Control and modeling of push-pull forward three-level converter for microgrid

Renewable energy sources are widely used in microgrid. Output voltage of them is often low and varies widely. Because diodes in three-level legs in traditional three-level (TL) converter are substituted by MOSFETs, the push-pull forward (PPF) TL converter is very suitable for wide and low input-voltage applications. It can operate at two-level and three-level modes. Modeling of the proposed converter is established. Control of the proposed converter is designed, which contains output voltage loop and current limit loop. In addition, control block diagrams of both modes can be simplified to one control diagram. By adding input voltage feedforward, influences of input voltage on output voltage and inductor current can be eliminated. The divider in the input voltage feedforward is simplified by two piecewise linear functions, which can be easily implemented by operational amplifiers. Therefore, cost can be reduced. Simulation results of a 1-kW PPF TL converter verify the theoretical analysis.