A broadband high-efficiency electromagnetic detection transmitting system and control method

Abstract

The present application belongs to the technical field of frequency domain electromagnetic detection, and relates to a wideband efficient electromagnetic detection transmitting system and a control method. The control method comprises the following steps: calculating a target depth corresponding frequency range according to a skin depth formula; generating a linear frequency modulation signal and converting it into a Chirp-PWM control signal; driving an H-bridge inverter to output a high-power Chirp-PWM voltage signal; monitoring load impedance and dynamically adjusting IMN duty cycle parameters to adaptively adjust the equivalent impedance of the IMN, thereby realizing real-time impedance matching; and outputting a PWM control signal and transmitting the PWM control signal to the IMN to complete real-time dynamic impedance matching. The control method of the wideband efficient electromagnetic detection transmitting system can significantly improve the detection vertical resolution, accurately adapt to the target depth detection requirements, realize spectrum energy improvement, cover a wide frequency band in a single signal cycle, reduce transmission loss, greatly shorten the detection time, and reduce the transmitter capacity requirements.

Description

Technical Field

[0001] This invention belongs to the field of frequency domain electromagnetic detection technology, specifically relating to a controllable broadband frequency domain electromagnetic detection excitation method, and particularly to a broadband high-efficiency electromagnetic detection transmission system and control method. Background Technology

[0002] Frequency-domain electromagnetic methods, as a key detection technology, have been widely applied in many fields such as resource exploration, mineral exploration, and environmental assessment. A typical workflow for frequency-domain electromagnetic detection is as follows: the transmitter system provides alternating current containing specific frequency components through a transmitting antenna to establish a primary detection field; the receiver system records the electromagnetic response information and performs data post-processing to obtain the apparent resistivity information and imaging results of the detection area. According to the skin depth formula, detection signals of different frequencies are needed to cover the detection area. Effective transmission of broadband signals is also a core research direction for electromagnetic instruments in order to obtain high-quality imaging results and reliable detection data.

[0003] Regarding signal selection, the square wave frequency sweep scheme is the most widely used and technologically mature, but it struggles to address the issues of long operation time and high exploration costs. Dual-frequency and multi-frequency pseudo-random waves have been introduced into detection applications, significantly expanding the transmission bandwidth and positively impacting detection efficiency. However, these methods suffer from inherent limitations such as a limited number of frequency points and fixed main frequency intervals, restricting the improvement of detection resolution. While linear frequency modulation (Chirp) signals and digitized Chirp-PWM signals offer advantages in wide-band measurement and have been applied in fields such as railway impedance measurement and underground cable insulation detection, the existing technologies have relatively low operating frequencies and transmission power, making them unsuitable for frequency domain electromagnetic detection requirements.

[0004] In terms of impedance matching, capacitive impedance matching networks (IMNs) used in conjunction with inductive transducers can improve high-frequency transmission power and reduce transmitter capacity requirements. However, existing fixed-matching-frequency IMNs and narrow-band controllable IMNs cannot meet the real-time impedance matching requirements of Chirp-PWM signals in wideband, controllable-bandwidth transmission, resulting in traditional frequency-domain electromagnetic detection methods having problems such as limited effective transmission energy, low detection efficiency, and poor vertical resolution.

[0005] Therefore, there is an urgent need to develop a broadband, high-efficiency electromagnetic detection and transmission system and control method to effectively solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a broadband high-efficiency electromagnetic detection and transmission system, and a control method for such a system, in order to solve the problems of traditional frequency domain electromagnetic detection methods being limited by the uncontrollable functional form of the detection signal and the dispersed distribution of the main frequency, resulting in limited effective transmission energy within the target depth range, and consequently low detection efficiency and poor vertical resolution.

[0007] This invention is achieved through the following technical solution:

[0008] A broadband high-efficiency electromagnetic detection and transmission system consists of a DC power supply connected to a power amplifier, an IMN, and an equivalent load.

[0009] The power amplifier uses an H-bridge inverter and its output inductor. and capacitor It can amplify the Chirp-PWM control signal into a bipolar PWM signal with an amplitude equal to the DC power supply voltage, which can then be used as the transmission signal. In frequency domain electromagnetic exploration, grounding cables and magnetotelluric transducers are both inductive loads and can be equivalent to resistors. With inductance The series structure; the broadband IMN is used as a compensator, connected in series between the power amplifier and the equivalent load, and is supported by a fixed capacitor. Fixed capacitors and bidirectional switches composed of reverse-series IGBTs. Two-way switch composition.

[0010] A control method for a broadband, high-efficiency electromagnetic detection and transmission system includes the following steps:

[0011] A. Determine the required transmission frequency band based on the skin depth formula, and calculate the frequency range corresponding to the target depth;

[0012] B. Generate a linear frequency modulation signal, combine the Chirp wave expression of linear spread spectrum and the Chirp-PWM signal conversion formula to convert it into a Chirp-PWM control signal, and calculate the IMN capacitor parameters;

[0013] C. Drive the power amplifier, and the H-bridge inverter outputs a high-power Chirp-PWM voltage signal;

[0014] D. Monitor load impedance and dynamically adjust IMN duty cycle Identify the target load impedance, calculate the required instantaneous impedance, and, based on the pre-determined time-varying frequency law of the broadband Chirp-PWM signal within a single duty cycle, determine the target IMN duty cycle control law. It adaptively adjusts the equivalent impedance of the IMN to achieve real-time impedance matching;

[0015] E. Output PWM control signal, send the PWM control signal to the provided IMN to complete real-time dynamic impedance matching.

[0016] Further, in step A, the required radiofrequency band is determined using the skin depth formula shown in formula (1):

[0017] (1)

[0018] In the formula, To detect depth, To detect the resistivity of the medium in the region, For the detection frequency, the corresponding target depth range [ , The required transmission frequency band is [ , ],in, and The excitation frequency corresponds to the boundary of the detection area.

[0019] Furthermore, in step B, the Chirp wave expression for linear spread spectrum is:

[0020] (2)

[0021] In the formula, and These are the lowest and highest frequencies of the target frequency band, respectively. It is a linear frequency modulation period;

[0022] In digital signal processors, Chirp-PWM signal conversion is efficiently implemented in the following manner, denoted as: :

[0023] (3)

[0024] Combine formulas (2) and (3) to determine the Chirp-PWM signal.

[0025] Further, in step B, the IMN capacitance parameters are calculated, specifically as follows:

[0026] Available capacitive reactive power of controllable IMN structure The range is represented as:

[0027] (4)

[0028] In the formula, This is the load voltage value;

[0029] The minimum capacitive impedance that IMN can provide and maximum capacitive impedance They are respectively:

[0030] (5)

[0031] (6)

[0032] In the formula, , For fixed capacitors;

[0033] To achieve the highest transmit energy within the target frequency range, the available reactive power required by the IMN must cover the reactive power of the inductive load. scope:

[0034] (7)

[0035] In the formula, This represents the minimum reactive power of the inductor. This is the minimum equivalent inductance. The minimum frequency. This represents the maximum reactive power of the inductor. This is the maximum value of the equivalent inductance. This represents the maximum frequency.

[0036] Combining formulas (6) and (7), the component parameters required for IMN are calculated and within the available range [ , Select parameters within. and And reserve a margin;

[0037] (8)

[0038] (9)

[0039] Further, step C specifically involves: combining the desired transmission frequency range with formulas (2) and (3) to calculate the target Chirp-PWM voltage and current control signals. and As a reference signal; the output voltage of the power amplifier is acquired. and current The signal is transmitted to the digital signal processor controller and controlled by the proportional-integral control module and reference signal. and The comparison is performed; thus, the control power amplifier outputs a wideband Chirp-PWM voltage signal to the subsequent circuit, that is, the H-bridge inverter outputs a high-power Chirp-PWM voltage signal.

[0040] Further, step D, identifying the target load impedance, specifically involves:

[0041] According to the instantaneous reactive power theory, the instantaneous load power is calculated using formula (10):

[0042] (10)

[0043] In the formula, and They are respectively and The delayed signal, with a delay time t D As shown in formula (13):

[0044] (11)

[0045] In the formula, This refers to the instantaneous transmission frequency;

[0046] Calculate the load voltage value and reactive power :

[0047] (12)

[0048] (13)

[0049] Identify the target load impedance using formula (14) :

[0050] (14).

[0051] Furthermore, in step D, the required instantaneous impedance is calculated using formula (15):

[0052] (15).

[0053] Furthermore, in step D, the target IMN duty cycle control law is determined by formula (16) based on the time-varying frequency law of the broadband Chirp-PWM signal within a single working cycle. To achieve real-time impedance matching:

[0054] (16)

[0055] In the formula, For capacitor Capacitive resistance, For capacitor Capacitive reactance;

[0056] Based on the target duty cycle control law The equivalent impedance of the IMN is adaptively adjusted.

[0057] Further, in step E, a PI control module is added before the final control signal output to compare the load reactive power. With IMN reactive power Perform calibration.

[0058] Compared with the prior art, the beneficial effects of the present invention are:

[0059] 1. This invention achieves precise control of frequency distribution and bandwidth through linear spread spectrum technology. At the same time, relying on the dense frequency characteristics of the Chirp-PWM signal, the frequency spread factor reaches 20 times, which significantly improves the vertical resolution of detection and accurately adapts to the target depth detection requirements.

[0060] 2. This invention combines a real-time impedance matching network (IMN) with a dynamic impedance matching strategy to compensate for the reactive power of the load, solve the energy loss problem caused by impedance mismatch in traditional methods, and achieve an 85% improvement in spectral energy in the 15-20kHz frequency band, providing sufficient energy support for high-quality detection data acquisition.

[0061] 3. Through parameter optimization design and integrated control strategy, this invention can identify and dynamically adjust time-varying load parameters in real time, adapting to the requirements of wide load inductance and wide frequency range; at the same time, a single signal cycle can cover a wide frequency band, reducing transmission loss, significantly shortening detection time, reducing transmitter capacity requirements, and improving practical performance under complex geological conditions. Attached Figure Description

[0062] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0063] Figure 1 The diagram shows the transmitter structure and the impedance matching performance of the proposed IMN.

[0064] Figure 2 Flowchart for designing Chirp-PWM signal and IMN parameters;

[0065] Figure 3 Diagram of the integrated control strategy proposed for power amplifier control;

[0066] Figure 4 Diagram of the integrated control strategy proposed for compensator control;

[0067] Figure 5 The simulation results show the transmit current in the 15kHz-20kHz frequency band.

[0068] Figure 6 The simulation results of the transmission current in the 15kHz-20kHz frequency band are amplified;

[0069] Figure 7 Simulation results for the transmit current spectrum in the 15kHz-20kHz frequency band;

[0070] Figure 8 Simulation results for the transmit current spectrum in the 15kHz-17.5kHz frequency band;

[0071] Figure 9 The simulation results show the emitter current spectrum under the existing PWM method in the 15kHz-20kHz frequency band;

[0072] Figure 10 The simulation results show the emitter current spectrum under the existing PWM method in the 15kHz-17.5kHz frequency band.

[0073] Figure 11 The results are dynamic simulations of the transmit current when the frequency band switches from 15kHz-20kHz to 15kHz-17.5kHz.

[0074] Figure 12 The dynamic simulation results show the transmission current when the load switches from Group 1 to Group 2.

[0075] Figure 13 This is a flowchart illustrating the steps of the control method for the broadband high-efficiency electromagnetic detection and transmission system of the present invention. Detailed Implementation

[0076] The present invention will be further described below with reference to embodiments:

[0077] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0078] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0079] A linear frequency modulated (Chirp) wave is a type of broadband frequency modulation spread spectrum technique, and it is a sinusoidal signal whose frequency varies with time. The expression for a linear spread spectrum Chirp wave is:

[0080] ;

[0081] In the formula, and These are the lowest and highest frequencies of the target frequency band, respectively. T0 is the linear frequency modulation period, i.e., the chirp signal period. Inside, the signal frequency from Linear change to ) This frequency range is defined as the bandwidth. The instantaneous frequency expression is:

[0082] ;

[0083] Therefore, by adjusting the boundary frequency f (min) with f (max) This technology enables control over the frequency band of linear frequency modulated (LFM) signals, also known as chirp signals. Chirp signals offer significant advantages in broadband transmission: they can acquire electromagnetic response information over a wide frequency range within a single duty cycle, greatly improving detection efficiency and showing potential applications in buried target detection and geophysical exploration. However, according to Passevar's theorem, the spectral energy of the signal is limited within a single cycle, making chirp signals only suitable for low-power applications.

[0084] ;

[0085] In the formula, Let be the amplitude of the kth harmonic of the Chirp signal.

[0086] Chirp-PWM is a novel PWM scheme. Unlike traditional PWM schemes with a fixed switching frequency, its switching frequency varies according to the Chirp law. In digital signal processors, Chirp-PWM signal conversion can be efficiently implemented in the following way, denoted as... :

[0087] ;

[0088] To establish a strong primary transmitting magnetic field and ensure a sufficient signal-to-noise ratio, the broadband signal needs to be amplified into a high-power transmitting signal to meet practical application requirements. In this case, the load is an equivalent load consisting of ground inductance and ground resistance. In this scenario, the converted Chirp-PWM digital signal is used to drive the IGBT H-bridge power amplifier described below.

[0089] In practical applications, the load is an inductive load, and its impedance expression is:

[0090] ;

[0091] In the formula, This refers to the transmission frequency, which is also the detection frequency. The inductance is an imaginary unit. Typically, the inductance of a common grounded load ranges from 1mH to 5mH. The reactive power of the load accounts for a significant portion of the transmitter's power capacity, limiting the spectral energy of the transmitted current signal, while the strength of the transmitted current signal directly affects the strength of the excitation magnetic field. Therefore, a capacitive IMN is crucial, especially in high-frequency transmitted signals used for frequency-domain electromagnetic detection. According to the impedance matching principle, when the capacitive impedance of the IMN satisfies the following formula, impedance matching can be achieved with the load inductance for a specific transmission frequency, establishing a maximum power transmission path.

[0092] ;

[0093] For the designed broadband Chirp-PWM signal, the inductive impedance changes with time; at the same time, in frequency domain electromagnetic exploration, the load inductance exhibits slow time-varying characteristics. These characteristics result in a wide range of load inductive impedance, requiring the IMN to have flexible impedance control capabilities.

[0094] The equivalent impedance of the proposed broadband IMN is determined by a fixed capacitance. Fixed capacitors and control duty cycle The capacitive impedance it provides can be expressed as:

[0095] ;

[0096] Assuming complementary switches and The conduction time within one working cycle is respectively and So, what is the duty cycle of IMN? It can be represented as follows:

[0097] ;

[0098] By adjusting the duty cycle The proposed IMN can provide capacitive impedance that meets the impedance matching requirements of specific frequency bands and load impedances.

[0099] In summary, the transmitter system impedance of the proposed broadband IMN can be expressed as the following piecewise function:

[0100] ;

[0101] The proposed broadband IMN enables impedance matching within a controllable wide frequency range, thereby achieving effective transmit power.

[0102] In summary, the proposed broadband transmission method, combining linear spread spectrum and broadband impedance matching techniques, enables flexible frequency distribution and bandwidth configuration, thereby achieving efficient power transmission.

[0103] like Figure 1 As shown, the broadband high-efficiency electromagnetic detection and transmission system of the present invention consists of a DC power supply connected to a power amplifier, an IMN, and an equivalent load. The power amplifier employs an H-bridge inverter and its output inductor. and capacitor The Chirp-PWM control signal can be amplified into a bipolar PWM signal with an amplitude equal to the DC power supply voltage, which can then be used as the transmission signal. In frequency domain electromagnetic exploration, electromagnetic transducers such as grounding cables and the earth are inductive loads and can be equivalent to resistors. With inductance The series structure. A broadband IMN, acting as a compensator, is connected in series between the power amplifier and the equivalent load, and is supported by a fixed capacitor. Fixed capacitors and bidirectional switches composed of reverse-series IGBTs. Two-way switch Composition. Fast impedance matching can be achieved by adjusting the equivalent capacitance using a modulation strategy. (See figure.) , , and These are the DC power supply voltage, power amplifier output capacitor voltage, IMN voltage, and load voltage, respectively. , These are the output inductor current and load current of the power amplifier, respectively.

[0104] like Figure 13 As shown, the control method of the broadband high-efficiency electromagnetic detection and transmission system of the present invention includes the following steps:

[0105] A. Determine the required transmission frequency band based on the skin depth formula, and calculate the frequency range corresponding to the target depth;

[0106] B. Generate a linear frequency modulation signal, combine the Chirp wave expression of linear spread spectrum and the Chirp-PWM signal conversion formula to convert it into a Chirp-PWM control signal, and calculate the IMN capacitor parameters;

[0107] C. Drive the power amplifier, and the H-bridge inverter outputs a high-power Chirp-PWM voltage signal;

[0108] D. Monitor load impedance and dynamically adjust IMN duty cycle Identify the target load impedance, calculate the required instantaneous impedance, and, based on the pre-determined time-varying frequency law of the broadband Chirp-PWM signal within a single duty cycle, determine the target IMN duty cycle control law. It adaptively adjusts the equivalent impedance of the IMN to achieve real-time impedance matching;

[0109] E. Output PWM control signal, send the PWM control signal to the provided IMN to complete real-time dynamic impedance matching.

[0110] Specifically, in order to cover the target detection area, the required effective transmission frequency band can be determined by the skin depth formula shown in formula (1).

[0111] (1)

[0112] In the formula, To detect depth, To detect the resistivity of the medium in the region, For detection frequency. Corresponding target depth range [ , The required transmission frequency band is [ , ],in, and The excitation frequency corresponds to the boundary of the detection area.

[0113] The Chirp wave expression for linear spread spectrum is:

[0114] (2)

[0115] in, and These are the lowest and highest frequencies of the target frequency band, respectively. The frequency modulation period is linear. The Chirp-PWM signal follows the Chirp law. In a digital signal processor, Chirp-PWM signal conversion can be efficiently implemented in the following way, denoted as [equation missing]. :

[0116] (3)

[0117] Combining formulas (2) and (3), the Chirp-PWM signal can be further determined; the effective transmit bandwidth can be expressed as... .

[0118] The design goal of broadband IMN is to achieve impedance matching for inductive loads with varying frequency and inductance characteristics. For Figure 1 The controllable IMN structure shown can utilize capacitive reactive power. The range can be represented as:

[0119] (4)

[0120] In the formula, This is the load voltage value;

[0121] The minimum capacitive impedance that IMN can provide and maximum capacitive impedance They are respectively:

[0122] (5)

[0123] (6)

[0124] To achieve the highest transmit energy within the target frequency range, the available reactive power required by the IMN must cover the reactive power range of the inductive load:

[0125] (7)

[0126] In the formula, This represents the minimum reactive power of the inductor. This is the minimum equivalent inductance. The minimum frequency. This represents the maximum reactive power of the inductor. This is the maximum value of the equivalent inductance. This represents the maximum frequency.

[0127] Combining formulas (6) and (7), the component parameters required for IMN can be calculated, and within the available range [ , Select parameters within. and And reserve a margin.

[0128] (8)

[0129] (9).

[0130] Considering the requirements for wide frequency and wide load inductance range in frequency domain electromagnetic detection, Figure 2 The parameter design flow for the Chirp-PWM signal and IMN is given to ensure the highest transmit energy is obtained.

[0131] The proposed integrated control strategy is as follows: Figures 3-4 As shown, this includes broadband transmit signal control and real-time IMN control, as detailed below:

[0132] like Figure 3 As shown, the control objective of the power amplifier is to output the pre-designed Chirp-PWM transmit current. To achieve this objective: combining the desired transmit frequency range with formulas (2) and (3), the target Chirp-PWM control voltage and current signals are calculated. and As a reference signal; the output voltage of the power amplifier is acquired. and current The signal is transmitted to the Digital Signal Processor (DSP) controller, and then controlled by the proportional-integral (PI) control module to interact with the reference signal. and The comparison is performed; through the above process, the power amplifier is controlled to output a wideband Chirp-PWM voltage signal to the subsequent circuit.

[0133] like Figure 4 As shown, the control strategy of broadband IMN includes load impedance identification and dynamic impedance matching to achieve the highest transmit power. According to the instantaneous reactive power theory, the instantaneous load power can be calculated using formula (10):

[0134] (10)

[0135] In the formula, Instantaneous active power Instantaneous reactive power and They are respectively and Delayed signal, delay time As shown in formula (13):

[0136] (11)

[0137] In the formula, This is the instantaneous transmission frequency. Subsequently, the load voltage value is calculated. and reactive power :

[0138] (12)

[0139] (13).

[0140] Furthermore, the target load impedance can be identified by combining formula (14). :

[0141] (14)

[0142] The required instantaneous impedance can be calculated using formula (15):

[0143] (15)

[0144] Based on the time-varying frequency law of the broadband Chirp-PWM signal within a single working cycle, the target IMN duty cycle control law is determined by formula (16). To achieve real-time impedance matching:

[0145] (16)

[0146] In the formula, For capacitor Capacitive resistance, For capacitor Capacitance.

[0147] Based on the target duty cycle control law It can adaptively adjust the equivalent impedance of the IMN to provide capacitive reactive power for reverse compensation of the reactive power of variable inductive loads. Furthermore, a PI control module is added before the final control signal output to compare the load reactive power... With IMN reactive power Calibration was performed. Finally, the PWM control signal was transmitted to the proposed IMN to achieve dynamic impedance matching. The proposed controllable broadband transmission method and the above analysis were verified by simulation results. The simulation parameters are shown in Table 1. Figures 5-12 The launch performance of the proposed method is demonstrated through steady-state and dynamic case studies.

[0148] Table 1

[0149]

[0150] first, Figure 5 Steady-state simulation results of the transmit current waveform in the 15kHz~20kHz frequency band are presented. Figure 6 As shown in the magnified waveform, it can be seen that, through the proposed IMN, the transmitted signal is restored from a triangular wave to a relatively smooth sine wave.

[0151] To evaluate the effect of the emission energy enhancement, the spectral energy enhancement rate is defined. :

[0152] (17)

[0153] In the formula, and These represent the average amplitudes of the transmit current spectrum within the effective transmit frequency band before and after adding the IMN. Figure 7 and Figure 8 It can be seen that, under different bandwidth scenarios, the amplitude of the transmit current spectrum after adding IMN... The results reached 567% and 620% respectively, further verifying the broadband impedance matching capability of the proposed IMN under controllable bandwidth.

[0154] also, Figure 9 and Figure 10Simulation results for existing PWM transmit methods in the 15kHz-20kHz and 15kHz-17.5kHz frequency bands are presented for performance comparison. Combined with... Figures 11-12 The results show that the frequency distribution of the proposed broadband transmission method is denser in the required frequency bands of 15kHz-20kHz and 15kHz-17.5kHz, with frequency spread factors reaching 20 times and 8.5 times respectively, verifying the effectiveness of the proposed transmission method.

[0155] Secondly, the dynamic simulation results of frequency band switching and load switching are as follows: Figure 11 and Figure 12 As shown, the transient time for the transmit current to re-reach a steady state is less than 1 ms, and the overshoot does not exceed 1%, further verifying the effectiveness of the proposed load identification and dynamic impedance matching control method. Finally, Table 1 lists the simulation results of power performance under different scenarios, where... and These are the average active power and reactive power of the power amplifier, respectively. and These represent the average active power and reactive power of the proposed IMN, respectively. and The values ​​represent the average active power and reactive power of the load, respectively. The results show that the proposed method helps to improve transmit power, reduce transmitter capacity loss, and achieves compensator power loss of less than 2%.

[0156] Note that the design of the digital prototype model, the parameter settings for each material, and the selection of the measuring plane described above are merely preferred embodiments and technical principles of the present invention. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A control method for a broadband high-efficiency electromagnetic detection and transmission system, characterized in that, Includes the following steps: A. Determine the required transmission frequency band based on the skin depth formula, and calculate the frequency range corresponding to the target depth; B. Generate a linear frequency modulation signal, combine the Chirp wave expression of linear spread spectrum and the Chirp-PWM signal conversion formula to convert it into a Chirp-PWM control signal, and calculate the IMN capacitor parameters; C. Drive the power amplifier, and the H-bridge inverter outputs a high-power Chirp-PWM voltage signal; D. Monitor the load impedance and dynamically adjust the IMN duty cycle parameters, identify the target load impedance, calculate the required instantaneous impedance, combine the time-varying frequency law of the broadband Chirp-PWM signal in a single working cycle to determine the target IMN duty cycle control law, adaptively adjust the equivalent impedance of the IMN, and achieve real-time impedance matching. E. Output PWM control signal, send the PWM control signal to the provided IMN to complete real-time dynamic impedance matching; A wideband high-efficiency electromagnetic detection and transmission system consists of a DC power supply connected to a power amplifier, an IMN, and an equivalent load. The power amplifier uses an H-bridge inverter and its output inductor. and capacitor It can amplify the Chirp-PWM control signal into a bipolar PWM signal with an amplitude equal to the DC power supply voltage, which can then be used as the transmission signal. In frequency domain electromagnetic exploration, grounding cables and magnetotelluric transducers are both inductive loads and can be equivalent to resistors. With inductance The series structure; the broadband IMN is used as a compensator, connected in series between the power amplifier and the equivalent load, and is supported by a fixed capacitor. Fixed capacitors and bidirectional switches composed of reverse-series IGBTs. Two-way switch composition.

2. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 1, characterized in that, In step A, the required effective transmission frequency band is determined using the skin depth formula shown in formula (1): （1） in, To detect depth, To detect the resistivity of the medium in the region, For detection frequency, corresponding to the target depth range The required transmission frequency band is ,in, and The excitation frequency corresponds to the boundary of the detection area.

3. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 1, characterized in that, In step B, the Chirp wave expression for linear spread spectrum is: （2） In the formula, and These are the lowest and highest frequencies of the target frequency band, respectively. It is a linear frequency modulation period; In digital signal processors, Chirp-PWM signal conversion is efficiently implemented in the following manner, denoted as: : （3） Combine formulas (2) and (3) to determine the Chirp-PWM signal.

4. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 1, characterized in that, Step B, calculate the IMN capacitance parameters, specifically: Available capacitive reactive power of controllable IMN structure The range is represented as: （4） In the formula, This is the load voltage value; The minimum capacitive impedance that IMN can provide and maximum capacitive impedance They are respectively: （5） （6） To achieve the highest transmit energy within the target frequency range, the available reactive power required by the IMN must cover the reactive power range of the inductive load: （7） In the formula, This represents the minimum reactive power of the inductor. This is the minimum equivalent inductance. The minimum frequency. This represents the maximum reactive power of the inductor. This is the maximum value of the equivalent inductance. This represents the maximum frequency. Combining formulas (6) and (7), the component parameters required for IMN are calculated and are within the available range. Internal selection parameters and And reserve a margin; （8） （9）。 5. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 1, characterized in that, Step C specifically involves: combining the desired transmission frequency range with formulas (2) and (3), calculating the target Chirp-PWM voltage and current control signals. and As a reference signal; the output voltage of the power amplifier is acquired. and current The signal is transmitted to the digital signal processor controller and controlled by the proportional-integral control module and reference signal. and The comparison is performed; thus, the control power amplifier outputs a wideband Chirp-PWM voltage signal to the subsequent circuit, that is, the H-bridge inverter outputs a high-power Chirp-PWM voltage signal.

6. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 1, characterized in that, Step D, identify the target load impedance, specifically: Based on the theory of instantaneous reactive power, the instantaneous reactive power is calculated using formula (10). （10） In the formula, and They are respectively and Delayed signal, delay time As shown in formula (11): （11） In the formula, This refers to the instantaneous transmission frequency; Calculate the load voltage value and reactive power : （12） （13） Identify the target load impedance using formula (14) : （14）。 7. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 6, characterized in that, Step D, the required instantaneous impedance is calculated using formula (15): （15）。 8. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 6, characterized in that, Step D: Combining the time-varying frequency law of the broadband Chirp-PWM signal within a single working cycle, the target IMN duty cycle control law is determined by formula (16). To achieve real-time impedance matching: （16）； In the formula, For capacitor Capacitive resistance, For capacitor Capacitive reactance; Based on the target duty cycle pattern The equivalent impedance of the IMN is adaptively adjusted.

9. The control method for a broadband high-efficiency electromagnetic detection and transmission system according to claim 1, characterized in that, Step E: Add a PI control module before the final control signal output, by comparing the load reactive power. With IMN reactive power Perform calibration.

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