A non-disassembly direct identification method for characteristic parameters of single-tuned filters

Abstract

The present invention discloses a non-disassembly type direct identification method for characteristic parameters of a single-tuned filter, comprising the following steps: detecting the current of the single-tuned filter by using a current detection system, initializing the single-tuned filter to be tested to a zero state, applying a DC voltage source with a constant amplitude to the single-tuned filter to be tested, sampling its current and saving the sample, calculating a basic coefficient, a basic factor and an average basic factor, calculating an average estimated dynamic factor, calculating an estimated factor, and calculating the capacitance value, the inductance value and the resistance value of the single-tuned filter; the present invention takes the single-tuned filter as a detection object, monitors its characteristic parameters in real time, constructs a simulation model of the single-tuned filter, and verifies the identification method of the characteristic parameters in the filter through experiments. By analyzing the experimental results, it is confirmed that the identification method of the present invention can accurately estimate the size of the characteristic parameters of the single-tuned filter without disassembling or damaging the filter device.

Description

Technical Field

[0001] The present invention relates to the technical field of single-tuned filters, and in particular to a non-disassembly direct identification method for characteristic parameters of a single-tuned filter. Background Art

[0002] With the modernization of various sectors of the national economy, a large number of nonlinear loads, primarily power electronic equipment, are increasingly being used, and harmonic control is receiving increasing attention. Single-tuned filters, consisting of a series-connected filter reactor and filter capacitor, are the fundamental components of power system filtering. As single-tuned filters age and their operating temperature fluctuates, their internal components can experience temperature increases and malfunction. In these cases, the characteristic parameter values of various components within them may change, leading to aging and weakening of the filter's performance. Therefore, real-time monitoring of the internal component parameters of single-tuned filters is crucial for understanding their performance and ensuring their proper and effective use.

[0003] However, single-tuned filter products are often packaged. If these parameters are disassembled to test, it is easy to damage the single-tuned filter. It is currently very difficult to test these parameters without disassembling. Therefore, people have started research in this area. The filtering performance of a single-tuned filter actually depends on the values of the three lumped basic components of the filter's internal resistance, inductance, and capacitance, namely the size of the characteristic parameters R, L, and C. These parameters R, L, and C jointly determine the frequency characteristics of the single-tuned filter and characterize its filtering performance. The equivalent circuit model of a traditional single-tuned filter is as follows: Figure 1 As shown, it is mainly composed of capacitor C, inductor L and resistor R in series. Assume that its input voltage is u i (t), the capacitor voltage is u c (t), the current is i(t), for the capacitor C, we have:

[0004]

[0005] From circuit knowledge, we know that:

[0006]

[0007] Input voltage u i (t) is a step signal, that is:

[0008]

[0009] t<0 means before working, there is no voltage input, that is, u i(t) = 0, the voltage across the capacitor is 0V, and the current flowing through the capacitor is 0A, that is, the single-tuned filter is in the zero state. t ≥ 0 means that after operation, the input voltage u i (t) is a constant value U0. The characteristic polynomial of a single-tuned filter usually has two different negative real poles to ensure its good filtering performance. Combining equations (1.1) to (1.3), the voltage u in the time domain can be solved. c (t), current i(t). For a commercialized single-tuned filter, its u c (t) It is quite difficult.

[0010] Existing methods for identifying characteristic parameters of single-tuned filters generally only work after an actual fault has occurred in the single-tuned filter. They cannot predict or prevent the occurrence of a fault in advance, and they cannot directly obtain the size of the characteristic parameters in the single-tuned filter. Some identification methods only focus on the aging of capacitors and ignore the aging of other components such as inductors and resistors in the device. In addition, the calculation quality of other existing identification methods is greatly affected by the initial point, and may obtain a local optimal point rather than an overall optimal point, thereby generating a large error. Therefore, the present invention proposes a non-disassembly direct identification method for characteristic parameters of single-tuned filters to solve the problems existing in the prior art. Summary of the Invention

[0011] In response to the above problems, the purpose of the present invention is to propose a non-disassembly direct identification method for the characteristic parameters of a single-tuned filter, so as to solve the problems that most of the existing methods for identifying the characteristic parameters of a single-tuned filter cannot predict or prevent the occurrence of faults in advance, cannot directly obtain the size of the characteristic parameters in the single-tuned filter, ignore the aging of other components such as inductance and (or) resistance in the device, and have large errors.

[0012] In order to achieve the purpose of the present invention, the present invention is implemented by the following technical solution: a non-disassembly direct identification method of characteristic parameters of a single tuned filter, comprising the following steps:

[0013] Step 1: Prepare a constant DC voltage source with a voltage amplitude of U0 and a current detection system in advance, then initialize the single-tuned filter to be tested to a zero state, and then use the current detection system to detect the current i(t) of the single-tuned filter until the detected current i(t) is constantly zero;

[0014] Step 2: Connect the voltage source prepared in step 1 to the input of the single-tuned filter to be tested, and use the current detection system prepared in step 1 to sample the current of the single-tuned filter to be tested and save the sample. The sample is recorded as f(j) = i(jT), which represents the current collected in the jth sampling period, j = 1, 2, 3, ..., N, N is the number of samples, and the sampling period is T;

[0015] Step 3: Based on the sample f(j) saved in step 2, calculate the basic coefficients a(j), b(j), c(j), basic factors u1(j), u2(j), and average basic factors av1, av2, where j = 1, 2, 3, ..., q, q <N-2;

[0016] Step 4: Calculate the estimated dynamic factor A(j) based on the average basic factors av1 and av2 calculated in step 3, and then calculate the average estimated dynamic factor av based on the estimated dynamic factor A(j). a , where j = 1, 2, 3, ..., m, m <N-1;

[0017] Step 5: Calculate the estimated factors EP1 and EP2 based on the average basic factors av1 and av2 calculated in step 3;

[0018] Step 6: According to the average estimated dynamic factor av calculated in step 4 a The capacitance C, inductance L, and resistance R of the single tuned filter are calculated using the estimated factors EP1 and EP2 calculated in step 5, respectively.

[0019] A further improvement is that in step 1, the input terminal and the output terminal of the single tuned filter to be tested are grounded respectively to initialize them to a zero state.

[0020] A further improvement is that in step 3, the calculation formula of the basic coefficient a(j) is:

[0021] a(j)=f(j+1)f(j+1)-f(j)f(j+2);

[0022] The calculation formula of the basic coefficient b(j) is:

[0023] b(j)=f(j)f(j+3)-f(j+1)f(j+2);

[0024] The calculation formula of the basic coefficient c(j) is:

[0025] c(j)=f(j+2)f(j+2)-f(j+1)f(j+3).

[0026] A further improvement is that in step 3, the calculation formula of the basic factor u1(j) is:

[0027]

[0028] The calculation formula of the basic factor u2(j) is:

[0029]

[0030] A further improvement is that in step 3, the calculation formula of the average basic factor av1 is:

[0031]

[0032] The calculation formula of the average basic factor av2 is:

[0033]

[0034] A further improvement is that in step 4, the calculation formula of the estimated dynamic factor A(j) is:

[0035]

[0036] The average estimated dynamic factor av a The calculation formula is:

[0037]

[0038] A further improvement is that in step 5, the calculation formula of the estimated factor EP1 is:

[0039]

[0040] The calculation formula of the estimated factor EP2 is:

[0041]

[0042] A further improvement is that in step 6, the calculation formula for the capacitance value C of the single tuned filter is:

[0043]

[0044] The calculation formula of the inductance value L of the single tuned filter is:

[0045]

[0046] The calculation formula of the resistance value R of the single tuned filter is:

[0047]

[0048] The beneficial effects of the present invention are as follows: the present invention uses a single-tuned filter as the detection object, monitors the characteristic parameters of its internal components in real time, constructs a simulation model of the single-tuned filter based on the MATLAB / Simulink platform, and verifies the calculation method of the characteristic parameters of the filter's internal components through experiments. Analysis of the experimental results confirms that the identification method of the present invention can accurately estimate the size of the single-tuned filter's characteristic parameters by real-time monitoring of the filter's current without disassembling or damaging the filter device. It has the advantages of strong data acquisition timeliness, high accuracy, and no damage to the filter. It also has strong anti-interference ability, high identification accuracy, stable and reliable identification, and the overall method is easy to understand and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0050] Figure 1 Schematic diagram of an equivalent circuit model of a traditional single-tuned filter in the background technology of the present invention;

[0051] Figure 2 1 is a flow chart of a method for directly identifying characteristic parameters of a single tuned filter without disassembly according to the present invention;

[0052] Figure 3 Schematic diagram of a single tuned filter circuit model in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0054] See also Figure 2 、 Figure 3 In this embodiment, a circuit model of a single tuned filter circuit model is established in Simulink under the Matlab environment. Experiments are carried out on this circuit model to verify the method of the present invention. The specific steps are as follows:

[0055] Step 1: First, establish a single tuned filter circuit model, such as Figure 3 As shown, where capacitance C = 1×10-3 F, inductance L = 2.2 × 10 -3 H, resistance R = 20Ω, the gain of white noise is 0, that is, there is no noise interference input, and the step signal with an amplitude of 100000 controls the controlled voltage source to generate U o =100000V step voltage source u i (t) is used for the single tuned filter. The current sensor collects the single tuned filter current i(t). The voltage across the capacitor is initialized to 0V, and the inductor current is initialized to 0A, that is, the single tuned filter is initialized to the zero state;

[0056] Step 2: Set the sampling period T to T = 7.0 × 10 -7 seconds, start simulation, u i (t) is connected to the input of the single tuned filter. At the same time, the current sensor collects i(t) and saves it. Note that f(j) = i(jT), which represents the jth sampling value, j = 1, 2, 3, ..., N. When N = 2.1 × 10 5 When f(j) changes very little, the experiment ends and the sampling ends;

[0057] Step 3: Calculate the basic coefficients a(j), b(j), and c(j). The calculation formula for the basic coefficient a(j) is:

[0058] a(j)=f(j+1)f(j+1)-f(j)f(j+2)

[0059] The calculation formula of the basic coefficient b(j) is:

[0060] b(j)=f(j)f(j+3)-f(j+1)f(j+2)

[0061] The calculation formula of the basic coefficient c(j) is:

[0062] c(j)=f(j+2)f(j+2)-f(j+1)f(j+3)

[0063] Calculate the basic factors u1(j) and u2(j), where the calculation formula of the basic factor u1(j) is:

[0064]

[0065] The calculation formula of the basic factor u2(j) is:

[0066]

[0067] j=1, 2, 3,..., 98;

[0068] Calculate the average basic factors av1 and av2, where the calculation formula for the average basic factor av1 is:

[0069]

[0070] The calculation formula of the average basic factor av2 is:

[0071]

[0072] Step 4: Calculate the estimated dynamic factor A(j), the calculation formula is:

[0073]

[0074] j=1, 2, 3,..., 178;

[0075] Then calculate the average estimated dynamic factor av based on the estimated dynamic factor A(j) a , the calculation formula is:

[0076]

[0077] Step 5: Calculate the estimated factors EP1 and EP2, where the calculation formula for the estimated factor EP1 is:

[0078]

[0079] The calculation formula of the estimated factor EP2 is:

[0080]

[0081] Step 6: Calculate the capacitance C, inductance L, and resistance R of the single-tuned filter. The calculation formula for the capacitance C is:

[0082]

[0083] The calculation formula for the inductance value L is:

[0084]

[0085] The calculation formula for the resistance value R is:

[0086]

[0087] The characteristic parameters of the single-tuned filter identified by step 6 are: C = 0.000999999861F, L = 0.002200000000357H, R = 19.9999999896Ω. According to step 1, the true values of the characteristic parameters of the single-tuned filter in the experiment are: C = 0.001F, L = 0.0022H, R = 20Ω. Therefore, the characteristic parameter identification method of the single-tuned filter proposed by the present invention can be obtained. For the specific case in the experiment, the relative errors of C, L, and R are -1.39×10 -5 %, 1.62×10 -8 %, -5.2×10 -8 %, thus it can be seen that the single tuned filter characteristic parameter identification method proposed in the present invention can effectively identify the interference-free system with high identification accuracy.

[0088] In actual work, the input signal and the collected signal are always mixed with interference (interference usually appears as white noise). In order to see how much the identification method proposed by the present invention is affected by interference, Figure 3 The model shown incorporates a white noise signal module to simulate the interference signal to the system. The white noise module sets the power spectral density of the white noise to 0.1 and the number of seeds to 23341. By varying the noise amplitude, the interference intensity in a real working environment is simulated, with the noise-to-signal ratios set to 3.1%, 6.2%, 15.5%, -1.55%, -3.09%, and -15%, respectively. Similarly, each time the interference amplitude or noise-to-signal ratio is varied, steps 1 through 6 are repeated to perform an identification experiment. Table 1 records the results of six typical identification experiments using the method of the present invention with interference.

[0089] Table 1 Identification of characteristic parameters of single tuned filter with white noise interference signal

[0090]

[0091] As can be seen from Table 1 above, the identification method proposed in the present invention can effectively identify the characteristic parameters of a single-tuned filter, and the identification accuracy of each characteristic parameter is similar. As the amplitude of the white noise increases or the noise-to-signal ratio increases, the identification error of this method becomes larger and larger. In general, the identification method proposed in the present invention has a strong anti-interference ability. For example, when the noise-to-signal ratio reaches 15%, the identification error of each characteristic parameter is about 1.8%. These results show that the identification method proposed in the present invention has a strong anti-interference ability, high identification accuracy, and stable and reliable identification.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A non-disassembly direct identification method for characteristic parameters of a single tuned filter, characterized in that: The following steps are involved: Step 1: Prepare a constant DC voltage source with a voltage amplitude of U0 and a current detection system in advance, then initialize the single-tuned filter to be tested to a zero state, and then use the current detection system to detect the current i(t) of the single-tuned filter until the detected current i(t) is constantly zero; Step 2: Connect the voltage source prepared in step 1 to the input of the single-tuned filter to be tested, and use the current detection system prepared in step 1 to sample the current of the single-tuned filter to be tested and save the sample. The sample is recorded as f(j) = i(jT), which represents the current collected in the jth sampling period, j = 1, 2, 3, ..., N, N is the number of samples, and the sampling period is T; Step 3: Based on the sample f(j) saved in step 2, calculate the basic coefficients a(j), b(j), c(j), basic factors u1(j), u2(j), and average basic factors av1, av2, where j = 1, 2, 3, ..., q, q <N-2; The calculation formula of the basic coefficient a(j) is: a(j)=f(j+1)f(j+1)-f(j)f(j+2); The calculation formula of the basic coefficient b(j) is: b(j)=f(j)f(j+3)-f(j+1)f(j+2); The calculation formula of the basic coefficient c(j) is: c(j)=f(j+2)f(j+2)-f(j+1)f(j+3); The calculation formula of the basic factor u1(j) is: The calculation formula of the basic factor u2(j) is: The calculation formula of the average basic factor av1 is: The calculation formula of the average basic factor av2 is: Step 4: Calculate the estimated dynamic factor A(j) based on the average basic factors av1 and av2 calculated in step 3, and then calculate the average estimated dynamic factor av based on the estimated dynamic factor A(j). a , where j = 1, 2, 3, ..., m, m <N-1; The calculation formula of the estimated dynamic factor A(j) is: The average estimated dynamic factor av a The calculation formula is: Step 5: Calculate the estimated factors EP1 and EP2 based on the average basic factors av1 and av2 calculated in step 3; The calculation formula of the estimated factor EP1 is: The calculation formula of the estimated factor EP2 is: Step 6: According to the average estimated dynamic factor av calculated in step 4 a The capacitance C, inductance L, and resistance R of the single tuned filter are calculated using the estimated factors EP1 and EP2 calculated in step 5, respectively.

2. The method for directly identifying characteristic parameters of a single-tuned filter without disassembly according to claim 1, wherein: In the step 1, the input terminal and the output terminal of the single tuned filter to be tested are grounded respectively to initialize the filter to a zero state.

3. The method for directly identifying characteristic parameters of a single-tuned filter without disassembly according to claim 1, wherein: In step 6, the calculation formula for the capacitance value C of the single tuned filter is: The calculation formula of the inductance value L of the single tuned filter is: The calculation formula of the resistance value R of the single tuned filter is:

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