WO2022213185A1 - Sous-module de convertisseur à source de tension multiniveau comprenant des branches parallèles conductrices de courant comprenant de multiples dispositifs de stockage d'énergie, et procédés associés - Google Patents

Sous-module de convertisseur à source de tension multiniveau comprenant des branches parallèles conductrices de courant comprenant de multiples dispositifs de stockage d'énergie, et procédés associés Download PDF

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Publication number
WO2022213185A1
WO2022213185A1 PCT/CA2022/050513 CA2022050513W WO2022213185A1 WO 2022213185 A1 WO2022213185 A1 WO 2022213185A1 CA 2022050513 W CA2022050513 W CA 2022050513W WO 2022213185 A1 WO2022213185 A1 WO 2022213185A1
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Prior art keywords
submodule
submodules
voltage
energy storage
current
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PCT/CA2022/050513
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English (en)
Inventor
Mojtaba Mohaddes Khorassani
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Transgrid Solutions Inc.
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Publication of WO2022213185A1 publication Critical patent/WO2022213185A1/fr

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    • 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
    • H02M7/4833—Capacitor voltage balancing
    • 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

Definitions

  • the present invention relates to a submodule for a modular multi-level voltage sourced converter, and more particularly to such a submodule with multiple parallel current-conducting branches and energy storage devices, and related methods.
  • VSC Voltage Source (or Sourced) Converters
  • HVDC High Voltage Direct Current
  • MVDC Medium Voltage Direct Current
  • STATCOM Static Compensators
  • a VSC can be built in multiple different topologies.
  • a common topology is the modular multi-level converter (MMC) which comprises a plurality of smaller units called submodules [A. Lesnicar and R. Marquardt, "An innovative modular multilevel converter topology suitable for a wide power range," 2003 IEEE Bologna Power Tech Conference Proceedings, 2003, pp. 6 pp. Vol.3-].
  • MMC modular multi-level converter
  • FIG. 1 shows the structure of a three phase modular multi-level voltage source converter commonly used for AC to DC (and vice versa) energy conversion applications.
  • Figure 2 shows the structure of an MMC converter commonly used for reactive power compensation applications, i.e. STATCOM.
  • this MMC topology comprises two arms for each of its phases A through C (Ph A , Ph B and Ph c ), an upper arm 2 and a lower arm 3.
  • Each arm 2 or 3 comprises a plurality of series connected units that are commonly referred to as “submodules” SM.
  • submodules submodules
  • each submodule comprises a capacitor and two or more electronic switches to allow the capacitor to be inserted into the circuit (either in forward or reverse polarity) or bypassed or blocked.
  • IGBT Injection-enhanced gate transistor
  • IGCT integrated gate-commutated thyristor
  • BIGT Bi-mode Insulated Gate Transistor
  • Converters utilizing full bridge submodules have several functional advantages compared to HB submodules, most notably they are capable of suppressing fault current in case of a short circuit between DC terminals.
  • a converter arm comprising FB submodules can withstand voltages in both polarities, which makes it suitable for connection in delta as shown in Figure 2.
  • the application of the full bridge submodules is mostly limited to the STATCOM due to the higher capital cost and higher losses compared to the HB submodules.
  • a submodule for a modular multilevel voltage sourced converter comprising: two terminals for electrically connecting the submodule within the modular multilevel voltage sourced converter and defining a submodule voltage; first and second energy storage devices each adapted to provide a substantially constant voltage having a value and a polarity; a first pairing of antiparallel-connected unidirectional-current conducting electronic components electrically connected in series with the first energy storage device to form a first branch of the submodule which is electrically connected between the terminals and along which current can flow between the terminals such that the submodule voltage is substantially equal to the substantially constant voltage of the first energy storage device; wherein the first pairing of electronic components includes a first power electronic switch which is configured to conduct current in response to a control signal; a second pairing of antiparallel-connected unidirectional-current conducting electronic components electrically connected in series with the second energy storage device to form a second branch of the submodule which is electrically connected between the terminals in parallel to the first branch and along which
  • This provides an arrangement for a submodule which can produce voltages of opposite polarities with fewer power electronic switches than a full-bridge submodule, resulting in lower losses.
  • the values of the substantially constant voltages of the first and second energy storage devices are substantially the same.
  • the first and second power electronic switches are oriented to conduct current in opposite directions between the terminals of the submodule.
  • each of the first and second power electronic switches is oriented to conduct current in a direction out of a positive terminal of a corresponding one of the first and second energy storage devices.
  • control arrangement is further configured for sending the control signals to the pairings of electronic components in such manners as to operate the submodule in a nonconductive state in which the first and second pairings of electronic components are deactivated to not conduct current through either one of the branches.
  • each of the first and second pairings of electronic components further include a user-uncontrollable unidirectional current-conducting component oriented to conduct current in opposite directions between the terminals of the submodule.
  • each user-uncontrollable unidirectional current-conducting component is oriented to conduct current in a direction into the positive terminal of a corresponding one of the first and second energy storage devices.
  • the submodules in the chain comprise a set of the submodules with multiple energy storage devices
  • each submodule of the set comprises a pair of parallel selectively current-conducting branches between terminals of the submodule, wherein the branches of each submodule of said set comprise energy storage devices arranged to provide substantially constant voltages having a substantially common value but opposite polarity relative to the terminals of the submodule
  • the method comprising: receiving (i) measurements of voltages of the first and second energy storage devices of the submodules of the set, and (ii) a measurement of current through the chain of the submodules; determining a prescribed number of the submodules of said set to
  • This arrangement provides a means of maintaining voltages of the energy storage devices of the submodules with multiple energy storage devices at a prescribed reference value.
  • the reference value is typically based on a rating of the voltage sourced converter in which the chain of the series-connected submodules is implemented.
  • the energy storage devices are capacitive elements such as capacitors.
  • the value of the voltages of the energy storage devices in the submodules of the multiple energy storage device type are substantially the same.
  • operating selected ones of the submodules in inserted states of the common polarity comprises selecting the prescribed number of submodules based on the measured voltages of the energy storage devices thereof independent of the current-conducting branch corresponding to the common polarity.
  • a particular submodule is selected to operate in the inserted state as long as a measured voltage of energy storage devices in one of its branches satisfies the corresponding criterion, regardless of whether that branch will actually conduct current.
  • a voltage sourced converter comprising: a pair of connection terminals through which electrical power is transferred; a plurality of power electronic submodules each including at least one energy storage device arranged to maintain a substantially constant voltage and electronic switches operatively connecting the at least one energy storage device to terminals of the respective submodule such that current can be selectively guided through the at least one energy storage device; wherein the submodules are electrically connected in series between the connection terminals; wherein the submodules comprise one or more binary-level submodules configured to form, at the terminals of a corresponding one of the binary-level submodules, a voltage of (i) a substantially constant value and a first polarity, or (ii) the substantially constant value and a second opposite polarity; wherein the submodules comprise at least one three-level submodule configured to form, at the terminals of a corresponding one of the three-level submodules, a voltage of (i) a substantially constant value and
  • the binary-level submodule is the submodule recited earlier in this section.
  • the three-level submodule is a full-bridge submodule.
  • a method for controlling a three-level power electronic submodule in a series chain of power electronic submodules in a voltage sourced converter wherein the chain also includes a plurality of binary-level power electronic submodules each configured to form, at terminals of a respective one of the binary-level submodules, a voltage of (i) a substantially constant predetermined value and a first polarity, or (ii) the substantially constant predetermined value and a second opposite polarity, and wherein the three-level power electronic submodule is configured to form, at terminals thereof, a voltage of (i) a substantially constant value and a first polarity, (ii) the substantially constant value and a second opposite polarity, or (iii) substantially zero, the method comprising: receiving (i) a target voltage for the chain of power electronic submodules, and (ii) an actual total voltage of the binary-level power electronic submodules in the chain; comparing a difference between the target
  • the actual total voltage of the binary-level power electronic submodules in the chain is obtained by measurement of voltage either of the entire chain and the three-level power electronic submodule or of the individual binary-level power electronic submodules, which voltage measurements are subsequently used to determine or calculate the voltage of the chain.
  • the first and second threshold values are based on a difference between a prescribed voltage value of the energy storage device and a measured voltage value thereof.
  • the prescribed voltage value is the constant value.
  • the energy storage device can charge or discharge, its voltage may fluctuate slightly.
  • the first and second threshold values are predetermined values adjusted by the difference between the prescribed voltage value of the energy storage device and the measured voltage value thereof.
  • the predetermined values are based on a modulator used for controlling the chain of power electronic submodules to form a desired voltage thereacross.
  • the difference between the prescribed voltage value of the energy storage device and the measured voltage value thereof is additive or subtractive to the predetermined values based on a direction of current through the chain of the submodules.
  • the difference is added to the predetermined values to increase the threshold values, and when the direction of the current corresponds to charging of the energy storage device, the difference is subtracted from the predetermined values to lower the threshold values.
  • FIG 1 is a schematic diagram of a typical three-phase modular multi-level converter (MMC) commonly used in AC/DC conversion application;
  • MMC modular multi-level converter
  • FIG. 2 is a schematic diagram of a typical 3-phase MMC commonly used in STATCOM application
  • Figure 3 is a schematic diagram of a conventional half bridge submodule
  • Figures 4A and 4B are schematic diagrams of conventional full bridge and semi-full bridge submodules, respectively;
  • FIGS. 5 and 6 are a schematic diagrams of arrangements of submodule according to the present invention, which may be referred to hereinafter as Dcap for convenient reference;
  • Figure 7 is a flowchart of an arrangement of method for forming a prescribed voltage across a series chain of power electronic submodules according to the present invention.
  • Figure 8 is a schematic diagram of a control system implementing the arrangement of method of Figure 7;
  • Figures 9 and 10 are schematic diagrams of MMCs with different topologies, the former which has six arms and the latter which has three arms in delta configuration;
  • Figure 11 is a flowchart of an arrangement of method for controlling a three-level power electronic submodule in a series chain of power electronic submodules also including submodules of arrangements according to the present invention
  • Figure 12 is a schematic diagram of a control system implementing the arrangement of method of Figure 11 ;
  • Figures 13A and 13B are waveforms of arm voltage in kV over time for a MMC having only Dcap submodules and having a combination of Dcap and full-bridge submodules, respectively.
  • a submodule 10 for a voltage sourced converter particularly of a modular multilevel type (typically referred to in short as MMC), and related methods for controlling series chains of submodules, often implemented in a MMC, which include such a submodule as 10.
  • MMC modular multilevel type
  • the novel submodule 10 may be referred to hereinafter as Dcap or the Dcap submodule for convenient reference.
  • the submodule 10 comprises a pair of parallel selectively current conducting branches between terminals of the submodule, and plural or multiple energy storage devices.
  • the energy storage devices are arranged in the branches to provide substantially constant voltages having a substantially common value but opposite polarity relative to the terminals of the submodule. These voltages form a predetermined set of selectable voltages to be formed at the submodule terminals based on electronic switching of switches in the branches.
  • there is one energy storage device in each parallel branch and typically the energy storage devices are capacitive elements such as capacitors.
  • the values of the voltages of the energy storage devices in the submodules of the multiple energy storage device type are substantially the same.
  • the submodule comprises:
  • first and second energy storage devices C1 and C2 such as capacitors, each adapted to provide a substantially constant voltage having a value and a polarity
  • the second energy storage device C2 in the second branch 33 has opposite polarity to the first energy storage device C1 in the first branch 23. Also, it will be appreciated that the values of the substantially constant voltages of the first and second energy storage devices are substantially the same.
  • Each of the first and second pairings 20, 30 of electronic components includes a respective power electronic switch S1 , S2, for example an insulated gate bipolar transistor (IGBT) as shown in Figure 6, which is configured to conduct current in response to a control signal.
  • the control signal acts to activate the respective power electronic switch to operate in a conductive state in which the switch conducts electrical current. In the conductive state, the respective power electronic switch conducts current in a single direction and is therefore unidirectional.
  • the switch is conductive while the control signal is applied thereto.
  • the first and second power electronic switches S1 , S2 are oriented to conduct current in opposite directions between the terminals T1 , T2 of the submodule. More specifically, each respective power electronic switch S1 , S2 is oriented to conduct current in a direction out of a positive terminal of a corresponding one of the first and second energy storage devices C1 , C2. In other words, the respective power electronic switch is oriented to conduct current out of the positive terminal of the energy storage device with which it is electrically connected in series.
  • each pairing of antiparallel-connected unidirectional-current conducting electronic components 20, 30 comprises a user-uncontrollable unidirectional current-conducting component D1 , D2, for example a diode, oriented to conduct current in opposite directions (to one another) between the terminals T1 , T2 of the submodule.
  • D1 , D2 are controllable or can be activated to the conductive state by voltage formed across their connection terminals and not (additionally) by a control signal.
  • each user-uncontrollable unidirectional current-conducting component D1 , D2 is oriented to conduct current in a direction into the positive terminal of the corresponding first or second energy storage devices C1 , C2 with which the component is electrically connected in series.
  • the submodule 10 includes a control arrangement 40 configured for sending or applying the control signals to the pairings of the electronic components 20, 30, and more specifically to the respective power electronic switches S1 , S2 of the two bidirectional switches 20, 30.
  • the control arrangement 40 may be a controller uniquely associated with the submodule 10 or may be a controller of the VSC within which the respective novel submodule is implemented.
  • the controller 40 is operatively communicated with the bidirectional switches 20, 30 in both current-conducting branches.
  • the controller 40 generally comprises a processor and a non-transitory readable storage medium having computer readable codes stored thereon which when executed by the processor act to operate the respective submodule 10 in:
  • the controller 40 does not send control signals to the first and second power electronic switches S1 , S2 so that they are concurrently nonconductive.
  • the complementary current conducting components D1 and D2 which are control signal-free components, may be conductive depending on the direction of current through the submodule, these components D1 and D2 are oriented to conduct current in a direction corresponding to charging of the corresponding energy storage device, which is opposite to a usual direction of current flow through the corresponding branch, so normally no current will flow between the submodule terminals in the nonconductive state.
  • the first and second bidirectional switches are deactivated to substantially resist current flow between the terminals of the submodule.
  • the nonconductive state is implemented when it is desired to stop current flow through the series chain of submodules, for example to clear a fault.
  • current may flow through the submodule via the diodes in the branches in the first few milliseconds of the fault.
  • This provides an arrangement for a submodule which can produce voltages of opposite polarities with fewer power electronic switches than a full-bridge submodule, resulting in lower losses.
  • the submodule 10 uses multiple energy storage devices C1 , C2 which selectively carry current based on the selected or desired submodule voltage Vsm
  • a method is provided when implementing a plurality of such submodules in a series chain of power electronic submodules, for example in an arm of a MMC, for selecting specific ones of the Dcap type submodules to form a prescribed voltage across the chain with a polarity and a voltage value, so that the energy storage device voltages of the individual submodules can be balanced, that is maintained substantially constant.
  • this general method for operating Dcap submodules may be performed whether all of the submodules in the series chain are of the Dcap type or if the series chain includes a mixture of different types of submodules, one of which is Dcap.
  • the types of submodules implemented affect the voltages that can be formed across the series chain.
  • the method generally comprises the steps of:
  • step 40 receiving (i) measurements of voltages of the first and second energy storage devices of the Dcap submodules, indicated in Figure 8 at Vc1_1 through Vc1_N and Vc2_1 through Vc2_N of submodules Dcapi through Dcap N , and (ii) a measurement of current through the chain of the submodules indicated at larm;
  • step 42 determining a prescribed number of the Dcap submodules (Np in Figure 8, output of a Modulator) to be operated in a common polarity based on the prescribed voltage Vref to be formed across the chain;
  • step 46 ranking the measured voltages of the energy storage devices of the Dcap submodules, collectively referred to as Vc in Figure 8;
  • the Dcap submodules can only form non-zero submodule voltages, remaining ones of the Dcap submodules not selected to operate in the common polarity at step 44 are selected to operate in the opposite polarity (i.e., they still conduct current through one of the energy storage devices to form a fixed voltage at the terminals of the corresponding submodule) and not in the nonconductive state.
  • a step of measuring the voltages of the energy storage devices in each branch of each Dcap submodule and measuring the current through the series chain of submodules precedes the step of receiving these measurements.
  • the measuring step is applied to each storage device of each submodule.
  • the steps of measuring/receiving actual voltages and current and determining the number of Dcap submodules to be used in forming the desired, prescribed voltage may be performed concurrently or sequentially, for example in the order recited above.
  • step 42 the set of predetermined voltages formable by the series chain of submodules will be taken into account, which as previously discussed will vary depending on the types of submodules implemented.
  • the step of operating the selected submodules in the common polarity comprises generating control signals to be applied to the electronic switches of the submodules, as represented by ‘Firing Pulses’ output from a ‘Balancing/Firing’ block of Figure 8.
  • each operating state thereof is considered to be an ‘inserted state’ in which current passes through an energy storage device of the submodule.
  • each Dcap submodule can only be operated in the inserted state (i.e., non-zero submodule terminal voltage). Therefore, the step of selecting the Dcap submodules to be operated in the inserted state of the common polarity is effectively a step of assigning one of the two fixed voltage states to all of the Dcap submodules in the series chain.
  • the step of operating selected Dcap submodules in the common polarity comprises selecting the prescribed number of submodules based on the measured voltages of the energy storage devices thereof independent of the current-conducting branch corresponding to the common polarity.
  • a particular submodule is selected to operate with the common polarity of the prescribed voltage as long as a measured voltage of energy storage devices in one of its branches satisfies the corresponding criterion, regardless of whether that branch will actually conduct current. This prevents overcharging of the energy storage devices.
  • This arrangement provides a means of maintaining voltages of the energy storage devices of the Dcap submodules with multiple energy storage devices at a prescribed reference value.
  • the reference value is typically based on a rating of the voltage sourced converter in which the chain of the series-connected submodules is implemented and a number or quantity of submodules in the chain, that is an arm of the VSC.
  • a novel hybrid MMC topology such as 70 or 71 is disclosed which comprises arms or valves 73 each having combinations or mixtures of the Dcap submodules, which can form only non-zero submodule voltages, and three-level submodules, which are configured to form a plurality of non-zero submodule voltages, typically two of the same value but opposite polarity, and a zero submodule voltage, for example full bridge as illustrated in Figures 9 and 10.
  • the voltage sourced converter 70 or 71 comprises a pair of connection terminals through which electrical power is transferred, for example terminals Ph A and D1 in the arrangement of Figure 9, and a plurality of power electronic submodules (in the arm 73) each including at least one energy storage device arranged to maintain a substantially constant voltage and electronic switches operatively connecting the one or more energy storage devices to terminals of the respective submodule such that current can be selectively guided through the at least one energy storage device.
  • the submodules are electrically connected in series between the connection terminals.
  • the submodules in the series chain include one or more binary-level submodules represented by Dcap in Figures 9 and 10, which are configured to form, at the terminals of a corresponding one of the binary-level submodules, a voltage of (i) a substantially constant value and a first polarity, or (ii) the substantially constant value and a second opposite polarity.
  • the submodules in the series chain also include at least one three-level submodule, represented by FB in Figures 9 and 10, which is configured to form, at the terminals of a corresponding one of the three-level submodules, a voltage of (i) a substantially constant value and a first polarity, (ii) the substantially constant value and of a second opposite polarity, or (iii) substantially zero.
  • FB three-level submodule
  • the constant values are nominal values for which the submodule is rated.
  • a number of the three-level submodules in the chain is less than a number of the binary-level submodules therein.
  • the three-level submodule is a full-bridge submodule as shown in Figures
  • control method generally comprises the steps of:
  • step 80 receiving (i) a target voltage for the chain of power electronic submodules (Vref_arm in Figure 12), and (ii) an actual total voltage of the Dcap submodules in the chain of power electronic submodules (Varm - V_FB);
  • -as indicated at step 82 comparing a difference between the target voltage and the actual total voltage to a pair of non-zero positive threshold values (Th1 and Th2 in Figure 12) associated with a voltage step across the chain of power electronic submodules when one of the binary-level power electronic submodules is toggled between the voltages of opposite polarities; and -as indicated at step 84, based on the comparison operating the three-level power electronic submodule to form the voltage of: a) the substantially constant value and the first polarity, which can be considered a fixed forward polarity state, if the difference is greater than a higher one of the threshold values, as represented by box 87, b) the substantially constant value and the second polarity, which can be considered a fixed reverse polarity state, if the difference is less than a lower one of the threshold values, as represented by box 88, or c) substantially zero, which can be considered a zero voltage state, if the difference is between the threshold values, as represented by box 89.
  • the first and second threshold values are based on a difference between a prescribed voltage value of the energy storage device of the (three-level) submodule (Vc_ref in Figure 12) and a measured voltage value thereof (Vc_FB in Figure 12).
  • Vc_ref a prescribed voltage value of the energy storage device of the (three-level) submodule
  • Vc_FB a measured voltage value thereof
  • the prescribed voltage value is the constant value for which the three-level submodule is rated.
  • the energy storage device can charge or discharge, its (actual or measured) voltage may fluctuate slightly.
  • the first and second threshold values are predetermined values adjusted by the difference between the prescribed voltage value of the energy storage device (of the three-level submodule) and the measured voltage value thereof (ATh).
  • This is represented in Figure 12 by operations upstream from summation operators which respectively receive one the threshold values Th1 and Th2 as input.
  • the predetermined values are based on a modulator used for controlling the chain of power electronic submodules to form a desired voltage thereacross.
  • the difference between the prescribed voltage value of the energy storage device and the measured voltage value thereof, which is used to determine the threshold values is additive or subtractive to the predetermined values based on a direction of current through the chain of the submodules. For example, when the direction of the current corresponds to discharging of the energy storage device, the difference is added to the predetermined values to increase the threshold values, and when the direction of the current corresponds to charging of the energy storage device, the difference is subtracted from the predetermined values to lower the threshold values.
  • the actual total voltage of the Dcap submodules in the chain is obtained by measurement of voltage either of the entire chain and measurement of the FB submodule(s) or of the individual Dcap submodules, which voltage measurements are subsequently used to determine or calculate the voltage of the chain.
  • the difference is calculated or computed, which is represented in Figure 11 as a separate step 92 following receipt of measurements at 80 and before the comparing step at 82.
  • the DCap submodule comprises two electronic switches S1 and S2 (which can be switched ON and OFF while carrying current, such as IGBT, IEGT, BIGT, IGCT or MOSFET), two DC capacitors C1 and C2 and two diodes D1 and D2.
  • the diodes D1 and D2 are connected in parallel to the upper and lower IGBTs S1 and S2 respectively, each with its anode connected to the emitter of the IGBT and its cathode to the collector of the IGBT.
  • Terminal T1 of the submodule is connected to the common node between S1 and S2.
  • the Capacitors C1 and C2 are connected between the collector of S1 and the emitter of S2.
  • the terminal T2 of the submodule is connected to the common node between C1 and C2.
  • capacitors C1 and C2 are charged and their voltages are charged to Vc1 and Vc2.
  • a controller circuit maintains Vc1 and Vc2 near a predetermined target voltage Vc_ref.
  • the submodule has three states of operation: blocked, positive and negative.
  • S1 When the submodule is in the positive state S1 is turned on and S2 is turned off.
  • DCap submodule however utilizes only two power electronic switches (e.g. IGBTs) and therefore has lower losses.
  • the invention also includes the methodology to maintain the capacitor voltages nearly equal among all submodules of each valve for a converter comprising dual capacitor submodules.
  • a new converter arrangement is also introduced where the valves comprise a mixture of DCap and regular FB submodules. This arrangement can reduce the harmonic currents at the converter AC terminals.
  • the DCap submodules are connected in a chain to make an arm (also referred to as a valve) as for example shown in Figures 1 and 2 or Figures 8 and 9.
  • the total voltage across each arm Varm x is determined by the number of the submodules that are in positive or negative state in that arm.
  • the controller described further below selects the submodules to be in positive or negative state to achieve the desired arm voltage while maintaining all submodule capacitor voltages near the target level.
  • FIG. 8 shows the schematic diagram of the novel controller for one arm of the VSC.
  • the controllers for all arms are similar.
  • the converter arm comprises N submodules.
  • the desired arm voltage Vref_arm is determined by the upper-level controls and is applied to a modulator that determines the number of submodules Np to be in the positive states.
  • the modulator utilizes existing technology (normally based on the Nearest Level Selection or Pulse Width Modulation techniques) and is not discussed any further here.
  • the output Np of the modulator is given to the balancing function block. This block also receives the capacitor voltages Vc1 and Vc2 from all submodules and the arm current larm.
  • the Np submodules are selected to be turned on in positive state according to the following algorithm:
  • submodule k will be selected to be turned on in positive state. If the second highest capacitor voltage is Vc2J then the j th submodule will be selected. If the third highest capacitor voltage is Vc2_k which belongs to a submodule that is previously selected, then it is ignored.
  • the firing pulses are issued to the selected submodules by the firing system to turn on in the positive state. All other submodules are turned on in the negative state.
  • the voltage across a converter arm Varm step changes every time Np changes.
  • the change AVarm is almost equal to twice the submodule capacitor voltage i.e. AVarm » 2xVc_ref. This is because every time the number of submodules in positive state is increased by one the number of submodules in negative state is reduced by one, therefore the arm voltage is increased by the sum of the voltages of the outgoing negative submodule and incoming positive submodule.
  • each arm comprises one FB submodule and N-1 DCap submodules.
  • the FB submodule is turned on in the correct direction between DCap submodule switchings such that additional steps are added to the arm voltage.
  • Figures 13A and 13B show example arm voltage waveforms for a STATCOM to clarify the concept.
  • the STATCOM utilizes the converter arrangement of Figure 10.
  • the FB submodule is deactivated (permanently bypassed) while in Figure 13B the FB submodule is switched according to the above algorithm.
  • Various control logics can be used to switch the FB submodule at proper time and direction.
  • the following paragraph describes one possible controller circuit for switching FB at proper time and direction while maintaining its capacitor voltage near the target voltage Vc_ref.
  • Figure 12 shows a controller for the FB submodule.
  • the arm reference voltage Vref_arm is compared with the actual arm voltage Varm minus the voltage across the FB submodule, i.e. Varm - V_FB. If the difference is less than the first threshold level Th1 the FB is turned on in the negative direction; if the difference is more than the second threshold Th2 the FB is turned on in the positive direction, and if the difference is between Th1 and Th2 the FB is bypassed.
  • Th1 and Th2 are selected based on the type of modulator, for a nearest level modulator Th1 and Th2 are respectively equal to -1/3 and +1/3 of the arm voltage step size (without FB submodule).
  • a threshold levels are adjusted by adding ATh to maintain the FB capacitor voltage Vc_FB near the target value Vc_ref.
  • ATh is proportional to the difference between the actual and target values of FB capacitor voltage (Vc_ref - Vc_FB ). Depending on the direction of the arm current ATh can be positive or negative.
  • FIG 5 shows an embodiment of the DCap submodule which is a generalized version of the embodiment shown in Figure 6, but it utilizes any electronic switch that can be turned on and off (while carrying current) via an electronic command.
  • Examples of such devices are Injection- Enhanced Gate Transistor (IEGT), Bi-mode Insulated Gate Transistor (BIGT), Integrated Gate- Commutated Thyristor (IGCT) and Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET).
  • IEGT Injection- Enhanced Gate Transistor
  • BIGT Bi-mode Insulated Gate Transistor
  • IGCT Integrated Gate- Commutated Thyristor
  • MOSFET Metal-Oxide-Semiconductor Field-Effect Transistor
  • Figure 9 shows an embodiment of the novel converter arrangement with six arms where each arm utilizes N-1 DCap submodules and one FB submodule.
  • Another embodiment of the novel converter arrangement is similar to the embodiment shown in Figure 9, but utilizes N-k DCap submodules and k FB submodules where k ⁇ N.
  • the topology of the converter is similar to the embodiment shown in Figure 10, but each arm utilizes N-k DCap submodules and k FB submodules (k ⁇ N).
  • the present invention relates to a submodule comprising two capacitors and two power electronic switching devices that is capable of changing the polarity of its terminal voltage. Additionally, a method for switching the Dual Capacitor (DCap) submodules is provided that maintains all submodule capacitor voltages nearly equal within each VSC arm. A novel converter arrangement is also presented where each converter valve comprises a mixture of DCap and FB submodules.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)

Abstract

Un sous-module pour un convertisseur modulaire à source de tension multiniveau comprend des branches parallèles conductrices de courant entre des bornes de connexion externes du sous-module, et chaque branche comprend un pairage antiparallèle de composants électroniques conducteurs de courant unidirectionnel et d'un dispositif de stockage d'énergie qui fournit une tension sensiblement constante. Toutefois, les dispositifs de stockage d'énergie présentent une polarité opposée par rapport aux bornes de connexion de sous-module. Ainsi, le sous-module peut être actionné pour fournir un état de polarité directe fixe lorsqu'un courant est sélectivement conduit à travers l'une des branches, ou un état de polarité inverse fixe lorsqu'un courant est sélectivement conduit à travers l'autre branche. Des procédés associés sont également divulgués.
PCT/CA2022/050513 2021-04-05 2022-04-05 Sous-module de convertisseur à source de tension multiniveau comprenant des branches parallèles conductrices de courant comprenant de multiples dispositifs de stockage d'énergie, et procédés associés WO2022213185A1 (fr)

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013126660A2 (fr) * 2012-02-24 2013-08-29 Board Of Trustees Of Michigan State University Régulateur de flux d'énergie unifié sans transformateur

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013126660A2 (fr) * 2012-02-24 2013-08-29 Board Of Trustees Of Michigan State University Régulateur de flux d'énergie unifié sans transformateur

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
GHAT MAHENDRA B.; SHUKLA ANSHUMAN; MATHEW EBIN CHERIAN: "A new hybrid modular multilevel converter with increased output voltage levels", 2017 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE), IEEE, 1 October 2017 (2017-10-01), pages 1634 - 1641, XP033247002, DOI: 10.1109/ECCE.2017.8095988 *
ZENG RONG; XU LIE; YAO LIANGZHONG; WILLIAMS BARRY W.: "Design and Operation of a Hybrid Modular Multilevel Converter", IEEE TRANSACTIONS ON POWER ELECTRONICS, INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, USA, vol. 30, no. 3, 1 March 2015 (2015-03-01), USA , pages 1137 - 1146, XP011561445, ISSN: 0885-8993, DOI: 10.1109/TPEL.2014.2320822 *

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