Analysis, modeling and design of a True Bridgeless Single Stage PFC with galvanic isolation

Abstract

Power Factor Correction (PFC) has been established for a long time to fulfill the harmonic standards. To meet the demand for a compact, efficient solution, a so-called True Bridgeless Single Stage PFC was recently introduced. By eliminating the input rectifier the efficiency is significantly improved. In addition, this topology provides galvanic isolation while employing only one single active switch. In this paper a True Bridgeless Single Stage PFC is analyzed, designed and characterized through measurements on a hardware realization. To optimize the converter with respect to efficiency, power density or cost, analytical expressions for all occurring voltages and currents in each component are derived. With the derived small signal model, the current and voltage compensator can be designed optimally, to ensure a stable and fast control behavior. In addition, a non-dissipative clamp circuit is introduced to limit the switch voltage without causing significant losses. The results of the theoretical analysis are verified by simulation and experimental measurements. I. INTRODUCTIONTypically, in single phase systems, a boost PFC solution is employed which meets all the requirements with respect to the established standards and achieves at the same time an acceptable efficiency at the European voltage level. To satisfy the demand for universal input voltage, all the commonly employed PFC converters possess one major drawback. The input rectifier reduces the efficiency by approximately 3 % at low line (85 V), which often results in an overall efficiency lower than 93 %. Thus, the main objective is to eliminate the input rectifier to prevent this drop of efficiency. Several attempts have been proposed in the past to overcome this issue [1]- [8]. By replacing two diodes of the input rectifier with active switches, the low line efficiency can be improved; however there still remains one diode forward voltage drop which causes non-negligible losses. Additionally, in many applications galvanic isolation of the output is required. This leads to a multistage approach, typically with a boost PFC as input stage and a DC-DC stage for galvanic isolation. This causes additional losses as the output power must be processed in both stages. Typically this popular solution results in as many as 12 switches and up to four magnetic components. This often results in an overall efficiency of less than 90 %. In the past several attempts have been made to find possibilities of combining the current shaping PFC function with the DC-DC converter including galvanic isolation, so called single stage PFC converters. In all presented cases the input rectifier

Single-Phase Bridgeless PFC Topology Derivation and Performance Benchmarking

“…On the other hand, another solution to achieve 'bridgeless' is using one single modified converter cell with the bidirectional switch, which can handle both polarities of the input power [18], [27], [28]. These type converters need a crucial and carefully designed resonant circuit in the bidirectional inductor current path, rather than just freewheeling diodes in the ordinary converter cells [18], [28].…”

“…On the other hand, another solution to achieve 'bridgeless' is using one single modified converter cell with the bidirectional switch, which can handle both polarities of the input power [18], [27], [28]. These type converters need a crucial and carefully designed resonant circuit in the bidirectional inductor current path, rather than just freewheeling diodes in the ordinary converter cells [18], [28]. Meanwhile, the leakage inductance in the transformer can be used to implement the resonant circuit, so this type of bridgeless topologies are more suitable in galvanic isolation applications [18], [28].…”

“…These type converters need a crucial and carefully designed resonant circuit in the bidirectional inductor current path, rather than just freewheeling diodes in the ordinary converter cells [18], [28]. Meanwhile, the leakage inductance in the transformer can be used to implement the resonant circuit, so this type of bridgeless topologies are more suitable in galvanic isolation applications [18], [28]. This paper only focuses on the first solution using two converter cells.…”

Survey on Photo-Voltaic Powered Interleaved Converter System

“…Nigsch et al [74] proposed a bridgeless single stage PFC converter for efficient solution to fulfill the harmonic standards. Efficiency is improved by removing the input rectifier and providing galvanic isolation by allowing single switch active at a time.…”

A single-stage full bridgeless boost half-bridge AC/DC converter with bidirectional switch

“…The input current which continuously flow in each mode of circuit operation [24]- [28] will minimize the deterioration of the input current and in return, high input power factor can be achieved. Further improvement with resonance circuit [29] contributes to converter efficiency. There is no excess current or voltages because it diverted to resonance circuit.…”