Improved Module Power and Loss Balancing Through Carrier-Reassignment PWM in a 17-Level CHB-Based EV Charger

Cascaded H-bridge (CHB) based electric vehicle chargers are widely recognized for their modularity, scalability, and robust fault-tolerant capability. Such converters are often modulated using level-shifted carrier-based PWM (LSPWM) schemes due to computational simplicity and ease of implementation, but results in significant power imbalance among the modules. This power imbalance can be mitigated by reassigning carriers to modules, called Carrier-Reassignment PWM (CR-PWM). A First-In-First-Out (FIFO) based CRPWM is very easy to implement and provides some improvement over LSPWM, but fails to achieve perfect power balance. This paper proposes a novel carrier-reassignment scheme specifically designed for a 17-level CHB stage with eight reassignments per fundamental cycle, resulting in near-perfect power balance among modules. The redistribution of power also results in improvements in semiconductor losses - both conduction and switching loss. Loss models for the semiconductor devices were created through hardware double-pulse tests, SPICE and PLECS models, and integrated with MATLAB/Simulink to validate the proposed PWM scheme.