Fixed Switching Frequency Control Using Trapezoidal Current Mode to Achieve ZVS in Three-Level DC–DC Converters
Zhigang Yao, Xinyu He, Muyang Liu, J. Liu, Ziheng Xiao, Yi Tang
Abstract
Generally, the variable switching frequency method is used to operate power converters in triangular current mode (TCM) or near critical conduction mode (CRM) to achieve zero-voltage switching (ZVS). However, this approach faces significant challenges: high peak inductor current, and complex controller design due to varied digital delays in variable frequency operation. To address these challenges, this article proposes a novel fixed switching frequency control method using trapezoidal current mode (TZCM) to mitigate the inductor peak current while realizing ZVS for three-level dc–dc converters. A relationship between the average inductor current and the two duty cycles is modeled to determine the appropriate trapezoidal current shape in near-CRM. By simultaneously adjusting two duty cycles and alternating them within each switching period, ZVS is successfully achieved at a fixed switching frequency. Compared with traditional methods, the proposed method not only improves the converter efficiency, especially at light loads, but also pioneers a fixed frequency scheme for achieving ZVS applicable to all three-level dc–dc converters. The proposed control is experimentally validated on a 2 kW prototype, achieving an efficiency of 99.12%.