A Time-Frequency Variable Energy Protection Method and Device for Digital Control Systems under Strong Electromagnetic Pulses

Abstract

The present invention discloses a method and device for time-frequency variable energy protection of a digital control system against strong electromagnetic pulses. The method includes: acquiring the terminal coupling interference waveform of the digital control system; determining whether damage will be caused to the controller terminal or the filter terminal based on the terminal coupling interference waveform to determine the final coupling interference waveform; performing time-frequency energy analysis according to the final coupling interference waveform; and determining a multi-stage filter based on the frequency band and energy distribution results. The present invention determines the magnitude of the coupling interference energy and the possibility of generating interference in the control system by judging the amplitude of the time-domain waveform of the electromagnetic pulse coupling voltage and coupling current, and uses the time-frequency domain analysis method to integrate the time-domain characteristics and frequency-domain characteristics of the non-damaging interference signal coupling signal of the digital controller on a two-dimensional image, intuitively giving the sensitive frequency band of the coupling signal of the control system and the energy distribution on each sensitive frequency band, and solving the device selection of the sensitive frequency band and device energy of the multi-stage filter.

Description

Technical Field

[0001] The present invention belongs to the technical field of strong electromagnetic pulse protection, and particularly relates to a method and device for protecting the time-frequency variable energy of a digital control system against strong electromagnetic pulses. Background Art

[0002] With the continuous progress of digital control technology and the continuous development of high-power electromagnetic pulse technology, the strong electromagnetic pulse interference and damage to control systems have received extensive attention. The digital control systems of equipment have complex factors such as complex spatial layout structures, diverse terminal loads, and difficult-to-evaluate shielding grounding. Therefore, strong electromagnetic pulses will couple complex interference waveforms at the terminals of digital control systems. Therefore, it is difficult to optimize the cost, volume, and order of the terminal protection circuit during the process of carrying out strong electromagnetic pulse protection. Usually, the trial production method is adopted, which has a large amount of labor and poor effects. Therefore, there is an urgent need to propose a new design method for protecting the terminals of strong electrical pulses, which can quickly achieve effective suppression of interference waveforms and enhance the reinforcement of strong electromagnetic pulse interference and damage at the terminals of digital control systems.

[0003] For the design of strong electromagnetic pulse protection filters in digital control systems, amplitude limiting and RLC filtering are mainly adopted. The structural design of amplitude limiting components tends to be integrated and simplified, and components such as gas discharge tubes, TVS, and varistors are mainly selected. During the design process of RLC filters, due to the existence of distributed parameters of components, the filters will only have good filtering effects near the resonance parameters. The manufacture of wide-band filters is difficult, and large over-redundancy will be caused during the absorption and use of wide-band energy, increasing the design cost and volume of the filters and restricting the application of the filters in some aviation equipment. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and device for protecting the time-frequency variable energy of a digital control system against strong electromagnetic pulses, so as to enhance the strong electromagnetic pulse protection ability of the digital control system, optimize the volume of the terminal protection circuit, and reduce the protection cost.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] In the first aspect, the present invention provides a method for protecting the time-frequency variable energy of a digital control system against strong electromagnetic pulses, including:

[0007] Obtain the terminal coupling interference waveform of the digital control system;

[0008] Judge whether it will cause damage to the controller terminal or the filter terminal according to the terminal coupling interference waveform, and determine the final coupling interference waveform;

[0009] Conduct time-frequency energy analysis according to the final coupling interference waveform;

[0010] Determine a multi-stage filter according to the frequency band and energy distribution results.

[0011] Optionally, the determining the final coupled interference waveform specifically includes:

[0012] Combine the terminal coupled interference waveform parameters with the allowable damage threshold of the digital control device to determine whether damage will be caused to the controller terminal or the filter terminal. If damage can be caused, limit the interference waveform to obtain the limited coupled interference waveform as the final coupled interference waveform; if damage cannot be caused, directly use the terminal coupled interference waveform as the final coupled interference waveform.

[0013] Optionally, the performing time-frequency energy analysis according to the final coupled interference waveform specifically includes:

[0014] Convert the collected discrete measurement signals into a two-dimensional complex time-frequency domain matrix, where the rows and columns correspond to the frequency and time distributions respectively. Obtain the amplitude and phase information of the sampled signals at the corresponding frequencies and times through the corresponding row and column vectors, that is, the time-frequency domain signals.

[0015] Optionally, the collected discrete measurement signals are obtained by the following method:

[0016]

[0017] In the formula, the signal duration is t, the time sampling interval is T, then the number of signal sampling points is N = t / T; let f → n / (NT), τ → kT, when f ≠ 0, the S transform is written as a function of X(f);

[0018] Discretize the S transform to obtain:

[0019]

[0020] In the formula, k, m = 0, 1, …, N - 1; n = 1, 2, …, N - 1;

[0021] When n = 0,

[0022]

[0023] Therefore, all elements of the S transform are obtained as:

[0024]

[0025] Optionally, use the two-dimensional complex time-frequency domain matrix and Fourier transform to convert the measured time-domain signal into a frequency-domain signal, and analyze the sensitive frequency band in which the electromagnetic pulse is coupled into the control system in the frequency-domain signal;

[0026] By performing time-frequency domain analysis, the time-domain characteristics and frequency-domain characteristics of the coupled signal are integrated onto a two-dimensional image, reconstructing the time-frequency curve of the strong electromagnetic pulse in the bounded wave simulator, and obtaining the sensitive frequency band of the control system's coupled signal and the energy distribution on each sensitive frequency band.

[0027] Optionally, determining the multi-stage filter according to the frequency band and energy distribution results specifically includes:

[0028] According to the sensitive frequency band of the control system's coupled signal and the energy distribution on each sensitive frequency band:

[0029] When the amplitude of the signal coupled by the external strong electromagnetic pulse interference entering the control system is small, it will not cause damage to the control system. Connect the corresponding filtering components in the filter according to the sensitive frequency band;

[0030] When the amplitude of the coupled interference signal is large, turn on the limiting component through the connecting switch to discharge the coupled electromagnetic energy. At the same time, increase the filtering loop nodes, analyze the coupled signal after limiting, and connect the corresponding filtering components in the filter according to the relative relationship between the position and energy of the sensitive frequency band.

[0031] In a second aspect, the present invention provides a device for protecting a digital control system against time-frequency variable energy of strong electromagnetic pulses as described in the first aspect, including:

[0032] A housing, inside which a multi-stage differential mode suppression cavity and a common mode suppression cavity are provided;

[0033] A common mode interference suppression capacitor and a limiting component are connected inside the common mode suppression cavity, and a differential mode filtering resistor and a differential mode filtering capacitor are connected inside the multi-stage differential mode suppression cavity.

[0034] Optionally, the limiting component is selected to be conducted or disconnected from the overall circuit through a connecting switch.

[0035] Optionally, the housing is divided into a multi-stage differential mode suppression cavity and a common mode suppression cavity by setting baffles. The common mode interference suppression capacitor is provided as a pair on both sides of the limiting component and penetrates into the multi-stage differential mode suppression cavity to be connected to the differential mode filtering resistor or the differential mode filtering capacitor.

[0036] Optionally, the differential mode filtering resistor and the differential mode filtering capacitor are provided in several numbers, and each differential mode filtering capacitor is connected in parallel after being connected in series with two differential mode filtering resistors.

[0037] Optionally, aviation connectors are provided at both ends of the housing, and a cover plate for closing is provided at the top of the housing.

[0038] Optionally, the limiting component includes a MOV or GDT or TVS limiting component.

[0039] Advantages and benefits of the present invention:

[0040] The time-frequency variable energy protection method for the digital control system against strong electromagnetic pulses conducts time-frequency energy analysis for the final coupled interference waveform, determines a multi-stage filter according to the energy analysis results, judges the magnitude of the coupled interference energy and the possibility of generating interference in the control system through the time-domain waveform amplitudes of the electromagnetic pulse coupled voltage and coupled current, and integrates the time-domain characteristics and frequency-domain characteristics of the coupled signal on a two-dimensional image by using the time-frequency domain analysis method, which can intuitively give the sensitive frequency band of the coupled signal in the control system and the energy distribution on each sensitive frequency band, so as to determine the corresponding filtering devices connected in the filter.

[0041] When the amplitude of the signal coupled by the external strong electromagnetic pulse interference into the control system is small, the time-frequency domain analysis method is used to analyze the frequency band of the small-amplitude coupled interference signal and the energy of different coupled frequency bands, and the corresponding filtering devices of the filter are selected according to the sensitive frequency band for elimination. When the amplitude of the coupled interference signal is large, the limiting component set in the filter is connected to discharge the coupled electromagnetic energy. Similarly, the coupled signal after limiting is analyzed, and the corresponding filtering devices of the filter are selected according to the sensitive frequency band for elimination. Description of the drawings

[0042] Figure 1 It is the flowchart of the filtering process for the coupled interference of the present invention;

[0043] Figure 2 It is the flowchart of the S-transform calculation of the present invention;

[0044] Figure 3 It is the time-frequency domain diagram of the coupled voltage of the present invention;

[0045] Figure 4 It is the frequency domain curve diagram of the coupled voltage of the present invention;

[0046] Figure 5 It is the time domain curve diagram of the coupled voltage of the present invention;

[0047] Figure 6 It is the form diagram of the filter circuit and the termination impedance of the present invention;

[0048] Figure 7 It is the attenuation parameter diagram of the filter of the present invention;

[0049] Figure 8 It is the multi-stage filtering principle diagram of the present invention;

[0050] Figure 9 It is the top view sectional view of the filter of the present invention;

[0051] Figure 10 It is the front view sectional view of the filter of the present invention.

[0052] In the figure: 1 - housing, 2 - cover plate, 3 - aviation connector, 4 - multi - stage differential - mode suppression cavity, 5 - common - mode suppression cavity, 6 - baffle, 7 - common - mode interference suppression capacitor, 8 - limiting component, 9 - differential - mode filtering resistor, 10 - differential - mode filtering capacitor. Specific embodiments

[0053] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0054] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "plurality" is two or more.

[0055] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0056] Embodiment 1:

[0057] As Figures 1 to 8 shown, a method for protecting the time - frequency variable energy of a digital control system from strong electromagnetic pulses is provided, including:

[0058] Obtain the terminal coupling interference waveform of the digital control system;

[0059] Judge whether it will cause damage to the controller terminal or the filter terminal according to the terminal coupling interference waveform, and determine the final coupling interference waveform;

[0060] Conduct time - frequency energy analysis according to the final coupling interference waveform;

[0061] Determine a multi-stage filter according to the frequency band and energy distribution results.

[0062] Reference Figure 1 As shown, in this embodiment, a strong electromagnetic pulse irradiation test is used to simulate the strong electromagnetic environment of a digital control system under real working conditions, and the coupled voltage or current waveform is obtained, including the influence of various distribution parameters, nonlinear characteristics, and terminal load characteristics. Combining with the allowable damage threshold of the terminal devices of the digital controller, it is judged whether the coupled waveform will cause damage to the controller terminal or damage to the filter terminal. If damage occurs, gas discharge tubes, MOVs, GDTs, and TVS limiters are used to limit the interference waveform, and the limited interference waveform obtained is used as the final coupled interference waveform. If no damage occurs, the terminal coupled interference waveform is used as the final coupled interference waveform.

[0063] After determining the final coupled interference waveform, time-frequency energy analysis is carried out, including analyzing the frequency band of the coupled interference and analyzing the energy of different coupled frequency bands. According to the time-frequency energy analysis, that is, the frequency band and energy distribution, the design of the multi-stage filter is determined, specifically including selecting the type of filter, selecting devices according to the sensitive frequency band, and selecting devices according to the energy.

[0064] Reference Figure 1 And Figure 2 As shown, in this embodiment, the magnitude of the time-domain waveform of the electromagnetic pulse coupled voltage and current can be used to judge the magnitude of the energy of the coupled interference and the possibility of interfering with the control system. The Fourier transform can be used to convert the measured time-domain signal into a frequency-domain signal, and the sensitive frequency band of the electromagnetic pulse coupled into the control system can be analyzed in the frequency-domain signal. However, neither the time-domain signal nor the frequency-domain signal can intuitively represent the sensitive frequency band of the electromagnetic pulse coupled signal and the energy distribution on each sensitive frequency band at the same time.

[0065] Therefore, the time-frequency domain analysis method is used to integrate the time-domain characteristics and frequency-domain characteristics of the coupled signal on a two-dimensional image, which can intuitively give the sensitive frequency band of the control system coupled signal and the energy distribution on each sensitive frequency band, providing a basis for the selection of the filtered frequency band and the energy value of the components in the design process of the electromagnetic pulse coupled interference filter.

[0066] Reference Figure 2 As shown, in this embodiment, the specific analysis is as follows:

[0067] The S transform (Stockwell Transform, ST) is a new wavelet transform proposed based on the STFT and Morlet wavelet. It is a combined extension of the previous two wavelet transforms

[140] . The S transform is composed of the product of a Gaussian function and a simple harmonic wave. The former performs stretching and translation, while the latter only performs stretching transformation in the time domain. The expression of the S transform of the signal x(t) is shown in Equation (1):

[0068]

[0069] where f is the frequency, t is the time, and b is the displacement parameter on the time axis. Let the Gaussian window function be:

[0070]

[0071] It can be seen from Equation (1) that the width of the window function is inversely proportional to the frequency. Therefore, the window function is wider in the low-frequency band in the S transform, and thus a higher frequency resolution is obtained. The opposite is true in the high-frequency band.

[0072] In the actual measurement process, the signals we collect are usually discrete. Therefore, the discrete S transform of the sampled signal is often performed in the frequency domain through the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT).

[0073] Suppose the signal duration is t and the time sampling interval is T. Then the number of signal sampling points is N = t / T; let f → n / (NT), τ → kT. When f ≠ 0, the S transform can be written as a function of X(f), that is:

[0074]

[0075] Discretize the obtained S transform to get:

[0076]

[0077] where k, m = 0, 1, …, N - 1; n = 1, 2, …, N - 1.

[0078] And when n = 0

[0079]

[0080] Therefore, all elements of the S transform can be obtained as:

[0081]

[0082] It can be seen from this that the collected discrete measurement signals are transformed into a two-dimensional complex time-frequency domain matrix, where the rows and columns are respectively set as frequency and time. By selecting row and column vectors, the complex results of the S-transform of the sampled signals at the corresponding frequencies and times can be obtained, that is, the results contain the amplitude and phase information of the signals.

[0083] Reference Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, in this embodiment, the S-transform and synchrosqueezing method are adopted. The synchrosqueezing is a time-frequency analysis method in the prior art. The time-frequency domain algorithm programmed by Matlab is used to process the strong electric field pulse signals in the bounded wave simulator. As Figure 3 shown is the time-frequency domain diagram of the pulse electric field in the bounded wave simulator. From this time-frequency domain diagram, it can be obtained that the strong electromagnetic pulse has relatively wide spectral components. At the same time, the duration and power size of the strong electromagnetic pulse can be observed. Figure 4 shown is the frequency domain curve of the electric field in the bounded wave simulator, which proves the wide spectral characteristic of the electromagnetic pulse. Figure 5 shown is the time domain waveform of the D-dot probe. The time domain curve of the strong electromagnetic pulse in the bounded wave simulator is reconstructed by using the poem obtained from the time-frequency domain analysis results, and the reconstructed time domain curve is consistent with the measurement structure. At the same time, it proves that the frequency domain analysis method can meet the analysis requirements of the strong electromagnetic pulse signals.

[0084] Reference Figure 4 and Figure 5 shown, in this embodiment, the frequency domain curve diagram of the coupling voltage and the time domain curve diagram of the coupling voltage are the analysis diagrams of the coupled differential mode voltage signals at the PCB terminal of the engine fuel regulation system for the rotational speed. Figure 4 and Figure 5 show that under the action of the strong electromagnetic pulse field, the rotational speed acquisition system only has a strong coupling ability for some frequency bands. In these sensitive frequency bands, the electromagnetic pulse energy is more likely to be coupled into the rotational speed acquisition system, causing interference or damage to the engine fuel regulation system. It can be obtained from the frequency domain curve of the coupling voltage signal of the engine rotational speed acquisition system that the sensitive frequency points under the action of the strong electromagnetic pulse are mainly distributed at 40 MHz, 60 MHz, 150 MHz, and 300 MHz, and the durations of different frequency bands are different. According to the time-frequency domain diagram of the coupling voltage signal of the rotational speed sensor PCB terminal, the coupling interference characteristics of the rotational speed acquisition system under the action of the strong electromagnetic pulse can be obtained.

[0085] Reference Figure 6 , Figure 7 and Figure 8 shown, in this embodiment, the distributed parameters existing in the components will reduce the performance of the filter, making the filter unable to eliminate the interference of the strong electromagnetic pulse from the wide frequency band. The S11 attenuation curves of the single-stage and two-stage filters are asFigure 7 As shown, the coupled signal is a multi-band and variable-energy interference. It is difficult for a single-stage filter to eliminate the interference on all frequency bands. The design of a wide-band filter will cause over-redundancy in non-sensitive frequency bands, increasing the design cost and volume of the filter. The number of filter stages corresponds to the number of sensitive frequency bands of the interference signal, and the maximum attenuation frequency of each stage of the filter is located at the center of the sensitive frequency band;

[0086] Therefore, when the overall shielding performance of the control system is good, the amplitude of the external strong electromagnetic pulse interference coupled into the control system is small and will not damage the control system. However, this small-amplitude coupling will interfere with the control system. The time-frequency domain analysis method is used to analyze the frequency bands of the small-amplitude coupling interference signal and the energy of different coupling frequency bands. Among them, the sensitive frequency band corresponds to the filtering level in the filter, and the corresponding filtering device of the filter is selected and eliminated according to the sensitive frequency band;

[0087] When the amplitude of the coupled interference signal is large, the limiting component is connected through the connecting switch to discharge the coupled electromagnetic energy. However, the limiting component still cannot eliminate the interference of the electromagnetic pulse. A filtering link should be added. Similarly, the coupled signal after limiting is analyzed to obtain the relative relationship between the position and energy of the sensitive frequency band. Among them, the sensitive frequency band corresponds to the filtering level in the filter, and the corresponding device of the filter is selected according to the relative relationship between the position and energy of the sensitive frequency band.

[0088] Embodiment 2:

[0089] As Figure 9 and Figure 10 shown, a time-frequency variable-energy protection device for a strong electromagnetic pulse of a digital control system in this embodiment includes:

[0090] A housing 1, and a multi-stage differential-mode suppression cavity 4 and a common-mode suppression cavity 5 are arranged inside the housing 1;

[0091] Referring to Figure 9 and Figure 10 shown, in this embodiment, a baffle 6 is arranged inside the housing 1 to divide it into a multi-stage differential-mode suppression cavity 4 and a common-mode suppression cavity 5. Aviation connectors 3 are arranged at both ends of the housing 1 for connecting external devices. Among them, a cover plate 2 is connected to the top of the housing 1 through bolt holes and bolts.

[0092] Referring to Figure 9 shown, in this embodiment, a common-mode interference suppression capacitor 7 and a limiting component 8 are connected and arranged inside the common-mode suppression cavity 5. Among them, the limiting component 8 is selectively conducted and disconnected from the overall circuit through the connecting switch. In this embodiment, the common-mode interference suppression capacitor 7 is preferably set as a pair, namely C4 and C5 respectively. Among them, C4 and C5 are correspondingly arranged on both sides of the limiting component 8 and penetrate into the multi-stage differential-mode suppression cavity 4 to be connected with a differential-mode filtering resistor 9 or a differential-mode filtering capacitor 10;

[0093] In this embodiment, the limiter 8 includes a MOV, GDT or TVS limiter.

[0094] Reference Figure 9 As shown, in this embodiment, a differential-mode filtering resistor 9 and a differential-mode filtering capacitor 10 are connected and arranged inside the multi-stage differential-mode suppression cavity 4. In this embodiment, the differential-mode filtering resistor 9 and the differential-mode filtering capacitor 10 are preferably arranged in three pairs. Each pair includes one differential-mode filtering capacitor 10 connected in series with two differential-mode filtering resistors 9, and the differential-mode filtering capacitors 10 of each pair are in a parallel relationship with each other. Specifically, the differential-mode filtering resistor 9 includes R1, R2, R3, R4, R5 and R6, and the differential-mode filtering capacitor 10 includes C1, C2 and C3. Among them, C1 is respectively connected in series with R1 and R2, C2 is respectively connected in series with R3 and R4, and C3 is respectively connected in series with R5 and R6 and then C1, C2 and C3 are connected in parallel with each other. Each differential-mode filtering capacitor 10 and the differential-mode filtering resistor 9 in series therewith are of one level. During use, the externally coupled interference signal runs from inside the common-mode suppression cavity 5 to inside the multi-stage differential-mode suppression cavity 4. When the amplitude of the externally coupled interference signal is large, it will damage the subsequent devices. At this time, the connection switch turns on the limiter 8 to discharge the large electromagnetic energy coupled externally. After the discharge is completed, filtering is performed through the differential-mode filtering resistor 9 and the differential-mode filtering capacitor 10 in the multi-stage differential-mode suppression cavity 4. When the amplitude of the externally coupled interference signal is small, the connection switch does not turn on the limiter 8, and the externally coupled interference signal directly enters the multi-stage differential-mode suppression cavity 4. The filter stage number of the filter in the multi-stage differential-mode suppression cavity 4 and the energy tolerance value of the device are selected, and filtering is performed through the differential-mode filtering resistor 9 and the differential-mode filtering capacitor 10;

[0095] Finally, the suppression of strong electromagnetic pulse coupling interference with high intensity and low intensity is realized. At the same time, the energy tolerance value and volume of the filtering device are minimized. While realizing the efficient design of the filter, the volume of the filter is reduced and the cost of the filter is lowered.

[0096] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention. These all fall within the protection scope of the present invention.

Claims

1. A time-frequency variable energy protection method for digital control systems under strong electromagnetic pulses, characterized in that: It includes: Obtain the terminal coupling interference waveform of the digital control system; Judge whether it will cause damage to the controller terminal or the filter terminal according to the terminal coupling interference waveform, and determine the final coupling interference waveform: Combine the terminal coupling interference waveform parameters with the allowable damage threshold of the digital controller device to judge whether it will cause damage to the controller terminal or the filter terminal. If damage can be caused, limit the interference waveform to obtain the limited coupling interference waveform as the final coupling interference waveform; if no damage can be caused, directly use the terminal coupling interference waveform as the final coupling interference waveform; Conduct time-frequency energy analysis according to the final coupling interference waveform: Convert the collected discrete measurement signals into a two-dimensional complex time-frequency domain matrix, where the rows and columns correspond to the frequency and time distributions respectively, and obtain the amplitude and phase information of the sampling signals at the corresponding frequencies and times through the corresponding row and column vectors, that is, the time-frequency domain signals; Determine the multi-stage filter according to the frequency band and energy distribution results; The collected discrete measurement signals are obtained through the following method: ， Among them, f is the frequency, the signal duration is t, and the time sampling interval is T, then the number of signal sampling points is ; Let , , when , the S transform is written as function; Perform discrete processing on the S transform, and we can get: ， Among them, , ; When then ， Therefore, all elements of the S transform are: 。 2. A time-frequency variable energy protection method for digital control systems under strong electromagnetic pulses according to claim 1, characterized in that: Use the two-dimensional complex time-frequency domain matrix and Fourier transform to convert the measured time-domain signal into a frequency-domain signal, and analyze the sensitive frequency band of the electromagnetic pulse coupling into the control system in the frequency-domain signal; Integrate the time-domain characteristics and frequency-domain characteristics of the coupling signal on a two-dimensional image through time-frequency domain analysis, reconstruct the time-frequency domain curve of the strong electromagnetic pulse in the bounded wave simulator, and obtain the sensitive frequency band of the coupling signal of the control system and the energy distribution on each sensitive frequency band.

3. A time-frequency variable energy protection method for digital control systems under strong electromagnetic pulses according to claim 2, characterized in that: The determination of the multi-stage filter according to the frequency band and energy distribution results specifically includes: According to the sensitive frequency band of the coupling signal of the control system and the energy distribution on each sensitive frequency band: When the amplitude of the signal coupled by the external strong electromagnetic pulse interference into the control system is small and will not cause damage to the control system, connect the corresponding filtering devices in the filter according to the sensitive frequency band; When the amplitude of the coupling interference signal is large, turn on the limiting component through the connecting switch to discharge the coupling electromagnetic energy, and at the same time increase the filter ring nodes, analyze the limited coupling signal, and connect the corresponding filtering devices in the filter according to the relative relationship between the position and energy of the sensitive frequency band.

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