188宝金博页面版

Technical Field of the Invention[0001] The present invention is directed. in general,to power conversion and, more specifically, toa switch-ing networkand method of reducing input current totalharmonic distortion (THD) for a boost converter.Backqround ofthe Invention[0002] Over the past ten years, increasing attentionhas been focused on input current total harmonie dis-tortion (THD) due tothe increasing use of nonlinearloads that tend to degrade AC line quality. THD stand-ards, suchas IEC-1000.3.2 promulgated bythe Interna-tionalE lectrotechnical Commission, address input cur-rents of, for example, 16 amperes or tess per phase.Although no international standards for high power rec-tifiCation eXist at the present time, some countries, e.g.,India and Brazil, have imposed their own requirementson input current THD to protect their AC line quality.[0003] For producing lowTHD input currents in three-phase rectification, there are three different convention-al approaches. The first approach utilizes six controlla-ble power switches to actively control the three inputphase currents. Separate current control loopsare usedto pattern each ofthe three input phase current wave-forms, resulting in lowerTHD input currents. This powerfactor correction (PFC) approach, however, requirescomplex and relatively expensive control and powerconversion circuitry. For example, to implementthe cur-rent control loops, multiple current sensors are requiredto detect the input currents. Either digital signal procès-sors (DSPs) or multiple analog controllers are requiredto process the information. Furthermore, the powerstage requises six separate switches with independentdrivers, with at least three ofthe drivers "floating."[0004] The second approach to producing low THDinput currents is to employ three single-phase PFC"units" to forma three-phase unit. In single-phase PFCunits. input currents are controlled by the duty cycle ofa power switch to follow the input voltage emulatingaresistive load, which in turn, reduces theTHD in the in-put current. IIa single-phase unit has already been de-veloped,a three-phase unitcan be readily implemented.A major limitation with this approach isthe relatively highcost due tothe replication of control and power circuitryrequired to construit the three-phase unit.[0005] A single-switch boost concerter operating indiscontinuous conduction mode (DCM) witha high out-put voltage is the third approachto reducing THD in theinput currents. In this boost converter, the decay timeofa boost inductor current, overa switching cycle, is de-termined primarily by the difference between the outputDC voltage and the input cottage du ring the switchingcycle. The greaterthe difference, the fasterthe inductorcurrents are reduced to zero. Consequently, the input101520253035404550552lower costs.A serious limitation, however, is thatthe re-quired output voltage forachieving an acceptable THDvalue is typically very high. The required high outputvoltage (for achieving low THD input currents) compli-cates the selection ofthe power switching componentsandthe designofthe successive, or cascaded load, DC/DC converters, especially when theAC input voltagesare as high as 440 volts rms.[0006] Accordingly, what is needed in the art is an im-proved power converter that overcomes the above-de-scribed limitations. More specifically, what is needed inthe art isa power converter that has the desirable fea-turesofthe above-described converters, suchas simplecontrol, simple power stage, low outputvoltage and lowinput current THD without their limitations.Summaryofthe Invention[0007] To address the above-described deficienciesof the prior art, the present invention provides forusewitha boost converter having first, second and third in-put inductors,a switching network, method of reducinginput current total harmonic distortion (THD) associatedwiththe boost converter, and boost converter employingthe switching network and method.[0008] In one embodiment, the switching network in-cludesa first switch coupled between correspondingrails of the boost converter. The switching network alsoincludes first, second and third L-C resonant networkswye-coupledtoa common nodeand coupledtothe first,second and third input inductors, respectively. The firstswitch and the first, second and third L-C resonant net-works cooperate to create resonant voltages across,and induce phase currentsthrough, the first, secondandthird input inductors to reduce input current THD asso-ciated with the boost converter.[0009] The present invention therefore introducesaswitching networkfor a boost converter that creates res-onant voltages across, and induces phase currentsthrough. the first, secondand third input inductors to re-duce input current THD associated with the boost con-verter. The operation ofthe first switch ofthe switchingnetwork facilitates the resonance betweenthe inductorsand capacitors ofthe L-C resonant networks. Asa re-sult, resonant voltages are applied across the respec-tive input inductors and, ultimately, the input currentTHD is reduced in all three phasesofthe boost convert-er.[0010] In one embodiment ofthe present invention,the switching network further includesa second switchcoupledtothe first switch and first and second interme-diate capacitors coupled between the correspondingrails. An intermediate node of the first and secondswitches is coupled toan intermediate node ofthe firstand second intermediate capacitors.[0011] In one embodiment ofthe present invention,