A parallel voltage source type valve group control method and control device

Abstract

The application provides a parallel voltage source type valve group control method and control device. The parallel voltage source type valve group comprises at least two parallel voltage source type valve group units. When the parallel voltage source type valve group operates, the method comprises: selecting one voltage source type valve group unit as a first voltage source type valve group unit to control operation in a direct current voltage control mode; other voltage source type valve group units are second voltage source type valve group units to control operation in a power control mode or a direct current control mode; when the absolute value difference between the direct current voltage actual value of the second voltage source type valve group unit and the absolute value of the direct current voltage reference value exceeds a first voltage threshold value, or the absolute value difference between the direct current voltage reference value of the second voltage source type valve group unit and the absolute value of the direct current voltage actual value exceeds a second voltage threshold value, or a fault signal of a current source type valve group or a voltage source type valve group connected in series with the parallel voltage source type valve group is received, the second voltage source type valve group unit switches to operate in the direct current voltage control mode.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a parallel voltage source valve group control method and control device. Background Technology

[0002] In multi-terminal DC transmission systems or DC grids based on voltage source converters, the voltage source converters are interconnected via DC lines. The system selects one voltage source converter at one station to control the DC voltage, while voltage source converters at other stations control the power. When the voltage source converter controlling the DC voltage fails or is blocked, its DC voltage control function is transferred to the voltage source converters at other stations. Existing technology achieves this transfer of DC voltage control by adding voltage droop control to the voltage source converter controlling the power.

[0003] When voltage source converters are directly connected in parallel within the same converter station, voltage droop control suffers from slow regulation speed and cannot achieve rapid DC voltage control takeover. When a fault occurs in a multi-terminal DC transmission system or DC grid, causing an increase in DC current, the increased DC current preferentially flows into the voltage source converter controlling the DC voltage, leading to overvoltage. Because parallel voltage source converters cannot effectively and evenly distribute the increased DC current during a fault, larger voltage source converter capacities or additional current bleeders are required to avoid their own overvoltage, increasing project investment costs. Summary of the Invention

[0004] This application provides a parallel voltage source valve group control method. The parallel voltage source valve group includes at least two parallel voltage source valve group units, each voltage source valve group unit including a voltage source converter. When the parallel voltage source valve group is running, the method includes: selecting one of the voltage source valve group units as a first voltage source valve group unit, and controlling the first voltage source valve group unit to operate in a DC voltage control mode; selecting the other voltage source valve group units besides the first voltage source valve group unit as second voltage source valve group units, and controlling the second voltage source valve group units to operate in a power control mode. The second voltage source valve group unit can be switched to DC voltage control mode or DC current control mode. When the difference between the absolute value of the actual DC voltage of the second voltage source valve group unit and the absolute value of the DC voltage reference value exceeds the first voltage threshold of the second voltage source valve group unit, or the difference between the absolute value of the DC voltage reference value and the absolute value of the actual DC voltage of the second voltage source valve group unit exceeds the second voltage threshold of the second voltage source valve group unit, or / and a fault signal is received from a current source valve group or voltage source valve group connected in series with the parallel voltage source valve group, the second voltage source valve group unit switches to DC voltage control mode.

[0005] According to some embodiments, the power control mode includes a DC power control mode or an AC power control mode.

[0006] According to some embodiments, the DC voltage reference value is the same in all control modes.

[0007] According to some embodiments, the first voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the first voltage threshold of different voltage source valve group units in the second voltage source valve group unit can be different; the second voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the second voltage threshold of different voltage source valve group units in the second voltage source valve group unit can be different.

[0008] According to some embodiments, the fault signal of the current source valve group connected in series with the parallel voltage source valve group includes: a commutation failure signal, a protection trip signal, a lockout signal, a bypass pair activation signal, or a bypass switch activation signal of the current source valve group connected in series with the parallel voltage source valve group; the fault signal of the voltage source valve group connected in series with the parallel voltage source valve group includes: a protection trip signal, a lockout signal, or a bypass switch activation signal of the voltage source valve group connected in series with the parallel voltage source valve group.

[0009] According to some embodiments, the control method further includes: after the second voltage source valve group unit switches to operate in DC voltage control mode, it switches to operate in power control or DC current control mode after a first time threshold delay; or when it is detected that the difference between the absolute value of the actual DC voltage of the second voltage source valve group unit and the absolute value of the DC voltage reference value does not exceed a third voltage threshold or the difference between the absolute value of the DC voltage reference value of the second voltage source valve group unit and the absolute value of the DC voltage does not exceed a fourth voltage threshold of the second voltage source valve group unit, it switches to operate in power control or DC current control mode; wherein, the range of the first time threshold is... The third voltage threshold is between 2ms and 2s; the third voltage threshold range is 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the third voltage threshold of different voltage source valve group units in the second voltage source valve group unit can be different; the fourth voltage threshold range is 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the fourth voltage threshold of different voltage source valve group units in the second voltage source valve group unit can be different; or when the fault signal of the current source valve group or voltage source valve group connected in series with the parallel voltage source valve group disappears, it switches to power control or DC current control mode.

[0010] According to some embodiments, the control method further includes: after the second voltage source valve group unit switches to operate in DC voltage control mode, after delaying a first time threshold, it switches to operate in power control or DC current control mode, and after delaying a second time threshold, it is allowed to operate in DC voltage control mode again; the second time threshold is between 2ms and 2s.

[0011] According to some embodiments, the control method further includes: timing and / or counting the number of times the second voltage source valve group unit operates under DC voltage control; the timing is the calculation of the time of operation under DC voltage control; the counting is the number of times it operates under DC voltage control; when the timing exceeds a third time threshold and / or the counting exceeds a first count threshold, an alarm is issued, or the DC current flowing into the parallel voltage source valve group is reduced, or the parallel voltage source valve group is locked; the third time threshold is between 2ms and 2s; the first count threshold is between 1 and 10.

[0012] According to some embodiments, the control method further includes: when the difference between the absolute value of the actual DC voltage of the second voltage source valve group unit and the absolute value of the DC voltage reference value exceeds a first voltage threshold of the second voltage source valve group unit, the second voltage source valve group unit switches to DC voltage control mode and reduces the DC current flowing into the parallel voltage source valve group; or when the difference between the absolute value of the actual DC voltage of the second voltage source valve group unit and the absolute value of the DC voltage reference value exceeds a fifth voltage threshold of the second voltage source valve group unit, the second voltage source valve group unit switches to DC voltage control mode and reduces the DC current flowing into the parallel voltage source valve group; the fifth voltage threshold is in the range of 0.1 to 1.0 times the rated DC voltage of the second voltage source valve group unit, and the fifth voltage threshold is greater than the first voltage threshold.

[0013] According to some embodiments, reducing the DC current flowing into the parallel voltage source valve group is achieved by controlling the power source of the parallel voltage source valve group to reduce the power output. The power source includes other voltage source valve groups or current source valve groups that supply power to the parallel voltage source valve group.

[0014] According to some embodiments, when the second voltage source valve group unit switches to operate in DC voltage control mode, circulation control between parallel voltage source valve group units is added.

[0015] According to some embodiments, the DC voltage control mode employs a proportional-integral (PI) regulator, and the circulating current control is based on the DC voltage error of the PI regulator plus a DC current error of k times. Specifically, when the parallel voltage source valve group units have the same capacity, the DC current error is the difference between the average DC current of the parallel voltage source valve group and the DC current of the second voltage source valve group unit; when the parallel voltage source valve group units have different capacities, the DC current error is the difference between the capacity of the second voltage source valve group unit divided by the total capacity of the parallel voltage source valve group, multiplied by the difference between the total DC current of the parallel voltage source valve group and the DC current of the second voltage source valve group unit.

[0016] According to some embodiments, the value range of k is from 0.001 to 100, where k is any value within the range or k takes different values ​​within the range depending on the segmented intervals of different DC currents.

[0017] According to some embodiments, the voltage source converter is a converter composed of fully controllable power semiconductor devices that can be turned off, including at least one of a two-level converter, a diode-clamped multilevel converter, a modular multilevel converter (MMC), a hybrid multilevel converter (HMC), a cascaded two-level converter (CSL), and a stacked two-level converter (CTL).

[0018] This application also provides a parallel voltage source valve group control device, applying the parallel voltage source valve group control method described above. The device includes a detection unit and a control unit. The detection unit detects the DC voltage of the second voltage source valve group unit. The control unit selects one of the voltage source valve group units as the first voltage source valve group unit and controls the first voltage source valve group unit to operate in DC voltage control mode. The other voltage source valve group units besides the first voltage source valve group unit are used as the second voltage source valve group units, and the second voltage source valve group units are controlled to operate in power control mode. The second voltage source valve group unit switches to DC voltage control mode when the absolute difference between the actual DC voltage value and the absolute value of the DC voltage reference value of the second voltage source valve group unit exceeds the first voltage threshold of the second voltage source valve group unit, or the absolute difference between the absolute value of the DC voltage reference value and the absolute value of the DC voltage of the second voltage source valve group unit exceeds the second voltage threshold of the second voltage source valve group unit, or / and a fault signal is received from a current source valve group or voltage source valve group connected in series with the parallel voltage source valve group.

[0019] The technical solution provided in this application detects whether the difference between the actual value and the reference value of the DC voltage of the voltage source valve group unit operating in power control mode or DC current control mode exceeds a first voltage threshold. When the first voltage threshold is exceeded, the voltage source valve group unit operating in power control mode or DC current control mode switches to DC voltage control mode. Compared with the previous automatic increase in power output to assist in voltage control, the overvoltage level of the parallel voltage source valve group is significantly reduced during transient faults. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a parallel voltage source type valve group according to an embodiment of this application.

[0022] Figure 2A This is a schematic diagram of a voltage source type valve group topology according to an embodiment of this application.

[0023] Figure 2B This is a schematic diagram of another voltage source type valve group topology according to an embodiment of this application.

[0024] Figure 2C This is a schematic diagram of another voltage source type valve group topology according to an embodiment of this application.

[0025] Figure 2D This is a schematic diagram of another voltage source type valve group topology according to an embodiment of this application.

[0026] Figure 3 This is a schematic flowchart of a parallel voltage source valve group control method according to an embodiment of this application.

[0027] Figure 4 This is a schematic flowchart of another parallel voltage source valve group control method according to an embodiment of this application.

[0028] Figure 5 This is a schematic diagram of a DC pole of a high-voltage direct current transmission system according to an embodiment of this application.

[0029] Figure 6 This is a schematic flowchart of another parallel voltage source valve group control method according to an embodiment of this application.

[0030] Figure 7 This is a schematic flowchart of another parallel voltage source valve group control method according to an embodiment of this application.

[0031] Figure 8 This is a block diagram illustrating the voltage control principle of a voltage source valve group operating under voltage control, according to an embodiment of this application.

[0032] Figure 9 This is a block diagram illustrating the addition of circulating current control after a voltage source valve group operating under power control or DC current control is switched to DC voltage control according to an embodiment of this application.

[0033] Figure 10 This is a functional block diagram of a parallel voltage source type valve group control device provided in this application. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0036] Figure 1 This is a parallel voltage source type valve group according to an embodiment of this application.

[0037] The parallel voltage source type valve group includes three voltage source converters connected in parallel. The positive terminal X3 of voltage source type valve group unit 1, the positive terminal X5 of voltage source type valve group unit 2, and the positive terminal X7 of voltage source type valve group unit 3 are connected to the positive bus terminal X1, and the negative terminal X4 of voltage source type valve group unit 1, the negative terminal X6 of voltage source type valve group unit 2, and the negative terminal X8 of voltage source type valve group unit 3 are connected to the negative bus terminal X2.

[0038] According to some embodiments, the voltage source type valve group unit includes a voltage source converter.

[0039] According to some embodiments, the voltage source valve group unit includes a voltage source converter and a current-limiting reactor connected in series.

[0040] According to some embodiments, the voltage source type valve group unit includes a voltage source converter and a disconnecting switch connected in series. The switch includes, but is not limited to, at least one of a power electronic switch, a mechanical switch, or a mechanical disconnector.

[0041] ud1 is the DC voltage of voltage source type valve group unit 1, idc1p is the positive bus current of voltage source type valve group unit 1, and idc1n is the negative bus current of voltage source type valve group unit 1. ud2 is the DC voltage of voltage source type valve group unit 2, idc2p is the positive bus current of voltage source type valve group unit 2, and idc2n is the negative bus current of voltage source type valve group unit 2. ud3 is the DC voltage of voltage source type valve group unit 3, idc3p is the positive bus current of voltage source type valve group unit 3, and idc3n is the negative bus current of voltage source type valve group unit 3.

[0042] Figure 2A This is a schematic diagram of a voltage source type valve group topology according to an embodiment of this application.

[0043] In this embodiment, the voltage source type valve group unit includes a voltage source converter 4 and a negative bus disconnect switch 5 connected in series.

[0044] The voltage source converter 4 includes, but is not limited to, at least one of a two-level converter, a diode-clamped multilevel converter, a modular multilevel converter (MMC), a hybrid multilevel converter (HMC), a two-level cascaded converter (CSL), and a stacked two-level converter (CTL), wherein the converter includes a fully controllable power semiconductor device that can be turned off.

[0045] Figure 2B This is a schematic diagram of another voltage source type valve group topology according to an embodiment of this application.

[0046] In this embodiment, the voltage source type valve group unit includes a voltage source converter 4, a positive bus current-limiting reactor 6, and a negative bus disconnecting switch 5 connected in series.

[0047] The voltage source converter 4 includes, but is not limited to, at least one of a two-level converter, a diode-clamped multilevel converter, a modular multilevel converter (MMC), a hybrid multilevel converter (HMC), a two-level cascaded converter (CSL), and a stacked two-level converter (CTL), wherein the converter includes a fully controllable power semiconductor device that can be turned off.

[0048] Figure 2C This is a schematic diagram of another voltage source type valve group topology according to an embodiment of this application.

[0049] In this embodiment, the voltage source type valve group unit includes a voltage source converter 4, a positive bus current-limiting reactor 6, a negative bus current-limiting reactor 8, a positive bus disconnect switch 7, and a negative bus disconnect switch 5 connected in series.

[0050] The voltage source converter 4 includes, but is not limited to, at least one of a two-level converter, a diode-clamped multilevel converter, a modular multilevel converter (MMC), a hybrid multilevel converter (HMC), a two-level cascaded converter (CSL), and a stacked two-level converter (CTL), wherein the converter includes a fully controllable power semiconductor device that can be turned off.

[0051] Figure 2D This is a schematic diagram of another voltage source type valve group topology according to an embodiment of this application.

[0052] The voltage source type valve group unit includes a voltage source converter 4, a positive bus current limiting reactor 6, a negative bus current limiting reactor 8, a positive bus disconnect switch 7, a negative bus disconnect switch 5, a positive bus disconnect switch 9, a positive bus disconnect switch 10, a negative bus disconnect switch 11, and a negative bus disconnect switch 12 connected in series.

[0053] The voltage source converter 4 includes, but is not limited to, at least one of a two-level converter, a diode-clamped multilevel converter, a modular multilevel converter (MMC), a hybrid multilevel converter (HMC), a two-level cascaded converter (CSL), and a stacked two-level converter (CTL), wherein the converter includes a fully controllable power semiconductor device that can be turned off.

[0054] Figure 3 This is a schematic flowchart of a parallel voltage source valve group control method according to an embodiment of this application.

[0055] In S110, one of the voltage source valve group units is selected as the first voltage source valve group unit, and the first voltage source valve group unit is controlled to operate in DC voltage control mode.

[0056] According to some embodiments, such as Figure 1 The voltage source type valve group unit 1 shown operates in DC voltage control mode.

[0057] In S120, other voltage source valve group units besides the first voltage source valve group unit are used as second voltage source valve group units, and the second voltage source valve group unit is controlled to operate in power control mode or DC current control mode.

[0058] In this embodiment, voltage source valve group unit 2 and voltage source valve group unit 3 serve as the second voltage source valve group unit and operate in power control mode. The power control mode includes DC power control mode or AC power control mode.

[0059] In S130, when the absolute value of the difference between the actual DC voltage value and the DC voltage reference value of the second voltage source valve group unit exceeds the first voltage threshold, the second voltage source valve group unit switches to operation in DC voltage control mode.

[0060] The DC voltage reference value is the same in all control modes. The first voltage threshold value of the second voltage source valve unit is in the range of 0.01 to 0.3 times the rated DC voltage of the second voltage source valve unit.

[0061] by Figure 1 For example, the difference between the absolute value of the actual DC voltage ud2 of voltage source valve unit 2 and the absolute value of the reference value udref is checked to see if it exceeds the first voltage threshold Δud1 of voltage source valve unit 2. Δud1 is between 0.01 and 0.3 times the rated DC voltage. The difference between the absolute value of the actual DC voltage ud3 of voltage source valve unit 3 and the absolute value of the reference value udref is checked to see if it exceeds the first voltage threshold Δud2 of voltage source valve unit 3. Δud2 is between 0.01 and 0.3 times the rated DC voltage. The value of the first voltage threshold is related to the capacity of the voltage source converter; when the capacity is the same, the first voltage threshold is the same; the larger the capacity, the lower the first voltage threshold.

[0062] When the absolute value of the actual DC voltage differs from the absolute value of the reference voltage by no more than the first voltage threshold, the voltage source valve group operating in power control mode or DC current control mode will continue to operate in power control mode or DC current control mode. When the absolute value of the actual DC voltage differs from the absolute value of the reference voltage by more than the first voltage threshold, the voltage source valve group unit operating in power control mode or DC current control mode will switch to DC voltage control mode.

[0063] by Figure 1 For example, when |ud2|-|udref|≤Δud1, the voltage source valve group unit 2 still operates in power control mode; when |ud3-udref|≤Δud2, the voltage source valve group unit 3 still operates in power control mode.

[0064] When |ud2|-|udref|>Δud1, the voltage source valve unit 2 switches to DC voltage control mode; when |ud3|-|udref|>Δud2, the voltage source valve unit 3 switches to DC voltage control mode.

[0065] According to some embodiments, after the second voltage source valve group unit switches to operation in DC voltage control mode, optionally, the DC current flowing into the parallel voltage source valve group is reduced. Reducing the DC current flowing into the parallel voltage source valve group is achieved by controlling the power source of the parallel voltage source valve group to reduce its power output. The power source includes other voltage source valve groups or current source valve groups that supply power to the parallel voltage source valve group.

[0066] When a voltage source valve unit operating in power control mode or DC current control mode switches to DC voltage control mode, and the difference between the absolute value of the actual DC voltage and the absolute value of the reference voltage does not exceed the first voltage threshold, the voltage source valve unit operating in DC voltage control mode switches to power control mode or DC current control mode.

[0067] by Figure 1 For example, when |ud2|-|udref|≤Δud1, the voltage source valve group unit 2 switches to power control mode or DC current control mode; when |ud3|-|udref|≤Δud2, the voltage source valve group unit 3 switches to power control mode or DC current control mode.

[0068] Figure 4 This is a schematic flowchart of another parallel voltage source valve group control method according to an embodiment of this application.

[0069] According to some embodiments, and Figure 3 The difference in the embodiment is that hysteresis comparison is used in S230.

[0070] In S230, when the absolute value of the difference between the actual DC voltage value and the DC voltage reference value of the second voltage source valve group unit exceeds the first voltage threshold, the second voltage source valve group unit switches to operation in DC voltage control mode.

[0071] The DC voltage reference value is the same in all control modes. The first voltage threshold value of the second voltage source valve unit is in the range of 0.01 to 0.3 times the rated DC voltage of the second voltage source valve unit.

[0072] by Figure 1 For example, the difference between the absolute value of the actual DC voltage ud2 of voltage source valve unit 2 and the absolute value of the reference value udref is detected to see if it exceeds the first voltage threshold Δud1 of voltage source valve unit 2. The difference between the absolute value of the actual DC voltage ud3 of voltage source valve unit 3 and the absolute value of the reference value udref is detected to see if it exceeds the first voltage threshold Δud2 of voltage source valve unit 3. Δud2 is set to 0.01 to 0.3 times the rated DC voltage. The value of the first voltage threshold is related to the capacity of the voltage source converter; for the same capacity, the first voltage threshold is the same; the larger the capacity, the lower the first voltage threshold.

[0073] When the absolute difference between the actual DC voltage value and the absolute value of the reference voltage does not exceed the first voltage threshold, the voltage source valve group operating in power control mode or DC current control mode will continue to operate in power control mode or DC current control mode. When the first voltage threshold is exceeded, the voltage source valve group unit operating in power control mode or DC current control mode will switch to DC voltage control mode.

[0074] by Figure 1 For example, when |ud2|-|udref|≤Δud1, the voltage source valve group unit 2 still operates in power control mode; when |ud3-udref|≤Δud2, the voltage source valve group unit 3 still operates in power control mode.

[0075] When |ud2|-|udref|>Δud1, the voltage source valve unit 2 switches to DC voltage control mode; when |ud3|-|udref|>Δud2, the voltage source valve unit 3 switches to DC voltage control mode.

[0076] According to some embodiments, after the second voltage source valve group unit switches to operation in DC voltage control mode, optionally, the DC current flowing into the parallel voltage source valve group is reduced, or further, if it is determined that the difference between the absolute value of the actual DC voltage of the second voltage source valve group unit and the absolute value of the DC voltage reference value exceeds the fifth voltage threshold of the second voltage source valve group unit, the DC current flowing into the parallel voltage source valve group is reduced. Reducing the DC current flowing into the parallel voltage source valve group is achieved by controlling the power source of the parallel voltage source valve group to reduce its power output. The power source includes other voltage source valve groups or current source valve groups that supply power to the parallel voltage source valve group.

[0077] The fifth voltage threshold ranges from 0.1 to 1.0 times the rated DC voltage of the second voltage source valve unit, and the fifth voltage threshold is greater than the first voltage threshold.

[0078] When a voltage source valve unit operating in power control mode or DC current control mode switches to DC voltage control mode, and the difference between the absolute value of the actual DC voltage and the absolute value of the reference voltage does not exceed the third voltage threshold, the voltage source valve unit operating in DC voltage control mode switches to power control mode or DC current control mode.

[0079] When |ud2|-|udref|≤Δud3, voltage source valve unit 2 switches to power control mode or DC current control mode; when |ud3|-|udref|≤Δud4, voltage source valve unit 3 switches to power control mode or DC current control mode. Where Δud3<Δud1, Δud4<Δud2.

[0080] Figure 5 This is a schematic diagram of a DC pole of a high-voltage direct current transmission system according to an embodiment of this application.

[0081] The rectifier station 37 of the high-voltage direct current transmission system adopts a series topology of current source valve groups 39 and 40, while the inverter station 38 adopts a series topology of current source valve group 41 and parallel voltage source valve group 42. The rectifier station 37 and the inverter station 38 are connected by DC line 15.

[0082] The current source valve group of rectifier station 37 includes a grid-commutated converter 21, a bypass switch 23, a bypass disconnector 24, a disconnector 25, and a disconnector 26. The grid-commutated converter 21 is connected to the secondary winding of the converter transformer 22, and the primary winding of the converter transformer 22 is connected to the AC bus 16 via AC switch 15. An AC filter 36 is connected to the AC bus 16 via AC switch 35. The pole buses of rectifier station 37 are equipped with smoothing reactors 27, and the neutral bus is equipped with a neutral bus switch 29, which is connected to the grounding line 30. A DC filter 43 is connected between the pole buses and the neutral bus. It should be noted that the AC grid is three-phase; however, in… Figure 5 For clarity, only one phase is shown.

[0083] The current-source valve group of inverter station 38 includes a grid-commutated converter 21, a bypass switch 23, a bypass disconnector 24, a disconnector 25, and a disconnector 26. The grid-commutated converter 21 is connected to the secondary winding of the converter transformer 22. The primary winding of the converter transformer 22 is connected to the AC bus 16 via AC switch 15. The AC filter 34 is connected to the AC bus 16 via AC switch 33. The parallel voltage-source valve group of inverter station 38 includes three parallel voltage-source valve group units 1, 2, and 3, a bypass switch 17, a bypass disconnector 18, a disconnector 19, and a disconnector 20. Each voltage-source valve group unit includes a voltage-source converter 4, a positive bus disconnector 7, and a negative bus disconnector 5. The three voltage-source converters are connected to the positive bus 31 via the positive bus disconnector 7 and to the negative bus 32 via the negative bus disconnector 5. The voltage source converter includes a bridge arm reactor 14, which is connected to the secondary winding of the converter transformer 13. The primary winding of the converter transformer 13 is connected to the AC bus 16 via an AC switch 15. The pole buses of the inverter station 38 are equipped with smoothing reactors 27, and the pole neutral bus is equipped with a pole neutral bus switch 29, which is connected to the grounding line 30. A DC filter 28 is connected between the pole buses and the pole neutral point.

[0084] During normal operation, the current source valve group of rectifier station 37 operates in DC current control mode, the current source valve group of inverter station 38 operates in DC voltage control mode, and one of the parallel voltage source valve groups of inverter station operates in DC voltage control mode, while the rest operate in power control mode. For example, if the first voltage source valve group unit 1 is in DC voltage control mode, the second voltage source valve group unit 2 and the voltage source valve group unit 3 are in power control mode.

[0085] When a three-phase short circuit occurs on the AC bus 16 connected to voltage source valve group unit 1, power cannot be delivered normally, resulting in the actual DC voltage value being higher than the reference value. Voltage source valve group units 2 and 3 detect whether the absolute value of the difference between the actual DC voltage value and the reference value exceeds a first voltage threshold. When the absolute value exceeds the first voltage threshold, voltage source valve group units 2 and 3 switch to DC voltage control mode, increasing power output to suppress the rise in DC voltage, thereby suppressing overvoltage in the parallel voltage source valve group. After a delay of the first time threshold (such as inter-station communication delay), rectifier station 37 reduces the transmission power, and voltage source valve group units 2 and 3 switch to power control mode.

[0086] Figure 6 This is a schematic flowchart of another parallel voltage source type valve group control method according to an embodiment of this application, applicable to, for example... Figure 5 The topology shown.

[0087] According to some embodiments, and Figure 3 The difference in the embodiment lies in S330.

[0088] In S330, when the second voltage source valve group unit receives a fault signal from a current source valve group or a voltage source valve group connected in series with the parallel voltage source valve group, the second voltage source valve group unit switches to operation in DC voltage control mode.

[0089] like Figure 5 As shown, when voltage source valve group unit 2 receives a fault signal from current source valve group 41 connected in series with the parallel voltage source valve group, voltage source valve group unit 2 switches to DC voltage control mode; otherwise, it continues to operate in power control mode. When voltage source valve group unit 3 receives a fault signal from current source valve group 41, voltage source valve group unit 3 switches to DC voltage control mode; otherwise, it continues to operate in power control mode.

[0090] Fault signals for current source valve groups include, but are not limited to, commutation failure signals, protection trip signals, lockout signals, bypass pair activation signals, or bypass switch activation signals.

[0091] Fault signals for voltage source valve groups include, but are not limited to, voltage source valve group protection trip signals, lockout signals, or bypass switch closing signals.

[0092] Figure 7 This is a schematic flowchart of another parallel voltage source type valve group control method according to an embodiment of this application. Figure 3 or Figure 4 or Figure 6 Based on the previous implementation, delay logic was added.

[0093] In S430, when the absolute value of the difference between the actual DC voltage value and the DC voltage reference value of the second voltage source valve group unit exceeds the first voltage threshold and the flag bit is 0, the second voltage source valve group unit switches to operate in DC voltage control mode.

[0094] The DC voltage reference value is the same in all control modes. The first voltage threshold value of the second voltage source valve unit is in the range of 0.01 to 0.3 times the rated DC voltage of the second voltage source valve unit.

[0095] The test checks whether the difference between the absolute value of the actual DC voltage ud2 of voltage source valve unit 2 and the absolute value of the reference value udref exceeds the first voltage threshold Δud1 of voltage source valve unit 2. The test also checks whether the difference between the absolute value of the actual DC voltage ud3 of voltage source valve unit 3 and the absolute value of the reference value udref exceeds the first voltage threshold Δud2 of voltage source valve unit 3. Δud2 is set to 0.01 to 0.3 times the rated DC voltage. The value of the first voltage threshold is related to the capacity of the voltage source converter; for the same capacity, the first voltage threshold is the same; the larger the capacity, the lower the first voltage threshold.

[0096] When the absolute difference between the actual DC voltage value and the absolute value of the reference voltage does not exceed the first voltage threshold or the flag bit is 1, the voltage source valve group operating in power control mode or DC current control mode will continue to operate in power control mode or DC current control mode. When the first voltage threshold is exceeded and the flag bit is 0, the voltage source valve group unit operating in power control mode or DC current control mode will switch to DC voltage control mode.

[0097] When |ud2|-|udref|≤Δud1 or flag1=1, voltage source valve unit 2 still operates in power control mode; when |ud3-udref|≤Δud2 or flag2=1, voltage source valve unit 3 still operates in power control mode.

[0098] When |ud2|-|udref|>Δud1 and flag1=0, voltage source valve unit 2 switches to DC voltage control mode; when |ud3|-|udref|>Δud2 and flag2=0, voltage source valve unit 3 switches to DC voltage control mode.

[0099] According to some embodiments, after the second voltage source valve group unit switches to operation in DC voltage control mode, optionally, the DC current flowing into the parallel voltage source valve group is reduced. Reducing the DC current flowing into the parallel voltage source valve group is achieved by controlling the power source of the parallel voltage source valve group to reduce its power output. The power source includes other voltage source valve groups or current source valve groups that supply power to the parallel voltage source valve group.

[0100] After a voltage source valve unit operating in power control mode or DC current control mode switches to DC voltage control mode, if it exceeds the first time threshold in DC voltage control mode, the flag bit is set to 1, and it restarts in power control mode or DC current control mode. After a second time threshold is delayed, it is allowed to operate in DC voltage control mode again.

[0101] The first time threshold is between 2ms and 2s, and the second time threshold is between 2ms and 2s.

[0102] flag1 is the flag bit for voltage source valve group unit 2, and flag2 is the flag bit for voltage source valve group unit 3. Δt1 is the first time threshold for voltage source valve group unit 2, Δt2 is the first time threshold for voltage source valve group unit 3, Δt3 is the second time threshold for voltage source valve group unit 2, and Δt4 is the second time threshold for voltage source valve group unit 3. The values ​​of Δt1 and Δt2 need to be determined based on the response time of the DC transmission system, the fault duration, and the capacity of the voltage source valve group. The response time mainly includes inter-station communication delay and control device calculation delay, typically ranging from 2ms to 2s. The fault duration is mainly the time from the occurrence of the fault to its disappearance, typically ranging from 10ms to 2s. The larger the capacity of the voltage source valve group, the larger the first time threshold.

[0103] The second voltage source valve group unit operates under DC voltage control for timing and / or counting; timing refers to the time spent operating under DC voltage control; counting refers to the number of times the unit operates under DC voltage control; when the timing exceeds a third time threshold and / or the counting exceeds a first count threshold, an alarm is issued, or the DC current flowing into the parallel voltage source valve group is reduced, or the parallel voltage source valve group is locked; the third time threshold ranges from 2ms to 2s; the first count threshold ranges from 1 to 10.

[0104] exist Figures 3 to 7In this embodiment, when the absolute value of the DC voltage reference value of the second voltage source valve group unit differs from the absolute value of the actual DC voltage value, exceeding the second voltage threshold of the second voltage source valve group unit, it can also be used as a condition for operating under DC voltage control. This is applicable to applications where parallel voltage source valve groups are used as rectifier-side power output. The second voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit.

[0105] Figure 8 This is a block diagram illustrating the voltage control principle of a voltage source valve group operating under voltage control, according to an embodiment of this application.

[0106] The deviation between the actual DC voltage value and the reference DC voltage value of the second voltage source valve unit is adjusted by a PI controller to obtain the reference value of the active current.

[0107] Figure 9 This is a block diagram illustrating the addition of circulating current control after a second voltage source valve group unit, which operates in power control mode or DC current control mode, is switched to DC voltage control mode according to an embodiment of this application.

[0108] like Figure 9 As shown, in Figure 8 Based on the control, after the second voltage source valve group unit, which is operating in power control mode or DC current control mode, switches to operating in DC voltage control mode, circulating current control is added.

[0109] The DC voltage control mode uses a proportional-integral regulator, and the circulating current control is based on the DC voltage error of the proportional-integral regulator plus a DC current error of k times.

[0110] When the parallel voltage source valve group units have the same capacity, the DC current error is the difference between the average DC current of the parallel voltage source valve group units and the DC current of the second voltage source valve group unit.

[0111] When the capacity of the parallel voltage source valve group units is different, the DC current error is the difference between the total DC current of the parallel voltage source valve group and the DC current of the second voltage source valve group, multiplied by the capacity of the second voltage source valve group divided by the total capacity of the parallel voltage source valve groups.

[0112] by Figure 1 Taking voltage source valve group unit 2 as an example of three voltage source valve group units operating in parallel, assuming that the three voltage source valve group units operating in parallel have the same capacity, in Figure 8 The voltage control block diagram adds k times the DC current error iderr to the DC voltage error of the proportional-integral regulator, iderr=(idc1p+idc2p+idc3p) / 3-idc2p, where the positive bus current can also be replaced by the negative bus current.

[0113] The value of k ranges from 0.001 to 100, where k is any value within the range or k takes different values ​​within the range depending on the segmented intervals of different DC currents.

[0114] Figure 10 This is a functional block diagram of a parallel voltage source type valve group control device provided in this application. The parallel voltage source type valve group control device 43 includes a detection unit 44 and a control unit 45.

[0115] The detection unit 44 is used to detect the DC voltage of the second voltage source type valve group unit.

[0116] The control unit 45 is used to select one of the voltage source valve group units as the first voltage source valve group unit and control the first voltage source valve group unit to operate in DC voltage control mode; other voltage source valve group units besides the first voltage source valve group unit are used as the second voltage source valve group units and control the second voltage source valve group units to operate in power control mode or DC current control mode; when the absolute value of the actual DC voltage of the second voltage source valve group unit is greater than the absolute value of the reference DC voltage value, or the absolute value of the reference DC voltage of the second voltage source valve group unit is greater than the absolute value of the actual DC voltage value, or / and a fault signal is received from a current source valve group or voltage source valve group connected in series with the parallel voltage source valve group, the second voltage source valve group unit switches to operate in DC voltage control mode.

[0117] The technical solution provided in this application detects whether the difference between the actual value and the reference value of the DC voltage of the voltage source valve group unit operating in power control mode or DC current control mode exceeds a first voltage threshold. When the first voltage threshold is exceeded, the voltage source valve group unit operating in power control mode or DC current control mode switches to DC voltage control mode. Compared with the previous power, the power output is automatically increased to assist in controlling the voltage. In the event of a transient fault, the overvoltage level of the parallel voltage source valve group is significantly reduced.

[0118] The above embodiments are only for illustrating the technical concept of this application and should not be used to limit the scope of protection of this application. Any modifications made to the technical solution based on the technical concept proposed in this application shall fall within the scope of protection of this application.

Claims

1. A method for controlling a parallel voltage source valve group, wherein the parallel voltage source valve group comprises at least two parallel voltage source valve group units, each voltage source valve group unit comprising a voltage source converter, and the method comprises: Select one of the voltage source valve group units as the first voltage source valve group unit, and control the first voltage source valve group unit to operate in DC voltage control mode; Other voltage source valve group units besides the first voltage source valve group unit serve as the second voltage source valve group unit, controlling the second voltage source valve group unit to operate in power control mode or DC current control mode; When the absolute difference between the actual DC voltage of the second voltage source valve group unit and the absolute difference between the reference DC voltage value exceeds the first voltage threshold of the second voltage source valve group unit, or when the absolute difference between the reference DC voltage of the second voltage source valve group unit and the actual DC voltage value exceeds the second voltage threshold of the second voltage source valve group unit, or / and when a fault signal is received from a current source valve group or voltage source valve group connected in series with the parallel voltage source valve group, the second voltage source valve group unit switches to operation in DC voltage control mode. The first voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the first voltage threshold can be different for different voltage source valve group units within the second voltage source valve group unit. The second voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the second voltage threshold can be different for different voltage source valve group units within the second voltage source valve group unit.

2. The control method as described in claim 1, wherein, The power control mode includes either DC power control mode or AC power control mode.

3. The control method as described in claim 1, wherein, The DC voltage reference value is the same in all control modes.

4. The control method as described in claim 1, wherein, The fault signals of the current source valve group connected in series with the parallel voltage source valve group include: The commutation failure signal, protection trip signal, lockout signal, bypass pair activation signal, or bypass switch activation signal of the current source valve group connected in series with the parallel voltage source valve group; The fault signals of the voltage source valve group connected in series with the parallel voltage source valve group include: The voltage source valve group protection trip signal, lockout signal or bypass switch signal connected in series with the parallel voltage source valve group.

5. The control method according to claim 1, further comprising: After the second voltage source valve unit switches to DC voltage control mode, After a delay and a first time threshold, the system switches to either power control or DC current control mode. or When the absolute value of the actual DC voltage of the second voltage source valve unit is detected to be less than the absolute value of the DC voltage reference value, and the difference between the absolute value of the DC voltage reference value and the absolute value of the DC voltage of the second voltage source valve unit is detected to be less than the third voltage threshold, or the difference between the absolute value of the DC voltage reference value and the absolute value of the DC voltage of the second voltage source valve unit is detected to be less than the fourth voltage threshold of the second voltage source valve unit, the system switches to power control or DC current control mode; wherein, The first time threshold ranges from 2ms to 2s; the third voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the third voltage threshold can be different for different voltage source valve group units within the second voltage source valve group unit; the fourth voltage threshold ranges from 0.01 to 0.3 times the rated DC voltage of the second voltage source valve group unit, and the fourth voltage threshold can be different for different voltage source valve group units within the second voltage source valve group unit; or When the fault signal of the current source valve group or voltage source valve group connected in series with the parallel voltage source valve group disappears, the system switches to power control or DC current control mode.

6. The control method according to claim 5 further includes: After the second voltage source valve unit switches to DC voltage control mode, it switches to power control or DC current control mode after a first time threshold delay, and then allows it to switch back to DC voltage control mode after a second time threshold delay. The second time threshold ranges from 2ms to 2s.

7. The control method according to claim 1 or 5, further comprising: The second voltage source valve group unit operates under DC voltage control for a timed and / or counted occurrences; the timed operation is the calculation of the time spent under DC voltage control. The count refers to the number of times the operation is performed under DC voltage control. When the timing exceeds the third time threshold or / and the count exceeds the first count threshold, an alarm is issued, or the DC current flowing into the parallel voltage source valve group is reduced, or the parallel voltage source valve group is locked. The third time threshold ranges from 2ms to 2s; the first number threshold ranges from 1 to 10.

8. The control method according to claim 1, further comprising: When the absolute value of the actual DC voltage of the second voltage source valve group unit exceeds the absolute value of the DC voltage reference value, the second voltage source valve group unit switches to DC voltage control mode and reduces the DC current flowing into the parallel voltage source valve group. Alternatively, when the absolute value of the actual DC voltage of the second voltage source valve group unit differs from the absolute value of the DC voltage reference value by more than the fifth voltage threshold of the second voltage source valve group unit, the second voltage source valve group unit switches to DC voltage control mode and reduces the DC current flowing into the parallel voltage source valve group. The fifth voltage threshold ranges from 0.1 to 1.0 times the rated DC voltage of the second voltage source valve group unit, and the fifth voltage threshold is greater than the first voltage threshold.

9. The control method according to claim 8, wherein, Reducing the DC current flowing into the parallel voltage source valve group is achieved by controlling the power source of the parallel voltage source valve group to reduce the power output. The power source includes other voltage source valve groups or current source valve groups that supply power to the parallel voltage source valve group.

10. The control method according to claim 1, wherein, When the second voltage source valve group unit switches to DC voltage control mode, the circulating current control between the parallel voltage source valve group units is added.

11. The control method according to claim 10, wherein, The DC voltage control mode employs a proportional-integral (PI) regulator, and the circulating current control adds k times the DC current error to the DC voltage error of the PI regulator. When the parallel voltage source valve group units have the same capacity, the DC current error is the difference between the average DC current of the parallel voltage source valve group and the DC current of the second voltage source valve group unit. When the capacities of the parallel voltage source valve group units are different, the DC current error is the difference between the total DC current of the parallel voltage source valve group and the DC current of the second voltage source valve group unit, calculated by dividing the capacity of the second voltage source valve group unit by the total capacity of the parallel voltage source valve group.

12. The control method according to claim 11, wherein, The value range of k is from 0.001 to 100, where k is any value within the range or k takes different values ​​within the range depending on the segmented intervals of different DC currents.

13. The control method according to claim 1, wherein, The voltage source converter is a converter composed of fully controllable power semiconductor devices that can be turned off, including at least one of two-level converters, diode-clamped multilevel converters, modular multilevel converters (MMC), hybrid multilevel converters (HMC), cascaded two-level converters (CSL), and stacked two-level converters (CTL).

14. A parallel voltage source valve group control device, employing the parallel voltage source valve group control method as described in any one of claims 1 to 13, the device comprising: The detection unit detects the DC voltage of the second voltage source type valve group unit; The control unit selects one of the voltage source valve group units as the first voltage source valve group unit and controls the first voltage source valve group unit to operate in DC voltage control mode; other voltage source valve group units besides the first voltage source valve group unit are selected as the second voltage source valve group units and controlled to operate in power control mode or DC current control mode; when the absolute value of the actual DC voltage of the second voltage source valve group unit is greater than the absolute value of the reference DC voltage, the difference between the actual DC voltage and the reference DC voltage of the second voltage source valve group unit exceeds the first voltage threshold of the second voltage source valve group unit, or the absolute value of the reference DC voltage and the actual DC voltage exceeds the second voltage threshold of the second voltage source valve group unit, or / and a fault signal is received from a current source valve group or voltage source valve group connected in series with the parallel voltage source valve group, the second voltage source valve group unit switches to operate in DC voltage control mode.

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