Non-detachable direct identification method for characteristic parameters of single-tuned filter

Abstract

The invention discloses a non-detachable direct identification method for characteristic parameters of a single-tuned filter, which comprises the following steps of: detecting the current of the single-tuned filter by using a current detection system, initializing the single-tuned filter to be detected to be in a zero state, applying a direct-current voltage source with constant amplitude to the single-tuned filter to be detected, sampling the current of the single-tuned filter, storing a sample, calculating a basic coefficient, a basic factor and an average basic factor, calculating an average estimation dynamic factor, calculating an estimation factor, and calculating a capacitance value, an inductance value and a resistance value of the single-tuned filter; according to the method, the single-tuned filter is used as a detection object, the characteristic parameters of the single-tuned filter are monitored in real time, a simulation model of the single-tuned filter is constructed, the identification method of the characteristic parameters in the filter is verified through experiments, and the identification method is confirmed to be accurate and reliable on the premise that the filter device is not disassembled and not damaged through analysis of experimental results. And the characteristic parameters of the single-tuned filter can be accurately estimated.

Description

Technical Field

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

[0002] With the development of modernization in various industries of the national economy, a large number of nonlinear loads, mainly various power electronic equipment, have been increasingly widely used, and the problem of harmonic control is receiving more and more attention. The single-tuned filter, which is composed of a filter reactor and a filter capacitor in series, is the basic unit of the power system filter device. With the increase in the use time of the single-tuned filter and the change in the operating environment temperature, its internal components will correspondingly increase in temperature and fail to work normally. In this case, the characteristic parameter values ​​of various types of components inside it may change and age day by day, thereby weakening the filtering performance of the filter. Therefore, real-time monitoring of the parameters of the internal components of the single-tuned filter is of great practical significance for grasping the filtering performance of the single-tuned filter and its reasonable 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 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), 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 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 working, 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. By combining equations (1.1) to (1.3), the voltage u in the time domain can be solved. c (t), current i(t). For a commercial single-tuned filter, its u c (t) It is quite difficult.

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

[0011] In view of the above problems, the purpose of the present invention is to propose a non-disassembly direct identification method of 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 are unable to 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 the inductor and (or) resistor 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 scheme: a non-disassembly direct identification method of characteristic parameters of a single tuned filter comprises 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 end 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: According to 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 respectively using the estimated factors EP1 and EP2 calculated in step 5.

[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 of 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 a 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 internal components of the filter through experiments. Through the analysis of 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 by real-time monitoring of the current of the single tuned filter without disassembling or damaging the filter device, and has the advantages of strong timeliness of data acquisition, high accuracy and no damage to the filter, and has strong anti-interference ability, high identification accuracy, stable and reliable identification, and the method as a whole 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

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

[0051] Figure 2 It 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 technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are 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, and an experiment is carried out on the 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), where 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 average base 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 of the estimated factor EP1 is:

[0078]

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

[0080]

[0081] Step 6: Calculate the capacitance value C, inductance value L and resistance value R of the single tuned filter, where the calculation formula of the capacitance value C is:

[0082]

[0083] The calculation formula of inductance value L is:

[0084]

[0085] The calculation formula of 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, there is always interference (usually in the form of white noise) in the input signal and the collected signal. In order to see how much the identification method proposed in the present invention is affected by interference, Figure 3 A white noise signal module is added to the model shown to simulate the interference signal to the system. The white noise module sets the power spectrum density of the white noise to 0.1 and the number of seeds to 23341. By changing the amplitude of the noise, the interference intensity in the actual working environment is simulated, and the noise-to-signal ratio of the interference is set to 3.1%, 6.2%, 15.5%, -1.55%, -3.09%, and -15%. Similarly, each time the interference amplitude or noise-to-signal ratio is changed, the above steps 1 to 6 are repeated to perform an identification experiment. Table 1 records the identification experiment results of the method of the present invention with typical six interference bands.

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

[0090]

[0091] It can be seen from Table 1 above that 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. With the increase of the white noise amplitude or the increase of the noise-to-signal ratio, 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 situations 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-disassembly direct identification method of 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 end 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: According to 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; 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; Step 5: Calculate the estimated factors EP1 and EP2 based on the average basic factors av1 and av2 calculated in step 3; 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 respectively using the estimated factors EP1 and EP2 calculated in step 5.

2. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: 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 single tuned filter to a zero state.

3. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: In the step 3, 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).

4. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: In the step 3, the calculation formula of the basic factor u1(j) is: The calculation formula of the basic factor u2(j) is:

5. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: In step 3, the calculation formula of the average basic factor av1 is: The calculation formula of the average basic factor av2 is:

6. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: In the step 4, the calculation formula of the estimated dynamic factor A(j) is: The average estimated dynamic factor av a The calculation formula is:

7. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: In step 5, the calculation formula of the estimated factor EP1 is: The calculation formula of the estimated factor EP2 is:

8. The non-disassembly direct identification method of characteristic parameters of a single tuned filter according to claim 1, characterized in that: In step six, the calculation formula of 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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