A wind power grid-connected evaluation method based on frequency modulation cost

Abstract

A kind of wind power grid-connected evaluation method based on frequency modulation cost, it is related to a kind of wind power grid-connected evaluation method, in order to solve the existing power system frequency model does not consider automatic gain control link and does not consider the case where wind farm participates in frequency modulation, leading to poor reliability of frequency modulation problem.The present application establishes power system frequency model with wind farm grid-connected power as disturbance source, and establishes objective function according to power system frequency modulation cost and wind farm output electric energy benefit;Using objective function, the constraint condition that makes the power system frequency modulation cost lowest and wind farm output electric energy benefit highest is determined;The power system frequency model is optimized using the constraint condition, and the output quantity of the optimized power system frequency model is solved, and the power system frequency deviation value caused by wind turbine is obtained.The beneficial effect is to solve the problem of high power system frequency modulation cost and large frequency deviation.

Description

Technical Field

[0001] This invention relates to a method for evaluating the grid connection capacity of wind power; Background Technology

[0002] With the construction and commissioning of multiple new energy transmission channels, the power transmission capacity of wind-rich areas will be further improved, making these areas typical wind power "export-oriented" regional power grids. However, due to the randomness and intermittency of wind power, the peak-to-valley difference of the power transmitted by the regional power grid is large and highly volatile, posing a risk to the frequency stability of the receiving-end power grid's safe and stable operation. Currently, using wind power grid-connected power as a source of frequency disturbance to establish a power system frequency model to study its impact on frequency deviation, and establishing a power system frequency regulation cost optimization model to determine the frequency bands that can be directly connected to the grid, is a good solution. However, existing power system frequency models do not consider automatic gain control and do not consider the participation of wind farms in frequency regulation, so the reliability of the conclusions cannot be guaranteed. Summary of the Invention

[0003] The purpose of this invention is to address the problem of poor frequency regulation reliability caused by the lack of consideration for automatic gain control and wind farm participation in existing power system frequency models. This invention proposes a wind power grid connection evaluation method based on frequency regulation cost.

[0004] The present invention discloses a wind power grid connection assessment method based on frequency regulation cost, which includes the following steps:

[0005] Step 1: Establish a power system frequency model using the grid-connected power of the wind farm as the disturbance source. The input of this power system frequency model is the power system frequency reference value, the disturbance is the power signal in different frequency bands, and the output is the frequency deviation of the power system.

[0006] Step 2: Establish an objective function based on the power system frequency regulation cost and the revenue from wind farm electricity generation;

[0007] Step 3: Using the objective function established in Step 2, determine the constraints that minimize the frequency regulation cost of the power system and maximize the revenue from the electricity generated by the wind farm.

[0008] Step 4: Optimize the power system frequency model established in Step 1 using the constraints obtained in Step 3, and solve the output of the optimized power system frequency model to obtain the power system frequency deviation value caused by the wind turbine.

[0009] Furthermore, the method for establishing the power system frequency model in step one includes determining the transfer function of the prime mover and its governor, determining the transfer function of the generator inertia and constant power load, and determining the transfer function of the AGC.

[0010] The transfer function of the prime mover and its governor is:

[0011]

[0012] Where G1(s) is the transfer function of the prime mover and its governor; s is the independent variable of the function; η R C represents the proportion of generating units in the power system that do not participate in primary frequency regulation. ∑ The ratio of the high-pressure cylinder in the equivalent turbine of the power system; T ∑R R is the time constant of the reheater. ∑0 This is the equivalent droop coefficient for all speed controllers in the circuit system;

[0013] The transfer function of the generator inertia and constant power load element is:

[0014]

[0015] Where G2(s) is the transfer function of the generator inertia and constant power load elements, M ∑0 η is the equivalent inertia of all existing generators with inertia in the power system. M Where D represents the proportion of inertial generator units in the power system, and D is the frequency coefficient of the load.

[0016] The transfer function of the AGC process is:

[0017]

[0018] Among them, K ∑i K represents the equivalent integral gain of all generating units in the power system capable of secondary frequency regulation; ∑p The equivalent proportional coefficients of all generating units in the power system capable of secondary frequency regulation.

[0019] Furthermore, in the transfer function of the prime mover and its governor, the proportion η of units in the power system that do not participate in primary frequency regulation is... R The calculation method is as follows:

[0020]

[0021] Where, ∑S R＝∞ This represents the sum of the capacities of generating units in the power system that do not participate in primary frequency regulation. Let S be the total installed capacity of the power system, n be the number of conventional generating units in the power system, and S be the total installed capacity of the power system. i Let be the rated capacity of the i-th unit.

[0022] Furthermore, in the transfer function of the generator inertia and constant power load links, the proportion η of inertial units in the power system is... M The calculation method is as follows:

[0023]

[0024] Where, ∑S M＝0 It is the sum of the capacity of units or power sources in the power system that do not have inertia.

[0025] Furthermore, the objective function established in step two is specifically as follows:

[0026] f ED = -c×Z+(1-c)×W

[0027] Among them, f ED denoted as , where is the total revenue of the wind farm after it is connected to the grid. A positive result indicates that the wind farm will generate net revenue, while a negative result indicates that the system still needs to invest in regulation costs. c is a weighting coefficient, c∈[0,1]. Z is the total frequency regulation cost of the wind farm connected to the grid, and W is the total revenue of the wind farm's electricity output.

[0028] Furthermore, the total revenue W from the electricity generated by the wind farm in the objective function is calculated as follows:

[0029]

[0030] Where, d i Let P be the output coefficient of the i-th wind turbine. wiav is the actual active power output of the i-th wind turbine; m is the number of wind turbines installed in the power system;

[0031] The above refers to the actual active power output P of the i-th wind turbine. wiav The specific calculation method is as follows:

[0032]

[0033] Among them, v ci v is the cut-in wind speed of the fan; co For the cut-out velocity of the fan; v r P is the rated wind speed of the fan; wr v represents the rated power of a single fan, and v represents the wind speed.

[0034] Furthermore, the calculation method for the total frequency regulation cost Z of the wind power grid-connected power system in the objective function is as follows:

[0035] Z = Z1 + Z2

[0036] Z1 represents the frequency regulation cost caused by overestimating wind power output, and Z2 represents the frequency regulation cost caused by underestimating wind power output.

[0037] The calculation method for the frequency regulation cost Z1 caused by the overestimation of wind power output is as follows:

[0038]

[0039] Where, k rwi To overestimate the cost factor of frequency modulation; P wi To contribute to the planned operation of the i-th wind turbine unit; P is the probability density function of the active power output of the wind farm. w This represents the total active power output of m wind turbine units;

[0040] The calculation method for the frequency regulation cost Z2 caused by the underestimation of wind power output is as follows:

[0041]

[0042] Where, k pwi This is to underestimate the cost factor of frequency modulation.

[0043] Furthermore, the probability density function of the active power output of the wind farm The specific calculation method is as follows:

[0044]

[0045] Among them, P wf Contributing power to the wind farm; P wfr Rated active power output for wind farms; The active power output of the wind farm is P wf The probability density value at that time. for The first derivative; δ[P wf [(t)] represents the independent variable P. wf The unit impulse function of (t) in P wf At (t) = 0, its value is an infinite number; the integral of the unit impulse function is 1; the derivative of the unit step function is the unit impulse function. P (0) indicates that the probability function of active power output of the wind farm is in P wf =0; Φ P (P wfr ) represents the probability function of active power output of a wind farm in P wf =P wfr The value at time;

[0046] The The specific calculation method is as follows:

[0047]

[0048] Where, ξ w λ is the wake effect coefficient of the wind farm; k is the shape coefficient of the Weibull distribution, which determines the shape of the distribution curve; λ is the scale coefficient, which reflects the magnitude of the average wind speed. Let v be the probability density value of the wind speed.

[0049] The Φ P The specific calculation method for (0) is as follows:

[0050]

[0051] in, Let v be the probability density value of the wind speed.

[0052] The probability density value of the wind speed v The specific calculation method is as follows:

[0053]

[0054] The Φ P (P wfr The specific calculation method is as follows:

[0055]

[0056] Furthermore, the constraints determined in step three include: power balance constraints without considering network losses, unit output constraints, unit output ramp-up constraints, and power system frequency deviation threshold constraints.

[0057] The power balance constraint that does not consider network losses is:

[0058]

[0059] Where n is the number of existing thermal power units, P Gj For the active power output of the jth thermal power unit, P load The total load of the power system;

[0060] The unit output constraints include thermal power unit output constraints and wind power unit output constraints;

[0061] The output constraints of thermal power units are:

[0062] P Gjmin ≤P Gj ≤P Gjmax (j = 1, 2, ..., n)

[0063] Among them, P Gjmin P represents the minimum active power output of the j-th thermal power unit. Gjmax This represents the maximum active power output of the j-th thermal power unit.

[0064] Wind turbine output constraints:

[0065] 0≤P wiav ≤P wri(i = 1, 2, ..., m)

[0066] Among them, P wri Let be the rated power of the i-th wind turbine unit;

[0067] The unit's output ramp-up constraint is:

[0068]

[0069] Among them, U Rj D represents the rate of ascent and descent of the j-th thermal power unit. Rj Let P be the descent and ramp rate of the j-th thermal power unit; ΔT is the dispatch time interval; P is the descent and ramp rate of the j-th thermal power unit. Gj,h P represents the active power output of the j-th thermal power unit at time h; Gj,h-1 These represent the active power output of the j-th thermal power unit at time h-1.

[0070] The power system frequency deviation threshold constraint is:

[0071]

[0072] Where q1 is the system frequency deviation threshold caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and q2 is the system frequency deviation threshold caused by a step change in wind turbine power when the wind farm participates in frequency regulation.

[0073] Furthermore, the power system frequency deviation value obtained in step four includes the system frequency deviation caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and the system frequency deviation caused by a step change in wind turbine power when the wind farm participates in frequency regulation.

[0074] When the wind farm does not participate in frequency regulation, the specific calculation method for the system frequency deviation caused by a step change in wind turbine power is as follows:

[0075]

[0076] Where, Δω ∞ ΔP represents the system frequency deviation caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and ΔP is the change in wind turbine output power between adjacent time points.

[0077] When a wind farm participates in frequency regulation, the system frequency deviation caused by a step change in wind turbine power is:

[0078]

[0079] Where, Δω' ∞Let A be the system frequency deviation caused by a step change in wind turbine power when the wind farm participates in frequency regulation, and let η be the wind farm frequency regulation gain and η be the power generation coefficient of conventional units.

[0080] The beneficial effects of this invention are as follows: This invention establishes a power system frequency model using the grid-connected power of wind farms as the disturbance source. By comprehensively considering the frequency regulation effects of the prime mover and its governor, generator inertia, constant power load, and AGC, the wind power frequency band that meets the system frequency deviation threshold requirement can be obtained by solving the model output. Furthermore, by filtering out the part that makes the power system frequency regulation cost too high through the power system frequency regulation cost and the electricity revenue generated by the wind farm, the frequency regulation cost is effectively reduced. Moreover, the ability of wind farms to participate in system frequency regulation is fully utilized, which has the advantages of flexibility and controllability. This invention can solve the problems of high frequency regulation cost and large frequency deviation in existing power systems. Attached Figure Description

[0081] Figure 1 This is a schematic diagram of a wind power grid connection evaluation method based on frequency regulation cost as described in Specific Implementation Method 1.

[0082] Figure 2 This is a schematic diagram of the power system frequency model under the condition that the wind farm does not participate in frequency regulation in Specific Implementation Method 1;

[0083] Figure 3 This is a schematic diagram of the power system frequency model under the condition that the wind farm participates in frequency regulation in Specific Implementation Method 1;

[0084] Figure 4 This is a single-line diagram of the IEEE-9 node power system provided in Specific Implementation Method 1;

[0085] Figure 5 This is a diagram showing the frequency deviation of each bus in operating condition 1 during the simulation.

[0086] Figure 6 This is a diagram showing the frequency deviation of each bus in operating condition 2 during the simulation.

[0087] Figure 7 This is a diagram showing the frequency deviation of each bus in operating condition 3 during the simulation.

[0088] Figure 8 This is a diagram showing the frequency deviation of each bus in operating condition 4 during the simulation.

[0089] Figure 9 This is a schematic diagram of the probability density curve of active power output of a wind farm provided in Specific Implementation Method 1. Detailed Implementation

[0090] Specific implementation method one: Combining Figures 1 to 9This embodiment describes a wind power grid connection assessment method based on frequency regulation cost, which includes the following steps:

[0091] Step 1: Establish a power system frequency model using the grid-connected power of the wind farm as the disturbance source. The input of this power system frequency model is the power system frequency reference value, the disturbance is the power signal in different frequency bands, and the output is the frequency deviation of the power system.

[0092] Step 2: Establish an objective function based on the power system frequency regulation cost and the revenue from wind farm electricity generation;

[0093] Step 3: Using the objective function established in Step 2, determine the constraints that minimize the frequency regulation cost of the power system and maximize the revenue from the electricity generated by the wind farm.

[0094] Step 4: Optimize the power system frequency model established in Step 1 using the constraints obtained in Step 3, and solve the output of the optimized power system frequency model to obtain the power system frequency deviation value caused by the wind turbine.

[0095] In this embodiment, the method for establishing the power system frequency model in step one includes determining the transfer function of the prime mover and its governor, determining the transfer function of the generator inertia and constant power load, and determining the transfer function of the AGC (Automatic Generation Control) stage.

[0096] The transfer function of the prime mover and its governor is:

[0097]

[0098] Where G1(s) is the transfer function of the prime mover and its governor; s is the independent variable of the function; η R C represents the proportion of generating units in the power system that do not participate in primary frequency regulation. ∑ The ratio of the high-pressure cylinder in the equivalent turbine of the power system; T ∑R R is the time constant of the reheater. ∑0 This is the equivalent droop coefficient for all speed controllers in the circuit system;

[0099] The transfer function of the generator inertia and constant power load element is:

[0100]

[0101] Where G2(s) is the transfer function of the generator inertia and constant power load elements, M ∑0 η is the equivalent inertia of all existing generators with inertia in the power system. M Where D represents the proportion of inertial generator units in the power system, and D is the frequency coefficient of the load.

[0102] The transfer function of the AGC process is:

[0103]

[0104] Among them, K ∑i K represents the equivalent integral gain of all generating units in the power system capable of secondary frequency regulation; ∑p The equivalent proportional coefficients of all generating units in the power system capable of secondary frequency regulation.

[0105] In this embodiment, the proportion η of units in the power system that do not participate in primary frequency regulation is included in the transfer function of the prime mover and its governor. R The calculation method is as follows:

[0106]

[0107] Where, ∑S R＝∞ This represents the sum of the capacities of generating units in the power system that do not participate in primary frequency regulation. Let S be the total installed capacity of the power system, n be the number of conventional generating units in the power system, and S be the total installed capacity of the power system. i Let be the rated capacity of the i-th unit.

[0108] In this embodiment, the proportion η of inertial units in the power system in the transfer function of the generator inertia and constant power load links is... M The calculation method is as follows:

[0109]

[0110] Where, ∑S M＝0 It is the sum of the capacity of units or power sources in the power system that do not have inertia.

[0111] In this embodiment, the objective function established in step two is specifically as follows:

[0112] f ED = -c×Z+(1-c)×W

[0113] Among them, f ED denoted as , where is the total revenue of the wind farm after it is connected to the grid. A positive result indicates that the wind farm will generate net revenue, while a negative result indicates that the system still needs to invest in regulation costs. c is a weighting coefficient, c∈[0,1]. Z is the total frequency regulation cost of the wind farm connected to the grid, and W is the total revenue of the wind farm's electricity output.

[0114] In this embodiment, the total revenue W from the electricity generated by the wind farm in the objective function is calculated as follows:

[0115]

[0116] Where, di Let P be the output coefficient of the i-th wind turbine. wiav The actual active power output of the i-th wind turbine is expressed in kW; m represents the number of wind turbines installed in the power system.

[0117] The above refers to the actual active power output P of the i-th wind turbine. wiav The specific calculation method is as follows:

[0118]

[0119] Among them, v ci v is the cut-in wind speed of the fan; co For the cut-out velocity of the fan; v r P is the rated wind speed of the fan; wr v represents the rated power of a single fan, and v represents the wind speed.

[0120] In this embodiment, the method for calculating the total frequency regulation cost Z of the wind power grid-connected power system in the objective function is as follows:

[0121] Z = Z1 + Z2

[0122] Z1 represents the frequency regulation cost caused by overestimating wind power output, and Z2 represents the frequency regulation cost caused by underestimating wind power output.

[0123] It should be understood that when the actual output of a wind farm is less than the expected output, existing turbines need to increase their output to compensate for the difference, resulting in frequency regulation costs due to an overestimation of wind power output. Conversely, when the actual output of a wind farm is greater than the expected output, due to regulations, all wind power must be fed into the grid. In this case, the system must reduce the output of conventional turbines to maintain power balance, which inevitably leads to regulation costs, i.e., frequency regulation costs due to an underestimation of wind power output. Therefore, the total frequency regulation cost of a wind-connected power system should be the superposition of two mutually exclusive cost functions: the frequency regulation cost due to an overestimation of wind power output and the frequency regulation cost due to an underestimation of wind power output.

[0124] The calculation method for the frequency regulation cost Z1 caused by the overestimation of wind power output is as follows:

[0125]

[0126] Where, k rwi To overestimate the cost factor of frequency modulation; P wi To contribute to the planned operation of the i-th wind turbine unit; P is the probability density function of the active power output of the wind farm. w This represents the total active power output of m wind turbine units;

[0127] The calculation method for the frequency regulation cost Z2 caused by the underestimation of wind power output is as follows:

[0128]

[0129] Where, k pwi This is to underestimate the cost factor of frequency modulation.

[0130] In this embodiment, the probability density function of the active power output of the wind farm is... The specific calculation method is as follows:

[0131]

[0132] Among them, P wf Power output of a wind farm, measured in kW; P wfr Rated active power output of a wind farm, in kW; The active power output of the wind farm is P wf The probability density value at that time. for The first derivative; δ[P wf [(t)] represents the independent variable P. wf The unit impulse function of (t) in P wf At (t) = 0, its value is an infinite number; the integral of the unit impulse function is 1; the derivative of the unit step function is the unit impulse function. P (0) indicates that the probability function of active power output of the wind farm is in P wf =0; Φ P (P wfr ) represents the probability function of active power output of a wind farm in P wf =P wfr The value at time;

[0133] The The specific calculation method is as follows:

[0134]

[0135] Where, ξ w λ is the wake effect coefficient of the wind farm; k is the shape coefficient of the Weibull distribution, which determines the shape of the distribution curve; λ is the scale coefficient, which reflects the magnitude of the average wind speed, in m / s. Let v be the probability density value of the wind speed.

[0136] The Φ P The specific calculation method for (0) is as follows:

[0137]

[0138] in, Let v be the probability density value of the wind speed.

[0139] The probability density value of the wind speed v The specific calculation method is as follows:

[0140]

[0141] The Φ P (P wfr The specific calculation method is as follows:

[0142]

[0143] In this embodiment, the constraints determined in step three include: power balance constraints without considering network losses, unit output constraints, unit output ramp-up constraints, and power system frequency deviation threshold constraints.

[0144] The power balance constraint that does not consider network losses is:

[0145]

[0146] Where n is the number of existing thermal power units, P Gj For the active power output of the jth thermal power unit, P load The total load of the power system;

[0147] The unit output constraints include thermal power unit output constraints and wind power unit output constraints;

[0148] The output constraints of thermal power units are:

[0149] P Gjmin ≤P Gj ≤P Gjmax (j = 1, 2, ..., n)

[0150] Among them, P Gjmin P represents the minimum active power output of the j-th thermal power unit. Gjmax This represents the maximum active power output of the j-th thermal power unit.

[0151] Wind turbine output constraints:

[0152] 0≤P wiav ≤P wri (i = 1, 2, ..., m)

[0153] Among them, P wri Let be the rated power of the i-th wind turbine unit;

[0154] The unit's output ramp-up constraint is:

[0155]

[0156] Among them, U Rj D represents the rate of ascent and descent of the j-th thermal power unit. RjLet P be the descent and ramp rate of the j-th thermal power unit; ΔT is the dispatch time interval; P is the descent and ramp rate of the j-th thermal power unit. Gj,h P represents the active power output of the j-th thermal power unit at time h; Gj,h-1 These represent the active power output of the j-th thermal power unit at time h-1.

[0157] The power system frequency deviation threshold constraint is:

[0158]

[0159] Where q1 is the system frequency deviation threshold caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and q2 is the system frequency deviation threshold caused by a step change in wind turbine power when the wind farm participates in frequency regulation.

[0160] Solving the above optimization model, if max f ED >0, this frequency band can be directly connected to the grid; this maximum value is the final optimized result; max f ED <0 indicates that the generated electricity revenue is insufficient to cover frequency regulation costs, and this frequency band is the abandoned wind power frequency band.

[0161] In this embodiment, the power system frequency deviation value obtained in step four includes the system frequency deviation caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and the system frequency deviation caused by a step change in wind turbine power when the wind farm participates in frequency regulation.

[0162] When the wind farm does not participate in frequency regulation, the specific calculation method for the system frequency deviation caused by a step change in wind turbine power is as follows:

[0163]

[0164] Where, Δω ∞ ΔP represents the system frequency deviation caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and ΔP is the change in wind turbine output power between adjacent time points.

[0165] When a wind farm participates in frequency regulation, the system frequency deviation caused by a step change in wind turbine power is:

[0166]

[0167] Where, Δω' ∞ Let A be the system frequency deviation caused by a step change in wind turbine power when the wind farm participates in frequency regulation, and let η be the wind farm frequency regulation gain and η be the power generation coefficient of conventional units.

[0168] The generation factor of conventional generating units is calculated based on the generation output of conventional synchronous generating units and the system load power. The specific calculation method is as follows:

[0169]

[0170] By solving for the frequency deviation of the output quantity, the following conclusions can be drawn:

[0171] (1) When a wind power signal in a certain random frequency band is added to the power system as a disturbance source, it will affect the frequency characteristics of the system. The frequency deviation will change accordingly. The frequency deviation of the wind power grid-connected power system is related to the system's frequency regulation parameters, wind power ratio, load frequency characteristics, wind speed and its changes.

[0172] (2) The system frequency deviation Δω has a linear relationship with the wind power change ΔP. That is, as the wind power change increases, the frequency deviation will increase linearly. Therefore, the fluctuation of wind power connected to the grid exceeding the limit will cause the system frequency to exceed the operating limit, reducing the stability of the grid operation. Therefore, in order to ensure the stability of the power system frequency, it is necessary to set a system frequency deviation threshold and identify the wind power frequency band that causes the frequency deviation to exceed the threshold. At this time, this part of the wind power frequency band will be directly discarded.

[0173] For example, based on an IEEE-9 node power system with a total installed capacity of 500MW (traditional generator units + wind turbines), a load level of 315MW, and a system frequency of 50Hz, a simulation model was designed to study the impact of power fluctuations on the system frequency in different frequency bands. The single-line diagram of the system is as follows: Figure 4 As shown, four different operating conditions were designed for simulation. The original wind power data, the high-frequency part after EMD decomposition, the medium-frequency part after EMD decomposition, and the low-frequency part after EMD decomposition were injected into the power grid at bus 5. Then, the frequency deviation at bus 5, 6, and 8 was observed. The four different operating conditions are as follows.

[0174] Operating Condition 1: Raw Power Data Injection. The fan injects power into busbar 5 via a controllable current source. Figure 5 The frequency deviations of each bus are shown. Among them, bus 5 has the largest deviation, bus 6 has a medium deviation, and bus 8 has the smallest deviation.

[0175] Operating Condition 2: High-frequency power data injection, frequency deviation of each bus as follows Figure 6 As shown, the deviation of busbar 5 is similar to that of busbar 6 and busbar 8.

[0176] Operating Condition 3: Injection of intermediate frequency power data; frequency deviation of each bus as follows: Figure 7 As shown, the deviation of busbar 5 is similar to that of busbar 6, while the deviation of busbar 8 is the smallest.

[0177] Operating Condition 4: Low-frequency power data injection, frequency deviation of each bus as follows Figure 8As shown, the deviation of busbar 5 is similar to that of busbar 6 and busbar 8.

[0178] Simulation Result Analysis:

[0179] According to the frequency deviation diagrams for operating conditions 2, 3, and 4, the wind power in the mid-frequency range fluctuates significantly, thus having a substantial impact on the system's frequency deviation (generating a frequency deviation of ±0.3Hz to ±0.4Hz). In contrast, the fluctuations in the high and low frequencies are smaller, resulting in a smaller impact on the system's frequency deviation (generating frequency deviations of less than 0.05Hz). Simulation results based on actual wind farm operating data show a linear relationship between wind power fluctuations and system frequency deviation, which verifies the reliability of the conclusion.

[0180] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A wind power grid connection evaluation method based on frequency regulation cost, characterized in that, The grid connection assessment method includes the following steps: Step 1: Establish a power system frequency model using the grid-connected power of the wind farm as the disturbance source. The input of this power system frequency model is the power system frequency reference value, the disturbance is the power signal in different frequency bands, and the output is the frequency deviation of the power system. Step 2: Establish an objective function based on the power system frequency regulation cost and the revenue from wind farm electricity generation; The objective function is as follows: in, This represents the total revenue of the wind farm after it is connected to the grid. A positive result indicates that the wind farm will generate net revenue, while a negative result indicates that the system still needs to invest in adjustment costs. These are weighting coefficients. , The total frequency regulation cost of the wind power grid-connected power system. The total revenue generated by the wind farm; Total frequency regulation cost of wind power grid-connected power systems The calculation method is as follows: in, Frequency regulation costs resulting from overestimation of wind power output Frequency regulation costs resulting from underestimation of wind power output; The frequency regulation cost caused by the overestimation of wind power output The calculation method is as follows: in, To overestimate the cost factor of frequency modulation; For the first Planned output of the typhoon turbine units; For the first The actual active power output of the typhoon generator; Let be the probability density function of the active power output of the wind farm; for Total active power output of typhoon generator units; The frequency regulation cost caused by the underestimation of wind power output The calculation method is as follows: in, To underestimate the cost factor of frequency modulation; For the first Rated power of typhoon generator sets; Step 3: Using the objective function established in Step 2, determine the constraints that minimize the frequency regulation cost of the power system and maximize the revenue from the electricity generated by the wind farm. Step 4: Optimize the power system frequency model established in Step 1 using the constraints obtained in Step 3, and solve the output of the optimized power system frequency model to obtain the power system frequency deviation value caused by the wind turbine.

2. The wind power grid connection evaluation method based on frequency regulation cost according to claim 1, characterized in that, The method for establishing the power system frequency model in step one includes determining the transfer function of the prime mover and its governor, determining the transfer function of the generator inertia and constant power load, and determining the transfer function of the AGC. The transfer function of the prime mover and its governor is: in, The transfer function of the prime mover and its governor; is the independent variable of the function; The proportion of generating units in the power system that do not participate in primary frequency regulation; The ratio of the high-pressure cylinder in the equivalent turbine of the power system; The time constant of the reheater. This is the equivalent droop coefficient for all speed controllers in the circuit system; The transfer function of the generator inertia and constant power load element is: in, Let be the transfer function for generator inertia and constant power load components. The equivalent inertia of all existing generators with inertia in the power system. The proportion of inertial units in the power system. The frequency coefficient of the load; The transfer function of the AGC process is: in, The equivalent integral gain for all generating units in the power system capable of secondary frequency regulation; The equivalent proportional coefficients of all generating units in the power system capable of secondary frequency regulation.

3. The wind power grid connection evaluation method based on frequency regulation cost according to claim 2, characterized in that, The proportion of units in the power system that do not participate in primary frequency regulation in the transfer function of the prime mover and its governor components. The calculation method is as follows: in, This represents the sum of the capacities of generating units in the power system that do not participate in primary frequency regulation. The total installed capacity of the power system This refers to the number of conventional generating units in the power system. For the first Rated capacity of the unit.

4. The wind power grid connection evaluation method based on frequency regulation cost according to claim 3, characterized in that, The proportion of inertial units in the power system in the transfer function of the generator inertia and constant power load links. The calculation method is as follows: in, It is the sum of the capacity of units or power sources in the power system that do not have inertia.

5. The wind power grid connection evaluation method based on frequency regulation cost according to claim 1, characterized in that, The objective function defines the total revenue generated by the wind farm. The calculation method is as follows: in, For the first The output coefficient of the typhoon generator unit For the first The actual active power output of the typhoon generator; The number of wind turbines installed in the power system; The above is the first Actual active power output of typhoon generators The specific calculation method is as follows: in, The cut-in wind speed of the fan; This refers to the cut-off velocity of the fan. This refers to the rated wind speed of the fan. This refers to the rated power of a single fan. This refers to wind speed.

6. The wind power grid connection evaluation method based on frequency regulation cost according to claim 1, characterized in that, The probability density function of the active power output of the wind farm The specific calculation method is as follows: in, Contribute to the wind farm; Rated active power output for wind farms; Contributing to the wind farm The probability density value at that time. for The first derivative; Indicates that the independent variable is The unit impulse function, in Its value is an infinite number, the integral value of the unit impulse function is 1, and the derivative of the unit step function is the unit impulse function; The probability function representing the active power output of a wind farm is... The possible values ​​of ; The probability function representing the active power output of a wind farm is... The value at time; The The specific calculation method is as follows: in, The wake effect coefficient of the wind farm; λ is the shape coefficient of the Weibull distribution, which determines the shape of the distribution curve, and λ is the scale coefficient, which reflects the magnitude of the average wind speed. Wind speed The probability density value; The The specific calculation method is as follows: in, Wind speed The probability density value; The wind speed probability density value The specific calculation method is as follows: The The specific calculation method is as follows: 。 7. The wind power grid connection evaluation method based on frequency regulation cost according to claim 6, characterized in that, The constraints determined in step three include: power balance constraints without considering network losses, unit output constraints, unit output ramping constraints, and power system frequency deviation threshold constraints. The power balance constraint that does not consider network losses is: in, The number of existing thermal power units. For the first The active power output of the thermal power units in Taiwan The total load of the power system; The unit output constraints include thermal power unit output constraints and wind power unit output constraints; The output constraints of thermal power units are: in, For the first The minimum active power output of a thermal power unit; For the first The maximum active power output of the thermal power unit; Wind turbine output constraints: in, For the first Rated power of typhoon generator sets; The unit's output ramp-up constraint is: in, For the first The rate of ascent and ramp-up of the thermal power unit; For the first The rate of descent and ramp-up of the thermal power unit; For scheduling time intervals, For the first Taiwan thermal power unit in the Contributing effort at all times; The first Taiwan thermal power unit in the Contributing effort at all times; The power system frequency deviation threshold constraint is: in, This is the threshold value for system frequency deviation caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation. This is the threshold value for system frequency deviation caused by a step change in wind turbine power when the wind farm participates in frequency regulation.

8. The wind power grid connection evaluation method based on frequency regulation cost according to claim 2, characterized in that, The power system frequency deviation values ​​obtained in step four include those caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation, and those caused by a step change in wind turbine power when the wind farm participates in frequency regulation. When the wind farm does not participate in frequency regulation, the specific calculation method for the system frequency deviation caused by a step change in wind turbine power is as follows: in, This refers to the system frequency deviation caused by a step change in wind turbine power when the wind farm does not participate in frequency regulation. This represents the change in the wind turbine's output power between adjacent time points; When a wind farm participates in frequency regulation, the system frequency deviation caused by a step change in wind turbine power is: in, This refers to the system frequency deviation caused by a step change in wind turbine power when the wind farm participates in frequency regulation. For wind farm frequency regulation gain, This represents the power generation factor for conventional generating units.

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