Stability and performance assessment of single-phase T/4 PLLs with secondary control path in current sensorless bridgeless PFCs

Abstract

Bridgeless power factor correction (PFC) stages and the associated current shaping techniques require grid synchronization to ensure unity displacement power factor. In controllers with no current sensor, line current rebuilding algorithms are especially sensitive to synchronization issues. Phase-locked loops (PLLs) are used to synchronize the control of grid-connected converters, and may include a secondary control path to improve their dynamics in the case of grid disturbances. This paper presents linear models of T/4 PLLs with secondary control paths. The T /4 PLL structures are digitized and their performance evaluated. The stability conditions are determined. The PLL signal is utilized for current sensorless bridgeless PFCs, in the current estimation algorithm to reduce the estimation error, and as the reference in the current controller. The effect of the response of different PLLs on the PFC under grid disturbances is evaluated experimentally.