Dynamic Phasor Modeling of Resonant Dual-Active-Bridge Inverters

Due to their merits of high efficiency and power density, resonant dual-active-bridge (DAB) inverters are receiving heightened attention in microinverters. However, the existing models of resonant DAB inverters, such as the first harmonic approximation (FHA) model, are nonlinear without any steady-state operating point and suffer from low accuracy. This paper first proposes the dynamic phasor model of resonant DAB inverters that allows the analysis of the resonant inductor current even without any relevant current sensor. Then, by linearizing the proposed large-signal model around the steady-state operating point, this paper proposes the high-precision linear small-signal dynamic phasor model of resonant DAB inverters. Moreover, this paper derives the analytical expression for the Fourier coefficients of switch functions using the double Fourier series. Simulation and experiments validate the accuracy of the proposed model. The voltage error of the proposed large-signal model under a 50% load change is less than 3%, leading to an accuracy improvement of over 20% compared with the conventional FHA model. Notably, the voltage error of the proposed small-signal model is less than 2%.