Line current differential protection false information detection method based on delay observer

Abstract

The invention discloses a line current differential protection false information detection method based on a delay observer, and is applied to the technical field of line current differential protection. Comprising the following steps: establishing a distribution parameter model of the power transmission line, and discretizing the distribution parameter model to obtain a discrete model of the power transmission line; constructing a delay observer based on the discrete model of the power transmission line, solving a parameter matrix of the delay observer, and estimating a negative sequence voltage predicted value at the current moment; reading a negative sequence voltage measured value at the current moment, and calculating an error between the negative sequence voltage predicted value and the negative sequence voltage measured value; and if the error is greater than a preset error threshold value, judging that the line current differential protection system is attacked by false information injection. According to the method, false information injection can be effectively identified by monitoring the negative sequence voltage prediction error, and the reliability of current differential protection and the safe operation level of a power grid are improved.

Description

Technical Field

[0001] This invention relates to the field of line current differential protection technology, and more specifically to a method for detecting false information in line current differential protection based on a delay observer. Background Technology

[0002] The power system is a fundamental engineering project of the energy system. In recent years, power monitoring systems have become a major battleground for national and regional security competition. Although the network security of power monitoring systems has made significant progress and is effectively guaranteed, in the field of relay protection, the instability and vulnerability of information control units can still affect the safe and reliable operation of the power physical system. Among these, differential current protection, due to its high reliability, has become the main protection scheme for the main grid connection lines of various new energy power plants in the context of new power system construction. However, the transmission of line current differential protection signals usually relies on communication networks, thus heavily depending on wide area network systems and clock systems. Furthermore, it is difficult to implement corresponding encryption measures in line protection, which may make the signal transmission of microprocessor-based protection devices susceptible to network attacks. This can lead to false tripping signals from relay protection equipment, causing circuit breaker malfunctions and threatening the safe and stable operation of the power grid. Correctly identifying such malicious attack signals has become a key measure to ensure the safe and stable operation of power monitoring systems. Therefore, how to provide a method for detecting false information in line current differential protection based on delay observers is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0003] In view of this, the present invention provides a method for detecting false information in line current differential protection based on a delay observer, which solves the problem of protection maloperation or failure to operate caused by communication data tampering in the prior art, and improves the reliability of power grid operation.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for detecting false information in line current differential protection based on a delay observer includes the following steps: S1: Establish a distributed parameter model for the transmission line, and discretize the distributed parameter model to obtain a discrete model of the transmission line; S2, Set Delay δ A delay observer is constructed based on a discrete model of the transmission line. The delay observer is based on... k - δ Time to k System state measurement estimation within time t. k - δ The predicted system state at time +1; S3. Solve for the parameter matrix of the delayed observer and estimate the predicted negative sequence voltage value at the current time based on the delayed observer; S4. Read the current negative sequence voltage measurement value and calculate the error between the negative sequence voltage prediction value and the negative sequence voltage measurement value; S5. If the error between the predicted negative sequence voltage value and the measured negative sequence voltage value is greater than the preset error threshold, it is determined that the line current differential protection system has been subjected to a false information injection attack.

[0005] Optionally, S1 is as follows: Establish a distributed parameter model for the transmission line: ; Discretizing the distributed parameter model yields a discrete model of the transmission line: ; ; ; In the formula, Given the differential matrix of the input for the continuous line model, , This is the state parameter matrix of the continuous line model. Given the known input matrix of the line continuity model, For the unknown input matrix of the line continuity model, and Given the known input matrix of the discrete line model, , This is the state parameter matrix of the discrete model of the line. For the unknown input matrix of the discrete model of the line, The sampling frequency.

[0006] Optionally, S2 is as follows: Define the measured output of the system, and obtain the output equation: ; Using the discrete model of the transmission line as the input equation of the system, the basic structure of the delay observer is defined: ; ; In the formula, This is the output matrix of the discrete model of the line. , The parameter matrix of the discrete output equation of the line. for k The input sample value matrix is ​​known at time +1. for k The estimated matrix of the input is known at time +1. for k to k + δ The output parameter matrix equation at time t, , Here is the parameter matrix of the state observer. , , , k to k + δ The output parameter column vector at time t.

[0007] Optionally, the parameter matrix for solving the delayed observer in S3 is as follows: Define matrices Θ and Γ: ; ; Define matrix Φ as: ; Given inequality constraints: ; ; Define constants α ∈(0,1), μ >0, P It is a positive definite symmetric matrix. I It is the identity matrix. Z , H To accommodate the matrix to be solved in terms of the dimension of the matrix inequality, we find a corresponding matrix that simultaneously satisfies the constraints, thus obtaining... L = P -1 Z and Q = L - A n Θ.

[0008] Optionally, in S3, the predicted negative sequence voltage value at the current time is estimated based on the delayed observer as follows: ; The negative sequence voltage value at each moment can be calculated using the following formula: ; Let be the negative sequence voltage value at time t. , , These are the positive sequence voltage values ​​of phases a, b, and c at the corresponding times. Sampling frequency, This is the fundamental frequency of the power transmission system.

[0009] Optionally, the preset error threshold in S5 is 20%.

[0010] As can be seen from the above technical solutions, compared with the prior art, the present invention provides a method for detecting false information in line current differential protection based on a delay observer, which has the following beneficial effects: The present invention constructs a delay state observer through a line distributed parameter model, which can effectively identify false information injection by monitoring the negative sequence voltage prediction error, thereby improving the reliability of current differential protection and the level of safe operation of the power grid. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0012] Figure 1 This is a flowchart of the method for detecting false information in line current differential protection according to the present invention; Figure 2 This is a schematic diagram showing the location of the line current differential protection device of the present invention; Figure 3 This is a differential characteristic curve diagram of the present invention; Figure 4 This is a schematic diagram of the transmission line model of the present invention; Figure 5 This is a differential curve diagram of the transmission line model AB under phase-to-phase fault according to the present invention; Figure 6 This is a differential curve diagram of the present invention when false information injection occurs at a=2; Figure 7 This is a differential curve diagram of the present invention when false information injection occurs at a=3; Figure 8 This is a differential curve diagram of the present invention when false information injection occurs at a=4; Figure 9 This is a differential curve diagram of the present invention when false information injection occurs at a=5; Figure 10 This is a schematic diagram of a power transmission line model during a short-circuit fault, as described in this invention. Figure 11 This is a schematic diagram of the positive sequence voltage during a normal AB phase-to-phase fault according to the present invention; Figure 12 This is a schematic diagram of the negative sequence voltage during a normal AB phase-to-phase fault according to the present invention; Figure 13 This is a schematic diagram of the positive sequence voltage during the injection of false information according to the present invention; Figure 14 This is a schematic diagram of the negative sequence voltage during the injection of false information in this invention. Detailed Implementation

[0013] 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] This invention discloses a method for detecting false information in line current differential protection based on a delay observer, such as... Figure 1 As shown, it includes the following steps: S1: Establish a distributed parameter model for the transmission line, and discretize the distributed parameter model to obtain a discrete model of the transmission line; S2, Set Delay δ A delay observer is constructed based on a discrete model of the transmission line. The delay observer is based on... k - δ Time to k System state measurement estimation within time t. k - δ The predicted system state at time +1; S3. Solve for the parameter matrix of the delayed observer and estimate the predicted negative sequence voltage value at the current time based on the delayed observer; S4. Read the current negative sequence voltage measurement value and calculate the error between the negative sequence voltage prediction value and the negative sequence voltage measurement value; S5. If the error between the predicted negative sequence voltage value and the measured negative sequence voltage value is greater than the preset error threshold, it is determined that the line current differential protection system has been subjected to a false information injection attack.

[0015] The specific mechanisms by which misinformation works are as follows: Figure 2 As shown, the line current differential protection devices are located on both sides of the line. The collected current signals are transmitted to the other end via optical fiber. Taking T1 as an example, since both the measuring device and the protection device are deployed in the substation, the voltage and current signals measured at this end can be considered reliable. That is, after intruding into the power monitoring system, only the data at the other end can be tampered with. In actual lines, the protection device usually samples the current at 5kHz or 6.6kHz and determines whether a line fault has occurred based on the set parameter values. The mainstream differential protection device mainly relies on the differential characteristic curve to determine the fault, such as... Figure 3 As shown. Among them. I diff Indicates differential current. Ires It represents the suppression of current, which is defined as: ; ; In the formula, and They represent k The current sample value at time t, when it satisfies When the line differential protection enters the operating zone, the line differential protection operates. for I res The function is defined as: ; In the formula, , , These are all line differential protection setting values. Attackers can cause line protection to malfunction by tampering with remote data.

[0016] Furthermore, S1 specifically refers to: Establish a distributed parameter model for the transmission line: ; Discretizing the distributed parameter model yields a discrete model of the transmission line: ; ; ; In the formula, Given the differential matrix of the input for the continuous line model, , This is the state parameter matrix of the continuous line model. Given the known input matrix of the line continuity model, For the unknown input matrix of the line continuity model, and Given the known input matrix of the discrete line model, , This is the state parameter matrix of the discrete model of the line. For the unknown input matrix of the discrete model of the line, The sampling frequency.

[0017] In this embodiment of the invention, a power transmission line model is constructed, such as... Figure 4As shown in the figure, the line represents a 10kV line, connected to the system on the left and containing the electrical load and distributed photovoltaic power station on the right. Kx represents the circuit breaker and protection device, and IBDG represents the distributed photovoltaic power station. The transmission line is represented by a pi-type circuit. The total length of the line is 2350m. The power flow parameters of the power system on the left are: P=14.41MW, Q=7.58MVar, U=10.14kV. The cumulative load power is: P=15.3MW, Q=7.48MVar. The photovoltaic power station feedback power is: P=2.64MW, Q=0.14MVar. The positive sequence and zero sequence parameters of the line are shown in Table 1, where Xl is the reactance per unit length of the line and Xc is the capacitive reactance per unit length of the line. Table 1. Positive and Zero Sequence Parameters of the Line

[0018] The normal fault is set as follows: a two-phase short circuit occurs at a distance of x=20m from the m side of the line, and the differential current signal can be obtained as follows. Figure 5 As shown, within each current cycle, I diff Almost all located in I op Above, the line protection is operating normally. The line attack method is set as follows: starting from 0.3s, the attacker modifies the remote current signal i2 to a·i2. Taking a=2, 3, 4, and 5 respectively, the differential current signal is obtained as follows: Figures 6-9 As shown. It can be seen that when a≤4, I diff Almost all of them are located in I op Below, therefore the differential protection does not operate. When a>4, the differential protection will malfunction.

[0019] The positive and negative sequence model of the transmission line established in this embodiment can Figure 10 It is stated that the total length of the transmission line is l x represents the distance from the fault location k to the line end m, and L, R, and C represent the reactance, resistance, and capacitive reactance per unit distance of the line, respectively. The protection devices on both sides of the line are connected via optical fiber. m (t), u n (t), i m (t), i n (t) represents the voltage and current measured on both sides of the line, u k (t) represents the fault point voltage, i f (t) represents the fault current. Based on this, the differential equation of the line can be obtained: ; Since the sampling voltage, sampling current, and other signals are all discrete values, the above formula is defined as the distributed parameter model of the transmission line. .

[0020] Furthermore, S2 specifically refers to: Define the measured output of the system, and obtain the output equation: ; Using the discrete model of the transmission line as the input equation of the system, the basic structure of the delay observer is defined: ; ; In the formula, This is the output matrix of the discrete model of the line. , The parameter matrix of the discrete output equation of the line. for k The input sample value matrix is ​​known at time +1. for k The estimated matrix of the input is known at time +1. for k to k + δ The output parameter matrix equation at time t, , Here is the parameter matrix of the state observer. , , , k to k + δ The output parameter column vector at each time step. In this embodiment, we select... δ =2.

[0021] In this embodiment of the invention, the current sampling value is set as the target of attack in the circuit model. Therefore, the voltage across m and n is selected as the output quantity, resulting in the output equation: ; Its standard form is .

[0022] Furthermore, the parameter matrix for solving the delayed observer in S3 is as follows: Define matrices Θ and Γ: ; ; Define matrix Φ as: ; Given inequality constraints: ; ; Define constants α ∈(0,1), μ >0, P It is a positive definite symmetric matrix. I It is the identity matrix. Z , H To accommodate the matrix to be solved in terms of the dimension of the matrix inequality, we find a corresponding matrix that simultaneously satisfies the constraints, thus obtaining... L = P -1 Z and Q = L - A n Θ.

[0023] Furthermore, in S3, the estimation of the current negative sequence voltage prediction value based on the delayed observer is specifically as follows: ; The negative sequence voltage value at each moment can be calculated using the following formula: ; Let be the negative sequence voltage value at time t. , , These are the positive sequence voltage values ​​of phases a, b, and c at the corresponding times. Sampling frequency, This is the fundamental frequency of the power transmission system.

[0024] In this embodiment of the invention, the parameter matrix when an A / B phase-to-A circuit occurs at a distance of 20m from the m side is: ; ; Using the SDPT3 solution method, a priority fixation method is adopted. α The solution method for the value involves solving inequality constraints, constructing a delayed observer, and obtaining the measurement and prediction results of the positive and negative sequence voltages on the m-side through iterative calculations. Figure 11-14 As shown, where Figure 11 , Figure 12 These are the predicted positive and negative sequence voltage values ​​under the condition of phase-to-phase fault (AB). Figure 13 , Figure 14 These are the predicted values ​​of positive and negative sequence voltages under false information intrusion conditions. It can be seen that under both normal fault conditions and false information intrusion, the predicted positive-sequence voltage values ​​are highly consistent with the actual observed values. Under normal fault conditions, the predicted negative-sequence voltage values ​​are also highly consistent with the actual observed values. However, under false information intrusion, the predicted negative-sequence voltage values ​​show a significant error compared to the actual observed values. Calculations show that the accuracy error of the negative-sequence voltage prediction only exceeds 20% under false information intrusion conditions; the accuracy in other cases remains within 20%. Therefore, the accuracy of the negative-sequence voltage prediction over a certain period can be used to determine whether false information injection has occurred.

[0025] Furthermore, the preset error threshold in S5 is 20%.

[0026] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0027] Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting false information of line current differential protection based on delay observer, characterized in that, Includes the following steps: S1: Establish a distributed parameter model for the transmission line, and discretize the distributed parameter model to obtain a discrete model of the transmission line; S2, set delay δ , construct a delay observer based on a discrete model of the power transmission line, the delay observer estimating k - δ the system state measurement value from the time instant k to the time instant k - δ the system state prediction value at the time instant +1; S3. Solve for the parameter matrix of the delayed observer and estimate the predicted negative sequence voltage value at the current time based on the delayed observer; S4. Read the current negative sequence voltage measurement value and calculate the error between the negative sequence voltage prediction value and the negative sequence voltage measurement value; S5. If the error between the predicted negative sequence voltage value and the measured negative sequence voltage value is greater than the preset error threshold, it is determined that the line current differential protection system has been subjected to a false information injection attack.

2. The method of claim 1, wherein the method further comprises: S1 specifically refers to: Establish a distributed parameter model for the transmission line: ； Discretizing the distributed parameter model yields a discrete model of the transmission line: ； ； ； wherein is the differential matrix of the known inputs for the continuous model of the line, , is the state parameter matrix of the continuous model of the line, is the known input matrix of the continuous model of the line, is the unknown input matrix of the continuous model of the line, and is the known input matrix of the discrete model of the line, , is the state parameter matrix of the discrete model of the line, is the unknown input matrix of the discrete model of the line, is the sampling frequency.

3. The method of claim 1, wherein the method further comprises: S2 specifically refers to: Define the measured output of the system, and obtain the output equation: ； Using the discrete model of the transmission line as the input equation of the system, the basic structure of the delay observer is defined: ； ； wherein is the output matrix of the line discrete model, , is the parameter matrix of the line discrete output equation, is the k is the matrix of the sampled values of the known inputs at time is the k is the matrix of the estimated values of the known inputs at time is the k to k + δ is the output parameter matrix equation at time , is the parameter matrix of the state observer, , , , k to k + δ is the output parameter column vector at time 4. The method for detecting false information in line current differential protection based on a delay observer according to claim 1, characterized in that, The parameter matrix for solving the delayed observer in S3 is as follows: Define matrices Θ and Γ: ； ； Define matrix Φ as: ； Given inequality constraints: ； ； Define constants α ∈(0,1), μ >0, P It is a positive definite symmetric matrix. I It is the identity matrix. Z , H To accommodate the matrix to be solved in terms of the dimension of the matrix inequality, we find a corresponding matrix that simultaneously satisfies the constraints, thus obtaining... L = P -1 Z and Q = L - A n Θ.

5. The method for detecting false information in line current differential protection based on a delay observer according to claim 1, characterized in that, In S3, the estimation of the current negative sequence voltage prediction value based on the delayed observer is as follows: ； The negative sequence voltage value at each moment can be calculated using the following formula: ； Let be the negative sequence voltage value at time t. , , These are the positive sequence voltage values ​​of phases a, b, and c at the corresponding times. Sampling frequency, This is the fundamental frequency of the power transmission system.

6. The method for detecting false information in line current differential protection based on a delay observer according to claim 1, characterized in that, The preset error threshold in S5 is 20%.

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