This FB converter can supply 230 Vrms (DC +, DC-, or AC) to a resistive load #Ro through an inductive filter #L. The upper part of the schematic handles the different modulation strategies while the lower part contains the FB (H-bridge) and the power circuit. For conciseness, the diodes are omitted.
By default, control switches #MOD1 and #MOD2 are set in the configuration \ / to enable PWM modulation. In this configuration, the control switch #MOD3 can select between unipolar and bipolar modulation. Both PWM modes handle DC and AC conversion by the control of the modulation signal #vm such as
$v_{AB1}(t)=V_d\cdot v_m(t)$
where $v_{AB1}(t)$ is the instantaneoues average value of $v_{AB}$ over one switching frequency. While Bipolar mode drives leg A and B simultaneously when #vm crosses the carrier signal #vc, unipolar PWM shifts leg B by inverting the modulation signal.
Switching #MOD1 and #MOD2 to their configuration / \ enables Square Wave modulation where the output voltage amplitude is controlled by the delay between #vswA and #vswB.
