Current Distortion Mitigation in Grid-Connected Three Phase NPC Converter in Presence of Grid Harmonic Voltage Pollution

The present paper reports the design of a grid-connected three-phase neutral point clamped (NPC) converter. Specifically, the voltage balancing, the LCL filter and the control system have been modelled and experimentally validated. Finally, the effect of the grid voltage harmonics on the NPC output currents was investigated, taking into account the voltage distortion defined according to the quality standard. The mitigation of the current distortions induced by the fifth and the seventh voltage harmonics was carried out using a notch filter compensator that has been specifically designed for this purpose. The mitigation of the proposed harmonic compensator under different operating conditions characterised by the presence of these voltage harmonics has been evaluated by means of an experimental test bench.