A High Efficiency Asymmetric Three-Level Buck–Boost Converter for Battery Charging Applications

Owing to its reduced switching and inductor losses compared to traditional two-level converters, asymmetric three-level buck–boost (3LBB) converter shows its potential in universal serial bus (USB) power delivery (PD) charger application. To fully leverage its advantages across wide input and output voltage ranges, this work provides a detailed analysis of 3LBB operation modes. A novel operation mode is identified, accompanied by a corresponding modulation strategy. The proposed strategy ensures both optimized efficiency and seamless transitions between different modes. Additionally, to address the challenge of flying capacitor voltage balancing in multilevel converters, a novel balancing technique incorporating both duty cycle and phase-shift compensation is proposed. This method provides active balancing across all operating conditions and significantly enhances voltage regulation on flying capacitor under light loads compared to existing approaches. Collectively, the proposed control strategies yield substantial efficiency improvements. A 240 W prototype complying with USB PD 3.1 standards was experimentally validated. The prototype verifies the effectiveness of the proposed operation modes and voltage balancing method. An efficiency improvement of 3.2% under full load is achieved compared to two-level converter.