An Adaptive Duty Cycle Current Observer for Bridgeless PFC Converter Considering Miller Effect

Inductor current acquisition is critical for bridgeless power factor correction (PFC) converters where the inductor current flows bidirectionally, leading to complex current sensing scheme. Consequently, the current senseless technique, achieved through the current reconstruction, is emerging as an efficient alternative. However, the state observer is neglecting the effect of discrepancies, due to the Miller effect, between the reconstructed current and the actual one. This article analyzes the impact of duty cycle error induced by the Miller effect on observed current and then develops an adaptive current observer capable of compensating for this error. Further based on the proposed adaptive current observer, current senseless feedforward control scheme, which introduces the observed information of load and secondary voltage ripple into the control loop as well, is designed to enhance the dynamic performance of the bridgeless PFC converter. Finally, an experimental prototype of a 144W bridgeless PFC converter is established for validation. Experimental results show the proposed duty-cycle adaptive observer significantly improves the accuracy of inductor current observation. Compared to the traditional observer-based control scheme, the proposed feedforward control scheme improves the load dynamic response to 10 ms and controls the total harmonic distortion (THD) of the inductor current within 5%.