Research On Three-phase Single-stage Full-bridge APFC Technology In Unbalance Grid

The rectifier diode used on the input side of the power electronic devices commonly, will bring the negative impact of harmonic “pollution”. Active power factor correction technology is an effective way to improve the power factor through controlling the input current waveform effect by improving the rectifier unit of the equipment. So the APFC technology is widely concerned.Three-phase single-stage active power factor correction circuit has become a hot research in recent years for its simple structure and high efficiency. Current type isolation full-bridge topology has also been applied to the three-phase single-stage APFC circuits due to its characatoristics of soft switching control, input and output isolation, eliminating the straight-arm switch, etc.In this paper, the PFC principle of the current type isolation full-bridge topology is analyzed, as well as the working process of the topology with the passive buffer part in a switching cycle. The condition to remain the converter working in the DCM mode is given, so that the basis for the experimental parameters design is provided, which can ensure the converter working properly.Since there are many other non-linear, impact, rich harmonics and unbalanced electricity load in the network which can affect the power supply, three-phase grid would have a certain imbalance. In this paper, the affect on the three-phase current type isolation full-bridge topology causing by unbalance grid is anyalysed. The reason for shifting phase-angle between the input current and voltage is explained. The quantitative relationship between the shifting phase-angle and the unbalanced rate is given. And the existing of third-harmonic in the input current is explained qualitatively.Since the current type isolation full-bridge topology works under DCM mode, its input current contains many low-order harmonics, even with the filter. In this paper, harmonic injection is taken to reduce the low-order harmonics. The principle of harmonic injection under balance and unbalance grid is analyzed. The digital control scheme of harmonic injection is given. And the method to the closed loop regulation of injection volume is given.The experimental platform is built based on the theoretical analysis and simulation. The working process on the current-isolation full-bridge PFC circuit is verified. And using harmonic injection under balance and unbalance guid to limit the input current harmonic content is achieved. The correctness of the theory is demonstrated by the experimental results.