CN117878940B - Cascading failure blocking control method and system considering source-network-load coordination - Google Patents
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Abstract
The invention relates to a cascading failure blocking control method and system considering source-network-load coordination, wherein the method comprises the following steps: the space-time characteristics of element fault cascade evolution are considered, an overload leading type cascading failure simulation model is established, a failure chain is generated, and a power failure risk index is calculated; calculating time-risk comprehensive importance indexes by considering the system fault reaction capacity and coping cost performance, and determining the optimal input position of the blocking control strategy in fault development; respectively considering the rapid and flexible network topology switching characteristics and the load grading characteristics of the climbing of the gas turbine unit at the source, network and load sides, constructing a blocking control model based on source-network-load joint adjustment, and solving to obtain an optimal blocking control strategy; and controlling the power transmission network based on the optimal input position and the optimal blocking control strategy. Compared with the prior art, the invention has the advantages of effectively relieving the power failure risk of the cascading failure, obviously improving the economical efficiency and reliability of blocking control, and the like.
Description
Technical Field
The invention relates to the technical field of power transmission network fault control, in particular to a cascading failure blocking control method and system considering source-network-load coordination.
Background
As extreme disasters increase and new energy becomes more permeable, safe operation of the power system is more susceptible to disturbance, and the construction of the elastic power grid is becoming more important. The transmission network is generally complex in structure and large in scale, so that the possibility of blackout caused by cascading faults is remarkably increased under the background of high failure rate of power elements caused by extreme weather. This requires that the grid should be flexible, and one of its characteristics is the ability to adequately resist, absorb, respond and adapt during extreme disturbances to maintain high operating levels and power performance. The annual blackout report shows that most blackout accidents are induced by cascading failures, and the local small interference such as generator and transmission line failures is continuously amplified through the connection action of network topology, so that the network elements are continuously withdrawn to have a malignant cascade effect, which causes serious economic loss and bad social influence. Therefore, the risk of cascading failures is evaluated, a corresponding blocking control strategy is provided, and the method has important theoretical value and practical significance for establishing a sound system safety defense system and improving the elasticity of the power grid in extreme weather.
And no effective cascading failure blocking control strategy is disclosed in the prior art.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the cascading failure blocking control method and system which can effectively relieve the power failure risk of the cascading failure and remarkably improve the economical efficiency and the reliability of blocking control and account for source-network-load cooperation.
The aim of the invention can be achieved by the following technical scheme:
a cascading failure blocking control method considering source-network-load cooperation comprises the following steps:
Acquiring network parameters and system initial states of a power transmission network, establishing an overload leading type cascading failure simulation model by considering space-time characteristics of element failure cascading evolution, generating a failure chain, and calculating a power failure risk index;
Based on the fault chain and the power failure risk index, calculating a time-risk comprehensive importance index by considering the system fault reaction capacity and coping cost performance, and determining the optimal input position of the blocking control strategy in fault development;
Respectively considering the rapid and flexible network topology switching characteristics and the load grading characteristics of the climbing of the gas turbine unit at the source, network and load sides, constructing a blocking control model based on source-network-load joint adjustment, and solving to obtain an optimal blocking control strategy;
and controlling the power transmission network based on the optimal input position and the optimal blocking control strategy.
Further, the space-time characteristics of the element fault cascade evolution comprise a time evolution model based on overload protection and a line outage probability model.
Further, the space-time characteristic model of the element fault cascade evolution is as follows:
Wherein Δo ij,k(ts,ts+Δts) is the overload severity of overload line k increasing during the time t s to t s+Δts of the s-th failure link; f ij,k (t) is the active power flow of a line k connecting the node i and the node j at the moment t; the tidal current transmission capacity of the line k; o ij,k(ts) is the total cumulative overload at time t s; s all is the total fault ring number of the cascading faults; an overload cumulative value defined as the overload line operating at a power flow exceeding 50% of its transmission capacity for 5 s; Time s required for cutting off the overload line k from the moment; The fault line of the (s+1) th fault link and the time required for switching on and off; s overL,s is an overload line set in the system when the cascading failure progresses to the S-th failure link.
Further, the line outage probability model is as follows:
Wherein p is the line outage probability; p 0 is the hidden fault probability of protection; p 1 is the line power flow exceeds the line transmission capacity limit The outage probability at the time; f ij,k is the active power flow of line k.
Further, the step of generating the fault chain includes:
step 1: setting a linkage evolution start time t=0;
step 2: taking N-k random broken lines as the source faults for inducing cascading faults;
Step 3: updating network topology parameters, judging whether the network topology parameters are separated into regional islands, if so, turning to step 7, otherwise, turning to the next step;
Step 4: judging whether a node island is formed, if so, entering the next step, otherwise, entering the step 6;
step 5: balancing the power of a source side and a load side of the system;
Step 6: calculating the direct current power flow of the system, judging whether an overload circuit exists, if so, switching off the circuit which needs to be switched off in the next fault link according to the fault circuit in the next fault link and the time required by switching off, updating the evolution time, and turning to the step 3, otherwise, entering the next step;
step 7: and calculating load loss, arranging time evolution information, and outputting a fault chain.
Further, the power failure risk index has the following expression:
wherein, The probability when the fault link R x evolves to the fault link m; load loss for the failure chain f x.
Further, the time-risk comprehensive importance index is:
wherein, The time-risk comprehensive importance index is used; the risk influence degree index of the fault link is obtained based on the power failure risk index; The time adequacy index is obtained based on the occurrence time of a fault link in the fault chain and the time spent by the evolution of the fault chain.
Further, the objective function of the blocking control model based on the source-network-load joint adjustment is the total control cost of the source side and the load side, and the load loss amount from low to high according to the importance degree is minimum, and the constraint conditions comprise source side constraint, network side constraint and load side constraint.
Further, a YALMIP toolkit and Gurobi solver are invoked to solve the blocking control model based on the source-network-load joint adjustment.
The present invention also provides a source-network-load synergy-taking-into account cascading failure blocking control system comprising one or more processors, memory, and one or more programs stored in the memory, the one or more programs comprising instructions for executing the source-network-load synergy-taking-into account cascading failure blocking control method as described above.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, by considering the load grading characteristic, three-level loads with lower importance of each node can participate in scheduling as much as possible, so that the load cutting-off amount is effectively prevented from accumulating on a few nodes, the important two-level load is cut off, the huge control cost is realized, and the power failure risk of the cascading failure is effectively relieved.
(2) The invention respectively considers the quick climbing, flexible topology switching characteristic and load grading characteristic of the gas turbine units at the source, the network and the load side, formulates a cascading failure blocking control strategy, improves the elasticity of the system when encountering a failure, and can greatly improve the economical efficiency and the reliability of regulation.
Drawings
FIG. 1 is a schematic flow chart of the present invention;
FIG. 2 is a flow chart of cascading failure simulation;
FIG. 3 is a source-net-load cooperative control mode;
FIG. 4 is a space-time evolution of a fault chain;
FIG. 5 is a graph of gas turbine output at different ramp rates;
FIG. 6 shows control results at different numbers of breaks;
fig. 7 is a comparison of the two-stage loads before and after control without considering the load classification characteristic.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
Example 1
The present embodiment provides a cascading failure blocking control method considering source-network-load coordination, as shown in fig. 1, the method includes the following steps:
s1, taking the space-time characteristics of element fault cascade evolution into consideration, and establishing an overload leading type cascading failure simulation model and a risk assessment model.
The cascading failures mainly comprise three types according to driving factors: overload leading type, cooperation leading type and structure leading type, wherein overload leading type cascading failure blackout accident is more common. Most overload leading type cascading faults exist in a major power failure initiation stage and a protective device successive slow action stage, and are specifically represented by the process that a circuit is tripped due to overload of power flow, and then network power flow is redistributed, so that other circuits are tripped successively due to overload of power flow. During the overload leading type cascading failure propagation period, the network structure is not seriously damaged, the physical quantity changes of power, voltage and the like are relatively slow, the system is basically in a stable state, and the failure defense time is relatively sufficient. In the embodiment, the space-time characteristics of the fault cascade evolution are considered, and the defense research is mainly conducted on overload leading type cascading faults.
In this embodiment, the space-time characteristics of the element fault cascade evolution include a time evolution model based on overload protection and a line outage probability model.
(1) Time evolution model based on overload protection
The larger the line load rate is, the longer the overload duration is, the more serious the line overload degree is, and the overload severity increased in a certain time is reflected by using an overload cumulative function, as shown in the formula (1):
Wherein Δo ij,k(ts,ts+Δts) is the overload severity of overload line k increasing during the time t s to t s+Δts of the s-th failure link; f ij,k (t) is the active power flow of a line k connecting the node i and the node j at the moment t; Is the tidal current transmission capacity of line k.
Total cumulative overload at time t s O ij,k(ts) is as shown in formula (2):
wherein s all is the total failure ring number of the cascading failure.
The overload cumulative value O ij,k reaches its critical valueIn the event of overload protection, line k will be cut off.Is defined as the cumulative overload value of the overload line when it is operated for 5s at a power flow exceeding 50% of its transmission capacity, as shown in formula (3).
At time t s, the time required for cutting off the k distance of the overload circuitAs shown in formula (4). Faulty line of the (s+1) th faulty link and time required for breakingAs shown in formula (5).
S overL,s is an overload line set in the system when the cascading failure progresses to the S-th failure link.
(2) Line outage probability model
The circuit operation reliability model comprehensively considers the influence of the real-time operation state of the circuit and the hidden fault of the relay protection, indicates that the circuit outage probability is closely related to the circuit power flow, a curve of the outage probability along with the change of the power flow is shown in fig. 1, and the mathematical expression can be represented by adopting the formula (6) and the formula (7):
wherein, Is a line transmission capacity limit.
(3) Cascading failure simulation model
The simulation flow of the cascading failure time-space evolution is shown in figure 2, wherein the regional island is a subnet formed by connecting two or more nodes by lines; a nodal island is an isolated node of a wireless link connection. The specific generation steps of the fault chain are as follows:
step 1: setting a power network parameter, determining a system initial state, and setting a linkage evolution starting time t=0.
Step 2: n-k random wire breakage is used as a source fault for inducing cascading failure.
Step 3: updating network topology parameters, judging whether the network topology parameters are split into regional islands, and if so, switching to the step 7; otherwise, the next step is carried out.
Step 4: judging whether a node island is formed, if so, entering the next step; otherwise go to step 6.
Step 5: balance system source side and load side power.
Step 6: calculating system direct current power flow, judging whether an overload circuit exists or not, if so, switching off the circuit to be switched off in the next fault link according to the formula (5), updating evolution time, and switching to the step (3); otherwise, go to the next step.
Step 7: and calculating load loss, arranging time evolution information, and outputting a fault chain.
(4) Cascading failure risk assessment model
According to the generated sequential fault chain, the evolution paths of the fault chain set f and the x-th fault chain f x can be expressed as:
Г＝{Г1,Г2,…,Гw} (8)
Гx＝{Гx,1,Гx,2,…,Гx,y} (9)
Wherein, f x,j is the j-th failure link of the failure link f x, i.e. failure link j, x=1, 2, …, w, j=1, 2, …, y.
Probability of failure chain f x occurrenceCan be expressed as:
wherein, Is the probability of occurrence of the failure chain f x; p (gamma x,y|Гx,1,Гx,2,…,Гx,y-1) is the probability of occurrence of the fault link y under the condition that the previous y-1 fault links occur; Is the probability of the failure chain f x evolving to the failure link m.
In the embodiment, the severity of the accident is quantified by the sum of the products of the probability of occurrence of the fault chain to each link and the load loss generated by the link, so as to ensure that as long as the fault link occurs, the risk is inevitably monotonically not reduced, and the power failure risk index is expressed as a formula (11):
wherein, The probability when the fault link R x evolves to the fault link m; Load loss for the failure chain f x; y represents the total number of failed links in the failed chain Γ x.
S2, considering the system fault reaction capability and coping cost performance, providing a time-risk comprehensive importance index, and determining the optimal input position of the blocking control strategy in fault development.
The embodiment defines the time adequacy index as shown in formula (12)And (5) characterizing fault reaction and coping capacity of the system at a time level.
Wherein,The time it takes for the failure chain f x to evolve; The moment when a failure link m of the failure link f x losing the load occurs; The time when the fault link or the initial fault link based on the previous load loss of the fault link m occurs.
The risk influence degree index of the failure link in this embodiment is shown as (13).
Wherein,The failure risk is the failure risk when the failure link m of the failure load in the failure link R x occurs; the failure wind risk is generated when the last load loss failure link or the initial failure link based on the failure link m occurs.
Time-risk comprehensive importance index of each failure link in this embodimentThe following is shown:
The larger the dispatching department is, the more reinforced the fault response and the coping capability are, and the more cost-effective blocking is carried out on the cascading faults. Thus, in And the blocking control strategy is put into the position of the largest fault link, so that the fault cascade evolution is reliably restrained, and the blackout risk of the cascading accident is effectively reduced.
S3, respectively considering the climbing rapidity, flexible network topology switching characteristics and load grading characteristics of the gas turbine unit at the source, network and load sides, and constructing a blocking control model based on source-network-load joint adjustment.
By coordinating source-network-load side resources and characteristics, blocking control of cascading failures is realized, and elasticity of a system is improved. The blocking control mode which takes source-network-load cooperation into account when the power grid fails in series is shown in fig. 3.
The goal of the source-network-load cooperative control is to minimize the load loss from low to high according to the total control cost of the source and the load side and the importance, and the objective function is as follows:
minΨ＝ΨG,reg+ΨG,trip+ΨL,trip (15)
Wherein ψ is the total control cost; the power generator output adjustment cost, the cutting cost and the load cutting cost are respectively indicated by the psi G,reg,ΨG,trip and the psi L,trip; And (3) with Respectively, up-regulating the cost coefficient of the unit active power of the generator at the node i, down-regulating the cost coefficient of the unit active power of the generator, cutting the cost coefficient of the unit active power of the generator and cutting the unitCost factor of the stage load; n G and N L are the number of generator nodes and load nodes respectively; And (3) with The generator output at the node i before and after the blocking control; And (3) with At node i before and after blocking control, respectivelyStage load size.
The constraint conditions of the blocking control model based on the source-network-load joint adjustment mainly comprise source side constraint, network side constraint and load side constraint.
(1) Source side constraint
In the embodiment, the power balance of the system is maintained and the power flow distribution is changed by taking the control means of adjusting the output and the cut-off of the coal-fired unit and the gas-fired unit in the source measurement so as to achieve the aim of eliminating cascading failures as much as possible. The specific constraint to be satisfied is represented by the following formula (19) -formula (25):
Wherein, T i,ramp,Ri,ramp and u i are respectively the climbing time, the climbing speed and the running state of the generator at the node i, wherein u i =1 represents the normal running of the generator, and u i =0 represents the shutdown of the generator; And (3) with The climbing rates of the gas unit and the coal-fired unit are respectively; η i is a rapidness factor, and since the climbing speed of the gas unit is faster than that of the coal-fired unit, η i is more than or equal to 1; The time taken for the line k to open from this moment on; And (3) with Respectively the upper and lower limits of the output of the generator at the node i; And (3) with Respectively the upper limit and the lower limit which can be reached by the generator at the node i in the allowed time; t i,ramp is the climbing time of the generator rotor at the node i; And (3) with Respectively a node set of the generator before blocking control, a node set of the coal-fired unit and a node set of the gas-fired unit; s overL is a system overload line set.
Considering the climbing rapidity of the gas unit by the constraints, wherein the formula (19) is the climbing output constraint of the generator; the formula (20) is a generator state constraint; formula (21) is a hill climbing rapidity constraint of the gas turbine compared with the coal-fired unit; equation (22) -equation (24) is the upper and lower limit constraint of the climbing output of the generator; equation (25) is the allowable generator ramp time constraint.
The product of integer variable and continuous variable exists in the formula (19), which is a nonlinear term and is linearized into a large M method:
Where M 1 is a sufficiently large positive number.
(2) Net side restraint
On the network side, a plurality of lines are actively disconnected, so that the network topology structure and the power flow distribution are changed, and the network can be quickly adjusted and adapted when the network is faced to faults. The constraint to be satisfied is represented by the following formula (27) -formula (33):
[Fij,k-bij,k(θi-θj)]vij,k＝0,k∈Φbef (28)
vij,k∈{0,1},k∈Φbef (29)
Wherein Λ i is the set of nodes j connected to node i; b ij,k is the admittance value of line k; v ij,k is the running state of line k, v ij,k =1 indicates that line k is running normally, and v ij,k =0 indicates that line k is open; phi bef is a line set in the system before blocking control; θ i and θ j are the voltage phase angles at node i and node j, respectively; And (3) with The maximum value of the number of lines and the maximum value of the allowed line disconnection in the system before blocking control; And (3) with The maximum value and the minimum value of the phase angle of the voltage at the node i are respectively; theta s The phase angle of the balance node and the initial phase angle, respectively.
The constraints take into account flexible network topology switching characteristics, wherein the formula (27) is a node power balance constraint; formula (28) is a line tide constraint; formula (29) is a line state constraint; formula (30) is a line capacity constraint; equation (31) is a constraint on the number of open circuits allowed; equation (32) is a node voltage phase angle constraint; equation (33) is the balanced node voltage phase angle constraint.
The large M method is used to transform equation (28) to its linear form as shown in equation (34) and to obtain the transmission capacity constraint as shown in equation (35).
Wherein M 2 is a sufficiently large positive number; to block the collection of the openable lines in the pre-control system.
(3) Load side constraint
The three-level load is cut down from low importance to high importance as a control means, the primary load cutting constraint is shown as a formula (36), the secondary load and the tertiary load cutting constraint are shown as a formula (37), the primary load is not cut down, and the tertiary load with lower importance of each node is participated in scheduling as much as possible.
Wherein,And (3) withThe primary load size before blocking control and after blocking control at the node i are respectively; at node i Maximum cut-out of stage load.
S4, solving a blocking control model considering the source-network-load synergy, and in a specific embodiment, calling YALMIP a tool kit and a Gurobi solver to solve the optimization problem. The obtained blocking control strategy comprises a source side output force adjustment decision, a network side topology switching decision and a load side load removal decision.
In order to verify the effectiveness of the method, the embodiment uses an IEEE 39 section test system to verify the proposed method and analyze the control effect, and related parameters are as follows: hidden fault p 0 = 0.01 for relay protection; p 1 = 1 when the power flow exceeds the transmission capacity limit; the power reference value is 100 MV.A.
For convenience of research, the present embodiment defines a blackout risk reduction indexIndex of load lossThe average output adjustment rate Δp GT with the system gas turbine is as follows:
Wherein: the power failure risk for the failure chain f x; the power failure risk after blocking control; And (3) with The load before and after the blocking control are respectively; And (3) with The output of the gas turbine before blocking control and after blocking control at the node i are respectively; To block the number of the gas units before control.
The cascading failure evolution paths and risks are analyzed as shown in fig. 4. Since the blocking control strategy is suppressed against the developing cascading failure, the initial failure is known, that is, the initial failure occurrence probability is 1. For ease of analysis, it is assumed that the occurrence time of the initial failure is 0. Taking the case of unexpected event disconnection of the line 5-8 and the line 17-18, the power flow of the line 5-8 and the line 17-18 is transferred after the disconnection at the moment 0, so that the power flow of the line 3-18 exceeds the transmission capacity limit, and the overload trip is carried out at the outage probability of 1 at the time of 4.31s, so that the load loss and the power failure risk of the fault link 2 are 158MW. Further, the flow of electricity carried by the lines 7-8 is diverted, and the overload trips with a outage probability of 0.25 at 24.22s, resulting in a blackout risk of 39.69MW for the failed link 3. And then, the overload trip of the lines 9-39 is necessarily caused when the power flow exceeds the capacity limit and the system is disconnected, so that the load loss of the fault link 4 is 528.50MW and the power failure risk is 172.45MW. Thus, without blocking control, the final load loss of the failed chain was 686.50MW and the risk of outage was 172.45MW.
Then, the input position of the blocking control strategy in the cascading failure is analyzed based on the failure chain. According to the information shown in fig. 4, the fault links where the load loss occurs are 2 and 4, and thus possible blocking control positions are defined as a position and B position between the fault link 1 and the fault link 2 and between the fault link 2 and the fault link 4, respectively. And respectively calculating the time adequacy index, the risk influence index and the time-risk comprehensive importance index of the fault link 2 and the fault link 4 as shown in the table 1.
TABLE 1 three index distribution of failure links
To explore the optimal input positions of the blocking control strategy, the blocking control strategy was input at the position a and the position B, respectively, and the control effect is shown in table 2. From the above, the control effect of the blocking control strategy put into the position B is far better than that of the position A. The control cost and the cut load amount when the blocking control strategy is put into the B position are both nearly 1/10 of those of the A position, the power failure risk at the B position is reduced by 41.26%, and the power failure risk at the A position is increased by 70.33% instead.
TABLE 2 different position control effects
In order to explore the influence of the climbing rapidity of the gas turbine on the blocking control of the cascading failures, a comparison scene is set as follows:
scene 1: η i =18.8, The air inflow of the gas turbine unit is sufficient, and the climbing speed of the gas turbine unit is large enough;
Scene 2: η i =12.5, The air inflow of the gas turbine unit is sufficient, and the climbing speed is relatively high;
Scene 3: η i =9.4, The air inflow of the gas turbine set is insufficient, and the climbing speed of the gas turbine set is small;
scene 4: η i =1 and, The node is considered to be connected into a thermal power unit with the fastest climbing speed in the system without considering the climbing speed of the gas turbine.
Table 3 shows blocking control results for different ramp rates in scenarios 1-4. As can be seen from table 3, as the intake air amount of the gas turbine unit increases, the control effect is also enhanced, and the economical efficiency and reliability of the blocking control are also improved.
TABLE 3 control results at different ramp rates
The output conditions of 3 gas units in the system under the conditions 1 to 4 are shown in figure 5. It can be seen that when no gas units are included in the system, the average rate of adjustment of the coal-fired unit output at nodes 32, 35 and 38 before and after control is only 0.16%. However, at the three nodes, as the gas turbine replaces the coal-fired unit and the climbing rate increases, the average adjustment rate of the gas turbine output increases, namely 1.5%, 1.99% and 2.44% respectively.
In order to study the influence of flexibility of network topology switching on blocking control, the embodiment sets 9 cases that the number of open-circuit lines is 0-8 respectively, assuming that the air inflow of the gas turbine is sufficient. The specific open circuit under the condition of different open circuit numbers can be calculated according to the model, the specific open circuit is shown in table 4, and the corresponding control result is shown in fig. 6.
As is clear from table 4, when the number of open lines is 0, that is, when the original network structure is used for power flow transmission without considering flexibility of the switching topology, the effect of blocking control is poor. The network structure formed by the circuit tripping is unreasonable at present, and the transmission mechanism of the power output by the generator node to the load node has defects, so that the power flow always has a blocking phenomenon, and the source side and the load side are required to be greatly adjusted, so that the economy and the reliability are not high. When only one line 8-9 is disconnected, the control cost is reduced to 5123.52 dollars, the cut load amount is 49.71MW, and the reduction of power failure risk is reduced to 41.26%. Because the network topology structure is optimized after the lines 8-9 are disconnected and the line blocking phenomenon is improved, the transmission defect between the generator node and the load node is obviously overcome, so that a blocking control strategy with better effect exists. After the subsequent 5 lines are disconnected successively, it can be seen that the control cost and the power failure risk are not changed, because the network topology and the transmission capability may not be further improved due to the disconnection of more lines, and the network topology switching characteristic has exerted the maximum effect on the control strategy. When the number of open circuits is 7, the control effect is reduced, the control cost is increased to 18843.28 dollars, the cut load amount is increased to 174.92MW, and the power failure risk reduction amount is increased to 174.92MW. When the number of open circuits is 8, the control effect further deteriorates. When the open circuit is too many, the network topology structure is not improved, but is damaged to a certain extent, so that the transmission capacity is seriously damaged, the adjustment force of the generator and the load is forced to be increased, and finally the economical efficiency and the reliability of the blocking control are obviously reduced.
TABLE 4 open circuit at different open numbers
In order to deeply analyze the influence of load classification characteristics on the blocking control strategy, the air inflow of the gas turbine is supposed to be sufficient, and the following two scenes are set:
scene 1: considering load classification characteristics;
Scene 2: irrespective of the load classification characteristic.
Table 5 control results with and without consideration of load classification characteristics
The load shedding strategy in different scenes directly affects the economy of blocking control, and table 5 shows the control results of scene 1 and scene 2 from the control cost point of view, whereinAnd (3) withThe loss amounts of the primary load, the secondary load and the tertiary load are respectively. It can be seen that when considering the load classification characteristic, the total control cost of the blocking control strategy is 20224.44 dollars, the primary and secondary load losses are 0, and the tertiary load loss is 189.10MW. When the load grading characteristic is not considered, the total control cost of the blocking control strategy reaches 63073.53 dollars, and the secondary load shedding amount reaches 41.21MW and almost reaches 22% of the total shedding amount although the total load shedding amount is 189.10MW and the primary load shedding amount is 0. In the blocking control without considering the load classification characteristic, the node where the secondary load is cut off and the corresponding cut-off amount are shown in fig. 7.
The method is characterized in that in a blocking control strategy considering the load grading characteristics, different levels of loads are treated differently, three-level loads are cut off preferentially, and only partial secondary loads are cut off under the condition that cascading failures cannot be blocked after three-level loads are cut off. Therefore, in the scene 1, when the effective control of the cascading failure can be realized after the three-stage load is cut off, the two-stage load is not cut off, so that the economical efficiency of the control means is higher. In the blocking control strategy without considering the load grading characteristics, the loads of different levels are not treated differently, and the non-differential cutting is carried out, so that the three-level load cutting quantity at a plurality of nodes is distributed unevenly, and the three-level loads at part of nodes are not effectively participated in the scheduling. This results in the accumulation of load shedding amounts at a few nodes, and eventually, in the case where all three-level loads at node 1, node 12, node 26 and node 31 are shed, a part of the two-level loads are further shed, resulting in serious control costs, so that the economy of the control measures is lowered.
Based on the analysis, the invention respectively considers the quick climbing, flexible topology switching characteristic and load grading characteristic of the gas turbine units at the source, the network and the load side to formulate a cascading failure blocking control strategy, thereby improving the elasticity of the system when encountering faults and greatly improving the economical efficiency and the reliability of regulation and control.
For the comparative analysis of the advantages of the strategy provided by the invention compared with the traditional strategy, the following two scenes are set on the assumption that the natural gas inflow is sufficient:
Scene 1: source-net-load cooperative blocking control;
scene 2: traditional source-charge cooperative blocking control.
Table 6 shows blocking control results for scenario 1 and scenario 2. It can be seen that the control effect of scene 1 is much better than that of scene 2. The blocking control strategy in scenario 1 controls less than 7% of the cost of scenario 2 and cuts less than 22% of the load of scenario 2. Meanwhile, the power failure risk reduction amount of the blocking control strategy of the scene 1 reaches 41.26 percent, and exceeds 15.26 percent compared with the scene 2.
TABLE 6 blocking control results under different synergistic modes
The blocking control strategy of the scene 1 considers the synergy of the three sides of the source, the network and the load, and realizes good cooperative control and coordination transmission relation of the generator, the network structure and the load. In addition, the rapidity of climbing of the gas turbine, the flexible topology switching characteristic of the network and the characteristic of the load fan also play a good promotion role in blocking cascading failures. Therefore, the control cost of the scene 1 is low, the reduction of the power failure risk is large, and the control effect is good. In the scenario 2, the coal-fired unit and the load are adjusted or cut off only by relying on the traditional regulation and control mode of the source-load side, and the synergic action of the source-network-load side and the characteristic or resource of each side capable of participating in scheduling are not utilized, so that the system cannot adjust the power flow distribution state of the system through the optimal control means, and the control reliability and the control economy are far inferior to those of the scenario 1.
Example 2
The present invention also provides a source-grid-load synergy-taking-into account cascading failure blocking control system comprising one or more processors, memory, and one or more programs stored in the memory, the one or more programs comprising instructions for performing the source-grid-load synergy-taking-into account grid cascading failure blocking control method as described in embodiment 1.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The scheme in the embodiment of the invention can be realized by adopting various computer languages, such as object-oriented programming language Java, an transliteration script language JavaScript and the like.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (7)
1. The cascading failure blocking control method considering source-network-load coordination is characterized by comprising the following steps of:
Acquiring network parameters and system initial states of a power transmission network, establishing an overload leading type cascading failure simulation model by considering space-time characteristics of element failure cascading evolution, generating a failure chain, and calculating a power failure risk index;
Based on the fault chain and the power failure risk index, calculating a time-risk comprehensive importance index by considering the system fault reaction capacity and coping cost performance, and determining the optimal input position of the blocking control strategy in fault development;
Respectively considering the rapid and flexible network topology switching characteristics and the load grading characteristics of the climbing of the gas turbine unit at the source, network and load sides, constructing a blocking control model based on source-network-load joint adjustment, and solving to obtain an optimal blocking control strategy;
controlling the power transmission network based on the optimal input position and the optimal blocking control strategy;
The time-space characteristics of the element fault cascade evolution comprise a time evolution model based on overload protection and a line outage probability model;
the space-time characteristic model of the element fault cascade evolution is as follows:
Wherein Δo ij,k(ts,ts+Δts) is the overload severity of overload line k increasing during the time t s to t s+Δts of the s-th failure link; f ij,k (t) is the active power flow of a line k connecting the node i and the node j at the moment t; the tidal current transmission capacity of the line k; o ij,k(ts,ts+Δts) is the total cumulative overload at time t s; s all is the total fault ring number of the cascading faults; an overload cumulative value defined as the overload line operating at a power flow exceeding 50% of its transmission capacity for 5 s; the time required for the overload line k to be removed from the moment; the fault line of the (s+1) th fault link and the time required for switching on and off; s overL,s is an overload line set in the system when the cascading failure progresses to the S-th failure link;
the line outage probability model is as follows:
Wherein p is the line outage probability; p 0 is the hidden fault probability of protection; p 1 is the line power flow exceeds the line transmission capacity limit The outage probability at the time; f ij,k is the active power flow of line k.
2. The cascading failure blocking control method considering source-network-load synergy as claimed in claim 1, wherein said step of generating a failure chain comprises:
step 1: setting a linkage evolution start time t=0;
step 2: determining an originating fault;
Step 3: updating network topology parameters, judging whether the network topology parameters are separated into regional islands, if so, turning to step 7, otherwise, turning to the next step;
Step 4: judging whether a node island is formed, if so, entering the next step, otherwise, entering the step 6;
step 5: balancing the power of a source side and a load side of the system;
Step 6: calculating the direct current power flow of the system, judging whether an overload circuit exists, if so, switching off the circuit which needs to be switched off in the next fault link according to the fault circuit in the next fault link and the time required by switching off, updating the evolution time, and turning to the step 3, otherwise, entering the next step;
step 7: and calculating load loss, arranging time evolution information, and outputting a fault chain.
3. The cascading failure blocking control method according to claim 1, wherein the power outage risk index is expressed as follows:
wherein, The probability when the fault chain Γ x evolves to the fault link m; Load loss for the failed chain Γ x.
4. The cascading failure blocking control method considering source-network-load coordination according to claim 1, wherein the time-risk comprehensive importance index is:
wherein, The time-risk comprehensive importance index is used; the risk influence degree index of the fault link is obtained based on the power failure risk index; The time adequacy index is obtained based on the occurrence time of a fault link in the fault chain and the time spent by the evolution of the fault chain.
5. The method for blocking control of cascading failures in view of source-network-load coordination according to claim 1, wherein the objective function of the blocking control model based on source-network-load joint adjustment is the total control cost of source and load sides and the minimum load loss amount from low to high according to importance, and the constraint conditions include source side constraint, network side constraint and load side constraint.
6. The cascading failure blocking control method taking into account source-net-load coordination according to claim 1, wherein a YALMIP toolkit and Gurobi solver are invoked to solve the blocking control model based on source-net-load joint adjustment.
7. A source-network-load cooperative cascading failure blocking control system comprising one or more processors, memory, and one or more programs stored in the memory, the one or more programs comprising instructions for performing the source-network-load cooperative cascading failure blocking control method in accordance with any one of claims 1-6.
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