Control of a series input boost pre-regulator with unbalanced load

Conventional diode bridge rectifiers have poor input power quality due to high harmonic content in input current which leads to low power factor and high total harmonic distortion (THD). In order to extract maximum power from the supply it is advantageous to operate a rectifier at unity power factor with minimal harmonics. Therefore, UPF pre-regulators are used in modern rectifiers. When realizing pre-regulators for higher voltage application, a common strategy is to use multilevel structures which have the advantage of using lower voltage devices to implement higher voltage conversion stages. In this paper a series input boost power factor per-regulator is used to implement an AC-DC rectifier. As the number of series stages increases, the problem of un-equal loading at the output of each boost pre-regulator becomes an issue. A weighed average current mode control is proposed which maintains equal voltage at the output of the pre-regulator even under unbalanced loading conditions. The proposed control is verified using simulation and a scale down laboratory prototype.