energies Article A Novel Three-Phase Six-Switch PFC Rectifier with Zero-Voltage-Switching and Zero-Current-Switching Features Chun-Wei Lin 1,*, Chang-Yi Peng 2 and Huang-Jen Chiu 1 1 Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan; [email protected] 2 Department of Electrical Engineering, Chung-Yuan Christian University, Taoyuan 32023, Taiwan; [email protected] * Correspondence: [email protected]; Tel.: +886-937-880-025 Received: 18 March 2019; Accepted: 19 March 2019; Published: 22 March 2019 Abstract: A novel three-phase power-factor-correction (PFC) rectifier with zero-voltage-switching (ZVS) in six main switches and zero-current-switching (ZCS) in the auxiliary switch is proposed, analyzed, and experimentally verified. The main feature of the proposed auxiliary circuit is used to reduce the switching loss when the six main switches are turned on and the one auxiliary switch is turned off. In this paper, a detailed operating analysis of the proposed circuit is given. Modeling and analysis are verified by experimental results based on a three-phase 7 kW rectifier. The soft-switched PFC rectifier shows an improvement in efficiency of 2.25% compared to its hard-switched counterpart at 220 V under full load. Keywords: three-phase rectifier; PFC; switch-mode rectifier; ZVS; ZCS 1. Introduction Power electronic converters play a critical role in the energy industry due to their ability to optimally control and condition the power they deliver to a load. In addition, they are required to control and condition the power they draw from energy sources to support their optimal operation. This is achieved by compliance to EMI and harmonic standards such as EN6100-3-2 and efficiency standards such as 80Plus [1]. Soft-switching technologies are a primary enabler for improving efficiency by minimizing switching losses and reducing EMI and harmonics by “soft” ending the edges of the switching transitions [2–12]. References [8] and [9] report soft-switching techniques that includes zero-voltage-switching (ZVS) and zero-current-switching (ZCS). Three-phase rectifiers with active power-factor-correction (PFC) control achieve an improved power factor and lower harmonic content [10–13]. Active PFC rectifiers using a boost (current source) front end achieve better input current wave-shaping and lower harmonic distortion compared to their buck-derived counterparts [14]. Three single-phase PFC rectifiers are used in [15] to synthesize a three-phase PFC rectifier. Reference [16] reports the use of space vector modulation (SVM) to achieve a high power factor in a three-phase six-switch rectifier. Soft-switching techniques employed in three-phase rectifiers are reported in [17–19] to improve efficiency and EMI performance. Soft-switching using a passive lossless snubber is presented in [17]. Although this approach can improve the efficiency, the circuit suffers from higher component stress. In [18], an active snubber is used to achieve soft-switching at the expense of higher control complexity and switching stress in the auxiliary switch. In [19–22], the zero-voltage-transition and control technique was applied in a three-phase PFC rectifier. Although the main switches can achieve ZVS at turn-on, the auxiliary switch was hard-switched operated at turn-off. Energies 2019, 12, 1119; doi:10.3390/en12061119 www.mdpi.com/journal/energies Energies 2019, 12, 1119 2 of 12 A conventional three-phase six-switch PFC rectifier is shown in Figure1. A novel soft-switched AA conventional conventional three-phase three-phase six-switch six-switch PFC PFC rectifier rectifier is is shown shown in in Figure Figure 1. 1. A A novel novel soft-switched soft-switched three-phase active rectifier using an active auxiliary circuit is proposed in this paper. The principal three-phasethree-phase activeactive rectifierrectifier using using anan activeactive auxiliaryauxiliary circuitcircuit isis proposedproposed inin thisthis paper.paper. TheThe principalprincipal performance improvement is the achievement of ZVS at turn-on for the six rectifier switches and performanceperformance improvement improvement is is the the achievement achievement of of ZVS ZVS at at turn-on turn-on for for the the six six re rectifierctifier switches switches and and ZCS ZCS ZCS at turn-off for the one auxiliary switch. A detailed description of the operation of the proposed atat turn-off turn-off for for the the one one auxiliary auxiliary switch. switch. A A detailed detailed description description of of the the operatio operationn of of the the proposed proposed soft- soft- soft-switched rectifier is presented in Section2. Validation of the design through simulation and switchedswitched rectifierrectifier isis presentedpresented inin SectionSection 2.2. ValidationValidation ofof thethe designdesign throughthrough simulationsimulation andand experimental results are shown in Section3 followed by concluding remarks in Section4. experimentalexperimental results results are are shown shown in in Section Section 3 3 followed followed by by concluding concluding remarks remarks in in Section Section 4. 4. −− ++ −− ++ −− ++ FigureFigure 1 1.1. .A A conventional conventional three-phase three-phase six-switch six-switch power-factor-correction power-factor-correction (PFC) (PFC) rectifier.rectifier. rectifier. 2. Proposed Three-Phase Six-Switch Soft-switching PFC Rectifier 2.2. Proposed Proposed Three-Phase Three-Phase Six-Switch Six-Switch Soft-switching Soft-switching PFC PFC Rectifier Rectifier The proposed three-phase six-switch soft-switching PFC rectifier is shown in Figure2. The circuit TheThe proposedproposed three-phasethree-phase six-switchsix-switch soft-switchisoft-switchingng PFCPFC rectifierrectifier isis shownshown inin FigureFigure 2.2. TheThe inside the dotted box is a soft-switching assist circuit to achieve ZVS in the main switches and ZCS in the circuitcircuit inside inside the the dotted dotted box box is is a a soft-switching soft-switching assist assist circuit circuit to to achieve achieve ZVS ZVS in in the the main main switches switches and and auxiliary switch. The soft-switching assist circuit consists of the auxiliary switch SA, resonant inductor ZCSZCS inin thethe auxiliaryauxiliary switch.switch. TheThe soft-switchingsoft-switching assistassist circuitcircuit consistsconsists ofof thethe auxiliaryauxiliary switchswitch SSAA, , LR, transformer Tr, barrier diode DR1, clamp circuit RC–DC–CC, and resonant capacitor (the capacitance resonantresonant inductorinductor LLRR, , transformertransformer TTr,r , barrierbarrier diodediode DDR1R1, , clampclamp circuitcircuit RRCC–D–DCC–C–CCC, , andand resonantresonant employs the parasitic capacitance of main switch). capacitorcapacitor (the (the capacitance capacitance employs employs the the pa parasiticrasitic capacitance capacitance of of main main switch). switch). −− ++ −− ++ −− ++ Figure 2. The circuit of the proposed soft-switching PFC rectifier. FigureFigure 2. 2. The The circuit circuit of of the the proposed proposed soft-switching soft-switching PFC PFC rectifier. rectifier. Three phase line voltages VRN, VSN, VTN for a balanced three-phase system are shown in Figure3. ThreeThree phase phase line line voltages voltages V VRNRN, ,V VSNSN, ,V VTNTN for for a a balanced balanced three-phase three-phase system system are are shown shown in in Figure Figure The 60◦ symmetry in the three-phase voltages is evident from Figure3. The operation of the three-phase 3.3. The The 60 60°° symmetry symmetry in in the the three-phase three-phase voltages voltages is is eviden evidentt from from Figure Figure 3. 3. The The operation operation of of the the three- three- PFC using the 60◦ symmetry is described in detail in [11]. phasephase PFC PFC using using the the 60 60°° symmetry symmetry is is described described in in detail detail in in [11]. [11]. 22 Energies 2019, 12, 1119 3 of 12 0 ωt 0 ωt Figure 3. The line cycle in three-phase balance power system. Figure 3. The line cycle in three-phase balance power system. In orderIn order to simplify to simplify theFigure analysis, the 3. analysis, The lineInterval cycle Interval in1 three-ph(0°–60°) 1 (0◦ase –60can balance◦ )be can selected power be selected system.for the for analysis the analysis of the of the switchingswitching cycles cycles as the as operation the operation over overthe rectifier the rectifier is identical is identical in the in other the other60° segments. 60◦ segments. The following The following In order to simplify the analysis, Interval 1 (0°–60°) can be selected for the analysis of the assumptionsassumptions are made are made to support to support the operating the operating analysis: analysis: switching cycles as the operation over the rectifier is identical in the other 60° segments. The following (1) Input inductance LB is large enough to allow the input current to be considered as a current assumptions are made to support the operating analysis: (1)sourceInput over inductance a switchingL period;B is large enough to allow the input current to be considered as a current source(1) Input over inductance a switching LB is period; large enough to allow the input current to be considered as a current (2) Input capacitance CL is large enough to be equivalent to the ideal voltage source VO; and source over a switching period; (2)(3) TheInput output capacitance capacitanceCL is of large the clamp enough circuit to be C equivalentC is large enough to the idealto allow voltage its voltage source VVC Oto; andbe (2) Input capacitance CL is large enough to be equivalent to the ideal voltage source VO; and (3)consideredThe output a voltage capacitance source over of the a switching clamp circuit period.CC is large enough to allow its voltage VC to be (3) The output capacitance of the clamp circuit CC is large enough to allow its voltage VC to be Underconsidered the assumptions a voltage listed source abov overe, the a switchingsimplified period.circuit diagram is shown in Figure 4 and the considered a voltage source over a switching period.