Abstract:

In order to solve the problem of poor performance of PF and THD caused by negative resonant current and input filter capacitor under constant on time(COT) control strategy, an improved variable on time (VOT) control strategy is proposed. The operating principle and operating process of making the average inductance current approach to the sine wave in the power frequency cycle by adaptively increasing the conduction time to offset the negative resonant current and reducing the phase difference are analyzed in detail. The main circuit is combined for key parameter design, a prototype with rated power of 320 W is developed. The comparative experiment of COT control strategy and improved VOT control strategy is carried out. The computer simulation and experimental results show that the PF of the improved VOT control strategy is increased from 0.726 to 0.801, and the THD is reduced from 27.92% to 18.4% when the 265 V high voltage input 20% load is working. At 40%~100% load, the requirements of PF>0.9 and THD<15% are met, which verifies the effectiveness of the proposed control strategy.

Key words: power factor correction(PFC), critical conduction mode(CRM), improved variable on time(VOT) control, line characteristics