Research on the harmonic compensation strategy for improving the low-voltage ride-through performance of CHB PV inverter during inter-phase short-circuit fault.

When an asymmetric low-voltage ride-through (LVRT) fault occurs, the interaction between negative-sequence component of grid voltages and positive-sequence currents may cause active power backflow from the ac side to one phase of the three-phase isolated cascaded H-bridge (CHB) photovoltaic (PV) inverter, resulting in the inverter has no balanced operating point and eventually shut down, unable to meet the grid-connected standards. Although the existing methods can solve this problem under certain operating conditions, there is still a large active power backflow operation area during inter-phase short-circuit faults. Therefore, a harmonic compensation strategy for improving the LVRT performance of CHB PV inverter is first proposed. Specifically, the modulation voltage of non-fault phase is extended to three symmetrical voltages with the same amplitude and fixed phase difference, and then their maximum and minimum harmonic voltage is calculated and combined with the fundamental-frequency adaptive zero-sequence voltage to compensate for the three-phase modulation voltages. Secondly, the quantitative comparison with existing methods from two dimensions shows that the proposed method can lower the non-fault phase modulation voltage amplitude and further reduce the active power backflow zone. Finally, experimental results from a low-voltage and low-power prototype validate the effectiveness and feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]