An optimized scheduling method considering the mismatch relationship of power generation flow in cascade hydropower stations

Abstract

The present invention discloses an optimized scheduling method considering the mismatching relationship of power generation flow rates of cascade hydropower stations, which includes the following steps: Step 1, establish an objective function capable of obtaining the maximum power generation of the hydropower station; Step 2, confirm the value of the penalty coefficient and establish conventional constraint conditions and unconventional constraint conditions; Step 3, confirm the upstream and downstream relationships of the hydropower stations; Step 4, obtain the full-load flow rates of the units of the upstream hydropower station and the full-load flow rates of the units of the downstream hydropower station; Step 5, obtain the variables related to the calculated output of the upstream hydropower station and the downstream hydropower station; Step 6, determine whether the full-load flow rate of the units of the upstream hydropower station is greater than the full-load flow rate of the units of the downstream hydropower station; Step 7, on the basis of Step 6, obtain the maximum power generation of the hydropower station by substituting the variables into the objective function. The present invention seeks the best matching relationship between the upstream and downstream outflows by using the regulation ability of the upstream power station for the optimized scheduling of cascade power stations while fully considering the installed flow rate conditions of the downstream power station.

Description

Technical Field

[0001] The present invention relates to the technical field of reservoir optimal operation calculation, and more specifically, to an optimal operation method considering the mismatch relationship of power generation flow rates of cascade hydropower stations. Background Art

[0002] In reservoir optimal operation, the risk of water abandonment is mainly considered during the flood season. This is because the water inflow during the flood season is large and the inflow rate is uneven, so water abandonment is likely to occur. In China, many scholars have studied the problem of water abandonment risk during the flood season. They mainly quantify it by considering the water abandonment risk in the objective function and select a plan that not only ensures the completion of power generation but also reduces the water abandonment risk to ensure the comprehensive benefits of the power station. Currently, the research on water abandonment control mainly focuses on the flood season. However, on the one hand, there is little research on the water abandonment control method before the flood season, and generally, the output is punished to increase the guarantee rate. Therefore, introducing a penalty coefficient to reduce the water abandonment volume before the flood season is also a good method; on the other hand, in the operation of cascade hydropower stations, how to reasonably match the outflow of the upstream power station with the maximum full-load generation flow rate of the downstream power station to maximize the comprehensive benefits of the cascade, especially during the flood season, there are few relevant solutions. Therefore, we use the regulation ability of the upstream power station to optimize the operation of the cascade hydropower stations under the condition of fully considering the maximum full-load generation flow rate of the downstream power station to seek the best matching relationship between the power generation flows of the upstream and downstream power stations. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention provides an optimal operation method considering the mismatch relationship of power generation flow rates of cascade hydropower stations, and uses the regulation ability of the upstream power station to optimize the operation of the cascade hydropower stations under the condition of fully considering the maximum full-load generation flow rate of the downstream power station to seek the best matching relationship between the upstream and downstream outflows.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: an optimal operation method considering the mismatch relationship of power generation flow rates of cascade hydropower stations, including the following steps:

[0005] Step 1, establish an objective function capable of obtaining the maximum power generation of the hydropower station; the objective function is a function for calculating the power generation from the output within a unit time period;

[0006] Step 2, confirm the value of the penalty coefficient, and establish conventional constraint conditions and unconventional constraint conditions; the unconventional constraint condition is a limiting condition for the water abandonment volume of the downstream power station by introducing the penalty coefficient;

[0007] Step 3, confirm the upstream and downstream relationships of the hydropower stations, and determine the upstream hydropower station and the downstream hydropower station;

[0008] Step 4, obtain the full-load generation flow rate of the upstream hydropower station and the full-load generation flow rate of the downstream hydropower station;

[0009] Step 5: Obtain the variables related to the calculated output of the upstream hydropower station and the downstream hydropower station;

[0010] Step 6: Determine whether the full-load flow rate of the units of the upstream hydropower station is greater than that of the downstream hydropower station; if so, exclude the variables in Step 5 under the conventional constraints and the unconventional constraints; if not, exclude the variables in Step 5 under the conventional constraints;

[0011] Step 7: On the basis of Step 6, obtain the maximum power generation of the hydropower station by substituting the variables into the objective function.

[0012] Specifically, the objective function is

[0013]

[0014] In the formula: E is the calculated maximum power generation; T is the total number of time periods, t ∈ [1, T]; N t is the output at the t-th time period; K is the output coefficient; is the power generation flow rate at the t-th time period; is the average head at the t-th time period; Δt is the time period interval length, with a daily calculation time period.

[0015] Specifically, the conventional constraints include water balance constraint, reservoir water level constraint, storage capacity curve constraint, downstream water level-flow relationship constraint, hydropower station head constraint, hydropower station total output constraint, forecasted output limit, power generation flow rate limit constraint, abandoned water flow rate limit constraint, out-flow constraint, initial water level and termination water level constraint.

[0016] Specifically, the conventional constraints also include non-negativity constraint conditions, and the extraordinary constraint conditions require that all variables of the conventional constraint conditions must be non-negative values.

[0017] Specifically, the unconventional constraint condition is

[0018]

[0019] In the formula: q t is the out-flow of the upstream power station at the t-th time period; Qqj t is the interval flow rate of the downstream power station at the t-th time period, obtained by subtracting the out-flow of the upstream power station from the in-flow of the downstream power station; a is the penalty coefficient; q′ t is the upstream power station reservoir flow rate at the t-th time period after penalty; is the full-load flow rate of the downstream power station units at the t-th time period.

[0020] Specifically, the steps for determining the value of the penalty coefficient include the following steps:

[0021] (1) Take different penalty coefficients and calculate the total power generation and total water abandonment of the power station according to the above steps;

[0022] (2) Compare the results of total power generation and total water abandonment under different penalty coefficients;

[0023] (3) Take the penalty coefficient value when the power generation is as large as possible and the water abandonment is as small as possible.

[0024] In particular, in step (5), the variables related to the output include the unit power generation flow rate and the water head of the upstream hydropower station and the downstream hydropower station.

[0025] The beneficial effects of the present invention are as follows:

[0026] By introducing a penalty coefficient, the present invention constructs the connection of the upstream and downstream discharge flows, thereby establishing the maximum full-load flow constraint of the downstream power station. By selecting an appropriate penalty coefficient, the outlet flow of the upstream power station can be optimized and regulated, so as to match the maximum full-load flow of the upstream and downstream power stations, finally meet the maximum power generation flow constraint of the downstream power station, reduce the total water abandonment of the cascade, and increase the total power generation of the cascade. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is the flowchart of the method of the embodiment of the present invention;

[0029] Figure 2 It is the change diagram of the total cascade power generation and the total cascade water abandonment from January to March under different penalty coefficients in the embodiment of the present invention;

[0030] Figure 3 It is the change diagram of the total cascade power generation and the total cascade water abandonment from April to May under different penalty coefficients in the embodiment of the present invention;

[0031] Figure 4 It is the comparison diagram of the total water abandonment from January to March in each year considering and not considering the downstream power station constraint in the embodiment of the present invention;

[0032] Figure 5 It is the comparison diagram of the total water abandonment from April to May in each year considering and not considering the downstream power station constraint in the embodiment of the present invention. Detailed Embodiment

[0033] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the protection scope of the present invention more clearly defined.

[0034] It should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0035] In addition, the terms "horizontal", "vertical", "hanging", etc. do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0036] In the description of the present invention, it should also be noted that unless otherwise clearly specified and limited, the terms "set", "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0037] As Figure 1 shown, an optimal scheduling method considering the mismatch relationship of the power generation flow of cascade hydropower stations in this embodiment

[0038] Taking Xijin Power Station, Xianyitan Power Station and Guihang Power Station as examples in this embodiment, since the inflow during the period of water level decline from April to May in Xijin Power Station is large and there is more water abandonment, this embodiment studies separately for January - March and April - May.

[0039] Step 1, establish an objective function that can obtain the maximum power generation of the hydropower station;

[0040] The objective function is to maximize the power generation of the hydropower stations with regulation ability during the scheduling period T, that is:

[0041]

[0042] Where: E is the calculated maximum power generation, T is the total number of time periods, t ∈ [1, T], and N t is the output in the t-th time period; K is the output coefficient, is the power generation flow in the t-th time period, is the average head in the t-th time period, and Δt is the time period interval length, with the day as the calculation time period.

[0043] Step 2: Confirm the value of the penalty coefficient and establish conventional constraints and unconventional constraints. The unconventional constraint is the constraint condition for the water rejection of the downstream power station by introducing the penalty coefficient;

[0044] Confirming the value of the penalty coefficient includes the following steps:

[0045] (1) Take different penalty coefficients and calculate the total power generation and total water rejection of the power station according to the above steps;

[0046] (2) Compare the results of the total power generation and total water rejection under different penalty coefficients;

[0047] (3) Take the value of the penalty coefficient when the power generation is as large as possible and the water rejection is as small as possible.

[0048] The conventional constraints are:

[0049] (1) Water balance constraint, that is:

[0050]

[0051] Where: V t-1 and V t are the reservoir capacities at the beginning and end of the t-th time period respectively; are the average inflow and outflow flows in the t-th time period respectively.

[0052] (2) Reservoir water level constraint, that is:

[0053]

[0054] Where: is the upstream water level at the end of the t-th time period; are the allowable minimum and maximum water levels at the end of the t-th time period respectively.

[0055] (3) Reservoir capacity curve constraint, that is:

[0056]

[0057] Where: f ZV (*) is the function of the relationship between the upstream water level and the reservoir capacity.

[0058] (4) Downstream water level - flow relationship constraint. That is:

[0059]

[0060] In the formula: is the average tail water level at time t; f ZQ (*) is the function of the relationship between the tail water level and the flow rate.

[0061] (5) Hydropower station head constraint condition, that is:

[0062]

[0063] In the formula: ΔH t 、 are the head loss at time t, the upstream water level at the beginning of time t, and the upstream water level at the end of time t respectively; f ΔH (*) is the hydropower station head loss function, is the flow rate for power generation at time t, H min and H max are the minimum and maximum heads, is the average head at time t.

[0064] (6) Hydropower station total output constraint condition, that is:

[0065]

[0066] In the formula: are the upper and lower limits of the output at time t respectively; generally determined by the comprehensive factors such as the installed capacity of the hydropower station, the rated output of the unit, the vibration area, and the peak shaving requirements.

[0067] (7) Anticipated output limit condition, that is:

[0068]

[0069] In the formula: f yx (*) is the head anticipated output function.

[0070] (9) Power generation flow rate limit condition, that is:

[0071]

[0072] In the formula: is the maximum flow passing capacity of the hydropower station unit at time t.

[0073] (10) Waste water flow rate limit condition, that is:

[0074]

[0075] In the formula: is the waste water flow rate at time t, is the maximum waste water flow rate, f xl (*) is the tail water level discharging capacity function.

[0076] (11) Discharge flow constraint condition, that is:

[0077]

[0078] In the formula: is the minimum discharge flow of the power station at time period t, which is determined by the requirements of downstream comprehensive utilization (such as irrigation, water supply, shipping, ecological environment, etc.).

[0079] (12) Initial water level and terminal water level constraint conditions, that is:

[0080]

[0081] In the formula: Z c , Z m are the initial water level and the final water level of the reservoir operation period respectively.

[0082] (13) Non - negative constraint condition, that is, all variables in the above (1)-(12) constraint conditions must be non - negative values.

[0083] The unconventional constraint condition is shown as the following formula:

[0084]

[0085] In the formula: q t is the upstream power station discharge flow at time period t, Qqj t is the downstream power station interval flow at time period t, which is obtained by subtracting the upstream power station discharge flow from the downstream power station inflow. a is the penalty coefficient, q′ t is the upstream power station reservoir flow after penalty at time period t, is the full - load flow of the downstream power station units at time period t.

[0086] Step three, confirm the upstream and downstream relationship of the hydropower stations, and determine the upstream hydropower station and the downstream hydropower station. In this embodiment, from top to bottom are Xijin Power Station, Xianyitan Power Station, and Guihang Power Station in sequence, that is, Xijin Power Station is upstream of Xianyitan Power Station and Guihang Power Station, and Xianyitan Power Station is upstream of Guihang Power Station.

[0087] Step four, obtain the full - load flow of the upstream hydropower station units and the full - load flow of the downstream hydropower station units.

[0088] Step five, obtain the variables related to the calculated output of the upstream hydropower station and the downstream hydropower station.

[0089] Step six, determine whether the full - load flow of the upstream hydropower station units is greater than the full - load flow of the downstream hydropower station units; if so, exclude the variables in step five under the conventional constraint conditions and the unconventional constraint conditions; if not, exclude the variables in step five under the conventional constraint conditions.

[0090] Step 7: On the basis of Step 6, the maximum power generation of the hydropower station is obtained by substituting variables into the objective function.

[0091] (1) For January - March: Since the full - load discharge of the Xianyitan Power Station is greater than that of the Guihang Power Station, when there is water abandonment in the Xianyitan Power Station, there will surely be water abandonment in the Guihang Power Station. Therefore, mainly consider the penalty of water abandonment in the Guihang Power Station on the discharge of the Xijin Power Station, that is:

[0092]

[0093] (2) April - May: At this time, the incoming water of the Xijin Power Station is relatively large. Mainly consider the situation that the Xianyitan Power Station tries not to have water abandonment and the Guihang Power Station can have water abandonment. Therefore, mainly consider the penalty of water abandonment in the Xianyitan Power Station on the discharge of the Xijin Power Station during this period, that is:

[0094]

[0095] In formulas (14) - (15): q is the discharge of the Xijin Power Station, Qqj xyt and Qqj gh are the flow rates between the Xianyitan and Guihang Power Stations, respectively obtained by subtracting the upstream power station's discharge from the incoming water flow rate. a is the penalty coefficient, q′ is the discharge of the Xijin Power Station after penalty, 714 m 3 / s and 1604 m 3 / s are the full - load discharge of the Guihang and Xianyitan Power Stations respectively.

[0096] Solution steps

[0097] This example uses dynamic programming for solution and calculates through sequential recurrence equations, including the following steps:

[0098] (1) Divide the range between the dead water level and the normal storage level at intervals of 0.1 m;

[0099] (2) According to the divided water levels, assume the initial and final reservoir water levels Z t and Z t+1 for each time period t;

[0100] (3) According to the incoming water flow rate Q t , Z t and Z t+1 , the discharge q t can be calculated. If , exclude this situation;

[0101] (4) According to q t , the downstream water level Z xy can be calculated, and then the water head H t is obtained. If H t <H min , N = 0; If Ht >H max , exclude this case;

[0102] (5) According to the Xianyitan and Guihang constraints, the punished Xijin outflow discharge q′ can be calculated t ;

[0103] (6) According to H t , can calculate Compare q′ t with . If Q fd = q′ t ; otherwise,

[0104] (7) If exclude this case;

[0105] (8) According to Q fd , the power generation E can be calculated through N t = KQ fd H t ; t ;

[0106] (9) Finally, calculate the cumulative power generation E based on the non-excluded cases, and select the optimal operating water level by taking the maximum cumulative power generation.

[0107] Determination of the penalty coefficient

[0108] (1) Determination of the penalty coefficient from January to March

[0109] The penalty coefficient takes values from 0 to 1, with an interval of 0.1. Calculate the optimal scheduling results for each penalty coefficient, as shown in Figure 2 . Figure 2 is the variation diagram of the total cascade power generation and total water abandonment from January to March under different penalty coefficients. In order to make the total cascade power generation as large as possible and the total water abandonment as small as possible, the penalty coefficient is finally selected as 0.5.

[0110] (2) Determination of the penalty coefficient from April to May

[0111] Similarly, the optimal scheduling results for each penalty coefficient from April to May can be obtained, as shown in Figure 3 . Figure 3 is the variation diagram of the total cascade power generation and total water abandonment from April to May under different penalty coefficients. In order to make the total cascade power generation as large as possible and the total water abandonment as small as possible, the penalty coefficient is finally selected as 0.8.

[0112] Step 7, based on Step 6, obtain the maximum power generation of the hydropower station by substituting variables.

[0113] The main steps of this embodiment are as follows:

[0114] (1) Divide the interval between the dead water level and the normal storage level at 0.1 m intervals;

[0115] (2) Assume the initial and final reservoir water levels Z t and Z t+1 for each time period t according to the divided water levels;

[0116] (3) Calculate the outflow discharge q t according to the inflow discharge Q t , Z t+1 , if t exclude this case; Exclude this case;

[0117] (4) Calculate the downstream water level Z t according to q xy , and then obtain the water head H t . If H t <H min , N = 0; if H t >H max , exclude this case;

[0118] (5) Calculate the punished Xijin outflow discharge q′t according to the Xianyitan and Guihang constraint conditions;

[0119] (6) According to H t , calculate Compare q′ t with . If Q fd =q′ t ; otherwise,

[0120] (7) If exclude this case;

[0121] (8) According to Q fd , calculate the generated electricity E t through N fd =KQ t H t ;

[0122] (9) Finally, calculate the cumulative generated electricity E based on the non-excluded cases, and select the optimal operating water level by taking the maximum cumulative generated electricity.

[0123] The final effect is as follows:

[0124] Take the measured initial and final water levels of Xijin from January to March and from April to May from 2004 to 2020 as the calculated initial and final water levels. Aiming at the maximum power generation of Xijin Power Station, two calculation schemes are set for different constraint conditions:

[0125] (1) Scheme 1: Only consider the optimal dispatching calculation of Xijin Power Station;

[0126] (2) Scheme 2: Consider the optimal dispatching calculation of the matching relationship between the power generation flows of Xijin Power Station, Xianyitan Power Station and Guihang Power Station.

[0127] The final calculation results are shown in Table 1, Table 2 and Figure 4 、 Figure 5 . It is found that when the calculation period is from January to March, after considering the matching relationship, the total cascade power generation increases by 0.81%, the total cascade water abandonment decreases by 17.67%, the power generations of Xianyitan Power Station and Guihang Power Station increase by 1.19% and 4.61% respectively, and the water abandonments decrease by 10.13% and 24.08% respectively; when the calculation period is from April to May, after considering the matching relationship, the total cascade power generation increases by 0.43%, the total cascade water abandonment decreases by 3.51%, the power generations of Xianyitan Power Station and Guihang Power Station increase by 1.96% and 1.06% respectively, and the water abandonments decrease by 12.54% and 1.99% respectively. Therefore, this method has a significant effect on reducing the water abandonment of downstream power stations and increasing power generation.

[0128] Table 1 Results of power generation and water abandonment from January to March before and after considering the matching relationship of installed capacity flow

[0129]

[0130] Table 2 Results of power generation and water abandonment from April to May before and after considering the matching relationship of installed capacity flow

[0131]

[0132]

[0133] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, the patent owner can make various deformations or modifications within the scope of the appended claims. As long as they do not exceed the protection scope described by the claims of the present invention, they should be within the protection scope of the present invention. Specific examples are used in this article to elaborate on the principles and embodiments of the present invention. The description of the above examples is only used to help understand the method and its core idea of the present invention. The above is only the preferred embodiment of the present invention. It should be noted that due to the limited nature of written expression and the objectively infinite specific structures, for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements, refinements or changes can be made, or the above technical features can be combined in an appropriate manner; these improvements, refinements, changes or combinations, or directly applying the concept and technical solution of the invention to other occasions without improvement, should all be regarded as within the protection scope of the present invention.

Claims

1. An optimal scheduling method considering the mismatch relationship of power generation flow in cascade hydropower stations, characterized in that: It includes the following steps: Step 1, establish an objective function capable of obtaining the maximum power generation of the hydropower station; the objective function is a function that calculates the power generation through the output in a unit time period; the objective function is Where: E is the calculated maximum power generation; T is the total number of time periods, ; is the output in the time period; is the output coefficient; is the power generation flow rate in the time period; is the average head in the time period; is the time interval length, with a day as the calculation time period; Step 2, confirm the value of the penalty coefficient, and establish conventional constraints and unconventional constraints; the unconventional constraint is a constraint condition for restricting the water abandonment volume of the downstream power station by introducing the penalty coefficient; the confirmation of the value of the penalty coefficient includes the following steps: (1) Take different penalty coefficients, and calculate the total power generation and total water abandonment volume of the power station according to the above steps; (2) Compare the results of the total power generation and total water abandonment volume under different penalty coefficients; (3) Take the penalty coefficient value in the case where the power generation is as large as possible and the water abandonment volume is as small as possible; The unconventional constraint condition is: In the formula: is the outflow from the upstream power station during period t; is the inflow from the downstream power station during period t, which is obtained by subtracting the outflow from the upstream power station from the inflow to the downstream power station; is the penalty coefficient; is the reservoir flow of the upstream power station during period t after penalty; is the full-load flow of the downstream power station's units during period t; Step 3, confirm the upstream and downstream relationships of the hydropower stations, and determine the upstream hydropower station and the downstream hydropower station; Step 4, obtain the full-load flow of the units of the upstream hydropower station and the full-load flow of the units of the downstream hydropower station; Step 5, obtain the variables related to the calculated output of the upstream hydropower station and the downstream hydropower station; Step 6, judge whether the full-load flow of the units of the upstream hydropower station is greater than the full-load flow of the units of the downstream hydropower station; if so, exclude the variables in Step 5 under the conventional constraints and unconventional constraints; if not, exclude the variables in Step 5 under the conventional constraints; Step 7, on the basis of Step 6, substitute the variables into the objective function to obtain the maximum power generation of the hydropower station.

2. The optimal scheduling method considering the mismatch relationship of power generation flow in cascade hydropower stations according to claim 1, characterized in that: The conventional constraints include water balance constraint, reservoir water level constraint, storage capacity curve constraint, downstream water level-flow relationship constraint, hydropower station head constraint, hydropower station total output constraint, predicted output limit, power generation flow limit constraint, water abandonment flow limit constraint, out-flow constraint, initial water level and termination water level constraint.

3. The optimal scheduling method considering the mismatch relationship of power generation flow in cascade hydropower stations according to claim 2, characterized in that: The conventional constraints also include non-negativity constraint conditions, and the non-negativity constraint conditions require that all variables of the conventional constraints must be non-negative values.

4. The optimal scheduling method considering the mismatch relationship of power generation flow in cascade hydropower stations according to claim 1, characterized in that: In step (5), the variables related to the output include the power generation flow and the head of the units of the upstream hydropower station and the downstream hydropower station.

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