Fully Digital Current Control Techniques for Active Flying Capacitor Balancing in Three-Level Buck Converters

The challenge of balancing the flying capacitor (FC) voltage without sensing it remains a critical issue in multilevel FC converters. This paper proposes an automatic voltage balancing technique using digital current-mode control with emulating ramps and sampling the inductor valley current twice per switching cycle. Thereafter, a current error correction logic has been incorporated in an additional loop for faster FC voltage balancing. The slope requirement of the emulating ramp has been determined analytically from the steady-state stability analysis. The proposed technique works satisfactorily, even during the start-up process and various relevant transients that this converter may experience during the operation time. Along with simulation results, experimental case studies have endorsed the robustness of the proposed technique for a 48V to 12V, 200KHz laboratory hardware prototype.