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LCL Filter Design and Inductor Current Ripple Analysis for 3-level NPC Grid Inter-face Converter

Fig. 1. . 3-level NPC converter with LCL filter
The capacitor and grid side inductor L2 is designed based on the attenuation requirement and the reactive power consumption. The grid code harmonic and the inverter output voltage spectrum together setup the attenuation requirement for the LCL filter. The L2 inductance is designed to meet that requirement. Finally, the resonant peak of the LCL filter is considered with the passive damping circuit. Different damping circuit topologies for the LCL filter are compared and investigated in detail. The RLC damping circuit is selected based on the damping result, component size, and the power loss. The filter design is verified by both simulation and a 200kVA 3-level NPC converter hardware.

Fig. 2. Inverter side current ripple waveform
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