A short-offset transient electromagnetic launch system

Abstract

The invention discloses a short-offset transient electromagnetic transmitting system, comprising: an electromagnetic transmitter with four transmitting power supplies P1, P2, P3, and P4, five groups of grounding electrodes A, B, C, D, and F, and eight transmitting wires LA, LB1, LB2, LC1, LC2, LD1, LD2, and LE, wherein the grounding electrode A and the grounding electrode B are connected to the transmitting power supply P1 through the wire A and the wire LB1; the grounding electrode B and the grounding electrode C are connected to the transmitting power supply P2 through the wire LB2 and the wire LC1; the grounding electrode C and the grounding electrode D are connected to the transmitting power supply P3 through the wire LC2 and the wire LD1; the grounding electrode D and the grounding electrode E are connected to the transmitting power supply P4 through the wire LD2 and the wire LE; the wire LA and the wire LB1 are pulled from the transmitter to the position of the grounding electrode B through a twisted pair; the wire LD2 and the wire LE are pulled from the transmitter to the position of the electrode grounding D through a twisted pair. The technical solution of the invention is adopted to effectively adapt the electromagnetic transmitting system to the SOTEM method.

Description

Technical Field

[0001] The invention belongs to the technical field of geophysical exploration, and in particular relates to a short-offset transient electromagnetic transmitting system. Background Art

[0002] Artificial source electromagnetic method is one of the mainstream methods for mineral resource exploration. It uses grounding wires or closed loops as antennas to excite the earth and extract underground electrical structure information by observing the earth response signal. According to the distance between the observation area and the transmitting source, it can generally be divided into far-source method and near-source method. For a long time, far-source methods (such as CSAMT, LOTEM, etc.) have become the mainstream of artificial source electromagnetic methods due to their relatively simple solutions and have been widely promoted worldwide. In the near-source area, although the signal is stronger and the bandwidth is larger, it is more conducive to achieving deep and high-precision detection, but the wave field conditions in the near-source area are complex, so the development of the near-source method is relatively lagging. Since 2000, researchers at the University of Edinburgh in the United Kingdom have proposed a near-source method MTEM (Multi-transient Electromagnetic) based on multi-channel arrangement to achieve fine identification of underground travel structures. Since then, research on near-source methods has gradually become a research hotspot again worldwide. Since 2013, the short-offset transient electromagnetic method (SOTEM) has been proposed. This method has the advantages of large detection depth and strong resolution.

[0003] At present, in actual SOTEM observations, although the existing electromagnetic equipment can obtain data stably, the actual detection effect cannot meet expectations, indicating that the equipment is not well adapted to the method. From the perspective of equipment, in the traditional far-source method, the transmission and reception distance is large, and the signal amplitude and bandwidth are significantly attenuated. The equipment that matches the far-source method mainly considers achieving deep detection by increasing the transmission power and suppressing the sensor noise level. However, because the signal bandwidth itself is limited (about 10 kHz) under far-source observation conditions, the equipment only considers a smaller bandwidth in the whole process, that is, the existing equipment mainly realizes high-power transmission and low-noise observation under narrow bandwidth conditions. In actual work, the existing electromagnetic transmitter is weakly adaptable to the SOTEM method, which is mainly reflected in the fact that the bandwidth of the transmission current is smaller than the bandwidth requirement of the SOTEM method.

[0004] In addition, the transmitting pole distance of the SOTEM transmitter is usually up to 1km, and the wire inductance is as high as 2.5-3mH. The characteristic that the inductor current lags behind the inductor voltage severely limits the bandwidth of the transmitting current. In order to achieve high-bandwidth current transmission, constant voltage clamping technology is generally used to speed up the current conversion speed. At present, mainstream electromagnetic equipment on the market usually adopts active constant voltage clamping solutions, and the clamping voltage is generally 1000V. In order to achieve faster conversion of the transmitting current, the clamping voltage needs to be increased. However, the voltage resistance characteristics of power devices limit the further increase of voltage, and also have safety risks. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a short-offset transient electromagnetic transmitting system.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A short-offset transient electromagnetic transmitting system comprises: an electromagnetic transmitter with four transmitting power supplies P1, P2, P3 and P4, five groups of grounding electrodes A, B, C, D and F and eight transmitting wires LA, LB1, LB2, LC1, LC2, LD1, LD2 and LE, wherein the grounding electrode A and the grounding electrode B are connected to the transmitting power supply P1 through the wire A and the wire LB1; the grounding electrode B and the grounding electrode C are connected to the transmitting power supply P2 through the wire LB2 and the wire LC1; the grounding electrode C and the grounding electrode D are connected to the transmitting power supply P3 through the wire LC2 and the wire LD1; the grounding electrode D and the grounding electrode E are connected to the transmitting power supply P4 through the wire LD2 and the wire LE; the wire LA and the wire LB1 are pulled from the transmitter to the position of the grounding electrode B through a twisted pair mode; the wire LD2 and the wire LE are pulled from the transmitter to the position of the electrode grounding D through a twisted pair mode.

[0008] Preferably, the electromagnetic transmitter includes: a diesel generator, a three-phase rectifier module, an inverter isolation power supply module, a constant current voltage regulation module and an output inverter module; wherein the diesel generator is used to provide 380V three-phase AC power; the three-phase rectifier module converts the three-phase AC power into 540V DC; the inverter isolation power supply module obtains four groups of 1000V isolated power supplies through 1 inverter bridge, 4 transformers, 4 high-frequency rectifier bridges and LC filters; the constant current voltage regulation module is used to control the output voltage and realize output constant current regulation; the output inverter module generates four groups of output transmission power supplies P1, P2, P3, and P4.

[0009] Preferably, the output inversion is output inversion using a bootstrap high-voltage clamping technology.

[0010] Preferably, the four groups of transmitting power supplies P1, P2, P3, and P4 are relatively independent, and according to the output load, the switching devices Q1-Q4 are adjusted in real time to control the duty cycle signal so as to achieve substantially unchanged output current.

[0011] The present invention divides the 1km long pole distance into 4 short pole distances through 5 groups of ground electrodes, connects the ground electrodes to 4 groups of output power supplies respectively using 8 stranded wires, and designs a bootstrap UHV clamping technology to further accelerate current conversion. The technical solution of the present invention enables the electromagnetic transmitting system to effectively adapt to the SOTEM method, and realizes rapid conversion of the transmitting current under high power conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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 embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0013] Figure 1 This is a schematic diagram of the relationship between the inductance of a 1km long wire and the wire radius;

[0014] Figure 2 This is a schematic diagram of the relationship between the inductance and the length of the wire when the wire radius is 3mm;

[0015] Figure 3 It is a schematic diagram of the structure of a short offset transient electromagnetic launch system;

[0016] Figure 4 It is a schematic diagram of the structure of the electromagnetic transmitter;

[0017] Figure 5 It is a schematic diagram of the output inverter structure based on the bootstrap high voltage clamping technology;

[0018] Figure 6 Schematic diagram of the bootstrap capacitor charging process;

[0019] Figure 7 It is a schematic diagram of bootstrap high voltage clamp control and output voltage and current waveform;

[0020] Figure 8 Schematic diagram of simulation results based on bootstrap high-voltage clamping technology. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments 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.

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Embodiment 1:

[0024] The embodiment of the present invention provides a short-offset transient electromagnetic transmitting system, which divides a 1km long pole distance into four short pole distances through five groups of grounding electrodes, uses eight twisted-wire conductors to connect the electrodes to four groups of isolated transmitting power supplies respectively, and designs a bootstrap ultra-high voltage clamping technology to further accelerate current conversion.

[0025] For a 1km long conductor, if the mutual coupling between the conductor and the ground is ignored, the relationship between the conductor inductance and the conductor radius is as follows: Figure 1 shown.

[0026] For a copper conductor with a current of 100A, a conservative estimate is that its cross-sectional area is 25mm 2 , the radius is about 3mm, and the corresponding inductance is about 2.532mH. If the wire radius is set to 3mm, the relationship between the wire inductance and the wire length is as follows: Figure 2 shown.

[0027] The 1km pole distance is divided into 4 equal parts by 5 electrodes, each pole distance is 250m, and the corresponding wire inductance with a radius of 3mm is 0.5637mH.

[0028] like Figure 3 As shown, an embodiment of the present invention provides a short-offset transient electromagnetic transmission system, including: an electromagnetic transmitter with four transmission power supplies P1, P2, P3, and P4, five groups of ground electrodes A, B, C, D, and F, and eight transmission wires LA, LB1, LB2, LC1, LC2, LD1, LD2, and LE, wherein the ground electrode A and the ground electrode B are connected to the transmission power supply P1 through the wire A and the wire LB1; the ground electrode B and the ground electrode C are connected to the transmission power supply P2 through the wire LB2 and the wire LC1; the ground electrode C and the ground electrode D are connected to the transmission power supply P3 through the wire LC2 and the wire LD1; the ground electrode D and the ground electrode E are connected to the transmission power supply P4 through the wire LD2 and the wire LE; the wire LA and the wire LB1 are pulled from the transmitter to the ground electrode B position by twisting; the wire LD2 and the wire LE are pulled from the transmitter to the electrode ground D position by twisting. The magnetic fields around the twisted wires with opposite currents are offset, and their inductance can be ignored.

[0029] Since the P1, P2, P3, and P4 transmitting power supplies are isolated from each other, loop cross-current problems are avoided. Assuming that the transmitting wire inductance is L and the grounding resistance is R, the current cut-off time is:

[0030] ;

[0031] It can be seen that the current shut-off time is related to the grounding resistance and the wire inductance. Under the condition of a certain grounding resistance, the 1km long wire inductance of 2.5mH ​​is divided into four small inductors with an inductance of 0.5637mH, and the shut-off time is reduced by about 78%.

[0032] As an implementation method of the embodiment of the present invention, Figure 4 As shown, the electromagnetic transmitter includes: a diesel generator, a three-phase rectifier module, an inverter isolation power supply module, a constant current voltage regulation module and an output inverter module; wherein the diesel generator is used to provide 380V three-phase AC power; the three-phase rectifier module converts the three-phase AC power into 540V DC; the inverter isolation power supply module obtains four groups of 1000V isolated power supplies through 1 inverter bridge, 4 transformers, 4 high-frequency rectifier bridges and LC filters; the constant current voltage regulation module is used to control the output voltage and realize output constant current regulation; the output inverter module generates four groups of output transmission power supplies P1, P2, P3, and P4.

[0033] Furthermore, the four groups of transmitting power supplies P1, P2, P3, and P4 are relatively independent, and according to the output load, the switching devices Q1-Q4 are adjusted in real time to control the duty cycle signal, so that the output current remains basically unchanged.

[0034] The four power supplies P1, P2, P3, and P4 have the same structure. Here, the power supply P4 is taken as an example to illustrate the connection relationship of the system, and the other power supplies are similar.

[0035] The diesel generator outputs three-phase electricity Va, Vb and Vc.

[0036] The three-phase rectifier module converts the three-phase alternating current Va, Vb and Vc into direct current by using the unidirectional conductivity of the diode. The three-phase rectifier module is composed of diodes D1-D6 and capacitor C. The anode of D1 is connected to the cathode of D2 and connected to the generator Va; the anode of D3 is connected to the cathode of D4 and connected to the generator Vb; the anode of D5 is connected to the cathode of D6 and connected to the generator Vc; the cathodes of D1, D3 and D5 are connected and connected to one end of the non-polar capacitor C as the positive power supply of the three-phase rectifier; the anodes of D2, D4 and D6 are connected and connected to the other end of the non-polar capacitor C as the negative power supply of the three-phase rectifier.

[0037] The inverter isolation power supply module uses the switching mode of the H bridge composed of the control power switch device to make the output positive and negative alternate, converting DC into AC, obtaining isolated AC through the isolation transformer, and then using the rectifier bridge to convert the AC into DC with larger ripple, and finally using the inductor capacitor filter to obtain low ripple DC. The inverter isolation power supply module is composed of IGBT power switch tubes S1-S4, transformer T4, fast recovery diodes D41-D44, inductor L41 and capacitor C41, wherein the collector of S1 is connected to the collector of S3 and connected to the positive three-phase rectifier power supply at one end of the non-polar capacitor C; the emitter of S2 is connected to the emitter of S4 and connected to the negative three-phase rectifier power supply at the other end of the non-polar capacitor C; the emitter of S1 is connected to the collector of S2 and connected to the same-name terminal of the primary side of the transformer T4; the emitter of S3 is connected to the collector of S4 The anodes of D41 and D42 are connected and connected to the non-like-named terminals of the primary side of the transformer T4; the anode of D43 is connected to the cathode of D44 and connected to the non-like-named terminals of the secondary side of the transformer T4; the cathodes of D41 and D43 are connected and connected to one end of the inductor L41, and the other end of L41 is connected to one end of the non-polarized capacitor C41 as the positive inverter isolation power supply; the anodes of D42 and D44 are connected and connected to the other end of the non-polarized capacitor C41 as the negative inverter isolation power supply.

[0038] The constant current voltage regulation module is based on the BUCK circuit principle, and the output voltage is proportional to the pulse width modulation PWM duty cycle. The module is based on the pulse width modulation PWM control method, and achieves the purpose of constant current voltage regulation by adjusting the duty cycle. The constant current voltage regulation module is composed of IGBT power switch tubes Q4, D45, L42, C42 and D46, wherein the collector of Q4 is connected to the positive inverter isolation power supply at one end of the non-polar capacitor C41; the emitter of Q4 is connected to the cathode of the diode D45 and connected to one end of the inductor L42, and the other end of L42 is connected to one end of the non-polar capacitor C42 and connected to the anode of the diode D46, and the cathode of the diode D46 is used as the positive constant current voltage regulation power supply; the other end of the non-polar capacitor C42 is connected to the anode of the diode D45, and connected to the negative inverter isolation power supply at the other end of the capacitor C41 as the negative constant current voltage regulation power supply.

[0039] The output inverter module uses the switching mode of the H bridge composed of the control power switching device to make the output positive and negative alternate, and convert the direct current into alternating current. The output inverter module is composed of K4, C4, K41, K42, K43 and K44, wherein the emitter of K4 is connected to the collector of K41 and K43, and is connected to the cathode of the diode D46 of the positive constant current voltage regulating power supply; the collector of K4 is connected to one end of the capacitor C4, and the other end of C4 is connected to the emitter of K42 and K44, and is connected to the anode of D42, D44 and D45 of the negative constant current voltage regulating power supply; the emitter of K41 and the collector of K42 are connected and serve as one end of the output power supply P4 to the emitter electrode; the emitter of K43 and the collector of K44 are connected and serve as the other end of the output power supply P4 to the other emitter electrode.

[0040] The typical emission waveform of the SOTEM method is a bipolar square wave with a duty cycle of 50%. The transient signal generated by the ground after the pulse is turned off is observed. In order to achieve rapid conversion of the output current, the output inverter module adopts the bootstrap high-voltage clamping technology. Here, the power supply P4 is used as an example to expand the connection relationship of the system. Figure 5 The other power supplies are similarly configured.

[0041] Since diode D46 has unidirectional conductivity, when the cathode voltage of D46 is greater than the anode voltage, D46 is cut off, otherwise it is turned on. In the initial state, the voltage of bootstrap capacitor C4 is equal to the constant current voltage regulation output voltage. Since P4 is connected to the electrode with a long wire, the wire has a strong inductance. After the inverter bridge emission current is turned off, the commutation current of the wire inductance charges capacitor D4. The charging process of bootstrap capacitor C4 is as follows: Figure 6 shown.

[0042] In order to achieve rapid current conversion, the bootstrap capacitor C4 is first charged. When the charging voltage reaches the preset voltage value, the control of the power switch device K4 is turned on, and the voltage on the bootstrap capacitor C4 is used to quickly magnetize and demagnetize the inductive load of the output inverter, that is, to convert the magnetic energy on the long wire and the electric energy on the capacitor back and forth, so as to achieve high-bandwidth conversion of the emission current. When the bootstrap capacitor C4 is charged, the on-off control of the inverter bridge switch devices K41-K44 and the bootstrap switch device K4, and the emission waveform P4 and the emission current I4 are as shown in FIG. Figure 7 shown.

[0043] Furthermore, a simulation model of output inversion based on bootstrap high-voltage clamping technology is constructed. The transmitting voltage is set to 1000V, the transmitting 1km long wire inductance is 2.5mH, the grounding resistance is 50Ω, and the output frequency is 1kHz with a duty cycle of 50% bipolar square wave. When the bootstrap capacitor voltage reaches 2000V, the power switch device K4 begins to be controlled normally. The output inverter bridge diagonal control signals V1 and V2 are "AND" operated and the signal delayed by 30us is "XOR" operated to control the power switch device K4. The simulation results are as follows: Figure 8 shown.

[0044] It can be seen that at the beginning of startup, the voltage of the bootstrap capacitor gradually rises until it reaches 2000V and then stabilizes, and begins to work normally. During the capacitor voltage rising stage, the current off time is about 33us. As the bootstrap capacitor voltage reaches 2000V, the power switch device K4 begins to enter the working state. At this time, the current off time is about 20us. The system has a significant effect of accelerating current conversion.

[0045] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A short-offset transient electromagnetic launch system, characterized in that: include: An electromagnetic transmitter having four transmitting power sources P1, P2, P3, P4, five groups of grounding electrodes A, B, C, D, E and eight transmitting wires LA, LB1, LB2, LC1, LC2, LD1, LD2, LE, wherein the grounding electrode A and the grounding electrode B are connected to the transmitting power source P1 through the wire LA and the wire LB1; the grounding electrode B and the grounding electrode C are connected to the transmitting power source P2 through the wire LB2 and the wire LC1; the grounding electrode C and the grounding electrode D are connected to the transmitting power source P3 through the wire LC2 and the wire LD1; the grounding electrode D and the grounding electrode E are connected to the transmitting power source P4 through the wire LD2 and the wire LE; the wire LA and the wire LB1 are pulled from the transmitter to the position of the grounding electrode B through a twisted pair; the wire LD2 and the wire LE are pulled from the transmitter to the position of the electrode grounding D through a twisted pair; The electromagnetic transmitter includes: a diesel generator, a three-phase rectifier module, an inverter isolation power supply module, a constant current voltage regulation module and an output inverter module; wherein the diesel generator is used to provide 380V three-phase AC power; the three-phase rectifier module converts the three-phase AC power into 540V DC; the inverter isolation power supply module obtains four groups of 1000V isolated power supplies through 1 inverter bridge, 4 transformers, 4 high-frequency rectifier bridges and LC filters; the constant current voltage regulation module is used to control the output voltage and realize the output constant current regulation; the output inverter module generates four groups of transmitting power supplies P1, P2, P3, P4; Output inversion adopts bootstrap high voltage clamping technology; The four groups of transmitting power supplies P1, P2, P3, and P4 are relatively independent. According to the output load, the switching devices Q1-Q4 are adjusted in real time to control the duty cycle signal so that the output current remains basically unchanged.

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