CN109546677B - Safety control strategy solving method for large-scale offshore wind power flexible sending-out system - Google Patents
Safety control strategy solving method for large-scale offshore wind power flexible sending-out system Download PDFInfo
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Abstract
The invention discloses a safety control strategy solving method for a large-scale offshore wind power flexible sending-out system. On the basis of the existing planning research of offshore wind power access to a power grid, the influence of flexible offshore wind power output on the safety and stability of the power grid needs to be further researched, and a safety and stability control strategy suitable for large-scale access and flexible output of offshore wind power is provided. The method of the invention comprises the following steps: step1, establishing a large-system coordination control mathematical model aiming at a large-scale offshore wind power flexible sending-out system; and 2, formulating a solving strategy by utilizing a large system coordination control mathematical model. The invention focuses on a basic method of safety and stability control, and makes a safety control strategy by establishing a coordination control mathematical model and a solving model, thereby keeping the system stable.
Description
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to a safety control strategy solving method for a large-scale offshore wind power flexible sending-out system.
Background
At present, the problem of energy supply shortage is becoming more serious. The method aims at solving the problem of the spear between the rapid increase of the energy demand and the reduction of the energy, and simultaneously coping with the greenhouse effect and controlling the carbon emission. By the end of 2015 years, the wind power installation capacity of China is high, the newly increased installed capacity of 3297 ten thousand kilowatts of wind power all the year around is increased, and the accumulated grid-connected installed capacity reaches 1.29 hundred million kilowatts. The integrated grid-connected wind power installed capacity reaches more than 2 hundred million kilowatts in 2020 proposed in national response climate change planning (2014-2020); the offshore wind power is expected to become a new power for the development of the wind power industry in China by virtue of a plurality of advantages of the offshore wind power.
Offshore wind power presents challenges to the stabilization of ac mains networks. After the large-scale wind power is flexibly connected to the grid through the power electronic device, the power disturbance, the fan fault, the direct-current line fault and the like of a wind power system can all bring influence on an alternating-current system, the time constant of the multi-end flexible direct-current fault is much shorter than that of the alternating-current system, and whether the original safety control measures of the alternating-current system can be adapted to the influence needs further analysis and demonstration; further, a safety control measure scheme meeting the large-scale offshore wind power grid connection requirement needs to be researched; on the basis of the existing offshore wind power access power grid planning research, the influence of offshore wind power flexible output on the safety and stability of a power grid needs to be further researched, and a safety and stability control strategy which is suitable for large-scale offshore wind power access and flexible output is provided.
Disclosure of Invention
The invention aims to provide a method for solving a safety control strategy of a large-scale offshore wind power flexible sending-out system, which can be used for making the safety control strategy.
The purpose of the invention is realized by the following technical scheme: a safety control strategy solving method for a large-scale offshore wind power flexible sending-out system comprises the following steps:
step1, establishing a large-system coordination control mathematical model aiming at a large-scale offshore wind power flexible sending-out system;
step2, formulating a solving strategy by utilizing a large system coordination control mathematical model;
in the step1, the process of establishing the large-system coordination control mathematical model for the large-scale offshore wind power flexible sending-out system specifically comprises the following steps:
first, the minimum cumulative amount of frequency roll-off and the minimum amount of the wind turbine are used as the objective function of the coordination control, as follows:
in the formula, f [ t ]i]For a time t on the frequency response curveiA corresponding frequency value; f. ofNIs the rated frequency of the system; Δ tiCalculating a time step taken for the frequency response; n is the total number of sampling points; slThe number of the nodes capable of cutting the fan; pljThe number of switchable fans is the node j; cljThe power generation weight coefficient of the corresponding fan; u. ofljα and β are weight coefficients of frequency drop cumulant and fan cutting amount respectively;
then, introducing equality constraint conditions of the coordination control into a mathematical model, wherein the equality constraint conditions comprise power flow constraint, dynamic constraint and network constraint;
and finally, introducing inequality constraint conditions of coordinated control into the mathematical model, wherein the inequality constraints comprise running inequality constraints, stable inequality constraints and control measure inequality constraints.
In addition to the above method, the inequality constraint is:
in the formula (I), the compound is shown in the specification,
the minimum and maximum active output of the generator at the node i;
the minimum and maximum reactive output of the generator at the node i is obtained; vi min、Vi maxThe minimum and maximum allowable values of the voltage amplitude at the node i are obtained; f. ofi min、fi maxIs the minimum and maximum allowable value of the frequency at the node i;
the current flow is seen for the line between node i and node j.
In addition to the above method, the stable inequality constraint is:
wherein η is a stability margin function, u1、u2、…unPower adjustment for control measures, epsilon being stability margin threshold, deltafi max、Δfi minUpper and lower limits, Δ V, of frequency fluctuation at node ii max、ΔVi minThe upper and lower limits of the voltage fluctuation at node i,
upper and lower limits of line power flow fluctuation between node i and node j.
In addition to the above method, the inequality constraint of the control measure is:
in the formula (I), the compound is shown in the specification,
the maximum allowable machine cutting amount at the node i;
is the maximum load shedding allowed at node i; u. ofgiFor the cutter control variable at node i, [0,1 ]]Indicating cutThe machine amount accounts for the proportion of the total output of the node generator; u. ofliFor node i, the load shedding control variable, [0,1 ]]The load shedding amount accounts for the proportion of the total load power of the node; u. oftlineThe state variable of the extra-high voltage tie line is 0, which indicates that the extra-high voltage tie line is not disconnected, and 1, which indicates that the extra-high voltage tie line is disconnected.
As a supplement to the above method, in step2, the specific step of formulating the solution strategy by using the large system coordination control mathematical model includes:
1) decision making starting criterion
The dynamic safety of the system is monitored in real time by means of a wide area measurement system, when a decision starting criterion is detected to be met, the system is influenced by large interference, transient stability rapid analysis is started, the decision starting criterion is the change degree of power angle difference between units within a certain time or the active fluctuation of a section, and a threshold value is selected according to engineering experience;
2) fast analysis of transient stability
After the transient stability rapid analysis is started, judging the system stability through a real-time measurement value of the WAMS, estimating the system stability margin, and estimating and predicting the disturbed system track if necessary in order to accelerate the transient stability analysis;
3) forming control strategies based on sensitivity analysis
When the transient stability analysis obtains the system instability, starting a control strategy based on a sensitivity analysis method to restore the stability of the system, and issuing an instruction to control the system after obtaining the control strategy; the control strategy based on the sensitivity analysis method mainly utilizes the sensitivity of each node for adjusting the output load shedding amount to select and adjust the output unit and the load shedding point, and distributes the total output adjustment amount and the load shedding amount.
As a supplement to the above method, the decision of the control strategy includes the decision of the thermal power unit control strategy, the wind power unit control strategy and the load shedding strategy, and if the thermal power unit control strategy does not make the system frequency recover stably, the output of the wind power unit needs to be adjusted; and if the thermal power generating unit and the wind power generating unit do not enable the system frequency to recover stably through the control strategy, load shedding operation is required.
The strategy decision process considering the control cost is as follows, firstly, a candidate control measure space is determined, then a unit control quantity is added to a control measure Z along a control k direction to obtain a measure Z ', under the condition of an expected fault i and a working condition J, integration is carried out, a target function J is obtained through calculation of a mathematical model, a stability margin η is obtained, meanwhile, a cost C of the control measure Z' is obtained, a performance cost ratio of the control measure Z along the control k direction is obtained according to the stability margin η and the cost C, a search direction is further determined, the mathematical model is converted into a dynamic programming problem containing constraint conditions, optimization solution of the control strategy is carried out, then, simulation verification is carried out, if the strategy is invalid, the control strategy is re-formulated, and if the strategy is valid, a final control strategy is obtained.
As a supplement to the method, the process of making the thermal power unit control strategy includes instability mode judgment, selection of an output adjustment place, distribution of an adjustment amount, and execution and return of control, and the specific flow is as follows:
judging the instability mode of the system according to the measurement data of the WAMS, and if the system has single-machine instability, immediately executing the power-off control to cut off the instability thermal power generating unit; otherwise, analyzing the control sensitivity of each thermal power generating unit node on the system stability;
calculating the sensitivity of different site adjustments to the target function, and performing site priority ordering according to the comprehensive index of the sensitivity;
and selecting some generator nodes with high effectiveness indexes as implementation places of output adjustment, and gradually allocating adjustment amount in a mode of preferentially allocating the high-sensitivity generator set according to the principle of balancing the mechanical power and the electromagnetic power of the generator.
As a supplement to the above method, the process of making the control strategy of the wind turbine generator includes selection of an output adjustment location, allocation of an adjustment amount, and execution and return of control, and the specific flow is as follows:
calculating the sensitivity of different site adjustments to the target function, and performing output adjustment site priority ranking according to the comprehensive index of the sensitivity;
and selecting some generator nodes with high effectiveness indexes as implementation places of output adjustment control, and gradually distributing the adjustment amount in a mode of preferentially distributing the high-sensitivity generator set according to the principle of balancing the mechanical power and the electromagnetic power of the generator.
As a supplement to the above method, the process of making the load shedding policy includes selection of a load shedding location, distribution of load shedding amount, and execution and return of control, and the specific flow is as follows:
calculating the sensitivity of load shedding at different places to the target function, and performing priority ranking of the load shedding places according to the comprehensive index of the sensitivity;
and selecting some load nodes with high comprehensive indexes of effectiveness as implementation places of load shedding control, and carrying out priority ranking on the generator tripping places according to the comprehensive indexes of sensitivity.
The invention has the following beneficial effects: the invention focuses on a basic method of safety and stability control, and makes a safety control strategy by establishing a cooperative control mathematical model and a solving model, thereby keeping the system stable.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a flow chart of a coordinated control decision provided by an embodiment of the present invention;
fig. 2 is a process diagram of policy decision considering control cost according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating an implementation process of a control strategy according to an embodiment of the present invention;
fig. 4 is a flow chart of a control decision of a thermal power generating unit according to an embodiment of the present invention;
fig. 5 is a flow chart of a control decision of a wind turbine provided in an embodiment of the present invention;
fig. 6 is a flowchart of load shedding control decision provided by the embodiment of the present invention;
FIG. 7 is a diagram of a small power grid according to an embodiment of the present invention;
FIG. 8 is a diagram of system frequency deviation under a fault according to an embodiment of the present invention;
fig. 9 is a diagram of a system frequency deviation after the output of the thermal power generating unit LX is adjusted according to the embodiment of the present invention;
fig. 10 is a diagram of a system frequency deviation after the output of the thermal power plant LH is adjusted according to the embodiment of the present invention;
fig. 11 is a diagram of system frequency deviation after adjusting the DB output of the wind turbine generator according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a method for solving a safety control strategy of a large-scale offshore wind power flexible sending-out system. The method comprises the steps of firstly, establishing a large-system coordination control mathematical model suitable for a large-scale offshore wind power flexible output system; then, a solving strategy is made by utilizing the model, and simulation verification is carried out.
Step1, establishing a coordination control mathematical model
Besides a general algebraic differential equation (DAE), a mathematical model for the transient stability coordinated control of the power system also needs events such as generator tripping load control, branch overload successive disconnection, low-frequency low-voltage automatic load shedding control and the like described by a differential equation and a logic statement.
Therefore, the mathematical model thereof includes:
(1) differential equation of motion state variable
(2) Differential equation of non-moving state variable
(3) Tidal flow equations and other algebraic equations
0＝g(x,y,z,u) (3)
(4) Differential equations describing successive events, e.g.
wk＝φ(wk-1,wk-2,…,wk-m) (4)
(5) Logic equations describing various logical relationships
(6) There are also various procedures in operation in engineering that need to be described by knowledge expression, such as "if (statement), the (action) statement.
The mathematical model is a logic-difference-differential-algebraic equation (LDDAE) that contains strong non-autonomy, strong non-linearity (including switching characteristics). The bounded stability problem of this equation is very complex and its solution cannot be separated from the numerical integration. The safety and stability coordination control measures are reflected on the change of the mathematical model after the occurrence of large disturbance.
First, objective function of safety strategy solution
When the measures of adjusting the output of the fan, adjusting the output of the thermal power plant and controlling the load shedding are adopted, the maximum output of the fan is considered when the system is recovered to be stable, and the frequency drop cumulant and the minimum amount of the fan shedding are used as target functions of the coordination control. The large system coordination control problem can be described as:
wherein, f [ t ]i]Is a frequency responseShould be at time t on the curveiA corresponding frequency value; f. ofNIs the rated frequency of the system; Δ tiCalculating a time step taken for the frequency response; n is the total number of sampling points; slThe number of the nodes capable of cutting the fan; pljThe amount of the switchable fan is the node j; cljThe power generation weight coefficient of the corresponding fan; u. ofljα and β are respectively the weight coefficients of the frequency drop cumulant and the fan cutting amount.
Second, constraint conditions for solving security policy
The constraint conditions for coordinated control include equality constraints and inequality constraints, which are described as follows:
constraint conditions
x(0)＝x0(8)
Constraint of equality
0＝g(x,y,u) (9)
Stability margin constraint
η(u1,u2,u3)>ε (10)
Constraint of inequality
h(x,y,u)≤0 (11)
The equality constraint of the coordination control comprises a power flow constraint, a dynamic constraint and a network constraint.
(1) And (3) power flow constraint:
before disturbance
After disturbance
Wherein
PGi0、QGi0Injecting active power and reactive power of a node into the generator at the node i before disturbance; pLi0、QLi0The active power and the reactive power consumed by the load at the node i before disturbance; pGicl、QGiclInjecting active power and reactive power of the node into the generator at the node i after disturbance; pLicl、QLiclThe active power and the reactive power consumed by the load at the node i after disturbance; vi、VjThe voltage amplitudes of node i and node j; thetaijIs the voltage phase angle difference between node i and node j; y isij＝Gij+jBijIs the admittance matrix between nodes i and j; n is the total number of nodes.
(2) And (3) dynamic constraint:
pre-disturbance system
Disturbance in motion system
Post-disturbance system
If there are multiple switching actions during the fault and the artificial control strategy is also used as a disturbance, the dynamic equations of the system in the above disturbance comprise a set of differential algebraic equations as follows:
wherein the state variable x ═ δ1,δ2,…,δn,ω1,ω2,…,ωn]；
Algebraic variable y ═ V1,V2,…,VN,θ1,θ2,…,θN]；
Emergency control action control variable u ═ ξ1,ξ2,…,ξn,ζ1,ζ2,…,ζn]
Wherein the dynamic equation comprising the generator i is
Load equation at node i
(3) Network constraint:
the inequality constraints for coordinated control include run inequality constraints, stable inequality constraints, and control measure inequality constraints.
(1) Constraint of running inequality
Wherein
The minimum and maximum active output of the generator at the node i;
the minimum and maximum reactive output of the generator at the node i is obtained; vi min、Vi maxThe minimum and maximum allowable values of the voltage amplitude at the node i are obtained; f. ofi min、fi maxIs the minimum, maximum allowed value of the frequency at node i.
The apparent flow of the line between node i and node j.
(2) Stable inequality constraint
Where η is a stability margin function, u1、u2、…unThe power adjustment quantity is the control measures of fan output adjustment quantity, thermal power unit output adjustment quantity, load shedding quantity and the like, epsilon is a stability margin threshold value, and delta fi max、Δfi minIs the upper and lower limits, Δ V, of the frequency fluctuation at node ii max、ΔVi minThe upper and lower limits of the voltage fluctuation at node i,
the upper and lower limits of the line power flow fluctuation between node i and node j.
(3) Control measure inequality constraints
Wherein
The maximum allowable machine cutting amount at the node i;
is the maximum load shedding allowed at node i; u. ofgiFor the cutter control variable at node i, [0,1 ]]Representing the proportion of the amount of the machine cutting to the total output of the node generator; u. ofliFor node i, the load shedding control variable, [0,1 ]]The load shedding amount accounts for the proportion of the total load power of the node; u. oftlineThe state variable of the extra-high voltage tie line is 0, which indicates that the extra-high voltage tie line is not disconnected, and 1, which indicates that the extra-high voltage tie line is disconnected.
Step2, solving strategy of coordination control model
The flow of online safety and stability coordination control decision is shown in fig. 1, and the process thereof can be roughly composed of the following three parts:
(1) decision making starting criterion
The dynamic safety of the system is monitored in real time by means of a wide area measurement system, when a decision starting criterion is detected to be met, the system is influenced by large interference, transient stability analysis is started, the decision starting criterion is frequently used for the change degree of the power angle difference between the modules within a certain time or the active fluctuation of the section, and the threshold value can be selected according to engineering experience.
(2) Fast analysis of transient stability
And after the transient stability rapid analysis is started, judging the stability of the system through a real-time measurement value of the WAMS, and estimating the stability margin of the system. In order to accelerate the transient stability analysis, the disturbed system trajectory may be estimated and predicted if necessary.
(3) Formation of a linear control strategy based on sensitivity analysis
When the stability analysis shows that the system is unstable, stability control must be started to restore the system to be stable. The decision of the linear control strategy mainly utilizes the sensitivity of each node for adjusting the output shear load quantity to select and adjust the output unit and the shear load point and distribute the total output adjustment quantity and the shear load quantity. And issuing an instruction to control the system after the control strategy is obtained.
The strategy decision process considering the control cost is shown in FIG. 2, firstly, a candidate control measure space is determined, then, a unit control quantity is added to a control measure Z along a control k direction to obtain a measure Z ', under the conditions of expected faults i and working conditions J, integration is carried out, a target function J is obtained through calculation of a mathematical model, a stability margin η is further obtained, meanwhile, a cost C of the control measure Z' is obtained, a performance cost ratio of the increment of the control measure Z along the control k direction is obtained according to the stability margin η and the cost C, a search direction is further determined, the mathematical model is converted into a dynamic programming problem containing constraint conditions, optimization solution of the control strategy is carried out, then, simulation verification is carried out, if the strategy is invalid, the control strategy is re-formulated, and if the strategy is valid, a final control strategy is obtained.
The decision of the control strategy comprises the decision of a thermal power generating unit control strategy, a wind generating unit control strategy and a load shedding strategy. For a certain fault, the control strategy is executed as shown in fig. 3. The three control strategies are formulated as follows:
thermal power generating unit control strategy
The method comprises the following steps of determining a destabilization mode, selecting an output adjusting place, distributing an adjusting amount, and executing and returning control. The decision flow is shown in fig. 4.
Step1 instability mode discrimination
Judging the instability mode of the system according to the measurement data of the WAMS, and if the system has single-machine instability, immediately executing the power-off control to cut off the instability thermal power generating unit; otherwise, the control sensitivity of each thermal power generating unit node on the system stability is analyzed.
Selection of Step2 force adjustment location
The sensitivity of the different location adjustments to the objective function (6) is calculated. And adjusting the site priority ranking according to the comprehensive indexes of the sensitivity.
Step3 distribution of adjustment quantity
And selecting some generator nodes with higher effectiveness indexes as implementation sites of output adjustment. And gradually distributing the adjustment amount in a mode of preferentially distributing the set with higher sensitivity according to the principle of balancing the mechanical power and the electromagnetic power of the generator.
Wind turbine generator set control strategy
And if the thermal power generating unit control strategy does not enable the system frequency to recover stably, the output of the wind power generating unit needs to be adjusted. The control strategy of the wind generating set is similar to that of the thermal power generating set, but the wind generating set is controlled after the thermal power generating set is controlled, so that the instability mode does not need to be judged. The establishment process comprises selection of a force adjustment place, distribution of adjustment amount, execution and return of control. The decision flow is shown in fig. 5.
Selection of Step1 force adjustment location
The sensitivity of the different site adjustments to the objective function is calculated. And (4) performing output adjustment site priority ranking according to the comprehensive indexes of the sensitivity.
Step2 distribution of adjustment quantity
And selecting some generator nodes with higher effectiveness indexes as implementation sites of output adjustment control. And gradually distributing the adjustment amount in a mode of preferentially distributing the set with higher sensitivity according to the principle of balancing the mechanical power and the electromagnetic power of the generator.
Load shedding strategy
The process of making the load shedding strategy comprises the calculation of the sensitivity and the distribution of the load shedding amount. The decision flow is shown in fig. 6.
Selection of Step1 load site
The sensitivity of the load shedding at different positions to the objective function (6) is calculated. And carrying out load shedding place priority sequencing according to the comprehensive index of the sensitivity.
Calculation and distribution of Step2 load capacity
And selecting some load nodes with higher comprehensive effectiveness indexes as the implementation places of load shedding control. And carrying out the priority ranking of the generator tripping places according to the comprehensive indexes of the sensitivity.
Simulation verification:
fig. 7 shows a power grid used in this example, in which a five-terminal flexible line and two wind farms are connected.
The simulation verification adopts the fault types of fault (N-4) and wind power shock during maintenance, the set specific fault is the access of 400MW wind power and a flexible line, and the ZH-ZHAN line (500kV) is maintained; on the ZSAFN side of CX-ZSAFN line (500Kv), 1 circuit is short-circuited in three phases, and 2 circuits are in the same trip in three phases; and the power of the DB fan and the QS fan is suddenly reduced by 300 MW.
After the fault occurs, real-time measurement data acquired by the wide-area measurement system of the power system meets decision starting criteria, then rapid analysis of transient stability is carried out, and the track of the frequency deviation of the system is shown in fig. 8. The stability judgment is carried out according to the track of the system frequency deviation, and the system frequency is continuously reduced, so that the system frequency cannot be kept stable under the fault, and a linear control strategy based on a sensitivity analysis method needs to be formulated.
According to the control strategy implementation shown in fig. 3, the control strategy for the fault is as follows:
step 1: and judging that the system is not subjected to single machine instability, and analyzing the control sensitivity of each thermal power generating unit node on the system stability.
Step 2: and calculating the sensitivity of the output of the thermal power generating unit to the target function at different places. And performing output adjustment site priority ranking according to the comprehensive indexes of the sensitivity, wherein the LX thermal power plant ranks the first place, and the LH thermal power plant ranks the second place.
Step 3: the unit with higher sensitivity is preferentially distributed, namely, the LX thermal power plant increases the output of 320MW, the system frequency is not recovered to be stable, and the system frequency deviation is shown in FIG. 9; then the LH thermal power plant increases the output power by 100MW, the system frequency is still not stabilized, and the system frequency deviation is shown in fig. 10.
Step 4: and calculating the sensitivity of the output of the wind turbine generator to the target function at different places. And (4) performing output adjustment site priority sequencing according to the comprehensive indicator of the sensitivity, wherein the DB fan is arranged at the first position, and the QS fan is arranged at the second position.
Step 5: the sensitivity is higher, the unit is preferentially distributed, so that the DB fan increases the output of 100MW, the system frequency is recovered stably, and the system frequency deviation is shown in figure 11.
Claims (10)
1. A method for solving a safety control strategy of a large-scale offshore wind power flexible sending-out system is characterized by comprising the following steps:
step1, establishing a large-system coordination control mathematical model aiming at a large-scale offshore wind power flexible sending-out system;
step2, formulating a solving strategy by utilizing a large system coordination control mathematical model;
in the step1, the process of establishing the large-system coordination control mathematical model for the large-scale offshore wind power flexible sending-out system specifically comprises the following steps:
first, the minimum cumulative amount of frequency roll-off and the minimum amount of the wind turbine are used as the objective function of the coordination control, as follows:
in the formula, f [ t ]i]For a time t on the frequency response curveiA corresponding frequency value; f. ofNIs the rated frequency of the system; Δ tiCalculating a time step taken for the frequency response; n is the total number of sampling points; slThe number of the nodes capable of cutting the fan; pljThe number of cutable fans for node j; cljThe power generation weight coefficient of the corresponding fan; u. ofljα and β are weight coefficients of frequency drop cumulant and fan cutting amount respectively;
then, introducing equality constraint conditions of the coordination control into a mathematical model, wherein the equality constraint conditions comprise power flow constraint, dynamic constraint and network constraint;
and finally, introducing inequality constraint conditions of coordinated control into the mathematical model, wherein the inequality constraints comprise running inequality constraints, stable inequality constraints and control measure inequality constraints.
2. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 1, wherein the operating inequality constraints are as follows:
in the formula (I), the compound is shown in the specification,
the minimum and maximum active output of the generator at the node i;
the minimum and maximum reactive output of the generator at the node i is obtained; vi min、Vi maxThe minimum and maximum allowable values of the voltage amplitude at the node i are obtained; f. ofi min、fi maxIs the minimum and maximum allowable value of the frequency at the node i;
is the minimum and maximum allowable value of the apparent power flow of the line between the node i and the node j.
3. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 1, wherein the stable inequality constraint is as follows:
wherein η is a stability margin function, u1、u2、…unPower adjustment for control measures, epsilon being stability margin threshold, deltafi max、Δfi minUpper and lower limits, Δ V, of frequency fluctuation at node ii max、ΔVi minThe upper and lower limits of the voltage fluctuation at node i,
upper and lower limits of line power flow fluctuation between node i and node j.
4. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 1, wherein the inequality constraints of the control measures are as follows:
in the formula (I), the compound is shown in the specification,
the maximum allowable machine cutting amount at the node i;
for maximum allowed cut at node iThe load capacity; u. ofgiFor the cutter control variable at node i, [0,1 ]]Representing the proportion of the amount of the machine cutting to the total output of the node generator; u. ofliFor node i, the load shedding control variable, [0,1 ]]The load shedding amount accounts for the proportion of the total load power of the node; u. oftlineThe state variable of the extra-high voltage tie line is 0, which indicates that the extra-high voltage tie line is not disconnected, and 1, which indicates that the extra-high voltage tie line is disconnected.
5. The method for solving the safety control strategy of the large-scale offshore wind power flexible delivery system according to any one of claims 1 to 4, wherein in the step2, the specific step of formulating the solving strategy by using a large system coordination control mathematical model comprises the following steps:
1) decision making starting criterion
The dynamic safety of the system is monitored in real time by means of a wide area measurement system, when a decision starting criterion is detected to be met, the system is influenced by large interference, transient stability rapid analysis is started, the decision starting criterion is the change degree of power angle difference between units within a certain time or the active fluctuation of a section, and a threshold value is selected according to engineering experience;
2) fast analysis of transient stability
After the transient stability rapid analysis is started, judging the system stability through a real-time measurement value of the WAMS, estimating the system stability margin, and estimating and predicting the disturbed system track if necessary in order to accelerate the transient stability analysis;
3) formation of a linear control strategy based on sensitivity analysis
When the transient stability analysis obtains the system instability, starting a linear control strategy based on a sensitivity analysis method to enable the system to recover the stability, and issuing an instruction to control the system after obtaining the control strategy; the linear control strategy based on the sensitivity analysis method mainly utilizes the sensitivity of each node for adjusting the output shear load amount to select and adjust the output unit and the shear load point and distribute the total output adjustment amount and the shear load amount.
6. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 5, wherein the decision of the control strategy comprises a decision of a thermal power unit control strategy, a decision of a wind power unit control strategy and a load shedding strategy, and if the thermal power unit control strategy does not enable the system frequency to recover stably, the output of the wind power unit needs to be adjusted; and if the thermal power generating unit and the wind power generating unit do not enable the system frequency to recover stably through the control strategy, load shedding operation is required.
7. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 6 is characterized in that the strategy decision process considering the control cost comprises the steps of firstly determining a candidate control measure space, then increasing unit control quantity of the control measure Z along the direction of control k to obtain a measure Z ', carrying out integration under the conditions of expected faults i and working conditions J, obtaining a target function J through calculation of a mathematical model to obtain a stability margin η, meanwhile, obtaining a cost C of the control measure Z', obtaining a performance cost ratio of the increase of the control measure Z along the direction of control k according to the stability margin η and the cost C, further determining a search direction, converting the mathematical model into a dynamic programming problem containing constraint conditions, carrying out optimization solution on the control strategy, carrying out simulation verification, re-formulating the control strategy if the strategy is invalid, and obtaining a final control strategy if the strategy is valid.
8. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 6, wherein the process for making the thermal power generating unit control strategy comprises instability mode judgment, selection of output adjustment places, distribution of adjustment amount, execution and return of control, and the specific flow is as follows:
judging the instability mode of the system according to the measurement data of the WAMS, and if the system has single-machine instability, immediately executing the power-off control to cut off the instability thermal power generating unit; otherwise, analyzing the control sensitivity of each thermal power generating unit node on the system stability;
calculating the sensitivity of different site adjustments to the target function, and performing site priority ordering according to the comprehensive index of the sensitivity;
and selecting some generator nodes with high effectiveness indexes as implementation places of output adjustment, and gradually allocating adjustment amount in a mode of preferentially allocating the high-sensitivity generator set according to the principle of balancing the mechanical power and the electromagnetic power of the generator.
9. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 8, wherein the process for making the wind turbine control strategy comprises selection of an output adjusting place, distribution of an adjusting amount, execution and return of control, and the specific flow is as follows:
calculating the sensitivity of different site adjustments to the target function, and performing output adjustment site priority ranking according to the comprehensive index of the sensitivity;
and selecting some generator nodes with high effectiveness indexes as implementation places of output adjustment control, and gradually distributing the adjustment amount in a mode of preferentially distributing the high-sensitivity generator set according to the principle of balancing the mechanical power and the electromagnetic power of the generator.
10. The method for solving the safety control strategy of the large-scale offshore wind power flexible sending-out system according to claim 9, wherein the process for making the load shedding strategy comprises selection of load shedding places, distribution of load shedding amount, execution and return of control, and the specific flow is as follows:
calculating the sensitivity of load shedding in different places to the target function, and carrying out priority ranking on the load shedding places according to the comprehensive index of the sensitivity;
and selecting some load nodes with high comprehensive indexes of effectiveness as implementation places of load shedding control, and carrying out priority ranking on the generator tripping places according to the comprehensive indexes of sensitivity.
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