Filter design for three-level grid-connected inverter with low switching frequency

Aiming at the problems of poor dynamic control performance and difficult filter design for three-level grid-connected inverter with low switching frequency, a three-level discontinuous PWM strategy and its carrier-based implementation method are introduced. Considering the strategy´s output harmonic characteristics, an LLCL filter is adopted. Then, aiming at the resonance problem of LLCL filter, two simple passive damping schemes are comparatively analyzed from the aspects of damping effect, filtering performance and damping losses. The conclusion shows that the series resistor structure has better overall performance. Afterwards, the design principle of the filter parameter is proposed based on the bridge-side current ripple analysis and dominant harmonic component attenuation. Correctness and feasibility of the conclusions are validated by experimental results.