Converter for converting multipoint medium voltage direct current to single point high voltage direct current

Abstract

The present disclosure provides a converter (100) for converting a multipoint medium voltage direct current (MVDC) to a single point high voltage direct current (HVDC). The converter (100) includes primary side DC-Alternating Current (AC) circuits (110-1K0) including director portions (DPs) (113, 114) and wave-modulating portions (111-1, 112-1) connected in parallel to receive an input from a MVDC bus (101-1). The converter (100) includes secondary side AC-DC circuits (210-2K0) connected in series, where each of the secondary side AC-DC circuits (210-2K0) includes four DPs (211-214), where at least two DPs are connected in series between a second positive DC branch (X-1) and a second negative DC branch (X-2). The primary side DC-AC circuit(s) (110) and the secondary side AC-DC circuit (210) are connected via a single-phase transformer (301-1). The single-phase transformer (301-1) comprises a primary winding and a secondary winding.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of power converters. Inparticular, the present disclosure relates to a high-power hybrid multipoint DirectCurrent (DC)-DC converter for converting a multipoint medium voltage directcurrent (MVDC) to a single point high voltage direct current (HVDC).BACKGROUND

[0002] The following description of the related art is intended to providebackground information pertaining to the field of the disclosure. This section mayinclude certain aspects of the art that may be related to various features of thepresent disclosure. However, it should be appreciated that this section is used onlyto enhance the understanding of the reader with respect to the present disclosure,and not as admission of the prior art.

[0003] The escalating global demand for energy has prompted a surge inutilization of renewable energy sources to meet worldwide energy needs. There isa growing emphasis on expanding a capacity of renewable energy, necessitatingdevelopment of efficient and reliable power evacuation schemes to integrate largerenewable energy sources with load centers. Addressing the challenges ofefficiently evacuating power from renewable sources is a prevalent concern in bothindustry and academia.

[0004] Multi-point converters offer an attractive solution for achieving acompact, flexible and efficient power distribution network to enhance overall cost,footprint, and efficiency of substation. Researchers and industries are increasinglyconsidering multi-port converters as a more viable alternative for interconnectingHigh Voltage Direct Current (HVDC), Medium Voltage Direct Current (MVDC),and High Voltage Alternate Current (HVAC) systems, as opposed to employingmultiple two-port converters (TPC) including Alternate Current (AC) / DirectCurrent (DC) and DC / DC. The multipoint converters offer a straightforward scalingof voltage and power ratings without a need for series connection of power-semiconductor devices. But, compared to a two-level converter (TLC) with anequivalent power rating, the existing multipoint converters requires nearly doublethe number of power semiconductor devices and large number of cells (capacitor)which increases conduction losses and footprints. Consequently, this results inreduced power density and efficiency. In addition, the control and modulation ofexisting multipoint converters are complicated.

[0005] Therefore, there is, a need for multipoint converters, which requirelow number of switches, capacitors, low energy storage requirements, faultblocking capability, low initial cost, footprint, and a simple converter structure byovercoming the deficiencies in the prior art.OBJECTS OF THE PRESENT DISCLOSURE

[0006] Some of the objects of the present disclosure, which at least oneembodiment herein satisfies are as listed below.

[0007] One object of the present disclosure is to provide a high-powerhybrid multipoint Direct Current (DC)-DC converter for conversion of a multipointMedium Voltage Direct Current (MVDC) to a single point High Voltage DirectCurrent (HVDC) efficiently.

[0008] Another object of the present disclosure is to provide a high-powerhybrid multipoint DC-DC converter that is compact, flexible, and enables efficientpower distribution network.

[0009] Another object of the present disclosure is to provide a high-powerhybrid multipoint DC-DC converter that requires low number of switches,capacitors, low energy storage requirement, fault blocking capability, low initialcost, footprint, and a simple converter structure.SUMMARY

[0010] The present disclosure relates to the field of power converters. Inparticular, the present the present disclosure relates to a high-power hybridmultipoint DC-DC converter for converting a multipoint medium voltage directcurrent (MVDC) to a single point high voltage direct current (HVDC).

[0011] In an aspect, the present disclosure relates to a hybrid DC-DCconverter for converting a multipoint MVDC to a single point HVDC. Theconverter includes one or more primary side DC-Alternating Current (AC) circuits,where each of the one or more primary side DC-AC circuits includes at least twodirector portions and at least two wave-modulating portions that are connected inparallel between a first positive DC branch and a first negative DC branch of eachof the one or more primary side DC-AC circuit. The first positive DC branch andthe first negative DC branch are configured to receive an input from a MVDC bus.The converter includes one or more secondary side AC-DC circuits connected inseries, where each of the one or more secondary side AC-DC circuits include atleast four director portions, where at least two director portions of the at least fourdirector portions are connected in series between a second positive DC branch anda second negative DC branch of each of the one or more secondary side AC-DCcircuits. A middle point between the series connection of first and second directorportions of the at least four director portions form a first AC branch. A middle pointbetween the series connection of third and fourth director portions of the at leastfour director portions form a second AC branch. A single-phase transformerincludes a primary winding connected to the first AC branch and the second ACbranch of each of the one or more primary side DC-AC circuits, and a secondarywinding connected to the first AC branch and the second AC branch of each of theone or more secondary side AC-DC circuits.

[0012] In an embodiment, a middle point between the series connection ofthe at least two director portions may form the first AC branch, and a middle pointbetween the series connection of the at least two wave-modulating portions mayform the second AC branch.

[0013] In an embodiment, the at least two wave-modulating portions maybe formed by series-connection of a plurality of cells. Each cell may include at leastone of a unipolar capacitor, a bipolar capacitor, or a combination of the unipolarcapacitor and the bipolar capacitor.

[0014] In an embodiment, each of the at least two director portions of theone or more primary side DC-AC circuits and each of the at least four directorportions of the one or more secondary side AC-DC circuits may include a pluralityof series-connected Insulated-Gate Bipolar Transistors (IGBTs) with antiparalleldiodes, an antiparallel thyristor, or a thyristor with the antiparallel diode.

[0015] In an embodiment, one of the at least two wave-modulating portionsmay be connected with a first series inductor to limit a circulating current betweenat least one DC-link and one of the at least two wave-modulating portions.

[0016] In an embodiment, the first AC branch and the second AC branch ofeach of the one or more primary side DC-AC circuits may be connected to the firstAC branch and the second AC branch of each of the one or more secondary sideAC-DC circuits through the single-phase transformer.

[0017] In an embodiment, each of the one or more secondary side AC-DCcircuits may be connected in series to at least one second inductor. The at least onesecond inductor may be a leakage inductor of the single-phase transformer or anexternal inductor.

[0018] In an embodiment, the second positive DC branches of each of theone or more secondary side AC-DC circuits may be connected in series to a filterinductor, and the second positive DC branches are configured to receive an outputat a HVDC bus.

[0019] In an embodiment, the first AC branch and the second AC branch ofeach of the one or more primary side DC-AC circuits may be configured to receivean AC output from each of the one or more primary side DC-AC circuits.

[0020] In an embodiment, the at least two director portions of each of theone or more primary side DC-AC circuits and the at least four director portions ofeach of the one or more secondary side AC-DC circuits may be operated at afundamental frequency to generate a DC-link voltage.BRIEF DESCRIPTION F DRAWINGS

[0021] The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in, and constitute apart of this specification. The drawings illustrate exemplary embodiments of thepresent disclosure, and together with the description, serve to explain the principlesof the present disclosure.

[0022] In the figures, similar components, and / or features may have thesame reference label. Further, various components of the same type may bedistinguished by following the reference label with a second label that distinguishesamong the similar components. If only the first reference label is used in thespecification, the description is applicable to any one of the similar componentshaving the same first reference label irrespective of the second reference label.

[0023] FIG. 1 illustrates a circuit diagram of a converter (100) forconverting a K-point Medium Voltage Direct Current (MVDC) to a single pointHigh Voltage Direct Current (HVDC), in accordance with an embodiment ofpresent disclosure.

[0024] FIG. 2 illustrates a schematic view (200) of the converter shown inFIG. 1 for Current (HVDC), in accordance with an embodiment of presentdisclosure.

[0025] FIG. 3 illustrates a circuit diagram (300) of a converter for 3-pointMVDC to single point HVDC, in accordance with an embodiment of the presentdisclosure.

[0026] FIG. 4 illustrates a simplified circuit diagram (400) of a convertershown in FIG. 3 for 3-point MVDC to single point HVDC, in accordance with anembodiment of the present disclosure.

[0027] FIG. 5A illustrates a circuit diagram (500a) of a bidirectional switch,Insulator Gate Bipolar Transistor (IGBT) with an antiparallel diode used as aDirector Portion (DP), in accordance with an embodiment of the present disclosure.

[0028] FIG. 5B illustrates a circuit diagram (500b) of an antiparallelthyristor that may be used as the DP, in accordance with an embodiment of thepresent disclosure.

[0029] FIG. 5C illustrates a circuit diagram (500c) of a thyristor withantiparallel diode that may be used as the DP, in accordance with an embodimentof the present disclosure.

[0030] FIG. 6A illustrates a circuit diagram (600a) of N unipolar cellsconnected in series, in accordance with an embodiment of the present disclosure.

[0031] FIG. 6B illustrates a circuit diagram (600b) of N bipolar cellsconnected in series, in accordance with an embodiment of the present disclosure.

[0032] FIG. 6C illustrates a circuit diagram (600c) depicting a combinationof N cells connected in series, where each cell is either a unipolar or a bipolar cell,in accordance with an embodiment of the present disclosure.

[0033] FIG. 7 illustrates a schematic view (700) of a renewable energysource associated with the converter, in accordance with an embodiment of thepresent disclosure.

[0034] FIG. 8 illustrates a schematic view (800) of an output DC-bus bar ofthe converter, in accordance with an embodiment of the present disclosure.

[0035] FIG. 9A illustrates a sinusoidal modulation signal (900a), inaccordance with an embodiment of the present disclosure.

[0036] FIG. 9B illustrates a trapezoidal modulation signal (900b), inaccordance with an embodiment of the present disclosure.

[0037] FIG. 10 illustrates a graphical view (1000) representing a constantDC-bus voltage of the converter under variable load conditions, in accordance withan embodiment of the present disclosure.

[0038] FIG. 11 illustrates a graphical view (1100) depicting input andoutput power of the converter in real-time hardware experiments, in accordancewith an embodiment of the present disclosure.

[0039] FIGs. 12 -14 illustrate graphical views (1200-1400) depictingtransformer primary and secondary voltages for 2-MVDC point, 3-MVDC point,and 4-MVDC point converters using simulation experiments, respectively, inaccordance with an embodiment of the present disclosure.

[0040] FIGs. 15-16 illustrate schematic representations (1500, 1600)depicting the validation experiments using real-time hardware OPAL-RT (OP-4512), in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0041] The following is a detailed description of embodiments of thedisclosure depicted in the accompanying drawings. The embodiments are in suchdetail as to clearly communicate the disclosure. However, the amount of detailoffered is not intended to limit the anticipated variations of embodiments; on thecontrary, the intention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present disclosure as defined by theappended claims.

[0042] The ensuing description provides exemplary embodiments only, andis not intended to limit the scope, applicability, or configuration of the disclosure.Rather, the ensuing description of the exemplary embodiments will provide thoseskilled in the art with an enabling description for implementing an exemplaryembodiment. It should be understood that various changes may be made in thefunction and arrangement of elements without departing from the spirit and scopeof the invention as set forth.

[0043] Specific details are given in the following description to provide athorough understanding of the embodiments. However, it will be understood by oneof ordinary skill in the art that the embodiments may be practiced without thesespecific details. For example, circuits, systems, networks, processes, and othercomponents may be shown as components in block diagram form in order not toobscure the embodiments in unnecessary detail. In other instances, well-knowncircuits, processes, algorithms, structures, and techniques may be shown withoutunnecessary detail in order to avoid obscuring the embodiments.

[0044] Also, it is noted that individual embodiments may be described as aprocess which is depicted as a flowchart, a flow diagram, a data flow diagram, astructure diagram, or a block diagram. Although a flowchart may describe theoperations as a sequential process, many of the operations can be performed inparallel or concurrently. In addition, the order of the operations may be re-arranged.A process is terminated when its operations are completed but could have additionalsteps not included in a figure. A process may correspond to method, a function, aprocedure, a subroutine, a subprogram, etc. When a process corresponds to afunction, its termination can correspond to a return of the function to the callingfunction or the main function.

[0045] The word "exemplary" and / or "demonstrative" is used herein tomean serving as an example, instance, or illustration. For the avoidance of doubt,the subject matter disclosed herein is not limited by such examples. In addition, anyaspect or design described herein as "exemplary" and / or "demonstrative" is notnecessarily to be construed as preferred or advantageous over other aspects ordesigns, nor is it meant to preclude equivalent exemplary structures and techniquesknown to those of ordinary skill in the art. Furthermore, to the extent that the terms"includes," "has," "contains," and other similar words are used in either the detaileddescription or the claims, such terms are intended to be inclusive-in a mannersimilar to the term "comprising" as an open transition word-without precludingany additional or other elements.

[0046] Reference throughout this specification to "one embodiment" or "anembodiment" or "an instance" or "one instance" means that a particular feature,structure, or characteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, the appearances of thephrases "in one embodiment" or "in an embodiment" in various places throughoutthis specification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics may be combinedin any suitable manner in one or more embodiments.

[0047] The present disclosure relates to the field of power converters. Inparticular, the present the present disclosure relates to a converter for MVDC tosingle point HVDC. The present disclosure provides a high-power hybridmultipoint Direct Current (DC)-DC converter intended for integrating all types ofrenewable sources by connecting multiple Medium Voltage Direct Current(MVDC) points to a High Voltage Direct Current (HVDC) point.

[0048] The various aspects of the present disclosure have been describedwith reference to FIG. 1 to FIG. 16.

[0049] In an aspect, the present disclosure relates to a hybrid DC-DCconverter for converting a multipoint MVDC to a single point HVDC. FIG. 1.illustrates a circuit diagram of a converter (100) for K-point MVDC to single pointHVDC, and FIG. 2 illustrates a simplified version of the converter shown in FIG.1, in accordance with an embodiment of present disclosure. Referring to FIG. 1, theconverter (100) includes one or more primary side DC-Alternating Current (AC)circuits(110-1K0), and one or more secondary side AC-DC circuits (210-2K0). Theone or more secondary side AC-DC circuits (210-2K0) are connected in series. Kindependent numbers of the primary side DC-AC circuits (110-1K0) and Knumbers of series connected secondary side AC-DC circuits (210-2K0) may beconsidered for a K-point DC-DC circuit.

[0050] Hereinafter, in detailed description, claims and abstract, the one ormore primary side DC-AC circuits (110-1K0) may be collectively referred to as theprimary side DC-AC circuits (110) and individually referred to as the primary sideDC-AC circuit (110). Similarly, the one or more secondary side AC-DC circuits(210-2K0) may be collectively referred to as the secondary side AC-DC circuits(210) and individually referred to as the secondary side AC-DC circuit (210).

[0051] FIG. 3 illustrates a circuit diagram (300) of a converter for 3-pointMVDC to single point HVDC, and FIG. 4 illustrates a simplified circuit diagram(400) of the converter shown in FIG. 3, in accordance with an embodiment of thepresent disclosure. The versatility of present disclosure allows for further extensionto K-points, as demonstrated in FIGs. 1-2. In an embodiment, the converter (100)includes K hybrid DC-DC converters (HDC), where each HDC may include theprimary side DC-AC circuit (110) operating in a DC-AC converting mode, and thesecondary side AC-DC circuit (210) operating in an AC-DC converting mode,connected / linked via a single-phase transformer (301-1) and series leakageinductance (401-1). The secondary side AC-DC circuits (210, 220, ..., 2K0) areconnected in series. In an exemplary embodiment, an output from the seriesconnected secondary side AC-DC circuits (210, 220, ..., 2K0) may be connected toa HVDC grid (502) with series filter inductance (501).

[0052] In an embodiment, the primary side DC-AC circuit (110) mayinclude at least two director portions (113 and 114), and at least two wave-modulating portions (111-1 and 112-1) that are connected in parallel between a firstpositive DC branch (A-1) and a first negative DC branch (B-1) of the primary sideDC-AC circuit (110). The first positive DC branch (A-1) and the first negative DC11branch (B-1) may be configured to receive an input from a MVDC bus (101-1). Inan exemplary embodiment, power may be extracted from a terminal of individualrenewable energy source (RES) into the MVDC bus (101-1), as illustrated in FIG.7. The renewable energy sources may be based on wind and / or sunlight which maybe an input into the converter (100).

[0053] In an embodiment, a middle point between the series connection ofthe at least two director portions (113 and 114) may form the first AC branch (C1). In an embodiment, a middle point between the series connection of the at leasttwo wave-modulating portions (111-1 and 112-2) may form the second AC branch(D-1).

[0054] In an embodiment, the at least two wave-modulating portions (111-1 and 112-1) may be formed by a series-connection of a plurality of cells (Cell1,Cell2… CellN). The plurality of cells (Cell1, Cell2… CellN) may be the unipolarcells or bipolar cells or combination of unipolar cells and bipolar cells. FIGs. 6A-6C illustrate schematic views (600a, 600b, 600c) of N unipolar cells, N bipolarcells, and N cells, where each cell is either a unipolar cell or a bipolar cellrespectively. In an embodiment, one of the at least two wave-modulating portions(111-1 and 112-1) may be connected with a first series inductor to limit a circulatingcurrent between at least one DC-link and one of the at least two wave-modulatingportions (111-1 and 112-1). The circulating current may arise due to voltagefluctuations of cell's capacitor.

[0055] In an embodiment, the one or more similar AC-DC circuits (210-2K0) in secondary side may be connected in series. A secondary side AC-DCcircuits (210) may include at least four director portions (211-214). At least twodirector portions (211 and 212) of the at least four director portions (211-214) maybe connected in series between a second positive DC branch (X-1) and a secondnegative DC branch (X-2) of the secondary side AC-DC circuit (210). The secondpositive DC branch between (X-1) and X-(K+1) is configured to receive an outputat a HVDC bus (502). A middle point between the series connection of the first andsecond director portions (211 and 212) of the at least four director portions (211-214) may form a first AC branch (Y-1). A middle point between the seriesconnection of third and fourth director portions (213 and 214) of the at least fourdirector portions (211-214) may form a second AC branch (Z-1).

[0056] In an embodiment, the single-phase transformer (301-1) mayinclude a primary winding connected to a first AC branch (C-1) and a second ACbranch (D-1) of the primary side DC-AC circuit (110), and a secondary windingconnected to the first AC branch (Y-1) and the second AC branch (Z-1) of thesecondary side AC-DC circuit (210).

[0057] In an embodiment, each of the director portions among the at leasttwo director portions ((113,…1K3) and (114,…1K4)) of the one or more primaryside DC-AC circuits (110,…1K0) and the at least four director portions((211,..2K1), (212,…,2K2), (213,…,2K3), and (214,…,2K4)) of the one or moresecondary side AC-DC circuits (210,…, 2K0) may include a plurality of series-connected switches, for example, Insulated-Gate Bipolar Transistors (IGBTs) withthe antiparallel diode, or an antiparallel thyristor, or a thyristor with the antiparalleldiode. FIGs. 5A-5C illustrate circuit diagrams (500a-500c) of the IGBT with theantiparallel diode, the antiparallel thyristor, and the thyristor with antiparallel diode,respectively.

[0058] In an embodiment, the at least two director portions (113-1K3 and114-1K4) of the one or more primary side DC-AC circuits (110-1K0) and the atleast four director portions (211-2K1, 212-2K2 ,213-2K3, 214-2K4) of the one ormore secondary side AC-DC circuits (210-2K0) may be operated at a fundamentalfrequency to generate a DC-link voltage. The DC-link voltage may be generatedbetween the positive DC branches (X-1) and X-(K+1) of the one or more secondaryside AC-DC circuits (210-2K0). The operation of each of the director portions atthe fundamental frequency may reduce conduction losses and increase an overallefficiency of the convertor (100).

[0059] The number of half-bridge cells or full-bridge cells may besufficiently large to ensure that the output voltage, developed by a sequence of gatepulses like a pure sin wave or trapezoidal wave manifests as sinusoidal ortrapezoidal voltage waveforms respectively, as illustrated in FIGs. 9A and 9B. Inan exemplary embodiment, a trapezoidal modulation control strategy may beapplied to boost the DC-output voltage and give a batter current profile. Ascompared to sinusoidal modulation techniques, the trapezoidal modulationtechnique may reduce the sizes of the cells or the capacitors, DC-current filterinductance size, and also reduces switching losses of the semiconductor devices. Inan exemplary embodiment, instead of a trapezoidal modulation control strategy, theconverter (100) may be controlled to generate any other output voltage waveform.

[0060] In an exemplary embodiment, to balance an imbalance in the voltagebetween the K HDCs, advanced control techniques may be used by introducing acontrolled common mode voltage or current across each of the K HDCs. In anexemplary embodiment, an unequal nominal voltage of input DC-unit at theprimary side DC-AC circuits (110-1K0) may be controlled using the single-phasetransformers (301-1 -301-K) with appropriate transformation ratio while designingthe converter (100) (A hybrid DC-DC converter for converting multipoint MVDCto single point HVDC).

[0061] In an embodiment, the first AC branch (C-1, …., C-K) and thesecond AC branch (D-1, …, D-K) of one or more primary side DC-AC circuits(110-1K0) may be connected to the first AC branch (Y-1, …, Y-K) and the secondAC branch (Z-1, …, Z-K) of the one or more secondary side AC-DC circuits (210-2K0) through the single-phase transformer (301-1…, 301-K) and series inductance(401-1, …, 401-K). In an embodiment, at least one second inductor (401) may be,for example, a leakage inductor of the single-phase transformer (301-1) or anexternal inductor. In an embodiment, the second positive DC branch (X-1) of theone or more secondary side AC-DC circuits (210-2K0) may be connected in seriesto a filter inductor (501).

[0062] In an embodiment, one of the first AC branch (C-1) of primary sideDC-AC circuits (110-1K0), and the second AC branch (D-1) of the primary sideDC-AC circuits (110-1K0) may be configured to receive an AC output from one ofthe primary side DC-AC circuits (110-1K0).

[0063] In an exemplary embodiment, the voltage generated by the twoWMPs (111-1, and 112-1) from one of the primary side DC-AC circuits may beregulated by the corresponding director portions (113 and 114) respectively. Thedirector portions (113 and 114) may function as valves, facilitating the extractionof voltage from the WMPs (111-1, and 112-1) to generate a bipolar (AC) voltage.The maximum DP outputs Vdc_in1 (positive) and -Vdc_in1 (negative) may beobtained by switching on the switches in the director portions (113 and 114)respectively. The generated voltage across each of the transformer terminals (C1…, C-(k) and D-1…. D-(K)) may be sinusoidal or trapezoidal in nature whichdepend on control reference signal, as depicted in FIG 9A (sinusoidal) and FIG 9B(trapezoidal) respectively.

[0064] The AC-DC conversion operation at each of the secondary side AC-DC circuits (210-2K0) may generate a DC output. Two diagonal director portions(211-2K1 and 2214-2K4) of the secondary side AC-DC circuits (210-2K0) may beoperated at a same time, and other two director portions (212-2K2 and 213-2K3) ofthe secondary side AC-DC circuits (210-2K0) may operate complimentary of thedirector portions (211-2K1 and 214-2K4). In an exemplary embodiment, whereantiparallel thyristors or thyristor with antiparallel diode are used in thebidirectional switches used as switching devices, commutation of thyristor has tobe ensured. To deactivate the thyristor, the current passing through it must dropbelow a holding current, and a negative voltage must be applied across the thyristorfor a specified duration known as a turn-off time (tq).

[0065] In an exemplary embodiment, the converter (100) may include acontrol unit including at least one processor to control the operation of variousswitches of the converter (100), and applying various techniques describedhereinbefore. The processor may be implemented as one or more microprocessors,microcomputers, microcontrollers, digital signal processors, central processingunits, logic circuitries, and / or any devices that process data based on operationalinstructions.

[0066] The topology of the converter (100) was tested through simulationsfor 2-MVDC Point, 3-MVDC Point, and 4-MVDC Point using MATLAB / PSCAD,and 3-MVDC point simulation results were validated through real time hardware ina loop testing using OPAL-RT (OP-4512). The model parameters used for testingare detailed in Table I. FIG. 10 illustrates a graphical view (1000) representingconstant DC-bus voltage under variable load conditions, while FIG. 11 illustrates agraphical view (1100) depicting input and output power of the converter (100).Notably, the input power exhibits variations similar to the output power.Table 1: Simulation Parameters for 3-point Converter

[0067] FIGs. 12-14 illustrate graphical views (1200-1400) representingtransformer primary and secondary voltages for 2-MVDC point, 3-MVDC point,and 4-MVDC point converters using simulation experiments, respectively, inaccordance with an embodiment of the present disclosure. FIGs. 15-16 illustrateschematic representations (1500, 1600) depicting validation experiments usingreal-time hardware OPAL-RT (OP-4512), in accordance with an embodiment ofthe present disclosure. It's important to note that all parameters in the simulationresults are expressed in per-unit (pu) values corresponding to their respective ratedvalues.

[0068] While considerable emphasis has been placed herein on thepreferred embodiments, it will be appreciated that many embodiments can be madeand that many changes can be made in the preferred embodiments without departingfrom the principles of the disclosure. These and other changes in the preferredembodiments of the disclosure will be apparent to those skilled in the art from thedisclosure herein, whereby it is to be distinctly understood that the foregoingdescriptive matter is to be implemented merely as illustrative of the disclosure andnot as a limitation.ADVANTAGES OF THE PRESENT DESCRIPTION

[0069] The present disclosure provides a hybrid Direct Current (DC)-DCconverter for converting a multipoint Medium Voltage Direct Current (MVDC) toa single point High Voltage Direct Current (HVDC) in a more efficient manner.

[0070] The present disclosure provides a hybrid DC-DC converter that iscompact, flexible, and provides efficient power distribution network.

[0071] The present disclosure a hybrid DC-DC converter that requireslower number of devices and capacitors compared to that required in existingmultipoint converters, for a given dc-link voltage.

[0072] The present disclosure provides a hybrid DC-DC converter thatreduces a size of an arm inductor and a DC-side filter.

[0073] The present disclosure provides a hybrid DC-DC converter that hasa modular design, a soft-switching capability, reduced power-semiconductordevices, and a submodule capacitance.

[0074] The present disclosure reduces an overall footprint of the topologies,and provides efficient and reliable power evacuation from renewable energysources.

Claims

1. A hybrid Direct Current (DC)-DC converter (HDC) (100) for multipoint MVDC to single point High Voltage Direct Current (HVDC) applications comprising: an primary (input) side DC-Alternating Current (AC) unit (110) comprising at least two director portions (DPs) (113, 114), at least two wave-modulating portions (WMP) (111-1 and 112-1), and at least one DC source (101-1), wherein each DP (113 or 114) is series connections of switches, and series connection of the at least two DPs (113, 114) and the at least two WMPs (111-1 and 112-1) are connected in parallel between a positive DC speck A-1 and a negative DC speck B1, wherein a mid-speck between the series connection of the at least two DPs (113, 114) forms a first AC speck C-1, and a mid-speck between the series connection of the at least two WMPs (111-1 and 112-1) forms a second AC speck D-1, and wherein the positive DC speck A-1 and the negative DC speck B-1 are configured to receive input from a Medium Voltage Direct Current (MVDC) bus (101-1) while; and a secondary (output) side AC-DC unit (210) comprising at least four DPs (211-214), wherein two series connected DPs (211, 212) and (213 ,214) are connected in parallel between a positive DC speck X-1 and a negative DC speck X2 of the unit 210, wherein a mid-speck between the two series connected DPs (211 and 212) forms a first AC speck Y-1, and a mid-speck between two series connected DPs (213 and 214) forms a second AC speck Z-1,wherein the DC specks X-1 and X-(K+1) are configured with a series inductor (501) to receive an output at a HVDC bus (502), wherein primary winding specks of a single-phase transformer (301-1) are connected to the first and second AC specks (C-1 and D-1) of the unit (110), wherein secondary winding specks are connected to the first and second AC specks (Y-1 and Z-1) of the unit (210) through a series inductance (401-1); wherein K number of independent primary (input) side DC-AC units (110….1K0) and K number of series connected secondary (output) side AC-DC units (210….2K0) are considered for a K-point DC-DC circuit.

2. The HDC as claimed in claim 1, wherein one of the at least two WMPs (111- 1) is a series connection of N number of cells, wherein the cells are at least one of: unipolar, bipolar or a combination of both unipolar and bipolar cells, and wherein each cell comprises at least one energy storage element (capacitor) and at least two bidirectional switches comprising an insulated gate bipolar transistor (IGBT) with an antiparallel diode.

3. The HDC as claimed in claim 1, wherein the DPs (113…,1K3, 114….,1K4, 211….,2K1, 212….,2K2, 213….,2K3, 214….,2K4) have at least N number of predefined bidirectional switches comprising an IGBT with an antiparallel diode (500a), or an antiparallel thyristors valve (500b), or a thyristor with the antiparallel diode (500c) connected in series.

4. The HDC as claimed in claim 1, wherein the at least two WMPs (111-1, 112-1) are connected with series inductance (111-2, 112-2) which limits a circulating current between a dc-link and the at least two WMPs (111-1, 112-1), arising due to cell's capacitor voltage fluctuations.

5. The HDC as claimed in claim 1, wherein the first and second AC specks C-1 and D-1 of the primary side DC-AC unit (110) are connected to the first and second specks Y-1 and Z-1 of the secondary side AC-DC unit (210) through the single-phase transformer (301-1) and a series inductance (401-1).

6. The HDC as claimed in claim 5, wherein the series inductance (401-1) is a leakage inductance of the single-phase transformer (301-1) or an external inductor.

7. The HDC as claimed in claim 1, wherein the output DC specks X-1 and X- (K+1) of the secondary side AC-DC unit (210) are connected to the HVDC bus (501).

8. The HDC as claimed in claim 1, wherein the first and second AC specks C1 and D-1 are configured to receive an AC output from the unit (110), wherein one DP (113) and one WMP (111-1) are operated for a first half cycle of the AC output while another DP (114) and another WMP (112-1) are operated for a second half cycle of the AC output.

9. The HDC as claimed in claim 1, wherein the DPs (211-214) of the secondary side AC-DC unit (210) are operated at a fundamental frequency so that losses in the HDC are reduced, and an efficiency of the HDC is improved.