Design, study, modeling and control of a modified Sheppard-Taylor PFC

In this paper, a new single-phase Power Factor Corrector (PFC) based on the Sheppard-Taylor topology is studied. Compared to conventional buck, boost or buck-boost PFCs, this topology allows a better current tracking at the AC side, with a relatively reduced voltage at the DC side. Consequently, the high frequency AC filters required by the buck PFCs are avoided, and the voltage stresses on the boost switches are significantly reduced. Furthermore, the control detuning phenomenon, from which suffer most of the conventional PFCs, especially at very low input voltage, is avoided. This yields major improvements in the source current waveform. Compared to the conventional Sheppard-Taylor converter, this new topology allows lower voltage stresses across the capacitors and larger output voltage range for the same operating area. The converter is integrated as a PFC at the DC-end of a single-phase diode bridge. Pulse-Width-Modulated (PWM) multi-loops control schemes are proposed and developed in order to ensure a unity power factor at the AC-source side and a regulated voltage at the DC-load side. The first one uses the simple and robust hysteretic-based controller, the second one employs a conventional PI regulator, whereas the third one is based on the model nonlinearity compensation approach. The design of the last two control methods is based on the state-space averaged model of the converter. The performance of the different control strategies is evaluated through simulation experiments carried out on a numerical version of the converter. The implemented model of the converter is obtained by using the switching function technique. The control system is tested under both rated and disturbed operating conditions. The system performance is evaluated in terms of source current Total Harmonic Distortion (THD), input power factor, DC voltage stabilization, and regulation following load variations.