| In recent years, the power factor correction (PFC) has been widely used and made great progress.Active PFC technique has been the mainstream technology due to its high power factor (PF) and lowtotal harmonic distortion (THD). However, input current distortion at the vicinity of input voltage zerocrossings is a common problem of active PFC converters, especially under high ac line frequencies.At400Hz input, the total harmonic distortion of input current would exceed the limit immensely. Thepurpose of this thesis is to realize the PFC function with400Hz input frequency.According to the characteristics of single-phase PFC converter, this thesis introduces thedifficulties of PFC technique with400Hz input frequency, in addition, the advantages anddisadvantages of some existing improvement methods are mentioned. With modeling of the currentloop, this thesis analyzes the reason of zero-crossing distortion specifically and points out that themajor causes of zero-crossing distortion are the cusp distortion, discontinuous conduction mode,phase advance and the lack of the current loop’s critical damping. Based on these, this thesis pointsout that the multi-level(ML) technique can be adopted to reduce the zero-crossing distortion underhigh ac line frequencies effectively.The working principle of flying-capacitor Boost ML converter is analyzed. The thesisspecifically introduces the three-level(TL) converter and deduces its basic power functions. Next, thethesis analyzes the voltage control principle of the flying-capacitor along with the modeling anddecoupling of the TL converter according to the principle of average-voltage control.Based on analysis above, a flying-capacitor Boost TL converter is built in the lab. The paperenumerates the design processes in details. The experimental results prove that the mentionedprinciples can achieve the PFC function very well with400Hz input frequency. |
