A novel LCL filter parameter design method basing on resonant frequency optimization of three-level NPC grid connected inverter

For high power three-level NPC grid connected inverter, which has the characteristics of low switching frequency and complex harmonic distribution of output current waveform, it deduces the total output filter inductor expression and researches the relational expression between inductance ratio, damping ratio and resonant frequency, harmonic attenuation ratio, as well as damping power. Based on this, an optimized resonant frequency LCL filter design scheme which can also reduce the damping power loss of three-level NPC grid connected inverter is proposed. Through the comprehensive theoretical analysis, the proposed scheme calculates the range of key parameters of the LCL output filter, meanwhile, it ensures the filtering effect as well as reduces the system cost. By paralleling a small damping inductor with the damping resistor, it reduces the damping loss and increases the efficiency of the system. Feasibility and effectiveness of the optimized scheme are validated by simulation and experimental results.