An emergency control method of direct current blocking and coordinated multi-direct current power support

Abstract

The present application relates to the technical field of power system stability control, especially to an emergency control method for coordinated multi-DC power support after DC blocking, comprising the following steps: obtaining an emergency control input criterion based on the slope change characteristics in the first swing process of phase trajectory; applying the emergency control input criterion to an AC-DC hybrid system; determining a multi-DC emergency power support coordination control strategy based on the post-fault stable equilibrium point change characteristics; and building a simulation model for simulation. The present application obtains an emergency control input criterion based on the slope change characteristics in the first swing process of phase trajectory, establishes a mathematical relationship between the control quantity and the number of DC power support, and proposes an emergency control strategy for coordinated multi-DC power support to ensure the transient stability of the system after DC blocking. Finally, an improved electromechanical-electromagnetic hybrid simulation model of the IEEE 68-node AC-DC hybrid system is built, and the correctness and effectiveness of the proposed strategy are verified through simulation.

Description

Technical Field

[0001] This invention relates to the field of power system stability control technology, and in particular to an emergency control method for coordinated multi-DC power support after DC blocking. Background Technology

[0002] my country's energy bases and load centers are distributed in reverse order. With the goal of "carbon peaking and carbon neutrality," addressing regional power imbalances and promoting the consumption of new energy sources has become a crucial strategic task. Direct current (DC) transmission technology, with its long-distance, large-capacity, and low-loss characteristics, has been widely applied in my country's power transmission sector. As of June 2021, my country had built and put into operation 17 ultra-high-voltage (UHVDC) transmission lines, forming the world's largest and highest-voltage AC / DC hybrid power grid. DC commutation failures caused by AC faults are unavoidable. Furthermore, according to operating procedures, three consecutive commutation failures on a DC line within a short period will further lead to its blocking, greatly increasing the probability of system power angle instability. Therefore, researching emergency control strategies for system transient stability after DC blocking is of great significance. Due to the flexibility and economy of a sound DC emergency power support system, it is the preferred choice for emergency control of system transient stability after DC blocking. In existing technologies, the fault process from commutation failure to DC blocking affects the emergency control scheme for transient stability developed after the fault. As the severity of the fault increases, it is necessary to coordinate multiple healthy DC lines to participate in power support. Currently, there are few reports on transient stability emergency control strategies for coordinated emergency power support from multiple DC lines after DC line blocking. Summary of the Invention

[0003] The purpose of this invention is to address the deficiencies mentioned in the background art by proposing an emergency control method for coordinated multi-DC power support after DC blocking.

[0004] The technical solution adopted in this invention is as follows:

[0005] An emergency control method for coordinated multi-DC power support after DC blocking is provided, comprising the following steps:

[0006] S1.1: Based on the slope change characteristics during the initial swing of the phase trajectory, the emergency control activation criterion is obtained;

[0007] S1.2: Apply the emergency control activation criterion to AC / DC hybrid systems;

[0008] S1.3: Based on the characteristics of the change in the stable equilibrium point after a fault, determine the multi-DC emergency power support collaborative control strategy;

[0009] S1.4: Build an improved electromechanical-electromagnetic hybrid simulation model of the IEEE 68-node AC / DC hybrid system and perform simulation.

[0010] As a preferred embodiment of the present invention: In S1.1, for a single-machine infinite bus system, the dynamic characteristics of its synchronous generator are expressed as follows:

[0011]

[0012] Among them, P m P is the mechanical input power; n M is the electromagnetic output power; δ is the inertia coefficient; Δω is the power angle; D is the relative angular velocity; and D is the damping coefficient.

[0013] For a phase plane trajectory consisting of the work angle and relative angular velocity, its slope is expressed as:

[0014]

[0015] During the initial swing after a fault, for a stable scenario, the slope k of the phase trajectory after the fault... t It is negative and gradually decreases to -∞; for unstable scenarios, the slope k of the phase trajectory after the fault is... t It first decreases gradually, then increases.

[0016] As a preferred embodiment of the present invention, the following conditions are met for the post-stabilized system:

[0017]

[0018] Where, δ a and Δω a The power angle and relative angular velocity at any moment after the fault; δ b and Δω b Let Δω be the maximum power angle and angular velocity of the initial swing after the fault. For a stable system after the fault, Δω b =0.

[0019] As a preferred technical solution of the present invention: using a constant k c Instead of the changing k t ,

[0020]

[0021] When the system is determined to be in an unstable state after a fault, δ a and Δω a The corresponding power angle and relative angular velocity when transient stabilization emergency control is adopted.

[0022] As a preferred technical solution of the present invention: ε = k t -k c During the initial swing, if the system reaches a stable state after the fault, ε gradually decreases, and k t With kc There must be an intersection point; if the system is in an unstable state after the fault, then ε will first decrease and then increase, and k t With k c There must be no intersection.

[0023] As a preferred technical solution of the present invention: based on k during the initial swing process t With k c The following is a criterion for initiating transient stability emergency control, obtained from the curve of the change characteristic:

[0024] dε / dt>0 for 5·T

[0025] Among them, f e =50Hz is the system frequency;

[0026] After emergency control measures are taken, the system meets the following requirements:

[0027] k c ≥k t

[0028] Action quantity P when using transient stable emergency control a satisfy:

[0029] P a ≥P an =(k t -k c )MΔω a

[0030] Among them, P an This is the required control quantity.

[0031] As a preferred embodiment of the present invention: In S1.2, in the AC / DC hybrid system, the synchronous generators disturbed after a fault are divided into two groups. The DC sending-end generator group is defined as group K, and the DC receiving-end generator group is defined as group S. They are equivalent to a two-machine system connected by AC and DC lines. It is assumed that the synchronous generator has uniform damping, i.e., μ = D. i / M i Based on CCCOI-RM, the dynamic characteristics of the synchronous generators of the sending-end K group and the receiving-end S group are expressed as follows:

[0032]

[0033] Where X = K or S, δ X =∑ i∈X M i δ i / ∑ i∈X M i ω X =∑ i∈X M i ω i / ∑i∈X M i P eX =∑ i∈X P ei P mX =∑ i∈X P mi ;

[0034] get:

[0035]

[0036]

[0037] Among them, M E =M K M S / M K +M S ,P eE =(M S P eK -M K P eS ) / M E δ E =δ K -δ S ,

[0038] The slope of the phase trajectory of the AC / DC hybrid system is:

[0039]

[0040] at the same time:

[0041]

[0042] get:

[0043]

[0044] in, The unstable equilibrium point δ of the system network topology after emergency control measures are taken. Eu replace.

[0045] As a preferred embodiment of the present invention: in step S1.3, when DC power participates in emergency power support, the DC power is first increased to 1.3P. d It lasted for 3 seconds, then dropped to 1.1P. d Long-term operation; DC emergency power support is adopted to meet:

[0046]

[0047] Let the DC boost power ΔP dFor the sending-end system, this is equivalent to switching the machine ΔP. d For the receiving-end system, this is equivalent to shearing the load ΔP. d Then the equivalent increase in unbalanced power is:

[0048]

[0049] When DC is blocked, if the system meets the emergency power input criteria after the fault, the transient stability emergency control will be activated to ensure the safety and stability of the system after the fault.

[0050] As a preferred technical solution of the present invention: In S1.4, the simulation model is built as follows, using the New England power system as the sending end, and connected to the New York power system via three DC lines and one AC line; the transmission power of the DC lines DC1, DC2 and DC3 is P. d1 =P d2 =P d3 =500MW, and DC1 is an electromagnetic model. The synchronous generator has uniform damping, i.e., μ = D i / M i The simulation step size for the electromechanical model is 0.01s, the simulation compensation for the electromagnetic model is 50μs, and the total simulation time is 5s.

[0051] As a preferred embodiment of the present invention: after DC1 is blocked, DC2 and DC3 are used respectively to participate in the post-fault stable equilibrium point δ during emergency DC power support. sep2 <δ sep3 In this process, DC2 and DC3 are used sequentially to provide emergency DC power support, and the maximum value of the initial swing angle δ is taken. fm As an indicator for evaluating the effectiveness of support.

[0052] The emergency control method for coordinated multi-DC power support after DC blocking provided by this invention has the following advantages compared with the prior art:

[0053] This invention proposes an emergency control strategy involving coordinated multi-DC power support to ensure the transient stability of the system after DC blocking. First, based on the slope change characteristics during the initial phase trajectory swing, an emergency control activation criterion is obtained, and analytical expressions for the control quantity, control activation time, system inertia, and other parameters are derived. Second, a mathematical relationship between the control quantity and the number of DC power support entries is established, and the order of DC power support is determined based on the post-fault stability equilibrium point change characteristics. Finally, an improved electromechanical-electromagnetic hybrid simulation model of the IEEE 68-node AC / DC hybrid system is built, and simulations verify the correctness and effectiveness of the proposed strategy. Attached Figure Description

[0054] Figure 1 This is a flowchart of a preferred embodiment of the present invention;

[0055] Figure 2 This is a phase plane trajectory diagram of stable and unstable scenarios in a preferred embodiment of the present invention;

[0056] Figure 3 This is a slope diagram of phase trajectories for stable and unstable scenarios in a preferred embodiment of the present invention;

[0057] Figure 4 This is a diagram showing the characteristic of phase trajectory slope variation in a stable scenario according to a preferred embodiment of the present invention.

[0058] Figure 5 This is a diagram showing the characteristic of phase trajectory slope variation in an unstable scenario according to a preferred embodiment of the present invention.

[0059] Figure 6 This is a model diagram of an equivalent AC / DC hybrid system in a preferred embodiment of the present invention;

[0060] Figure 7 This is a diagram of a DC emergency support strategy in a preferred embodiment of the present invention;

[0061] Figure 8 This is a diagram of a multi-DC emergency power support coordination strategy in a preferred embodiment of the present invention;

[0062] Figure 9 This is an equivalent schematic diagram of DC power support in a preferred embodiment of the present invention;

[0063] Figure 10 This is a diagram of an improved IEEE-68 node AC / DC hybrid system in a preferred embodiment of the present invention;

[0064] Figure 11 This is an equivalent schematic diagram of DC power support in a preferred embodiment of the present invention;

[0065] Figure 12 This is a phase trajectory slope diagram for scenario 1 in a preferred embodiment of the present invention;

[0066] Figure 13 This is a DC power diagram for scenario 1 in a preferred embodiment of the present invention;

[0067] Figure 14 This is a slope diagram of the phase trajectory in scenario 2 of the preferred embodiment of the present invention;

[0068] Figure 15 This is a DC power diagram for scenario 2 in a preferred embodiment of the present invention. Detailed Implementation

[0069] It should be noted that, unless otherwise specified, the embodiments and features described in this embodiment can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0070] Reference Figure 1 A preferred embodiment of the present invention provides an emergency control method for coordinated multi-DC power support after DC blocking, comprising the following steps:

[0071] S1.1: Based on the slope change characteristics during the initial swing of the phase trajectory, the emergency control activation criterion is obtained;

[0072] S1.2: Apply the emergency control activation criterion to AC / DC hybrid systems;

[0073] S1.3: Based on the characteristics of the change in the stable equilibrium point after a fault, determine the multi-DC emergency power support collaborative control strategy;

[0074] S1.4: Build an improved electromechanical-electromagnetic hybrid simulation model of the IEEE 68-node AC / DC hybrid system and perform simulation.

[0075] In S1.1, for a single-machine infinite bus system, the dynamic characteristics of its synchronous generator are expressed as follows:

[0076]

[0077] Among them, P m P is the mechanical input power; n M is the electromagnetic output power; δ is the inertia coefficient; Δω is the power angle; D is the relative angular velocity; and D is the damping coefficient.

[0078] For a phase plane trajectory consisting of the work angle and relative angular velocity, its slope is expressed as:

[0079]

[0080] During the initial swing after a fault, for a stable scenario, the slope k of the phase trajectory after the fault... t It is negative and gradually decreases to -∞; for unstable scenarios, the slope k of the phase trajectory after the fault is... t It first decreases gradually, then increases.

[0081] For a post-stabilized system, the following conditions must be met:

[0082]

[0083] Where, δ a and Δω a The power angle and relative angular velocity at any moment after the fault; δ b and Δω b Let Δω be the maximum power angle and angular velocity of the initial swing after the fault. For a stable system after the fault, Δω b =0.

[0084] Using a constant k c Instead of the changing k t ,

[0085]

[0086] When the system is determined to be in an unstable state after a fault, δ a and Δω a The corresponding power angle and relative angular velocity when transient stabilization emergency control is adopted.

[0087] Define ε = k t -k c During the initial swing, if the system reaches a stable state after the fault, ε gradually decreases, and k t With k c There must be an intersection point; if the system is in an unstable state after the fault, then ε will first decrease and then increase, and k t With k c There must be no intersection.

[0088] Based on the k in the initial swing process t With k c The following is a criterion for initiating transient stability emergency control, obtained from the curve of the change characteristic:

[0089] dε / dt>0 for 5·T

[0090] Among them, f e =50Hz is the system frequency;

[0091] After emergency control measures are taken, the system meets the following requirements:

[0092] k c ≥k t

[0093] Action quantity P when using transient stable emergency control a satisfy:

[0094] P a ≥P an =(k t -k c )MΔω a

[0095] Among them, Pan This is the required control quantity.

[0096] In S1.2, in the AC / DC hybrid system, the synchronous generators disturbed after a fault are divided into two groups: the DC sending-end generator group is defined as group K, and the DC receiving-end generator group is defined as group S. These are considered equivalent to a two-generator system connected by AC and DC lines. It is assumed that the synchronous generators have uniform damping, i.e., μ = D. i / M i Based on CCCOI-RM, the dynamic characteristics of the synchronous generators of the sending-end K group and the receiving-end S group are expressed as follows:

[0097]

[0098] Where X = K or S, δ X =∑ i∈X M i δ i / ∑ i∈X M i ω X =∑ i∈X M i ω i / ∑ i∈X M i P eX =∑ i∈X P ei P mX =∑ i∈X P mi ;

[0099] get:

[0100]

[0101]

[0102] Among them, M E =M K M S / M K +M S ,P eE =(M S P eK -M K P eS ) / M E δ E =δ K -δ S ,

[0103] The slope of the phase trajectory of the AC / DC hybrid system is:

[0104]

[0105] at the same time:

[0106]

[0107] get:

[0108]

[0109] in, The unstable equilibrium point δ of the system network topology after emergency control measures are taken. Eu replace.

[0110] In S1.3, when DC power participates in emergency power support, the DC power is first increased to 1.3P. d It lasted for 3 seconds, then dropped to 1.1P. d Long-term operation; DC emergency power support is adopted to meet:

[0111]

[0112] Let the DC boost power ΔP d For the sending-end system, this is equivalent to switching the machine ΔP. d For the receiving-end system, this is equivalent to shearing the load ΔP. d Then the equivalent increase in unbalanced power is:

[0113]

[0114] When DC is blocked, if the system meets the emergency power input criteria after the fault, the transient stability emergency control will be activated to ensure the safety and stability of the system after the fault.

[0115] In S1.4, the simulation model is built as follows: the New England power system is used as the sending end, and it is connected to the New York power system via three DC lines and one AC line; the transmission power of the DC lines DC1, DC2 and DC3 is P. d1 =P d2 =P d3 =500MW, and DC1 is an electromagnetic model. The synchronous generator has uniform damping, i.e., μ = D i / M i The simulation step size for the electromechanical model is 0.01s, the simulation compensation for the electromagnetic model is 50μs, and the total simulation time is 5s.

[0116] After DC1 is blocked, DC2 and DC3 are used respectively to participate in the emergency DC power support to achieve the post-fault stable equilibrium point δ. sep2 <δ sep3 In this process, DC2 and DC3 are used sequentially to provide emergency DC power support, and the maximum value of the initial swing angle δ is taken. fmAs an indicator for evaluating the effectiveness of support.

[0117] In this embodiment, based on the phase plane trajectory of the single-machine infinite system, the phase trajectory and its slope variation characteristics under stable and unstable scenarios can be obtained, such as... Figure 2 , Figure 3 As shown, by Figure 2 , Figure 3 It can be seen that during the initial swing after the fault, for a stable scenario, the slope k of the phase trajectory after the fault... t It is negative and gradually decreases to -∞; while for unstable scenarios, the slope k of the phase trajectory after the fault is... t First, gradually decrease, then increase. For a system that has stabilized after a fault, use a constant k. c Instead of the changing k t ,

[0118]

[0119] When the system is determined to be in an unstable state after a fault, δ a and Δω a The corresponding power angle and relative angular velocity when transient stabilization emergency control is adopted.

[0120] Figure 4 , Figure 5 The slope k of the phase trajectory during the initial swing is given for both stable and unstable scenarios after the fault. t With constant k c The characteristic curve of change. Define ε = k t -k c ,Depend on Figure 4 , Figure 5 It can be seen that during the initial swing, if the system is in a stable state after the fault, ε gradually decreases, and k t With k c There must be an intersection point; if the system is in an unstable state after the fault, then ε will first decrease and then increase, and k t With k c There must be no intersection.

[0121] Based on the slope change characteristics during the initial swing of the phase trajectory, the emergency control input criterion is obtained;

[0122] dε / dt>0 for 5·T

[0123] Among them, f e =50Hz is the system frequency;

[0124] After emergency control measures are taken, the system meets the following requirements:

[0125] k c ≥k t

[0126] Action quantity P when using transient stable emergency control a satisfy:

[0127] P a ≥P an =(k t -k c )MΔω a

[0128] Among them, P an This is the required control quantity.

[0129] Further application to AC / DC hybrid systems: In AC / DC hybrid systems, the synchronous generators disturbed after a fault can be divided into two groups. The DC sending-end generator group is defined as group "K," and the DC sending-end generator group is defined as group "S." This group is then considered equivalent to a two-machine system connected by both AC and DC lines, such as... Figure 6 As shown.

[0130] Assume the synchronous generator has uniform damping, i.e., μ = D i / M i Based on CCCOI-RM, the dynamic characteristics of the synchronous generators of the sending-end K group and the receiving-end S group are expressed as follows:

[0131]

[0132] Where X = K or S, δ X =∑ i∈X M i δ i / ∑ i∈X M i ω X =∑ i∈X M i ω i / ∑ i∈X M i P eX =∑ i∈X P ei P mX =∑ i∈X P mi ;

[0133] get:

[0134]

[0135]

[0136] Among them, M E =M K M S / M K +M S ,PeE =(M S P eK -M K P eS ) / M E δ E =δ K -δ S ,

[0137] The slope of the phase trajectory of the AC / DC hybrid system is:

[0138]

[0139] at the same time:

[0140]

[0141] get:

[0142]

[0143] in, The unstable equilibrium point δ of the system network topology after emergency control measures are taken. Eu replace.

[0144] According to the DC operation regulations, DC power supplies have a short-term overload capacity of 0.30–0.50 and a long-term overload capacity of 0.05–0.10. Figure 7 As shown. To reduce the negative impact of power fluctuations on system safety and stability, in this paper, when DC participates in emergency power support, the DC power is first increased to 1.3P. d It lasted for 3 seconds, then dropped to 1.1P. d Long-term operation.

[0145] The following requirements must be met when using DC emergency power support:

[0146]

[0147] Let the DC boost power ΔP d For the sending-end system, this is equivalent to switching the machine ΔP. d For the receiving-end system, this is equivalent to shearing the load ΔP. d Then the equivalent increase in unbalanced power is:

[0148]

[0149] When DC power is blocked, if the post-fault system meets the emergency power input criteria, transient stability emergency control will be activated to ensure the safety and stability of the post-fault system. Furthermore, depending on the fault situation, emergency control measures may involve not only one healthy DC power source, but also multiple healthy DC power sources working together to provide power support, such as... Figure 8 As shown.

[0150] For AC / DC hybrid systems containing multiple DC lines, the order in which DC lines participate in support needs to be further determined. Once DC lines participate in support, the system's mechanical power P can be equated to this. m Reduced ΔP d ,like Figure 9 As shown, in an AC / DC hybrid system, the Post-Fault Stability Equilibrium (SEP) varies depending on the DC power participation. According to the equal area method, a smaller SEP indicates a larger post-fault deceleration area, resulting in better DC power support and prioritizing its participation in emergency power support.

[0151] An improved electromechanical-electromagnetic hybrid simulation model of an IEEE 16-machine, 68-node AC / DC hybrid system was constructed, with the network topology as follows: Figure 10 As shown. The New England power system, as the sending end, is connected to the New York power system, as the receiving end, via three DC lines and one AC line. The transmission power of the DC lines DC1, DC2, and DC3 is P. d1 =P d2 =P d3 =500MW, and DC1 is an electromagnetic model. The synchronous generator has uniform damping, i.e., μ = D i / M i The simulation step size for the electromechanical model is 0.01s, and the simulation step size for the electromagnetic model is 50μs, with a total simulation time of 5s.

[0152] Calculations show that after DC1 is blocked, the post-fault stable equilibrium point δ is obtained when DC2 and DC3 are used for emergency DC power support. sep2 <δ sep3 Theoretical analysis shows that the order of DC power support is DC2→DC3. DC2 and DC3 are used for emergency DC power support respectively, and the maximum initial swing angle δ is taken. fm As an indicator for evaluating the effectiveness of the support, Table 1 shows a comparison of different DC power support levels. The simulation results are consistent with the theoretical analysis.

[0153] Table 1

[0154] DC2 41.698 73.561 DC3 42.627 73.794

[0155] It should be noted that the DC power is urgently increased by ΔP d However, due to the influence of the system network structure and parameters, it only improved ΔP′ in practice.d This can be obtained through testing. The emergency boost in DC power can be considered a power surge, at which point the equivalent output electromagnetic power P... e This will increase accordingly; after the upgrade is complete, P e It will rapidly decline from its peak value; finally, under the influence of system damping, it will gradually converge to its steady-state value. Define P after the decline. e The change is the effective increase in DC power. Under steady-state operating conditions, the transmission power of DC2 and DC3 is increased by 30%, or 1.5 pu, respectively. Figure 11 As shown. It can be obtained that ΔP′ d3 =0.36pu.

[0156] Scene 1

[0157] A series of short-circuit faults were introduced at Bus-61 of the AC system, causing three commutation failures in DC1 within a short period of time, resulting in DC1 blockage. Detailed information for the three short-circuit faults is as follows: f (1) -0.40s, 0.01s; f (1) -0.20s, 0.01s; f (3) , 0.00s, 0.06s (fault type, fault occurrence time, fault duration).

[0158] Based on the emergency power activation criterion, the system will activate transient stability emergency control measures at t=0.54s. Figure 12 As shown in the cooperative strategy, assuming DC2 is engaged to provide power support, δ can be calculated. Eu =89.93°, and combined with the DC emergency power support, the time P to be activated for control can be calculated. an =0.36pu; while when using DC2, P a =0.42pu>P an Therefore, it can be seen that using only DC2 for emergency power support is sufficient to ensure the transient stability of the system after the fault, and this has been verified through simulation. Figure 12 , Figure 13 As shown.

[0159] Scene 2

[0160] A series of short-circuit faults were introduced at Bus-61 of the AC system, causing DC1 to experience three commutation failures within a short period, resulting in DC1 being blocked. The detailed information for the three short-circuit faults is as follows: f (1) -0.40s, 0.01s; f (1) -0.20s, 0.01s; f (3) , 0.00s, 0.08s.

[0161] Based on the emergency power input criterion, the system will initiate transient stability emergency control measures at t = 0.51s. At this point, if only DC2 provides power support, the system's safety and stability after the fault cannot be guaranteed. Assuming both DC2 and DC3 participate in power support, δ can be calculated. Em =92.18°, and combined with the DC emergency power support, the moment P is activated can be calculated. an =0.59pu; while when using DC2 and DC3, P a =0.78pu>P an Therefore, it can be seen that DC2 and DC3 can be used for emergency power support, and this has been verified through simulation. Figure 14 , Figure 15 As shown.

[0162] To investigate the conservatism of the transient stability emergency control scheme formulated by the proposed strategy, a series of AC faults were set at different locations in the near-zone AC system on the DC1 inverter side to simulate multiple commutation failures and blockouts of the DC circuit within a short period of time. Detailed information for the three short-circuit faults is as follows: f (1) -0.40s, 0.01s; f (1) -0.20s, 0.01s; f (3) , 0.00s, t L (Fault type, fault occurrence time, fault duration). Define Scheme 1: DC2 improved by 30%; Scheme 2: DC2 and DC3 improved by 30%. Using the proposed strategy and time-domain simulation, compare and analyze the longest possible duration t of the third fault under each scheme. L .

[0163] Table 2

[0164]

[0165] L1 and L2 are the AC lines between Bus61 and Bus30, and between Bus61 and Bus36, respectively.

[0166] As shown in Table 2, the proposed emergency control strategy's multi-DC collaborative power support scheme is 0–0.01 s more conservative than the time-domain simulation method, further demonstrating the correctness and effectiveness of the proposed emergency control strategy with multi-DC collaborative power support.

[0167] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0168] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An emergency control method for coordinated multi-DC power support after DC blockage, characterized in that: Includes the following steps: S1.1: Based on the slope change characteristics during the initial swing of the phase trajectory, the emergency control activation criterion is obtained; S1.2: Apply the emergency control activation criterion to AC / DC hybrid systems; S1.3: Based on the characteristics of the change in the stable equilibrium point after a fault, determine the multi-DC emergency power support collaborative control strategy; S1.4: Build and simulate an improved electromechanical-electromagnetic hybrid simulation model of the IEEE 68-node AC / DC hybrid system; In step S1.3, when DC power participates in emergency power support, the DC power is first increased to 1.

3. It lasted for 3 seconds, then dropped to 1.

1. Long-term operation; DC emergency power support is adopted to meet: ; Let be the slope of the phase trajectory. It is a constant; Assume DC boost power For the sending-end system, this is equivalent to machine switching. For the receiving-end system, this is equivalent to load shedding. Then the equivalent increase in unbalanced power is: ； When DC is blocked, if the system meets the emergency power input criteria after the fault, the transient stability emergency control will be activated to ensure the safety and stability of the system after the fault.

2. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 1, characterized in that: In S1.1, for a single-machine infinite bus system, the dynamic characteristics of its synchronous generator are expressed as follows: ； in, This refers to mechanical input power; Electromagnetic output power; The inertia coefficient; For the angle of attack; Relative angular velocity; The damping coefficient; For a phase plane trajectory consisting of the work angle and relative angular velocity, its slope is expressed as: ； During the initial swing after a fault, for a stable scenario, the slope of the phase trajectory after the fault... It is negative and gradually decreases to For unstable scenarios, the slope of the phase trajectory after the fault It first decreases gradually, then increases.

3. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 2, characterized in that: For a post-stabilized system, the following conditions must be met: ； in, and The power angle and relative angular velocity are given at any moment after the fault. and Given the maximum power angle and angular velocity of the initial swing after the fault, for a post-fault stabilization system, .

4. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 3, characterized in that: Using constants Instead of change , ； When the system is determined to be in an unstable state after a fault. and The corresponding power angle and relative angular velocity when transient stabilization emergency control is adopted.

5. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 4, characterized in that: Based on the initial swing process and The following is a criterion for initiating transient stability emergency control, derived from the curve of the change characteristic: ； in, For system frequency; After emergency control measures are taken, the system meets the following requirements: ； Action quantity when using transient stable emergency control satisfy: ； in, This is the required control quantity.

6. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 1, characterized in that: In S1.2, in the AC / DC hybrid system, the synchronous generators disturbed after a fault are divided into two groups: the DC sending-end generator group is defined as group K, and the DC receiving-end generator group is defined as group S. These are considered equivalent to a two-generator system connected by AC and DC lines. It is assumed that the synchronous generators have uniform damping, i.e. Based on CCCOI-RM, the dynamic characteristics of the synchronous generators of the sending-end K group and the receiving-end S group are expressed as follows: ； in, or , , , , ; get: ； in, , , , , ; The slope of the phase trajectory of the AC / DC hybrid system is: ； at the same time: ； get: ； in, The unstable equilibrium point of the system network topology after emergency control measures are taken. replace.

7. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 1, characterized in that: In S1.4, the simulation model is built as follows: the New England power system is used as the sending end, connected to the New York power system as the receiving end via three DC lines and one AC line; the transmission power of DC lines DC1, DC2, and DC3 is... Furthermore, DC1 is an electromagnetic model, and the synchronous generator has uniform damping, i.e. The simulation step size for the electromechanical model is 0.01s, and the compensation for the electromagnetic model simulation is 50. The total simulation duration is 5 seconds.

8. The emergency control method for coordinated multi-DC power support after DC blocking according to claim 7, characterized in that: After DC1 is blocked, DC2 and DC3 are used respectively to participate in the post-fault stabilization equilibrium point during emergency DC power support. In this process, DC2 and DC3 are used sequentially to provide emergency DC power support, and the maximum value of the initial swing angle is taken. As an indicator for evaluating the effectiveness of support.

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