A power grid harmonic detection method, system and computer device

Abstract

The application discloses a kind of power grid harmonic detection method, system and computer equipment, it is related to harmonic detection technical field, including the following steps: using improved phase-locked loop for accurate phase locking, then using adaptive algorithm LMS replaces the second-order low-pass filter in harmonic detection method based on instantaneous reactive power, by optimizing phase-locked loop parameter and introducing time optimal control strategy, it can quickly and accurately track power grid frequency and phase, to realize accurate phase locking and frequency compensation.In addition, the application then uses improved adaptive algorithm to accurately estimate fundamental content by adjusting step size and weight in real time, since LMS algorithm is strong and can quickly converge, therefore, harmonic component can be more accurately detected.

Description

Technical Field

[0001] This invention relates to the field of harmonic detection technology, and in particular to a method, system and computer device for detecting harmonics in a power grid. Background Technology

[0002] Due to the randomness and intermittency of new energy power generation, the low damping and abrupt changes of inertia, the nonlinearity and speed of power electronic converter links, as well as low base load during the day and large-scale backfeeding, prominent power quality problems such as overvoltage at the end of the active distribution network, three-phase imbalance, high harmonic content, electromagnetic resonance, system oscillation, voltage sag, and voltage rise are caused.

[0003] The application of a high proportion of power electronic devices in active power distribution networks greatly increases the nonlinearity of the system, making harmonic problems and the resulting synchronization problems particularly prominent. The accuracy and real-time performance of harmonic detection have become difficult issues for power quality optimization.

[0004] Accurate and rapid detection of harmonic content in the original waveform is crucial for achieving an efficient compensation system. Especially when multiple active filters work in tandem, only by accurately detecting the content of individual harmonics can a reasonable coordinated control strategy for total harmonic compensation be formulated. Therefore, accurate detection of harmonic content becomes the foundation and key to achieving power quality adjustment and control.

[0005] Harmonic detection methods are mainly divided into two categories: frequency domain and time domain. Frequency domain analysis methods, represented by Fourier transform and fast Fourier transform, extract harmonic components by converting the signal from the time domain to the frequency domain. However, these frequency domain methods have limitations when dealing with non-periodic or transient signals, such as high computational complexity, poor real-time performance, and unsuitability for real-time monitoring of harmonics under dynamically changing conditions. Time domain analysis methods detect harmonics by directly analyzing the instantaneous properties of the power signal in the time domain. Among them, instantaneous reactive power theory is a widely used time domain method. It can effectively detect and separate harmonic components when the three-phase voltage is balanced and distortion-free. However, when the power grid conditions are not ideal, the detection accuracy of pq theory will be affected, leading to errors in the detection results. In scenarios where multiple active filters work together, the limitations of these harmonic detection methods may be further amplified. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a method, system, and computer device for detecting harmonics in power grids, thereby solving the problem that the detection accuracy of pq theory in the prior art is affected, leading to errors in the detection results.

[0007] This invention specifically provides the following technical solution: a method for detecting harmonics in a power grid, comprising the following steps:

[0008] A third-order generalized integral phase-locked loop is set up using instantaneous reactive power theory, and the same sine and cosine signals as phase a voltage in the new energy power grid system are obtained through the third-order generalized integral phase-locked loop.

[0009] The instantaneous active current i is extracted by performing coordinate transformation on the three-phase current of the load using the aforementioned sine and cosine signals. p and instantaneous reactive current i q ;

[0010] The instantaneous active current i is analyzed using an adaptive filter LMS. p and instantaneous reactive current i q Processing to obtain the DC component And through the DC component Calculate the fundamental component i af i bf i cf and harmonic components i ah i bh i ch .

[0011] Preferably, before setting up the third-order generalized integral phase-locked loop using instantaneous reactive power theory, the three-phase current passing through the load under ideal conditions is obtained, specifically expressed as follows:

[0012]

[0013] Among them, I n This is the effective value of the phase current. This is the initial phase.

[0014] Preferably, the step of using the sine and cosine signals to perform coordinate transformation on the load current and extract the instantaneous active current i is... p and instantaneous reactive current i q The specific expression is:

[0015]

[0016] The coordinate transformation uses the dq transformation to convert the load current variables in the three-phase coordinate system to the dq coordinate system, where the d-axis represents the active component, the q-axis represents the reactive component, and i... α and i β Let i represent the final current components in the dq coordinate system. α and i β These are the current components after the three-phase current has undergone dq transformation.

[0017] After optimization, the detection uses instantaneous reactive power theory to set up a third-order generalized integral phase-locked loop, including the following steps:

[0018] If the voltage input signal contains a DC component, then the input signal is:

[0019]

[0020] Where A0 is the amplitude of the DC component, A1 is the amplitude of the AC component, and ω0 represents the fundamental grid frequency. For phase

[0021] The reconstructed TOGI integrator is obtained through the input signal, and its output expression is:

[0022]

[0023] Where k is the coefficient k in the TOGI integrator, u1(t) and u2(t)-u3(t) are orthogonal terms, neither of which contains a DC component, and u1(t) and u2(t)-u3(t) have the same amplitude, while u2(t)-u3(t) lags by 90° in phase;

[0024] The reconstructed TOGI integrator eliminates the DC component of the input, obtaining a quadrature output signal, as specifically expressed by:

[0025]

[0026] Among them, u M qu M The filtered quadrature signals are u1, u2, and u3, which are the three components output by the TOGI integrator. M qu M The voltage components obtained after passing through the TOGI integrator are U M (s) and qU M (s);

[0027] Due to U(s) to U M The closed-loop transfer function of U(s) is D(s), and the transfer function of U(s) to qU is... M If the closed-loop transfer function of D(s) is Q(s), then the specific expressions for the closed-loop transfer function D(s) and the closed-loop transfer function Q(s) are as follows:

[0028]

[0029] In the control system, s represents the complex variable of the transfer function, and U(s) is the input voltage;

[0030] Design a third-order generalized integral phase-locked loop using the closed-loop transfer function D(s) and the closed-loop transfer function Q(s);

[0031] An adaptive frequency-locking loop is introduced into the TOGI structure. After introducing the adaptive frequency-locking loop, the transfer functions are as follows:

[0032]

[0033] Where D′(s) and Q′(s) are the transfer functions of D(s) and Q(s) after the introduction of an adaptive frequency-locking loop, respectively;

[0034] Design a third-order generalized integral phase-locked loop with frequency locking using the aforementioned D′(s) and Q′(s).

[0035] Preferably, the use of an adaptive filter LMS for the instantaneous active current i p and instantaneous reactive current i q The process includes the following steps:

[0036] The steepest descent method is used to determine the optimal weights in the adaptive filter LMS, and the specific expression is as follows:

[0037]

[0038] Where w(t), μ and These are the gradient vectors of the filter weight coefficients, the step size function, and the weight coefficients w(t), respectively.

[0039] The specific expression for obtaining the least mean square adaptive LMS iteration relationship is as follows:

[0040]

[0041] For instantaneous active current i p The DC component is extracted using a filter.

[0042]

[0043] Assuming the input x(t) is always 1, the specific expression for the LMS iterative relationship is:

[0044]

[0045] Where y(t) is the LMS prediction output of the adaptive filter, w T (t) represents the weighting coefficient, d(t) represents the expected output, and e(t) represents the error between the expected output and the actual output.

[0046] Preferably, through the DC component Calculate the fundamental component i af i bf i cf and harmonic components i ah i bh i ch The specific expression is:

[0047]

[0048]

[0049] Among them, C 23 It is the α-β inverse transformation matrix.

[0050] Preferably, obtaining the relationship between e(t) and the variable step size of the adaptive filter LMS, and optimizing the variable step size function of the adaptive filter LMS based on the inversion cosine function, includes the following steps:

[0051] The expression for the variable step size μ of the adaptive filter LMS is obtained from the Gaussian error function:

[0052] μ(t)=β·erf(1-e α·|e(t)| )

[0053] Where α and β are parameters that change the shape and magnitude of the function;

[0054] Multiplying the variable step size μ(t) by the inverted cosine function yields the optimized variable step size function μ. * (t);

[0055] μ * (t)=β·erf(1-e α·|e(t)| )·(1+γ·|e(t)|)

[0056] Here, γ is a coefficient that is responsible for adjusting the shape of the step size function.

[0057] Preferably, the specific expression of the Gaussian error function is:

[0058]

[0059] Here, erf(x) is the Gaussian error function.

[0060] Preferably, the present invention provides a harmonic detection system for a power grid, comprising:

[0061] The signal acquisition module is used to set up a third-order generalized integral phase-locked loop using instantaneous reactive power theory, and to acquire sine and cosine signals with the same voltage as phase a in the new energy power grid system through the third-order generalized integral phase-locked loop.

[0062] The current processing module is used to perform coordinate transformation on the three-phase current of the load using the sine and cosine signals to extract the instantaneous active current i. p and instantaneous reactive current i q ;

[0063] The harmonic detection module is used to detect the instantaneous active current i using an adaptive filter LMS. p and instantaneous reactive current i q Processing to obtain the DC component And through the DC component Calculate the fundamental component i af i bf i cf and harmonic components i ah i bh i ch .

[0064] Preferably, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method.

[0065] Compared with the prior art, the present invention has the following significant advantages:

[0066] This invention utilizes instantaneous reactive power theory to accurately measure the harmonic components of current and voltage, and can make relatively accurate estimates of non-integer harmonics. An improved third-order generalized integral phase-locked loop (PLL) is used to adapt to non-ideal power grid conditions for phase-locking, achieving faster tracking speed and enabling it to capture and track the frequency and phase changes of the input signal more quickly. By introducing an improved variable-step-size LMS algorithm to replace the low-pass filter, the system can more effectively reduce the impact of noise signals and frequency phase-locking disturbances, thereby achieving faster response speed and stronger anti-interference capability. Attached Figure Description

[0067] Figure 1 This is a block diagram of the harmonic detection method of the present invention;

[0068] Figure 2 This is a typical TOGI-OSG flowchart;

[0069] Figure 3 To improve the block diagram of the TOGI-PLL phase-locked loop;

[0070] Figure 4 The diagram shows the TOGI-based adaptive PLL; (a) is the front-end structure diagram, and (b) is the back-end structure diagram with FLL.

[0071] Figure 5 This is a diagram of the three-phase voltage under non-ideal conditions.

[0072] Figure 6 This is based on an improved TOGI-PL1 phase-locked diagram;

[0073] Figure 7Here is a block diagram of a typical LMS algorithm;

[0074] Figure 8 The graphs show the relationship between the step size and the error related to the error function; where (a) is the graph for α and (b) is the graph for β.

[0075] Figure 9 To improve the relationship between step size and error related to the error function;

[0076] Figure 10 A comparison chart of various adaptive algorithms (LMS) for harmonic detection;

[0077] Figure 11 The images are harmonic FFT analysis diagrams before and after the improved variable step size detection; where (a) is the harmonic FFT diagram after the improved variable step size detection, and (b) is the harmonic FFT diagram before the improved variable step size detection.

[0078] Figure 12 The graph shows the fundamental current and harmonic current based on the new harmonic current detection. Detailed Implementation

[0079] 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, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0080] This invention proposes a method, system, and computer equipment for harmonic detection in power grids, which can improve detection accuracy and meet real-time requirements. This will provide important support for the stable operation and efficient management of new power systems in active distribution networks, and promote the continuous improvement of power quality.

[0081] For ease of understanding and explanation, this invention provides a method for detecting harmonics in a power grid, comprising the following steps:

[0082] Step S1: Use the instantaneous reactive power theory to set up a third-order generalized integral phase-locked loop (PLL), and use the third-order generalized integral PLL to obtain the same sine and cosine signals as phase a voltage in the new energy power grid system.

[0083] Step S2: Use sine and cosine signals to perform coordinate transformation on the three-phase current of the load and extract the instantaneous active current i. p and instantaneous reactive current i q .

[0084] Step S3: Use an adaptive filter LMS to analyze the instantaneous active current i p and instantaneous reactive current i q Processing to obtain the DC component And through DC component Calculate the fundamental component i af i bf i cf and harmonic components i ah i bh i ch .

[0085] Specifically, the present invention is as follows:

[0086] Using instantaneous reactive power theory, a phase-locked loop is set up to obtain sinusoidal signals of phase a voltage in phase with phase a. Based on the above definition, the load current is subjected to coordinate transformation, followed by Clark and Park transformations, to extract i. p i q The DC component is obtained after passing through the LPF. Then, the fundamental component i can be calculated from this. af i bf i cf Furthermore, the harmonic component i can be obtained. ah i bh i ch .

[0087] A third-order generalized integral phase-locked loop (PLL) is used to replace the traditional PLL, and improvements are made to the third-order generalized integral PLL to address phase-locking under non-ideal power grid conditions.

[0088] An adaptive algorithm is used to replace the traditional low-pass filter (LPF), and the step size of the adaptive algorithm is improved.

[0089] The above method combines harmonic current detection based on instantaneous reactive power theory with improved phase-locked loop and adaptive harmonic current detection methods, retaining the traditional i p -i q The harmonic current detection method has the advantages of wide applicability and strong algorithm versatility. At the same time, it can effectively avoid the low accuracy caused by the phase-locked loop accuracy problem and the limitation of the low-pass filter on the performance of the harmonic detection algorithm, thus balancing the algorithm's response speed and detection accuracy.

[0090] To perform harmonic current detection, the ideal three-phase voltages are first given:

[0091]

[0092] The expression for three-phase current is:

[0093]

[0094] Where E1 is the effective value of the phase voltage, I n This represents the effective value of the three-phase current. This is the initial phase.

[0095] i p -i q The detection method is based on the instantaneous active current i p and instantaneous reactive current i q The detection algorithm is derived based on the premise of [the above].

[0096]

[0097] The coordinate transformation uses the dq transformation to convert the load current variable in the three-phase coordinate system to the dq coordinate system, where the d-axis represents the active component of the variable, the q-axis represents the reactive component of the variable, and i... p and i q Let i represent the final current components in the dq coordinate system. α and i β These are the current components after the three-phase current has undergone dq transformation.

[0098] i p i q After being filtered by a low-pass filter, its DC component satisfies equation (1-4). Thus, the fundamental current and harmonic current obtained after the load current is filtered satisfy equations (1-5) and (1-6), respectively.

[0099]

[0100]

[0101]

[0102] Due to the large-scale grid connection of new energy sources, and under non-ideal grid conditions, in order to avoid the impact of measured voltage waveform distortion and spikes on the accuracy of the detection system, the phase-locked loop (PLL) is improved to achieve accurate and real-time grid phase-locking.

[0103] The traditional phase-locked loop is replaced with a third-order generalized integral phase-locked loop:

[0104] like Figure 2 The typical closed-loop transfer function of the TOGI structure is shown in (1-7):

[0105]

[0106] In the formula, u and k represent the input signal and gain coefficient, respectively, and ω0 represents the fundamental grid frequency.

[0107] Assuming the voltage input signal contains a DC component, the input signal is:

[0108]

[0109] Where A0 is the amplitude of the DC component and A1 is the amplitude of the AC component. For phase.

[0110] The TOGI integrator output is:

[0111]

[0112] From equation (1-9), we know that k is the coefficient k in the TOGI integrator, the u1(t) and u2(t)-u3(t) terms are orthogonal terms, neither of which contains a DC component, and the amplitudes of u1(t) and u2(t)-u3(t) are the same, while the phase of u2(t)-u3(t) lags by 90°. Therefore, TOGI can eliminate the DC component of the input.

[0113] Therefore, as Figure 3 The reconstructed quadrature output signal of TOGI can be expressed as:

[0114]

[0115] Among them, u M qu M The filtered output is an orthogonal signal; u1, u2, and u3 are the three components obtained through TOGI-OSG, respectively. M qu M The voltage components obtained after passing through the TOGI integrator are U M (s) and qU M (s).

[0116] Due to U(s) to U M The closed-loop transfer function of U(s) is D(s), which has the same expression as G1(s), as shown in equation (1-7). (U(s) to qU) M The closed-loop transfer function Q(s) of (s) can be expressed as:

[0117]

[0118] Where s is a complex variable representing the transfer function in the control system, and U(s) is the input voltage. M (s) represents the voltage component obtained after TOGI. A third-order generalized integral phase-locked loop is designed using the closed-loop transfer function D(s) and the closed-loop transfer function Q(s).

[0119] Improvements to the traditional TOGI to generate adaptive frequency references, such as... Figure 4Where (a) is the pre-stage structure of TOGI, and (b) is the improved TOGI. This allows for better tracking of the grid frequency. An adaptive frequency-locking loop is introduced into the TOGI structure, which can better resist external interference and noise and track the grid frequency to achieve adaptive frequency. After introducing the adaptive frequency-locking loop, the transfer functions are as follows:

[0120]

[0121] A third-order generalized integral phase-locked loop (PLL) with frequency locking is designed using D′(s) and Q′(s). A TOGI (Total Integral-Oxide-Gas) structure combined with an adaptive PLL is employed to track speed during filtering. The TOGI structure improves the accuracy of the PLL, while the adaptive frequency-locked loop enhances stability by improving the fixed-frequency input. By introducing the frequency-locked loop, frequency synchronization can be achieved. The frequency-locked loop tracks the frequency deviation of the input signal and adjusts based on feedback errors, ensuring that the output signal remains frequency-synchronized with the input signal. This results in faster tracking speeds, enabling more rapid acquisition and tracking of the frequency and phase changes of the input signal.

[0122] Perform case analysis, such as Figure 5 From 0 to 0.1 seconds, the grid voltage is ideal. From 0.1 to 0.25 seconds, the three-phase grid voltage becomes unbalanced. After 0.25 seconds, the 5th and 7th harmonics are injected into the grid voltage. An improved TOGI phase-locked loop is used for grid voltage phase locking, and the results are as follows. Figure 6 It can accurately lock the phase of the fundamental voltage.

[0123] Replace the low-pass filter with an improved variable step size adaptive filter (LMS):

[0124] Typically, we use the steepest descent method to determine the optimal weights in a neural network. In this method, each iteration is proportional to the gradient of the mean squared error. The iterative formula for the steepest descent method is shown in (1-13):

[0125]

[0126] Where w(t), μ and These are the gradient vectors of the filter weight coefficients, the step size function, and the weight coefficients w(t), respectively.

[0127] like Figure 7 The iterative relationship of Least Mean Square Adaptive (LMS):

[0128]

[0129] When the low-pass filter is replaced by an LMS filter, as shown in (1-4), i p The DC component is extracted using a filter. Therefore, we can assume that the input x(t) is always 1.

[0130]

[0131] Where y(t) is the predicted output of the LMS filter, w T (t) represents the weighting coefficient, d(t) represents the expected output, and e(t) represents the error between the expected output and the actual output.

[0132] The mathematical expression for the Gaussian error function is shown below:

[0133]

[0134] Here, erf(x) is the Gaussian error function.

[0135] Mathematical expression for variable step size μ based on Gaussian error function:

[0136] μ(t)=β·erf(1-e α·|e(t)| (1-17)

[0137] In the formula, α and β are parameters that change the shape and magnitude of the function.

[0138] like Figure 8 The relationship between variable step size μ(t) and e(t) is shown in the graph. Equation (1-17) expresses a variable step size where the step size changes too rapidly as e(t) approaches 0, making it difficult to achieve steady-state error. Therefore, when the variable step size μ(t) is multiplied by the function y = 1 + γ|x|, and e(t) approaches 0, the step size changes too rapidly. Thus, the new step size function satisfies formula (1-18):

[0139] μ(t)=β·erf(1-e α·e(t) )·(1+γ·|e(t)|) (1-18)

[0140] Here, γ is a coefficient that is responsible for adjusting the shape of the step size function.

[0141] like Figure 9 The improved relationship between variable step size μ(t) and e(t) is shown in the graph. Figure 8 , Figure 9 It is known that when γ = 1.5, the step size μ(t) changes rapidly when e(t) is large; when e(t) approaches 0, the step size μ(t) also approaches 0. This satisfies both speed and accuracy, reduces steady-state error, and thus better extracts the fundamental frequency content in the harmonics.

[0142] An example simulation was performed in Matlab / Simulink. The harmonic content was low from 0 to 0.15 seconds; after 0.15 seconds, the harmonic current was increased. Traditional second-order low-pass filters have the slowest response speed, and it is difficult to obtain the fundamental frequency content from the harmonics. The fixed-step LMS algorithm has the highest accuracy, but its response speed is too slow. Based on the variable-step LMS algorithm, μ(t) = β·erf(1-e α·|e(t)| The improved variable-step LMS algorithm has a faster response speed than the fixed-step algorithm and the second-order low-pass filter, but its accuracy is lower than that of the fixed-step algorithm. The improved variable-step LMS algorithm is μ(t) = β·erf(1-e^(-t / t)). α·e(t) The response speed of the algorithm is significantly improved compared to the variable step-size LMS algorithm, and the steady-state error is smaller than that of the previous variable step-size algorithm when e(t) approaches 0, thus obtaining the fundamental frequency content better. Figure 11 It is known that the harmonic content of the harmonic current is 19.74% after FFT analysis. The fundamental frequency obtained by the improved variable step size LMS algorithm has a harmonic content of 2.91% after FFT analysis.

[0143] like Figure 11 The simulation diagram shows a three-phase voltage source. Before 0.1 seconds, the grid voltage is in an ideal state. From 0.1 to 0.25 seconds, the three-phase voltage of the grid becomes unbalanced. After 0.25 seconds, the grid harmonic voltage is added, increasing the complexity of the grid situation.

[0144] like Figure 12 In a power system, the load is simulated as a nonlinear load, and the harmonic current contains a DC component. A harmonic detection method based on the variable step-size LMS algorithm is used. The figure shows the harmonic current and the resulting fundamental current waveform. It is evident that the improved variable step-size adaptive algorithm has a fast response speed and high accuracy.

[0145] Based on the above methods and statements, the present invention also includes a power grid harmonic detection system, comprising: a signal acquisition module, a current processing module, and a harmonic detection module.

[0146] The signal acquisition module is used to set up a third-order generalized integral phase-locked loop (PLL) based on instantaneous reactive power theory, and to acquire sine and cosine signals with the same phase-a voltage in the new energy power grid system through the third-order generalized integral PLL; the current processing module is used to perform coordinate transformation on the load current using the sine and cosine signals to extract the instantaneous active current i. p and instantaneous reactive current i q The harmonic detection module is used to detect the instantaneous active current i using an adaptive filter LMS. p and instantaneous reactive current i q Processing to obtain the DC component And through DC component Calculate the fundamental component i af i bfi cf and harmonic components i ah i bh i ch .

[0147] The present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of a harmonic detection method for a power grid.

[0148] The above description, in conjunction with specific preferred embodiments, provides a more detailed explanation of the present invention. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for detecting harmonics in a power grid, characterized in that, Includes the following steps: A third-order generalized integral phase-locked loop is set up using instantaneous reactive power theory, and the same sine and cosine signals as phase a voltage in the new energy power grid system are obtained through the third-order generalized integral phase-locked loop. The instantaneous active current is extracted by performing coordinate transformation on the three-phase current of the load using the aforementioned sine and cosine signals. and instantaneous reactive current ; The instantaneous active current is analyzed using an adaptive filter LMS. and instantaneous reactive current Processing to obtain the DC component , and through the DC component , Calculate the fundamental component , , and harmonic components , , ; Among them, the adaptive filter LMS is used to analyze the instantaneous active current. and instantaneous reactive current The process includes the following steps: The steepest descent method is used to determine the optimal weights in the adaptive filter LMS, and the specific expression is as follows: ； in, w ( t ), μ and These are the filter weight coefficients, step size function, and weight coefficients, respectively. w ( t The gradient vector of ). The specific expression for obtaining the least mean square adaptive LMS iteration relationship is as follows: ； For instantaneous active current The DC component is extracted using a filter. ; ； Let the input quantity be If the value is always 1, then the specific expression for the LMS iteration relationship is: ； in, y ( t The output of the adaptive filter LMS prediction is shown below. These are the weighting coefficients. d ( t () represents the expected output. e ( t The error between the expected output and the actual output is represented by ). Wherein, the acquisition of the e ( t The relationship between the variable step size of the adaptive filter LMS and the variable step size function of the adaptive filter LMS is determined, and the variable step size function of the adaptive filter LMS is optimized based on the incurvature cosine function, including the following steps: The variable step size of the adaptive filter LMS is obtained based on the Gaussian error function. expression: ； in, , Parameters to change the shape and magnitude of the function; The variable step size Multiplying by the inverted cosine function yields the optimized variable step size function. ; ； in, γ This is a coefficient that is responsible for adjusting the shape of the step size function.

2. The method for detecting harmonics in a power grid as described in claim 1, characterized in that, Before setting up the third-order generalized integral phase-locked loop using instantaneous reactive power theory, the three-phase current passing through the load under ideal conditions is obtained, specifically expressed as follows: ； in, I n This represents the effective value of the three-phase current. This is the initial phase.

3. The method for detecting harmonics in a power grid as described in claim 2, characterized in that, The load current is transformed using the sine and cosine signals to extract the instantaneous active current. and instantaneous reactive current The specific expression is: ； The coordinate transformation uses the dq transformation to convert the load current variables in the three-phase coordinate system to the dq coordinate system, where the d-axis represents the active component and the q-axis represents the reactive component. and They are respectively d - q The final current component in the coordinate system. and These are the current components after the three-phase current has undergone dq transformation.

4. The method for detecting harmonics in a power grid as described in claim 1, characterized in that, The method of setting up a third-order generalized integral phase-locked loop using instantaneous reactive power theory includes the following steps: If the voltage input signal contains a DC component, then the input signal is: ； in, A 0 This represents the amplitude of the DC component. A 1 represents the amplitude of the AC component. Indicates the fundamental frequency of the power grid. For phase; The reconstructed TOGI integrator is obtained through the input signal, and its output expression is: ； in, k The coefficients in the TOGI integrator k , and The terms are orthogonal, none of them contain a DC component, and and Same amplitude Phase lag of 90 degrees; The reconstructed TOGI integrator eliminates the DC component of the input, obtaining a quadrature output signal, as specifically expressed by: ； in, , The output is an orthogonal signal after filtering. u 1. u 2. u 3 represents the three components output by the TOGI integrator. , The voltage components obtained after passing through the TOGI integrator are respectively and ; because arrive The closed-loop transfer function is , arrive The closed-loop transfer function is Then the closed-loop transfer function and closed-loop transfer function The specific expression is: ； In the control system, s represents the complex variable of the transfer function. Input voltage; Through the closed-loop transfer function and closed-loop transfer function Design a third-order generalized integral phase-locked loop; An adaptive frequency-locking loop is introduced into the TOGI structure. After introducing the adaptive frequency-locking loop, the transfer functions are as follows: ； in, and After introducing an adaptive frequency-locking loop and The transfer function; Through the above and Design a third-order generalized integral phase-locked loop with frequency locking.

5. The method for detecting harmonics in a power grid as described in claim 1, characterized in that, Through the DC component , Calculate the fundamental component , , and harmonic components , , The specific expression is: ； ； Among them, C 23 for - β Inverse transformation matrix.

6. The method for detecting harmonics in a power grid as described in claim 1, characterized in that, The specific expression for the Gaussian error function is as follows: ； in, erf ( x ) is the Gaussian error function.

7. A system for a harmonic detection method for a power grid as described in any one of claims 1-6, characterized in that, include: The signal acquisition module is used to set up a third-order generalized integral phase-locked loop using instantaneous reactive power theory, and to acquire sine and cosine signals with the same voltage as phase a in the new energy power grid system through the third-order generalized integral phase-locked loop. The current processing module is used to perform coordinate transformation on the three-phase current of the load using the sine and cosine signals to extract the instantaneous active current. and instantaneous reactive current ; The harmonic detection module is used to detect the instantaneous active current using an adaptive filter LMS. and instantaneous reactive current Processing to obtain the DC component , and through the DC component , Calculate the fundamental component , , and harmonic components , , .

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method according to any one of claims 1-6.

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