A Reduced Carrier Count Triangular Modulation for Quasi Single-Stage AC-DC Dual Active Bridge

This paper presents reduced carrier count triangular modulation (TRM) for quasi single-stage (Q1S) bidirectional AC-DC dual active bridge (DAB). The conventional TRM is based on inner mode of duty cycle modulation of only one/single H-bridge for the single-stage bidirectional ac/dc converter. However, to realize conventional modulation technique at least three dissimilar carriers/counters are required. Carriers are dissimilar because, despite having the same frequency, each carrier has a different phase w.r.t each other at any switching instance. Moreover, to implement conventional TRM, six different enhanced pulse width modulated (EPWM) signals are required. In the proposed TRM instead of modulating single H-bridge, one leg of the H-bridge is modulated using sinusoidally modified variable time period PWM. The presented modulation technique can be realized using single carrier and required only four different EPWM signals. The proposed technique offers unity power factor (UPF) operation, zero current switch (ZCS) turn ON and OFF for the AC side bridge, zero voltage switch (ZVS) turn ON and ZCS OFF for one leg of DC bridge operating at fixed frequency and ZVS/ZCS turn ON for another leg operating at variable time period. The proposed technique is realized using TMS320F28335 microcontroller and tested on a scale down prototype of 450W for bidirectional power flow.