A Variable Switching Frequency-Based Triple-Phase-Shifted Loss Optimized Modulation Strategy for DAB-Based DC–AC Microinverter

In this article, a switching network loss optimized variable frequency-oriented pulsewidth modulation (PWM) control strategy for a single-stage single-phase dc–ac inverter is reported for the application of grid integration of solar PV. The converter is realized by employing a dc–dc high-frequency (HF) dual-active-bridge (DAB) stage followed by a low-frequency full-bridge unfolder. To synthesize a loss optimized modulation technique for the converter, the HF switching network losses are precisely quantified by employing a generalized-harmonic-approximation (GHA)-based DAB circuit model. Parallel to this, an analytical framework for computing the output voltage total harmonic distortion (THD) under any PWM control strategy is formulated and validated in this article. Furthermore, based on the mathematical models for loss and THD, a multivariable multiconstraint loss optimization algorithm is developed that outputs the optimal choice for the converter design as well as control parameters, ensuring an efficient power flow while yielding a better THD and improved electromagnetic interference (EMI) performance. Moreover, the proposed variable-frequency triple-phase-shift (TPS) DAB modulation scheme provides appropriate condition for the zero-voltage switching (ZVS) of the HF DAB legs over most part of the ac line cycle while ensuring a minimal turn-off switching current that leads to substantially lower switching loss. A GaN/SiC-based proof-of-concept connecting the 40-V/500 W-solar panel to the 120-V_rms ac grid is developed and its operation under the proposed control scheme is validated at the nominal operating point to verify the formulated analytical models and simulation results. The experimental results conclude that with the application of the proposed optimal modulation scheme, the dc–ac inverter achieves an efficiency and output voltage THD of 96.24% and 2.51%, respectively.