Pagsabot sa Electromagnetic Interference sa Common-mode alang sa Solid-state Transformers

     Ang makala-istoryahan kini mahitungod sa pagtumong sa gap ha pagsuroy sa komprehensibong review han mga karaniwan nga dc-link MLCs, na naglakip hin kanilhanng topological evolution, features, topologies comparison, modulation techniques, control strategies, ug industrial application areas.  Additional, ang future perspectives ug recommendations gindiskuto para maghatag hin mas maayo nga pagkaunawa han mga mananaliksik ug engineers ha potential applications ug advantages han mga converters ini.

1.Introduction.

     Hin consider an major evolutionary stages han MLCs, ang existing MLC topologies makaklasipika ha daghan nga families, as shown in the following figure. Ang unang family naghahatag hin CHB-based topologies ug adunay high modularity ug optimal number hin power switches para ha output levels [31]. Pero, ang multiple isolated DC sources ginkinahanglan, nga nagpapahimutang hin bulky isolation transformers o limitado ha mga aplikasyon nga adunay daghan nga isolated DC sources. Padayon pa, ang uneven power sharing ha cascaded power cells usa ka common challenge ha family ini. Ang ikaduha nga family naghahatag hin NPC-based topologies sama han 3L-NPC ug 3L-T2C converters. Ang mga converters ini characterized han robust power circuits ug straightforward protection. Pero, ang dc-link balancing usa ka essential requirement ha control design han mga topologies ini. Ang FC-based topologies gamiton an capacitors isip clamping components para padami an number hin levels, forming an MLC family characterized han high flexibility, high redundancies, ug fault-tolerant operation. Ang Hybrid MLCs gihimo ha basic cells han conventional topologies, ngadto hin combine several advantages han classical MLCs ha capability para mabuo an high number hin levels. Ang MMC topologies constituting an MLCs family nga represent a breakthrough ha HV applications tungod ha iya high efficiency ug high modularity.

2. Common Dc-Link Topologies.

   Ang three-level Active NPC (ANPC) structure nakakatugot han issue hin power loss sharing pinaagi han paggamit hin duha nga iba nga modulation techniques nga gitawag isip modulation patterns I ug II. Ha diin ang duha nga clamping diodes gisubli ha duha nga active switches para kontrolon an current flow direction ha zero states. Ang modulation pattern I nagpapadala hin most of the switching loss ha outer switches han matag leg, pero ang pattern II moven an switching losses ha inner switches. Ang Fc category naghahatag hin topologies nga gamiton an FCs without a clamped neutral point, ug accordingly, dili nagdala han issue hin dc-link balancing. Ha mga topologies ini, ang FCs ginamit para subli an dc-sources ha pag-generate hin voltage levels. Sa general, tungod ha modularity, ang family ini may capability para generate relatively higher levels konparado han NPC family. Padayon pa, ang flexibility, fault-tolerant operation, ug improved loss sharing ha switches prominent features han mga topologies ini. Ang Hybrid multilevel converters (HMLCs) combinen multiple fundamental topologies para gamiton an kanilhang respective advantages, ha pag-overcome han ilang limitations. Predominantly, ang hybrid topologies makakapadami han voltage balancing capabilities para ha both dc-link ug FCs, ug power loss distribution across switches, ha pagbawas han number hin required active ug passive components konparado han NPC ug FC topologies.

3. Modulation and Control.

    A classification of the major control techniques for multilevel converters is show in the picture below. As with the two-level converter, the cascaded control structure usually consists of outer and inner control stages in addition to the modulator block. Although the inner and outer loops are similar in the two-level and multilevel converters, the modulator stage, which is mainly required for scalar and field-oriented control (FOC) techniques, needs to be adapted as the number of levels goes higher. In this section, first, a review of the most popular, as well as advanced modulators, is presented. Also, the control techniques that do not require a separate modulator will be investigated in more detail.

4. Industrial Applications.

    Historically, ang CHB inverters characterized ha kanilhang modularity, fault tolerance, ug ability para generate a high number hin voltage levels pinaagi han cascading cells. Pero, ang requirement hin multiple isolated DC sources (rectifier+transformer from the industry point of view) limiting their applicability ha vast range hin power ratings. Indeed, ang CHB inverters mostly employed ha high-power applications (ranging from hundreds of kilowatts to megawatts) ha diin wala available components para ha such ratings. On the other side, ang common dc-link topologies characterized ha employment hin single DC source making them a good alternative ha various applications sama han 3-phase industrial systems. Indeed, sila makagamit ha many configurations sama han 3-Leg 3-Wire, 3-Leg 4-Wire, ug 4-Leg 4-Wire ha motor drives, PV inverters, fast DC chargers, etc.

Source: IEEE Xplore

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