Consider Fig. 1 below to understand the topic. When the primary switch S_m is turned on, no current flows to the grid because of the direction of the diodes on secondary side.
During that time the energy to the grid is supplied by the filter network.When the primary switch S_m is turned off, then the energy stored in the magnetizing inductance is transferred  to the grid in the form of current.

Figure 1: A flyback inverter