CN111353654A

CN111353654A - Direct-current transmitting-end hydropower station optimal scheduling method compatible with peak regulation requirements of receiving-end power grid

Info

Publication number: CN111353654A
Application number: CN202010177499.9A
Authority: CN
Inventors: 原文林; 卢璐; 苏承国; 吴洋; 周彬彬
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2020-03-13
Filing date: 2020-03-13
Publication date: 2020-06-30

Abstract

The invention discloses a direct current sending end hydropower station optimization scheduling method compatible with receiving end power grid peak regulation requirements, which is characterized in that modeling construction is carried out on hydropower short-term optimization scheduling problems to obtain a mathematical model, after calculation conditions are set, firstly, an objective function is linearized, nonlinear objective constraint is carried out on the nonlinear objective function in a linearization manner under the premise of precision allowance, then, an original high non-convex mixed integer nonlinear programming model is converted into a mixed integer linear programming model, and an optimization solver is used for solving the model on the basis. The model provided by the invention has higher calculation efficiency, the formulated power transmission plan effectively responds to the peak load regulation requirement of each receiving-end power grid, the peak-valley difference of the power grid is obviously reduced, the power transmission limit of the direct-current connecting line is met, the performability of the direct-current connecting line plan is improved, and the cross-regional coordinated operation of the transmitting-end hydropower station, the high-voltage direct-current connecting line and the receiving-end power grid is realized.

Description

Direct-current transmitting-end hydropower station optimal scheduling method compatible with peak regulation requirements of receiving-end power grid

Technical Field

The invention relates to the technical field of energy and electric power, in particular to an optimal scheduling method for a direct current sending end hydropower station.

Background

The feeding of high-power high-voltage direct current hydropower greatly relieves the energy shortage situation and the atmospheric pollution pressure in the east region, but the peak regulation requirement of a receiving-end power grid is rarely considered by a power transmission curve, so that the receiving-end power grid has to passively absorb a large amount of low-valley power under many conditions, the peak regulation pressure of the receiving-end power grid is further increased, the stable operation of the receiving-end power grid is not facilitated, and the absorption capacity of the receiving-end power grid on clean energy is also influenced. Therefore, it is necessary to change the scheduling operation and power transmission mode of the current high-voltage direct-current transmission terminal hydropower station. At present, research aiming at cross-regional power transmission of a hydropower station mainly focuses on optimizing scheduling operation and power cross-regional and cross-provincial distribution modes of a hydropower station at a transmitting end, and various limiting conditions of a high-voltage direct-current connecting line for cross-regional power transmission are not considered, such as limitations of power curve stepping of the direct-current connecting line, daily power transmission quantity and the like, so that optimization calculation results still face a plurality of technical problems in practical engineering application. Therefore, the invention fully considers the operation limitation of the transmitting end hydropower station, the transmission control requirement of the direct current connecting line and the load requirement of the receiving end power grid, researches and formulates a scientific and reasonable power generation plan and a power transmission mode of the high-voltage direct current transmitting end hydropower station, practically exerts the peak regulation capacity of the large hydropower station and relieves the clean energy consumption pressure of each receiving end power grid.

The optimization scheduling problem of the direct current transmitting end hydropower station essentially belongs to the short-term optimization scheduling problem of the hydropower station in the day ahead. At present, a plurality of solving methods for the problems comprise a Lagrange relaxation method, a dynamic programming and derivation algorithm thereof, an intelligent algorithm, a nonlinear programming method and the like, but the methods all face a plurality of difficulties when being applied to solving the scheduling problem of the high-voltage direct-current transmission end hydropower station. Due to the non-convex and non-linear of the model, the Lagrange relaxation method is difficult to obtain an accurate dual equation; because the operation constraint of each unit in the power station needs to be taken into consideration, the problem of 'dimension disaster' is often faced when the problem is solved by dynamic planning; intelligent algorithms such as genetic algorithm, differential evolution algorithm, particle swarm algorithm and bee colony algorithm have the problems of easy falling into local optimal solution, difficult effective processing of complex constraint, unstable calculation result and the like; the nonlinear programming method cannot consider the start-stop state of the unit, and therefore cannot be applied to the problem. The mixed integer linear programming is an optimization method for solving complex problems with deep research and relatively mature theory at present, and a satisfactory solution can be obtained within acceptable solution time by means of efficient commercial optimization software, so that the mixed integer linear programming is widely applied to the field of hydropower dispatching in recent years. The key point of using the method is how to carry out linearization treatment on the premise that the precision of a nonlinear target or constraint in the model is allowed, and then the original high non-convex mixed integer nonlinear programming model is converted into the mixed integer linear programming model.

Disclosure of Invention

The invention aims to provide a direct current transmitting end hydropower station optimal scheduling method compatible with peak shaving requirements of a receiving end power grid.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows.

A direct current sending end hydropower station optimization scheduling method compatible with receiving end power grid peak regulation requirements is characterized in that modeling construction is carried out on hydropower short-term optimization scheduling problems to obtain a mathematical model, after calculation conditions are set, firstly, an objective function is linearized, nonlinear objective constraint is carried out on the nonlinear objective function, linearization processing is carried out on the premise that precision is allowed, then an original high non-convex mixed integer nonlinear programming model is converted into a mixed integer linear programming model, and an optimization solver is used for solving the model on the basis.

As a preferred technical solution of the present invention, a method for converting an initial model into a mixed integer linear programming model comprises: firstly, establishing a short-term optimization scheduling model of the high-voltage direct-current transmitting-end hydropower station, and taking the minimum residual load peak-valley difference of the receiving-end power grid as a target function of the model so as to fully excavate the trans-regional peak regulation capability of the high-power hydropower station, reduce the peak regulation pressure of the receiving-end power grid and improve the clean energy consumption level of the receiving-end power grid; in addition to hydraulic constraint, unit operation constraint, waterhead influence and high-voltage direct-current connecting line power transmission limitation are increased; carrying out linearization processing on nonlinear factors such as nonlinear peak regulation objective functions in the model, unit generating heads, unit operation combined vibration regions, unit power characteristic curves, stepped power transmission curve limitation of a high-voltage direct-current connecting line and the like; aiming at nonlinear constraint of a power characteristic curve of the water turbine, a triangular internal linear interpolation method is constructed, and the power characteristic curve of the water turbine is linearized; and realizing the conversion from the original model to the standard mixed integer linear programming model.

As a preferred technical solution of the present invention, the linearization processing of the objective function includes the following steps:

firstly, constructing an objective function, and expressing the minimum difference between net load peaks and valleys of each receiving-end power grid as follows:

C′_g,t＝C_g,t-P_g,t(2)

in the formula: g is the total number of the transmission power grids of the hydropower station at the transmission end; g is the receiving end power grid number; t, t are scheduling period and scheduling period h, respectively; c_g,t、C′_g,tRespectively representing the original load and the residual load MW of the receiving-end power grid g in a period t; p_g,tThe output MW of the hydropower station to the power grid g in the t period is represented, namely the power of the direct current tie line g in the t period can be obtained by the formula (3);

wherein I is the unit number in the hydropower station, I_gSet of units for transmitting power to receiving grid g, P_i,tThe output MW of the unit i in the time period t is obtained;

further, auxiliary variables are introduced

And _gC′it is made to satisfy equation (4), thereby linearizing the objective function to solve:

at this time, equation (1) becomes:

the formula (5) comprises the peak regulation problem of a plurality of power grids, belongs to the multi-target problem, adopts a weight method to convert the peak regulation problem into a single-target scheduling problem, and takes the difference of the load magnitude of each power grid into consideration to carry out normalization processing on the residual load of the power grids; the objective function is transformed into the following function:

in the formula:

the maximum original load MW of the g-th power grid; w is a_gFor the weighting factors, equal weighting, i.e. w, is used in the invention _g1/G; in the formula (6)

The term represents the load peak-valley difference after the normalization of the ith power grid, namely the peak-valley difference rate, and is used for measuring the peak load pressure of the power grid.

As a preferred embodiment of the present invention, the constraint linearization process includes the following steps:

(1) and (3) water balance constraint:

in the formula: v_tIs the storage capacity m of the reservoir at the end of the t period³；I_tIs the warehousing flow m of the reservoir in the time period t³/s；S_tRepresenting water reject flow m of the plant during a period t³S; Δ t is a time period step h; q_tFor power generation of power station during time tFlow rate m³S; i and I are the total number of units and the number of the units contained in the hydropower station respectively; q. q.s_i,tGenerating flow m of unit i in t period³/s；

(2) Water level restraint:

Z_min≤Z_t≤Z_max(8)

in the formula: z_tRepresenting the dam front water level m of the reservoir at the end of the t period; z_max、Z_minRespectively the highest value m and the lowest value m of the front water level of the reservoir dam; z_beginThe actual water level m of the reservoir at the beginning of the dispatching period; z_endControlling the water level m for the target at the end of the dispatching period; considering that a certain deviation exists in the allowable control water level in the actual scheduling operation process, setting delta as the allowable deviation proportion of the control water level at the end of the period;

(3) unit output restraint:

0≤P_i,t≤u_i,tP_i,max,u_i,t∈{0,1} (10)

in the formula: p_i,maxThe maximum generating power MW of the unit i; u. of_i,tIs the running state variable of the unit i in the time period t, if the unit i is in the power generation state in the time period t, u _i,t1, otherwise u_i,t＝0；

(4) And (3) restraining the generating flow of the unit:

0≤q_i,t≤u_i,tq_i,max(11)

in the formula: q. q.s_i,maxMaximum generation flow m for unit i³/s；

(5) And (3) restraining the starting and stopping duration of the unit:

in the formula: x is the number of_i,t、x'_i,tRespectively, the start and stop operation variables of the unit j, if the unit i, x is started in the time period t _i,t1, otherwise x_i,t0, provided that unit i, x 'is shut down for period t'_i,t1, otherwise x'_i,t＝0；α_i、β_iRespectively setting the shortest duration h of the start and stop of the unit;

(6) and (3) restraining a vibration area of the unit:

the large hydroelectric generating set often has a plurality of vibration regions, and the output range is divided into a plurality of discontinuous intervals, so that the vibration region constraint of the generating set is expressed as:

in the formula:

PV _i,krespectively setting the upper limit MW and the lower limit MW of the output of the kth vibration area of the unit i;

dividing a unit output interval into K +1 safe operation areas by utilizing K unit vibration areas, wherein the constraint of the formula (14) is nonlinear constraint, and the nonlinear constraint linearization processing method is shown as the formula (15);

in the formula:

indicating that the output force of the unit i in the t period is in the kth safe operation area;

P _i,krespectively represents the upper limit and the lower limit of the output of the kth safe operation area of the unit i, and meets the requirementsP _i,1＝0，

Formula (10) may be replaced with formula (15);

(7) power generation water purification head restraint:

in the formula: h_i,tGenerating water purification heads m for the unit i in a time period t; zd_tThe tail water level m of the reservoir in the period t; hl (high pressure chemical vapor deposition)_i,tFor the generating head loss m of the unit i in the time period t, and for simplifying the calculation, the hl is assumed in the invention_i,tIs a constant; f. of_zv(·)、f_zq(. the) is the relation function of dam front water level-reservoir capacity and tail water level-outlet flow of the reservoir respectively;

f_zv(·)、f_zqthe (-) is a nonlinear function, and linear processing is carried out by adopting a piecewise linear interpolation function; taking the water level before the dam-reservoir capacity as an example; firstly, the storage capacity interval of reservoir is divided into [ V ]_min,V_max]Discretization is J sub-intervals, each demarcation point is defined as follows:

in the formula: v_j、Z_jRespectively the jth reservoir capacity interpolation point of the reservoir and the corresponding dam front water level;

then introducing a 0-1 integer variable R_j,tAnd satisfies the following constraints:

in the formula: r_j,tFor indicating variable, when the reservoir capacity of the reservoir in the t period is in the jth reservoir capacity subinterval_j,tNot all right 1, otherwise R _j,t0; the sub-interval of the storage capacity in which the storage capacity is positioned in the t period can be uniquely determined by the formula (18);

the reservoir dam front water level at the end of the t period can be expressed as

The linearization of the relation between the front water level and the reservoir capacity of the dam can be realized through the formulas (17) to (19), and the piecewise linear approximation is carried out on the tail water level-discharge relation function by the method, so that the linearization of the generating head of the unit is realized;

(8) unit dynamic characteristic constraint:

P_i,t＝f_i,pqh(q_i,t,H_i,t) (20)

in the formula: f. of_i,pqh() is a binary relation function between the output of the unit i, the generating flow and the generating head; formula (20) may be replaced with formula (15);

in the aspect of the power characteristic curve of the water turbine, a certain power characteristic curve is used for representing the power characteristic curves corresponding to all water heads in the whole water head subinterval, so that the accuracy of the model is reduced; the invention provides a water turbine power characteristic curve linearization method based on trigonometric internal linear interpolation to improve the accuracy of a model;

selecting 5 power characteristic curves in the maximum and minimum power generation water head intervals of the unit, wherein the power characteristic curves correspond to the high water heads respectively

Higher head

Medium head

Lower head

And low head

Meanwhile, the maximum output and the maximum power generation flow are considered, each power characteristic curve is divided into 2 sections, and therefore, the whole power characteristic curve of the water turbine is divided into 17 triangular subregions; the dynamic characteristics of a water turbine can be expressed as follows:

in the formula: l is the index of the triangular subregion, 1,2, …, 17; μ is the index of each vertex of the triangular subregion, μ ═ 1,2, 3;

respectively showing a water head m and a power generation flow m corresponding to the mu-th vertex of the first triangle³The power generation output MW and the power/s; theta_i,t,lTo indicate the variable, θ _i,t,l1 represents that the combination of the generated power, the water head and the generated flow of the unit in the t period is positioned in the sub-area of the l triangles;

represents the weight occupied by the μ -th vertex of the triangle l in the period t;

formula (21) shows that when the unit is in the power generation state, one and only one triangular sub-area is selected; formula (22) indicates that if the triangle l is selected, the sum of the weights of the three vertices is 1, otherwise, the weight of the three vertices is 0; the formula (23) is to interpolate the generating head, if the unit is in a generating state in the time period t, the generating head can be inevitably expressed by the head interpolation values of three vertexes of a certain triangle, otherwise the constraint is invalid; the formula (24) interpolates the generated flow and the generated output respectively;

(9) transmission constraint of the extra/ultra high voltage direct current tie line:

the power transmission power curve of the high-voltage direct-current connecting line is in a step shape, and reverse adjustment cannot be carried out in a short time, so that frequent adjustment of direct-current converting equipment is avoided, and the running reliability of the direct-current connecting line is ensured;

because the power transmission power of the direct current connecting line is in a step shape, a linear modeling method of a power transmission curve of the high-voltage direct current connecting line is adopted; dividing a transmission power curve of the direct current tie line into K grades, and if K equivalent generator sets exist, superposing output curves of the K equivalent generator sets to form a power transmission power curve of the direct current tie line;

(10) daily power transmission amount constraint:

in order to guarantee the generating income of the hydropower station at the transmitting end, the actual transmission electric quantity of the hydropower station needs to meet the transmission electric quantity specified in the trans-regional electric power trading contract signed by the transmitting end and the receiving end;

in the formula, E_gDaily power transmission quantity MWh specified in a power transaction contract signed for a transmitting-end hydropower station and a receiving-end power grid g; epsilon is the allowable deviation proportion of the actual power transmission quantity of the hydropower station at the sending end to the contract power quantity.

As a preferred technical solution of the present invention, in the (9) te/uhp dc link transmission constraint processing, for an equivalent generator set, constraint conditions of a conventional unit combination need to be satisfied, including the following constraints:

① force limit

v_g,k,tP_g,k,min≤P_g,k,t≤v_g,k,tP_g,k,max(26)

In the formula: k is the number of the equivalent unit; p_g,k,tThe output MW of the kth equivalent unit which transmits power to the power grid g in the period t; v. of_g,k,tThe operation state variable of the kth equivalent unit for transmitting power to the power grid g in the time period t, and v if the equivalent unit k is in the operation state in the time period t _g,k,t1, otherwise v_g,k,t＝0；P_g,k,max、P_g,k,minRespectively the output of the equivalent unit k,Lower limit MW, where P is set to ensure that the DC power curve is stepped_g,k,maxAnd P_g,k,minIf the output limit constraint is equal to the output limit constraint, the output limit constraint can be expressed as an expression (27), and the expression indicates that the equivalent unit k runs at fixed power as long as the equivalent unit k is started;

P_g,k,t＝v_g,k,tP_g,k,fix(27)

in the formula: p_g,k,fixThe output is the fixed output MW under the operation state of the equivalent unit k;

the sum of the output of all equivalent units in the time period t is equal to P in the formula (2)_g,tI.e. by

② Start-stop on/off duration constraints

In the formula: y is_g,k,t、y'_g,k,tRespectively indicating variables for starting and stopping the equivalent unit k, if the unit k is started in the time period t, y _g,k,t1, otherwise y _g,k,t0 for y'_g,k,tThe same process is carried out; tau is_g,k、γ_g,kRespectively setting the shortest duration h of starting and stopping the equivalent unit k;

③ shutdown limit

④ power back regulation limit

v_g,k+1,t≤v_g,k,t(32)

The above formula specifies the starting sequence among equivalent units; only when the equivalent unit k is in a starting state, the equivalent unit k +1 can be started; equations (29), (30) and (32) effectively prevent the reverse adjustment of the transmitted power in a short time.

As a preferred technical scheme of the invention, the optimization solver adopts a commercial Gurobi optimization solver.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

the invention establishes a short-term optimization scheduling model of the high-voltage direct-current transmission end hydropower station. The model takes the minimum residual load peak-valley difference of the receiving-end power grid as a target function, and aims to fully excavate the trans-regional peak regulation capability of the high-power hydropower station, reduce the peak regulation pressure of the receiving-end power grid and improve the clean energy consumption level of the receiving-end power grid. Besides traditional hydraulic constraints, the unit operation constraints, water head influences and high-voltage direct-current connecting line power transmission limits are fully considered. And aiming at nonlinear factors such as nonlinear peak-shaving objective functions in the model, unit generating heads, unit operation combined vibration regions, unit power characteristic curves, stepped power transmission curve limitation of a high-voltage direct-current connecting line and the like, a corresponding linearization processing strategy is provided. Aiming at the nonlinear constraint of the power characteristic curve of the water turbine, a triangular internal linear interpolation method is innovatively provided, and the power characteristic curve of the water turbine is linearized. The original model is converted into a standard mixed integer linear programming model, and then the model is solved by using a commercial optimization solver Gurobi. The method has the advantages that the Binjin direct-current sending end-stream Luo-Du hydropower station is taken as a research object, examples show that the model has high calculation efficiency, the formulated power transmission plan effectively responds to the peak load regulation requirements of each receiving end power grid, the peak-valley difference of the power grid is obviously reduced, the power transmission limit of the direct-current connecting line is met, the performability of the direct-current connecting line plan is improved, and the cross-region coordinated operation of the sending end hydropower station, the high-voltage direct-current connecting line and the receiving end power grid is realized.

Compared with the linear method of the power characteristic curve of the water turbine reported in the existing literature, the linear interpolation method in the triangle has the following two advantages that the power generation water head of the ① unit is continuous, theoretically, a linear model is more accurate, the linear fitting precision can be adjusted by controlling the number of the triangular sub-regions, the ② method does not need to be executed in multiple steps, understanding and operation are convenient, and the maximum power generation output and the maximum power generation flow of the unit can be effectively considered except the influence of the water head.

On the aspect of processing the transmission constraint of the extra-high voltage direct current connecting line, the multi-equivalent unit coordination modeling method for the power transmission power of the high voltage direct current connecting line controls a direct current transmission power plan in a mode of superposing the output of a plurality of equivalent units, fully utilizes the characteristics of flexibility and high adjusting speed of a direct current control mode on the premise of ensuring that the direct current power meets the constraint conditions such as step and the like, and develops the potential of cross-region clean energy consumption of the direct current connecting line to a greater extent; in practical application, parameters such as the number of equivalent units, fixed operation output, minimum start-stop time, maximum shutdown times and the like can be reasonably set according to historical operation data of a direct current connecting line and experience of scheduling personnel, the adjusting performance of converter station equipment, the upper and lower limits of the injection power of a receiving-end power grid and the like; in addition, in the flood season, the hydropower station usually runs close to the maximum power to reduce water abandon, so that the utilization rate of the direct current connecting line channel is very high, and a power adjusting space is lacked; therefore, the optimization model is more suitable for making the dispatching plan of the high-voltage direct-current transmission end hydropower station with the adjustment space still existing in the direct-current transmission power in the non-flood season.

The method takes a Bingjin direct current sending terminal-stream luohuang hydropower station as a research object, the example shows that the proposed model has higher calculation efficiency, the formulated power transmission plan effectively responds to the peak regulation requirement of each receiving terminal power grid, the peak-valley difference of the power grid is obviously reduced, the power transmission limit of a direct current tie line is met, the performability of the direct current tie line plan is improved, the cross-region coordinated operation of the sending terminal hydropower station, the high-voltage direct current tie line and the receiving terminal power grid is realized, through example research, the method provided by the invention has the advantages that ① not only considers the traditional hydraulic constraint of the hydropower station, but also fully considers the operation constraint of each unit and the influence of a water head on the generating characteristic of the unit, the accuracy of the model is improved, the stable operation and the generating yield of the power station are ensured, ② adopts an equivalent unit output superposition mode, a linearized model with the linear power transmission power limitation of the high-voltage direct current tie line is established, a new linear mathematical model with the high-voltage direct current tie line transmission power is fully developed, the direct current tie line transmission power grid power line transmission power is developed, the new linear power generation efficiency is improved, the new linear power generation efficiency of the white power grid power generation power station, the white load regulation model of the white power station, the white load regulation model is improved, the white power station, the white load regulation model, the white power station is improved, the white power station, the white load regulation model is improved, the white load regulation model of the white power station, the white power station of the white power station, the white power station of.

Drawings

Fig. 1 is a schematic diagram of a vibration region of a unit.

Fig. 2 is a schematic diagram of a hydraulic turbine dynamic characteristic curve triangle interpolation method.

Fig. 3 is a schematic diagram for modeling the transmission power of the high-voltage direct-current connecting line.

FIG. 4 is a flow chart of model construction.

Fig. 5 is a comparison graph of the remaining load of the power grid.

Fig. 6 is a schematic diagram of a generation plan of a brook ferry station.

Fig. 7 is a schematic structural diagram of a reservoir dam front water level process fig. 1 is a structural diagram of an embodiment of the invention.

Detailed Description

The following examples illustrate the invention in detail. The raw materials and various devices used in the invention are conventional commercially available products, and can be directly obtained by market purchase.

In the following description of embodiments, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It should also be understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

As used in this specification and the appended claims, the term "if" may be interpreted contextually as "when", "upon" or "in response to" determining "or" in response to detecting ". Similarly, the phrase "if it is determined" or "if a [ described condition or event ] is detected" may be interpreted contextually to mean "upon determining" or "in response to determining" or "upon detecting [ described condition or event ]" or "in response to detecting [ described condition or event ]".

Furthermore, in the description of the present application and the appended claims, the terms "first," "second," "third," and the like are used for distinguishing between descriptions and not necessarily for describing or implying relative importance.

Reference throughout this specification to "one embodiment" or "some embodiments," or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," or the like, in various places throughout this specification are not necessarily all referring to the same embodiment, but rather "one or more but not all embodiments" unless specifically stated otherwise. The terms "comprising," "including," "having," and variations thereof mean "including, but not limited to," unless expressly specified otherwise.

Example 1 objective function

When a power transmission plan of a hydropower station at a direct regulation transmitting end is formulated, the safe and stable operation of the hydropower station is ensured, and simultaneously the load characteristics of a receiving end power grid in the east region are considered, so that the peak regulation pressure of the power grids in the regions is relieved, and the consumption space of clean energy of the power grids is improved. The peak regulation targets which are commonly used at present are that the maximum entropy condensation function value is minimum and the residual load mean square error of the power grid is minimum, but both the maximum entropy condensation function value and the residual load mean square error of the power grid are difficult to linearize. Considering that the main measure of hydropower peak regulation is to generate more power at the peak load and generate less power or not at the valley load, the model takes the minimum difference between the net load peak and the valley of each receiving-end power grid as the target and is expressed as follows:

C_g′_,t＝C_g,t-P_g,t(2)

in the formula: g is the total number of the transmission power grids of the hydropower station at the transmission end; g is the receiving end power grid number; t, t are scheduling period and scheduling period (h), respectively; c_g,t、C′_g,tRespectively representing the original load and the residual load (MW) of the receiving-end power grid g in a period t; p_g,tThe output (MW) of the hydropower station to the grid g during the period t, i.e. the power of the dc link g during the period t, can be obtained from equation (3).

Wherein I is the unit number in the hydropower station, I_gSet of units for transmitting power to receiving grid g, P_i,tIs the output (MW) of the unit i in the period t.

The objective function is nonlinear, and auxiliary variables are introduced to linearize the objective function and better solve the objective function

And _gC′so that it satisfies the formula (4).

At this time, equation (1) becomes:

the formula (5) comprises the peak regulation problem of a plurality of power grids, belongs to the multi-target problem, adopts a weight method to convert the peak regulation problem into a single-target scheduling problem, and takes the difference of the load magnitude of each power grid into consideration to carry out normalization processing on the residual load of the power grids. The above requirements can be translated into the following objective functions:

in the formula:

maximum raw load (MW) for the g-th grid; w is a_gFor the weighting factors, equal weighting, i.e. w, is used in the invention _g1/G; in the formula (6)

Example 2 constraint Condition

(1) Water balance constraint

In the formula: v_tThe storage capacity (m) of the reservoir at the end of the t period³)；I_tIs the warehousing flow (m) of the reservoir in the period of t³/s)；S_tRepresenting the reject flow (m) of the plant during a period t³S); Δ t is the period step (h); q_tFor the generated flow (m) of the station during the time period t³S); i and I are the total number of units and the number of the units contained in the hydropower station respectively; q. q.s_i,tGenerating flow (m) of the unit i in the time period t³/s)。

(2) Water level restraint

Z_min≤Z_t≤Z_max(8)

In the formula: z_tRepresenting the dam front water level (m) of the reservoir at the end of the t period; z_max、Z_minRespectively the highest value (m) and the lowest value (m) of the reservoir dam front water level; z_beginThe actual water level (m) of the reservoir at the beginning of the dispatching period is used as the water level; z_endControlling the water level (m) for the target at the end of the scheduling period; in consideration of the fact that the allowable control water level has certain deviation in the actual scheduling operation process, delta is set as the allowable deviation ratio of the control water level at the end of the period.

(3) Unit output constraint

0≤P_i,t≤u_i,tP_i,max,u_i,t∈{0,1} (10)

In the formula: p_i,maxThe maximum generating power (MW) of the unit i; u. of_i,tIs the running state variable of the unit i in the time period t, if the unit i is in the power generation state in the time period tu _i,t1, otherwise u_i,t＝0。

(4) Unit generated current restriction

0≤q_i,t≤u_i,tq_i,max(11)

In the formula: q. q.s_i,maxMaximum generated flow (m) for unit i³/s)。

(5) Unit start-up and shut-down duration constraints

In the formula: x is the number of_i,t、x'_i,tRespectively, the start and stop operation variables of the unit j, if the unit i, x is started in the time period t _i,t1, otherwise x_i,t0, provided that unit i, x 'is shut down for period t'_i,t1, otherwise x'_i,t＝0；α_i、β_iThe shortest duration (h) of the start-up and the stop of the unit is respectively.

(6) Unit vibration zone restraint

in the formula:

PV _i,kthe upper limit (MW) and the lower limit (MW) of the output of the kth vibration area of the unit i are respectively.

K unit vibration areas are used for dividing the unit output area into K +1 safe operation areas, as shown in figure 1. The constraint of the formula (14) is a nonlinear constraint, and the nonlinear constraint linearization processing method is shown as a formula (15).

In the formula:

Formula (10) may be replaced with formula (15).

(7) Power generation water purification head restraint

In the formula: h_i,tA power generation water purification head (m) of the unit i in a time period t; zd_tIs the tail water level (m) of the reservoir in the period t; hl (high pressure chemical vapor deposition)_i,tFor generating head loss (m) of the unit i in the time period t, and for simplifying calculation, hl is assumed by the invention_i,tIs a constant; f. of_zv(·)、f_zq(. is) the relation functions of dam front water level-reservoir capacity and tail water level-outlet flow of reservoir.

f_zv(·)、f_zqThe (·) is a nonlinear function, and a piecewise linear interpolation function is adopted for linear processing. Take the water level before the dam-reservoir capacity as an example. Firstly, the storage capacity interval of reservoir is divided into [ V ]_min,V_max]Discretization is J sub-intervals, each demarcation point is defined as follows:

in the formula: v_j、Z_jRespectively the jth reservoir capacity interpolation point of the reservoir and the corresponding dam front water level.

Then introduced into0-1 integer variable R_j,tAnd satisfies the following constraints:

in the formula: r_j,tFor indicating variable, when the reservoir capacity of the reservoir in the t period is in the jth reservoir capacity subinterval_j,tNot all right 1, otherwise R _j,t0. The sub-interval of the storage capacity in which the storage capacity is positioned in the t period can be uniquely determined by the formula (18).

The relation linearization of the front dam water level-reservoir capacity can be realized through the formulas (17) - (19), and the tail water level-discharge quantity relation function is subjected to piecewise linear approximation by the method, so that the linearization of the generating head of the unit is realized.

(8) Unit dynamic characteristic constraint

P_i,t＝f_i,pqh(q_i,t,H_i,t) (20)

In the formula: f. of_i,pqhThe output of the unit i is a binary relation function between the output of the unit i, the generating flow and the generating head. Formula (20) may be replaced with formula (15).

In the aspect of the power characteristic curve of the water turbine, a certain power characteristic curve is used for representing the power characteristic curves corresponding to all water heads in the whole water head subinterval, so that the accuracy of the model is reduced. The invention provides a water wheel power characteristic curve linearization method based on trigonometric internal linear interpolation to improve the accuracy of a model.

As shown in FIG. 2, within the maximum and minimum possible generating head intervals of the unit, 5 power characteristic curves are selected, corresponding to the high head respectively

Higher head

Medium head

Lower head

And low head

Considering both the maximum output and the maximum generated flow (indicated by the dashed lines in fig. 2), each dynamic characteristic curve is divided into 2 segments, so that the entire turbine dynamic characteristic curve is divided into 17 triangular subregions. The dynamic characteristics of a water turbine can be expressed as follows:

respectively showing the water head (m) and the generated current (m) corresponding to the mu-th vertex of the first triangle³/s) and power generation output (MW); theta_i,t,lTo indicate the variable, θ _i,t,l1 represents that the combination of the generated power, the water head and the generated flow of the unit in the t period is positioned in the sub-area of the l triangles;

representing the weight taken up by the μ -th vertex of triangle/during time t.

Formula (21) shows that when the unit is in the power generation state, one and only one triangular sub-area is selected; formula (22) indicates that if the triangle l is selected, the sum of the weights of the three vertices is 1, otherwise, the weight of the three vertices is 0; the formula (23) is to interpolate the generating head, if the unit is in a generating state in the time period t, the generating head can be inevitably expressed by the head interpolation values of three vertexes of a certain triangle, otherwise the constraint is invalid; equation (24) interpolates the generated flow rate and the generated output, respectively.

Compared with the linearization method of the power characteristic curve of the water turbine reported in the existing literature, the linear interpolation method in the triangle provided by the invention has the following two advantages that the power generating head of the ① unit is continuous, the linearization model is more accurate theoretically, the accuracy of linear fitting can be adjusted by controlling the number of the triangular sub-regions, the ② method does not need to be executed in multiple steps, understanding and operation are convenient, and the maximum power generating output and the maximum power generating flow of the unit can be effectively considered besides the influence of the water head.

(9) Transmission constraint of extra/ultra high voltage DC link

As described above, the power transmission power curve of the high-voltage direct-current tie line should be stepped, and should not be adjusted reversely in a short time, so as to avoid frequent adjustment of the dc converter equipment and ensure the operational reliability of the dc tie line.

Considering that the power transmission power of the direct-current connecting line is in a step shape, the invention provides a linear modeling method of a power transmission curve of the high-voltage direct-current connecting line by taking the idea of unit combination modeling as reference. As shown in fig. 3, the transmission power curve of the dc link is divided into K steps, and assuming that there are K equivalent generator sets, the output curves of the K equivalent generator sets are superimposed to form a transmission power curve of the dc link. For these equivalent generator sets, the constraint conditions of the traditional unit combination need to be satisfied, which mainly includes the following constraints

① force limit

v_g,k,tP_g,k,min≤P_g,k,t≤v_g,k,tP_g,k,max(26)

In the formula: k is the number of the equivalent unit; p_g,k,tOutputting power (MW) of the kth equivalent unit which is transmitted to the power grid g in a period t; v. of_g,k,tThe operation state variable of the kth equivalent unit for transmitting power to the power grid g in the time period t, and v if the equivalent unit k is in the operation state in the time period t _g,k,t1, otherwise v_g,k,t＝0；P_g,k,max、P_g,k,minThe upper and lower limits (MW) of the output of the equivalent unit k, respectively, and P is set here to ensure that the curve of the DC transmission power is in a step shape_g,k,maxAnd P_g,k,minIf they are equal, the output limit constraint can be expressed as equation (27), which means that the equivalent unit k operates at a fixed power as long as it is powered on.

P_g,k,t＝v_g,k,tP_g,k,fix(27)

In the formula: p_g,k,fixThe fixed output (MW) is the fixed output under the operation state of the equivalent unit k.

② Start-stop on/off duration constraints

In the formula: y is_g,k,t、y'_g,k,tRespectively indicating variables for starting and stopping the equivalent unit k, if the unit k is started in the time period t, y _g,k,t1, otherwise y _g,k,t0, toFrom y'_g,k,tThe same process is carried out; tau is_g,k、γ_g,kRespectively the shortest duration (h) of the start-up and the stop of the equivalent unit k.

③ shutdown limit

④ power back regulation limit

v_g,k+1,t≤v_g,k,t(32)

The above formula specifies the start-up sequence between equivalent units. As shown in fig. 3, the equivalent unit k +1 can be turned on only when the equivalent unit k is in the on state. The equations (29), (30) and (32) can effectively prevent the reverse adjustment of the transmitted power in a short time. According to the method for the multi-equivalent unit coordination modeling of the power transmission power of the high-voltage direct-current connecting line, the direct-current transmission power plan is controlled in a mode of overlapping the output of a plurality of equivalent units, the characteristics of flexibility and high adjusting speed of a direct-current control mode are fully utilized on the premise that the direct-current power meets constraint conditions such as step and the like, and the potential of cross-region clean energy consumption of the direct-current connecting line is developed to a greater extent. In practical application, parameters such as the number of equivalent units, fixed operation output, minimum start-stop time, maximum shutdown times and the like can be reasonably set according to historical operation data of the direct current tie line and experience of scheduling personnel, the adjusting performance of converter station equipment, the upper and lower limits of the injection power of a receiving-end power grid and the like. In addition, in flood season, the hydropower station usually runs close to the maximum power to reduce water abandon, so that the utilization rate of the direct current connecting line channel is very high, and a power adjusting space is lacked. Therefore, the optimization model is more suitable for making the dispatching plan of the high-voltage direct-current transmission end hydropower station with the adjustment space still existing in the direct-current transmission power in the non-flood season.

(10) Daily power supply restraint

In order to guarantee the generating benefit of the hydropower station at the transmitting end, the actual transmission electric quantity of the hydropower station needs to meet the transmission electric quantity specified in the trans-regional electric power trading contract signed by the transmitting end and the receiving end.

In the formula, E_gDaily electric power transmission (MWh) specified in an electric power trading contract signed for the transmitting-end hydropower station and the receiving-end power grid g; epsilon is the allowable deviation proportion of the actual power transmission quantity of the hydropower station at the sending end to the contract power quantity.

The specific flow is shown in fig. 4:

example 3 example analysis

In order to verify the effectiveness of the on-demand model construction method, the model is applied to short-term power generation planning of a stream Luo-Du hydropower station at a certain day in the dry season. The Xiluodie hydropower station is a giant water conservancy project located at the downstream of Jinshajiang in China, the reservoir regulation performance is annual regulation, and the Xiluodie hydropower station comprises 18 units, and the total installed capacity is 1260 ten thousand kW. According to the current scheduling scheme, the 9 machine groups on the left bank are subjected to the scheduling of a national power scheduling center and directly transmit power to the Zhejiang power grid through a +/-800 kV extra-high voltage direct-current connecting line, and the 9 machine groups on the right bank are subjected to the scheduling of a southern power grid scheduling center and transmit power to the Guangdong power grid through a +/-500 kV extra-high voltage connecting line. The main operating parameters of the hydropower station/reservoir and the in-plant units are shown in table 1 and table 2, respectively. With 1d as a scheduling cycle and 1h as a scheduling period, the power station warehousing runoff and the load of each receiving end power grid refer to the historical actual value of the day, as shown in table 3. The operation parameters of the equivalent units of the high-voltage direct-current tie lines of each power grid of the stream ferry hydropower station are obtained by analyzing a large amount of historical operation data of each direct-current tie line, as shown in table 4. The daily electric quantity of the Xiludu hydropower station for sending to the Zhejiang power grid and the Guangdong power grid is 55200 MWh and 50900MWh respectively. In the large context of promoting clean energy consumption, the behavior of the hydropower station to abandon water in the non-flood period is generally not allowed, so S is set_t0. The allowable deviation of the control water level at the end of the dispatching period of the power station is 0.1%, and the allowable deviation of the actual power transmission amount of the direct current connecting line is set to be 3% (namely, delta is equal to 0.1%, and epsilon is equal to 3%).

TABLE 1 Xiluodie hydropower station operating parameters

TABLE 2 characteristic parameters of hydroelectric generating sets

TABLE 3 runoff in warehouse of Xiluodi hydropower station and loads of Zhejiang and Guangdong power grids

Table 4 direct current tie line represents equivalent unit operation parameters

The load balance result of each power grid and the ratio of the remaining load of each power grid after actual stream ferry power transmission on the current day are shown in fig. 5, and the statistical results of the load characteristic indexes of each power grid before and after optimization are shown in table 5. The results show that after the hydropower station peak load regulation is optimized, the load peak-valley difference of each power grid is reduced to different degrees, the load peak-valley difference of the Zhejiang power grid and the Guangdong power grid is reduced from 17159MW to 29994MW to 14559MW and 27794MW, and the reduction is 15.2% and 7.33% respectively. Meanwhile, the load peak-valley difference rate and the standard deviation of each power grid are also obviously reduced, which shows that the residual load curve after the optimized peak regulation tends to be more stable. But also can see that, after optimization, the peak regulation effect of the Zhejiang power grid is more obvious, the residual load is more stable, and the peak regulation effect of the Guangdong power grid is less obvious, and the analysis reason is as follows: on one hand, the load trends of the Zhejiang power grid and the Guangdong power grid are basically consistent, the load peak time periods are 9:00-16:00, and the load valley time periods are 1:00-8:00, which means that the two power grids have a competitive relationship for the demand of peak regulation power, and cannot exert complementary advantages; on the other hand, the highest load and peak-to-valley difference of the Guangdong power grid are 75135MW and 29994MW respectively, which are 1.7 times of those of the Zhejiang power grid, while the transmission power of the high-voltage direct-current connecting line cannot be adjusted randomly due to a plurality of limitations, and the power transmitted from the stream Luo-crossing hydropower station to the Guangdong power grid appears as 'water wagons per cup', so that the whole peak regulation effect of the Guangdong power grid is not obvious. However, compared with actual operation data, the indexes of the power grid such as the peak-to-valley difference, the peak-to-valley difference rate, the standard difference and the like obtained by the model calculation are lower than the actual operation indexes, particularly the power grid in Zhejiang, the peak-to-valley difference rate does not decrease or increase reversely after the direct-current transmission power is received, the peak-to-valley pressure is increased, and the peak-to-valley effect is extremely obvious after optimization. The model of the invention can realize better peak regulation effect by optimizing the power of the trans-regional direct current connecting line, simultaneously reduces the peak regulation pressure of two receiving end power grids, and reserves more space for clean energy consumption.

Table 5 statistical results of load characteristic indexes of each grid before and after optimization

Fig. 6 shows planned output (dc link transmission plan) of the left and right banks of the rabo ferry station. The left bank power station and the right bank power station operate at the minimum transmission power of the direct current tie line in the load valley period (such as 1:00-6:00) of the receiving end power grid respectively, and operate at the maximum transmission power in the load peak period (such as 10:00-18:00) of the receiving end power grid after short power boost so as to respond to the load fluctuation of the receiving end power grid as much as possible and relieve the peak shaving pressure of the receiving end power grid. Due to the introduction of the formulas (15), (26) and (32), the power transmission power curve of the direct current connecting line is in a step shape, the power transmission power does not reverse in a short time, the electric quantity transmitted to the Zhejiang power grid and the Guangdong power grid is 56200 MWh and 50800MWh respectively, the daily power transmission quantity requirement specified by a power transmission contract can be met, and the power generation benefit of the stream Luo-Chi power station is guaranteed. The direct current sending end hydropower station optimized dispatching model constructed by the invention can avoid frequent adjustment of direct current conversion equipment, and the manufactured power transmission plan can be accepted by sending end hydropower stations and direct current connecting line operators while the peak regulation capability of a receiving end power grid is improved, so that the method has higher practicability.

Fig. 7 shows the dam water level process of the rivulet ferry power station, and it can be seen that the dam water level rises within 1-8 hours and falls within 9-24 hours, and the water level variation amplitude reaches 0.48m in the scheduling period, so that the upper limit and the lower limit of the dam water level are always satisfied. The water level at the end of the dispatching period is 585.80m, and the deviation control requirement of the target end water level is met.

And the starting and stopping states of all the units of the brook ferry hydropower station in all time periods are shown in the table 6. The result shows that each unit meets the constraint that the minimum power generation and shutdown duration is 2h, and the shutdown times of each unit do not exceed 2 times within one day. The optimization model provided by the invention can effectively avoid frequent starting and stopping of the hydroelectric generating set and ensure safe and stable operation of the hydroelectric generating set.

TABLE 6 Start-stop states of units of the Xiluodie hydropower station

Note that √ denotes a power-on state, and × denotes a power-off state.

In conclusion, the embodiment shows that the short-term optimized dispatching model of the high-voltage direct-current transmitting-end hydropower station with the aim of minimum residual load peak-valley difference of the receiving-end power grid is constructed aiming at the current situation that a large number of large hydropower stations transmit power to the power grid of developed east regions through the high-voltage direct-current connecting lines but do not regulate peaks, and the validity of the model is verified by taking the short-term dispatching plan making of the stream Luo-ferry hydropower station as an example; the following conclusions were made:

(1) besides the traditional hydraulic constraint of the hydropower station, the operation constraint of each unit and the influence of a water head on the generating characteristic of the unit are also fully considered, the accuracy of the model is improved, and the stable operation and the generating benefit of the hydropower station are guaranteed;

(2) the method adopts an equivalent unit output superposition mode to establish a linear mathematical model of the transmission power limit of the high-voltage direct-current connecting line, not only gives full play to the characteristic that the direct-current connecting line can be quickly adjusted, but also avoids frequent switching of high-voltage direct-current converting equipment and improves the plan executability of the direct-current connecting line;

(3) aiming at nonlinear factors in a short-term optimization scheduling model of a direct-current transmitting end hydropower station, effective linearization processing strategies are respectively provided, an original MINLP model is converted into an MILP model, and efficient solving of the model is still realized by means of commercial optimization software with superior performance;

(4) after optimization, the load peak-valley difference of the Zhejiang power grid and the Guangdong power grid is respectively reduced by 15.2% and 7.33%, and compared with an actual power transmission plan, the load peak-valley difference adjusting method has the advantages that the load adjusting capacity of a large hydropower station on a receiving-end power grid can be better exerted, and a more obvious peak adjusting effect is obtained;

(5) the invention discloses a linear interpolation method for a triangular internal part, which is characterized in that the dynamic characteristic curve of a water turbine is a plurality of groups of output-power generation flow curve clusters under different power generation water heads, and the accuracy of a linear model is improved by linearizing the dynamic characteristic curve of the water turbine;

(6) with the continuous promotion of clean energy substitution in the east region of China, large-scale hydropower stations newly built in the southwest region, such as Wudongde and white crane beaches, continue to transmit power to the east region through direct current connecting lines, and new energy such as wind power and the like in the local region are continuously connected to the power grid.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.

Claims

1. A direct current sending end hydropower station optimal scheduling method compatible with receiving end power grid peak regulation requirements is characterized by comprising the following steps: modeling is carried out on the hydropower short-term optimization scheduling problem to obtain a mathematical model, after calculation conditions are set, firstly, an objective function is linearized, linearization processing is carried out on nonlinear target constraint on the premise that precision is allowed, then an original non-convex mixed integer nonlinear programming model is converted into a mixed integer linear programming model, and an optimization solver is used for solving the model on the basis.

2. The method for optimizing and scheduling the direct-current transmitting-end hydropower station compatible with the peak shaving requirement of the receiving-end power grid according to claim 1, is characterized in that: the method for converting the initial model into the mixed integer linear programming model comprises the following steps: firstly, establishing a short-term optimization scheduling model of the high-voltage direct-current transmitting-end hydropower station, and taking the minimum residual load peak-valley difference of the receiving-end power grid as a target function of the model so as to fully excavate the trans-regional peak regulation capability of the high-power hydropower station, reduce the peak regulation pressure of the receiving-end power grid and improve the clean energy consumption level of the receiving-end power grid; in addition to hydraulic constraint, unit operation constraint, waterhead influence and high-voltage direct-current connecting line power transmission limitation are increased; carrying out linearization processing on nonlinear factors such as nonlinear peak regulation objective functions in the model, unit generating heads, unit operation combined vibration regions, unit power characteristic curves, stepped power transmission curve limitation of a high-voltage direct-current connecting line and the like; aiming at nonlinear constraint of a power characteristic curve of the water turbine, a triangular internal linear interpolation method is constructed, and the power characteristic curve of the water turbine is linearized; and realizing the conversion from the original model to the standard mixed integer linear programming model.

3. The method for optimizing and scheduling the direct-current transmitting-end hydropower station compatible with the peak shaving requirement of the receiving-end power grid according to claim 1, is characterized in that: the linearization processing of the objective function comprises the following steps:

C′_g,t＝C_g,t-P_g,t(2)

further, auxiliary variables are introduced

at this time, equation (1) becomes:

in the formula:

the maximum original load MW of the g-th power grid; w is a_gFor the weighting factors, equal weighting, i.e. w, is used in the invention_g1/G; in the formula (6)

4. The method for optimizing and scheduling the direct-current transmitting-end hydropower station compatible with the peak shaving requirement of the receiving-end power grid according to claim 1, is characterized in that: the linearization process of the constraint condition comprises the following steps:

(1) and (3) water balance constraint:

in the formula: v_tIs the storage capacity m of the reservoir at the end of the t period³；I_tIs the warehousing flow m of the reservoir in the time period t³/s；S_tRepresenting water reject flow m of the plant during a period t³S; Δ t is a time period step h; q_tFor the generating flow m of the power station in the time period t³S; i and I are the total number of units and the number of the units contained in the hydropower station respectively; q. q.s_i,tGenerating flow m of unit i in t period³/s；

(2) Water level restraint:

Z_min≤Z_t≤Z_max(8)

in the formula: z_tRepresenting the dam front water level m of the reservoir at the end of the t period;Z_max、Z_minrespectively the highest value m and the lowest value m of the front water level of the reservoir dam; z_beginThe actual water level m of the reservoir at the beginning of the dispatching period; z_endControlling the water level m for the target at the end of the dispatching period; considering that a certain deviation exists in the allowable control water level in the actual scheduling operation process, setting delta as the allowable deviation proportion of the control water level at the end of the period;

(3) unit output restraint:

0≤P_i,t≤u_i,tP_i,max,u_i,t∈{0,1} (10)

in the formula: p_i,maxThe maximum generating power MW of the unit i; u. of_i,tIs the running state variable of the unit i in the time period t, if the unit i is in the power generation state in the time period t, u_i,t1, otherwise u_i,t＝0；

(4) And (3) restraining the generating flow of the unit:

0≤q_i,t≤u_i,tq_i,max(11)

in the formula: q. q.s_i,maxMaximum generation flow m for unit i³/s；

(5) And (3) restraining the starting and stopping duration of the unit:

in the formula: x is the number of_i,t、x'_i,tRespectively, the start and stop operation variables of the unit j, if the unit i, x is started in the time period t_i,t1, otherwise x_i,t0, provided that unit i, x 'is shut down for period t'_i,t1, otherwise x'_i,t＝0；α_i、β_iRespectively setting the shortest duration h of the start and stop of the unit;

(6) and (3) restraining a vibration area of the unit:

in the formula:

in the formula:

Formula (10) may be replaced with formula (15);

(7) power generation water purification head restraint:

in the formula: h_i,tGenerating water purification heads m for the unit i in a time period t; zd_tThe tail water level m of the reservoir in the period t; hl (high pressure chemical vapor deposition)_i,tAssuming hl for simplifying calculation for generating head loss m of the unit i in the time period t_i,tIs a constant; f. of_zv(·)、f_zq(. the) is the relation function of dam front water level-reservoir capacity and tail water level-outlet flow of the reservoir respectively;

in the formula: r_j,tFor indicating variable, when the reservoir capacity of the reservoir in the t period is in the jth reservoir capacity subinterval_j,tNot all right 1, otherwise R_j,t0; the sub-interval of the storage capacity in which the storage capacity is positioned in the t period can be uniquely determined by the formula (18);

(8) unit dynamic characteristic constraint:

P_i,t＝f_i,pqh(q_i,t,H_i,t) (20)

in the formula: f. of_i,pqhBetween output and generated flow and head of unit iA binary relation function; formula (20) may be replaced with formula (15);

Higher head

Medium head

Lower head

And low head

respectively showing a water head m and a power generation flow m corresponding to the mu-th vertex of the first triangle³The power generation output MW and the power/s; theta_i,t,lTo indicate the variable, θ_i,t,l1 represents that the combination of the generated power, the water head and the generated flow of the unit in the t period is positioned in the sub-area of the l triangles;

(10) daily power transmission amount constraint:

5. The optimal scheduling method of the direct current sending end hydropower station compatible with the peak shaving requirement of the receiving end power grid according to claim 4, characterized by comprising the following steps: in the transmission constraint processing of the ultra/ultra-high voltage direct current tie line (9), for an equivalent generator set, constraint conditions of a traditional unit combination need to be met, wherein the constraint conditions comprise the following constraints:

① force limit

v_g,k,tP_g,k,min≤P_g,k,t≤v_g,k,tP_g,k,max(26)

In the formula: k is the number of the equivalent unit; p_g,k,tThe output MW of the kth equivalent unit which transmits power to the power grid g in the period t; v. of_g,k,tThe operation state variable of the kth equivalent unit for transmitting power to the power grid g in the time period t, and v if the equivalent unit k is in the operation state in the time period t_g,k,t1, otherwise v_g,k,t＝0；P_g,k,max、P_g,k,minThe upper and lower limits MW of output of the equivalent unit k are respectively, and P is set here to ensure that the curve of the DC transmission power is in a step shape_g,k,maxAnd P_g,k,minIf they are equal, the constraint of output limit can be expressed as the formula (27), which means that the equivalent unit k is at a fixed power as long as it is turned onRunning;

P_g,k,t＝v_g,k,tP_g,k,fix(27)

② Start-stop on/off duration constraints

In the formula: y is_g,k,t、y'_g,k,tRespectively indicating variables for starting and stopping the equivalent unit k, if the unit k is started in the time period t, y_g,k,t1, otherwise y_g,k,t0 for y'_g,k,tThe same process is carried out; tau is_g,k、γ_g,kRespectively setting the shortest duration h of starting and stopping the equivalent unit k;

③ shutdown limit

④ power back regulation limit

v_g,k+1,t≤v_g,k,t(32)

6. The method for optimizing and scheduling the direct-current transmitting-end hydropower station compatible with the peak shaving requirement of the receiving-end power grid according to claim 1, is characterized in that: the optimization solver adopts a commercial Gurobi optimization solver.