A novel algorithm for increased power balance in cascaded H-bridge multilevel cells in a hybrid power amplifier

This paper concerns the issue of unbalanced output power among cells in cascaded H-bridge multilevel (CHBM) converters with conventional staircase modulation techniques under low modulation signals. This is a common condition in high-voltage/frequency hybrid power amplifiers (HPAs) consisting of a CHBM converter in series with a linear power amplifier (LPA). The online implementation of a modulation technique called split-voltage first-in first-out (SV-FIFO) that mitigates this issue is presented in this study. Differently from conventional techniques, it needs to take into consideration the magnitude and frequency of the reference voltage to generate the gating signals of the CHBM converter. This paper also introduces a design procedure for a series-type HPA and a means for generating online the gating signals of the CHBM converter, with SV-FIFO, and the reference signal for the LPA in closed loop with a mixed signal controller. Experimental results for a series-type HPA with a six-cell CHBM converter and a commercial LPA are provided to validate the design procedure of the HPA and demonstrate the enhanced (active) power balance of SV-FIFO and the effectiveness of the proposed control scheme for the HPA under transient and steady-state conditions.