A hybrid cascaded photovoltaic (PV) inverter with supercapacitor is proposed, and a synergistic modulation method adapted to the operation principle of the inverter is presented. This inverter contains a supercapacitor cell and several PV cells. The supercapacitor cell uses specific harmonic elimination (SHE) technique to eliminate a part of the low-frequency harmonics in its output voltage, while the PV cells adopt carrier phase-shift PWM (PS-PWM). And a compensation component calculated from the rest low-frequency harmonics generated by supercapacitor cell is added to the modulation index of PV cells, to further reduce the harmonics in the total output voltage. Experimental results show that compared with regular PS-PWM method, the proposed modulation method has less low-frequency harmonics and lower THD when the output voltages and dc voltages of the two types of cells are quite different.