Cooperative recovery control method and system after direct current simultaneous commutation failure

Abstract

The invention discloses a collaborative recovery control method and system after direct current simultaneous commutation failure. The method comprises the following steps: analyzing influence factors of simultaneous commutation failure of multi-infeed direct current on transient power angle stability and voltage stability of a receiving end system; determining that the influence of the active recovery process on the transient power angle stability of the receiving end after the direct current commutation failure can be jointly determined by the swinging direction of the receiving end relative to the power angle, the inertia proportion and the direct current feed-in position; a large amount of reactive power is further consumed on the rated basis in the reactive power recovery process after direct current commutation failure due to the overshoot characteristic of the reactive power recovery process, and the stability of the voltage at the receiving end can be deteriorated when multiple direct currents with the multi-infeed interaction factor larger than 0.15 are recovered at the same time. The transient power angle stability and the voltage stability of the receiving end system can be effectively improved in scenes of different fault positions, fault types and the like, and the safe and stable operation level of the receiving end system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stability control, and in particular to a coordinated recovery control method and system after a direct current simultaneous commutation failure. Background Art

[0002] In recent years, with the application of new energy and UHV lines, a regional power grid will build a "sun"-shaped UHV AC ring network, and some provinces will also feed two or even three UHV DC lines at the same time to form a DC group. On the one hand, the coupling between AC and DC systems and converter stations is serious, and the risk of simultaneous commutation failure of multiple DC lines caused by AC system failures at the receiving end increases; on the other hand, the impact of UHV large channel failures on the transient power angle and voltage of the system is becoming more and more prominent, seriously threatening the safe and stable operation of the ultra-large AC / DC hybrid power grid. Therefore, it is necessary to conduct in-depth research on the impact of simultaneous commutation failures of multiple DC lines on the transient stability of the receiving system, and propose effective methods to improve the transient stability of the system.

[0003] Extensive and in-depth research has been conducted on DC commutation failure and its influencing factors. In terms of the mechanism of DC commutation failure, the main causes of DC commutation failure caused by AC faults at the receiving end are summarized, which are divided into voltage amplitude reduction, zero-crossing offset and waveform distortion. From the perspective of the interaction between the external AC fault and the internal DC controller, the mechanism of subsequent commutation failure during the period when the AC fault at the receiving end has not been removed is revealed, and an improved control strategy is given. According to the constraints of the DC operating range, the inverter-side controller is optimized and designed respectively, and the voltage stability of the receiving-end system is improved by improving the reactive power recovery characteristics of the system. In terms of the influence mechanism of DC commutation failure on the transient stability of the system, the influence mechanism of the recovery speed after DC commutation failure on the transient stability of the sending-end system is revealed, and the influence of DC controller parameters on DC recovery is theoretically analyzed. For the weak sending-end system, a system stability risk assessment model is established based on the interconnection line capacity ratio and power flow entropy, which can accurately assess the impact of different commutation failure scenarios on the sending-end system. According to the residual acceleration area of ​​the rotor when the DC commutation fails and returns to a steady state, the minimum deceleration area to maintain the stability of the sending-end system is calculated, and then the minimum switching amount of the sending-end system is obtained to avoid system instability. However, there is little research on the impact of DC commutation failure on the transient stability of the receiving end. For multi-input DC receiving-end systems, in the scenario of AC faults and multiple DC commutation failures at the same time, the impact of the DC recovery process on the transient stability of the receiving end becomes increasingly complex and needs to be further studied. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above existing problems, the present invention is proposed.

[0006] Therefore, the present invention provides a coordinated recovery control method and system after simultaneous DC commutation failure to solve the problem of poor transient power angle and voltage stability of the system caused by simultaneous recovery of multiple DC lines after multiple DC lines in a multi-feed receiving-end system fail to commutate simultaneously due to a receiving-end AC system fault.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] In a first aspect, an embodiment of the present invention provides a coordinated recovery control method after a DC simultaneous commutation failure, comprising: establishing a system analysis model based on an actual power system, the system analysis model comprising a receiving end system model and a DC power flow analysis model;

[0009] According to the receiving-end system model, an analytical expression of the relative power angle difference of the receiving end in the process of active power recovery after DC commutation failure is derived with respect to DC power, and the influencing factors of the DC active power recovery process on the transient power angle of the receiving-end system are obtained;

[0010] Based on the regulation characteristics of the inverter-side DC controller, the factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure are obtained according to the DC power flow analysis model;

[0011] Based on the analysis of the factors affecting the voltage stability of the receiving system during the reactive power recovery process and the factors affecting the transient power angle of the receiving system during the DC active power recovery process, a recovery control strategy after multiple DC commutation failures is formed.

[0012] As a preferred solution of the coordinated recovery control method after the simultaneous commutation failure of the DC according to the present invention, it includes: the receiving end system model uses the complementary group inertia center-relative motion theory to simplify the multi-machine system of the multi-feed DC receiving end into a two-group machine system, and obtains the equivalent model of the receiving end multi-machine system, and converts the equivalent model of the receiving end multi-machine system into a single-machine infinite system model, which is expressed as:

[0013]

[0014]

[0015]

[0016]

[0017] Among them, P mA and P mB are the total mechanical input power of groups A and B, P eA and P eB are the total electromagnetic output power of groups A and B, M A and M B are the total inertia of groups A and B, δ E =δ A -δ B is the relative power angle between groups A and B, δ A and δ B are the equivalent power angles of groups A and B respectively;

[0018] The DC power flow analysis model is based on a high-voltage DC transmission system of a line converter, and the relationship between the voltage, current, DC power and reactive power of the inverter station in the model is expressed as:

[0019]

[0020] Among them, U di and I di are DC voltage and current respectively, N p is the number of bridges, x i is the equivalent commutation reactance, k i is the transformer ratio, U li is the commutation bus voltage, Q di is the DC power and reactive power consumed by the converter station, U di0 is the no-load DC voltage of the inverter station, is the power factor, P di is the i-th DC power fed into the receiving system, and γ is the cut-off angle.

[0021] As a preferred solution of the coordinated recovery control method after the DC simultaneous commutation failure of the present invention, it also includes: according to the power external characteristics of the DC commutation failure and its recovery process, a DC power mathematical model of the whole process from the DC commutation failure caused by the receiving end AC fault to its recovery is established, assuming that the power mathematical model is regarded as a power injection model in a short time after the fault is cleared, and a DC power flow analysis model is used for derivation, which is expressed as:

[0022] P G =B GG δ G -B GL (B LL -1 (P L +B LG δ G ))

[0023] Among them, P G is the generator node set, P L is a set of load nodes, where the inverter station node is considered as part of the load node, B GG , B GL , B LG and B LL are the corresponding susceptance matrices, δ G is the power angle of the synchronous generator.

[0024] As a preferred solution of the coordinated recovery control method after the failure of simultaneous DC commutation of the present invention, the factors affecting the transient power angle of the receiving system during the DC active power recovery process include: the fault theory is derived based on the receiving system model with two DC loops fed in, group A consisting of synchronous generators G1 and group B consisting of synchronous generators G2, and the electromagnetic power of the synchronous generator is 0 during the fault period;

[0025] When the AC fault at the receiving end is removed, assuming that the DC power is restored instantaneously, the electromagnetic power P of the synchronous generator with respect to the relative power angle at the receiving end is calculated within a short period of time after the fault. e1 It is expressed as:

[0026]

[0027] Where x is the electrical distance between the potential nodes in G1 and G2, and x L is the load node P L The electrical distance to the potential node in G1, δ is the relative power angle of the receiving end and δ = δ1-δ2, k dp1 and k dp2 are the electrical distances from the first DC and second DC feed-in nodes to the potential nodes within G1, respectively;

[0028] Based on the power balance, the electromagnetic power of G2 is:

[0029] P e2 =P L -P e1 -P d1 -P d2

[0030] Based on the electromagnetic power of the synchronous generator, the receiving system model is rewritten as:

[0031]

[0032]

[0033]

[0034] Wherein, m is the inertia ratio, and is defined as m=M1 / (M1+M2).

[0035] As a preferred solution of the coordinated recovery control method after the simultaneous DC commutation failure of the present invention, it also includes: after the AC fault at the receiving end is removed, there is a power recovery process with a time scale after the actual DC commutation failure, and the relative power angle difference in the DC active power recovery process is:

[0036]

[0037] Where Δδ=δ d -δ; the calculation solution of the relative power angle difference is obtained by its special solution (Δδ p (tt c )) and its corresponding homogeneous equation general solution (Δδ g (tt c ))constitute;

[0038] because

[0039] Relative power angle about ramp i The derivative is:

[0040]

[0041] When the receiving end is swung away from the power angle in the positive direction, if k dpi +m-1>0, the rapid recovery of DC i is beneficial to the transient stability of the receiving system; if k dpi +m-1<0, the rapid recovery of DC i is not conducive to the transient stability of the receiving system;

[0042] When the receiving end is swung in the opposite direction relative to the power angle, if k dpi +m-1>0, the rapid recovery of DC i is not conducive to the transient stability of the receiving system; if k dpi +m-1<0, the rapid recovery of DC i is beneficial to the transient stability of the receiving system;

[0043] Combined with the transient stability recovery of the receiving system, when the receiving system has n g When the number of generator nodes is n, the dynamic equation of the synchronous generator is g About n g Dimensional variable δ G The second-order differential equations of the receiving-end multi-machine system are composed of:

[0044]

[0045] Among them, n g is the number of generator nodes, and n g >2, n1 is the number of load nodes,

[0046] If the node of the lth DC feed-in is j, based on the receiving-end multi-machine system model and the grouping of the receiving-end multi-machine system, we can obtain:

[0047]

[0048] As a preferred solution of the coordinated recovery control method after the DC simultaneous commutation failure described in the present invention, the factors affecting the voltage stability of the receiving system during the reactive power recovery process after the DC commutation failure include: based on the power exchange relationship between the DC inverter station and the receiving AC system, during the DC system recovery process after the AC fault is cleared, the commutation bus voltage amplitude U li It is expressed as:

[0049]

[0050] Among them, U aci is the voltage amplitude of the equivalent bus Bus-aci of the receiving system, ΔU and ΔU′ are the longitudinal and transverse components of the voltage drop, respectively, r aci and x aci are the equivalent resistance and reactance between Bus-aci and Bus-i, P aci and Q aci Inject active and reactive power of the inverter station into the receiving system;

[0051] The commutation bus voltage amplitude U is obtained li About Q di The decoupling relationship is as follows: it is assumed that the line resistance and the voltage drop transverse component caused by active power are ignored; the commutation bus voltage amplitude U li Rewritten as:

[0052]

[0053] Assume U aci Constant, for U li About Q di Taking partial derivatives we get:

[0054]

[0055] For multi-infeed DC receiving-end AC systems, in order to characterize the voltage mutual influence level between the commutation buses on the multi-infeed DC inverter side, a multi-infeed interaction factor is introduced. For the inverter-side commutation buses i and j, the interaction factor F between the two nodes is MIFji is defined as:

[0056]

[0057] If F MIFji <0.15, it means that the voltages between the inverter-side commutation buses i and j have a weak mutual influence; if FMIFji ≥0.15, it means that the voltages between the inverter-side commutation buses i and j have a strong influence on each other.

[0058] As a preferred solution of the coordinated recovery control method after the DC simultaneous commutation failure of the present invention, the recovery control strategy after the analysis of multiple DC commutation failures includes:

[0059] The short-circuit ratio is used to characterize the strength of the receiving-end AC system, i.e., R SCR >3 represents a strong receiving system, R SCR ≤3 represents a weak receiving end system, in which an additional control strategy is introduced;

[0060] When the measured cut-off angle γ is lower than the set value γ set When the original leading trigger angle β i An angle G3 (γ set -γ), increase the commutation margin and reduce the risk of re-commutation failure; set the value γ set Calculated as γ set =γ lim =0.5(γ0+γ min ), where γ0 is the rated cut-off angle, γ min is the critical turn-off angle;

[0061] Based on the analysis of the transient power angle stability of the receiving system, the order of DC restoration is determined; the DC that is beneficial to the transient power angle stability is restored normally, while the DC that is not beneficial to stability needs to be restored slowly; for the favorable DC set, the DC is restored according to the electrical distance |k of the feeding position. dpDi +m-1|, the smaller the electrical distance, the slower the recovery should be; for unfavorable DC sets, the larger the electrical distance, the slower the recovery should be;

[0062] The slow recovery time difference between different recovery sets is set to ensure that the DC is restored as planned. At the same time, the recovery speed after DC commutation failure is controlled by adjusting the time constant of the low-voltage current limiting control to achieve orderly slow recovery.

[0063] In a second aspect, the present invention provides a coordinated recovery control system after a DC simultaneous commutation failure, comprising:

[0064] A model building module, used to establish a system analysis model based on an actual power system, wherein the system analysis model includes a receiving-end system model and a DC power flow analysis model;

[0065] An active power analysis module is used to derive an analytical expression of the relative power angle difference of the receiving end in the active power recovery process after the DC commutation failure according to the receiving end system model, and obtain the influencing factors of the DC active power recovery process on the transient power angle of the receiving end system;

[0066] A reactive power analysis module, which is used to obtain, based on the regulation characteristics of the inverter-side DC controller and the DC power flow analysis model, factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure;

[0067] The collaborative recovery control strategy formulation module is used to form a recovery control strategy after multiple DC commutation failures based on the analysis of the factors affecting the voltage stability of the receiving system during the reactive power recovery process and the factors affecting the transient power angle of the receiving system during the DC active power recovery process.

[0068] In a third aspect, the present invention provides a computing device, comprising:

[0069] Memory and processor;

[0070] The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the coordinated recovery control method after the DC simultaneous commutation failure are implemented.

[0071] In a fourth aspect, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the collaborative recovery control method after the simultaneous DC commutation failure.

[0072] Compared with the prior art, the present invention has the following beneficial effects: the present invention analyzes the influencing factors of simultaneous commutation failure of multi-infeed DC on the transient power angle stability and voltage stability of the receiving system, and determines that the influence of the active power recovery process after the DC commutation failure on the transient power angle stability of the receiving end can be jointly determined by the relative power angle swing direction of the receiving end, the inertia ratio and the DC feed-in position; the reactive power recovery process after the DC commutation failure will further consume a large amount of reactive power on the rated basis due to its overshoot characteristics, and the simultaneous recovery of multiple DCs with a multi-infeed interaction factor greater than 0.15 will deteriorate the voltage stability of the receiving end. Based on the analysis of influencing factors, through the coordinated recovery control strategy of multiple DCs, the transient power angle stability and voltage stability of the receiving system can be effectively improved in scenarios such as different fault locations and fault types, thereby improving the safe and stable operation level of the receiving system. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0074] Figure 1A schematic diagram of a method flow of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0075] Figure 2 A schematic diagram of simultaneous commutation failure of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0076] Figure 3 A receiving-end system equivalent model diagram of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0077] Figure 4 This is a commutation failure simulation result diagram of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention; wherein, Figure 4 (a) is the current of valve 1, Figure 4 (b) in the equation is DC power;

[0078] Figure 5 A schematic diagram of a coordinated recovery control method after a DC simultaneous commutation failure and a relative power angle swing when an AC fault occurs at the receiving end of the system according to an embodiment of the present invention;

[0079] Figure 6 An equivalent impedance diagram of a receiving-end system of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0080] Figure 7 A schematic diagram of power exchange of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0081] Figure 8 A schematic diagram of a DC controller of an inverter station of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0082] Fig. 9 A schematic diagram of reactive power consumption of inverter stations during the recovery period of a coordinated recovery control method after a DC simultaneous commutation failure and a system according to an embodiment of the present invention;

[0083] Fig.10 A coordinated recovery control method after simultaneous DC commutation failure and a coordinated recovery strategy diagram of multiple DCs in the system according to an embodiment of the present invention;

[0084] Fig.11 A logic diagram of an additional control strategy of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0085] Fig.12 A diagram of an IEEE-68 node system containing multiple-infeed DC according to a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention;

[0086] Fig.13 This is a simulation result diagram of a coordinated recovery control method and system for suppressing re-commutation failure after a DC simultaneous commutation failure according to an embodiment of the present invention; wherein, Fig.13 (a) is the B-phase current on the DC2 converter transformer valve side. Fig.13 (b) is the DC2 cut-off angle;

[0087] Fig.14 This is a simulation result diagram of scenario 1 of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention; wherein, Fig.14 (a) is the C-phase current on the DC2 converter valve side. Fig.14 (b) is the DC2 cut-off angle, Fig.14 (c) is the DC3 cut-off angle, Fig.14 (d) in the equation is DC3 power, Fig.14 (e) in the figure is the power angle curve. Fig.14 (f) in the figure is the voltage curve;

[0088] Fig.15 This is a simulation result diagram of scenario 2 of a coordinated recovery control method and system after a DC simultaneous commutation failure according to an embodiment of the present invention; wherein, Fig.15 (a) is the A-phase current on the DC2 converter valve side. Fig.15 (b) is the DC2 cut-off angle, Fig.15 (c) in the figure is the DC1 cut-off angle, Fig.15 (d) in the equation is the DC1 power. Fig.15 (e) in the figure is the power angle curve. Fig.15 (f) in the figure is the voltage curve. DETAILED DESCRIPTION

[0089] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0090] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0091] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0092] The present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0093] At the same time, in the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper, lower, inner and outer" are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second or third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0094] In the present invention, unless otherwise clearly specified and limited, the terms "install, connect, connect" should be understood in a broad sense, for example: it can be a fixed connection, a detachable connection or an integral connection; it can also be a mechanical connection, an electrical connection or a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0095] Example 1

[0096] Reference Figures 1 to 11 , is an embodiment of the present invention, which provides a coordinated recovery control method after a DC simultaneous commutation failure, comprising:

[0097] S1: Establishing a system analysis model based on an actual power system, wherein the system analysis model includes a receiving-end system model and a DC power flow analysis model;

[0098] It should be noted that if Figure 2As shown in the figure, for a multi-input DC receiving system, when a fault occurs in the AC system near the receiving inverter station, the DC commutation failure will occur. In severe cases, multiple DC commutation failures will occur simultaneously, seriously threatening the safe and stable operation of the receiving system. Ideally, the converter valves will commutate once every 60° electrical angle. Due to the AC fault at the receiving end, the commutation bus voltage drops, which will cause the converter valve to be unable to shut down during commutation, resulting in commutation failure.

[0099] For a multi-DC feed-in receiving end system, under the same AC fault, although the commutation time of the converter valve is different, the difference will not be 60° electrical angle. Therefore, the phenomenon of commutation failure of two or more DC circuits within 60° electrical angle is called multi-DC simultaneous commutation failure. If an AC fault occurs at time t0, the commutation failure times of DC i and DC j are t CFi and t CFj , and t CFi and t CFj The phase difference time does not exceed 60° electrical angle.

[0100] Furthermore, when considering the actual commutation process, the conduction time of each valve is 120°+μ, where the commutation angle μ<90°, so the valve current non-zero time t f1 Whether the electrical angle is greater than 180° is used to determine the occurrence of commutation failure, expressed as:

[0101]

[0102] Among them, f0 is the rated frequency of the system.

[0103] Taking into account the measurement delay, the practical criterion for the simultaneous commutation failure of multiple DCs is the number of DCs N that satisfy the above formula within one converter commutation cycle (1 / f0): CF ≥2.

[0104] like Figure 3 As shown, in the embodiment of the present application, the receiving end system model uses the complementary group inertia center-relative motion theory to simplify the multi-machine system of the multi-feed DC receiving end into two-group machine systems, which are complementary groups A and B, to obtain an equivalent model of the receiving end multi-machine system, and convert the equivalent model of the receiving end multi-machine system into a single-machine infinite system model, which is expressed as:

[0105]

[0106]

[0107]

[0108]

[0109] Among them, P mA and P mB are the total mechanical input power of groups A and B, P eA and P eB are the total electromagnetic output power of groups A and B, M A and M B are the total inertia of groups A and B, δ E =δ A -δ B is the relative power angle between groups A and B, δ A and δ B are the equivalent power angles of groups A and B respectively;

[0110] The DC power flow analysis model is based on a high-voltage DC transmission system of a line converter, and the relationship between the voltage, current, DC power and reactive power of the inverter station in the model is expressed as:

[0111]

[0112] Among them, U di and I di are DC voltage and current respectively, N p is the number of bridges, x i is the equivalent commutation reactance, k i is the transformer ratio, U li is the commutation bus voltage, Q di is the DC power and reactive power consumed by the converter station, U di0 is the no-load DC voltage of the inverter station, is the power factor, P di is the i-th DC power fed into the receiving system, and γ is the cut-off angle.

[0113] In an optional embodiment, if Figure 4 As shown in the figure, when the AC system failure at the receiving end simultaneously causes the DC commutation failure, the DC power will drop instantly; from the DC commutation failure to the AC fault removal, the DC power will maintain a low value under the regulation of the DC controller; after the AC fault is removed, the DC power will recover to the rated value under the regulation of the DC controller. Therefore, according to the power external characteristics of the DC commutation failure and its recovery process, a DC power mathematical model of the whole process from the DC commutation failure caused by the AC fault at the receiving end to its recovery is established, that is, assuming that the rated DC power is P d-1 , commutation failure causes the DC power to drop to P d-2 , and maintain this value before the AC fault is removed. Finally, the ramp function is used to characterize the DC power recovery process after the fault is removed. The DC power mathematical model is expressed as:

[0114]

[0115] Among them, t0 is the time when the AC fault occurs, t c is the AC fault removal time, k d Characterizes the DC power recovery speed.

[0116] For EHV / UHV networks, DC lines affect power angle stability by injecting active power to change the power flow distribution. G About power angle δ G DC power P d The expression of the relative power angle difference can be obtained by solving the second-order differential equation, and then the influence trend of the DC power recovery process on the transient stability of the system can be roughly determined. To this end, this application adopts the following two simplified assumptions: the DC model is regarded as a power injection model in a short period of time after the fault is cleared; and the DC power flow model is used for derivation.

[0117] Based on the above simplified assumptions, the following relationship can be obtained:

[0118]

[0119] Among them, P G is the set of generator nodes, P L is a set of load nodes, where the inverter station node is considered as part of the load node, B GG , B GL , B LG and B LL are the corresponding susceptance matrices, δ G is the power angle of the synchronous generator, δ L is the phase angle of the load node.

[0120] In the embodiment of the present application, it also includes: according to the power external characteristics of the DC commutation failure and its recovery process, a DC power mathematical model of the whole process from the DC commutation failure caused by the receiving end AC fault to its recovery is established. It is assumed that the power mathematical model is regarded as a power injection model in a short time after the fault is cleared, and a DC power flow analysis model is used for derivation, which is expressed as:

[0121] P G =B GG δ G -B GL (B LL -1 (P L +B LG δ G ))

[0122] S2: According to the receiving-end system model, derive an analytical expression of the relative power angle difference of the receiving end in the process of active power recovery after DC commutation failure with respect to DC power, and obtain the influencing factors of the DC active power recovery process on the transient power angle of the receiving-end system;

[0123] In the embodiment of the present application, the fault theory is derived based on a receiving-end system model that feeds two DC loops, where group A consists of synchronous generators G1 and group B consists of synchronous generators G2, and the electromagnetic power of the synchronous generator is 0 during the fault period.

[0124] It should be noted that in the embodiment of the present application, the electromagnetic power of the synchronous generator during the fault period is an approximate value of 0.

[0125] For example, Figure 5 As shown in the figure, taking the receiving-end two-machine system fed with two DC loops as an example, considering the most serious three-phase short-circuit fault for derivation, there are:

[0126]

[0127] When P m1 / M1>P m2 / M2, the relative power angle of the receiving end will swing forward, and when P m1 / M1 <P m2 / M2, the relative power angle of the receiving end will swing in the opposite direction.

[0128] The influence of the DC recovery process on the transient power angle stability of the receiving end is further analyzed. For the two-machine system at the receiving end, its equivalent impedance diagram is as follows: Figure 6 As shown, based on the calculation formula of the generator node set, an analytical expression of the DC power of the receiving end relative power angle in the receiving end system within a short time after the fault can be obtained.

[0129] In the embodiment of the present application, the factors affecting the transient power angle of the receiving system during the DC active power recovery process include: when the AC fault at the receiving end is removed, assuming that the DC power is instantly restored, then within a short period of time after the fault, the electromagnetic power P of the synchronous generator with respect to the relative power angle of the receiving end is calculated. e1 It is expressed as:

[0130]

[0131] Where x is the electrical distance between the potential nodes in G1 and G2, and x L is the load node P L The electrical distance to the potential node in G1, δ is the relative power angle of the receiving end and δ = δ1-δ2, k dp1 and k dp2 are the electrical distances from the first DC and second DC feed-in nodes to the potential nodes within G1, respectively;

[0132] Based on the power balance, the electromagnetic power of G2 is:

[0133] P e2 =P L -P e1 -Pd1 -P d2

[0134] Based on the electromagnetic power of the synchronous generator, the receiving system model is rewritten as:

[0135]

[0136]

[0137]

[0138] Wherein, m is the inertia ratio, and is defined as m=M1 / (M1+M2).

[0139] In an optional embodiment, by Figure 4 It can be seen that after the AC fault at the receiving end is removed, there is a power recovery process of about 100ms after the DC commutation fails. In this short period of time, the electromagnetic power P of G1 is e1d It can be expressed as:

[0140]

[0141] Then the electromagnetic power P of G2 is e2d for

[0142] P e2d =P L -P e1d -P d1 ramp(k d1 ,tt c )(1-k dp1 )

[0143] -P d2 ramp(k d2 ,tt c )(1-k dp2 )

[0144] From the electromagnetic power of G1 and G2, we can get P Eed for:

[0145]

[0146] Also because

[0147] P Md =P M =P m1 -m(P L -P d1 -P d2 )

[0148] During the recovery process:

[0149]

[0150] In the embodiment of the present application, it also includes: after the receiving end AC fault is removed, there is a power recovery process with a time scale after the actual DC commutation fails, and the relative power angle difference in the DC active power recovery process is:

[0151]

[0152] Where Δδ=δ d -δ; the calculation solution of the relative power angle difference is obtained by its special solution (Δδ p (tt c )) and its corresponding homogeneous equation general solution (Δδ g (tt c )) is composed of, specifically, expressed as:

[0153] Δδ(tt c )=Δδ p (tt c )+Δδ g (tt c )

[0154] One of the particular solutions and its corresponding general solution to the homogeneous equation is:

[0155]

[0156] because The analytical solution of the relative power angle difference is:

[0157]

[0158] Furthermore, the relative power angle about ramp i The derivative is:

[0159]

[0160] In the embodiment of the present application, it can be seen from the swing direction of the relative power angle of the receiving end caused by the AC fault at the receiving end and the relative power angle derivation process that when the relative power angle of the receiving end swings in the positive direction, if k dpi +m-1>0, the rapid recovery of DC i is beneficial to the transient stability of the receiving system; if k dpi +m-1<0, the rapid recovery of DC i is not conducive to the transient stability of the receiving system;

[0161] When the receiving end is swung in the opposite direction relative to the power angle, if k dpi +m-1>0, the rapid recovery of DC i is not conducive to the transient stability of the receiving system; if k dpi +m-1<0, the rapid recovery of DC i is beneficial to the transient stability of the receiving system.

[0162] It should be noted that for the multi-machine system at the receiving end, although the dynamic equation of its synchronous generator cannot obtain an analytical solution to the relative power angle difference, the conclusion derived based on the two-machine system at the receiving end is still applicable.

[0163] In the embodiment of the present application, combined with the transient stability recovery of the receiving system, when the receiving system has n g When the number of generator nodes is n, the dynamic equation of the synchronous generator is g About n g Dimensional variable δ G The second-order differential equations of the receiving-end multi-machine system are composed of:

[0164]

[0165] Among them, n g is the number of generator nodes, and n g >2, n1 is the number of load nodes,

[0166] If the node of the lth DC feed-in is j, based on the receiving-end multi-machine system model and the grouping of the receiving-end multi-machine system, we can obtain:

[0167]

[0168] S3: Based on the regulation characteristics of the inverter-side DC controller and the DC power flow analysis model, factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure are obtained;

[0169] In the embodiment of the present application, the factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure include: based on the power exchange relationship between the DC inverter station and the receiving-end AC system;

[0170] For example, Figure 7 Taking a single DC feed-in receiving system as an example, the power exchange between the DC inverter station and the receiving AC system has the following relationship:

[0171]

[0172] Among them, P aci and Q aci Inject active and reactive power of the inverter station into the receiving system, Q ci The reactive power generated by the reactive power compensation equipment in the station.

[0173] In the embodiment of the present application, during the DC system recovery process after the AC fault is cleared, the commutation bus voltage amplitude U li It is expressed as:

[0174]

[0175] Among them, U aci is the voltage amplitude of the equivalent bus Bus-aci of the receiving system, ΔU and ΔU′ are the longitudinal and transverse components of the voltage drop, respectively, r aci and x aci are the equivalent resistance and reactance between Bus-aci and Bus-i, P aci and Q aci Inject active and reactive power of the inverter station into the receiving system;

[0176] The commutation bus voltage amplitude U is obtained li About Q di The decoupling relationship is as follows: it is assumed that the line resistance and the voltage drop transverse component caused by active power are ignored; the commutation bus voltage amplitude U li Rewritten as:

[0177]

[0178] Assume U aci Constant, for U li About Q di Taking partial derivatives we get:

[0179]

[0180] It should be noted that by li About Q di The partial derivative shows that the inverter station bus voltage will change with the reactive power Q consumed. di Assuming the inverter station voltage U li It is known from the DC power flow analysis model that during the recovery process, Q di Related to the turn-off angle γ and DC current I di Further according to Figure 8 As shown, its controller contains a PI link, which leads to γ ​​and I di The recovery process has overshoot characteristics, which ultimately leads to the Q di It also has overshoot characteristics, such as Fig. 9 As shown, during the recovery process after the commutation failure, the maximum reactive power consumption of the inverter station will exceed 1.1 times of the rated reactive power consumption. This will cause the inverter station to convert from sending reactive power to the AC system to absorbing reactive power to the AC system during the recovery process, weakening the voltage stability of the receiving system.

[0181] For multi-infeed DC receiving-end AC systems, in order to characterize the voltage mutual influence level between the commutation buses on the multi-infeed DC inverter side, a multi-infeed interaction factor is introduced. For the inverter-side commutation buses i and j, the interaction factor F between the two nodes is MIFji is defined as:

[0182]

[0183] If F MIFji <0.15, it means that the voltages between the inverter-side commutation buses i and j have a weak mutual influence; if F MIFji ≥0.15, it means that the voltages between the inverter-side commutation buses i and j have a strong influence on each other.

[0184] It should be noted that when the multi-input interaction factor between the two-input DC is large and commutation failure occurs at the same time, according to theoretical analysis, in the recovery process after the commutation failure, multiple inverter stations will absorb a large amount of reactive power to the AC system at the same time during the recovery process, seriously threatening the voltage stability in the vicinity of the converter station of the receiving system.

[0185] S4: forming a recovery control strategy after multiple DC commutation failures based on the analysis of the factors affecting the voltage stability of the receiving system during the reactive power recovery process and the factors affecting the transient power angle of the receiving system during the DC active power recovery process;

[0186] In the embodiment of the present application, for a multi-input DC receiving system, when a serious AC fault occurs and causes multiple DC circuits to fail to switch simultaneously, the impact of DC recovery on the transient power angle stability and voltage stability of the receiving system is comprehensively considered to determine the coordinated recovery strategy of multiple DC circuits, such as Fig.10 As shown;

[0187] The short-circuit ratio is further used to characterize the strength of the AC system at the receiving end, that is, R SCR >3 represents a strong receiving system, R SCR ≤3 represents a weak receiving system. In the scenario where DC is fed into a weak AC system, the DC may fail to commutate again during the recovery process. To prevent the DC from failing to commutate again during the recovery process after the AC fault is removed, it is assumed that the turn-off angle γ error provided by the system is within an acceptable range during this period. Figure 8 The inverter station DC controller shown in the figure is based on the proposed Fig.11 The additional control strategy shown in the figure is used when the measured cut-off angle γ is lower than the set value γ set When the original leading trigger angle δ i An angle G3 (γ set -γ), increasing the commutation margin and reducing the risk of re-commutation failure; since the additional control strategy is put into use after the AC fault is removed, the signal of whether the AC fault at the receiving end is removed can be provided by the protection device, and the setting value γ in this application set Calculated as γ set =γ lim =0.5(γ0+γ min ), where γ0 is the rated cut-off angle, γ min is the critical turn-off angle;

[0188] Based on the analysis of the transient power angle stability of the receiving system, the order of DC restoration is determined; the DC that is beneficial to the transient power angle stability is restored normally, while the DC that is not beneficial to the stability needs to be restored slowly; for the DC in the F MIFji The DC recovery of ≥0.15 is further ranked, i.e. the favorable DC set, according to the electrical distance of the feed-in location The smaller the electrical distance, the slower the recovery should be; for unfavorable DC sets, the larger the electrical distance, the slower the recovery should be;

[0189] The slow recovery time difference between different recovery sets is set to ensure that the DC is restored as planned. At the same time, the recovery speed after DC commutation failure is controlled by adjusting the time constant of the low-voltage current limiting control to achieve orderly slow recovery.

[0190] For example, on the one hand, according to the mentioned influencing factors, it is necessary to coordinate multiple DC to recover in the prescribed order; on the other hand, it is also necessary to ensure that the DC power is restored to the rated value as soon as possible. Figure 4 From the simulation results of commutation failure shown in the figure, it can be seen that the DC power recovery process after AC fault removal lasts about 100ms. In summary, the slow recovery time difference of different DC recovery sets can be set to about 50ms. In addition, since the recovery process after DC commutation failure is mainly affected by low-voltage current limiting control, the recovery speed after DC commutation failure can be sensitively changed by increasing the time constant T1, thereby achieving slow recovery of DC.

[0191] The above is a schematic scheme of a coordinated recovery control method after a DC simultaneous commutation failure in this embodiment. It should be noted that the technical scheme of the coordinated recovery control system after a DC simultaneous commutation failure and the technical scheme of the coordinated recovery control method after a DC simultaneous commutation failure described above belong to the same concept. For details not described in detail in the technical scheme of the coordinated recovery control system after a DC simultaneous commutation failure in this embodiment, please refer to the description of the technical scheme of the coordinated recovery control method after a DC simultaneous commutation failure described above.

[0192] In this embodiment, a coordinated recovery control system after a DC simultaneous commutation failure includes:

[0193] A model building module, used to establish a system analysis model based on an actual power system, wherein the system analysis model includes a receiving-end system model and a DC power flow analysis model;

[0194] An active power analysis module is used to derive an analytical expression of the relative power angle difference of the receiving end in the active power recovery process after the DC commutation failure according to the receiving end system model, and obtain the influencing factors of the DC active power recovery process on the transient power angle of the receiving end system;

[0195] A reactive power analysis module, which is used to obtain, based on the regulation characteristics of the inverter-side DC controller and the DC power flow analysis model, factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure;

[0196] The collaborative recovery control strategy formulation module is used to form a recovery control strategy after multiple DC commutation failures based on the analysis of the factors affecting the voltage stability of the receiving system during the reactive power recovery process and the factors affecting the transient power angle of the receiving system during the DC active power recovery process.

[0197] This embodiment further provides a computing device, which is applicable to the coordinated recovery control method after a DC simultaneous commutation failure, and includes:

[0198] A memory and a processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement the coordinated recovery control method after the failure of DC simultaneous commutation as proposed in the above embodiment.

[0199] This embodiment also provides a storage medium on which a computer program is stored. When the program is executed by a processor, the coordinated recovery control method after the failure of simultaneous DC commutation as proposed in the above embodiment is implemented.

[0200] The storage medium proposed in this embodiment and the collaborative recovery control method after DC simultaneous commutation failure proposed in the above embodiment belong to the same inventive concept. The technical details not fully described in this embodiment can be referred to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0201] Through the above description of the implementation methods, the technicians in the relevant field can clearly understand that the present invention can be implemented by means of software and necessary general hardware, and of course can also be implemented by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ReadOnly, Memory, ROM), random access memory (RandomAccess Memory, RAM), flash memory (FLASH), hard disk or optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform the methods of various embodiments of the present invention.

[0202] Example 2

[0203] Reference Figure 12 to Figure 15 , is an embodiment of the present invention. This embodiment is different from the first embodiment in that this embodiment verifies the beneficial effects of the present invention through simulation experiments.

[0204] This embodiment is based on the IEEE-68 node system and builds the following in ADPSS: Fig.12 The electromechanical-electromagnetic hybrid simulation model of the multi-DC-fed AC receiving system is shown in Figure 1. Fig.12 It can be seen that the system consists of two regional power grids, the New England System and the New York System, and the two regional power grids are connected by four tie lines, forming two natural complementary groups, denoted as 'A' and 'B' groups. Group A includes synchronous generators G1-G9, and Group B includes synchronous generators G 10 -G 16 At the same time, the receiving system feeds three DC lines, DC1, DC2 and DC3, and R SCR1 =5.02, R SCR2 =2.68 and R SCR3 =3.70, which indicates that the AC system near the receiving end fed by DC1 and DC3 is strong enough, while the AC system near the receiving end fed by DC2 is not strong enough. During the recovery process, it is necessary to prevent the recurrence of commutation failure due to too fast recovery speed. Therefore, the electromechanical models of the AC system and DC1 and DC3 were built in PSASP, and the electromagnetic model of DC2 was built in ETSDAC.

[0205] Further calculations show that m = 0.346, k dpE1 =0.14, k dpE2 = 0.22 and k dpE3 =0.14, the interaction factor between the two nodes is calculated to obtain F MIIF12 =0.70, F MIIF13 = 0.50 and F MIIF23 =0.30. For DC2 fed into the weak receiving end system. The correctness and effectiveness of the proposed theoretical analysis and coordinated control strategy are verified in different scenarios. Based on the above analysis, the following two recovery control strategies after simultaneous commutation failure of multiple DCs are defined:

[0206] Strategy 1: Simultaneous recovery, i.e. T 11 =0.04s, T 12 =0.04s, T 13 =0.04s;

[0207] Strategy 2: Adopt the proposed collaborative recovery control strategy, namely T 11 =0.08s, T 12 =0.04s, T 13 =0.06s or T 11 =0.04s, T 12 =0.08s, T 13 =0.06s.

[0208] 1) Additional control strategy simulation verification

[0209] In order to verify the effectiveness of the proposed additional control strategy in suppressing commutation failure in the recovery process of DC after AC fault removal, a three-phase short circuit fault is set at Bus-18. The simulation results with and without the proposed additional control strategy are shown in Figure 2. Fig.13 shown.

[0210] Depend on Fig.13 From the blue curves in (a) and (b), we can see that the AC fault at the receiving end caused the DC commutation failure, and the commutation failure occurred again during the recovery process after the AC fault was removed. Fig.13 From the red curves in (a) and (b), it can be seen that the adoption of the proposed additional control strategy during the recovery process suppresses the commutation failure of the DC during the recovery process, which verifies the effectiveness of the proposed additional control strategy.

[0211] 2) Simulation verification of collaborative recovery control strategy

[0212] Under the premise of ensuring that no commutation failure occurs during the recovery process of DC after AC fault removal, the following fault scenarios are set to verify the correctness and effectiveness of the proposed coordinated recovery control strategy.

[0213] Scenario 1: A single-phase short-circuit grounding fault is set at Bus-68. The simulation comparison results with and without the proposed collaborative recovery control strategy are shown in Figure 1. Fig.14 shown.

[0214] Depend on Fig.14 (a), (b), (c) and (d) show that the AC fault at the receiving end causes multiple DC commutation failures at the same time, and further Fig.14 (e) It can be seen that after the fault occurs, the receiving end relative power angle swings in the opposite direction. Based on theoretical analysis, it can be seen that in this scenario, the coordinated recovery strategy is that DC1 recovers normally, and DC3 and DC2 recover slowly for one and two time levels respectively, as shown in Figure 2. Fig.14 (d) is shown by the red and blue curves. Fig.14 By comparing the blue and red curves in (e), it can be seen that when the proposed coordinated recovery strategy is adopted, the relative power angle first swing amplitude of the receiving end decreases by nearly 2°, which improves the transient power angle stability of the receiving end system. Fig.14 Comparison of the blue and red curves in (f) shows that when the proposed coordinated recovery strategy is adopted, the minimum bus voltage at Bus-18 increases by 0.14 pu during the recovery process, which improves the voltage stability of the receiving system. Fig.14 The simulation comparison results verify the correctness of the proposed theoretical analysis and the effectiveness of the collaborative recovery control strategy.

[0215] Scenario 2: A three-phase short circuit fault is set at Bus-18. The simulation comparison results with and without the proposed collaborative recovery control strategy are shown in Figure 2. Fig.15 shown.

[0216] Depend on Fig.15 (a), (b), (c) and (d) show that the AC fault at the receiving end causes multiple DC commutation failures at the same time, and further Fig.15 (e) It can be seen that after the fault occurs, the receiving end relative power angle swings forward. Based on theoretical analysis, it can be seen that in this scenario, the coordinated recovery strategy is that DC2 recovers normally, and DC3 and DC1 recover slowly for one and two time levels respectively. Fig.15 By comparing the blue and red curves in (e), it can be seen that when the proposed coordinated recovery strategy is adopted, the relative power angle first swing amplitude of the receiving end decreases by 3°, which improves the transient power angle stability of the receiving end system. Fig.15 From the comparison of the blue and red curves in (f), it can be seen that when the proposed coordinated recovery strategy is adopted, the minimum bus voltage at Bus-18 is increased by 0.02pu during the recovery process because the commutation failure is avoided, which improves the voltage stability of the receiving system. Fig.14 and Fig.15 The simulation comparison results further verify the correctness of the proposed theoretical analysis and the effectiveness of the collaborative recovery control strategy.

[0217] Furthermore, different types of faults are set at different locations near the converter station of the receiving system, and multiple DC commutation failures are caused at the same time. The simulation comparison results are shown in Table 1, where f (1) 、f (2) and f (3) They are single-phase grounding fault, two-phase short circuit fault and three-phase short circuit fault respectively.

[0218] Table 1 Comparison of simulation results under different fault locations and fault types

[0219]

[0220] From the comparative simulation results shown in Table 1, it can be seen that after adopting the proposed coordinated recovery control strategy after simultaneous commutation failure of multiple DC systems, the transient power angle and voltage stability of the receiving system have been improved to varying degrees, which not only verifies the correctness of the proposed theoretical analysis, but also verifies the effectiveness of the proposed coordinated recovery control strategy.

[0221] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A coordinated recovery control method after a DC simultaneous commutation failure, characterized in that: include: Establishing a system analysis model based on an actual power system, wherein the system analysis model includes a receiving-end system model and a DC power flow analysis model; According to the receiving-end system model, an analytical expression of the relative power angle difference of the receiving end in the process of active power recovery after DC commutation failure is derived with respect to DC power, and the influencing factors of the DC active power recovery process on the transient power angle of the receiving-end system are obtained; Based on the regulation characteristics of the inverter-side DC controller, the factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure are obtained according to the DC power flow analysis model; Based on the analysis of the factors affecting the voltage stability of the receiving system during the reactive power recovery process and the factors affecting the transient power angle of the receiving system during the DC active power recovery process, a recovery control strategy after multiple DC commutation failures is formed.

2. The coordinated recovery control method after DC simultaneous commutation failure according to claim 1, characterized in that: include: The receiving-end system model uses the complementary group inertia center-relative motion theory to simplify the multi-machine system of the multi-input DC receiving end into a two-group machine system, and obtains the equivalent model of the receiving-end multi-machine system. The equivalent model of the receiving-end multi-machine system is then converted into a single-machine infinite system model, which is expressed as: Among them, P mA and P mB are the total mechanical input power of groups A and B, P eA and P eB are the total electromagnetic output power of groups A and B, M A and M B are the total inertia of groups A and B, δ E =δ A -δ B is the relative power angle between groups A and B, δ A and δ B are the equivalent power angles of groups A and B respectively; The DC power flow analysis model is based on a high-voltage DC transmission system of a line converter, and the relationship between the voltage, current, DC power and reactive power of the inverter station in the model is expressed as: Among them, U di and I di are DC voltage and current respectively, N p is the number of bridges, x i is the equivalent commutation reactance, k i is the transformer ratio, U li is the commutation bus voltage, Q di is the DC power and reactive power consumed by the converter station, U di0 is the no-load DC voltage of the inverter station, is the power factor, P di is the i-th DC power fed into the receiving system, and γ is the cut-off angle.

3. The coordinated recovery control method after DC simultaneous commutation failure according to claim 2, characterized in that: It also includes: according to the power external characteristics of the DC commutation failure and its recovery process, a DC power mathematical model of the whole process from the DC commutation failure caused by the AC fault at the receiving end to its recovery is established. It is assumed that the power mathematical model is regarded as a power injection model in a short time after the fault is cleared, and the DC power flow analysis model is used for derivation, which is expressed as: P G =B GG d G -B GL (B LL - 1 (P L +B LG d G )) Among them, P G is the set of generator nodes, P L is a set of load nodes, where the inverter station node is considered as part of the load node, B GG , B GL , B LG and B LL are the corresponding susceptance matrices, δ G is the power angle of the synchronous generator.

4. The coordinated recovery control method after DC simultaneous commutation failure according to claim 3 is characterized in that: The factors affecting the transient power angle of the receiving system during the DC active power recovery process include: the fault theory is derived based on the receiving system model with two DC loops fed in, group A consisting of synchronous generator G1 and group B consisting of synchronous generator G2, and the electromagnetic power of the synchronous generator is 0 during the fault period; When the AC fault at the receiving end is removed, assuming that the DC power is restored instantaneously, the electromagnetic power P of the synchronous generator with respect to the relative power angle at the receiving end is calculated within a short period of time after the fault. e1 It is expressed as: Where x is the electrical distance between the potential nodes in G1 and G2, and x L is the load node P L The electrical distance to the potential node in G1, δ is the relative power angle of the receiving end and δ = δ1-δ2, k dp1 and k dp2 are the electrical distances from the first DC and second DC feed-in nodes to the potential nodes within G1, respectively; Based on the power balance, the electromagnetic power of G2 is: P e2 =P L -P e1 -P d1 -P d2 Based on the electromagnetic power of the synchronous generator, the receiving system model is rewritten as: Wherein, m is the inertia ratio, and is defined as m=M1 / (M1+M2).

5. The coordinated recovery control method after DC simultaneous commutation failure according to claim 4, characterized in that: Also includes: After the AC fault at the receiving end is removed, there is a time-scale power recovery process after the actual DC commutation fails. The relative power angle difference in the DC active power recovery process is: Where Δδ=δ d -δ; the calculation solution of the relative power angle difference is obtained by its special solution (Δδ p (tt c )) and its corresponding homogeneous equation general solution (Δδ g (tt c ))constitute; because Relative power angle about ramp i The derivative is: When the receiving end is swung away from the power angle in the positive direction, if k dpi +m-1>0, the rapid recovery of DC i is beneficial to the transient stability of the receiving system; if k dpi +m-1<0, the rapid recovery of DC i is not conducive to the transient stability of the receiving system; When the receiving end is swung in the opposite direction relative to the power angle, if k dpi +m-1>0, the rapid recovery of DC i is not conducive to the transient stability of the receiving system; if k dpi +m-1<0, the rapid recovery of DC i is beneficial to the transient stability of the receiving system; Combined with the transient stability recovery of the receiving system, when the receiving system has n g When the number of generator nodes is n, the dynamic equation of the synchronous generator is g About n g Dimensional variable δ G The second-order differential equations of the receiving-end multi-machine system are composed of: Among them, n g is the number of generator nodes, and n g >2, n1 is the number of load nodes, If the node of the lth DC feed-in is j, based on the receiving-end multi-machine system model and the grouping of the receiving-end multi-machine system, we can obtain:

6. The coordinated recovery control method after DC simultaneous commutation failure according to claim 5, characterized in that: The factors affecting the voltage stability of the receiving system during the reactive power recovery process after the DC commutation failure include: Based on the power exchange relationship between the DC inverter station and the receiving AC system, during the DC system recovery process after the AC fault is cleared, the commutation bus voltage amplitude U li It is expressed as: Among them, U aci is the voltage amplitude of the equivalent bus Bus-aci of the receiving system, ΔU and ΔU′ are the longitudinal and transverse components of the voltage drop, respectively, r aci and x aci are the equivalent resistance and reactance between Bus-aci and Bus-i, P aci and Q aci Inject active and reactive power of the inverter station into the receiving system; The commutation bus voltage amplitude U is obtained li About Q di The decoupling relationship is as follows: it is assumed that the line resistance and the voltage drop transverse component caused by active power are ignored; the commutation bus voltage amplitude U li Rewritten as: Assume U aci Constant, for U li About Q di Taking partial derivatives we get: For multi-infeed DC receiving-end AC systems, in order to characterize the voltage mutual influence level between the commutation buses on the multi-infeed DC inverter side, a multi-infeed interaction factor is introduced. For the inverter-side commutation buses i and j, the interaction factor F between the two nodes is MIFji is defined as: If F MIFji <0.15, it means that the voltages between the inverter-side commutation buses i and j have a weak mutual influence; if F MIFji ≥0.15, it means that the voltages between the inverter-side commutation buses i and j have a strong influence on each other.

7. The coordinated recovery control method after DC simultaneous commutation failure according to claim 6, characterized in that: The recovery control strategy after the analysis of multiple DC commutation failures includes: The short-circuit ratio is used to characterize the strength of the receiving-end AC system, i.e., R SCR >3 represents a strong receiving system, R SCR ≤3 represents a weak receiving end system, in which an additional control strategy is introduced; When the measured cut-off angle γ is lower than the set value γ set When the original leading trigger angle β i An angle G3 (γ set -γ), increase the commutation margin and reduce the risk of re-commutation failure; set the value γ set Calculated as γ set =γ lim =0.5(γ0+γ min ), where γ0 is the rated cut-off angle, γ min is the critical turn-off angle; Based on the analysis of the transient power angle stability of the receiving system, the order of DC restoration is determined; the DC that is beneficial to the transient power angle stability is restored normally, while the DC that is not beneficial to stability needs to be restored slowly; for the favorable DC set, the DC is restored according to the electrical distance of the feeding position. The smaller the electrical distance, the slower the recovery should be; for unfavorable DC sets, the larger the electrical distance, the slower the recovery should be; The slow recovery time difference between different recovery sets is set to ensure that the DC is restored as planned. At the same time, the recovery speed after DC commutation failure is controlled by adjusting the time constant of the low-voltage current limiting control to achieve orderly slow recovery.

8. A coordinated recovery control system after a DC simultaneous commutation failure, characterized in that: include: A model building module, used to establish a system analysis model based on an actual power system, wherein the system analysis model includes a receiving-end system model and a DC power flow analysis model; An active power analysis module is used to derive an analytical expression of the relative power angle difference of the receiving end in the active power recovery process after the DC commutation failure according to the receiving end system model, and obtain the influencing factors of the DC active power recovery process on the transient power angle of the receiving end system; A reactive power analysis module, which is used to obtain, based on the regulation characteristics of the inverter-side DC controller and the DC power flow analysis model, factors affecting the voltage stability of the receiving-end system during the reactive power recovery process after the DC commutation failure; The collaborative recovery control strategy formulation module is used to form a recovery control strategy after multiple DC commutation failures based on the analysis of the factors affecting the voltage stability of the receiving system during the reactive power recovery process and the factors affecting the transient power angle of the receiving system during the DC active power recovery process.

9. An electronic device, comprising: Memory and processor; The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the coordinated recovery control method after the simultaneous DC commutation failure described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the coordinated recovery control method after simultaneous DC commutation failure as described in any one of claims 1 to 7.

Images