A coordinated recovery control method and system after direct current simultaneous commutation failure

Abstract

The application discloses a kind of direct current simultaneous commutation failure after coordinated recovery control method and system, comprising: by analyzing the influence factor of multiple feed-in direct current simultaneous commutation failure on the transient power angle stability and voltage stability of receiving terminal system, determine the influence of active recovery process after direct current commutation failure on the transient power angle stability of receiving terminal can be determined by the relative power angle swing direction of receiving terminal, inertia ratio and direct current feed-in position;The recovery process of reactive power after direct current commutation failure will further consume a large amount of reactive power on the basis of rated due to its overshoot characteristic, for the multiple direct current simultaneous recovery of multiple feed-in interaction factor greater than 0.15 will deteriorate the voltage stability of receiving terminal, based on the analysis of influence factor, through the recovery control strategy of coordinated multiple direct current, the transient power angle stability and voltage stability of receiving terminal system can be effectively improved in different fault location and fault type scene, and the safe and stable operation level of receiving terminal system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system stability control, and particularly relates to a coordinated recovery control method and system after DC simultaneous commutation failure. BACKGROUND

[0002] In recent years, with the application of new energy and extra-high voltage lines, a regional power grid will be built into a "day" type extra-high voltage AC loop network, and some provinces will also feed in two or even three extra-high voltage DC lines, forming a DC group. On the one hand, the AC-DC system and the coupling between the converter stations are serious, and the risk of multiple DCs simultaneously commutation failure caused by the fault of the receiving end AC system is rising; on the other hand, the fault of the extra-high voltage large channel has a more and more prominent impact on the transient power angle and voltage of the system, which seriously threatens the safe and stable operation of the large-scale AC-DC hybrid power grid. Therefore, it is necessary to deeply study the influence of multiple DCs simultaneously commutation failure on the transient stability of the receiving end system and propose an effective method to improve the transient stability of the system.

[0003] Existing researches on DC commutation failure and its influencing factors have been extensive and in-depth; in terms of the mechanism of DC commutation failure, the main reasons for the DC commutation failure caused by the fault of the receiving end AC system are summarized, which are divided into voltage amplitude reduction, zero crossing point offset and waveform distortion; from the mutual interaction of external AC fault and internal DC controller, the mechanism of subsequent commutation failure during the period when the fault of the receiving end AC system has not been removed is revealed, and an improved control strategy is given. According to the limitation condition of the DC operable range, the inverter side controller is optimized and designed respectively, and the voltage stability of the receiving end system is improved by improving the system reactive power recovery characteristics. 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 the DC controller parameters on the DC recovery is theoretically analyzed. For the weak sending end system, based on the tie line capacity ratio and the power flow entropy, a system security and stability risk assessment model is established, which can accurately evaluate the influence degree of different commutation failure scenarios on the sending end system. According to the residual acceleration area of the rotor when the DC commutation failure is recovered to the steady state, the minimum deceleration area to maintain the stability of the sending end system is calculated, and the minimum generator tripping amount of the sending end system is obtained, which avoids the instability of the system. However, the influence of DC commutation failure on the receiving end transient stability is rarely studied. For the multi-infeed DC receiving end system, under the scenario of AC fault and superimposed multiple DCs simultaneously commutation failure, the influence of the DC recovery process on the receiving end transient stability is increasingly complex, and it is urgent to be deeply studied. SUMMARY

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

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

[0006] Therefore, the present application provides a coordinated recovery control method and system after DC simultaneous commutation failure to solve the problem of poor system transient power angle and voltage stability caused by simultaneous recovery of multiple DCs after simultaneous commutation failure of multiple DCs in a multi-infeed receiving end system due to faults in the receiving end AC system.

[0007] To solve the above technical problems, the present application provides the following technical solutions.

[0008] In a first aspect, the embodiments of the present application provide a coordinated recovery control method after 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 active power recovery process after DC commutation failure is derived, and the influence 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 influence factors of the reactive power recovery process on the voltage stability of the receiving end system are obtained according to the DC power flow analysis model;

[0011] Based on the influence factors of the reactive power recovery process on the voltage stability of the receiving end system and the influence factors of the DC active power recovery process on the transient power angle of the receiving end system, a recovery control strategy after DC commutation failure is formed.

[0012] As a preferred scheme of the coordinated recovery control method after DC simultaneous commutation failure, the receiving end system model simplifies the multi-infeed DC receiving end multi-machine system into a two-group machine system using the complementary group inertia center-relative motion theory to obtain an equivalent model of the receiving end multi-machine system, and the equivalent model of the receiving end multi-machine system is converted into a single-machine infinite system model, which is represented as:

[0013]

[0014]

[0015]

[0016]

[0017] Among them, P mA and P mB The total mechanical input power P for groups A and B are respectively. eA and P eB M represents the total electromagnetic output power of groups A and B, respectively. A and M B Let δ be the total inertia of groups A and B, respectively. E =δ A -δ B δ is the relative work angle between groups A and B. A and δ B These are the equivalent angles of energy for groups A and B, respectively.

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

[0019]

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

[0021] As a preferred embodiment of the coordinated recovery control method after simultaneous DC commutation failure described in this invention, it further includes: establishing a DC power mathematical model of the entire process from DC commutation failure caused by a receiving-end AC fault to its recovery, based on the power external characteristics of the DC commutation failure and its recovery process. Assuming that the power mathematical model is considered as a power injection model for a short period after fault clearance, the model is derived using a DC power flow analysis model, expressed as:

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

[0023] where P G is the generator node set, P L is the load node set, where the inverter station node is considered as part of the load node set, 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 DC simultaneous commutation failure according to the application, the factors affecting the transient power angle of the receiving end system in the DC active recovery process include: fault theory derivation is performed on a receiving end system model in which two DCs are fed in, a group G1 is composed of synchronous generators G1, and a group G2 is composed of synchronous generators G2, and the electromagnetic power of the synchronous generator is 0 during the fault;

[0025] When the receiving end AC fault is removed, it is assumed that the DC power is instantaneously restored, and in a short time after the fault, the electromagnetic power P e1 of the synchronous generator about the receiving end relative power angle δ is calculated and expressed as:

[0026]

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

[0028] Based on power balance, the electromagnetic power P e2 of G2 can be obtained as:

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

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

[0031]

[0032]

[0033]

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

[0035] As a preferred scheme of the coordinated recovery control method after DC simultaneous commutation failure, the method further comprises: after the AC fault is removed at the receiving end, there is a time scale of power recovery process after the actual DC commutation failure, and there is a relative power angle difference in the DC active power recovery process, which is:

[0036]

[0037] Wherein, Δδ = δ d -δ; the calculation solution of the relative power angle difference is composed of its particular solution (Δδ p (t-t c )) and its corresponding homogeneous equation general solution (Δδ g (t-t c ));

[0038] Because

[0039] The derivative of the relative power angle with respect to ramp i can be obtained as:

[0040]

[0041] When the relative power angle of the receiving end is positively opened, if k dpi +m-1>0, the fast recovery of the DC i is beneficial to the transient stability of the receiving end system; if k dpi +m-1<0, the fast recovery of the DC i is not conducive to the transient stability of the receiving end system.

[0042] When the relative power angle of the receiving end is reversely opened, if k dpi +m-1>0, the fast recovery of the DC i is not conducive to the transient stability of the receiving end system; if k dpi +m-1<0, the fast recovery of the DC i is beneficial to the transient stability of the receiving end system.

[0043] Combined with the transient stability recovery of the receiving end system, when there are n g generator nodes in the receiving end system, the dynamic equation of the synchronous generator is composed of n g second-order differential equations about n g dimensional variables δ G , and the generator node set of the receiving end multi-machine system is represented as:

[0044]

[0045] Wherein, 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 feeder is j, the following is obtained based on the multi-machine system model of the receiving end and the grouping of the multi-machine system of the receiving end:

[0047]

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

[0049]

[0050] wherein U aci is the voltage amplitude of the equivalent bus Bus-aci of the receiving end system, ΔU and ΔU' are the longitudinal component and the transverse component 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 are the active power and the reactive power injected by the inverter station of the receiving end system.

[0051] In order to obtain the voltage amplitude U li of the commutation bus, the decoupling relationship of Q di is assumed to ignore the line resistance and the transverse component of the voltage drop caused by the active power; the voltage amplitude U li of the commutation bus is rewritten as:

[0052]

[0053] Assuming that U aci is constant, the partial derivative of U li with respect to Q di is obtained as:

[0054]

[0055] For a multi-infeed DC receiving end AC system, in order to depict the voltage mutual influence level between the commutation buses of the inverter side of the multi-infeed DC, a multi-infeed interaction factor is introduced, and for the commutation buses i and j of the inverter side, the definition of the interaction factor F MIFji between the two nodes is:

[0056]

[0057] If F MIFji <0.15, it indicates that the voltage mutual influence between the commutation buses i and j of the inverter side is weak; if FMIFji ≥0.15, indicates that the voltage of the inverter side commutation bus i and j has a strong mutual influence.

[0058] As a preferred scheme of the coordinated recovery control method after DC simultaneous commutation failure, the analysis of the recovery control strategy after multiple DC commutation failures comprises:

[0059] The strength of the receiving end AC system is represented by the short-circuit ratio, i.e., R SCR > 3 represents a strong receiving end system, and R SCR ≤ 3 represents a weak receiving end system, and an additional control strategy is introduced under the weak receiving end system;

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

[0061] Based on the analysis of the transient power angle stability of the receiving end system, the order of DC recovery is determined; the DCs that are beneficial to the transient power angle stability are normally recovered, while the DCs that are not beneficial to the stability need to be slowly recovered; for the set of beneficial DCs, the smaller the electrical distance |k dpDi +m-1| is, the slower the recovery should be; for the set of non-beneficial DCs, the larger the electrical distance is, the slower the recovery should be;

[0062] The slow recovery time difference between different recovery sets is set to ensure that the DCs are recovered according to the plan, and 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 application provides a coordinated recovery control system after DC simultaneous commutation failure, comprising:

[0064] A model building module is configured to build a system analysis model based on an actual power system, wherein the system analysis model comprises a receiving end system model and a DC power flow analysis model;

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

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

[0067] A coordinated recovery control strategy formulation module is configured to analyze factors affecting voltage stability of the receiving end system during the reactive power recovery process and factors affecting transient power angle of the receiving end system during a DC active power recovery process to form a recovery control strategy after the multiple DC commutation failures.

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

[0069] a memory and a processor;

[0070] The memory is configured to store computer executable instructions, and the processor is configured to execute the computer executable instructions, so as to implement the steps of the coordinated recovery control method after the DC simultaneous commutation failure.

[0071] In a fourth aspect, the present application provides 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 the DC simultaneous commutation failure.

[0072] Compared with the prior art, the present application has the following beneficial effects: by analyzing factors affecting transient power angle stability and voltage stability of the receiving end system due to the multiple-infeed DC simultaneous commutation failure, it is determined 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 determined by the relative power angle swing direction, the inertia ratio and the DC infeed position; the reactive power recovery process after the DC commutation failure will further consume a large amount of reactive power on the basis of the rated value due to its overshoot characteristic, and for multiple DC simultaneous recovery with a multiple-infeed interaction factor greater than 0.15, the voltage stability of the receiving end will be deteriorated; based on the analysis of the influencing factors, a coordinated multiple DC recovery control strategy can effectively improve the transient power angle stability and voltage stability of the receiving end system under different fault positions and fault types, and improves the safe and stable operation level of the receiving end system. BRIEF DESCRIPTION OF DRAWINGS

[0073] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

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

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

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

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

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

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

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

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

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

[0083] Figure 10 A coordinated recovery strategy diagram of a coordinated recovery control method and system after DC simultaneous commutation failure according to an embodiment of the present application;

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

[0085] Figure 12 An IEEE-68 node system diagram of a multi-infeed DC for a simultaneous commutation failure after recovery control method and system of a DC according to an embodiment of the present application;

[0086] Figure 13 A simulation result diagram of a simultaneous commutation failure after recovery control method and system of a DC according to an embodiment of the present application; wherein, Figure 13 (a) is a B-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle; Figure 13 (a) is a B-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle;

[0087] Figure 14 A simulation result diagram of a simultaneous commutation failure after recovery control method and system of a DC according to an embodiment of the present application; wherein, Figure 14 (a) is a C-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 14 (a) is a C-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 14 (a) is a C-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 14 (a) is a C-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 14 (a) is a C-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 14 (a) is a C-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle;

[0088] Figure 15 A simulation result diagram of a simultaneous commutation failure after recovery control method and system of a DC according to an embodiment of the present application; wherein, Figure 15 (a) is an A-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 15 (a) is an A-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 15 (a) is an A-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 15 (a) is an A-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 15 (a) is an A-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle, Figure 15 (a) is an A-phase current of a DC2 converter transformer valve side in (b) is a DC2 extinction angle. DETAILED DESCRIPTION

[0089] It should be apparent to those of ordinary skill in the art that the above-described embodiments of the present application are only a part of the embodiments of the present application, and not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor should belong to the scope of protection of the present application.

[0090] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present application.

[0091] Secondly, the "one embodiment" or "an embodiment" referred to herein means a specific feature, structure, or characteristic under discussion. Each of the various aspects presented in this description can be implemented in many different embodiments. The various aspects presented in this description are not necessarily mutually exclusive, and can be used in combination with each other. Each of the various aspects presented in this description can be used independently of each other, or in combination with each other.

[0092] The present application is described in detail below with reference to the attached drawings. To facilitate an easy understanding of the present application, the cross-sectional views of the device structure are partially enlarged without following the general proportion, and the schematic views are only examples, which should not limit the scope of protection of the present application. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in the actual manufacture.

[0093] Meanwhile, in the description of the present application, it should be noted that the terms "upper, lower, inner and outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first, second or third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0094] Unless otherwise explicitly defined and limited, the terms "mounting, connecting, connection" in the present application should be understood broadly, for example: it can be fixed connection, detachable connection or integral connection; it can also be mechanical connection, electrical connection or direct connection, it can also be indirectly connected through intermediate medium, or it can be the internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0095] Embodiment 1

[0096] Reference Figures 1-11 For one embodiment of the present application, the embodiment provides a coordinated recovery control method after DC simultaneous commutation failure, comprising:

[0097] S1: 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;

[0098] It should be noted that, for example Figure 2As shown, for multi-infeed DC receiving-end systems, a fault in the AC system near the receiving-end inverter station will cause DC commutation failure. In severe cases, multiple DC lines will fail to commutate simultaneously, seriously threatening the safe and stable operation of the receiving-end system. Ideally, the converter valves will commutate once every 60° electrical angle. However, due to the voltage drop on the converter bus caused by the AC fault at the receiving end, the converter valves may fail to close during commutation, resulting in commutation failure.

[0099] For a multi-DC feed-in receiving-end system, under the same AC fault, although the commutation times of the converter valves are different, they will not differ by 60° electrical angle. Therefore, the phenomenon that two or more DC circuits fail to commutate within a 60° electrical angle time is called simultaneous commutation failure of multiple DC circuits. If an AC fault occurs at time t0, the times when DC circuits i and j fail to commutate are t0 and t1, respectively. CFi and t CFj , and t CFi and t CFj The phase difference time does not exceed 60° electrical angle.

[0100] Furthermore, considering the actual commutation process, the conduction time of each valve is 120° + μ, where the commutation angle μ < 90°. Therefore, the valve current non-zero time t can be used as a basis for calculation. f1 Commutation failure is determined by whether the electrical angle exceeds 180°, as shown below:

[0101]

[0102] Where f0 is the system's rated frequency.

[0103] Taking into account measurement delays, a practical criterion for multiple DC commutation failures occurring simultaneously can be defined as the number N of DCs satisfying the above formula within one converter commutation cycle (1 / f0). CF ≥2.

[0104] like Figure 3 As shown, in this embodiment of the 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 a two-group machine system, namely complementary groups A and B, to obtain the equivalent model of the receiving-end multi-machine system. The equivalent model of the receiving-end multi-machine system is then transformed into a single-machine infinite system model, expressed as:

[0105]

[0106]

[0107]

[0108]

[0109] Among them, P mA and P mB The total mechanical input power P represents the total mechanical input power of groups A and B, respectively. eA and P eB M represents the total electromagnetic output power of groups A and B, respectively. A and M B Let δ be the total inertia of groups A and B, respectively. E =δ A -δ B δ is the relative work angle between groups A and B. A and δ B These are the equivalent angles of energy for groups A and B, respectively.

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

[0111]

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

[0113] In an optional embodiment, such as Figure 4 As shown, when a fault in the receiving-end AC system simultaneously triggers DC commutation failure, the DC power will drop instantaneously. From the time of DC commutation failure until the AC fault is cleared, the DC power will remain low under the regulation of the DC controller. After the AC fault is cleared, the DC power will recover to its rated value under the regulation of the DC controller. Therefore, based on the power external characteristics of DC commutation failure and its recovery process, a mathematical model of DC power is established for the entire process from receiving-end AC fault leading to DC commutation failure to its recovery, assuming the rated DC power is P. d-1 Commutation failure caused the DC power to drop to P. d-2 This value is maintained until the AC fault is cleared. Finally, the ramp function is used to characterize the DC power recovery process after the fault is cleared. The DC power mathematical model is expressed as:

[0114]

[0115] Wherein, t0 is the time when the alternating current fault occurs, t c is the time when the alternating current fault is removed, k d characterizes the direct current power recovery speed.

[0116] For the super / ultra high voltage network, the direct current line affects the power angle stability by injecting active power to change the power flow distribution. If the active power P G of the synchronous generator can be established, the expression of the power angle δ G of the direct current power P d is obtained, and then the expression of the relative power angle difference is obtained by solving the second order differential equation, the influence trend of the direct current power recovery process on the transient stability of the system can be roughly judged. Therefore, the following two simplifying assumptions are adopted in the application: the direct current model is regarded as a power injection model in a short time after the fault is removed; and the direct current power flow model is used for derivation.

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

[0118]

[0119] Wherein, P G is the generator node set, P L is the load node set, wherein the inverter station node is regarded as part of the load node, B GG , B GL , B LG and B LL are corresponding susceptance matrices, δ G is the power angle of the synchronous generator, and δ L is the phase angle of the load node.

[0120] In the embodiment of the application, the following is further included: a direct current power mathematical model of the whole process from the direct current commutation failure caused by the alternating current fault at the receiving end to the recovery of the direct current commutation failure is established according to the power external characteristics of the direct current commutation failure and the recovery process thereof, it is assumed that the power mathematical model is regarded as a power injection model in a short time after the fault is removed, and the direct current power flow analysis model is used for derivation, and 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, an analytical expression of the relative power angle difference about the direct current power in the active power recovery process after the direct current commutation failure is derived, and the influence factor of the direct current active power recovery process on the transient power angle of the receiving end system is obtained;

[0123] In this embodiment, a fault theory derivation is performed using a receiving-end system model with two DC feeds, where group A consists of synchronous generator G1 and group B consists of synchronous generator G2. During the fault, the electromagnetic power of the synchronous generators is 0.

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

[0125] For example, such as Figure 5 As shown, taking a two-machine system with two DC feeds at the receiving end as an example, considering the most severe three-phase short-circuit fault for derivation, the following exists during the fault period:

[0126]

[0127] When P m1 / M1>P m2 When / M2, the relative work angle at the receiving end will swing in the positive direction, while when P m1 / M1 <P m2 When the power angle of the receiving end is / M2, the relative power angle will swing in the opposite direction.

[0128] Further analysis is needed to determine the impact of the DC recovery process on the transient power angle stability at the receiving end. For the two-machine system at the receiving end, its equivalent impedance diagram is as follows: Figure 6 As shown, the analytical expression of the relative power angle of the receiving end system with respect to DC power in the short time after a fault can be obtained from the calculation formula based on the generator node set.

[0129] In this embodiment of the application, the factors affecting the transient power angle of the receiving-end system during the DC active power recovery process include: assuming that the DC power recovers instantaneously when the AC fault at the receiving end is cleared, the electromagnetic power P of the synchronous generator with respect to the relative power angle at the receiving end is calculated within a short time after the fault. e1 Represented as:

[0130]

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

[0132] Based on power balance, the electromagnetic power of G2 can be obtained as follows:

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

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

[0135]

[0136]

[0137]

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

[0139] In an optional embodiment, the electromagnetic power P Figure 4 It is known that after the actual receiving end AC fault is removed, there is a power recovery process of about 100 ms after the DC commutation failure, so the electromagnetic power P e1d of G1 in a short time can be expressed as:

[0140]

[0141] The electromagnetic power P e2d of G2 can be expressed as:

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

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

[0144] The electromagnetic power P Eed of G1 and G2 can be obtained as:

[0145]

[0146] Since

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

[0148] Therefore, during the recovery process, we have:

[0149]

[0150] In the embodiment of the present application, the power recovery process exists in a time scale after the AC fault is removed at the receiving end and after the actual DC commutation failure, and the relative power angle difference in the DC active power recovery process is:

[0151]

[0152] wherein, Δδ = δ d - δ; the calculation solution of the relative power angle difference is composed of a particular solution (Δδ p (t-t c )) and a general solution (Δδ g (t-t c )) of the corresponding homogeneous equation, and is specifically represented as:

[0153] Δδ(t-t c ) = Δδ p (t-t c ) + Δδ g (t-t c )

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

[0155]

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

[0157]

[0158] Further, the derivative of the relative power angle with respect to ramp i is:

[0159]

[0160] In the embodiment of the present application, in combination with the fact that the receiving end relative power angle swings in the positive direction and the derivative process of the relative power angle, when the receiving end relative power angle swings in the positive direction, if k dpi +m-1>0, then the fast recovery of the DC i is beneficial to the transient stability of the receiving end system; if k dpi +m-1<0, then the fast recovery of the DC i is not beneficial to the transient stability of the receiving end system.

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

[0162] It should be noted that, for a multi-machine system at the receiving end, although the dynamic equations of the synchronous generator cannot be solved analytically for the relative power angle difference, the conclusions derived from the two-machine system at the receiving end are still applicable.

[0163] In this embodiment of the application, considering the transient stability recovery of the receiving system, when the receiving system has n g When the number of generator nodes is n, its synchronous generator dynamic equation is n g A number about n g dimensional variable δ G The generator node set of the receiving-end multi-machine system is composed of a system of second-order differential equations, and can be represented as follows:

[0164]

[0165] Where, n g Let n be the number of generator nodes, and n is the number of generator nodes. g >2, where n1 is the number of load nodes.

[0166] If the node of the l-th DC feed is j, then based on the receiving-end multi-machine system model and the clustering of the receiving-end multi-machine system, we get:

[0167]

[0168] S3: 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 DC commutation failure are obtained according to the DC power flow analysis model.

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

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

[0171]

[0172] Among them, P aci and Q aci To inject the active and reactive power of the inverter station into the receiving-end system, Q ci The reactive power generated by the reactive power compensation equipment within the station.

[0173] In this embodiment of the application, during the DC system recovery process after the AC fault is cleared, the converter bus voltage amplitude U li Represented as:

[0174]

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

[0176] To obtain the converter bus voltage amplitude U li Regarding Q di The decoupling relationship is assumed to be negligible, assuming that the line resistance and the voltage drop due to active power are ignored; the converter bus voltage amplitude U li Rewritten as:

[0177]

[0178] Assume U aci Constant, for U li Regarding Q di Taking the partial derivative, we get:

[0179]

[0180] It should be noted that, based on U li Regarding Q di Taking the partial derivative, we can see that the inverter station converter bus voltage will increase with the reactive power Q it consumes. di It increases and then decreases. Assume the inverter station voltage U... li Certainly, as can be seen from the DC power flow analysis model, during the recovery process, Q... di Related to turn-off angle γ and DC current I di Related. Further based on, for example Figure 8 As shown, its controller contains a PI element, causing γ and I to... di The recovery process of both exhibits overshoot characteristics, which ultimately leads to Q-strain issues during the recovery process after commutation failure. di It also has overshoot characteristics, such as Figure 9 As shown, during the recovery process after a commutation failure, the maximum reactive power consumption of the inverter station will exceed 1.1 times the rated reactive power consumption. This will cause the inverter station to switch from sending reactive power to the AC system to absorbing reactive power from the AC system during the recovery process, thus weakening the voltage stability of the receiving-end system.

[0181] For multi-infeed DC receiving-end AC systems, to characterize the voltage interaction level between the converter buses on the inverter side, a multi-infeed interaction factor is introduced. For converter buses i and j on the inverter side, the interaction factor F between the two nodes is... MIFji The definition of is:

[0182]

[0183] If F MIFji <0.15, it means that the voltage interaction between the inverter side converter buses i and j is weak; if F MIFji ≥0.15, it means that the voltage interaction between the inverter side converter buses i and j is strong.

[0184] It should be noted that when the multi-infeed interaction factor between two infeed DCs is large and the commutation failure occurs at the same time, according to the theoretical analysis, in the recovery process after the commutation failure, multiple inverter stations will simultaneously absorb a large amount of reactive power in the recovery process, which seriously threatens the voltage stability of the near area of the receiving end system.

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

[0186] In the embodiments of the present application, for a multi-infeed DC receiving end system, when a serious AC fault occurs and causes multiple DCs to simultaneously experience commutation failure, the influence of DC recovery on the transient power angle stability and voltage stability of the receiving end system is comprehensively considered to determine the coordinated recovery strategy of multiple DCs as shown in Figure 10 ;

[0187] Further, the short-circuit ratio is used to represent the strength of the receiving end AC system, that is, R SCR > 3 represents a strong receiving end system, and R SCR ≤ 3 represents a weak receiving end system. In the scenario of DC infeed into a weak AC system, the DC may experience commutation failure again in the recovery process. In order to suppress the re-commutation failure in the recovery process of the DC after the AC fault is removed, assuming that the error of the off-angle γ provided by the system during this period is within an acceptable range, an additional control strategy as shown in Figure 8 is proposed on the basis of the DC controller of the inverter station as shown in Figure 11 When the measured off-angle γ is lower than the set value γ set , by superimposing an angle G3(γ set -γ) on the original leading trigger angle δ i , the commutation margin is increased and the risk of re-commutation failure is reduced. Since the additional control strategy is put into operation after the AC fault is removed, the signal of whether the receiving end AC fault is removed can be provided by the protection device. The set value γ set of the present application is calculated as γ set = γ lim = 0.5(γ0+γ min ), where γ0 is the rated off-angle and γ min is the critical off-angle.

[0188] Based on the analysis of the transient power angle stability of the receiving end system, the sequence of DC restoration is determined; the DC that is beneficial to the transient power angle stability is normally restored, while the DC that is not beneficial to the stability needs to be slowly restored; for the DC set F MIFji ≥0.15, the DC is further sorted, that is, the DC set is beneficial, and the electrical distance of the feeding position is The smaller the electrical distance is, the slower the restoration should be; for the DC set that is not beneficial, the larger the electrical distance is, the slower the restoration should be;

[0189] The slow restoration time difference between different restoration sets is set to ensure that the DC is restored according to the plan, and the recovery speed after the DC commutation failure is controlled by adjusting the time constant of the low-voltage current limiting control, so as to realize the orderly slow restoration.

[0190] Exemplarily, on one hand, according to the influence factors, the multiple DCs need to be restored in a specified sequence; on the other hand, the DC power needs to be restored to the vicinity of the rated value as soon as possible. Further, according to the simulation results of the commutation failure shown in Figure 4 It can be seen from the simulation results of the commutation failure shown in the simulation results of the commutation failure that the DC power recovery process after the AC fault is removed lasts for about 100 ms. Therefore, the slow restoration time difference of the DC restoration set is about 50 ms. In addition, since the recovery process after the DC commutation failure is mainly affected by the low-voltage current limiting control, the recovery speed after the DC commutation failure can be changed by increasing the time constant T1, so as to realize the slow restoration of the DC.

[0191] The above is a schematic scheme of the DC simultaneous commutation failure cooperative recovery control method of the embodiment. It should be noted that the technical scheme of the DC simultaneous commutation failure cooperative recovery control system belongs to the same concept as the technical scheme of the DC simultaneous commutation failure cooperative recovery control method described above, and the details of the technical scheme of the DC simultaneous commutation failure cooperative recovery control system in the embodiment are not described in detail, which can be referred to the description of the technical scheme of the DC simultaneous commutation failure cooperative recovery control method.

[0192] The DC simultaneous commutation failure cooperative recovery control system in the embodiment comprises:

[0193] A model building module is configured to build a system analysis model based on an actual power system, wherein the system analysis model comprises a receiving end system model and a DC power flow analysis model;

[0194] An active analysis module is configured to derive an analytical expression of a relative power angle difference of a receiving end with respect to DC power in an active recovery process after DC commutation failure based on the receiving end system model, and obtain an influence factor of the DC active recovery process on the transient power angle of the receiving end system;

[0195] A reactive power analysis module is configured to obtain factors affecting voltage stability of the receiving end system in a reactive power recovery process after the DC commutation failure based on an inverter-side DC controller regulation characteristic and the DC power flow analysis model;

[0196] A coordinated recovery control strategy formulation module is configured to analyze factors affecting voltage stability of the receiving end system in the reactive power recovery process and factors affecting transient power angle of the receiving end system in a DC active power recovery process to form a recovery control strategy after the multiple DC commutation failures.

[0197] The embodiment also provides a computing device suitable for the coordinated recovery control method after the multiple DC commutation failures.

[0198] The memory is configured to store computer executable instructions, and the processor is configured to execute the computer executable instructions to implement the coordinated recovery control method after the multiple DC commutation failures.

[0199] The embodiment also provides a storage medium having a computer program stored thereon, and the computer program is executed by a processor to implement the coordinated recovery control method after the multiple DC commutation failures.

[0200] The storage medium proposed in the embodiment belongs to the same inventive concept as the coordinated recovery control method after the multiple DC commutation failures proposed in the above embodiment, and the technical details not described in the embodiment can be referred to the above embodiment, and the embodiment has the same beneficial effects as the above embodiment.

[0201] From the above description about the embodiments, those skilled in the art can clearly understand that the present application can be realized by means of software and necessary universal hardware, and of course can be realized by hardware, but in many cases the former is a better embodiment. Based on such understanding, the technical solutions of the present application or the part that contributes to the prior art can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as a floppy disk, a read-only memory (ROM), a random access memory (RAM), a FLASH memory, a hard disk or an optical disk, and includes a number of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute the methods of various embodiments of the present application.

[0202] Embodiment 2

[0203] Reference Figures 12-15 For an embodiment of the present application, which is different from the first embodiment, the embodiment verifies the beneficial effects of the present application through simulation experiments.

[0204] This example is based on IEEE-68 node system, and the electromechanical-electromagnetic hybrid simulation model of multi-DC-infeed receiving AC system is built in ADPSS as shown in Figure 12 Figure 12 It can be seen that the system is composed of New England System and New York System two regional power grids, and the two regional power grids are connected by four tie lines, forming two natural complementary groups, which are recorded as 'A' and 'B' groups. A group contains synchronous generators G1-G9, and B group contains synchronous generators G 10 -G 16 At the same time, the receiving end system is fed by DC1, DC2 and DC3, and R SCR1 = 5.02, R SCR2 = 2.68 and R SCR3 = 3.70, which shows that the near-zone AC system of the receiving end fed by DC1 and DC3 is strong enough, while the near-zone AC system of the receiving end fed by DC2 is not strong enough, and needs to be prevented from commutation failure again due to too fast recovery speed. Therefore, the electromechanical model of the AC system and DC1 and DC3 is built in PSASP, and the electromagnetic model of DC2 is built in ETSDAC.

[0205] Further, m = 0.346, k dpE1 = 0.14, k dpE2 = 0.22 and k dpE3 = 0.14 are calculated, and F MIIF12 = 0.70, F MIIF13 = 0.50 and F MIIF23 = 0.30 are calculated. For DC2 fed to the weak receiving end system, the correctness and effectiveness of the proposed theoretical analysis and coordinated control strategy are verified under different scenarios. According to the above analysis, the following two recovery control strategies after multi-DC simultaneous commutation failure are defined:

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

[0207] Strategy 2: the proposed coordinated recovery control strategy, i.e. 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] To verify the effectiveness of the proposed additional control strategy in suppressing commutation failure of DC during the recovery process after AC fault clearing, a three-phase short-circuit fault is set at Bus-18. The simulation comparison results with and without the proposed additional control strategy are shown in Figure 13

[0210] From the blue curves in Figure 13 (a) and (b), it can be seen that the commutation failure of DC occurs due to the AC fault at the receiving end, and the commutation failure occurs again during the recovery process after AC fault clearing. Further from the red curves in Figure 13 (a) and (b), it can be seen that the commutation failure of DC during the recovery process is suppressed due to the proposed additional control strategy, verifying the effectiveness of the proposed additional control strategy.

[0211] 2) Coordinated recovery control strategy simulation verification

[0212] Under the premise of ensuring that the DC does not experience commutation failure during the recovery process after AC fault clearing, 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 coordinated recovery control strategy are shown in Figure 14

[0214] From Figure 14 (a), (b), (c), and (d), it can be seen that the commutation failure of multiple DCs occurs simultaneously due to the AC fault at the receiving end. Further from Figure 14 (e), it can be seen that the relative power angle at the receiving end reverses and spreads out. Based on theoretical analysis, it is known that in this scenario, the coordinated recovery strategy is to recover DC1 normally, and DC3 and DC2 recover slowly for one and two time levels, respectively, as shown by the red and blue curves in Figure 14 (d). From the comparison of the blue and red curves in Figure 14 (e), it can be seen that when the proposed coordinated recovery strategy is adopted, the first swing amplitude of the relative power angle at the receiving end decreases by nearly 2°, improving the transient power angle stability of the receiving end system. Further from the comparison of the blue and red curves in Figure 14 (f), it can be seen that when the proposed coordinated recovery strategy is adopted, the lowest bus voltage at Bus-18 during the recovery process increases by 0.14 p.u., improving the voltage stability of the receiving end system. Figure 14 The simulation comparison results verify the correctness of the proposed theoretical analysis and the effectiveness of the coordinated recovery control strategy.

[0215] ​​Scenario 2: A three-phase short-circuit fault is set at Bus-18. The simulation comparison results of using and not using the proposed collaborative recovery control strategy are as follows: Figure 15 As shown.

[0216] Depend on Figure 15 From (a), (b), (c), and (d), it can be seen that an AC fault at the receiving end causes multiple DC commutation failures to occur simultaneously, and further... Figure 15 (e) It can be seen that after the fault occurs, the relative power angle at the receiving end swings positively. Based on theoretical analysis, in this scenario, the collaborative recovery strategy is that DC2 recovers normally, while DC3 and DC1 recover slowly for one and two time stages, respectively. Figure 15 As shown in (e), comparing the blue and red curves reveals that when the proposed collaborative recovery strategy is employed, the initial amplitude of the relative power angle at the receiving end decreases by 3°, improving the transient power angle stability of the receiving-end system. Further... Figure 15 As can be seen from the comparison of the blue and red curves in (f), when the proposed collaborative recovery strategy is adopted, the minimum bus voltage at Bus-18 is increased by 0.02 pu during the recovery process due to the avoidance of commutation failure, thus improving the voltage stability of the receiving-end system. Figure 14 and Figure 15 The simulation comparison results further verified the correctness of the proposed theoretical analysis and the effectiveness of the collaborative recovery control strategy.

[0217] Furthermore, different types of faults were set at different locations near the converter station in the receiving-end system, causing multiple DC lines to fail simultaneously. The simulation comparison results are shown in Table 1, where f (1) f (2) and f (3) These are single-phase ground 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] As shown in Table 1, the simulation results demonstrate that the proposed collaborative recovery control strategy after multiple DC commutation failures improves the transient power angle and voltage stability of the receiving-end system to varying degrees. This not only verifies the correctness of the theoretical analysis but also the effectiveness of the proposed collaborative recovery control strategy.

[0221] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for coordinated recovery control after DC simultaneous commutation failure, characterized in that 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; deducing, according to the receiving end system model, an analytical expression of a relative power angle difference of the receiving end in an active power recovery process after DC commutation failure, obtaining an influence factor of the DC active power recovery process on transient power angle of the receiving end system; obtaining, based on a regulation characteristic of a DC controller at an inverter side, an influence factor of a voltage stability of the receiving end system in a reactive power recovery process after the DC commutation failure according to the DC power flow analysis model; The factors affecting the voltage stability of the receiving end system during the reactive power recovery process after DC commutation failure include: based on the power exchange relationship between the DC inverter station and the receiving end AC system, during the DC system recovery process after the AC fault is cleared, the amplitude of the commutation bus voltage is represented as: ； wherein, is the voltage amplitude of the equivalent bus Bus-aci of the receiving system, and are the longitudinal and transversal components of the voltage drop, respectively, and are the equivalent resistance and reactance between Bus-aci and Bus-i, respectively, and are the active and reactive power injected by the inverter station of the receiving system. To get the amplitude of the converter bus voltage With respect to The decoupling relation of the active power and the amplitude of the converter bus voltage is given by assuming that the line resistance and the voltage drop caused by the active power are ignored; the amplitude of the converter bus voltage is rewritten as: ； Assume Constant, to About The partial derivative is ； For multi-infeed AC system at the receiving end of DC, in order to depict the level of mutual influence of voltage among multi-infeed DC inversion side converter bus, the multi-infeed interaction factor is introduced, and the voltage among multi-infeed DC inversion side converter bus is calculated by using the multi-infeed interaction factor and The definition of the interaction factor between two nodes is as follows: ； If <0.15, it means that the voltage interaction between the converter bus on the inverter side and the converter bus on the generator side is weak; if ≥ 0.15, it means that the voltage interaction between the converter bus on the inverter side and the converter bus on the generator side is strong. If <0.15, it means that the voltage interaction between the converter bus on the inverter side and the converter bus on the generator side is weak; if ≥ 0.15, it means that the voltage interaction between the converter bus on the inverter side and the converter bus on the generator side is strong. If forming a recovery control strategy after multiple DC commutation failures based on the influence factor of the voltage stability of the receiving end system in the reactive power recovery process and the influence factor of the DC active power recovery process on the transient power angle of the receiving end system.

2. The method according to claim 1, wherein Comprising: the receiving end system model simplifies a multi-infeed DC receiving end multi-machine system into a two-group machine system by using a complementary group inertia center-relative motion theory, obtains an 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: ； ； ； ； wherein, and PmechAand PmechBare the total mechanical input power of the A and B groups, respectively, and PemgAand PemgBare the total electromagnetic output power of the A and B groups, respectively, and JinAand JinBare the total inertia of the A and B groups, respectively, is the relative power angle between the A and B groups, and are the equivalent power angles of the A and B groups, respectively. the DC power flow analysis model is based on a line-commutated converter high-voltage DC transmission system, and a relationship among voltage, current, DC power and reactive power of an inverter station of the model is expressed as: ； wherein, and are direct voltage and current, respectively, is the number of bridges, is the equivalent commutation reactance, is the transformer ratio of the converter transformer, is the converter bus voltage, is the DC power and the reactive power consumed by the converter station, is the no-load DC voltage at the inverter station, is the power factor, is the first harmonic of the DC power fed into the receiving system, is the second harmonic of the DC power fed into the receiving system, is the turn-off angle.

3. The method according to claim 2, wherein the control method is characterized by, Further comprising: establishing a DC power mathematical model of a whole process from DC commutation failure caused by an AC fault at the receiving end to recovery of the DC commutation failure according to power external characteristics of the DC commutation failure and the recovery process, assuming that the power mathematical model is a power injection model in a short time after the AC fault is cleared, and deducing by using the DC power flow analysis model, which is expressed as: ； wherein, is a set of generator nodes, is a set of load nodes, wherein the inverter station node is considered as part of the load nodes, , , and are, respectively, the corresponding susceptance matrices, is the power angle of the synchronous generator.

4. The method according to claim 3, wherein the control method is characterized by The factors influencing the transient power angle of the receiving-end system during the DC active recovery process include: the receiving-end system model consisting of two DC feed-in circuits, group A consisting of synchronous generators , and group B consisting of synchronous generators , and the electromagnetic power of the synchronous generator being 0 during the fault. In the case of AC fault clearing at the receiving end, assuming that the DC power is instantaneously restored, the electromagnetic power of the synchronous generator with respect to the relative power angle at the receiving end is calculated in a short time after the fault is represented as: ； wherein is and the electrical distance between the internal potential nodes, is the load node to the electrical distance to the internal potential nodes, is the receiving end relative power angle and , and are the electrical distances from the first and second DC feed-in nodes to the internal potential nodes, respectively. Based on the power balance, the electromagnetic power is obtained as ​ ； rewriting the receiving end system model based on electromagnetic power of a synchronous generator as: ； ； ； wherein, is the inertia ratio, and is defined by .

5. The method according to claim 4, wherein the control method is characterized by Further comprising: after the AC fault at the receiving end is cleared, there is a power recovery process in a time scale after the actual DC commutation failure, and there is a relative power angle difference in the DC active power recovery process, which is expressed as: ； wherein ; the calculation solution of the relative power angle difference is composed of its particular solution and its corresponding homogeneous equation general solution ; Because , , With respect to the relative power angle The derivative gives: ； When the receiving end relative power angle is positively away, if , the DC fast recovery is beneficial to the transient stability of the receiving end system; if , the DC fast recovery is not beneficial to the transient stability of the receiving end system; When the receiving end relative power angle reverses away, if , the DC fast recovery is not conducive to the transient stability of the receiving end system; if , the DC fast recovery is conducive to the transient stability of the receiving end system; In combination with the transient stability recovery condition of the receiving end system, when the receiving end system has generator nodes, the dynamic equation of the synchronous generator is a second-order differential equation system with variables, and the generator node set of the receiving end multi-machine system is represented as​ ； wherein is the number of generator nodes, and , is the number of load nodes, , ; If the node where the direct current is fed in is a node where the direct current is fed in is then based on the model of the multi-machine system at the receiving end and the grouping of the multi-machine system at the receiving end, it is obtained that 。 6. The method according to claim 5, wherein the control method is characterized by forming the recovery control strategy after multiple DC commutation failures comprises: The strength of the receiving end AC system is characterized by short circuit ratio, i.e. representing a strong receiving end system, representing a weak receiving end system, under which an additional control strategy is introduced; When the measured extinction angle is lower than the set value , the commutation margin is increased and the risk of re-commutation failure is reduced by superimposing an angle on the original leading trigger angle ( ); the set value is calculated as , wherein is the rated extinction angle, is the critical extinction angle; Based on the analysis of the transient power angle stability of the receiving system, the sequence 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 set of beneficial DC, the smaller the electrical distance of the feeding position is, the slower the restoration should be ; for the set of non-beneficial DC, the larger the electrical distance is, the slower the restoration should be; setting a slow recovery time difference between different recovery sets to ensure that the DC is recovered according to a plan, and adjusting a time constant of low-voltage current limiting control to control a recovery speed after the DC commutation failure, so as to realize slow recovery in an order.

7. A coordinated recovery control system after DC simultaneous commutation failure, applied to the method of any one of claims 1-6, characterized in that, Comprising: a model building module configured to establish 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; an active analysis module configured to deduce, according to the receiving end system model, an analytical expression of a relative power angle difference of the receiving end in an active power recovery process after DC commutation failure, obtaining an influence factor of the DC active power recovery process on transient power angle of the receiving end system; a reactive analysis module configured to obtain, based on a regulation characteristic of a DC controller at an inverter side, an influence factor of a voltage stability of the receiving end system in a reactive power recovery process after the DC commutation failure according to the DC power flow analysis model; a collaborative recovery control strategy formulation module configured to form a recovery control strategy after multiple DC commutation failures based on the influence factor of the voltage stability of the receiving end system in the reactive power recovery process and the influence factor of the DC active power recovery process on the transient power angle of the receiving end system. 8.An electronic device, comprising: a memory and a processor; The memory is configured to store computer-executable instructions, and the processor is configured to execute the computer-executable instructions, and the computer-executable instructions, when executed by the processor, implement the steps of the coordinated recovery control method after simultaneous commutation failure of direct current according to any one of claims 1 to 6. 9.A computer-readable storage medium storing computer-executable instructions, and the computer-executable instructions, when executed by a processor, implement the steps of the coordinated recovery control method after simultaneous commutation failure of direct current according to any one of claims 1 to 6.

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