A frequency safety fast judgment method based on an extended SFR model

Abstract

The application discloses a kind of based on the frequency safety fast judgment method of extended SFR model, comprising the following steps: for real-time detection of power grid, construct each frequency response expression, establish the relevant information of collection judgment power grid, including the capacity of generator, load size, the size of new energy output etc.;Determine whether the relevant parameter is updated, and update the parameter of extended SFR model, so as to obtain the corresponding calculation parameter of new state, or use the parameter of last calculation period;The frequency safety when N-1 fault occurs is quickly calculated from the collected data, and finally the frequency is quickly judged.The frequency safety fast judgment method based on the extended SFR model provided by the application can predict the frequency safety, thereby enhancing the stability of power system, and has important academic significance and engineering practical value.

Description

Technical Field

[0001] This invention relates to the field of power system frequency security technology, and in particular to a method for rapid frequency security assessment based on an extended SFR model. Background Technology

[0002] The new power system, primarily based on new energy sources, will bring a series of challenges to the power grid. As the proportion of new energy sources continues to rise, the power supply structure is shifting from being dominated by controllable, continuously output coal-fired power plants to being dominated by new energy units with high uncertainty and low controllability. Furthermore, the introduction of numerous power electronic devices has led to the gradual replacement of AC transmission with DC inter-regional transmission. Large-scale integration of new energy sources and DC inter-regional transmission has replaced some of the synchronous machines in the original synchronous grid, altering the characteristics and form of system inertia. This low inertia problem changes the system's frequency characteristics, challenging traditional inertia response systems and analysis methods. Simultaneously, the injection of new energy sources increases the random factors in the power system, significantly impacting its economic, safe, and stable operation. Therefore, researching solutions to frequency security, identifying the rate of frequency change and the minimum frequency point, and preventing events such as secondary frequency drops are particularly important.

[0003] To address these issues, we have designed a fast frequency security determination method based on the extended SFR model. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies, such as poor frequency security calculation capabilities and difficulty in making clear, fast, and accurate judgments. This invention proposes a fast frequency security judgment method based on the extended SFR model, which can be used for scheduling and planning as well as for real-time judgment of power systems. It has significant academic and engineering practical value.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for rapid frequency security determination based on an extended SFR model, the method comprising the following steps:

[0007] Step S1: Establish the transfer function of the extended SFR model, whose expression is:

[0008]

[0009] in,

[0010]

[0011] H(s)=H1(s)+H2(s)+H3(s)+H4(s)+H5(s),

[0012] H1(s) represents the prime mover-governor section, which is constructed using the traditional SFR model. The expression for H1(s) is:

[0013]

[0014] H2(s) is the frequency response of the induction motor, and its expression is:

[0015]

[0016] H3(s) is the frequency response of the virtual synchronous machine control in the grid-type converter. The expression for H3(s) is:

[0017] H4(s) is the frequency response of the grid-connected converter. The expression for H4(s) is:

[0018]

[0019] H5(s) is the frequency response caused by low-frequency load shearing, and the expression for H5(s) is:

[0020]

[0021] In the above formula, the total generator capacity S sys For reference capacity, H svs Let T be the equivalent inertia time constant of the generator, D be the equivalent damping coefficient of the system, including the damping coefficients of the generator and the load, R be the static droop coefficient of the governor, and T be the equivalent inertia time constant of the generator. R F is the reheat time constant of the prime mover. H T represents the proportion of the output power of the high-pressure cylinder of the prime mover. d To match the inertial response delay of the grid converter, T p To match the frequency regulation response delay of the grid converter, K d To determine the inertial response coefficient of the grid-type converter, K p K is the primary frequency regulation coefficient of the grid converter. RE-CSC T is the proportional gain for frequency regulation of the grid-type converter, which is the ratio of its own capacity to the reference capacity. VSC For the response delay of the grid-type converter, H VSC and D VSC K represents the inertial constant and damping coefficient for virtual synchronous control of a grid-type converter. RE-VSC The proportional gain for the grid-connected converter participating in frequency regulation is given by , where is the ratio of its own capacity to the reference capacity, s is the complex frequency, and a, b, and T are also given. im These are all constants related to the parameters of the induction motor itself, which can be obtained through parameter identification, K L P is the ratio of the induction motor load capacity to the reference capacity. dFor the magnitude of low-frequency load shedding, T tr This is the load shedding response delay.

[0022] Step S2 involves collecting frequency-related information from the power grid in real time, including the total generating capacity S. sys Induction motor load L inc Induction motor load ratio K L With grid-type new energy capacity S CSC Grid-type new energy power generation capacity S VSC Configuration details such as low-frequency load reduction;

[0023] Step S3 and related parameters are obtained through model aggregation and parameter identification, including relevant parameters of the prime mover-governor and the equivalent inertial time constant H of the generator. svs And the damping coefficient D of the system, and the inertial constant H of the virtual synchronous control of the grid-type converter. VSC and damping coefficient D VSC ;

[0024] Step S4: Check if the parameters have been updated. If not, use the previously set parameters and only update the changed load size, new energy power generation size, and total power generation capacity.

[0025] Step S5 and the N-1 frequency security check mechanism are used to find the maximum value of the current active power deficit, calculate the system's frequency change rate and minimum frequency point under the power deficit, and the expression for calculating the frequency change rate is as follows:

[0026]

[0027] The expression for calculating the lowest frequency point is:

[0028]

[0029] In the formula, L -1 ΔP represents the inverse Laplace transform, and ΔP represents the power deficit.

[0030] Step S6: When the lowest frequency point is lower than the warning value or the frequency change rate is greater than the warning value, a safety warning is activated; otherwise, proceed to the next judgment cycle.

[0031] Further preferred, according to step S2, frequency-related information is collected from the power grid in real time, and the response ratio calculation parameters are as follows:

[0032]

[0033] Substitute the above ratio calculation parameters into the corresponding expression in step S1 for calculation.

[0034] In a further preferred embodiment, in step S3, taking the prime mover-governor as the research object, the relevant parameters of the model aggregation are expressed as follows:

[0035]

[0036]

[0037]

[0038]

[0039] In the formula, X is the exponential coefficient, representing {T} G T c F H T R The quantity of}, K mi S is the proportional coefficient of the generator. i For the current generator capacity, κ i These are weighting coefficients;

[0040] Taking the induction motor as the research object, let the load size of the asynchronous generator with each parameter be L. i The induction motor's own parameters are a i and b i The proportion is λ i =L i / L inc ,get:

[0041] T m =∑λ i T im a m =∑λ i a i b m =∑λ i b i .

[0042] In a further preferred embodiment, in step S3, the relevant parameters are obtained through parameter identification by conducting experiments on the new energy power station or load side, obtaining frequency signals, and then identifying the relevant parameters by obtaining frequency curves.

[0043] In a further preferred embodiment, in step S4, since the parameters change during operation, the parameters will be updated in the next judgment, automatically updating the relevant parameters. If not, the parameters from the previous judgment cycle will be used, only changing the frequency-related information collected in real time from the power grid, including the total power generation capacity S. sys Induction motor load size L inc Induction motor load ratio K L The size of grid-connected new energy power generation capacity S CSCand the size of grid-connected new energy power generation capacity S VSC Configuration details for low-frequency load reduction.

[0044] Further preferred methods utilize current state parameters to verify generator disconnection and DC blocking faults, ensuring that the lowest frequency point and frequency change rate are within the allowable range after an accident occurs.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows: The frequency security rapid judgment method based on the extended SFR model of the present invention can, on the one hand, clearly identify the frequency change rate and the frequency minimum point to prevent secondary drop events, and on the other hand, it can quickly perform frequency security calculations, calculate the frequency security problems caused by multiple response resources under the current power grid, automatically update parameters, adapt to multiple environments in actual online judgment, and predict frequency security, thereby enhancing the stability of the power system. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the extended SFR model, which is a fast frequency security determination method based on the extended SFR model proposed in this invention.

[0047] Figure 2 This is a schematic diagram comparing the lowest frequency points with new energy control in a frequency security rapid judgment method based on the extended SFR model proposed in this invention.

[0048] Figure 3 This is a schematic diagram of the frequency change rate in a certain region, based on a fast frequency security determination method using an extended SFR model proposed in this invention.

[0049] Figure 4 The load curve of this region is provided by the frequency security fast judgment method based on the extended SFR model proposed in this invention.

[0050] Figure 5 This invention proposes a method for rapid frequency security determination based on an extended SFR model for assessing the output of new energy sources in this region.

[0051] Figure 6 This invention proposes a fast frequency security determination method based on an extended SFR model for DC outside the region.

[0052] Figure 7 This is a flowchart illustrating a method for rapid frequency security determination based on an extended SFR model proposed in this invention. Detailed Implementation

[0053] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0054] See Figure 1 and Figure 7 This example uses the extended SFR model with 2021 data from a certain region as an example. Assuming the power deficit is the amount of power transmitted by a DC power source in that region, the rate of change of frequency (RoCoF) and the lowest frequency point of the system under a large power deficit at each moment are calculated to simulate the real-time judgment process. This embodiment proposes a fast frequency security judgment method based on the extended SFR model, including the following steps:

[0055] Step S1: For real-time power grid monitoring, establish the transfer function of the extended SFR model and construct the frequency response expressions:

[0056] in,

[0057]

[0058] H(s)=H1(s)+H2(s)+H3(s)+H4(s)+H5(s),

[0059] H1(s) represents the prime mover-governor section, which is constructed using the traditional SFR model. The expression for H1(s) is:

[0060]

[0061] H2(s) is the frequency response of the induction motor, and its expression is:

[0062]

[0063] H3(s) is the frequency response of the virtual synchronous machine control in the grid-type converter. The expression for H3(s) is:

[0064] H4(s) is the frequency response of the grid-connected converter. The expression for H4(s) is:

[0065]

[0066] H5(s) is the frequency response caused by low-frequency load shearing, and the expression for H5(s) is:

[0067]

[0068] In the above formula, the total generator capacity Ssys For reference capacity, ΔP represents the per-unit power deficit, and Δf is the per-unit value of the frequency deviation, which is the same as the per-unit value of the generator speed deviation. Figure 1 (indicated by the Chinese annotation), H svs Let T be the equivalent inertia time constant of the generator, D be the equivalent damping coefficient of the system, including the damping coefficients of the generator and the load, R be the static droop coefficient of the governor, and T be the equivalent inertia time constant of the generator. R F is the reheat time constant of the prime mover. H T represents the proportion of the output power of the high-pressure cylinder of the prime mover. d To match the inertial response delay of the grid converter, T p To match the frequency regulation response delay of the grid converter, K d To determine the inertial response coefficient of the grid-type converter, K p K is the primary frequency regulation coefficient of the grid converter. RE-CSC T is the proportional gain for frequency regulation of the grid-type converter, which is the ratio of its own capacity to the reference capacity. VSC For the response delay of the grid-type converter, H VSC and D VSC K represents the inertial constant and damping coefficient for virtual synchronous control of a grid-type converter. RE-VSC The proportional gain for the grid-connected converter participating in frequency regulation is given by , where is the ratio of its own capacity to the reference capacity, S is the complex frequency, and a, b, and T are also given. im These are all constants related to the parameters of the induction motor itself, which can be obtained through parameter identification, K L P is the ratio of the induction motor load capacity to the reference capacity. d For the magnitude of low-frequency load shedding, T tr The load shedding response delay can be ignored for ease of calculation.

[0069] Step S2 involves collecting the capacity of each response resource. Taking real-time frequency security assessment as an example, frequency-related information is collected from the power grid in real time, including the total generating capacity S. sys Induction motor load L inc Induction motor load ratio K L With grid-type new energy capacity S CSC Grid-type new energy power generation capacity S VSC Load size, the output of new energy sources, and the configuration of low-frequency load shedding, etc. Figures 4-6 The graphs show the load curve changes, the output of new energy sources changes over time, and the proportion of DC power transmission from outside the region (DC transmission ratio) changes over time. Relevant information can also be obtained from these graphs.

[0070] Figure 1 The corresponding response ratio calculation parameters are:

[0071]

[0072] Substitute the above ratio calculation parameters into the corresponding expression in step S1 for calculation.

[0073] Step S3 and related parameters are obtained through model aggregation and parameter identification, or provided by the operator, including relevant parameters of the prime mover-governer and the generator's equivalent inertial time constant H. svs And the damping coefficient D of the system, and the inertial constant H of the virtual synchronous control of the grid-type converter. VSC and damping coefficient D VSC .

[0074] Taking the prime mover-governor as the research object, the relevant parameters of the model aggregation are expressed as follows:

[0075]

[0076]

[0077]

[0078]

[0079] In the formula, X is a denotation coefficient, representing {T} G T c F H T R The quantity of}, K mi S is the proportional coefficient of the generator. i For the current generator capacity, κ i These are weighting coefficients;

[0080] Taking the induction motor as the research object, let the load size of the asynchronous generator with each parameter be L. i The induction motor's own parameters are a i and b i The proportion is λ i =L i / L inc ,get:

[0081] T m =∑λ i T im a m =∑λ i a i b m =∑λ i b i .

[0082] The relevant parameters are obtained through parameter identification as follows: experiments are conducted on the renewable energy power station or load side, and the frequency signal is used to obtain the frequency curve for identification, thereby obtaining the relevant parameters; the parameter identification method is given in Table 1 in the example:

[0083] Table 1. Parameters used in the example.

[0084]

[0085] Step S4: Update the parameters of the extended SFR model. Check if the parameters have been updated. If not, use the previously set parameter aggregation, only updating the changed load size, renewable energy output, and total generating capacity. If so, update the relevant parameters for aggregation. Since the parameters change during operation, they will be updated in the next judgment. Automatically update the relevant parameters. If not, use the parameters from the previous judgment cycle, only changing the frequency-related information collected from the grid in real time, including the total generating capacity S. sys Induction motor load size L inc Induction motor load ratio K L The size of grid-connected new energy power generation capacity S CSC and the size of grid-connected new energy power generation capacity S VSC Configuration details for low-frequency load reduction.

[0086] Step S5: Utilize the N-1 frequency safety check mechanism to verify and find the maximum value of the current active power deficit. Calculate the system's frequency change rate and minimum frequency point under the maximum power deficit. Since the grid-type converter responds very quickly, T can be neglected. VSC The impact, Figure 3 The diagram illustrates the rate of frequency change in this region. The fast calculation expression for the rate of frequency change (RoCoF) is as follows:

[0087]

[0088] Figure 2 This diagram illustrates the comparison of the lowest frequency points in this embodiment with and without renewable energy control (Frequency nadir in the diagram represents the lowest frequency point). The lowest frequency point can be obtained by calculating the step response using Laplace variation, which is much faster than time-domain simulation. The calculation expression is as follows:

[0089]

[0090] In the formula, L -1 ΔP represents the inverse Laplace transform, and ΔP represents the power deficit.

[0091] The current state parameters are used to check for faults such as generator disconnection and DC blockage, ensuring that the lowest frequency point and frequency change rate are within the allowable range after an accident occurs.

[0092] Step S6: If the lowest frequency point is lower than the warning value or the frequency change rate is greater than the warning value, the detection fails and a safety warning is activated; otherwise, the detection passes, the current judgment cycle ends, and the next judgment cycle begins.

[0093] In this embodiment, if the frequency change rate is 0.2 Hz / s as the criterion, all frequency judgment points are within the safe range. Based on the extended SFR model, frequency security can be quickly judged. According to the above method, frequency security calculation can be performed quickly to calculate the frequency security problems caused by multiple response resources under the current power grid, thereby realizing the rapid judgment of frequency security.

[0094] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for rapid frequency security determination based on an extended SFR model, characterized in that, The method includes the following steps: Step S1: Establish the transfer function of the extended SFR model, whose expression is: in, H(s)=H1(s)+H2(s)+H3(s)+H4(s)+H5(s), H1(s) represents the prime mover-governor section, which is constructed using the traditional SFR model. The expression for H1(s) is: H2(s) is the frequency response of the induction motor, and its expression is: H3(s) is the frequency response of the virtual synchronous machine control in the grid-type converter. The expression for H3(s) is: H4(s) is the frequency response of the grid-connected converter. The expression for H4(s) is: H5(s) is the frequency response caused by low-frequency load shearing, and the expression for H5(s) is: In the above formula, the total generator capacity S sys For reference capacity, H svs Let T be the equivalent inertia time constant of the generator, D be the equivalent damping coefficient of the system, including the damping coefficients of the generator and the load, R be the static droop coefficient of the governor, and T be the equivalent inertia time constant of the generator. R F is the reheat time constant of the prime mover. H T represents the proportion of the output power of the high-pressure cylinder of the prime mover. d To match the inertial response delay of the grid converter, T p To match the frequency regulation response delay of the grid converter, K d To determine the inertial response coefficient of the grid-type converter, K p K is the primary frequency regulation coefficient of the grid converter. RE-CSC T is the proportional gain for frequency regulation of the grid-type converter, which is the ratio of its own capacity to the reference capacity. VSC For the response delay of the grid-type converter, H VSC and D VSC K represents the inertial constant and damping coefficient for virtual synchronous control of a grid-type converter. RE-VSC The proportional gain for the grid-connected converter participating in frequency regulation is given by , where is the ratio of its own capacity to the reference capacity, S is the complex frequency, and a, b, and T are also given. im These are all constants related to the parameters of the induction motor itself, which can be obtained through parameter identification, K L P is the ratio of the induction motor load capacity to the reference capacity. d For the magnitude of low-frequency load shedding, T tr For load shedding response delay; Step S2 involves collecting frequency-related information from the power grid in real time, including the total generating capacity S. sys Induction motor load L inc Induction motor load ratio K L With grid-type new energy capacity S CSC Grid-type new energy power generation capacity S VSC Configuration details for low-frequency load reduction; Step S3 and related parameters are obtained through model aggregation and parameter identification, including relevant parameters of the prime mover-governor and the equivalent inertial time constant H of the generator. svs And the damping coefficient D of the system, and the inertial constant H of the virtual synchronous control of the grid-type converter. VSC and damping coefficient D VSC ; Step S4: Check if the parameters have been updated. If not, use the previously set parameters and only update the changed load size, new energy power generation size, and total power generation capacity. Step S5 and the N-1 frequency security check mechanism are used to find the maximum value of the current active power deficit, calculate the system's frequency change rate and minimum frequency point under the power deficit, and the expression for calculating the frequency change rate is as follows: The expression for calculating the lowest frequency point is: In the formula, L -1 ΔP represents the inverse Laplace transform, and ΔP represents the power deficit. Step S6: When the lowest frequency point is lower than the warning value or the frequency change rate is greater than the warning value, a safety warning is activated; otherwise, proceed to the next judgment cycle.

2. The method for rapid frequency security determination based on the extended SFR model according to claim 1, characterized in that, Based on step S2, frequency-related information is collected from the power grid in real time, and the response ratio calculation parameters are as follows: Substitute the above ratio calculation parameters into the corresponding expression in step S1 for calculation.

3. The method for rapid frequency security determination based on the extended SFR model according to claim 1, characterized in that, In step S3, the relevant parameters for model aggregation are expressed as follows: In the formula, X is the exponential coefficient, representing {T} G T c， F H T R The quantity of}, K mi S is the proportional coefficient of the generator. i For the current generator capacity, κ i These are weighting coefficients; Taking the induction motor as the research object, let the load size of the asynchronous generator with each parameter be L. i The induction motor's own parameters are a i and b i The proportion is λ i =L i / L inc ,get: T m =∑λ i T im ,a m =∑λ i a i ,b m =∑λ i b i 。 4. The method for rapid frequency security determination based on the extended SFR model according to claim 1, characterized in that, In step S3, the relevant parameters are obtained through parameter identification as follows: experiments are conducted on the new energy power station or load side, and the frequency signal is obtained. The frequency curve is then used for identification to obtain the relevant parameters.

5. The method for rapid frequency security determination based on the extended SFR model according to claim 1, characterized in that, In step S4, since the parameters change during operation, they will be updated in the next judgment. The relevant parameters will be automatically updated. If no updates are available, the parameters from the previous judgment cycle will be used, only changing the frequency-related information collected in real-time from the power grid, including the total generating capacity S. sys Induction motor load size L inc Induction motor load ratio K L The size of grid-connected new energy power generation capacity S CSC and the size of grid-connected new energy power generation capacity S VSC Configuration details for low-frequency load reduction.

6. The method for rapid frequency security determination based on the extended SFR model according to claim 1, characterized in that, The current state parameters are used to check for faults such as generator disconnection and DC blockage, ensuring that the lowest frequency point and frequency change rate are within the allowable range after a certain accident.

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