Analysis of high DC bus voltage stress in the design of single stage single switch switch mode rectifier

Single stage single switch switch mode rectifier (S4 SMR) is the integration of input power factor correction (PFC) stage with the dc-dc output stage utilizing a single switch and having isolation between input and output. Converter topology is selected to possess sufficient degree of freedom to allow the input voltage, energy storage capacitor voltage and the load voltage to vary independently. In this design input PFC stage is discontinuous current mode (DCM) boost topology, which is cascaded by a continuous mode converter providing wide bandwidth response. Analytical expressions are derived for boost inductance by applying equal area criterion (EAC), critical inductance of output flyback converter, voltage transfer function and relationship between duty ratio and output load. Based on this a 100 W, 230 V, 50 Hz A.C./ 50 V D.C S4 SMR was designed, fabricated and tested. Simulation results using SABER software package and actual test results are compared and analyzed. Under open loop condition voltage stress of twice the rated voltage is observed but under closed loop condition output voltage regulation using duty ratio control, the voltage stress is quite insignificant. Input current waveform is found to be sinusoidal and in phase with the AC input voltage with a predominant component of fundamental frequency.