Coordination control method for multi-type embedded direct current suppression continuous commutation failure

Abstract

The invention discloses a coordinated control method for suppressing continuous commutation failure by multi-type embedded direct current, which relates to the technical field of operation control of a power system, and comprises the following steps of: firstly, establishing a power interaction relationship among multi-type embedded direct current lines, and designing a commutation failure improvement mode of different types of embedded direct current to an embedded LCC-HVDC (Low Current Converter-High Voltage Direct Current); furthermore, the invention provides a coordinated control method for suppressing the continuous commutation failure of the embedded LCC-HVDC by the multi-type embedded direct current, and the controlled direct current or direct current power setting value of each embedded direct current system is comprehensively adjusted according to the specific voltage drop and expected voltage caused by the alternating current fault. Reactive compensation is provided by using multi-type embedded direct current to improve voltage recovery and avoid continuous commutation failure. According to the multi-type embedded direct current coordination control, continuous commutation failure can be effectively inhibited under faults of different severity degrees, and repeated power impact on a power grid is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of power system operation control, in particular to a coordinated control method for multi-type embedded direct current suppression of continuous commutation failure. Background Art

[0002] In regional power grids with limited transmission corridors, embedded DC can significantly improve the grid's transmission capacity and controllability, facilitating resource allocation within the grid. It is currently a hot topic of research in the field of power system analysis and operational control, with significant theoretical significance and engineering application value. Embedded DC systems using thyristor devices still face the risk of commutation failure. During the recovery process after a commutation failure, internal interactions within the embedded LCC-HVDC (grid-commutated converter-type high-voltage direct current transmission) and SLCC-HVDC (multi-source adaptive commutated converter-type high-voltage direct current transmission) control systems can lead to continuous commutation failures, which are more detrimental to the grid. This can cause multiple power surges and even cascading failures, threatening grid operational stability. Therefore, for highly coupled AC / DC hybrid power grids containing embedded DC, researching multiple types of embedded DC continuous commutation failure suppression technologies to ensure stable power system operation is of great practical significance.

[0003] Methods for mitigating continuous commutation failures primarily include converter topology improvements, additional device configuration, and control system optimization. These studies have reduced the risk of continuous commutation failures under specific conditions, but they only leverage the limited control capabilities of long-distance, large-scale LCC-HVDC systems. In multi-type DC transmission systems, studies have quantified the contributions of SVGs (static var generators) and VSCs (voltage source converters) to LCC-HVDC commutation failure immunity and fault recovery time. However, no coordinated control during commutation failure recovery has been investigated. Furthermore, existing research has not considered hybrid AC / DC grid scenarios that include embedded LCC-HVDC and other types of embedded DC. The reactive power support capabilities of multi-type embedded DC for embedded LCC-HVDC require further exploration. The power and voltage interactions between multiple embedded DC transmission systems and the mechanisms for mitigating commutation failures need to be clarified. Coordinated control of systems with three types of embedded DC transmission will be more complex, with closer interactions between electrical quantities, worthy of further research and exploration. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a coordinated control method for multi-type embedded DC systems to suppress continuous commutation failures, thereby utilizing the coordinated control capabilities of multi-type embedded DC systems to suppress continuous commutation failures of embedded LCC-HVDC systems.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] A coordinated control method for multiple types of embedded DC suppression continuous commutation failures proposed in the present invention includes:

[0007] Establish the power interaction relationship between multiple types of embedded DC lines;

[0008] Based on the power interaction relationship, a method is designed to improve the ability of multiple types of embedded DC to resist embedded LCC-HVDC commutation failure;

[0009] Based on the improvement method, each embedded DC controlled current or power is comprehensively adjusted according to the voltage drop caused by the AC fault and the expected bus voltage.

[0010] As a further optimization scheme of the coordinated control method for suppressing continuous commutation failure of multiple types of embedded DC lines according to the present invention, the power interaction relationship between the multiple types of embedded DC lines includes:

[0011] The receiving-end AC bus voltage U1 connected to the inverter and the reactive power Q transmitted from the inverter station AC bus to the AC subsystem r1 The voltage-reactive power relationship between them is:

[0012]

[0013] Among them, U1 and δ1 are the effective value and phase angle of the AC voltage at the receiving end AC busbar of the embedded LCC-HVDC inverter side; E1 and δ s1 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s1 and θ s1 are the equivalent impedance and impedance angle of the AC subsystem respectively;

[0014] Get U1's reactive power transfer Q r1 Partial derivative of:

[0015]

[0016] Then, according to the reactive power balance relationship of the AC busbar on the inverter side of the embedded LCC-HVDC, the DC current I d1 Partial derivative of:

[0017]

[0018] Among them, I d1 is the embedded LCC-HVDC DC current, U d1 is the DC voltage on the inverter side, U d01 is the ideal no-load DC voltage on the inverter side, Q d1 Consume reactive power for the inverter station; XT1 is the commutation reactance of each phase.

[0019] As a further optimization scheme for the coordinated control method for suppressing continuous commutation failures of multiple embedded DC systems described in the present invention, a method for improving the ability of multiple embedded DC systems to resist commutation failures of embedded LCC-HVDC systems is designed. The method includes improving the ability of the embedded LCC-HVDC system and adjacent embedded SLCC-HVDC systems and VSC-HVDC systems to resist commutation failures. The adjacent embedded SLCC-HVDC system and VSC-HVDC system improve the ability of the embedded LCC-HVDC system to resist commutation failures by enhancing reactive power compensation for the embedded LCC-HVDC system.

[0020] The voltage-reactive relationship between the AC bus voltage and the corresponding AC subsystem is:

[0021]

[0022] Among them, U2 and δ2 are the effective value and phase angle of the AC voltage at the receiving end AC busbar of the embedded SLCC-HVDC inverter side; E2 and δ s2 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s2 and θ s2 are the equivalent impedance and impedance angle of the AC subsystem respectively; Q r2 is the reactive power transmitted from the inverter station AC bus to the AC subsystem, U3 and δ3 are the effective value and phase angle of the AC voltage at the receiving end AC bus on the embedded VSC-HVDC inverter side, respectively; E3 and δ s3 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s3 and θ s3 are the equivalent impedance and impedance angle of the AC subsystem respectively; Q r3 Reactive power transmitted from the inverter station AC bus to the AC subsystem;

[0023] Improve the reactive power transmitted from the embedded SLCC-HVDC and VSC-HVDC inverter stations to the corresponding AC subsystems, and increase the connected AC bus voltage:

[0024] Q r2 =-Q d2 +Q c2 +Q sSVG -Q t21 -Q t23 (6)

[0025] Q r3 =Q d3 -Q t31 -Q t32 -Q t34 (7)

[0026] Among them, Q d2 Consumes reactive power for embedded SLCC-HVDC inverter station; Q c2 Reactive power provided by the AC filter; Q sSVG Reactive power provided to SVG; Q t21 and Q t23 They are the reactive power transmission from embedded SLCC-HVDC to LCC and VSC tie lines, Q d3 Output reactive power for embedded VSC-HVDC inverter station; Q t31 , Q t23 and Q t34 They are the reactive power transmission from embedded VSC-HVDC to SLCC, VSC and AC transmission line tie line;

[0027] Promote the AC bus voltage recovery of embedded SLCC-HVDC and VSC-HVDC, thereby improving the reactive compensation Q to embedded LCC-HVDC t21 and Q t31 , improve the embedded LCC-HVDC commutation failure resistance capability; for embedded SLCC-HVDC, to promote the AC bus voltage recovery, first consider increasing the reactive power Q provided by SVG sSVG When the required SVG reactive power compensation exceeds the maximum capacity of SVG, SVG switches to reactive power control under the maximum capacity of SVG; in addition, Q is reduced. d2 By reducing the embedded SLCC-HVDC DC current I d2 Implement,adjustment according to the minimum current limit to provide reactive power compensation for,embedded LCC-HVDC;

[0028] For embedded VSC-HVDC, AC bus voltage recovery is promoted by increasing the inverter station output reactive power Q d3 When the required VSC output reactive power exceeds the maximum capacity of the VSC, the VSC switches to reactive power control under the maximum capacity of the VSC; in addition, the DC power is reduced and the VSC output reactive power capacity is increased to provide reactive compensation for the embedded LCC-HVDC.

[0029] As a further optimization scheme of the coordinated control method for suppressing continuous commutation failure of multiple embedded DC systems according to the present invention, the controlled current or power of each embedded DC system is adjusted comprehensively according to the voltage drop caused by the AC fault and the expected bus voltage, as follows:

[0030] During steady-state operation, the initially controlled DC current or DC power of each embedded DC system is set to the rated value; in the event of an AC fault or significant AC bus voltage drop, the DC current or DC power is adjusted to the minimum allowable value; in the event of an intermediate voltage drop, multiple types of embedded DC systems are coordinated and controlled according to the specific voltage drop;

[0031] When an AC fault occurs on the AC bus connected to the inverter side of the embedded LCC-HVDC, the AC bus voltage connected to the embedded LCC-HVDC drops to the actual value of the AC bus voltage U 1f To promote U 1f Return to steady-state value U 1ref , the reactive power support required by embedded LCC-HVDC is calculated as:

[0032]

[0033] Among them, △Q r1 Reactive power support required for embedded LCC-HVDC; Q r1 (U 1ref ) and Q r1 (U 1f ) are the reactive power transmitted from the inverter station AC bus to the AC subsystem under the expected value and actual value of the AC bus voltage respectively; I d1c is the DC controlled current of the embedded LCC-HVDC under coordinated control after the fault; U 2f and U 3f are the AC bus voltages connected to the embedded SLCC-HVDC and VSC-HVDC without coordinated control after a fault; U 2c and U 3c are the AC bus voltages connected to the embedded SLCC-HVDC and VSC-HVDC when coordinated control is in place after a fault; Q d1 (U 1f ,I d1 ) is the reactive power consumed by the inverter station under the actual value of the AC bus voltage and the initial value of the DC controlled current; Q d1 (U 1ref ,I d1c ) is the reactive power consumed by the inverter station under the expected value of the AC bus voltage and the expected value of the DC controlled current; Q c1 (U 1f ) is the reactive power provided by the AC filter under the actual value of the AC bus voltage; Q c1 (U 1ref ) is the reactive power provided by the AC filter under the expected value of the AC bus voltage; Q t12 (U 1f ,U 2f) is the reactive power transmission on the tie line from embedded LCC-HVDC to SLCC under the actual value of the AC bus voltage connected to the embedded LCC-HVDC and SLCC-HVDC; Q t12 (U 1ref ,U 2c ) is the reactive power transmission on the tie line from embedded LCC-HVDC to SLCC under the expected value of the AC bus voltage connected to the embedded LCC-HVDC and SLCC-HVDC; Q t13 (U 1f ,U 3f ) is the reactive power transmission on the tie line from the embedded LCC-HVDC to the VSC-HVDC under the actual value of the AC bus voltage connected to the embedded LCC-HVDC and VSC-HVDC; Q t13 (U 1ref ,U 3c ) is the reactive power transmission on the tie line from the embedded LCC-HVDC to the VSC under the expected value of the AC bus voltage connected to the embedded LCC-HVDC and VSC-HVDC;

[0034] The reactive power support capacity required by the embedded LCC-HVDC is calculated to obtain the desired DC controlled current or DC controlled power for various embedded DC systems. By reducing the reactive power consumption of the inverter station or improving reactive power compensation, the AC bus voltage is restored to a steady-state value, thus suppressing continuous commutation failure of the embedded LCC-HVDC.

[0035] As a further optimization scheme of the coordinated control method for multi-type embedded DC suppression of continuous commutation failure described in the present invention,

[0036] U 2f and U 3f According to U 1f The initial steady-state control target is derived from the initial values ​​of the DC controlled currents of the embedded LCC-HVDC and SLCC-HVDC, and the initial value of the DC controlled power of the embedded VSC-HVDC.

[0037] As a further optimization scheme for the coordinated control method for suppressing continuous commutation failure of a multi-type embedded DC system according to the present invention, under the coordinated control of the multi-type embedded DC system, controller settings for the multi-type embedded DC system are obtained based on the actual value and reference value of the AC bus voltage after the fault. The controller settings for the multi-type embedded DC system include the DC controlled currents of the embedded LCC-HVDC and SLCC-HVDC under the coordinated control after the fault, and the DC controlled power of the embedded VSC-HVDC under the coordinated control after the fault.

[0038] An embodiment of the present invention also provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the computer program, the steps of the coordinated control method for multi-type embedded DC suppression continuous commutation failure as described above are implemented.

[0039] An embodiment of the present invention further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the steps of the coordinated control method for multi-type embedded DC suppression continuous commutation failure are implemented.

[0040] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0041] (1) The present invention provides an effective coordinated control solution for improving transient voltage stability and coping with continuous commutation failures in various embedded DC systems, thereby avoiding the risk of repeated power shocks and cascading failures caused by continuous commutation failures in AC / DC hybrid power grids, and providing technical support for embedded DC power flow control functions.

[0042] (2) This method fully exploits the potential of multi-type embedded DC control, has fast action speed, and does not require additional equipment investment, so it has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A specific flow chart of the method in a specific embodiment of the present invention;

[0044] Figure 2 Figure 1 shows the system response characteristics after commutation failure caused by a three-phase AC fault in Example 1; where (a) is the embedded LCC turn-off angle, (b) is the embedded SLCC turn-off angle, (c) is the embedded LCC reactive power exchange, (d) is the embedded LCC inverter-side AC bus voltage, (e) is the embedded SLCC inverter-side AC bus voltage, (f) is the embedded VSC inverter-side AC bus voltage, (g) is the controller setting under coordinated control, (h) is the controller setting under VDCOL control, (i) is the DC transmission power under coordinated control, and (j) is the DC transmission power under VDCOL control.

[0045] Figure 3Figure 2 shows the system response characteristics after commutation failure caused by a single-phase AC fault in Example 2; where (a) is the embedded LCC turn-off angle, (b) is the embedded SLCC turn-off angle, (c) is the embedded LCC reactive power exchange, (d) is the embedded LCC inverter-side AC bus voltage, (e) is the embedded SLCC inverter-side AC bus voltage, (f) is the embedded VSC inverter-side AC bus voltage, (g) is the controller setting under coordinated control, (h) is the controller setting under VDCOL control, (i) is the DC transmission power under coordinated control, and (j) is the DC transmission power under VDCOL control.

[0046] Figure 4 Figure 3 shows the system response characteristics under different receiving-end AC system short-circuit ratios in Example 3; where (a) is the embedded LCC turn-off angle, (b) is the embedded SLCC turn-off angle, (c) is the embedded LCC reactive power exchange, (d) is the embedded LCC inverter-side AC bus voltage, (e) is the embedded SLCC inverter-side AC bus voltage, (f) is the embedded VSC inverter-side AC bus voltage, (g) is the controller setting under coordinated control, (h) is the controller setting under VDCOL control, (i) is the DC transmission power under coordinated control, and (j) is the DC transmission power under VDCOL control. DETAILED DESCRIPTION

[0047] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] This specific embodiment discloses a coordinated control method for multiple types of embedded DC suppression continuous commutation failures. The specific flow chart of the method is as follows: Figure 1 As shown, the following steps are included:

[0049] The commutation failure of the embedded LCC-HVDC is closely related to the AC bus voltage connected to its own inverter side. Promoting the recovery of the AC bus voltage is directly beneficial to the recovery of the commutation failure. The receiving end AC bus voltage U1 connected to the inverter and the reactive power transmission Q from the inverter station to the AC subsystem are r1 The voltage-reactive power relationship between them is:

[0050]

[0051] Where U1 and δ1 are the effective value and phase angle of the AC voltage at the receiving end of the embedded LCC-HVDC inverter side; E1 and δ s1 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s1 and θ s1 are the equivalent impedance and impedance angle of the AC subsystem respectively; Q r1It is the reactive power transmission between the AC bus and the AC subsystem.

[0052] The AC bus voltage U1 with respect to reactive power transfer Q can be obtained r1 Partial derivative of:

[0053]

[0054] Then, according to the reactive power balance relationship of the AC busbar on the inverter side of the embedded LCC-HVDC, the AC busbar voltage U1 with respect to the embedded LCC-HVDC DC current I can be obtained. d1 Partial derivative of:

[0055]

[0056] Where, I d1 is the embedded LCC-HVDC DC current, U d1 is the DC voltage on the inverter side, U d01 is the ideal no-load DC voltage on the inverter side, Q d1 Consume reactive power for the inverter station; X T1 is the commutation reactance of each phase.

[0057] Embedded LCC-HVDC DC current I d1 The higher it is, the lower the AC bus voltage U1 connected to the inverter side is, which is more unfavorable for commutation failure recovery. Therefore, continuous commutation failure can be suppressed by reducing the DC current of the embedded LCC-HVDC itself.

[0058] Embedded SLCC-HVDC and VSC-HVDC (voltage source converter type high voltage direct current transmission) enhance the embedded LCC-HVDC's ability to withstand commutation failures indirectly by improving its reactive power compensation. The reactive power coupling interaction between each transmission line at the receiving end through the tie line is mainly determined by the voltage difference between the AC buses. Increasing the AC bus voltage connected to the embedded SLCC-HVDC and VSC-HVDC will help improve reactive power compensation, thereby improving the embedded LCC-HVDC's ability to withstand commutation failures. The voltage-reactive power relationship between the AC bus voltage and the corresponding AC subsystem is:

[0059]

[0060] Where, each variable is the variable in equation (1) corresponding to embedded SLCC-HVDC and VSC-HVDC.

[0061] Improving the reactive power transmitted from the embedded SLCC-HVDC and VSC-HVDC inverter stations to the corresponding AC subsystems can increase the connected AC bus voltage:

[0062] Q r2 =-Qd2 +Q c2 +Q sSVG -Q t21 -Q t23 (6)

[0063] Q r3 =Q d3 -Q t31 -Q t32 -Q t34 (7)

[0064] Where Q d2 Consumes reactive power for embedded SLCC-HVDC inverter station; Q c2 Reactive power provided by the AC filter; Q sSVG Reactive power provided to SVG; Q t21 and Q t23 They are the reactive power transmission from embedded SLCC-HVDC to LCC (grid commutated converter) and VSC tie line. d3 Output reactive power for embedded VSC-HVDC inverter station; Q t31 , Q t23 and Q t34 They are the reactive power transmission from embedded VSC-HVDC to SLCC (multi-source adaptive commutation converter), VSC and AC transmission line tie line.

[0065] Promote the AC bus voltage recovery of embedded SLCC-HVDC and VSC-HVDC, thereby improving the reactive compensation Q to embedded LCC-HVDC t21 and Q t31 , which can improve the ability of embedded LCC-HVDC to resist commutation failure. For embedded SLCC-HVDC, the first consideration to promote the recovery of AC bus voltage is to increase the reactive power Q provided by SVG. sSVG When the required SVG reactive power compensation exceeds its capacity, the SVG switches to reactive power control at the maximum capacity; in addition, it can also reduce the reactive power Q consumed by the inverter station. d2 , specifically by reducing the DC current I d2 The minimum current limit is adjusted to provide more reactive power compensation for the embedded LCC-HVDC. For the embedded VSC-HVDC, the AC bus voltage recovery is promoted by increasing the reactive power Q output by the inverter station. d3 When the required VSC output reactive power exceeds its capacity, the VSC switches to reactive power control at its maximum capacity. In addition, the DC power can be temporarily reduced to increase the VSC output reactive power capacity, providing more reactive compensation for the embedded LCC-HVDC.

[0066] Embedded LCC-HVDC has a stronger reactive power support capability for faults on the connected AC bus than SLCC and VSC, and should be prioritized in coordinated control design to improve recovery after AC faults. Embedded SLCC-HVDC and VSC-HVDC provide similar reactive power support to LCC, but given the superior controllability and flexibility of VSC, which can simultaneously control both active and reactive power and provide more stable DC power transmission, VSC adjustments should be prioritized over SLCC adjustments. To maximize the coordinated control capabilities of a multi-type embedded DC system, control should be performed in the order of embedded LCC-HVDC, VSC-HVDC, and SLCC-HVDC.

[0067] During normal steady-state operation, the initial controlled DC current or DC power of each embedded DC system is set to the rated value; in the event of a serious AC fault and a significant AC bus voltage drop, it is adjusted to the minimum allowable DC current or DC power; when the intermediate voltage drops, the multi-type embedded DC is coordinated and controlled according to the specific voltage drop. An AC fault on the AC bus connected to the inverter side of the embedded LCC-HVDC will cause the AC bus voltage to drop to a certain value U 1f , in order to promote its return to the steady-state value U 1ref , the required reactive power support can be calculated as:

[0068]

[0069] Where: I d1c is the DC current of the embedded LCC-HVDC under coordinated control after the fault; U 2f 、U 3f 、U 2c 、U 3c The AC bus voltages connected to the embedded SLCC-HVDC and VSC-HVDC without and with coordinated control after a fault, respectively.

[0070] The desired setting values ​​of the controlled DC current or DC power of various embedded DC systems are calculated by the required reactive power support capacity. By reducing the reactive power consumption of the inverter station or improving reactive power compensation, the AC bus voltage is promoted to return to a steady-state value, thereby suppressing continuous commutation failure of the embedded LCC-HVDC.

[0071] AC bus voltage U connected to embedded SLCC-HVDC and VSC-HVDC after AC fault 2f and U 3f The actual voltage U of the AC bus connected to the embedded LCC-HVDC caused by the fault can be 1f and the initial steady-state control target (I d1 , I d2 、Pd3 ) is derived to be used for the calculation of reactive power transmission on the tie line between subsequent transmission lines and the setting of embedded DC controllers. Under the proposed multi-type embedded DC coordinated control, the controller settings of the multi-type embedded DC system (I d1 , I d2 、P d3 ) can be jointly obtained based on the actual value of the AC bus voltage after the fault, providing guidance for reducing the specific DC transmission power. When the AC bus voltage decreases due to a fault, the proposed multi-type embedded DC coordinated control leads to a reduction in DC transmission power, reducing the reactive power required by the embedded LCC-HVDC and SLCC-HVDC inverter stations and increasing the reactive power supply capacity of the embedded VSC-HVDC. The changes in multi-type embedded DC transmission power and the corresponding reactive power changes will support the transmission of reactive power from the embedded LCC-HVDC AC bus to the AC subsystem, improve AC bus voltage recovery after a fault, and suppress continuous commutation failures.

[0072] Figures 2 to 4 Three examples are presented to demonstrate the effectiveness of the process proposed in this invention. Figure 2 This is the system response characteristic after commutation failure caused by three-phase AC fault in Example 1; Figure 2 (a) is the turn-off angle of the embedded LCC. Figure 2 (b) is the turn-off angle of embedded SLCC. Figure 2 (c) in the figure is the embedded LCC reactive power exchange. Figure 2 (d) is the AC bus voltage on the inverter side of the embedded LCC. Figure 2 (e) is the AC bus voltage on the embedded SLCC inverter side, Figure 2 (f) is the AC bus voltage on the inverter side of the embedded VSC. Figure 2 (g) in the figure is the controller setting under coordinated control. Figure 2 (h) in the figure is the controller setting under VDCOL (low voltage current limiting) control. Figure 2 (i) in the equation is the DC transmission power under coordinated control, Figure 2 (j) in the figure is the DC transmission power under VDCOL control. Figure 3 This is the system response characteristic after commutation failure caused by single-phase AC fault in Example 2; Figure 3 (a) is the turn-off angle of the embedded LCC. Figure 3 (b) is the turn-off angle of embedded SLCC. Figure 3 (c) in the figure is the embedded LCC reactive power exchange. Figure 3 (d) is the AC bus voltage on the inverter side of the embedded LCC. Figure 3 (e) is the AC bus voltage on the embedded SLCC inverter side, Figure 3 (f) is the AC bus voltage on the inverter side of the embedded VSC. Figure 3 (g) in the figure is the controller setting under coordinated control. Figure 3 (h) in the figure is the controller setting under VDCOL control. Figure 3 (i) in the equation is the DC transmission power under coordinated control, Figure 3 (j) in the figure is the DC transmission power under VDCOL control. Figure 4 The system response characteristics of Example 3 under different receiving-end AC system short-circuit ratios; Figure 4 (a) is the turn-off angle of the embedded LCC. Figure 4 (b) is the turn-off angle of embedded SLCC. Figure 4 (c) in the figure is the embedded LCC reactive power exchange. Figure 4 (d) is the AC bus voltage on the inverter side of the embedded LCC. Figure 4 (e) is the AC bus voltage on the embedded SLCC inverter side, Figure 4 (f) is the AC bus voltage on the inverter side of the embedded VSC. Figure 4 (g) in the figure is the controller setting under coordinated control. Figure 4 (h) in the figure is the controller setting under VDCOL control. Figure 4 (i) in the equation is the DC transmission power under coordinated control, Figure 4 (j) in the figure is the DC transmission power under VDCOL control.

[0073] Case 1 is the response characteristics of the AC / DC hybrid system after a symmetrical three-phase AC fault causes commutation failure. Figure 2 It can be seen that under the proposed coordinated control, the embedded LCC-HVDC can smoothly recover to a stable operating state without continuous commutation failure. However, under traditional VDCOL control, the switching process between the DC current control and the turn-off angle control of the inverter-side controller fails to transition smoothly, resulting in continuous commutation failure in the embedded LCC-HVDC, causing repeated power shocks to the AC / DC hybrid grid. At the same time, the AC bus voltage connected to the embedded SLCC-HVDC decreases due to grid voltage coupling. Under the proposed coordinated control, the embedded SLCC-HVDC does not experience commutation failure, while a single commutation failure occurs under traditional VDCOL control. The proposed control method achieves coordinated regulation of multiple types of embedded DC systems and effectively improves the commutation failure resistance of embedded LCC-HVDC and SLCC-HVDC.

[0074] Example 2 is the response characteristics of the AC / DC hybrid system after commutation failure caused by an asymmetric single-phase AC fault. Figure 3It can be seen that under the proposed coordinated control, both the embedded LCC-HVDC and SLCC-HVDC were able to smoothly recover to a stable operating state without experiencing continuous commutation failures. However, under traditional VDCOL control, both the embedded LCC-HVDC and SLCC-HVDC experienced continuous commutation failures, and the embedded SLCC-HVDC experienced multiple continuous commutation failures. These commutation failures were more severe than those caused by three-phase AC faults, and the recovery time to stable operation was longer, resulting in repeated power shocks to the AC / DC hybrid power grid. The proposed multi-type embedded DC coordinated control can also effectively suppress continuous commutation failures in the embedded LCC-HVDC and SLCC-HVDC under asymmetric faults, promote fault voltage recovery, improve the operating performance and power characteristics of the AC / DC hybrid power grid, and avoid repeated power shocks caused by continuous commutation failures to the AC / DC hybrid power grid.

[0075] Example 3 shows the dynamic response characteristics after a three-phase AC fault occurs under a higher short-circuit ratio of the receiving AC system. Figure 4 It can be seen that when connected to a receiving AC system with a higher short-circuit ratio, the AC / DC hybrid grid has a more stable fault recovery process and lower commutation failure severity, even under more severe three-phase AC faults and more severe AC bus voltage drops. Under coordinated control, both the embedded LCC-HVDC and SLCC-HVDC were able to smoothly recover to stable operation without experiencing continuous commutation failures. Under traditional VDCOL control, the embedded LCC-HVDC experienced continuous commutation failures, causing repeated power shocks to the AC / DC hybrid grid. The embedded SLCC-HVDC did not experience continuous commutation failures in this scenario, demonstrating that the enhanced strength of the receiving AC system improves the operational performance of the AC / DC hybrid grid test system in terms of commutation failures. The proposed multi-type embedded DC coordinated control also effectively suppresses continuous commutation failures in the embedded LCC-HVDC when the short-circuit ratio of the receiving AC system changes, promotes fault voltage recovery, and avoids repeated power shocks caused by continuous commutation failures on the AC / DC hybrid grid.

[0076] The present invention aims to utilize the power interaction relationship between multiple types of embedded DC lines to provide reactive power support, enhance the transient voltage stability and continuous commutation failure suppression capabilities of the embedded LCC-HVDC, and thus avoid repeated power shocks and cascading failure risks to the AC / DC hybrid power grid.

[0077] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A coordinated control method for multiple embedded DC suppression of continuous commutation failure, characterized in that: include: Establish the power interaction relationship between multiple types of embedded DC lines; Based on the power interaction relationship, a method is designed to improve the ability of multiple types of embedded DC to resist embedded LCC-HVDC commutation failure; Based on the improvement method, each embedded DC controlled current or power is comprehensively adjusted according to the voltage drop caused by the AC fault and the expected bus voltage.

2. The coordinated control method for multi-type embedded DC suppression of continuous commutation failure according to claim 1 is characterized in that: Power interaction relationships between multiple types of embedded DC links, including: The receiving-end AC bus voltage U1 connected to the inverter and the reactive power Q transmitted from the inverter station AC bus to the AC subsystem r1 The voltage-reactive power relationship between them is: Among them, U1 and δ1 are the effective value and phase angle of the AC voltage at the receiving end AC busbar of the embedded LCC-HVDC inverter side; E1 and δ s1 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s1 and θ s1 are the equivalent impedance and impedance angle of the AC subsystem respectively; Get U1's reactive power transfer Q r1 Partial derivative of: Then, according to the reactive power balance relationship of the AC busbar on the inverter side of the embedded LCC-HVDC, the DC current I d1 Partial derivative of: Among them, I d1 is the embedded LCC-HVDC DC current, U d1 is the DC voltage on the inverter side, U d01 is the ideal no-load DC voltage on the inverter side, Q d1 Consumes reactive power for the inverter station; X T1 is the commutation reactance of each phase.

3. The coordinated control method for multiple embedded DC suppression continuous commutation failures according to claim 2 is characterized in that: Design a method to improve the ability of multiple types of embedded DC to resist commutation failure of embedded LCC-HVDC, wherein the improvement method includes improving the ability of embedded LCC-HVDC and adjacent embedded SLCC-HVDC and VSC-HVDC to resist commutation failure. The adjacent embedded SLCC-HVDC and VSC-HVDC improve the ability of embedded LCC-HVDC to resist commutation failure by improving reactive power compensation for the embedded LCC-HVDC. The voltage-reactive relationship between the AC bus voltage and the corresponding AC subsystem is: Among them, U2 and δ2 are the effective value and phase angle of the AC voltage at the receiving end AC busbar of the embedded SLCC-HVDC inverter side; E2 and δ s2 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s2 and θ s2 are the equivalent impedance and impedance angle of the AC subsystem respectively; Q r2 is the reactive power transmitted from the inverter station AC bus to the AC subsystem, U3 and δ3 are the effective value and phase angle of the AC voltage at the receiving end AC bus on the embedded VSC-HVDC inverter side, respectively; E3 and δ s3 are the effective value and phase angle of the AC voltage of the equivalent power supply of the AC subsystem; Z s3 and θ s3 are the equivalent impedance and impedance angle of the AC subsystem respectively; Q r3 Reactive power transmitted from the inverter station AC bus to the AC subsystem; Improve the reactive power transmitted from the embedded SLCC-HVDC and VSC-HVDC inverter stations to the corresponding AC subsystems, and increase the connected AC bus voltage: Q r2 =-Q d2 +Q c2 +Q sSVG -Q t21 -Q t23 (6) Q r3 =Q d3 -Q t31 -Q t32 -Q t34 (7) Among them, Q d2 Consumes reactive power for embedded SLCC-HVDC inverter station; Q c2 Reactive power provided by the AC filter; Q sSVG Reactive power provided to SVG; Q t21 and Q t23 They are the reactive power transmission from embedded SLCC-HVDC to LCC and VSC tie lines, Q d3 Output reactive power for embedded VSC-HVDC inverter station; Q t31 , Q t23 and Q t34 They are the reactive power transmission from embedded VSC-HVDC to SLCC, VSC and AC transmission line tie line; Promote the AC bus voltage recovery of embedded SLCC-HVDC and VSC-HVDC, thereby improving the reactive compensation Q to embedded LCC-HVDC t21 and Q t31 , improve the embedded LCC-HVDC commutation failure resistance capability; for embedded SLCC-HVDC, to promote the AC bus voltage recovery, first consider increasing the reactive power Q provided by SVG sSVG When the required SVG reactive power compensation exceeds the maximum capacity of SVG, SVG switches to reactive power control under the maximum capacity of SVG; in addition, Q is reduced. d2 By reducing the embedded SLCC-HVDC DC current I d2 Implement,adjustment according to the minimum current limit to provide reactive power compensation for,embedded LCC-HVDC; For embedded VSC-HVDC, AC bus voltage recovery is promoted by increasing the inverter station output reactive power Q d3 When the required VSC output reactive power exceeds the maximum capacity of the VSC, the VSC switches to reactive power control under the maximum capacity of the VSC; in addition, the DC power is reduced and the VSC output reactive power capacity is increased to provide reactive compensation for the embedded LCC-HVDC.

4. The coordinated control method for multi-type embedded DC suppression of continuous commutation failure according to claim 1 is characterized in that: The current or power of each embedded DC controlled device is adjusted comprehensively based on the voltage drop caused by the AC fault and the expected bus voltage, as follows: During steady-state operation, the initially controlled DC current or DC power of each embedded DC system is set to the rated value; in the event of an AC fault or significant AC bus voltage drop, the DC current or DC power is adjusted to the minimum allowable value; in the event of an intermediate voltage drop, multiple types of embedded DC systems are coordinated and controlled according to the specific voltage drop; When an AC fault occurs on the AC bus connected to the inverter side of the embedded LCC-HVDC, the AC bus voltage connected to the embedded LCC-HVDC drops to the actual value of the AC bus voltage U 1f To promote U 1f Return to steady-state value U 1ref , the reactive power support required by embedded LCC-HVDC is calculated as: Among them, △Q r1 Reactive power support required for embedded LCC-HVDC; Q r1 (U 1ref ) and Q r1 (U 1f ) are the reactive power transmitted from the inverter station AC bus to the AC subsystem under the expected value and actual value of the AC bus voltage respectively; I d1c is the DC controlled current of the embedded LCC-HVDC under coordinated control after the fault; U 2f and U 3f are the AC bus voltages connected to the embedded SLCC-HVDC and VSC-HVDC without coordinated control after a fault; U 2c and U 3c are the AC bus voltages connected to the embedded SLCC-HVDC and VSC-HVDC when coordinated control is in place after a fault; Q d1 (U 1f ,I d1 ) is the reactive power consumed by the inverter station under the actual value of the AC bus voltage and the initial value of the DC controlled current; Q d1 (U 1ref ,I d1c ) is the reactive power consumed by the inverter station under the expected value of the AC bus voltage and the expected value of the DC controlled current; Q c1 (U 1f ) is the reactive power provided by the AC filter under the actual value of the AC bus voltage; Q c1 (U 1ref ) is the reactive power provided by the AC filter under the expected value of the AC bus voltage; Q t12 (U 1f ,U 2f ) is the reactive power transmission on the tie line from embedded LCC-HVDC to SLCC under the actual value of the AC bus voltage connected to the embedded LCC-HVDC and SLCC-HVDC; Q t12 (U 1ref ,U 2c ) is the reactive power transmission on the tie line from embedded LCC-HVDC to SLCC under the expected value of the AC bus voltage connected to the embedded LCC-HVDC and SLCC-HVDC; Q t13 (U 1f ,U 3f ) is the reactive power transmission on the tie line from the embedded LCC-HVDC to the VSC-HVDC under the actual value of the AC bus voltage connected to the embedded LCC-HVDC and VSC-HVDC; Q t13 (U 1ref ,U 3c ) is the reactive power transmission on the tie line from the embedded LCC-HVDC to the VSC under the expected value of the AC bus voltage connected to the embedded LCC-HVDC and VSC-HVDC; The reactive power support capacity required by the embedded LCC-HVDC is calculated to obtain the desired DC controlled current or DC controlled power for various embedded DC systems. By reducing the reactive power consumption of the inverter station or improving reactive power compensation, the AC bus voltage is restored to a steady-state value, thus suppressing continuous commutation failure of the embedded LCC-HVDC.

5. The coordinated control method for multi-type embedded DC suppression of continuous commutation failure according to claim 4 is characterized in that: U 2f and U 3f According to U 1f The initial steady-state control target is derived from the initial values ​​of the DC controlled currents of the embedded LCC-HVDC and SLCC-HVDC, and the initial value of the DC controlled power of the embedded VSC-HVDC.

6. The coordinated control method for multiple embedded DC suppression continuous commutation failures according to claim 5, characterized in that: Under the coordinated control of multi-type embedded DC systems, the controller settings of the multi-type embedded DC systems are obtained based on the actual value and reference value of the AC bus voltage after the fault. The controller settings of the multi-type embedded DC systems include the DC controlled currents of the embedded LCC-HVDC and SLCC-HVDC under the coordinated control after the fault, and the DC controlled power of the embedded VSC-HVDC under the coordinated control after the fault.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, the steps of the coordinated control method for multi-type embedded DC suppression continuous commutation failure according to any one of claims 1 to 6 are implemented.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the coordinated control method for multi-type embedded DC suppression continuous commutation failure according to any one of claims 1 to 6 are implemented.

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