The resonant network consists of a capacitor, leakage inductances, and the magnetizing inductance of the transformer.
The resonant network filters the higher harmonic currents. Essentially, only sinusoidal current is allowed to flow through the resonant network even though a square wave voltage is applied to the resonant network.
The current (Ip) lags the voltage applied to the resonant network (that is, the fundamental component of the square wave voltage (Vd) applied to the half-bridge totem pole), which allows the MOSFETs to be turned on with zero voltage.
As shown in Figure 4, the MOSFET turns on while the voltage across the MOSFET is zero by flowing current through the anti-parallel diode.