Fault splitting device source load bidirectional identification method and system based on harmonic impedance

Abstract

The invention discloses a fault splitting device source load bidirectional identification method and system based on harmonic impedance, and relates to the technical field of new energy field station source load state identification, and the method comprises the steps: obtaining a grid-connected point voltage and current sampling value of a new energy field station, and calculating the fundamental frequency of the new energy field station; judging whether the fundamental wave frequency is within a preset fundamental wave frequency range or not; if yes, the fundamental wave power of the voltage and current sampling values of the grid-connected point is calculated, and the source load state of the new energy station is identified based on the fundamental wave power and the power direction criterion; if not, calculating a harmonic impedance module value of the voltage and current sampling value of the grid-connected point, and judging whether a line tripping signal sent by the fault splitting strategy station device is received or not; if not, identifying the source load state of the new energy station based on the harmonic impedance criterion; and if yes, identifying the source load state of the new energy station based on the harmonic impedance difference criterion. The technical problem that the source load characteristics of the new energy station cannot be accurately distinguished in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of source-load status identification technology for new energy power stations, specifically to a bidirectional source-load identification method and system based on a fault disconnection device using harmonic impedance. Background Technology

[0002] Fault-breaking devices are critical equipment in power systems to ensure stable grid operation. When a grid fault occurs, these devices can quickly identify the fault and take timely measures to isolate the faulty section from the normally operating grid, preventing the fault from spreading and proliferating. This not only protects electrical equipment from damage but also ensures normal power supply to other parts of the grid, reducing the scope and duration of power outages and improving the reliability and stability of the grid.

[0003] With the development of new energy technologies, more and more wind power, photovoltaic, and other new energy power plants are being connected to the power grid. These new energy power plants have bidirectional source-load characteristics, meaning they can act as both power suppliers (sources) and power consumers (loads). This bidirectional characteristic makes the role of new energy power plants in the power grid more complex, and traditional fault detection and disconnection methods are insufficient to accurately identify their status. Therefore, developing new fault disconnection technologies tailored to the specific characteristics of new energy power plants is particularly important.

[0004] Traditional fault location source-load identification methods typically rely on power direction criteria. However, in power grids connected to renewable energy power plants, the power direction criteria are prone to errors during calculation due to frequency instability and significant fluctuations, leading to misjudgments. Particularly under conditions of drastic frequency fluctuations, the reliability of the power direction criteria decreases significantly, failing to accurately distinguish the source-load characteristics of renewable energy power plants and impacting the timeliness and effectiveness of fault handling. Summary of the Invention

[0005] The purpose of this invention is to provide a source-load bidirectional identification method and system for a fault disconnection device based on harmonic impedance in order to solve at least one of the above-mentioned technical problems.

[0006] In a first aspect, embodiments of the present invention provide a source-load bidirectional identification method for a fault-splitting device based on harmonic impedance, applied to a fault-splitting acquisition station device installed in a renewable energy power station, wherein the fault-splitting acquisition station device is communicatively connected to a fault-splitting strategy station device installed in a terminal substation; the method includes: acquiring sampled values ​​of the grid connection point voltage and current of the renewable energy power station; calculating the fundamental frequency of the renewable energy power station based on the sampled values ​​of the grid connection point voltage and current; determining whether the fundamental frequency is within a preset fundamental frequency range; if so, calculating the grid connection point voltage... The fundamental power of the current sampling value is used to identify the source-load status of the new energy power station based on the fundamental power and power direction criterion; if not, the harmonic impedance magnitude of the grid connection point voltage and current sampling value is calculated, and it is determined whether a line trip signal sent by the fault disconnection strategy station device is received; if the line trip signal is not received, the source-load status of the new energy power station is identified based on the harmonic impedance magnitude and harmonic impedance criterion; if the line trip signal is received, the source-load status of the new energy power station is identified based on the harmonic impedance magnitude and harmonic impedance difference criterion.

[0007] Further, based on the sampled voltage and current values ​​at the grid connection point, the fundamental frequency of the new energy power station is calculated, including: performing a discrete Fourier transform recursive calculation on the sampled voltage and current values ​​at the grid connection point to obtain the real part and imaginary part of the harmonic vectors of the sampled values; calculating the fundamental positive-sequence voltage based on the real part and the imaginary part of the harmonic vectors; and calculating the fundamental frequency of the new energy power station based on the angular change rate of the fundamental positive-sequence voltage.

[0008] Furthermore, the preset fundamental frequency range includes the maximum frequency stability limit range of the large power grid.

[0009] Furthermore, the fundamental power of the grid connection point voltage and current sampling values ​​includes:

[0010] P a0 (k)=U as0 (k)*I as0 (k)+U ac0 (k)*I ac0 (k);

[0011] Pb0(k)=Ub s0 (k)*Ib s0 (k)+Ub c0 (k)*Ib c0 (k);

[0012] P c0 (k)=U cs0 (k)*I cs0 (k)+U cc0 (k)*I cc0 (k);

[0013] Among them, P a0 (k), P b0 (k), P c0 (k) represents the fundamental power of the three-phase fundamental sampling, U ac0 (k), U bc0 (k), U cc0 (k) represent the real phasor parts of the fundamental three-phase voltage, I ac0 (k), I bc0 (k), I cc0 (k) represents the real phasor part of the fundamental three-phase current, U as0 (k), U bs0 (k), U cs0 (k) represent the imaginary phasor parts of the fundamental three-phase voltage, I as0 (k), I bs0 (k), I cs0 (k) represent the imaginary phasor parts of the fundamental three-phase current; the source-load state of the new energy power station is identified based on the fundamental power and power direction criteria, including: when P... a0 (k), P b0 (k), P c0 When at least two of (k) are less than 0, the new energy power station is the source end; when P is satisfied... a0 (k), P b0 (k), P c0 When at least two of (k) are greater than or equal to 0, the new energy power station is the load end.

[0014] Further, the harmonic impedance magnitude includes the sum of the positive-sequence harmonic impedance and the impedances of multiple harmonics; wherein, the positive-sequence harmonic impedance includes:

[0015]

[0016] The sum of the multiple harmonic impedances includes:

[0017]

[0018] Where i is the harmonic order, U i (k), I i (k) represent the harmonic positive sequence voltage and current, respectively, Z i (k) is the harmonic positive sequence impedance, Z pi (k) represents the sum of multiple consecutive harmonic impedances at the current moment.

[0019] Furthermore, the source-load state of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance criterion, including: when Z... pi (k)≥Z setWhen Z is in the process of being considered a power source, the new energy power station is the source end; when Z is in the process of being pi (k)<Z set At that time, the new energy power station is the load end; where Z set This is the preset impedance threshold.

[0020] Furthermore, the source-load state of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance difference criterion, including: if Z max (k)-Zsub(k)<Z difset Then the new energy power station is the source end; if Z max (k)-Zsub(k)≥Z difset Then the new energy power station is the load end; where Z max (k) is the maximum harmonic impedance in the positive sequence impedance of multiple harmonics, Z sub (k) represents the second largest harmonic impedance in the positive sequence impedance of multiple harmonics, Z difset This is a preset impedance difference threshold.

[0021] Furthermore, the method also includes: sending the source-load status of the new energy power station to the fault-disconnection strategy station device, so that the fault-disconnection strategy station device can determine the target source-load control strategy based on the source-load status.

[0022] Secondly, embodiments of the present invention also provide a source-load bidirectional identification system for a fault-splitting device based on harmonic impedance, applied to a fault-splitting acquisition station device installed in a renewable energy power station. The fault-splitting acquisition station device is communicatively connected to a fault-splitting strategy station device installed in a terminal substation. The system includes: an acquisition module, a calculation module, and an identification module. The acquisition module is used to acquire sampled values ​​of the grid connection point voltage and current of the renewable energy power station. The calculation module is used to calculate the fundamental frequency of the renewable energy power station based on the sampled values ​​of the grid connection point voltage and current. The identification module is used to determine whether the fundamental frequency is within a preset range. Within the fundamental frequency range; if so, calculate the fundamental power of the sampled voltage and current values ​​at the grid connection point, and identify the source-load status of the new energy power station based on the fundamental power and power direction criterion; if not, calculate the harmonic impedance magnitude of the sampled voltage and current values ​​at the grid connection point, and determine whether a line trip signal sent by the fault disconnection strategy station device has been received; if no line trip signal is received, identify the source-load status of the new energy power station based on the harmonic impedance magnitude and harmonic impedance criterion; if the line trip signal is received, identify the source-load status of the new energy power station based on the harmonic impedance magnitude and harmonic impedance difference criterion.

[0023] Thirdly, embodiments of the present invention also provide an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method described in the first aspect above.

[0024] This invention provides a method and system for bidirectional source-load identification of a fault disconnection device based on harmonic impedance. A fault disconnection acquisition station is added at the grid connection point of a new energy power station to collect voltage and current signals from the grid connection point. By analyzing the harmonic components in these signals, the harmonic impedance is calculated. Utilizing the good stability and directionality of harmonic impedance, the magnitude and characteristics of the harmonic impedance can effectively determine whether the new energy power station is at the source or load end, alleviating the technical problem in existing technologies that cannot accurately distinguish the source-load characteristics of new energy power stations. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 A flowchart illustrating a bidirectional source-load identification method for a fault disconnection device based on harmonic impedance, provided in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram illustrating the connection between a fault isolation acquisition station device and a fault isolation strategy station device according to an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of a source-load bidirectional identification system for a fault disconnection device based on harmonic impedance, provided in an embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] Figure 1This is a flowchart of a source-load bidirectional identification method for a fault disconnection device based on harmonic impedance according to an embodiment of the present invention. The method is applied to a fault disconnection acquisition station device installed in a new energy power station, and the fault disconnection acquisition station device is communicatively connected to a fault disconnection strategy station device installed in a terminal substation.

[0032] Figure 2 This is a schematic diagram illustrating the connection between a fault isolation acquisition station device and a fault isolation strategy station device according to an embodiment of the present invention. Figure 2 As shown, in an optional embodiment of the present invention, a fault disconnection strategy station device 2 is installed in the terminal substation 1, and a fault disconnection acquisition station device 4 is installed in the new energy power station 3. Data is transmitted between the fault disconnection strategy station device 2 and the fault disconnection acquisition station device 4 via a 2M fiber optic leased line.

[0033] Specifically, such as Figure 1 As shown, the method provided in this embodiment of the invention includes the following steps:

[0034] Step S102: Obtain the sampled values ​​of the grid connection point voltage and current of the new energy power station.

[0035] Step S104: Calculate the fundamental frequency of the new energy power station based on the sampled voltage and current values ​​at the grid connection point.

[0036] Step S106: Determine whether the fundamental frequency is within the preset fundamental frequency range; if yes, proceed to step S108; if no, proceed to step S110.

[0037] Step S108: Calculate the fundamental power of the sampled voltage and current values ​​at the grid connection point, and identify the source-load status of the new energy power station based on the fundamental power and power direction criteria.

[0038] Step S110: Calculate the harmonic impedance magnitude of the sampled voltage and current values ​​at the grid connection point.

[0039] Step S112: Determine whether a line trip signal has been received from the fault disconnection strategy station device; if not, proceed to step S114; if yes, proceed to step S116.

[0040] Step S114: Identify the source-load status of the new energy power station based on the harmonic impedance modulus and harmonic impedance criteria.

[0041] Step S116: Identify the source-load status of the new energy power station based on the harmonic impedance modulus and harmonic impedance difference criteria.

[0042] Specifically, step S104 also includes the following steps:

[0043] Step S1041: Perform discrete Fourier transform recursive calculation on the sampled values ​​of voltage and current at the grid connection point to obtain the real part of the harmonic vector and the imaginary part of the harmonic vector of the sampled values.

[0044] Step S1042: Calculate the fundamental positive sequence voltage based on the real part and imaginary part of the harmonic vector;

[0045] Step S1043: Calculate the fundamental frequency of the new energy power station based on the angle change rate of the fundamental positive sequence voltage.

[0046] In this embodiment of the invention, the fault isolation acquisition station device samples the grid connection point voltage and current data at N points per cycle within a set time interval, and performs discrete Fourier transform recursive calculation on the sampled values, as shown in the following expression:

[0047]

[0048] Where k is the current number of sampling points, N is the number of sampling points at equal intervals per cycle, i is the harmonic order, and x(k) is the original sampled signal quantity of the current sampling point k, including the fundamental frequency, the attenuated DC component, and each harmonic component; A ci (k) represents the real part of the i-th harmonic phasor of the voltage and current data sampling, A si (k) represents the imaginary part of the i-th harmonic phasor of the voltage and current data sampling;

[0049] When the input sample value x(k) is a voltage, the fundamental wave and positive sequence voltage are calculated recursively using the discrete Fourier transform formula above, yielding the fundamental wave positive sequence voltage as follows:

[0050]

[0051] Among them, U c0 (k), U s0 (k) represent the real and imaginary parts of the phasor of the fundamental positive-sequence voltage, respectively, U ac0 (k), U bc0 (k), U cc0 (k) represents the real phasor part of the fundamental three-phase voltage, U as0 (k), U bs0 (k), U cs0 (k) represents the imaginary phasor part of the fundamental three-phase voltage;

[0052] The current system frequency is calculated using the rate of change of the fundamental positive-sequence voltage. The frequency calculation formula is as follows:

[0053]

[0054] Where f(k) is the current frequency of the system with the fundamental positive sequence voltage.

[0055] In one optional embodiment of the present invention, the preset fundamental frequency range includes the frequency stability limit range of the large power grid. Preferably, the frequency stability limit range of the large power grid is 48Hz-52Hz.

[0056] In an optional embodiment of the present invention, when the fundamental frequency is in the range of 48Hz-52Hz, step S108 recursively calculates the fundamental power of the three-phase voltage and current samples based on the discrete Fourier transform. Specifically, the fundamental power of the grid-connected point voltage and current sample values ​​includes:

[0057] P a0 (k)=U as0 (k)*I as0 (k)+U ac0 (k)*I ac0 (k);

[0058] Pb0(k)=Ub s0 (k)*Ib s0 (k)+Ub c0 (k)*Ib c0 (k);

[0059] P c0 (k)=U cs0 (k)*I cs0 (k)+U cc0 (k)*I cc0 (k);

[0060] Among them, P a0 (k), P b0 (k), P c0 (k) represents the fundamental power of the three-phase fundamental sampling, U ac0 (k), U bc0 (k), U cc0 (k) represent the real phasor parts of the fundamental three-phase voltage, I ac0 (k), I bc0 (k), I cc0 (k) represents the real phasor part of the fundamental three-phase current, U as0 (k), U bs0 (k), U cs0 (k) represent the imaginary phasor parts of the fundamental three-phase voltage, I as0 (k), I bs0 (k), I cs0 (k) represents the imaginary phasor part of the fundamental three-phase current;

[0061] Identifying the source-load status of renewable energy power plants based on fundamental power and power direction criteria includes:

[0062] When P is satisfied a0(k), P b0 (k), P c0 When at least two of (k) are less than 0, the new energy power station is the source end;

[0063] When P is satisfied a0 (k), P b0 (k), P c0 When at least two of (k) are greater than or equal to 0, the new energy power station is the load end.

[0064] In an optional embodiment of the invention, when the fundamental frequency is outside the 48Hz-52Hz range and the fault disconnection acquisition station device does not receive a line tripping signal from the fault disconnection strategy station device, step S114 recursively calculates the sampled harmonic positive sequence impedance based on the discrete Fourier transform. Specifically, the harmonic impedance magnitude includes the sum of the harmonic positive sequence impedance and multiple harmonic impedances; wherein,

[0065] Harmonic positive sequence impedance includes:

[0066]

[0067] The sum of multiple harmonic impedances includes:

[0068]

[0069] Where i is the harmonic order, U i (k), I i (k) represent the harmonic positive sequence voltage and current, respectively, Z i (k) is the harmonic positive sequence impedance, Z pi (k) represents the sum of multiple consecutive harmonic impedances at the current moment.

[0070] Specifically, the source-load status of renewable energy power plants is identified based on harmonic impedance modulus and harmonic impedance criteria, including:

[0071] When Z pi (k)≥Z set At that time, the new energy power station is the source end;

[0072] When Z pi (k)<Z set At that time, the new energy power station is the load end;

[0073] Among them, Z set This is the preset impedance threshold.

[0074] In an optional embodiment of the present invention, when the fundamental frequency is outside the range of 48Hz to 52Hz and the fault tripping acquisition station receives the line tripping signal from the fault tripping strategy station, the maximum harmonic impedance Z(k) among the 2nd to 50th harmonics is extracted. maxThe second largest harmonic impedance Z(k) sub Step S116 includes:

[0075] If Z max (k)-Zsub(k)<Z difset Then the new energy power station is the source end;

[0076] If Z max (k)-Zsub(k)≥Z difset Then the new energy power station is the load end;

[0077] Among them, Z max (k) is the maximum harmonic impedance in the positive sequence impedance of multiple harmonics, Z sub (k) represents the second largest harmonic impedance in the positive sequence impedance of multiple harmonics, Z difset This is a preset impedance difference threshold.

[0078] Preferably, the method provided in this embodiment of the invention further includes: sending the source-load status of the new energy power station to the fault-disconnection strategy station device, so that the fault-disconnection strategy station device can determine the target source-load control strategy based on the source-load status.

[0079] As described above, the embodiments of the present invention provide a source-load bidirectional identification method for fault disconnection devices based on harmonic impedance. A fault disconnection acquisition station device is added at the grid connection point of the new energy power station to collect voltage and current signals at the grid connection point. By analyzing the harmonic components in these signals, the harmonic impedance is calculated. Utilizing the good stability and directionality of harmonic impedance, the magnitude and characteristics of the harmonic impedance can effectively determine whether the new energy power station is at the source end or the load end, alleviating the technical problem of existing technologies that cannot accurately distinguish the source-load characteristics of new energy power stations.

[0080] The basic principle of this invention is that even under drastic fluctuations in power grid frequency, the harmonic impedance of the power grid can still fully reflect its characteristics. Specifically, the source end exhibits a lower output impedance, and its impedance value remains stable across multiple harmonics, while the load end typically has higher impedance characteristics and varies significantly across different frequencies. This invention provides reliable bidirectional source-load identification under unstable frequency conditions, improving the accuracy and reliability of fault isolation devices.

[0081] The method provided by this invention can effectively improve the fault resolution capability of new energy power plants after they are connected to the power grid, and ensure the safe and stable operation of the power grid.

[0082] Example 2

[0083] Based on the above-described solution of the present invention, the solution of the present invention will be described in detail below with three specific embodiments.

[0084] Implementation method 1:

[0085] This embodiment selects a relatively stable state of the photovoltaic power station simulation system.

[0086] (1) Install a fault disconnection strategy station (i.e., fault disconnection strategy station device) at the terminal substation and a fault disconnection acquisition station (i.e., fault disconnection acquisition station device) at the photovoltaic power station. The strategy station sends the line trip status to the acquisition station, and the acquisition station sends the photovoltaic power station source and load status to the strategy station.

[0087] (2) The data acquisition station samples the voltage and current data at 48 points per cycle within a set time interval, and performs discrete Fourier transform recursive calculation on the sampled values. The expression is as follows:

[0088]

[0089] Among them, A ci (k) represents the real part of the i-th harmonic phasor of the voltage and current data sampling, A si (k) represents the imaginary part of the i-th harmonic phasor of the voltage and current data sampling.

[0090] Furthermore, the current system frequency is calculated using the rate of change of the fundamental positive-sequence voltage. The frequency calculation formula is as follows:

[0091]

[0092] Where f(k) is the current frequency of the system with the fundamental positive sequence voltage.

[0093] In this embodiment, the system frequency is 49.6 Hz.

[0094] (3) The fundamental power of the three-phase voltage and current samples is calculated recursively based on the discrete Fourier transform, as shown in the following formula:

[0095] P a0 (k)=U as0 (k)*I as0 (k)+U ac0 (k)*I ac0 (k);

[0096] Pb0(k)=Ub s0 (k)*Ib s0 (k)+Ub c0 (k)*Ib c0 (k);

[0097] P c0 (k)=U cs0 (k)*I cs0 (k)+U cc0 (k)*I cc0 (k);

[0098] Among them, P a0 (k), P b0 (k), P c0 (k) represents the power sampled from the fundamental three phases, U ac0 (k), U bc0 (k), U cc0 (k), I ac0 (k), I bc0 (k), I cc0 (k) represents the real phasor parts of the fundamental three-phase voltage and the three-phase current, respectively. as0 (k), U bs0 (k), U cs0 (k), I as0 (k), I bs0 (k), I cs0 (k) represents the imaginary phasor parts of the fundamental three-phase voltage and the three-phase current, respectively.

[0099] Calculations show that the fundamental power of phase A is -5.35MW, the fundamental power of phase B is -5.14MW, and the fundamental power of phase C is -4.97MW, all of which are less than 0. This indicates that the photovoltaic power station is at the source end at this time.

[0100] (4) The data acquisition station transmits the current source-end discrimination result of the photovoltaic power station to the strategy station, and the strategy station selects the corresponding source-end control strategy according to the discrimination result.

[0101] Implementation Method 2:

[0102] This embodiment selects the state where the photovoltaic power station simulation system experiences frequency oscillations.

[0103] (1) Install a fault disconnection strategy station at the terminal substation and a fault disconnection acquisition station at the photovoltaic power station. The strategy station sends the line tripping status to the acquisition station, and the acquisition station sends the photovoltaic power station source and load status to the strategy station.

[0104] (2) The data acquisition station samples the voltage and current data at 48 points per cycle within a set time interval, and performs discrete Fourier transform recursive calculation on the sampled values. The expression is as follows:

[0105]

[0106] Among them, A ci (k) represents the real part of the i-th harmonic phasor of the voltage and current data sampling, A si (k) represents the imaginary part of the i-th harmonic phasor of the voltage and current data sampling.

[0107] Furthermore, the current system frequency is calculated using the rate of change of the fundamental positive-sequence voltage. The frequency calculation formula is as follows:

[0108]

[0109] Where f(k) is the current frequency of the system with the fundamental positive sequence voltage.

[0110] In this embodiment, the system frequency fluctuates between 35Hz and 65Hz.

[0111] (3) The fundamental power of the three-phase voltage and current samples is calculated recursively based on the discrete Fourier transform, as shown in the following formula:

[0112] P a0 (k)=U as0 (k)*I as0 (k)+U ac0 (k)*I ac0 (k);

[0113] Pb0(k)=Ub s0 (k)*Ib s0 (k)+Ub c0 (k)*Ib c0 (k);

[0114] P c0 (k)=U cs0 (k)*I cs0 (k)+U cc0 (k)*I cc0 (k);

[0115] Among them, P a0 (k), P b0 (k), P c0 (k) represents the power sampled from the fundamental three phases, U ac0 (k), U bc0 (k), U cc0 (k), I ac0 (k), I bc0 (k), I cc0 (k) represents the real phasor parts of the fundamental three-phase voltage and the three-phase current, respectively. as0 (k), U bs0 (k), U cs0 (k), I as0 (k), I bs0 (k), I cs0 (k) represents the imaginary phasor parts of the fundamental three-phase voltage and the three-phase current, respectively.

[0116] Calculations show that the fundamental power of phase A fluctuates between -4.31MW and 2.76MW, the fundamental power of phase B fluctuates between -4.21MW and 2.36MW, and the fundamental power of phase C fluctuates between -4.65MW and 2.23MW, making it impossible to determine the source-load status of the photovoltaic power station.

[0117] (4) Based on the inverter load values ​​and characteristics of the photovoltaic power station simulation system, the harmonic impedance threshold is set to 50Ω.

[0118] The sampled harmonic positive-sequence impedance is calculated recursively using the discrete Fourier transform step, as shown in the following formula:

[0119]

[0120] Where i is the order of the harmonic, taking values ​​in the range [1, 50], U i (k), I i (k) represent the harmonic positive sequence voltage and current, respectively, Z i (k) Harmonic positive sequence impedance, Z pi (k) The sum of the impedances of the 1st to 50th harmonics at the current time.

[0121] The sum of the impedances of the 1st to 500th harmonics at the grid connection point is 16.31Ω, indicating that the photovoltaic power station is at the source end at this time.

[0122] (5) The data acquisition station transmits the current source-end discrimination result of the photovoltaic power station to the strategy station, and the strategy station selects the source-end control strategy based on the discrimination result.

[0123] Implementation Method 3:

[0124] This implementation example selects the state where the photovoltaic power station simulation system experiences frequency oscillations.

[0125] (1) Install a fault disconnection strategy station at the terminal substation and a fault disconnection acquisition station at the photovoltaic power station. The strategy station sends the line tripping status to the acquisition station, and the acquisition station sends the photovoltaic power station source and load status to the strategy station.

[0126] (2) The data acquisition station samples the voltage and current data at 48 points per cycle within a set time interval, and performs discrete Fourier transform recursive calculation on the sampled values. The expression is as follows:

[0127]

[0128] Among them, A ci (k) represents the real part of the i-th harmonic phasor of the voltage and current data sampling, A si (k) represents the imaginary part of the i-th harmonic phasor of the voltage and current data sampling.

[0129] Furthermore, the current system frequency is calculated using the rate of change of the fundamental positive-sequence voltage. The frequency calculation formula is as follows:

[0130]

[0131] Where f(k) is the current frequency of the system with the fundamental positive sequence voltage.

[0132] In this embodiment, the system frequency fluctuates between 35Hz and 65Hz.

[0133] (3) The fundamental power of the three-phase voltage and current samples is calculated recursively based on the discrete Fourier transform, as shown in the following formula:

[0134] P a0 (k)=U as0 (k)*I as0 (k)+U ac0 (k)*I ac0 (k);

[0135] Pb0(k)=Ub s0 (k)*Ib s0 (k)+Ub c0 (k)*Ib c0 (k);

[0136] P c0 (k)=U cs0 (k)*I cs0 (k)+U cc0 (k)*I cc0 (k);

[0137] Among them, P a0 (k), P b0 (k), P c0 (k) represents the power sampled from the fundamental three phases, U ac0 (k), U bc0 (k), U cc0 (k), I ac0 (k), I bc0 (k), I cc0 (k) represents the real phasor parts of the fundamental three-phase voltage and the three-phase current, respectively. as0 (k), U bs0 (k), U cs0 (k), I as0 (k), I bs0 (k), I cs0 (k) represents the imaginary phasor parts of the fundamental three-phase voltage and the three-phase current, respectively.

[0138] Calculations show that the fundamental power of phase A fluctuates between -4.31MW and 2.76MW, the fundamental power of phase B fluctuates between -4.21MW and 2.36MW, and the fundamental power of phase C fluctuates between -4.65MW and 2.23MW, making it impossible to determine the source-load status of the photovoltaic power station.

[0139] At this point, the line tripped, and the current signal at the grid connection point contained high levels of 300Hz and 450Hz harmonics, with the 300Hz harmonic accounting for 3.58% and the 450Hz harmonic accounting for 1.73%. The voltage signal also contained high levels of 300Hz and 450Hz harmonics, with the 300Hz harmonic accounting for 0.69% and the 400Hz harmonic accounting for 0.36%.

[0140] Based on the inverter load values ​​and characteristics of the photovoltaic power station simulation system, the harmonic impedance difference threshold is set to 10Ω.

[0141] The sampled harmonic positive-sequence impedance is calculated recursively using the discrete Fourier transform step, as shown in the following formula:

[0142]

[0143] Where i is the order of the harmonic, taking values ​​in the range [2, 50], U i (k), I i (k) represent the harmonic positive sequence voltage and current, respectively, Z i (k) Harmonic positive sequence impedance.

[0144] The 300Hz harmonic impedance at the grid connection point is 167.31Ω and the 450Hz harmonic impedance is 138.26Ω, indicating that the photovoltaic power station is at the load end at this time.

[0145] (4) The data acquisition station transmits the current load-side discrimination result of the photovoltaic power station to the strategy station, and the strategy station selects the load-side control strategy based on the discrimination result.

[0146] Example 3

[0147] Figure 3 This is a schematic diagram of a source-load bidirectional identification system for a fault routing device based on harmonic impedance according to an embodiment of the present invention. The system is applied to a fault routing acquisition station device installed in a new energy power station, and the fault routing acquisition station device is communicatively connected to a fault routing strategy station device installed in a terminal substation. Figure 3 As shown, the system includes: a data acquisition module 10, a calculation module 20, and a recognition module 30.

[0148] Specifically, the acquisition module 10 is used to acquire the sampled values ​​of the grid connection point voltage and current of the new energy power station;

[0149] Calculation module 20 is used to calculate the fundamental frequency of the new energy power station based on the sampled voltage and current values ​​at the grid connection point;

[0150] The recognition module 30 is used for:

[0151] Determine whether the fundamental frequency is within the preset fundamental frequency range;

[0152] If so, calculate the fundamental power of the voltage and current samples at the grid connection point, and identify the source-load status of the new energy power station based on the fundamental power and power direction criteria;

[0153] If not, calculate the harmonic impedance modulus of the voltage and current samples at the grid connection point, and determine whether a line trip signal has been received from the fault disconnection strategy station device.

[0154] If no line trip signal is received, the source and load status of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance criteria.

[0155] If a line trip signal is received, the source and load status of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance difference criteria.

[0156] Specifically, the calculation module 20 is also used for:

[0157] The real part and imaginary part of the harmonic vector of the sampled voltage and current at the grid connection point are obtained by performing discrete Fourier transform recursive calculation on the sampled voltage and current.

[0158] Calculate the fundamental positive-sequence voltage based on the real part and imaginary part of the harmonic vector.

[0159] The fundamental frequency of a new energy power station is calculated based on the angular change rate of the fundamental positive sequence voltage.

[0160] This invention also provides an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method described in Embodiment 1 above.

[0161] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0162] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A bidirectional source-load identification method for a fault disconnection device based on harmonic impedance, characterized in that, A fault-clearing data acquisition station device is applied to a new energy power station, wherein the fault-clearing data acquisition station device is communicatively connected to a fault-clearing strategy station device installed in a terminal substation; the method includes: Obtain the grid connection point voltage and current sampling values ​​of the new energy power station; Based on the sampled voltage and current values ​​at the grid connection point, the fundamental frequency of the new energy power station is calculated; Determine whether the fundamental frequency is within the preset fundamental frequency range; If so, calculate the fundamental power of the sampled voltage and current values ​​at the grid connection point, and identify the source-load status of the new energy power station based on the fundamental power and power direction criteria; If not, calculate the harmonic impedance modulus of the voltage and current sampled values ​​at the grid connection point, and determine whether a line trip signal sent by the fault disconnection strategy station device has been received. If the line trip signal is not received, the source-load status of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance criterion. If the line trip signal is received, the source-load status of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance difference criterion.

2. The method according to claim 1, characterized in that: Based on the sampled voltage and current values ​​at the grid connection point, the fundamental frequency of the new energy power station is calculated, including: The sampled voltage and current values ​​at the grid connection point are recursively calculated using discrete Fourier transform to obtain the real part of the harmonic vector and the imaginary part of the harmonic vector of the sampled values. The fundamental positive sequence voltage is calculated based on the real part and the imaginary part of the harmonic vector. The fundamental frequency of the new energy power station is calculated based on the angular change rate of the fundamental positive sequence voltage.

3. The method according to claim 1, characterized in that: The preset fundamental frequency range includes the maximum frequency stability limit range of the large power grid.

4. The method according to claim 1, characterized in that: The fundamental power of the grid connection point voltage and current sampling values ​​includes: P a0 (k)=U as0 (k)*I as0 (k)+U ac0 (k)*I ac0 (k); P b0 (k)=U bs0 (k)*I bs0 (k)+U bc0 (k)*I bc0 (k); P c0 (k)=U cs0 (k)*I cs0 (k)+U cc0 (k)*I cc0 (k); Among them, P a0 (k), P b0 (k), P c0 (k) represents the fundamental power of the three-phase fundamental sampling, U ac0 (k), U bc0 (k), U cc0 (k) represent the real phasor parts of the fundamental three-phase voltage, I ac0 (k), I bc0 (k), I cc0 (k) represents the real phasor part of the fundamental three-phase current, U as0 (k), U bs0 (k), U cs0 (k) represent the imaginary phasor parts of the fundamental three-phase voltage, I as0 (k), I bs0 (k), I cs0 (k) represents the imaginary phasor part of the fundamental three-phase current; Identifying the source-load status of the renewable energy power station based on the fundamental power and power direction criteria includes: When P is satisfied a0 (k), P b0 (k), P c0 When at least two of (k) are less than 0, the new energy power station is a source end; When P is satisfied a0 (k), P b0 (k), P c0 When at least two of (k) are greater than or equal to 0, the new energy power station is the load end.

5. The method according to claim 1, characterized in that: The harmonic impedance magnitude includes the sum of the positive-sequence harmonic impedance and the higher harmonic impedances; wherein, The harmonic positive sequence impedance includes: The sum of the multiple harmonic impedances includes: Where i is the harmonic order, U i (k), I i (k) represent the harmonic positive sequence voltage and current, respectively, Z i (k) is the harmonic positive sequence impedance, Z pi (k) represents the sum of multiple consecutive harmonic impedances at the current moment.

6. The method according to claim 5, characterized in that: Identifying the source-load status of the new energy power station based on the harmonic impedance modulus and harmonic impedance criterion includes: When Z pi (k)≥Z set At that time, the new energy power station is the source end; When Z pi (k)<Z set At that time, the new energy power station is the load end; Among them, Z set This is the preset impedance threshold.

7. The method according to claim 5, characterized in that: Identifying the source-load status of the new energy power station based on the harmonic impedance modulus and harmonic impedance difference criterion includes: If Z max (k)-Zsub(k)<Z difset Then the new energy power station is the source end; If Z max (k)-Zsub(k)≥Z difset Then the new energy power station is the load end; Among them, Z max (k) is the maximum harmonic impedance in the positive sequence impedance of multiple harmonics, Z sub (k) represents the second largest harmonic impedance in the positive sequence impedance of multiple harmonics, Z difset This is a preset impedance difference threshold.

8. The method according to claim 1, characterized in that: The method further includes: sending the source-load status of the new energy power station to the fault-disconnection strategy station device, so that the fault-disconnection strategy station device can determine the target source-load control strategy based on the source-load status.

9. A source-load bidirectional identification system for a fault disconnection device based on harmonic impedance, characterized in that, A fault-clearing data acquisition station device is applied to a new energy power plant, and the fault-clearing data acquisition station device is communicatively connected to a fault-clearing strategy station device installed in a terminal substation; the system includes: a data acquisition module, a calculation module, and an identification module; wherein, The acquisition module is used to acquire the grid connection point voltage and current sampling values ​​of the new energy power station; The calculation module is used to calculate the fundamental frequency of the new energy power station based on the sampled voltage and current values ​​at the grid connection point. The identification module is used for: Determine whether the fundamental frequency is within the preset fundamental frequency range; If so, calculate the fundamental power of the sampled voltage and current values ​​at the grid connection point, and identify the source-load status of the new energy power station based on the fundamental power and power direction criteria; If not, calculate the harmonic impedance modulus of the voltage and current sampled values ​​at the grid connection point, and determine whether a line trip signal sent by the fault disconnection strategy station device has been received. If the line trip signal is not received, the source-load status of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance criterion. If the line trip signal is received, the source-load status of the new energy power station is identified based on the harmonic impedance modulus and harmonic impedance difference criterion.

10. An electronic device, characterized in that, include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as claimed in any one of claims 1-8.

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