Square component injection to improve current distortion of CRM Flyback APFCs with wide input voltage and variable load

Critical Conduction Mode (CRM) Flyback APFCs is widely used in High Brightness Light Emitting Diodes (HB-LEDs) driver. But with high input voltage or light load, its line current distortion deteriorates because of the peak distortion. In this paper, an improved control strategy is introduced to solve this problem. It is realized by the injection of sin²θ component to primary reference current. Nonetheless, the excessive injected content would lead to serious zero-crossing distortion. Consequently, this paper analyzes the relationship between the injected sin²θ component and current distortion. On the basis of that, the best injected ratio range which can realize the effectively trade-off between peak distortion and zero-crossing distortion is deduced and finally testified by experimental results.