM. This hybrid approach enhances waveform quality and improves thermal performance by reducing losses in specific components. To address the high cost of WBG devices, a hybrid strategy is suggested, replacing high-loss components with WBG devices while retaining silicon devices elsewhere. The study identifies optimal switch combinations based on loss analysis using practical data and thermal models. Results highlight trade-offs between cost and performance, presenting a cost-effective solution for high-performance FC converters. This work offers valuable insights into efficient EV charger design, supporting the development of advanced, sustainable charging technologies.