Improving light load power factor for GaN based Totem Pole bridgeless PFC using digital phase locked loop based vector cancellation & tracking error compensation

Abstract

The paper proposes a digital based control method which can be used on power factor correction (PFC) circuit to improve converter power factor (P.F.) at light load conditions. A major contributor to a non-unity P.F. is the need of input capacitor to alleviate differential mode electromagnetic interference (EMI) conducted back to the AC source. At light load, the overall system impedance (EMI filter and PFC circuit) becomes more capacitive which leads to large phase difference between voltage and current and results in a low power factor. A digital phase locked loop base vector cancellation (DPLLVC) technique is proposed in this digest to improve the light load P.F. This technique improves upon the previously proposed Phase Leading Filter Current Compensation (PLFCC) technique as it no longer requires a derivative of the input voltage, which can add noise. In addition to DPLLVC technique, a tracking error compensation scheme is added to further improve the PF under light loads. The scheme is tested and results reported on a 3.3KW Gallium-Nitride (GaN) based Totem Pole bridgeless PFC (TTPL PFC) design. With DPLLVC and tracking error compensation techniques, over 37% P.F. improvement is observed when compared to the results with PLFCC technique at 2% load.