This paper presents an accurate full-order continuous-time average model for a resonant-based inverter with variable switching frequency and phase shift control. A single-stage series-resonant dual active half bridge (SR-DAHB) inverter with combined phase shift and frequency modulation is studied. Four state variables are taken into account; resonant inductor current, resonant capacitor voltage, output filter capacitor voltage, and inverter's filter inductor current. Since the ripples in the state variables are not small, the dc and first terms of the Fourier series are used to represent the average of the state variables more accurately. In addition, the small signal transfer function of the control-to-output has been derived to design a closed-loop current regulator. Finally, a hybrid control architecture is proposed based on the large and small-signal models. Simulation and experimental results on a 1kV, 50kW SR-DAHB inverter prototype validate the accuracy of the proposed full-order state-space model.