Current source type hybrid direct current transmission system based on injection type power grid commutation converter

Abstract

The invention provides a current source type hybrid direct-current power transmission system based on an injection type power grid commutation converter, and relates to the field of high-voltage direct-current power transmission, and the system comprises a rectification station which at least comprises a thyristor-based power grid commutation converter and is used for converting alternating current into direct current; the inverter station at least comprises an injection type power grid commutation converter and is used for converting the direct current output by the rectifier station into alternating current; and the control module is used for controlling the operation of the rectifier station and the inverter station based on the trigger time sequence constraint, and has the advantages of completely inhibiting the commutation failure and reducing the loss.

Description

Technical Field

[0001] The present invention relates to the field of high voltage direct current (HVDC) power transmission, and in particular to a current source hybrid HVDC power transmission system based on an injection-type grid-commutated converter. Background Art

[0002] High Voltage Direct Current Transmission (HVDC) is widely used due to its advantages such as long transmission distances and large transmission capacity. Currently, HVDC systems are mainly divided into two technical paths based on the power devices used in the converter: one is the thyristor-based line commutated converter (LCC); the other is the modular multilevel converter (MMC) based on insulated gate bipolar transistors (IGBT). MMC has advantages such as no commutation failure, more flexible power decoupling control capabilities, the ability to supply power to passive systems, and no reactive power compensation issues. However, due to the current voltage level and transmission power being relatively small compared to LCC, high construction costs, and difficulties in achieving DC fault ride-through, the majority of DC transmission projects currently in operation are still based on LCC.

[0003] LCCs are widely adopted due to their advantages, including high voltage levels, large transmission capacity, and low system losses. However, issues such as commutation failure currently significantly hinder their further application. After commutation between two legs of a converter, if the valve that has just been switched off fails to restore its blocking capability within a period of reverse voltage, or if commutation is not completed during the reverse voltage period, then when the valve voltage transitions to the positive direction, the valve that was switched off will reverse phase to the valve that was originally scheduled to be switched off. This fault phenomenon is called commutation failure. Commutation failure can easily cause DC-side short circuits, voltage fluctuations, and power shortages, seriously impacting system stability. Commutation failure is a typical fault in LCC-HVDC. Because the inverter-side thyristor valves experience a shorter period of reverse voltage after current is shut off, commutation failure is more likely to occur than on the rectifier side. Furthermore, with the emergence of multiple DC feed-in systems with dense receiving points, continuous commutation failures are a high risk for multiple DC lines. Therefore, addressing commutation failure is urgent. Furthermore, LCCs primarily control reactive power to a limited extent by adjusting the firing angle. After considering the commutation process, the power factor is low, requiring significant reactive power compensation. Furthermore, their low switching frequency produces numerous characteristic and non-characteristic harmonics, which require the installation of filters of comparable capacity to eliminate them. This results in high investment and maintenance costs, and requires a large footprint. To address these LCC issues, research is currently proposing replacing thyristors with fully controlled reverse-resistance devices (IGCTs). While this solution can completely suppress commutation failures and offers power decoupling and passive power supply capabilities, the high-frequency modulation also results in significant system losses.

[0004] Therefore, it is necessary to provide a current source hybrid direct current transmission system based on an injection-type grid-commutated converter to completely suppress commutation failure and reduce losses. Summary of the Invention

[0005] The present invention provides a current source hybrid DC power transmission system based on an injection-type grid-commutated converter, comprising: a rectifier station, comprising at least a thyristor-based grid-commutated converter for converting AC power into DC power; an inverter station, comprising at least an injection-type grid-commutated converter for converting DC power output by the rectifier station into AC power; and a control module for controlling the operation of the rectifier station and the inverter station based on trigger timing constraints.

[0006] Furthermore, the injection-type grid-commutated converter includes an upper bridge group and a lower bridge group, and the structures of the upper bridge group and the lower bridge group are consistent: the AC side port of the upper bridge group is connected in parallel with the AC side port of the lower bridge group; the DC side port of the upper bridge group is connected in series with the DC side port of the lower bridge group.

[0007] Furthermore, the upper bridge group includes an upper bridge LCC thyristor main bridge and an upper bridge shunt module, and the upper bridge shunt module is provided between the upper bridge LCC thyristor main bridge and the AC side port of the upper bridge group.

[0008] Furthermore, the upper bridge shunt module includes a first upper bridge injection branch and a second upper bridge injection branch, and the structure of the first upper bridge injection branch is consistent with that of the second upper bridge injection branch; the upper bridge LCC thyristor main bridge includes an upper bridge Y-bridge thyristor group and an upper bridge D-bridge thyristor group, and the structure of the upper bridge Y-bridge thyristor group is consistent with that of the upper bridge D-bridge thyristor group; the upper bridge first injection branch is electrically connected to the upper bridge Y-bridge thyristor group, and the output end of the upper bridge Y-bridge thyristor group is electrically connected to the Y-type winding of the upper bridge phase-shifting transformer; the upper bridge second injection branch is electrically connected to the upper bridge D-bridge thyristor group, and the output end of the upper bridge D-bridge thyristor group is electrically connected to the D-type winding of the upper bridge phase-shifting transformer.

[0009] Furthermore, the first injection branch of the upper bridge includes a first fully-controlled injection switch, a second fully-controlled injection switch, and a first injection inductor. The first injection inductor is connected to the DC side port of the upper bridge group, and the first fully-controlled injection switch is connected in parallel with the second fully-controlled injection switch. The second injection branch of the upper bridge includes a third fully-controlled injection switch, a fourth fully-controlled injection switch, and a second injection inductor. The second injection inductor is connected to the DC side port of the upper bridge group, and the third fully-controlled injection switch is connected in parallel with the fourth fully-controlled injection switch. The output end of the first fully-controlled injection switch and the output end of the third fully-controlled injection switch are electrically connected to the upper bridge Y-bridge thyristor group, and the output end of the second fully-controlled injection switch and the output end of the fourth fully-controlled injection switch are electrically connected to the upper bridge D-bridge thyristor group. The upper bridge Y-bridge thyristor group includes an upper bridge Y-bridge 6-pulse three-phase bridge.

[0010] Furthermore, the trigger timing constraints include: the thyristor switching frequency of the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group of the upper bridge LCC thyristor main bridge is 50 Hz, the trigger pulse interval of adjacently numbered thyristor switches in the upper bridge Y-bridge thyristor group is 60°, the trigger pulse interval of adjacently numbered thyristor switches in the upper bridge D-bridge thyristor group is 60°, and the pulse width of the thyristor switches in the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group is 120°; the trigger pulse interval of thyristor switches with the same serial number in the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group is 30°, and the thyristor switches in the upper bridge Y-bridge thyristor group lead the thyristor switches with the same serial number in the upper bridge D-bridge thyristor group.

[0011] Furthermore, the trigger timing constraints include: the upper bridge shunt module adopts a seven-level injection form, the switching frequency is 300 Hz, and the width of each level is 5°; the switching pulse of the upper bridge shunt module provides a zero level for the upper bridge LCC thyristor main bridge at the natural commutation point.

[0012] Furthermore, the trigger timing constraint includes: the first fully-controlled injection switch of the upper bridge Y bridge and the second fully-controlled injection switch of the upper bridge Y bridge of the first injection branch of the upper bridge are complementary turned on; the third fully-controlled injection switch of the upper bridge Y bridge and the fourth fully-controlled injection switch of the upper bridge Y bridge of the second injection branch of the upper bridge are complementary turned on.

[0013] Furthermore, the thyristor-based grid-commutated converter includes a first 6-pulse thyristor converter, a second 6-pulse thyristor converter, a filter bank, and a reactive power compensation device. The filter bank and the reactive power compensation device are electrically connected to an AC bus. The AC side of the first 6-pulse thyristor converter and the AC side of the second 6-pulse thyristor converter are connected in parallel via a third phase-shifted dual-winding transformer, and the DC side of the first 6-pulse thyristor converter and the DC side of the second 6-pulse thyristor converter are connected in series.

[0014] Furthermore, the control module controls the operation of the rectifier station and the inverter station based on the trigger timing constraint, including: controlling the operation of the rectifier station using a constant DC current; and controlling the operation of the inverter station based on the trigger timing constraint.

[0015] Compared with the prior art, the current source hybrid DC transmission system based on the injection-type grid-commutated converter provided by the present invention has at least the following beneficial effects:

[0016] The main bridge adopts a parallel LCC structure, inheriting the high power density characteristics of LCC and enabling efficient power conversion. Due to its high power density, the injection-type grid-commutated converter can achieve large-capacity power transmission in a relatively small physical space, making it suitable for space-constrained application scenarios. The injection-type grid-commutated converter further modulates the constant DC current by cascading a shunt module composed of reverse-resistance fully controlled devices on the DC side, making the AC side current harmonics extremely low, close to the output characteristics of MMC. The presence of the shunt module enables the injection-type grid-commutated converter to have four-quadrant operation capabilities, which can flexibly control the transmission of active power and reactive power to meet the different needs of the power grid.

[0017] The shunt module enables the parallel-type LCC main bridge thyristor valves to achieve zero-current shutdown, effectively eliminating the risk of commutation failure. This is particularly important during AC system faults or disturbances, ensuring stable system operation. Suppressing commutation failures improves system reliability and reduces power outages caused by commutation failures.

[0018] Injection-type grid-commutated converters can operate in four quadrants, independently controlling the transmission of active and reactive power, achieving power decoupling. This helps maintain grid voltage stability and power balance. Four-quadrant operation allows injection-type grid-commutated converters to adapt to diverse grid operating conditions, including power generation, consumption, and reactive power compensation.

[0019] By utilizing fully controlled reverse-resistance components, the injection-type grid-commutated converter achieves zero-current shutdown during switching, reducing switching losses and improving overall system efficiency. Zero switching losses translate to lower energy loss and heat generation, reducing system operating and maintenance costs.

[0020] When a DC fault occurs, the injection-type grid-commutated converter can quickly clear the fault, restore DC voltage and current, and ensure the continuity of power transmission. The ability to quickly clear DC faults improves system stability and reduces the impact of faults on the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] This specification will be further described in the form of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting, and in these embodiments, like numbers represent like structures, wherein:

[0022] Figure 1 is a module diagram of a current source hybrid direct current transmission system based on an injection-type grid-commutated converter according to some embodiments of this specification;

[0023] Figure 2 is a circuit diagram of a rectifier station according to some embodiments of this specification;

[0024] Figure 3 is a circuit diagram of an inverter station according to some embodiments of this specification;

[0025] Figure 4 is a schematic diagram of a flow chart for controlling the operation of a rectifier station according to some embodiments of this specification;

[0026] Figure 5 is a schematic diagram of a trigger signal timing according to some embodiments of this specification;

[0027] Figure 6 is a schematic diagram of a flow chart of DC voltage control according to some embodiments of this specification;

[0028] Figure 7 is a schematic diagram of a flow chart of constant reactive power control according to some embodiments of this specification;

[0029] Figure 8 is a schematic diagram of the DC side current of an inverter station according to some embodiments of this specification;

[0030] Figure 9 is a schematic diagram of injecting a direct current into an upper bridge group according to some embodiments of this specification;

[0031] Figure 10is a schematic diagram of the AC side current of an inverter station according to some embodiments of this specification;

[0032] Figure 11 is a schematic diagram of a power waveform according to some embodiments of this specification;

[0033] Figure 12 is a schematic diagram of the DC side voltage of an inverter station according to some embodiments of this specification;

[0034] Figure 13 is a schematic diagram of the DC side current of an inverter station according to some embodiments of this specification;

[0035] Figure 14 is a schematic diagram of active power according to some embodiments of this specification. DETAILED DESCRIPTION

[0036] To more clearly illustrate the technical solutions of the embodiments of this specification, the following briefly describes the drawings required for describing the embodiments. Obviously, the drawings described below are merely examples or embodiments of this specification. Those skilled in the art can apply this specification to other similar scenarios based on these drawings without inventive effort. Unless otherwise apparent from the context or otherwise noted, the same reference numerals in the figures represent the same structure or operation.

[0037] Figure 1 is a module diagram of a current source hybrid DC transmission system based on an injection-type grid-commutated converter according to some embodiments of this specification, such as Figure 1 As shown, the current source hybrid direct current transmission system based on the injection type grid commutated converter may include a rectifier station, an inverter station and a control module.

[0038] A rectifier station, comprising at least a thyristor-based grid-commutated converter, is used to convert alternating current into direct current. Figure 1 In the example, the DC transmission line is an equivalent resistance R dc , DC side through smoothing reactor L dc Post-parallel DC filter (DC Filter, DCF), U i is the input AC voltage, I i is the input AC current, P i is the active power, Q i is the reactive power, j is the imaginary unit, L ac It is the AC side inductor used for filtering and limiting the current change rate. The subscripts "r" and "i" represent the rectifier side and the inverter side respectively.

[0039] Figure 2is a circuit diagram of a rectifier station according to some embodiments of this specification, such as Figure 2 As shown, specifically, the thyristor-based grid commutation converter includes a first 6-pulse thyristor converter ( Figure 2 Valve group T in Yh1 -T Yh6 ), the second 6-pulse thyristor converter ( Figure 2 Valve group T in Dl1 -T Yl6 ), filter bank and reactive power compensation equipment, the filter bank and reactive power compensation equipment are electrically connected to the AC bus, the AC side of the first 6-pulse thyristor converter and the AC side of the second 6-pulse thyristor converter are connected in parallel via a third phase-shifted double-winding transformer, and the DC side of the first 6-pulse thyristor converter and the DC side of the second 6-pulse thyristor converter are connected in series, thereby improving the DC voltage bearing capacity and reducing the AC and DC side harmonics to a certain extent.

[0040] Specifically, the filter group may include 11th and 13th order double tuned filters and a low pass filter. Yh1 -T Yh6 、T Dl1 -T Yl6 All are half-controlled thyristors.

[0041] The inverter station at least includes an injection-type grid-commutated converter, which is used to convert the direct current output by the rectifier station into alternating current.

[0042] Figure 3 is a circuit diagram of an inverter station according to some embodiments of this specification, such as Figure 3 As shown, specifically, the injection-type grid-commutated converter includes an upper bridge group and a lower bridge group, and the upper bridge group and the lower bridge group have the same structure.

[0043] The AC side port of the upper bridge group is connected in parallel with the AC side port of the lower bridge group; the DC side port of the upper bridge group is connected in series with the DC side port of the lower bridge group.

[0044] The upper bridge group includes an upper bridge LCC thyristor main bridge and an upper bridge shunt module. The upper bridge shunt module is arranged between the upper bridge LCC thyristor main bridge and the AC side port of the upper bridge group.

[0045] In some embodiments, the upper bridge shunt module includes an upper bridge first injection branch and an upper bridge second injection branch, and the upper bridge first injection branch and the upper bridge second injection branch have the same structure;

[0046] The upper bridge LCC thyristor main bridge includes the upper bridge Y bridge thyristor group ( Figure 3 Valve group T in Yh1 -T Yh6 ) and upper bridge D bridge thyristor group ( Figure 3Valve group T in Dh1 -T Dh6 ), the upper Y-bridge thyristor group has the same structure as the upper D-bridge thyristor group;

[0047] The first injection branch of the upper bridge is electrically connected to the upper bridge Y-bridge thyristor group, and the output end of the upper bridge Y-bridge thyristor group is electrically connected to the Y-type winding of the upper bridge phase-shifting transformer;

[0048] The second injection branch of the upper bridge is electrically connected to the D-bridge thyristor group of the upper bridge, and the output end of the D-bridge thyristor group of the upper bridge is electrically connected to the D-type winding of the upper bridge phase-shifting transformer.

[0049] In some embodiments, the first upper bridge injection branch includes a first upper bridge fully controlled injection switch T Yrh1 , the second fully controlled injection switch T Drh1 And the first injection inductor L h1 The first upper bridge injection inductor is connected to the DC side port of the upper bridge group, the first upper bridge fully controlled injection switch is connected in parallel with the second upper bridge fully controlled injection switch; the second upper bridge injection branch includes the third upper bridge fully controlled injection switch T Yrhn , the fourth fully controlled injection switch T Drhn And the second injection inductor L hn , the second injection inductor of the upper bridge is connected to the DC side port of the upper bridge group, the third fully controlled injection switch of the upper bridge is connected in parallel with the fourth fully controlled injection switch of the upper bridge; the output end of the first fully controlled injection switch of the upper bridge and the output end of the third fully controlled injection switch of the upper bridge are electrically connected to the upper bridge Y bridge thyristor group, the output end of the second fully controlled injection switch of the upper bridge and the output end of the fourth fully controlled injection switch of the upper bridge are electrically connected to the upper bridge D bridge thyristor group; the upper bridge Y bridge thyristor group includes an upper bridge Y bridge 6-pulse three-phase bridge ( Figure 3 Valve group T in Yh1 -T Yh6 ).

[0050] like Figure 3 As shown, the lower bridge group includes a lower bridge LCC thyristor main bridge and a lower bridge shunt module. A lower bridge shunt module is provided between the lower bridge LCC thyristor main bridge and the AC side port of the lower bridge group. The lower bridge LCC thyristor main bridge includes a lower bridge Y bridge thyristor group ( Figure 3 Valve group T in Yl1 -T Yl6 ) and the lower bridge D bridge thyristor group ( Figure 3 Valve group T in Dl1 -T Dl6 The lower bridge shunt module includes a lower bridge first injection branch and a lower bridge second injection branch. The lower bridge first injection branch includes a lower bridge first fully controlled injection switch T Yrl1 , lower bridge second fully controlled injection switch T Drl1 And the first injection inductor L of the lower bridge l1The second injection branch of the lower bridge includes the third fully controlled injection switch T Yrln , the fourth fully controlled injection switch T Drln And the lower bridge second injection inductor L ln .

[0051] The control module is used to control the operation of the rectifier station and the inverter station based on the trigger timing constraints.

[0052] Specifically include:

[0053] Use constant DC current to control the operation of the rectifier station;

[0054] Based on the trigger timing constraints, the inverter station operation is controlled.

[0055] Figure 4 is a flow chart of controlling the operation of a rectifier station according to some embodiments of this specification, such as Figure 4 As shown, specifically, the rectifier side DC current I dc(means) With the DC current reference value I dcref The error value obtained by comparison is limited by the PI regulator and output to the rectifier station to modulate the command trigger angle α r .

[0056] In some embodiments, triggering the timing constraints includes:

[0057] The thyristor switching frequency of the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group of the upper bridge LCC thyristor main bridge is 50Hz, the trigger pulse interval of the adjacent numbered thyristor switches in the upper bridge Y-bridge thyristor group is 60°, the trigger pulse interval of the adjacent numbered thyristor switches in the upper bridge D-bridge thyristor group is 60°, and the pulse width of the thyristor switches in the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group is 120°;

[0058] The trigger pulse interval of the thyristor switches with the same serial number in the upper Y-bridge thyristor group and the upper D-bridge thyristor group is 30°, and the thyristor switches in the upper Y-bridge thyristor group lead the thyristor switches with the same serial number in the upper D-bridge thyristor group;

[0059] The upper bridge shunt module adopts a seven-level injection form with a switching frequency of 300Hz and a width of 5° for each level. For the injection of seven levels, each switch of the upper bridge shunt module traverses all the set switch states within a 360° cycle.

[0060] The switching pulse of the upper bridge shunt module provides a zero level for the upper bridge LCC thyristor main bridge at the natural commutation point, ensuring that the upper bridge LCC thyristor main bridge can achieve zero current shutdown;

[0061] The first fully controlled injection switch of the upper bridge Y bridge and the second fully controlled injection switch of the upper bridge Y bridge of the first injection branch of the upper bridge are complementary turned on;

[0062] The third fully-controlled injection switch of the upper bridge Y bridge and the fourth fully-controlled injection switch of the upper bridge Y bridge of the second injection branch of the upper bridge are complementary turned on. At the same time, only one fully-controlled injection switch of an injection branch can be turned on.

[0063] The trigger timing constraints of the lower bridge group are the same as above and will not be repeated here.

[0064] Figure 5 is a schematic diagram of the trigger signal timing according to some embodiments of this specification, such as Figure 5 As shown, both the upper bridge group and the lower bridge group are triggered in this way, using the trigger angle α i1 , α i2 Control, double control variable α i1 , α i2 , which can realize power decoupling control. The thyristor-based grid-commutated converter of the rectifier station can be used Figure 4 The trigger signal timing is modulated as shown in the figure. * Indicates the trigger signal of the switch, for example, S Yhl T Yh1 The trigger signal, S Dhl T Dh1 trigger signal.

[0065] like Figure 6 and Figure 7 As shown, the control module can adopt DC voltage control and constant reactive power control to operate the inverter station.

[0066] DC side voltage U of the inverter station dci The calculation formula is:

[0067]

[0068] Where: trigger angle α i1 , α i2 are the trigger angles of the upper bridge group and the lower bridge group respectively; U iM is the AC bus phase voltage amplitude; k n is the turns ratio of the phase-shifting transformer.

[0069] Reactive power Q of the inverter station i The calculation formula is:

[0070] Q i =3u i i i (sinα i1 +sinα i2 )

[0071] Where: u i 、i iThey are respectively the effective value of the phase voltage on the AC side of the inverter station and the effective value of the line current on the AC side.

[0072] The relationship between the controlled quantity and the controlled quantity is:

[0073]

[0074] Among them, Δα i1 is the trigger angle α i1 The change in Δα i2 is the trigger angle α i2 The change in ΔQ i is the change in reactive power of the inverter station, ΔU dci is the change in DC side voltage of the inverter station, A i is the transfer function matrix.

[0075]

[0076] Among them, k is the harmonic order, i i is the effective value of the input current on the AC side of the rectifier station, u i is the effective value of the fundamental component of the AC side voltage.

[0077] Figure 6 In, f n (u i , α i1 , α i2 ) is the same as u i , α i1 , α i2 Related function, α i1u is α caused by DC voltage deviation i1 The adjustment amount, α i2u is α caused by DC voltage deviation i2 The adjustment amount, α i1Q is α caused by reactive power deviation i1 The adjustment amount, α i2Q is caused by reactive power deviation i2 Adjustment amount, Q i(means) is the reactive power value of the converter station obtained by actual measurement, Q ref is the reactive power reference value, f n (u i ,i i , α i1 , α i2 ) is the same as u i 、i i , α i1 , α i2 Related functions. Figure 7 Middle K i is the gain coefficient of the control system, k i1is the gain coefficient of the control system, k i2 is the gain coefficient of the control system.

[0078] The following is an experiment to illustrate the beneficial effects of the current source hybrid DC transmission system based on the injection type grid commutated converter.

[0079] Figure 9 middle, I dcYh is the Y-bridge current on the DC side of the upper bridge group, I dcDh is the D-bridge current on the DC side of the upper bridge group, Figure 10 In the inverter station, the AC side current i ia The AC side current i of the upper bridge group iha and the AC side current i of the lower bridge group ila In parallel, we can get Figures 8-11 As shown, without adding a filter, the AC side current i ia The total harmonic distortion is only about 2.5%. At this time, the AC side voltage u ia , current i ia In phase, it shows that unity power factor operation can be achieved without the need for external reactive power compensation. Figure 11 In Zone 1, the inverter station operates at unity power factor and steadily transmits power to the receiving grid. Zone 2: The inverter station maintains unity power factor while gradually increasing its active power transmission. Zone 3: The inverter station transmits active power to the receiving grid while also absorbing reactive power from the grid. Zone 4: The inverter station transmits active power to the receiving grid while also transmitting reactive power to the grid. RLCCs offer high-quality current quality, flexible power control, and four-quadrant operation capabilities.

[0080] The most common single-phase grounding fault was used to verify the inverter station's ability to resist commutation failure. Further experiments were conducted to obtain the following results: Figure 12-14 The experimental results shown in Figure 12-14 It can be seen that when a single-phase ground fault occurs in the sending grid between 1 and 1.1 seconds, the DC voltage and current drop to 0.25 pu and 0.5 pu, respectively. Once the fault is cleared, the DC voltage and current quickly recover to their rated values. During the fault, the inverter station can still transmit a certain amount of active power, and after the fault is cleared, the active power transmission capacity returns to the rated value. Therefore, the current-source hybrid DC transmission system based on the injection-type grid-commutated converter can effectively resist commutation failures and has good recovery characteristics.

[0081] Finally, it should be understood that the embodiments described in this specification are intended only to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly described and illustrated in this specification.

Claims

1. A current source hybrid DC transmission system based on an injection-type grid-commutated converter, characterized in that: include: a rectifier station comprising at least a thyristor-based grid-commutated converter for converting alternating current into direct current; An inverter station, comprising at least an injection-type grid-commutated converter, for converting the DC power outputted by the rectifier station into AC power; The control module is used to control the operation of the rectifier station and the inverter station based on the trigger timing constraints.

2. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 1, characterized in that: The injection-type grid-commutated converter includes an upper bridge group and a lower bridge group, and the upper bridge group and the lower bridge group have the same structure: The AC side port of the upper bridge group is connected in parallel with the AC side port of the lower bridge group; The DC side port of the upper bridge group is connected in series with the DC side port of the lower bridge group.

3. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 2, characterized in that: The upper bridge group includes an upper bridge LCC thyristor main bridge and an upper bridge shunt module. The upper bridge shunt module is provided between the upper bridge LCC thyristor main bridge and the AC side port of the upper bridge group.

4. The current source hybrid direct current transmission system based on injection-type grid-commutated converter according to claim 3, characterized in that: The upper bridge shunt module includes a first upper bridge injection branch and a second upper bridge injection branch, and the first upper bridge injection branch and the second upper bridge injection branch have the same structure; The upper LCC thyristor main bridge includes an upper Y-bridge thyristor group and an upper D-bridge thyristor group, and the upper Y-bridge thyristor group has the same structure as the upper D-bridge thyristor group; The first injection branch of the upper bridge is electrically connected to the upper bridge Y-bridge thyristor group, and the output end of the upper bridge Y-bridge thyristor group is electrically connected to the Y-type winding of the upper bridge phase-shifting transformer; The second injection branch of the upper bridge is electrically connected to the D-bridge thyristor group of the upper bridge, and the output end of the D-bridge thyristor group of the upper bridge is electrically connected to the D-type winding of the upper bridge phase-shifting transformer.

5. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 4, characterized in that: The first injection branch of the upper bridge includes a first fully-controlled injection switch of the upper bridge, a second fully-controlled injection switch of the upper bridge, and a first injection inductor of the upper bridge. The first injection inductor of the upper bridge is connected to the DC side port of the upper bridge group. The first fully-controlled injection switch of the upper bridge is connected in parallel with the second fully-controlled injection switch of the upper bridge. The second injection branch of the upper bridge includes a third fully-controlled injection switch of the upper bridge, a fourth fully-controlled injection switch of the upper bridge, and a second injection inductor of the upper bridge. The second injection inductor of the upper bridge is connected to the DC side port of the upper bridge group. The third fully-controlled injection switch of the upper bridge is connected in parallel with the fourth fully-controlled injection switch of the upper bridge. The output end of the first fully-controlled injection switch of the upper bridge and the output end of the third fully-controlled injection switch of the upper bridge are electrically connected to the upper bridge Y-bridge thyristor group, and the output end of the second fully-controlled injection switch of the upper bridge and the output end of the fourth fully-controlled injection switch of the upper bridge are electrically connected to the upper bridge D-bridge thyristor group; The upper Y-bridge thyristor group includes an upper Y-bridge 6-pulse three-phase bridge.

6. The current source hybrid direct current transmission system based on injection-type grid-commutated converter according to claim 5, characterized in that: The trigger timing constraints include: The thyristor switching frequency of the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group of the upper bridge LCC thyristor main bridge is 50Hz, the trigger pulse interval of the adjacent numbered thyristor switches in the upper bridge Y-bridge thyristor group is 60°, the trigger pulse interval of the adjacent numbered thyristor switches in the upper bridge D-bridge thyristor group is 60°, and the pulse width of the thyristor switches in the upper bridge Y-bridge thyristor group and the upper bridge D-bridge thyristor group is 120°; The trigger pulse interval of the thyristor switches with the same serial number in the upper Y-bridge thyristor group and the upper D-bridge thyristor group is 30°, and the thyristor switches in the upper Y-bridge thyristor group are ahead of the thyristor switches with the same serial number in the upper D-bridge thyristor group.

7. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 5 or 6, characterized in that: The trigger timing constraints include: The upper bridge shunt module adopts a seven-level injection form, the switching frequency is 300Hz, and the width of each level is 5°; The switching pulse of the upper bridge shunt module provides a zero level for the upper bridge LCC thyristor main bridge at the natural commutation point.

8. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 7, characterized in that: The trigger timing constraints include: The first fully controlled injection switch of the upper bridge Y bridge and the second fully controlled injection switch of the upper bridge Y bridge of the first injection branch of the upper bridge are complementary turned on; The third fully-controlled injection switch of the upper bridge Y-bridge of the second injection branch of the upper bridge and the fourth fully-controlled injection switch of the upper bridge Y-bridge are complementarily turned on.

9. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 8, characterized in that: The thyristor-based grid-commutated converter includes a first six-pulse thyristor converter, a second six-pulse thyristor converter, a filter bank, and a reactive power compensation device. The filter bank and reactive power compensation device are electrically connected to an AC bus. The AC side of the first six-pulse thyristor converter and the AC side of the second six-pulse thyristor converter are connected in parallel via a third phase-shifted dual-winding transformer, and the DC side of the first six-pulse thyristor converter and the DC side of the second six-pulse thyristor converter are connected in series.

10. The current source hybrid direct current transmission system based on injection type grid commutated converter according to claim 9, characterized in that: The control module controls the operation of the rectifier station and the inverter station based on the trigger timing constraints, including: Use constant DC current to control the operation of the rectifier station; Based on the trigger timing constraints, the inverter station operation is controlled.

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