| abstract |
A single-phase non-isolated photovoltaic grid-connected system without leakage current, the system includes: photovoltaic power module PV, DC-DC converter, NPC three-level inverter, LCL filter, and AC power grid. The photovoltaic power module PV is connected to the DC-DC converter, the DC-DC converter is connected to the NPC three-level inverter, the NPC three-level inverter is connected to the LCL filter, and the LCL filter is connected to the AC grid. The DC-DC converter of the front stage realizes the flexible adjustment of the boost ratio while ensuring the automatic voltage equalization of the output capacitor, so that the input capacitor voltage of the NPC inverter in the latter stage and the midpoint potential between the capacitors are stable, avoiding the inverse voltage. The distortion of the output AC volume of the inverter also omits the control of the midpoint potential balance of the input capacitor by the latter-stage inverter, which greatly simplifies the control strategy of the latter-stage inverter. The inverter output is followed by an LCL filter. The control of the inverter keeps the output current in the same phase as the grid voltage. On the other hand, the half-bridge structure at the rear stage makes the common-mode branch short-circuit, effectively suppressing the leakage current of the traditional non-isolated grid-connected system. |