Digital DC-Link Control Strategy For The Three-phase Solar Actively Clamped Resonant DC-link Inverter

Grid-tied solar inverters are one of the important elements of distributed power generation systems. Micro-Inverters connected to a single PV panel are becoming the trend for the future of grid-tied PV systems for a number of reasons including lower installation costs, plug-N-play operation and enhanced flexibility and modularity. The Actively Clamped Resonant DC-Link Inverter (ACRDCLI) has remarkable features of simple structure and high efficiency with only one auxiliary switch. However, the DC-Link loss of ACRDCLI is large, and there exists unfixed commutation delay, which causes sub-harmonics.In this paper, the operational principle of traditional and two-amplitude ACRDCLI is introduced, and then a digital DC-Link control strategy is proposed.By analyzing and calculating the DC-Link, the possible on-time of the clamp switch can be concluded, and we can generate fixed width signals to the clamp switch, so that the current sensor can be eliminated. Then digital signal processor is used to control the clamp switch so that the DC-Link and inverter bridge can coordinate mutually. In addition, by measuring and analyzing the unfixed commutation delay time, an appropriate part of the delay time will be shifted forward to reduce sub-harmonics. At last, the implementation of the digital control strategy is discussed.In order to verify the digital DC-Link control strategy, a micro-inverter experimental platform is used to do experiment. The results show that the digital DC-Link control strategy performs well, improves the control performance, and effectively reduces cost and sub-harmonics.