WO2017216291A1 - Convertisseur multiniveau modulaire et cellule de réduction des pertes par conduction de courant - Google Patents

Convertisseur multiniveau modulaire et cellule de réduction des pertes par conduction de courant Download PDF

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Publication number
WO2017216291A1
WO2017216291A1 PCT/EP2017/064669 EP2017064669W WO2017216291A1 WO 2017216291 A1 WO2017216291 A1 WO 2017216291A1 EP 2017064669 W EP2017064669 W EP 2017064669W WO 2017216291 A1 WO2017216291 A1 WO 2017216291A1
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WIPO (PCT)
Prior art keywords
switching unit
cell
branch
energy storage
storage element
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PCT/EP2017/064669
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English (en)
Inventor
Alireza NAMI
Frans Dijkhuizen
Muhammad Nawaz
Ingemar Blidberg
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Abb Schweiz Ag
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Publication of WO2017216291A1 publication Critical patent/WO2017216291A1/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/5388—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with asymmetrical configuration of switches
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present invention generally relates to modular multilevel converters. More particularly the present invention relates to a modular multilevel converter cell and a modular multilevel converter comprising such a cell.
  • Multilevel converters are of interest to use in a number of different power transmission environments. They may for in stance be used as voltage source converters in direct current power tran smission systems such as high voltage direct current (HVDC) and alternating current power transmission systems, such as flexible alternating current tran smission system (FACTS) . They may also be used as reactive compen sation circuits such as Static VAR compen sators. In order to reduce harmonic distortion in the output of power electronic converters, where the output voltages can assume several discrete levels, so called multilevel converters have been proposed. In particular, converters where a number of cascaded converter cells, each comprising a number of switching units and an energy storage unit in the form of a DC capacitor have been proposed.
  • Converter elements or cells in such a converter may for instance be of the half-bridge, full-bridge or double cell type. These may be connected in upper and lower phase arms of a phase leg.
  • a converter formed using cells has the advantage of low switching losses. However, the conduction losses are often high.
  • the present invention is directed towards providing a reduction of the current conduction losses in a modular multilevel converter.
  • This object is according to a first aspect achieved through a multilevel converter cell for providing at least one voltage contribution for assisting in the forming of an alternating current waveform, the cell comprising at least one energy storage element;
  • the first branch comprising a first and a second switching unit
  • one of the switching units of the first branch that is operative to bypass the energy storage element has a current conduction area that is larger than the current conduction area of the other switching unit of the first branch .
  • This object is according to a second aspect achieved through a modular multilevel converter for forming an alternating current waveform and comprising:
  • phase leg comprising a number of cells, where at least one cell of the phase leg comprises:
  • At least one energy storage element at least one energy storage element; and a first branch of series-connected switching units in parallel with an energy storage element, said first branch comprising a first and a second switching unit;
  • one of the switching units of the first branch that is operative to bypass the energy storage element has a current conduction area that is larger than the current conduction area of the other switching unit of the first branch .
  • the invention has a number of advantages. Through reducing the conduction losses, the efficiency of the converter is increased. This is furthermore achieved through a limited increase of the cell size and thereby also of the converter size. The reduction of the conduction losses also has the further advantage of relaxing the cooling requirements of the cells. The modified cells also serve to increase the surge current handling capability of the converter. The lower losses also allows for increasing the current/ power capability in the system .
  • fig. 2 schematically shows a full-bridge cell
  • fig. 3 schematically shows the structure of a first type of half-bridge cell
  • fig. 4 schematically shows the structure of a second type of half-bridge cell
  • fig. 5 schematically shows a half-bridge double cell
  • fig. 6 schematically shows a series half bridge cell
  • fig. 7 shows a plot of arm voltage and arm current of a phase arm in the converter
  • fig. 8 shows plots of total conduction losses and conduction losses through bypass and voltage contributing switching units of a converter
  • fig. 9 schematically shows one realization of the first type of half-bridge cell in order to reduce conduction losses
  • fig. 10 plots of total conduction losses and conduction losses through bypass and voltage contributing switching units of a converter with the half-bridge cell realization according to fig. 9.
  • Fig. 1 shows one variation of a multilevel converter in the form of a cell based voltage source converter 10 or modular multilevel converter (MMC) .
  • the converter operates to convert between alternating current (AC) and direct current (DC) .
  • the converter 10 in fig. 1 comprises a three-phase bridge made up of a number of phase legs. There are in this case three phase legs. It should however be realized that as an alternative there may be for in stance only two phase legs. There is thus a first phase leg PL1, a second phase leg PL2 and a third phase leg PL3.
  • the phase legs are more particularly connected between a first DC terminal DC1 and a second DC terminal DC2, where the first DC terminal may be connected to a first pole P I of a DC power transmission system, such as a High Voltage Direct Current (HVDC) power transmission system and the second DC terminal DC2 may be connected to ground, where the mid points of the phase legs are connected to corresponding alternating current terminals ACAl, ACB l,
  • a DC power transmission system such as a High Voltage Direct Current (HVDC) power transmission system
  • HVDC High Voltage Direct Current
  • a phase leg is in this example divided into two halves, a first upper half and a second lower half, where such a half is also termed a phase arm .
  • the first DC pole P I furthermore has a first potential Udp that may be positive.
  • the first pole P I may therefore also be termed a positive pole.
  • AC terminals ACAl, ACB2, ACC3 may in turn be connected to an AC system, such as a flexible alternating current tran smission system
  • a phase arm between the first pole P I and a first AC terminal ACA1, ACB1 and ACC1 may be termed a first phase arm or an upper phase arm, while a phase arm between the first AC terminal ACA1 and ground may be termed a second phase arm or a lower phase arm .
  • the type of voltage source converter shown in fig. 1 is only one example of a multilevel converter where the invention may be used. It is for instance possible to use the converter as a reactive
  • VAR Compensator such as a Static VAR Compensator.
  • the voltage source converter depicted in fig. 1 has an asymmetric monopole configuration . It is thus connected between a pole and ground. As an alternative it may be connected in a symmetric monopole
  • phase arms there would furthermore be a third and a fourth phase arm in the phase leg, where the second and third phase arms would be connected to ground, the first phase arm connected between the positive voltage of the first pole P I and the second phase arm and the fourth phase arm connected between the negative voltage of the second pole and the third phase arm .
  • a first AC terminal of a phase leg would in the symmetric bipole configuration be provided between the first and second phase arms, while a second AC terminal of the same phase leg would be provided between the third and fourth phase arms.
  • the phase arms are furthermore connected to the AC terminals via phase reactors.
  • the phase arms of the voltage source converter 10 in the example in fig. 1 comprise cells.
  • a cell is a unit that may be switched for providing a voltage contribution to the voltage on the corresponding AC terminal.
  • a cell then comprises one or more energy storage elements, for in stance in the form of capacitors, and the cell may be switched to provide a voltage contribution corresponding to the voltage of the energy storage element or a zero voltage contribution .
  • the cell in serts the voltage of the energy storage element. If more than one energy storage element is included in a cell it is possible with even further voltage contributions. When no voltage or a zero voltage is provided by the cell then the energy storage element is bypassed.
  • the cells are with advantage connected in series or in cascade in a phase arm .
  • the upper phase arm of the first phase leg PL1 includes five cells Clp l, C2p l, C3p l, C4p l and C5p l
  • the lower phase arm of the first phase leg PL1 includes five cells Cln 1, C2n 1, C3n 1, C4n l and C5n l.
  • Across the cells of the upper phase arm there is a first phase arm voltage Uvppa and through the upper phase arm there runs a first phase arm current Ivppa.
  • the upper phase arm is connected to the first pole P I it may also be considered to be a positive phase arm .
  • phase arm Across the cells of the lower phase arm there is a second phase arm voltage Uvpna and through the lower phase arm there run s a second phase arm current Ivpna.
  • the upper phase arm is furthermore joined to the AC terminal ACA1 via a first or upper arm reactor Laarm l, while the lower phase arm is joined to the same AC terminal ACA1 via a second or lower arm reactor Laarm2.
  • the upper phase arm of the second phase leg is furthermore joined to the AC terminal ACA1 via a first or upper arm reactor Laarm l, while the lower phase arm is joined to the same AC terminal ACA1 via a second or lower arm reactor Laarm2.
  • PL2 includes five cells Clp2, C2p2, C3p2, C4p2 and C5p2 while the lower phase arm of the second phase leg PL2 includes five cells Cln2, C2n2, C3n2, C4n2 and C5n2.
  • the upper phase arm of the third phase leg PL3 includes five cells Clp3, C2p3 , C3p3, C4p3 and C5p3 while the lower phase arm of the third phase leg PL3 includes five cells Cln3, C2n3 , C3n3,
  • the upper phase arms are furthermore joined to the corresponding AC terminals ACB1 and ACC1 via corresponding first or upper arm reactors Lbarm l and Lcarm l, respectively, while the lower phase arm s are joined to the same AC terminal ACB1 and ACC1 via corresponding second or lower arm reactors Lbarm2 and Lcarm2, respectively.
  • the number of cells provided in fig. 1 is only an example. It therefore has to be stressed that the number of cells in a phase arm may vary. It is often favorable to have many more cells in each phase arm , especially in HVDC applications. A phase arm may for in stance comprise hundreds of cells. There may however also be fewer.
  • Control of each cell in a phase arm is normally done through providing the cell with a control signal directed towards controlling the contribution of that cell to meeting a reference voltage.
  • the reference voltage may be provided for obtaining an AC waveform on the AC terminal of a phase leg, for in stance a sine wave. In order to control the cells there is therefore a control unit 12.
  • the control unit 12 is provided for controlling all the phase arms of the converter. However, in order to simplify the figure only the control of the upper phase arm of the first phase leg PL is indicated in fig. 1.
  • the control unit may be implemented through a computer.
  • phase arm s are controlled in a similar manner in order to form output waveform s on the three AC terminals AC1, AC2 and AC3.
  • Fig. 2 shows a first version of a full-bridge cell FBA.
  • the cell FBA is thus a full-bridge converter cell and includes an energy storage element, here in the form of a capacitor C, which is connected in parallel with a first group of switching units SI and S2.
  • the energy storage element C provides a voltage Udm, and therefore has a positive and negative end, where the positive end has a higher potential than the negative end.
  • the switching units SI and S2 in the first group are
  • each switching unit may be realized using a first type of semiconducting element that is a
  • the unidirectional conduction element such as a diode
  • a second type of semiconducting element in the form of a semiconducting element of the turn-off type such as a transistor like an IGBT (Insulated Gate Bipolar Transistor).
  • the diode may be anti-parallel to the transistor.
  • the first switching unit SI has a first transistor Tl with a first anti-parallel diode D l.
  • the first diode Dl is connected between the emitter and collector of the transistor Tl and has a direction of conductivity from the emitter to the collector as well as towards the positive end of the energy storage element C.
  • the second switching unit S2 has a second transistor T2 with a second anti-parallel diode D2.
  • the second diode D2 is connected in the same way in relation to the energy storage element C as the first diode D l, i.e. conducts current towards the positive end of the energy storage element C.
  • the first switching unit SI is furthermore connected to the positive end of the energy storage element C, while the second switching unit S2 is connected to the negative end of the energy storage element C.
  • the second group includes a third switching unit S3, here provided through a third
  • the fourth switching unit S4 is furthermore connected to the positive end of the energy storage element C, while the third switching unit
  • the switching units S3 and S4 in the second group are thus connected in series with each other.
  • the switching units S3 and S4 may also be denoted cell switches.
  • This full-bridge cell FBA comprises a first cell connection terminal TEFBAl and a second cell connection terminal TEFBA2, each providing a
  • the first cell connection terminal TEFBAl more particularly provides a connection from the phase arm to the junction between the first and the second switching units SI and S2, while the second cell connection terminal TEFBA2 provides a connection between the phase arm and a connection point between the third and fourth switching units S3 and S4.
  • the junction between the first and second switching units SI and S2 thus provides one cell connection terminal TEFBAl, while the junction between the third and fourth switching units S3 and S4 provides a second cell connection terminal TEFBA2.
  • connection terminals TEFBAl and TEFBA2 thus provide points where the cell FBA can be connected to a phase arm of a phase leg.
  • the first cell connection terminal TEFBAl thereby joins a phase arm with the connection point or junction between two of the series-connected switching units of the first group, here the first and second switching units SI and S2, while the second cell connection terminal TEFBA2 joins the upper phase arm with a connection point between two of the series connected switching units of the second group, here between the third and fourth switching units S3 and S4.
  • Fig. 3 schematically shows a first type of a half-bridge converter cell HBA that may be used in an upper phase arm of a phase leg.
  • This cell has a half- bridge cell structure where there is an energy storage element, here in the form of a capacitor C, which is connected in parallel with a group of switching units. Also this energy storage element C provides a voltage
  • each switching unit SI, S2 may be realized in the form of a switching element that may be a transistor like an IGBT together with an anti- parallel unidirectional conduction element, which may be a diode.
  • each switching unit SI, S2 may be realized in the form of a switching element that may be a transistor like an IGBT together with an anti- parallel unidirectional conduction element, which may be a diode.
  • first switching unit SI having a first transistor Tl with a first anti-parallel diode D l, where the diode D l has a direction of current conduction towards the positive end of the energy storage element C and a second switching unit S2 connected in series with the first switching unit Dl and having a second transistor T2 with anti-parallel second diode D2, where the diode D2 has the same direction of current conduction as the first diode Dl.
  • the first switching unit SI is connected to the positive end of the energy storage element C, while the second switching unit S2 is connected to the negative end of the energy storage element C.
  • first cell connection terminal TEHBA1 In order to provide the first type of half-bridge cell HBA based on the half- bridge cell structure, there is a first cell connection terminal TEHBA1 and a second cell connection terminal TEHBA2, each providing a connection for the cell to the upper phase arm of the phase leg of the voltage source converter.
  • the first cell connection terminal TEHBA1 more particularly provides a connection from the upper phase arm to the junction between the first switching unit SI and the capacitor C
  • the second cell connection terminal TEHBA2 provides a connection from the upper phase arm to the junction between the first and the second switching units SI and S2.
  • the second cell connection terminal TEHBA2 thus join s the phase arm with the connection point or junction between two of the series-connected switching units of the first group , here the first and second switching units S I and S2, while the first cell connection terminal TEHBA1 join s the upper phase arm with a connection point between the first switching unit S I and the positive end of the capacitor C.
  • Fig. 4 shows a second type of half-bridge cell HBB for connection in a lower phase arm of a phase leg.
  • This cell has the same type of cell structure as the first type of half-bridge cell. Therefore, it comprises a group of switching units comprising a first and second switching unit S I and S2 connected in the same way as the first and second switching units of the first type of half-bridge cell.
  • the first cell connection terminal TEHBB 1 provides a connection from the lower phase arm to the junction between the first and the second switching units S I and S2
  • the second cell connection terminal TEHBB2 provides a connection from the lower phase arm to the junction between the second switching unit S2 and the negative end of the capacitor C.
  • the half-bridge cell structure can be combined in a number of ways in order to obtain further cell types.
  • a first half bridge cell structure is connected to a second half bridge cell structure so that the negative end of the energy storage element CI of the first half bridge cell structure is connected to the positive end of the energy storage element C2 of the second half bridge cell structure.
  • the first and second switching units of the first cell structure are here also a first and second switching unit S I and S2 of the cell HBDC, while the first and second switching units of the second cell structure are a fifth and sixth switching unit S5 and S6 of the cell.
  • a first cell connection terminal TEDCl is provided at the junction between the first and second switching units S I and S2, while a second cell connection terminal TEDC2 is provided at the junction between the fifth and sixth switching units S5 and S6.
  • Fig. 6 schematically shows the series connection of two half-bridge cell structure for obtaining a series half bridge cell SHBC.
  • first and second half bridge cell structure where the negative end of the energy storage element CI of the first half-bridge cell structure is connected to the junction between the switching units of the second half bridge cell structure.
  • the first and second switching units of the first cell structure are also here a first and second switching unit S I and S2 of the cell SHBC, while the first and second switching units of the second cell structure are a seventh and eighth switching unit S7 and S8 of the cell.
  • the first cell connection terminal TESHB 1 is in this case provided at the junction between the first and second switching units S I and S2, while the second cell connection terminal TESHB2 is provided at the negative end of the energy storage element C2 of the second cell structure.
  • a cell As was mentioned earlier, the purpose of a cell is to provide a voltage contribution which is either a voltage of the cell capacitor or a zero voltage, where a half-bridge cell is only able to provide one polarity of the cell capacitor voltage but the full-bridge cell provides two polarities of the cell capacitor voltage.
  • a cell that gives a zero voltage contribution is in fact bypassed.
  • a switching unit functioning to provide such a bypass may then be termed a bypass switching unit.
  • a switching unit that is operative to bypass the energy storage element, i.e. to make the cell give a zero voltage contribution is thus termed a bypass switching unit.
  • one switching unit function s as a bypass switching unit
  • two switching units function as bypass switching units because the turning on of these switching units is used for bypassing the cell.
  • a bypass switching unit may in the case of a full-bridge cell be an assigned bypass switching unit, where the cell control may be set to only use assigned bypass switching units when controlling the cell to be bypassed.
  • a switching unit that is not used as a bypass switching unit may be termed a voltage contributing switching unit, since it is solely used for in serting the cell voltage into a phase arm when being turned on .
  • the first switching unit S I is a bypass switching unit and the second switching unit S2 is a voltage contributing switching unit
  • the second switching unit S2 is a bypass switching unit and the first switching unit S I is a voltage
  • the second and fifth switching units S2 and S5 are bypass switching units and the first and sixth switching units S I and S6 are voltage contributing switching units
  • the second and eighth switching units S2 and S8 are bypass switching units and the first and seventh switching units S I and S7 are voltage contributing switching units.
  • the invention is concerned with allowing conduction losses to be reduced in a voltage source converter. As will be shown now with reference being made to fig. 7 and 8 , these losses are closely related to the bypass switching units.
  • Fig. 7 shows a phase arm current Ivppa and an insertion index Ninspa, where the in sertion index is an index indicating the number of inserted cells. It therefore also corresponds to a phase arm voltage Vvppa of a converter with phase legs comprising half-bridge cells.
  • Fig. 8 shows the total conduction loss Ptot, the conduction loss Pbp of bypass switching units and the conduction loss Pvc of voltage contributing switching units of a converter using half-bridge cells.
  • Conduction loss (Ploss_ c) is the function of RMS (Root Mean Square) current L-ms, average current Iavg and the semiconductor on-state resistance R on as shown below:
  • Ploss_c (VT * ) where VT is the semiconductor threshold voltage.
  • bypass switching unit encounters a higher average and RMS current than a voltage contribution switching unit as shown in Figure 8 . From this it can also be gathered that the influence of the current conduction losses are higher in the bypass switching units than in the voltage contributing switching units. As shown , this results in that the contribution of the bypass switching unit in a half bridge MMC is almost 70 -80 % of the total conduction losses. Therefore, if a bypass switching unit (with lower Ron) is selected, it is possible to obtain a substantial decrease in the conduction losses in the MMC converter. One way to reduce the losses is through increasing the current conduction areas of the switching units. If this is only done for the bypass switching units then it is possible to obtain a substantial reduction of conduction losses with a limited converter size increase.
  • the bypass switching unit of a branch thus has a current conduction area that is larger than the current conduction area of the other switching unit of the branch.
  • each switching unit of a branch comprises a number of parallel semiconducting elements and that the bypass switching unit of the branch comprises more parallel semiconducting elements than the other switching unit of the branch.
  • a bypass switching unit of a branch comprises more parallel semiconducting elements of the first type than the other switching unit of the branch.
  • the number of parallel transistors may be the same. This is of advantage if the converter is to operate as a rectifier. If the converter is to operate as an inverter it is on the other hand possible that only the number of transistors is higher in the bypass switching unit than in the voltage contributing switching unit. It is thus possible that a bypass switching unit of a branch comprises more parallel semiconducting elements of the second type than the other switching unit of the branch. In this case the number of diodes may be the same in both types of switching units. Naturally it is also possible that there are both more transistors and diodes in the bypass switching unit of the branch than in the other switching unit of the branch .
  • switching units are provided or formed as modules comprising submodules with parallel semiconducting elements.
  • a submodule may then comprise only transistors, only diodes or a
  • bypass semiconducting unit comprises a module having six submodules
  • voltage contributing switching unit comprises a module only having four submodules.
  • switching units may be formed as modules comprising a group of parallel submodules implementing the semiconducting elements of the first and second types, where the bypass switching unit of a branch comprises more submodules than the other switching unit of the branch.
  • Fig. 9 shows an example of how the first type of half-bride cell may be realized using modules comprising a number of submodules.
  • the first switching unit SI is realized through a first module MA having six submodules SMA1, SMA2, SMA3, SMA4 SMA5 and SMA6, while the second switching unit S2 is realized through a second module
  • MB only having four submodules SMB1, SMB2, SMB3 and SMB4.
  • the first four submodules SMA1, SMA2, SMA3 and SMA4 of the first switching unit SI are identical to the submodules SMB1, SMB2, SMB3 and SMB4 of the second switching unit S2, it can be seen that there will be more semiconducting elements in the first switching unit S I, either transistors, diodes or both , than in the second switching unit S2.
  • Fig. 10 shows the conduction losses Pbp in the bypass switching units, the conduction losses Pvc in the voltage contributing switching units and the total conduction losses Ptot for an MMC converter employing modified half-bridge cells, i.e.
  • the full-bridge cell in fig. 2 two of the cells connected to the same end of the energy storage element C, either the positive or the negative end, will act as bypass switching units and consequently have more semiconducting elements than the other two switching units.
  • the first and fourth switching units S I and S4 as modules comprising six submodules and the second and third switching units S2 and S3 as modules limited to four submodules each .
  • the second and third switching units S2 and S3 are bypass switching units, in which case their modules may each comprise six submodules, while the first and the fourth switching units S I and S4 are made up of modules only having four submodules each .
  • the second switching unit S2 of the second type of half-bridge cell in fig. 4 may comprise a module made up of six submodules, while the first switching unit S I may be realized through a module only having four submodules.
  • the first and sixth switching units S I and S6 may each be realized through a module only having four
  • the second and fifth switching units S2 and S5 may each be realized through a module comprising six submodules.
  • the first and seventh switching units SI and S7 would each be realized through a module only having four submodules, while the second and eighth switching units S2 and S8 would each be realized through a module comprising six submodules.
  • the invention has a number of advantages. Through reducing the conduction losses the efficiency of the converter may be increased. This is furthermore achieved through a limited increase of the cell size and thereby also of the converter size. The reduction of the conduction losses also has the further advantage of relaxing the cooling requirements of the cells. Through the use of fixed sized modules with submodules an easily expandable standardized system can be used requiring little or no design changes. The modified cells also serve to increase the surge current handling capability of the converter.
  • the number of submodules in a module is not limited to four and six. These numbers were only given as examples because they represent currently existing module realizations.
  • the transistor is not limited to an IGBT. It may for in stance be an Junction Field Effect Tran sistor (J FET) or a SiC Metal- Oxide- Semiconductor Field-Effect Transistor (MOSFET) instead.
  • J FET Junction Field Effect Tran sistor
  • MOSFET SiC Metal- Oxide- Semiconductor Field-Effect Transistor
  • tran sistors may for instance also be an Integrated Gate-Commutated Thyristor (IGCT) .
  • IGCT Integrated Gate-Commutated Thyristor

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

Un convertisseur multiniveau permettant de former une forme d'onde de courant alternatif comprend au moins une cellule (HBA) comprenant au moins un élément de stockage d'énergie (C) et une première branche d'unités de commutation connectées en série en parallèle avec l'élément de stockage d'énergie (C). La première branche comprend une première et une seconde unité de commutation (S1, S2), l'une (S1) des unités de commutation qui a pour fonction de contourner l'élément de stockage d'énergie (C) présentant une zone de conduction de courant qui est supérieure à la zone de conduction de courant de l'autre unité de commutation (S2). Cette structure de cellule présente l'avantage de réduire les pertes de conduction à travers la cellule avec une augmentation limitée de la taille de cellule.
PCT/EP2017/064669 2016-06-15 2017-06-15 Convertisseur multiniveau modulaire et cellule de réduction des pertes par conduction de courant WO2017216291A1 (fr)

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