A Unified Two-Dimensional SVPWM and Phase Difference Boundary Analysis for Transformerless Back-to-Back Cascaded H-Bridge Converter

Conventional space vector pulse width modulation (SVPWM) schemes for back-to-back cascaded H-bridge (BTB-CHB) converters suffer from problems such as limited available sectors and the risk of capacitor short-circuit (CSC) faults under phase difference conditions. To address these issues, a two-dimensional (2-D) SVPWM strategy based on bilateral voltage balancing is proposed in this paper. The strategy optimizes the vector synthesis paths, expanding the boundary range of available sectors by 20%. It also ensures smooth transitions in port voltage levels, effectively reducing switching losses and voltage stress. Furthermore, the constraints between the modulation index and phase difference are clarified, providing a theoretical foundation for parameter design and stable operation. Simulation and experimental results demonstrate that the proposed method not only significantly extends the operational range, but also achieves steady-state performance while maintaining a fast dynamic response.