New energy enrichment power grid unit combination optimization method considering voltage frequency support

Abstract

The invention discloses a new energy enrichment power grid unit combination optimization method considering voltage frequency support. The method comprises the following steps: constructing a new energy grid-connected point voltage support strength constraint of a new energy enrichment power grid conventional unit combination; constructing a frequency safety constraint under a transmission channel fault of the new energy enrichment power grid conventional unit combination; a new energy enrichment power grid conventional unit combination model considering voltage frequency support is constructed and solved; while the delivery consumption level of the new energy enrichment power grid is improved, the wind-solar grid-connected point voltage support of the new energy enrichment power grid and the frequency support under the condition of the delivery channel fault of the new energy enrichment power grid are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of power output combination optimization, and in particular to a method for optimizing the combination of generator sets in a new energy-rich power grid while taking voltage and frequency support into consideration. Background Art

[0002] As the green transformation of electricity production continues, the share of clean energy generation, such as wind power and photovoltaic power, continues to rise. Total installed power generation capacity has reached 3.07 billion kilowatts, of which coal-fired power accounts for 1.17 billion kilowatts, or 38.1% of the total. Grid-connected wind power accounts for 470 million kilowatts, and grid-connected solar power for 710 million kilowatts, totaling 1.18 billion kilowatts, or 38.4% of the total. For the first time, the scale of installed renewable energy generation capacity has surpassed that of coal-fired power. Energy centers and load distribution are inversely proportional, with power grids in regions with abundant wind and solar resources absorbing new energy through transmission.

[0003] In regions rich in renewable energy, renewable energy is replacing synchronous generators in large numbers. Because renewable energy is connected to the grid using power electronic converter interfaces, which exhibit zero inertia, low interference immunity, weak support, and easily controlled switching, the grid's inertia, frequency, and voltage support capabilities decrease in these regions, exacerbating operational safety risks. Strategies for arranging the startup of conventional units in these regions to ensure safe system operation while maximizing renewable energy consumption are crucial.

[0004] Currently, conventional unit portfolio optimization for renewable energy integration primarily focuses on peak shaving and frequency regulation, primarily addressing uncertainties in renewable energy output, optimizing multiple objectives, constraints, and decision variables, and developing various combinatorial optimization algorithms. For power grids in regions rich in renewable energy, conventional units must support renewable energy integration, address frequency security issues caused by transmission channel failures, and ensure renewable energy absorption. Existing research has yet to identify technologies that maximize renewable energy absorption while simultaneously maintaining voltage support at the point of grid integration and frequency support in the event of transmission channel failures. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a method for optimizing the combination of units in a new energy-rich power grid that takes into account voltage and frequency support. This method improves the level of transmission and consumption of the new energy-rich power grid while ensuring the voltage support of the wind and solar grid connection points of the new energy-rich power grid and the frequency support under failure of the transmission channel of the new energy-rich power grid.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A method for optimizing the unit commitment of a renewable energy-rich power grid while taking voltage and frequency support into consideration includes the following steps:

[0008] S101. Construct voltage support strength constraints for new energy grid connection points of conventional generator sets in new energy-rich power grids.

[0009] S102. Construct frequency security constraints under transmission channel failures for conventional generator sets in a new energy-rich power grid;

[0010] S103. Construct and solve a combination model of conventional units in a new energy-rich power grid that takes voltage and frequency support into consideration.

[0011] Furthermore, the construction of voltage support strength constraints for new energy grid connection points of conventional generator sets in new energy-rich power grids includes the following steps:

[0012] Step 11: Based on the short-circuit capacity at the renewable energy grid connection point i and the rated capacity of the renewable energy at the renewable energy grid connection point i, determine the short-circuit ratio at the renewable energy grid connection point i, and control the short-circuit ratio at the renewable energy grid connection point i to be greater than or equal to the minimum short-circuit ratio at the renewable energy grid connection point i, so as to provide voltage support when the renewable energy is connected to the grid to ensure its safe operation;

[0013] Step 12: Construct a short-circuit current model at the energy grid connection point using the self-impedance at the energy grid connection point;

[0014] Step 13: Combining steps 11 and 12, the voltage strength support demand at the renewable energy grid connection point i is expressed as a constraint related to the start and stop status of conventional units. Its expression is as follows:

[0015]

[0016] Among them, G represents the set of conventional units in the new energy-rich grid, |G| represents the number of conventional units in the new energy-rich grid, and Z ii is the self-impedance at the new energy grid connection point i, I f,i is the short-circuit current at the new energy grid connection point, SCR th,i is the minimum short-circuit ratio requirement at the new energy grid connection point i, P N,i is the rated capacity of the new energy at the new energy grid connection point i, V N,i is the rated voltage of the busbar at the renewable energy grid connection point i, h scr It is the functional expression of the short-circuit current at the renewable energy grid connection point i with respect to the on / off status of the conventional units.

[0017] Furthermore, based on the rated voltage of the busbar at the renewable energy grid connection point i and the short-circuit current when the three-phase short circuit occurs at the renewable energy grid connection point i, the short-circuit capacity at the renewable energy grid connection point i is determined.

[0018] Furthermore, the short-circuit current model at the energy grid connection point is constructed through the self-impedance at the energy grid connection point. Its expression is as follows:

[0019]

[0020] Among them, Z ii is the self-impedance at the new energy grid connection point i, I f,i It is the short-circuit current at the renewable energy grid connection point.

[0021] The expression of the self-impedance matrix is ​​as follows:

[0022]

[0023] Among them, Z ii is the self-impedance at the renewable energy grid connection point i, is the i-th row and i-th column element of the AC grid impedance matrix Z, which can be obtained by inverting the admittance matrix. N is the total number of nodes in the AC grid, and x 12 、x 1N 、x N1 、x mj 、x nj is the reactance of the transmission line directly connected between nodes; for power nodes m, x” d,m is the subtransient reactance of the mth synchronous generator, o m It is the start and stop status of the mth synchronous generator, 1 means start, 0 means stop.

[0024] Furthermore, constructing frequency security constraints under transmission channel failures for conventional generator sets in a new energy-rich power grid includes the following steps:

[0025] Model the frequency deviation caused by a fault in the transmission channel of a renewable energy-rich power grid. For example, only the inertial response and primary frequency regulation of the synchronous generator set are considered, while the debugger control and the time constant difference of the prime mover are ignored. Based on the system frequency response model, the frequency deviation caused by a fault in the transmission channel of a renewable energy-rich power grid is expressed as follows:

[0026]

[0027] Among them, Δf(s) is the image function of frequency deviation, ΔP(s) is the image function of active unbalance, H sys is the system equivalent inertia, R sys is the system equivalent droop coefficient, D is the load damping coefficient, T g is the time constant of the system equivalent prime mover, H m is the inertia of the mth synchronous generator, S m is the installed capacity of the mth synchronous generator, o m is the start and stop status of the mth synchronous generator, 1 indicates start, 0 indicates stop; G represents the set of conventional generators in the renewable energy-rich grid;

[0028] Establish constraints on frequency steady-state deviation, maximum deviation and frequency rise rate at the time of fault occurrence. The frequency steady-state deviation, maximum deviation and frequency rise rate at the time of fault occurrence caused by faults in the transmission channel of the new energy-rich power grid shall not exceed the allowable values.

[0029] Furthermore, the frequency steady-state deviation constraint caused by the failure of the transmission channel of the renewable energy-rich power grid can be expressed as follows:

[0030]

[0031] Among them, ΔP is the active power imbalance caused by the failure of the transmission channel of the new energy-rich power grid, D is the load damping coefficient, and Δf ss is the frequency steady-state deviation, R sys is the system equivalent droop coefficient, is the functional expression of the system frequency steady-state deviation with respect to the start-stop state of conventional units, Δf th,ss is the allowable value of frequency steady-state deviation.

[0032] Furthermore, the maximum frequency deviation constraint caused by the failure of the transmission channel of the new energy-rich power grid can be determined by the overshoot allowable value M th,p express:

[0033]

[0034] Among them, M p is the overshoot of frequency deviation, is the function expression of the frequency deviation overshoot with respect to the start and stop status of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,max is the maximum allowable value of frequency deviation, M th,p is the maximum allowable value of frequency deviation overshoot, G sys is the system equivalent inertia, D is the load damping coefficient, T g is the time constant of the system equivalent prime mover, R sys is the system equivalent droop coefficient.

[0035] Furthermore, the frequency rise rate constraint at the time of fault occurrence can be expressed as:

[0036]

[0037] Where Δf v is the frequency rise rate, H sys is the system equivalent inertia, ΔP is the active power imbalance caused by the failure of the transmission channel of the new energy-rich power grid, h fvis the function expression of the frequency rise rate with respect to the on / off status of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,v is the allowable value of the frequency rise rate.

[0038] Furthermore, constructing and solving a conventional unit combination model for a renewable energy-rich power grid that takes voltage and frequency support into consideration includes the following steps:

[0039] Determine the objective function as in, They represent the output of hydropower unit and photovoltaic unit respectively, I represents the output of hydropower unit, and K represents the output of photovoltaic unit;

[0040] S31: Model the uncertainty of PV cluster output. The uncertainty of PV cluster output is described based on the installed capacity of the PV cluster, the minimum grid-connected power, and the day-ahead power forecast: in, and are the minimum grid-connected power and rated installed capacity of the photovoltaic power station v, and P v,t are the day-ahead power forecast value and actual output value of the photovoltaic power station v in period t, is the amount of photovoltaic power curtailment during the corresponding period;

[0041] S32: Constructing a hydraulic model for cascade hydropower stations;

[0042] S33: Construct constraints related to hydropower and thermal power operation and transmission channels;

[0043] By combining steps S31, S32 and S33, the conventional unit combination optimization of the new energy-rich power grid taking into account voltage and frequency support is obtained.

[0044] Furthermore, constructing a hydraulic model of a cascade hydropower station includes the following steps:

[0045] First, construct the water volume relationship model of cascade hydropower stations:

[0046] Secondly, a reservoir capacity-water level relationship model is constructed:

[0047] Then build the tailwater level-outflow relationship model: Then construct the head loss function model:

[0048] Finally, the unit dynamic characteristic relationship model is constructed:

[0049] Among them, C i,t is the storage capacity of power station i at the end of period t, is the inflow of power station i in period t, τ is the water lag time between power station i and its upstream power station i-1, is the outflow flow of power station i in period t, R is the flow rate of power station i-1 in the period t-τ after considering the water flow lag. i,t is the interval flow between power station i-1 and power station i in time period t, and are the power generation flow and abandoned water flow of power station i in period t, is the output of the nth unit of power station i in time period t, τ i,n is the triangular weight H of the nth unit in power station i i,n,t is the generating head of the nth unit of power station i in time period t.

[0050] Furthermore, the construction of constraints related to hydropower and thermal power operation and transmission channels includes the following steps:

[0051] Construct water level constraints for hydropower stations:

[0052] Hydropower station flow constraints:

[0053] Operation constraints of hydropower station units:

[0054] Upper and lower limits of active power output of thermal power units: Thermal power unit ramp constraints:

[0055] in, is the output value of each section of the thermal power unit; The upper limit of thermal power unit output; j The power-on status of the thermal power unit, 1 is on and 0 is off; DR k UR k are the ramp rate and ramp rate of thermal power units respectively; Δt is the scheduling time interval; P d,t , respectively represent the transmission power of the tie line in the pre-dispatching stage and the power absorbed by the load node; Transmission channel constraints: is the output of all hydropower units in time period t.

[0056] Compared with the existing technology, the advantages of this application are: it realizes that the frequency safety constraints established by the existing unit combination are mostly aimed at low-frequency problems. The present invention targets the high-frequency problems caused by the failure of the transmission channel of the new energy-rich power grid, establishes the relationship between the frequency safety requirements and the start and stop status of conventional units, thereby converting the frequency safety requirements under the failure of the transmission channel of the new energy-rich power grid into a constraint condition of the unit combination optimization model.

[0057] The present invention aims at the voltage support strength requirements of new energy grid-connected points in a new energy-rich power grid, establishes the relationship between the voltage support strength requirements of new energy grid-connected points and the start and stop status of conventional units, thereby converting the voltage support strength requirements of new energy grid-connected points in a new energy-rich power grid into a constraint condition of the unit combination optimization model.

[0058] Existing unit combinations only consider maximizing renewable energy consumption, frequency safety requirements in the event of power disturbances, or voltage support strength requirements at renewable energy grid connection points. The unit combination optimization method proposed in this invention maximizes renewable energy consumption while also taking into account voltage support strength requirements at renewable energy grid connection points in renewable energy-rich power grids and frequency safety requirements in the event of transmission channel failures. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0060] Figure 1 This is a schematic diagram of the steps of the method for optimizing the unit combination of a new energy-rich power grid taking into account voltage and frequency support of the present invention;

[0061] Figure 2 It is an improved IEEE39 node system of the present invention;

[0062] Figure 3 It is the IEEE39 node system photovoltaic, transmission and cascade hydropower daily power curve of the present invention;

[0063] Figure 4 is the daily power curve of each unit of the hydropower station 1 of the present invention;

[0064] Figure 5 is the daily power curve of each unit of the hydropower station 2 of the present invention;

[0065] Figure 6 It is the daily power curve of each unit of the hydropower station 3 of the present invention;

[0066] Figure 7 is the daily power curve of each unit of the hydropower station 4 of the present invention;

[0067] Figure 8 This is the system frequency curve of the present invention under external DC blocking. DETAILED DESCRIPTION

[0068] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0069] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0070] Example 1:

[0071] A method for optimizing the unit commitment of a renewable energy-rich power grid while taking voltage and frequency support into consideration includes the following steps:

[0072] S101. Construct voltage support strength constraints for new energy grid connection points of conventional generator sets in new energy-rich power grids.

[0073] Based on the short-circuit ratio index of new energy grid connection points, the relationship between the voltage support demand of wind and solar grid connection points in new energy-rich power grids and the start and stop status of conventional units is analyzed, and the voltage support strength constraint of the conventional unit combination in new energy-rich power grids is formed.

[0074] Constructing voltage support strength constraints for renewable energy grid connection points with conventional generator sets in renewable energy-rich grids includes the following steps:

[0075] Step 11: Based on the short-circuit capacity at the new energy grid connection point i and the rated capacity of the new energy at the new energy grid connection point i, determine the short-circuit ratio at the new energy grid connection point i, and control the short-circuit ratio at the new energy grid connection point i to be greater than or equal to the minimum short-circuit ratio at the new energy grid connection point i, so as to provide voltage support when the new energy is connected to the grid to ensure its safe operation; wherein, the short-circuit capacity at the new energy grid connection point i is determined based on the rated voltage of the busbar at the new energy grid connection point i and the short-circuit current when the three-phase short circuit occurs at the new energy grid connection point i;

[0076] Step 12: Construct a short-circuit current model at the energy grid connection point using the self-impedance at the energy grid connection point;

[0077] Step 13: Combining steps 11 and 12, the voltage strength support demand at the renewable energy grid connection point i is expressed as a constraint related to the start and stop status of conventional units. Its expression is as follows:

[0078]

[0079] Among them, Z ii is the self-impedance at the renewable energy grid connection point i, |G| represents the number of conventional units in the renewable energy-rich grid, I f,i is the short-circuit current at the new energy grid connection point, SCR th,i is the minimum short-circuit ratio requirement at the new energy grid connection point i, P N,i is the rated capacity of the new energy at the new energy grid connection point i, V N,i is the rated voltage of the busbar at the renewable energy grid connection point i, h scr It is the functional expression of the short-circuit current at the renewable energy grid connection point i with respect to the on / off status of the conventional units.

[0080] It should be noted that the grid connection of renewable energy requires voltage support from the AC grid to ensure its safe operation. This is described by the short-circuit ratio. Therefore, it is necessary to model the short-circuit ratio at the grid connection point of renewable energy. The expression is as follows:

[0081]

[0082] Among them, SCR i is the short-circuit ratio at the new energy grid connection point i, SCR th,i The minimum short-circuit ratio requirement at the new energy grid connection point i is generally set to 1.5, S ac,i is the short-circuit capacity at the new energy grid connection point i, P N,i is the rated capacity of the new energy at the new energy grid connection point i, V N,i is the rated voltage of the busbar at the new energy grid connection point i, I f,i Short-circuit current when three-phase short circuit occurs at the renewable energy grid connection point i.

[0083] It should be noted that, without considering the influence of operating voltage and load current, when the AC grid structure is given, the short-circuit current when a three-phase short circuit occurs at the renewable energy grid connection point can be expressed by the self-impedance at the renewable energy grid connection point, and its expression is as follows:

[0084]

[0085] Among them, Z ii is the self-impedance at the new energy grid connection point i, I f,iIt is the short-circuit current at the renewable energy grid connection point.

[0086] The expression of the self-impedance matrix is ​​as follows:

[0087]

[0088] Among them, Z ii is the self-impedance at the renewable energy grid connection point i, is the i-th row and i-th column element of the AC grid impedance matrix Z, which can be obtained by inverting the admittance matrix. N is the total number of nodes in the AC grid, and x 12 、x 1N 、x N1 、x mj 、x nj is the reactance of the transmission line directly connected between nodes; for power nodes m, x” d,m is the subtransient reactance of the mth synchronous generator, o m It is the start and stop status of the mth synchronous generator, 1 means start, 0 means stop.

[0089] S102. Construct frequency security constraints under transmission channel failures for conventional generator sets in a new energy-rich power grid;

[0090] Based on the average system frequency model, a dynamic response model of the frequency of a new energy high-penetration power grid is constructed to analyze the relationship between the frequency security under the failure of the transmission channel of the new energy-rich power grid and the start-up and shutdown status of conventional units, and to form the frequency security constraints of the combination of conventional units in the new energy-rich power grid.

[0091] Constructing frequency security constraints under transmission channel failures for conventional generator sets in a renewable energy-rich power grid includes the following steps:

[0092] Model the frequency deviation caused by a fault in the transmission channel of a renewable energy-rich power grid. For example, only the inertial response and primary frequency regulation of the synchronous generator set are considered, while the debugger control and the time constant difference of the prime mover are ignored. Based on the system frequency response model, the frequency deviation caused by a fault in the transmission channel of a renewable energy-rich power grid is expressed as follows:

[0093]

[0094] Among them, Δf(s) is the image function of frequency deviation, ΔP(s) is the image function of active unbalance, H sys is the system equivalent inertia, R sys is the system equivalent droop coefficient, D is the load damping coefficient, Tg is the time constant of the system equivalent prime mover, H m is the inertia of the mth synchronous generator, S m is the installed capacity of the mth synchronous generator, o mis the start and stop status of the mth synchronous generator, 1 indicates start, 0 indicates stop, and G represents the set of conventional units in the renewable energy-rich grid.

[0095] Establish constraints on frequency steady-state deviation, maximum deviation and frequency rise rate at the time of fault occurrence. The frequency steady-state deviation, maximum deviation and frequency rise rate at the time of fault occurrence caused by faults in the transmission channel of the new energy-rich power grid shall not exceed the allowable values.

[0096] It should be noted that to ensure the safe operation of a renewable energy-rich power grid, the frequency steady-state deviation, maximum deviation, and frequency rise rate at the time of the fault caused by a fault in the transmission channel of a renewable energy-rich power grid must not exceed the permitted values. The frequency steady-state deviation constraint caused by a fault in the transmission channel of a renewable energy-rich power grid can be expressed as follows:

[0097]

[0098] Among them, ΔP is the active power imbalance caused by the failure of the transmission channel of the new energy-rich power grid, D is the load damping coefficient, and Δf ss is the frequency steady-state deviation, R sys is the system equivalent droop coefficient, h fss is the functional expression of the system frequency steady-state deviation with respect to the on-off state of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,ss is the allowable value of frequency steady-state deviation.

[0099] The maximum frequency deviation constraint caused by the failure of the transmission channel of the new energy-rich power grid can be determined by the overshoot allowable value M th,p express:

[0100]

[0101] Among them, M p is the overshoot of frequency deviation, is the function expression of the frequency deviation overshoot with respect to the start and stop status of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,max is the maximum allowable value of frequency deviation, M th,p is the maximum allowable value of frequency deviation overshoot, H sys is the system equivalent inertia, D is the load damping coefficient, T g is the time constant of the system equivalent prime mover, R sys is the system equivalent droop coefficient.

[0102] The frequency rise rate constraint at the time of fault occurrence can be expressed as:

[0103]

[0104] Where Δf v is the frequency rise rate, H sys is the system equivalent inertia, ΔP is the active power imbalance caused by the failure of the transmission channel of the new energy-rich power grid, is the function expression of the frequency rise rate with respect to the on / off status of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,v is the allowable value of the frequency rise rate.

[0105] Based on the above equations, the grid frequency security demand under the failure of the transmission channel of the renewable energy-rich grid can be expressed as constraints related to the start and stop status of conventional units.

[0106] S103, constructing and solving a conventional unit combination model for a new energy-rich power grid that takes voltage and frequency support into consideration;

[0107] With the goal of maximizing the amount of new energy power consumed by the new energy-rich power grid, the start-up and shutdown status and output of conventional units in the new energy-rich power grid are set as decision variables, and considering the water level constraints of the hydropower station, the flow constraints of the hydropower station, the operation constraints of the hydropower station units, the start-up and shutdown constraints of the thermal power units, the operation constraints of the thermal power units, the power balance constraints, the transmission channel constraints, the voltage support strength constraints of the new energy grid connection points established in steps S101 and S102, and the grid frequency security constraints under transmission channel failures, etc., a combination model of conventional units in the new energy-rich power grid that takes into account voltage and frequency support is constructed and solved using an intelligent optimization algorithm.

[0108] Constructing and solving a conventional unit combination model for a renewable energy-rich grid that takes voltage and frequency support into account includes the following steps:

[0109] Determine the objective function as in, They represent the output of hydropower unit and photovoltaic unit respectively, I represents the output of hydropower unit, and K represents the output of photovoltaic unit;

[0110] S31: Model the uncertainty of PV cluster output. The uncertainty of PV cluster output is described based on the installed capacity of the PV cluster, the minimum grid-connected power, and the day-ahead power forecast: in, and are the minimum grid-connected power and rated installed capacity of the photovoltaic power station v, and P v,t are the day-ahead power forecast value and actual output value of the photovoltaic power station v in period t, is the amount of photovoltaic power curtailment during the corresponding period;

[0111] S32: Constructing a hydraulic model for cascade hydropower stations;

[0112] S33: Construct constraints related to hydropower and thermal power operation and transmission channels;

[0113] By combining steps S31, S32 and S33, the conventional unit combination optimization of the new energy-rich power grid taking into account voltage and frequency support is obtained.

[0114] The construction of hydraulic model of cascade hydropower station includes the following steps:

[0115] First, construct the water volume relationship model of cascade hydropower stations:

[0116] Secondly, a reservoir capacity-water level relationship model is constructed:

[0117] Then build the tailwater level-outflow relationship model: Then construct the head loss function model:

[0118] Finally, the unit dynamic characteristic relationship model is constructed:

[0119] Among them, C i,t is the storage capacity of power station i at the end of period t, is the inflow of power station i in period t, τ is the water lag time between power station i and its upstream power station i-1, is the outflow flow of power station i in period t, R is the flow rate of power station i-1 in the period t-τ after considering the water flow lag. i,t is the interval flow between power station i-1 and power station i in time period t, and are the power generation flow and abandoned water flow of power station i in period t, is the output of the nth unit of power station i in time period t, τ i,n is the triangular weight H of the nth unit in power station i i,n,t is the generating head of the nth unit of power station i in time period t.

[0120] Establishing constraints on hydropower and thermal power operation and transmission channels includes the following steps:

[0121] Construct water level constraints for hydropower stations:

[0122] Hydropower station flow constraints:

[0123] Operation constraints of hydropower station units:

[0124]

[0125] Upper and lower limits of active power output of thermal power units: Thermal power unit ramp constraints:

[0126] in, is the output value of each section of the thermal power unit; The upper limit of thermal power unit output; j The power-on status of the thermal power unit, 1 is on and 0 is off; DR k UR k are the ramp rate and ramp rate of thermal power units respectively; Δt is the scheduling time interval; P d,t , respectively represent the transmission power of the tie line in the pre-dispatching stage and the power absorbed by the load node; Transmission channel constraints: is the output of all hydropower units in time period t.

[0127] After the above steps, a unit combination optimization method for a new energy-rich power grid that takes voltage and frequency support into consideration can be obtained.

[0128] For example, Figure 2 The figure shows an improved IEEE 39 node system, serving as an exemplary application scenario of the present invention. In the IEEE 39 node system, nodes 33, 35, 36, and 37 are connected to a photovoltaic power station, nodes 31 and 32 are connected to a cascade hydropower station, and nodes 33, 34, and 35 are connected to a cascade hydropower station. Node 39 is the point of DC transmission.

[0129] according to Figure 2Improve the connection relationship of the IEEE39 node system, the reactance of the transmission lines, the sub-transient reactance of the synchronous generators, and the access nodes of the photovoltaic stations, and form the voltage support strength inequality constraint of the new energy grid connection point according to the aforementioned step S101; Based on the inertia and droop coefficient of each synchronous generator in the improved IEEE39 node system and the system load damping coefficient, form the system frequency steady-state deviation inequality constraint, the maximum deviation inequality constraint, and the frequency rise rate inequality constraint at the time of the fault occurrence according to the aforementioned step S102; Based on the system's load demand, external power demand, photovoltaic predicted output, etc. in the next 24 hours, with the maximum photovoltaic power generation as the goal, and the start-up and shutdown status and output of conventional synchronous units as decision variables, form an optimization model according to the aforementioned step S103, and use commercial optimization solution software such as cplex or gurobi to solve it, and obtain the output of the system's conventional synchronous units in the next 24 hours. Figure 3 As shown in Figure 1, the predicted photovoltaic output and external power demand of the IEEE39 node system in the next 24 hours are given, which is used to construct a conventional unit combination optimization model for the renewable energy-rich power grid that takes into account voltage and frequency support according to the aforementioned step 3. Figure 3 Some results of solving the optimization model are also given, namely the total hydropower output of the system in the next 24 hours and the output of each cascade hydropower plant; Figures 4 to 7 The output of each hydropower unit 1 to 4 of the cascade hydropower plant in the next 24 hours is given respectively.

[0130] like Figure 8 The figure shows the system frequency curve under DC outbound lockout. The solid line corresponds to the startup method obtained using the unit combination method proposed in this invention, while the dashed line corresponds to the startup method obtained using a conventional unit combination, which does not consider voltage and frequency support constraints. The startup method using the unit combination method proposed in this invention has a smaller frequency deviation under DC outbound lockout failure, reducing the risk of high-frequency disconnection of new energy units.

[0131] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems and units can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0132] The terms "first", "second" and "third" etc. in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0133] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for optimizing the unit combination of a new energy-rich power grid taking into account voltage and frequency support, characterized in that: The following steps are involved: S101. Construct voltage support strength constraints for new energy grid connection points of conventional generator sets in new energy-rich power grids. S102. Construct frequency security constraints under transmission channel failures for conventional generator sets in a new energy-rich power grid; S103, constructing and solving a conventional unit combination model for a new energy-rich power grid that takes voltage and frequency support into consideration; Constructing voltage support strength constraints for renewable energy grid connection points with conventional generator sets in renewable energy-rich grids includes the following steps: Step 11: Based on the short-circuit capacity at the renewable energy grid connection point i and the rated capacity of the renewable energy at the renewable energy grid connection point i, determine the short-circuit ratio at the renewable energy grid connection point i, and control the short-circuit ratio at the renewable energy grid connection point i to be greater than or equal to the minimum short-circuit ratio at the renewable energy grid connection point i, so as to provide voltage support when the renewable energy is connected to the grid to ensure its safe operation; Step 12: Construct a short-circuit current model at the energy grid connection point using the self-impedance at the energy grid connection point; Step 13: Combining steps 11 and 12, the voltage strength support demand at the renewable energy grid connection point i is expressed as a constraint related to the start and stop status of conventional units. Its expression is as follows: Among them, G represents the set of conventional units in the new energy-rich grid, |G| represents the number of conventional units in the new energy-rich grid, and Z ii is the self-impedance at the new energy grid connection point i, I f,i is the short-circuit current at the new energy grid connection point i, SCR th,i is the minimum short-circuit ratio requirement at the new energy grid connection point i, P N,i is the rated capacity of the new energy at the new energy grid connection point i, V N,i is the rated voltage of the busbar at the renewable energy grid connection point i, h scr It is the functional expression of the short-circuit current at the renewable energy grid connection point i with respect to the on / off status of the conventional units.

2. The method for optimizing the unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 1 is characterized in that: The short-circuit capacity at the renewable energy grid connection point i is determined based on the rated voltage of the busbar at the renewable energy grid connection point i and the short-circuit current when the three-phase short circuit occurs at the renewable energy grid connection point i.

3. The method for optimizing the unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 1 is characterized in that: The short-circuit current model at the new energy grid connection point is constructed by the self-impedance at the energy grid connection point, and its expression is as follows: Among them, Z ii is the self-impedance at the new energy grid connection point i, I f,i It is the short-circuit current at the renewable energy grid connection point; The expression of the self-impedance matrix is ​​as follows: Among them, Z ii is the self-impedance at the renewable energy grid connection point i, is the i-th row and i-th column element of the AC grid impedance matrix Z, which can be obtained by inverting the admittance matrix. N is the total number of nodes in the AC grid, and x 12 、x 1N 、x N1 、x mj 、x nj is the reactance of the transmission line directly connected between nodes; for power nodes m, x” d,m is the subtransient reactance of the mth synchronous generator, o m It is the start and stop status of the mth synchronous generator, 1 means start, 0 means stop.

4. The method for optimizing the unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 1 is characterized in that: The method of constructing frequency security constraints under transmission channel failure of conventional generator sets in a new energy-rich power grid includes the following steps: Model the frequency deviation caused by a fault in the transmission channel of a renewable energy-rich power grid. For example, only the inertial response and primary frequency regulation of the synchronous generator set are considered, while the debugger control and the time constant difference of the prime mover are ignored. Based on the system frequency response model, the frequency deviation caused by a fault in the transmission channel of a renewable energy-rich power grid is expressed as follows: Among them, Δf(s) is the image function of frequency deviation, ΔP(s) is the image function of active unbalance, H sys is the system equivalent inertia, R sys is the system equivalent droop coefficient, D is the load damping coefficient, T g is the time constant of the system equivalent prime mover, H m is the inertia of the mth synchronous generator, S m is the installed capacity of the mth synchronous generator, o m is the start and stop status of the mth synchronous generator, 1 indicates start, 0 indicates stop; G represents the set of conventional generators in the renewable energy-rich grid; Establish constraints on frequency steady-state deviation, maximum deviation and frequency rise rate at the time of fault occurrence. The frequency steady-state deviation, maximum deviation and frequency rise rate at the time of fault occurrence caused by faults in the transmission channel of the new energy-rich power grid shall not exceed the allowable values.

5. The method for optimizing the unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 4 is characterized in that: The frequency steady-state deviation constraint caused by the failure of the transmission channel of the new energy-rich power grid can be expressed as follows: Where Δf ss is the frequency steady-state deviation, ΔP is the active power imbalance caused by the failure of the transmission channel of the new energy-rich power grid, D is the load damping coefficient, R sys is the system equivalent droop coefficient, is the functional expression of the system frequency steady-state deviation with respect to the on-off state of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,ss is the allowable value of frequency steady-state deviation.

6. The method for optimizing unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 4 is characterized in that: The maximum frequency deviation constraint caused by the failure of the transmission channel of the new energy-rich power grid can be determined by the overshoot allowable value. express: Among them, M p is the overshoot of frequency deviation, is the function expression of the frequency deviation overshoot with respect to the start and stop status of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,max is the maximum allowable value of frequency deviation, M th,p is the maximum allowable value of frequency deviation overshoot, H sys is the system equivalent inertia, D is the load damping coefficient, T g is the time constant of the system equivalent prime mover, R sys is the system equivalent droop coefficient.

7. The method for optimizing unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 4 is characterized in that: The frequency rising rate constraint at the time of fault occurrence can be expressed as: Where Δf v is the frequency rise rate, H sys is the system equivalent inertia, ΔP is the active power imbalance caused by the failure of the transmission channel of the new energy-rich power grid, is the function expression of the frequency rise rate with respect to the on / off status of conventional units, G represents the set of conventional units in the renewable energy-rich grid, |G| represents the number of conventional units in the renewable energy-rich grid, Δf th,v is the allowable value of the frequency rise rate.

8. The method for optimizing unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 1 is characterized in that: The construction and solution of the conventional unit combination model of the new energy-rich power grid taking into account voltage and frequency support includes the following steps: Determine the objective function as in, They represent the output of hydropower unit and photovoltaic unit respectively, I represents the output of hydropower unit, and K represents the output of photovoltaic unit; S31: Model the uncertainty of PV cluster output. The uncertainty of PV cluster output is described based on the installed capacity of the PV cluster, the minimum grid-connected power, and the day-ahead power forecast: in, and are the minimum grid-connected power and rated installed capacity of the photovoltaic power station v, and P v,t are the day-ahead power forecast value and actual output value of the photovoltaic power station v in period t, is the amount of photovoltaic power curtailment during the corresponding period; S32: Constructing a hydraulic model for cascade hydropower stations; S33: Construct constraints related to hydropower and thermal power operation and transmission channels; By combining steps S31, S32 and S33, the conventional unit combination optimization of the new energy-rich power grid taking into account voltage and frequency support is obtained.

9. The method for optimizing unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 8 is characterized in that: Constructing a hydraulic model of cascade hydropower stations The following steps are involved: ； First, construct the water volume relationship model of cascade hydropower stations: Secondly, a reservoir capacity-water level relationship model is constructed: Then build the tailwater level-outflow relationship model: Then construct the head loss function model: Finally, the unit dynamic characteristic relationship model is constructed: Among them, C i,t is the storage capacity of power station i at the end of period t, is the inflow of power station i in period t, τ is the water lag time between power station i and its upstream power station i-1, is the outflow flow of power station i in period t, R is the flow rate of power station i-1 in the period t-τ after considering the water flow lag. i,t is the interval flow between power station i-1 and power station i in time period t, and are the power generation flow and abandoned water flow of power station i in period t, is the output of the nth unit of power station i in time period t, τ i,n is the triangular weight H of the nth unit in power station i i,n,t is the generating head of the nth unit of power station i in time period t.

10. The method for optimizing unit combination of a new energy-rich power grid taking into account voltage and frequency support according to claim 8, characterized in that: The construction of constraints related to hydropower and thermal power operation and transmission channels includes the following steps: Construct water level constraints for hydropower stations: Hydropower station flow constraints: Operation constraints of hydropower station units: Upper and lower limits of active power output of thermal power units: Thermal power unit ramp constraints: in, is the output value of each section of the thermal power unit; The upper limit of thermal power unit output; j The power-on status of the thermal power unit, 1 is on and 0 is off; DR k UR k are the ramp rate and ramp rate of thermal power units respectively; Δt is the scheduling time interval; P d,t , respectively represent the transmission power of the tie line in the pre-dispatching stage and the power absorbed by the load node; Transmission channel constraints: is the output of all hydropower units in time period t.

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