Post-fault multi-circuit direct current cooperative control method based on expansion equal area rule

Abstract

The invention discloses a post-fault multi-circuit direct current cooperative control method based on an expansion equal area rule. The method comprises the following steps: S1, dividing a critical cluster GS and a remaining cluster GA; s2, calculating support effect evaluation indexes of each direct-current converter station for all generators in the critical generator group GS to determine an optimal direct-current converter station; s3, if the fault is a three-phase short-circuit fault, the optimal direct current converter station power is reduced by f percentage points; if the fault is a direct current fault, increasing f percentage points; s4, if the symbol of the difference between the two equivalent angular velocities is switched, re-determining the optimal direct current converter station, and if the equivalent angular velocity of the critical cluster GS is greater than the equivalent angular velocity of the remaining cluster GA, improving the direct current power of the optimal direct current converter station by f percentage points; otherwise, reducing the optimal direct current power of the direct current converter station by f percentage points; and S5, repeating the steps S1 to S4 until the time of the direct-current power support reaches the short-time overload time limit ts of the converter station.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a post-fault multi-circuit direct current coordinated control method based on an extended equal area law. Background Art

[0002] As the access of new energy sources at the tens of millions of kilowatts has an increasing impact on the safety and stability of the system, the DC sending-end system presents a "double high" feature (a high proportion of new energy and a high proportion of power electronic equipment). Under the current conditions of weak AC support, the stable control of the DC transmission system of high-altitude clean energy bases faces huge challenges.

[0003] New energy generators such as photovoltaic and wind power do not have the same rotor dynamic characteristics as traditional thermal power generators, resulting in the active support capacity of the sending-end system being significantly insufficient compared to traditional power systems, and the damping effect on fault impacts is limited. When a DC locking fault or AC system fault occurs in the system, a large amount of unbalanced power accumulates at the sending end. At the same time, the large-scale power flow transfer in the system will cause the power angles of each generator at the sending end to continue to swing, which will pose a serious threat to the transient power angle stability of the system. Existing research mainly starts from the perspective of the receiving-end power grid, emphasizing that the range of DC power modulation must match the strength of the receiving-end power grid to prevent inappropriate DC power increase from inducing multiple DC continuous commutation failures. However, at this stage, most of my country's multi-circuit DC transmission projects use hybrid DC transmission formed by mixing conventional DC and flexible DC. The receiving station of hybrid DC is generally a voltage source converter station where commutation failure will not occur. There are also studies focusing on the supporting role of DC power support in AC / DC hybrid power grids for the safety and stability of the system after AC faults. Although this type of research comprehensively considers the safety and stability of the transmitting and receiving power grids, most of its research objects are single-circuit DC, and the consideration of DC fault scenarios is not comprehensive enough.

[0004] Therefore, in a multi-circuit large-capacity hybrid DC transmission system, how to construct a multi-circuit DC coordinated control method to address the transient power angle stability problem of the sending-end system is still a technical problem that needs to be solved urgently. Summary of the invention

[0005] In view of this, the present invention provides a post-fault multi-circuit DC coordinated control method based on the extended equal area law, which is used to at least solve the problem of transient power angle instability existing in multi-circuit DC transmission projects in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A post-fault multi-circuit DC coordinated control method based on the extended equal area law comprises the following steps: S1. Obtain the angular velocity monitoring data of all generators in the sending-end system after the fault, and divide the critical group according to the angular velocity monitoring data GS and the remaining fleet G A ; S2. Calculate the critical group of each DC converter station G S The support effect evaluation index of all generators in the system is used to determine the DC converter station with the best support effect as the best DC converter station; S3. If the fault type is a three-phase short circuit fault, then reduce the optimal DC converter station power f percentage points; if the fault type is a DC fault, the optimal DC converter station power is increased f percentage points; S4. Consider the dynamic process of the system and the critical cluster in the dynamic process G S and the remaining fleet G A The relative size of the equivalent angular velocity changes, that is, if the sign of the difference between the two equivalent angular velocities changes, the optimal DC converter station is re-determined; among them, if the critical group G S The equivalent angular velocity is greater than that of the rest of the fleet G A The equivalent angular velocity of the current optimal DC converter station is increased by f percentage points; otherwise, the DC power of the current optimal DC converter station will be reduced. f percentage points; S5. Repeat S1-S4 until the time for all DC power increase or decrease reaches the short-term overload time limit of the converter station. t s .

[0007] Preferably, the specific content of S1 includes: Monitor the angular velocity of all generators in the sending-end system after the fault and obtain the corresponding generator power angle curve; Calculate the angular velocity of the center of inertia of the entire sending end system based on the angular velocity of the generator , and the corresponding inertia center power angle curve is obtained; If the power angle curve of any generator in the sending end system deviates from the power angle curve of the center of inertia, the current generator is judged to be seriously disturbed and is classified as a critical group. G S ; Otherwise, it is classified as the remaining cluster G A .

[0008] Preferably, the center of inertia angular velocity The calculation method is: ; in, MT is the sum of the inertia time constants of all generators in the sending end system; and are the inertia time constant and angular velocity of the i-th generator in the sending end respectively; n is the number of generators in the sending end system.

[0009] Preferably, the support effect evaluation index in S2 is the modulation coefficient, and the modulation coefficient is calculated as follows: ; ; in, Any DC converter station in a multi-circuit DC sending system The modulation coefficient of x is the number of generators included in the critical cluster; It is a converter station For any generator in the critical group The synchronous power factor; Generator in the sending end system The inertia time constant of and Generator Internal potential and converter station The voltage amplitude of the commutation bus; represent and The phase difference between For generator Busbar and converter station The mutual admittance between the commutation buses; The reduction in generator acceleration power after DC emergency power support; and Generator Mechanical power and electromagnetic power; The power value increased or decreased by the DC converter station.

[0010] Preferably, the specific content of S4 includes: Critical Cluster G S and the remaining fleet G A The equivalent angular velocity is denoted as and ; Consider the dynamic process of the system and the critical cluster in the dynamic process G S and the remaining fleet G A The relative magnitude of the angular velocity changes, adjusting m The power of the current optimal DC converter station during the transient process within seconds: when When the equivalent system at the sending end is in the forward acceleration and forward deceleration stages, the DC power of the current optimal DC converter station is increased to reduce the positive sway acceleration area and increase the positive sway deceleration area; when When the sending-end equivalent system is in the reverse acceleration and reverse deceleration stage, the DC power of the current optimal DC converter station is reduced to increase the swing deceleration area and reduce the swing acceleration area.

[0011] Optimally, the critical cluster G S and the remaining fleet G A The equivalent angular velocity and The calculation method is: ; in, M GS and M GA They are respectively the critical clusters G S and the remaining fleet G A The sum of the inertia time constants of all generators; M k and They are the first k The inertia time constant and angular velocity of the generator; M t and For the remaining cluster t The inertia time constant and angular velocity of the generator; x and y are the number of generators in the critical cluster and the remaining cluster, respectively.

[0012] Preferably, the specific content of S5 includes: Repeat S1-S4 until the DC power support time reaches the short-term overload time limit of the converter station. t s ; If reached t s For all fault types, the power of the non-faulty DC converter station is increased to the long-term overload factor of the DC converter station. L c , until the power angle curve oscillation after the fault decays to a stable state.

[0013] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a post-fault multi-circuit DC coordinated control method based on the extended equal area rule, which has the following beneficial effects: The present invention firstly proposes a method for identifying a group of generators that are seriously disturbed after a fault based on the group equivalence concept in the extended equal area law, which is conducive to locating the generator group that is seriously disturbed after the fault occurs; secondly, on the basis of the identification method, the power adjustable characteristics of the DC converter station are utilized, and the unbalanced power generated by the fault is absorbed and the system equivalent acceleration area is reduced, and the system equivalent deceleration area is increased, so as to finally achieve the effect of maintaining the power angle stability of the sending-end system after the fault. By connecting the scheduling of DC power with the power angle stability of the entire sending-end system through the extended equal area law, the gap in the applicability of the sending-end system and the application of multiple DC circuits is filled. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 paying creative work.

[0015] Figure 1 A flowchart of a post-fault multi-circuit DC coordinated control method based on the extended equal area rule provided by the present invention; Figure 2 An equivalent two-machine system diagram provided for an embodiment of the present invention; Figure 3 The power angle-active power curve diagram of an equivalent single machine under two faults provided by the embodiment of the present invention, wherein Figure 3 (a) is a DC blocking fault. Figure 3 (b) is a three-phase N-1 fault. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] The present invention provides a post-fault multi-circuit DC coordinated control method based on the extended equal area rule, such as Figure 1 As shown, the following steps are included: S1. Obtain the angular velocity monitoring data of all generators in the sending-end system after the fault, and divide the critical group according to the angular velocity monitoring data G S and the remaining fleet G A ; S2. Calculate the critical group of each DC converter station G S The support effect evaluation index of all generators in the system is used to determine the DC converter station with the best support effect as the best DC converter station; S3. If the fault type is a three-phase short circuit fault, then reduce the optimal DC converter station power f percentage points; if the fault type is a DC fault, the optimal DC converter station power is increased f percentage points; S4. Consider the dynamic process of the system and the critical cluster in the dynamic process G S and the remaining fleet G A The relative size of the equivalent angular velocity changes, that is, if the sign of the difference between the two equivalent angular velocities changes, the optimal DC converter station is re-determined; among them, if the critical group G S The equivalent angular velocity is greater than that of the rest of the fleet G A The equivalent angular velocity of the current optimal DC converter station is increased by f percentage points; otherwise, the DC power of the current optimal DC converter station will be reduced. f percentage points; S5. Repeat S1-S4 until the time for all DC power increase or decrease reaches the short-term overload time limit of the converter station. t s .

[0018] It should be noted that: In this embodiment, the electromechanical transient simulation software is used to record the angular velocity of all generators in the sending-end system after the fault, and calculate the angular velocity of the center of inertia of the entire sending-end system ; In this embodiment, PSD-BPA is used as the time domain simulation software.

[0019] In the present invention, the DC power of the converter station is increased f The value obtained by adding 1 percentage point is the DC power overload limit of the converter station. In this embodiment, f The value is 30.

[0020] The following is an explanation of the content of the extended equal area law described in the present invention: 1. Cluster equivalence concept: The equivalent two-machine system diagram is as follows Figure 2 As shown in the figure, after the fault, a large amount of unbalanced power accumulates at the sending end, and all generators can be divided into two equivalent groups: the critical group is the group that is severely disturbed and has the first power angle to swing. G S The remaining groups were less disturbed. G A The rotor motion equations of the two equivalent machines are further simplified and equivalent, and the equivalent single-machine infinite system can be obtained, as shown in the following equation: ; in, M GS , M GA are the inertia time constants of the critical cluster and the remaining cluster respectively; P GS , P GA Active power generated by the critical group and the remaining group; U GS , U GA are the generator bus voltages of the critical group and the remaining group respectively; P dc is the DC power; X SA is the line reactance between two equivalent groups; is the angular velocity of the equivalent single machine; is the power angle of the equivalent single machine; the equivalent mechanical power of the equivalent single machine is , the equivalent electromagnetic power is .

[0021] 2. Equivalent area rule for expansion of equivalent single machine: The power angle-active power curves of an equivalent single machine under two fault conditions are as follows: Figure 3 When the DC blocking fault occurs, the power characteristics of the equivalent single machine remain unchanged, and the DC power can be regarded as a part of the equivalent mechanical power. Therefore, the impact of the fault can be regarded as the equivalent mechanical power of the system changing from a straight line to a straight line. becomes , the equivalent single machine acceleration area is S b’c’d’ , the equivalent single-machine deceleration area is S c’d’ , increasing DC power is beneficial to reducing the acceleration area, increasing the deceleration area, and avoiding equivalent single-machine acceleration; after a three-phase short-circuit fault occurs, the fault line is generally permanently cut off to eliminate the fault, so it is called a three-permanent N-1 fault. In this scenario, the change process of the power characteristic curve of the equivalent single machine (normal → fault → cut off) is curve 1 → curve 3 → curve 2, and the equivalent mechanical power remains unchanged. At this time, the acceleration area of ​​the equivalent single machine is S abce, the deceleration area is S def Therefore, increasing the DC power is beneficial to reducing the acceleration area, increasing the deceleration area, and avoiding equivalent single-machine acceleration. The above analysis is only for the positive swing (the system's positive acceleration and deceleration process), and the reverse swing (the system's reverse acceleration and deceleration process) can achieve the same effect by reducing the DC power.

[0022] In order to further implement the above technical solution, the specific contents of S1 include: Monitor the angular velocity of all generators in the sending-end system after the fault and obtain the corresponding generator power angle curve; Calculate the angular velocity of the center of inertia of the entire sending end system based on the angular velocity of the generator , and the corresponding inertia center power angle curve is obtained; If the power angle curve of any generator in the sending end system deviates from the power angle curve of the center of inertia, the current generator is judged to be seriously disturbed and is classified as a critical group. G S ; Otherwise, it is classified as the remaining cluster G A .

[0023] In order to further implement the above technical solution, the angular velocity of the center of inertia The calculation method is: ; in, M T is the sum of the inertia time constants of all generators in the sending end system; M i and are the inertia time constant and angular velocity of the i-th generator in the sending end respectively; n is the number of generators in the sending end system.

[0024] In order to further implement the above technical solution, the support effect evaluation index in S2 is the modulation coefficient, and the modulation coefficient is calculated as follows: ; ; in, Any DC converter station in a multi-circuit DC sending system The modulation coefficient of x is the number of generators included in the critical cluster; It is a converter station For any generator in the critical group The synchronous power factor; Generator in the sending end system The inertia time constant of and Generator Internal potential and converter station The voltage amplitude of the commutation bus; represent and The phase difference between For generator Busbar and converter station The mutual admittance between the commutation buses; The reduction in generator acceleration power after DC emergency power support; and Generator Mechanical power and electromagnetic power; The power value increased or decreased by the DC converter station.

[0025] In order to further implement the above technical solution, the specific contents of S4 include: Critical Cluster G S and the remaining fleet G A The equivalent angular velocity is denoted as and ; Consider the dynamic process of the system and the critical cluster in the dynamic process G S and the remaining fleet G A The relative magnitude of the equivalent angular velocity changes, adjusting m The power of the current optimal DC converter station during the transient process within seconds: when When the equivalent system at the sending end is in the forward acceleration and forward deceleration stages, the DC power of the current optimal DC converter station is increased to reduce the positive sway acceleration area and increase the positive sway deceleration area; when When the sending-end equivalent system is in the reverse acceleration and reverse deceleration stage, the DC power of the current optimal DC converter station is reduced to increase the swing deceleration area and reduce the swing acceleration area.

[0026] It should be noted that: In this embodiment, m The value is 3.

[0027] In order to further implement the above technical solutions, the critical cluster G S and the remaining fleet G A The equivalent angular velocity and The calculation method is: ; in,M GS and M GA They are respectively the critical clusters G S and the remaining fleet G A The sum of the inertia time constants of all generators; M k and They are the first k The inertia time constant and angular velocity of the generator; M t and For the remaining cluster t The inertia time constant and angular velocity of the generator; x and y are the number of generators in the critical cluster and the remaining cluster, respectively.

[0028] In order to further implement the above technical solution, the specific contents of S5 include: Repeat S1-S4 until the DC power support time reaches the short-term overload time limit of the converter station. t s ; If reached t s For all fault types, the power of the non-faulty DC converter station is increased to the long-term overload factor of the DC converter station. L c , until the power angle curve after the fault oscillates and decays to a stable state, that is, the oscillation decay approaches 0.

[0029] It should be noted that: In this embodiment, L c It is the long-term overload factor of the DC converter station, which is generally 1.05 times the rated power of the converter station.

[0030] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A post-fault multi-circuit DC coordinated control method based on the extended equal area rule, characterized in that: The following steps are involved: S1. Obtain the angular velocity monitoring data of all generators in the sending-end system after the fault, and divide the critical group according to the angular velocity monitoring data G S and the remaining fleet G A ; S2. Calculate the critical group of each DC converter station G S The support effect evaluation index of all generators in the system is used to determine the DC converter station with the best support effect as the best DC converter station; S3. If the fault type is a three-phase short circuit fault, then reduce the optimal DC converter station power f percentage points; if the fault type is a DC fault, the optimal DC converter station power is increased f percentage points; S4. Consider the dynamic process of the system and the critical cluster in the dynamic process G S and the remaining fleet G A The relative size of the equivalent angular velocity changes, that is, if the sign of the difference between the two equivalent angular velocities changes, the optimal DC converter station is re-determined; among them, if the critical group G S The equivalent angular velocity is greater than that of the rest of the fleet G A The equivalent angular velocity of the current optimal DC converter station is increased by f percentage points; otherwise, the DC power of the current optimal DC converter station will be reduced. f percentage points; S5. Repeat S1-S4 until the time for all DC power increase or decrease in S3-S4 reaches the short-term overload time limit of the converter station. t s .

2. The method for coordinated control of multiple DC circuits after a fault based on the extended equal area rule according to claim 1, characterized in that: The specific contents of S1 include: Monitor the angular velocity of all generators in the sending-end system after the fault and obtain the corresponding generator power angle curve; Calculate the angular velocity of the center of inertia of the entire sending end system based on the angular velocity of the generator , and the corresponding inertia center power angle curve is obtained; If the power angle curve of any generator in the sending end system deviates from the power angle curve of the center of inertia, the current generator is judged to be seriously disturbed and is classified as a critical group. G S ; Otherwise, it is classified as the remaining cluster G A .

3. The method for coordinated control of multiple DC circuits after a fault based on the extended equal area rule according to claim 2 is characterized in that: Angular velocity of center of inertia The calculation method is: ； in, M T is the sum of the inertia time constants of all generators in the sending end system; and are the inertia time constant and angular velocity of the i-th generator in the sending end respectively; n is the number of generators in the sending end system.

4. The method for coordinated control of multiple DC circuits after a fault based on the extended equal area rule according to claim 1 is characterized in that: The support effect evaluation index in S2 is the modulation coefficient, which is calculated as follows: ； ； in, Any DC converter station in a multi-circuit DC sending system The modulation coefficient of x is the number of generators included in the critical cluster; It is a converter station For any generator in the critical group The synchronous power factor; Generator in the sending end system The inertia time constant of and Generator Internal potential and converter station The voltage amplitude of the commutation bus; represent and The phase difference between For generator Busbar and converter station The mutual admittance between the commutation buses; The reduction in generator acceleration power after DC emergency power support; and Generator Mechanical power and electromagnetic power; The power value increased or decreased by the DC converter station.

5. The method for coordinated control of multiple DC circuits after a fault based on the extended equal area rule according to claim 1, characterized in that: The specific contents of S4 include: Critical Cluster and the remaining fleet The equivalent angular velocity is denoted as and ; Consider the dynamic process of the system and the critical cluster in the dynamic process G S and the remaining fleet G A The relative size of the equivalent angular velocity changes, adjust m The power of the current optimal DC converter station during the transient process within seconds: when When the equivalent system at the sending end is in the forward acceleration and forward deceleration stages, the DC power of the current optimal DC converter station is increased to reduce the positive sway acceleration area and increase the positive sway deceleration area; when When the sending-end equivalent system is in the reverse acceleration and reverse deceleration stage, the DC power of the current optimal DC converter station is reduced to increase the swing deceleration area and reduce the swing acceleration area.

6. The method for coordinated control of multiple DC circuits after a fault based on the extended equal area rule according to claim 5, characterized in that: Critical Cluster G S and the remaining fleet G A The equivalent angular velocity and The calculation method is: ； in, M GS and M GA They are respectively the critical clusters G S and the remaining fleet G A The sum of the inertia time constants of all generators; M k and They are the first k The inertia time constant and angular velocity of the generator; M t and For the remaining cluster t The inertia time constant and angular velocity of the generator; x and y are the number of generators in the critical cluster and the remaining cluster, respectively.

7. The method for coordinated control of multiple DC circuits after a fault based on the extended equal area rule according to claim 1, characterized in that: The specific contents of S5 include: Repeat S1-S4 until the DC power support time reaches the short-term overload time limit of the converter station. t s ; If reached t s For all fault types, the power of the non-faulty DC converter station is increased to the long-term overload factor of the DC converter station. L c , until the power angle curve oscillation after the fault decays to a stable state.

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