Investigation of a single phase multi-output ac-dc flyback rectifier with high power factor correction unit

Abstract

A new topology of power factor corrected AC-DC flyback rectifier-fed multilevel single phase inverter is proposed and developed here. The proposed circuit consists of AC-DC flyback rectifier and multilevel inverter. Conventional flyback AC-DC converter is made of a bridge rectifier followed by a DC-DC converter, resulting in low conversion efficiency. On the other hand, a complicated switching technique is used to operate multilevel inverter which makes the system burdensome to design. The limitation has been addressed here with improved system configuration and optimization in switching techniques.The proposed new topology of single phase AC-DC flyback converter uses normal single phase secondary winding transformer instead of secondary winding transformer with tertiary winding to avoid transformer core saturation due to DC current component in the transformer windings currents. Moreover, a single stage AC-DC conversion is used here, combining the rectification process and DC-DC conversion only in one step, resulting in higher efficiency, more accurate power factor correction and input current harmonic distortion reduction. Based on single phase single DC output concept, a new single phase multi-output AC-DC flyback rectifier topology has been proposed and developed. The application of the proposed converter has been investigated for a multilevel inverter system. Generally multilevel inverter is used owing to their low switching power loss and low output voltage distortion. But the existing multilevel inverter needs complicated frequency switching technique for their controls and these make the system difficult to design. To eliminate the use of complicated switching technique, a new switching topology for cascaded H-bridge multilevel inverter has been proposed. The implementation of the control signals of the inverter switches is easier with microcontrollers as only one signal is to be generated and other signals will be time shifted for rest of the switches of the inverter. The process allows simple frequency and phase shifting of the inverter output voltage by varying the time period and time shift of the original signal. The outputs from the proposed single phase multi-output AC-DC flyback rectifier have been fed to the multilevel inverter, operating with new switching scheme. The working principles of all the circuits have been explained. The performance of proposed flyback AC-DC rectifier with feedback control is compared with the traditional flyback AC-DC rectifier in terms of power factor, input current THD and converter efficiency. The proposed system performs better in all cases. The system can help to reduce the losses in conventional AC-DC flyback converter with improved power factor and THD.