CN113866835B - A time-domain three-waveform combination electromagnetic emission system and control method - Google Patents

Abstract

The invention relates to an electromagnetic emission system and a control method combined with three waveforms in the time domain. The purpose is to generate trapezoidal waves and triangular waves with different off-times, half-sine waves with different pulse widths and combined waveform emission currents. The transmitting system is composed of main control circuit, transmitting bridge circuit, RLC series resonant circuit, passive clamping circuit, transmitting coil and so on. Set the transmission parameters according to the exploration requirements, the main control circuit outputs the PWM signal through the optocoupler to drive the corresponding switch module in the transmission system; when the transmission bridge is connected, the passive clamping circuit supplies the transmission coil with Different clamping voltages are provided to realize controllable current off time; when the RLC series resonant circuit is turned on, the energy storage capacitor supplies power to the resonant circuit to generate a bipolar half-sine wave. Applying the electromagnetic emission system combined with three waveforms in the time domain to the SQUID-based induction-polarization dual-field detection can overcome the shallow detection blind zone and SQUID loss of lock, and improve the overall detection accuracy of the transient electromagnetic method.

Description

A time-domain three-waveform combination electromagnetic emission system and control method

technical field

The invention relates to an electromagnetic emission system and a control method combining three waveforms in the time domain, which are suitable for the field of electromagnetic geophysical exploration or geological structure detection, and especially provide an excitation source for the magnetic source time domain electromagnetic detection method.

Background technique

The magnetic source time-domain electromagnetic detection method uses ungrounded loops to emit bipolar pulse currents underground. The pulse currents can be square waves, trapezoidal waves, triangular waves, and half-sine waves. The time-varying signal of the secondary field is collected through the receiving coil or the Superconducting Quantum Interference Device (SQUID, Superconducting Quantum Interference Device) and the receiver, and the data is processed and interpreted to obtain rich resistivity or polarizability information of the underground medium. The transient electromagnetic method has the advantages of large detection depth, economy and convenience, and has been widely used in geological resource exploration and engineering detection.

Due to the limitations of detection instruments and data interpretation methods, the traditional time-domain electromagnetic method can only excite and interpret electromagnetic induction signals, the measurement parameters and interpretation parameters are single, and the accuracy of data interpretation is low, resulting in low precision of exploration results; The coil is an inductive load with a large parasitic inductance. After the emission current is turned off, the current will not decrease to zero immediately, but will decay exponentially. There will be overshoot and oscillation at the end of the current. These reasons cause the emission current The waveform quality is low, the shallow information is seriously lost, and the primary field cannot be offset and corrected during data interpretation; the poor performance of the transmitting system and the single interpretation parameter severely limit the further development and application of the transient electromagnetic method.

In order to meet the needs of simultaneous detection of deep and shallow layers, the traditional bipolar trapezoidal wave is no longer applicable, while the bipolar triangular wave has rich high-frequency components, small pulse width, and small propagation distance of electromagnetic waves. At this time, the receiving system can obtain The signal is mainly the signal of shallow geological bodies; the pulse width of the half-sine wave emission current is large, and the low-frequency components are rich, which can be used as an excitation source for the detection of deep geological bodies; the combination of triangular wave and half-sine wave emission current can realize different depth Geological bodies are detected to reduce the blind area of electromagnetic detection.

Dual-parameter joint detection is an effective method to improve the detection accuracy of TEM. The induced polarization effect is a common phenomenon existing in the earth. Research, simultaneous detection of the induced field and the excitation polarization signal can effectively improve the interpretation accuracy of the earth. The induced field (TEM) is the secondary induced magnetic field generated by the underground medium. The conductivity parameter of the underground medium can be obtained by interpreting the induced field; The polarization field is interpreted to obtain the polarizability parameters of the subsurface medium. The study found that both TEM and IP can detect water resources and metal mines. In the process of low-frequency time-domain electromagnetic detection, it is found that the induction field and the polarization field exist at the same time; Coexist with the polarization field, mainly the induction field, and the late stage is mainly the polarization field. There is a polarization charging effect during the turn-off of the emission current of the magnetic source. When the emission current amplitude is constant, the shorter the turn-off time, the shorter the polarization charging time, resulting in a weaker excited polarization field, which is suitable for induction field measurement; the turn-off time The longer , the longer the polarization charging time, resulting in a stronger excited polarization field, which is suitable for polarization field measurement. Therefore, the combination of trapezoidal wave and triangular wave emitting current with different off-times can be used to detect IP and TEM signals at the same time.

Superconducting Quantum Interference Device (SQUID, Superconducting Quantum Interference Device) has the characteristics of low noise, large bandwidth and high sensitivity (fT order), and has been successfully applied in transient electromagnetic field. Since the polarization field signal is very weak, traditional The receiving coil is difficult to obtain, and the SQUID is an ideal sensor for receiving the induction-polarization field signal. However, the SQUID sensor needs to work in a low electromagnetic noise environment, and its system slew rate (2.4mT/s) is also small, which puts forward new requirements for the transmitting system. The overshoot of the emission current and the tail oscillation will generate large electromagnetic interference, which may cause the SQUID system to lose lock and fail to work normally. Therefore, it is necessary to connect the absorption circuit during the shutdown process of the emission current to suppress the current overshoot and the tail oscillation. When the emission current changes too fast during the rising or falling process, the SQUID system will lose lock due to exceeding the slew rate. Although the low-voltage clamping circuit can prolong the off-time of the transmitting current, the effect is still limited, and the clamping circuit cannot be changed. The rising process of the emission current will cause the SQUID system to work unstable, and the phenomenon of loss of lock will still occur. For this reason, an RLC series resonant circuit is added to the transmitting system, and the bipolar half-sine wave generated by the emission current has a large pulse width, the rising part and falling part of the waveform are symmetrical, and the overall change of the transmitting current is slow, which can fully meet the requirements of the SQUID system. Need to prevent it from losing lock and work stably. In order to combine with the advantages of the linear turn-off of the trapezoidal wave, the emission current combined with the trapezoidal wave and the half-sine wave is used as the excitation source for SQUID system detection, which can significantly improve the stability and accuracy of the detection system.

Chinese patent CN107017610B discloses a transient electromagnetic transmitter passive constant voltage clamp fast turn-off circuit, TVS tubes are connected in series at both ends of the transmitting coil through electronic switches to provide passive clamping voltage for the coil; in addition, variable damping is used The matching snubber circuit absorbs the electric energy of reverse discharge of the coil. The clamp voltage adjustable circuit and the absorbing circuit are used to realize the rapid shutdown of the emission current.

Chinese patent CN108227011A discloses a dual-trapezoidal wave emission system and control method with controllable falling edges. A set of high-voltage transient suppressor diodes or a set of low-voltage transient suppressor diodes are connected in series through a switch module to form a high-voltage clamp. Bit or low-voltage clamping, to generate a set of trapezoidal emission currents with different off-times, and to realize the simultaneous detection of the dual parameters of resistivity and polarizability. The experimental results prove the effectiveness of the clamping voltage for changing the off-time of the emission current.

The above-mentioned method discloses a method for the passive clamping circuit to quickly or slowly turn off the current in the transmitting coil, all of which exert influence on the off-time of the trapezoidal wave transmitting current. However, for transient electromagnetic shallow detection and SQUID sensor-based induction-polarization field dual-field measurement, almost none of the existing transmitting systems can meet the requirements; and most transmitters can only emit trapezoidal wave emission current, The single waveform makes it difficult for the transmitting system to excite high-quality secondary fields in the face of complex geological conditions. How to transmit combined waveforms and transmit current with high waveform quality in time-domain electromagnetic detection, reduce the detection blind zone and realize the accurate measurement of the induction-polarization field dual field is a technical problem urgently solved by those skilled in the art.

Contents of the invention

The invention provides an electromagnetic emission system and control method combined with three waveforms in the time domain, aiming to solve the problems of single emission current waveform, limited shallow detection and loss of lock based on SQUID sensor measurement of induction-polarization field dual fields.

Embodiments of the present invention provide an electromagnetic emission system and control method combining three waveforms in time domain, including an external power supply, a main control circuit, a transmitting bridge circuit, a passive clamping circuit, an absorbing circuit, and an RLC series resonant circuit; the external The power supply supplies power to the transmitting bridge, and also charges the energy storage capacitor; the main control circuit, as the control part of the transmitting system, controls the switching module to work to generate different types of transmitting current waveforms; the transmitting bridge is composed of four switching modules An H bridge circuit is formed to provide bipolar trapezoidal wave or triangular wave emission current for the emission coil; the passive clamping circuit is composed of five groups of switch modules and four groups of transient suppression diodes (TVS). One group of transient suppression diodes is connected in series at both ends of the transmitting coil to provide a clamping voltage to the transmitting coil; the absorbing circuit is composed of a group of switch modules and a power resistor, which is used to absorb the electric energy of the reverse discharge of the transmitting current and suppress Oscillation at the tail of the current; the RLC series resonant circuit is composed of a transmitting coil, a non-polar capacitor and an inductor, and generates a bipolar half-sine wave transmitting current under the action of the energy storage capacitor and the switching module.

Further, the main control circuit outputs multiple PWM waves according to the set emission parameters and drives the corresponding switch modules in the emission system through the optocoupler, which can control the emission system to output the trapezoidal wave or triangular wave emission current with controllable off time, Half sine wave emission current with different pulse width; it can also output the emission current of combination of trapezoidal wave and triangular wave, combination of trapezoidal wave and half sine wave, combination of triangular wave and half sine wave.

Further, the PWM wave output by the main control circuit of the transmitting bridge passes through the optocoupler to drive the four switching modules of the bridge circuit on and off. When the pulse width of the PWM wave is greater than the inherent rise time between the power supply and the transmitting coil, it can generate Trapezoidal wave emission current with adjustable duty cycle and period; when the pulse width of PWM wave is less than the inherent rise time, it can generate triangular wave emission current with adjustable pulse width and period.

Further, in order to meet the requirements of high-power transmission, the switching modules in the transmitting bridge circuit, clamping circuit, absorbing circuit and RLC series resonant circuit usually use IGBT modules with high withstand voltage and large current resistance, MOSFET modules or other types switch module.

Further, the passive clamping circuit is composed of a group of general switch modules, four groups of switch modules and four groups of transient suppression diodes; the total switch module is controlled by the signal generated by the NOR gate logic circuit, so that it can Turn off, turn on during the cut-off period of the emission current; each group of TVS diodes is composed of multiple TVS diodes with the same voltage value connected in parallel, the clamping voltage of the four groups of TVS diodes is distributed from low voltage to high voltage, and the clamping voltage can be adjusted The selection range is generally 8.5V to 120V. The main control circuit controls a group of transient suppression diodes to be connected in series at both ends of the transmitting coil during the off period of the emission current, and controls the off time of the emission current according to the clamping voltage.

Further, the absorbing circuit is composed of a group of switch modules and a power resistor; the main control circuit controls the power resistor to be connected in series at both ends of the transmitting coil during the shutdown of the transmitting current, and the resistance value of the power resistor is generally 200% of the resistance value of the transmitting coil. times to 500 times; during the cut-off period of the transmitting current, when a group of TVS diodes are connected, the current in the transmitting coil first breaks down the TVS diodes and forms a loop. When the energy in the transmitting coil is not enough to maintain the TVS diodes In the breakdown state, the power resistor is connected to form a loop with the transmitting coil, which is used to absorb the remaining energy in the transmitting coil and suppress the overshoot and tail oscillation of the transmitting current; When not connected, the power resistor and the transmitting coil form a loop, which can quickly absorb the energy in the transmitting coil and reduce the off time of the transmitting current.

Further, the RLC series resonant circuit is composed of a transmitting coil, a non-polar capacitor and a magnetic ring inductance, the resistance in the transmitting coil and the inductance in the inductance are used as the resistance of the resonant circuit, and the inductance in the transmitting coil and the magnetic ring inductance are used as the inductance of the resonant circuit, Multiple parallel high withstand voltage non-polar capacitors are used as the capacitors of the resonant circuit; the external power supply charges the polarized energy storage capacitors, and the main control circuit controls the on-off of the switch module, and the two energy storage capacitors respectively supply power to the RLC series resonant circuit , to generate a bipolar half-sine wave emission current; the inductance and capacitance in the RLC series resonant circuit determine the pulse width of the half-sine wave emission current.

Compared with the prior art, the technical solution provided by the embodiments of the present invention has the beneficial effect that: the transmitting bridge of the present invention can transmit bipolar triangular waves or trapezoidal waves under the control of the main control circuit. During the turn-off period, TVS diodes with different clamping voltages are connected in series at both ends of the transmitting coil to realize the controllable off-time of the emission current, and the overshoot and tail oscillation of the emission current are suppressed by the connection of the absorption circuit to improve the emission The waveform quality of the current. By adopting the RLC series resonant circuit to transmit the bipolar half-sine wave transmission current, the slow change of the transmission current is realized, and the loss of lock of the SQUID sensor is suppressed. The combination of half sine wave and triangular wave emission current realizes simultaneous detection of geological bodies at different depths; the combination of triangular wave and trapezoidal wave emission current with different off-times realizes simultaneous measurement of induction-polarization field dual fields; the combination of trapezoidal wave and half sine wave emission current Realize high-precision detection based on the SQUID sensor; reduce the detection blind area of the time-domain electromagnetic method and improve work efficiency.

Description of drawings

Fig. 1 is the circuit diagram of high-power transient electromagnetic multi-waveform transmitting system and control method of the present invention;

Fig. 2 is the overall block diagram of transient electromagnetic multi-waveform transmitting system of the present invention;

Fig. 3 is a triangular wave and trapezoidal wave transmitting circuit diagram based on the controllable off-time of the transmitting bridge;

Fig. 4 is a half-sine wave transmitting circuit diagram based on the RLC series resonant circuit;

Fig. 5 is a trapezoidal wave emission current waveform and a clamping voltage diagram of different off-times;

Fig. 6 is a triangular wave emission current waveform diagram of different off-times;

Fig. 7 is a half-sine wave emission current waveform diagram of different amplitudes and pulse widths;

Fig. 8 is three kinds of combined emission current waveform diagrams;

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Example

Referring to Fig. 1 in conjunction with Fig. 2, a time-domain three-waveform combination electromagnetic emission system provided by the present invention is mainly composed of a main control circuit, a button part, a liquid crystal display, a low-power power supply, an optocoupler drive, a transmitting bridge, and an It is composed of source clamping circuit, absorbing circuit, RLC series resonant circuit, transient suppression diode, power resistor, energy storage capacitor, transmitting coil, high-power power supply and a series of switch modules. Among them, the low-power power supply supplies power to the main control circuit; the button part and the LCD display are used as the human-computer interaction part to select and determine the emission parameters; the optocoupler drive part boosts the PWM wave output by the main control circuit to control On-off of the switch module; the high-power power supply provides energy for the transmitting coil and the energy storage capacitor; the transmitting bridge is composed of four switching modules, which are used to generate bipolar triangular wave or trapezoidal wave transmitting current on the transmitting coil; passive clamping circuit Transient suppression diodes are connected in series at both ends of the transmitting coil, and the turn-off time of the transmitting current can be changed by applying different clamping voltages to the transmitting coil; the absorbing circuit and power resistors are connected in series at both ends of the transmitting coil, which can be used for fast switching off of the transmitting current Cut off and suppress current overshoot and tail oscillation; RLC series resonant circuit and energy storage capacitor are used to generate bipolar half-sine wave transmitting current on the transmitting coil.

The transmitting bridge is composed of switch modules Q1, Q2, Q3, and Q4 to form an H-bridge circuit, and the four switch modules are respectively located on the upper and lower bridge arms of the H-bridge circuit, and the transmitting coil is connected between the upper and lower bridge arms, and the transmitting coil is equivalent to a resistance r and inductance L1; the switch modules Q1, Q2, Q3, and Q4 are turned on and off according to a certain period and pulse width under the control of the main control circuit. When the pulse width is less than the inherent rise time between the power supply and the transmitting coil, The transmitting coil will generate a bipolar triangular wave transmitting current; when the pulse width is greater than the inherent rise time between the power supply and the transmitting coil, the transmitting coil will generate a bipolar trapezoidal wave transmitting current; in order to meet the requirements of high-power transmission, the switch module Q1, Q2, Q3, and Q4 are IGBTs, MOSFETs or other types of switches with high withstand voltage and high current withstand.

The passive clamping circuit is composed of a set of main switches Q7, Q8, four-component switches Q9, Q10, Q11, Q12, Q13, Q14, Q15, Q16 and four sets of transient suppression diodes TVS1, TVS2, TVS3, TVS4 ; The main switch Q7, Q8 is controlled by the logic signal generated by the NOR gate. It is opened when the emission current starts to be turned off, and it is closed when the emission current starts to rise. The four-component switch is controlled by the main control circuit. Select one of them The component switches are always open or all four sets of switches are closed; the clamping voltages of TVS1, TVS2, TVS3, and TVS4 are distributed from low to high, and each group of TVS diodes is composed of multiple TVSs with the same clamping voltage in parallel; when there is a component When the switch is turned on, a group of TVS diodes are connected in series at both ends of the transmitting coil to generate a clamping voltage and change the off-time of the transmitting current during the off-time of the transmitting current.

The absorbing circuit is composed of a group of switches Q5, Q6 and a power resistor R, the switches Q5, Q6 are controlled by the main control circuit, they are turned on when the emission current is turned off, and they are turned off when the emission current starts to rise; During the off period, the power resistor is connected in series at both ends of the transmitting coil. When a group of TVS is connected, the current in the transmitting coil will first break through the TVS tube and form a loop with the TVS. At this time, the power resistor is equivalent to an open circuit state. When the transmitting current decreases When it is too small to maintain the breakdown state of TVS, the transmitting coil forms a loop with the power resistor to release the remaining energy; when there is no TVS connected during the off period of the transmitting current, the transmitting coil directly forms a loop with the power resistor, due to the large resistance of the power resistor Due to the resistance of the transmitting coil, the current in the transmitting coil will be cut off quickly.

The RLC series resonant circuit is composed of energy storage capacitors C1, C2, circuit switching switches Q17, Q18, Q19, resonance control switches Q1, Q2, current flow control diodes D1, D2, non-polar capacitor C3, magnetic ring inductance L2 and transmitting coil composition; the energy storage capacitors C1 and C2 obtain the energy of the power supply, and supply power to the resonant circuit; the circuit switching switches Q17, Q18, and Q19 are controlled by the main control circuit. When Q17, Q18, and Q19 are kept open, the transmitting system launches Bipolar half sine wave, when Q17, Q18, Q19 keep disconnected, the transmitting system emits bipolar triangular wave or trapezoidal wave; the resonance control switch Q1, Q2 is controlled by the main control circuit to control the energy storage capacitor and resonance The on-off of the circuit changes the polarity of the half sine wave current; the current flow control diodes D1 and D2 are used to suppress the reverse current in the RLC resonant circuit, and end the resonant process when the current decreases to zero; the non-polar capacitor C3, the magnetic After the ring inductance L2 and the transmitting coil obtain the energy of the energy storage capacitor, they are first charged and then discharged to generate a half-sine wave transmitting current.

Referring to Fig. 3, the working process of the triangular wave and trapezoidal wave transmitting circuit with controllable off time is divided into four stages, which are forward power supply, forward stop power supply, reverse power supply and reverse stop power supply.

(1) Forward power supply: Switches Q1 and Q4 are turned on at the same time, and the current flow direction in the transmitting coil is E-D1-Q1-r-L1-Q4-D4. When the transmitting current increases from zero and then reaches a stable value, it is Trapezoidal wave; when the emission current increases from zero and then does not reach a stable value, it is a triangular wave.

(2) Forward stop power supply: switches Q1 and Q4 are turned off at the same time, at this time switches Q5, Q6, Q7, and Q8 are turned on, and the switches of one group of TVS tubes are kept on. At this time, the switches in TVS1, TVS2, TVS3, and TVS4 One of the TVS tubes is immediately connected in series with the transmitting coil to generate a clamping voltage V, the power supply voltage is U, and t is the moment after the start of the shutdown. At this time, the current in the transmitting coil satisfies the equation (1), and the shutdown time is t _d Equation (2) is satisfied, and the slope S of the falling edge satisfies Equation (3).

(3) Reverse power supply: switches Q5, Q6, Q7, and Q8 are turned off at the same time, switches Q2 and Q3 are turned on at the same time, and the current flow direction in the transmitting coil is E-D3-Q3-L1-r-Q2-D2. At this time, in the transmitting coil The direction of current flow changes.

(4) Reverse power supply stop: switches Q2 and Q3 are turned off at the same time, at this time switches Q5, Q6, Q7, and Q8 are turned on, a set of TVS tubes and power resistor R are connected in series with the transmitting coil, different clamping voltages determine different shutdown Time; the power resistor suppresses the current overshoot and tail oscillation.

Referring to FIG. 4 , the working process of the half-sine wave transmitting circuit based on the RLC series resonant circuit is divided into two stages, which are positive half-cycle resonance and negative half-cycle resonance.

(1) Positive half-cycle resonance: switch Q1 is turned on, and Q17, Q18, and Q19 of the switch switching circuit remain on. At this time, the energy storage capacitor C1 supplies power to the resonant circuit, and the current flow direction in the transmitting coil is C1-D1-Q1-r- L1-Q18-C3-L2-Q17-Q19, the half-sine wave pulse width satisfies equation (4). Generally, the switch Q1 is turned on for longer than the half-sine wave pulse width, so after the resonance is completed, the diode D1 acts , the emission current remains at zero and stabilizes.

(2) Negative half-cycle resonance: switch Q2 is turned on, switch Q1 is turned off, and Q17, Q18, and Q19 of the switch switching circuit remain on. At this time, the energy storage capacitor C2 supplies power to the resonant circuit, and the current flow in the transmitting coil is C2-Q17- L2-C3-Q18-L1-r-Q2-D2, the flow direction of the half-sine wave emission current changes, and the duration of switch Q2 opening is the same as that of switch Q1. After the resonance is completed, under the action of diode D2, the emission current remains to zero and stabilize.

The combination of trapezoidal wave and triangular wave has eight stages of emission current, forward trapezoidal wave emission, forward stop emission, forward triangular wave emission, forward stop emission, reverse trapezoidal wave emission, reverse stop emission, reverse triangle wave emission, reverse To stop emission; trapezoidal wave and half sine wave combined emission current is six stages, forward trapezoidal wave emission, forward stop emission, positive half-cycle resonance, reverse trapezoidal wave emission, reverse stop emission, negative half-cycle resonance; The combination of triangular wave and half sine wave has six stages of emission current, positive triangular wave emission, positive stop emission, positive half-cycle resonance, reverse triangle wave emission, reverse stop emission, and negative half-cycle resonance.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (7)

1. A control method of an electromagnetic emission system based on time domain three waveform combination is characterized in that: the device comprises an external power supply, a main control circuit, a transmitting bridge circuit, a passive clamping circuit, an absorption circuit and an RLC series resonance circuit; the main control circuit outputs multipath PWM waves according to the set emission parameters, the PWM waves drive a switch module acting on an emission bridge circuit through an optical coupler to control the electromagnetic emission system to output trapezoidal waves and triangular waves, the PWM waves drive a switch module acting on an RLC series resonant circuit through the optical coupler to control the electromagnetic emission system to output half sine wave emission currents, the PWM waves drive the switch module acting on the emission bridge circuit and the RLC series resonant circuit through the optical coupler at the same time to control the electromagnetic emission system to output emission currents of the trapezoidal waves and the triangular waves, the trapezoidal waves and the half sine waves and the triangular waves and the half sine waves; the PWM wave is driven by an optocoupler to act on a switch module of the passive clamping circuit and the absorption circuit and is used for changing the turn-off time of the emission current and inhibiting tail oscillation; the external power supply supplies power to the transmitting bridge circuit and also charges the energy storage capacitor; the main control circuit is used as a control part of the transmitting system and controls the switch module to work so as to generate different types of transmitting current waveforms; the transmitting bridge circuit is an H bridge circuit formed by four switch modules, and provides bipolar trapezoidal wave and triangular wave transmitting current for the transmitting coil; the passive clamp circuit is composed of five groups of switch modules and four groups of transient suppression diodes (TVS), and one group of transient suppression diodes are connected in series at two ends of a transmitting coil during the turn-off period of transmitting current to provide a clamp voltage for the transmitting coil; the absorption circuit consists of a group of switch modules and a power resistor and is used for absorbing electric energy of reverse discharge of emission current and inhibiting oscillation of the tail part of the current; the RLC series resonance circuit consists of a transmitting coil, a nonpolar capacitor and a magnetic ring inductor, and generates bipolar half sine wave transmitting current under the action of an energy storage capacitor and a switch module;

the specific process of outputting the current waveform by the trapezoid wave and the triangular wave combination by the transmitting system comprises the following steps:

the main control circuit outputs four paths of PWM waves, the two paths of PWM waves act on the Q1 and Q4 switch modules of the left half bridge of the H bridge, and a positive half-cycle trapezoidal wave and a positive half-cycle triangular wave are generated in the process; the other two paths of PWM waves act on the Q2 and Q3 switch modules of the right half-bridge of the H bridge, and negative half-cycle trapezoidal waves and negative half-cycle triangular waves are generated in the process; the emission system outputs bipolar trapezoidal wave and triangular wave combined current waveform in a cyclic reciprocating mode;

the specific process of outputting the trapezoid wave and half sine wave combined current waveform by the transmitting system comprises the following steps:

the main control circuit outputs five paths of PWM waves, the two paths of PWM waves act on the Q1 and Q4 switch modules of the left half bridge of the H bridge, and positive half-cycle trapezoidal waves are generated in the process; one path of PWM wave acts on Q17, Q18 and Q19 switch modules of the RLC series resonant circuit, and one path of PWM wave acts on Q1 switch module of the H bridge circuit, and in the process, C1 discharges to generate half sine wave of positive half period; when two paths of PWM waves act on the Q2 and Q3 switch modules of the right half bridge of the H bridge, negative half-cycle trapezoidal waves are generated in the process; one path of PWM wave acts on Q17, Q18 and Q19 switch modules of the RLC series resonant circuit, and one path of PWM wave acts on Q2 switch modules of the H bridge circuit, and in the process, C2 discharges to generate a half sine wave with a negative half period; the emission system outputs bipolar trapezoidal wave and half sine wave combined current waveform in a cyclic reciprocating mode;

the specific process of the current waveform combining the triangular wave and the half sine wave output by the transmitting system is as follows:

the main control circuit outputs five paths of PWM waves, two paths of narrow-bandwidth PWM waves act on Q1 and Q4 switch modules of a left half bridge of the H bridge, and a positive half-cycle triangular wave is generated in the process; one path of PWM wave acts on Q17, Q18 and Q19 switch modules of the RLC series resonant circuit, and one path of PWM wave acts on Q1 switch module of the H bridge circuit, and in the process, C1 discharges to generate half sine wave of positive half period; when two paths of narrow bandwidth PWM waves act on the Q2 and Q3 switch modules of the right half bridge of the H bridge, negative half-period triangular waves are generated in the process; one path of PWM wave acts on Q17, Q18 and Q19 switch modules of the RLC series resonant circuit, and one path of PWM wave acts on Q2 switch modules of the H bridge circuit, and in the process, C2 discharges to generate a half sine wave with a negative half period; with this cyclic reciprocation, the transmitting system outputs a bipolar triangular wave and half sine wave combined current waveform.

2. The method for controlling an electromagnetic emission system based on time domain three waveform combinations as claimed in claim 1, wherein: the main control circuit outputs multiple paths of PWM waves according to the set emission parameters and drives corresponding switch modules in the emission system through the optocouplers to control the emission system to independently output trapezoidal wave and triangular wave emission currents with controllable turn-off time and half sine wave emission currents with different pulse widths; or the emission system is controlled to output emission currents of the combination of the trapezoidal wave and the triangular wave, the combination of the trapezoidal wave and the half sine wave and the combination of the triangular wave and the half sine wave.

3. The method for controlling an electromagnetic emission system based on time domain three waveform combinations as claimed in claim 1, wherein: the emitting bridge is connected and disconnected by four switch modules of the optocoupler driving bridge circuit through PWM waves output by the main control circuit, and when the pulse width of the PWM waves is larger than the inherent rising time between the power supply and the emitting coil, trapezoidal wave emitting currents with adjustable duty ratio and period are generated; when the pulse width of the PWM wave is smaller than the inherent rising time, a triangular wave emission current with adjustable pulse width and period is generated.

4. The method for controlling an electromagnetic emission system based on time domain three waveform combinations as claimed in claim 1, wherein: the switch modules in the transmitting bridge circuit, the clamping circuit, the absorbing circuit and the RLC series resonant circuit are suitable for the requirement of high-power transmission, and the IGBT module or the MOSFET module with high withstand voltage and high withstand current is required to be selected.

5. The method for controlling an electromagnetic emission system based on time domain three waveform combinations as claimed in claim 1, wherein: the passive clamp circuit consists of a group of main switch modules, four groups of switch modules and four groups of transient suppression diodes; the master switch module is controlled by a signal generated by the NOR gate logic circuit, so that the master switch module is closed during the transmitting period and is opened during the transmitting current off period; each group of transient suppression diodes consists of a plurality of transient suppression diodes with the same clamping voltage value in parallel connection, the clamping voltage of the four groups of transient suppression diodes is distributed from low voltage to high voltage, the clamping voltage range is 8.5V to 120V, the main control circuit controls one group of transient suppression diodes to be connected in series with two ends of a transmitting coil in the transmitting current turn-off period, and the turn-off time of the transmitting current is controlled according to the difference of the clamping voltage.

6. The method for controlling an electromagnetic emission system based on time domain three waveform combinations as claimed in claim 1, wherein: the absorption circuit consists of a group of switch modules and a power resistor; the main control circuit controls the power resistor to be connected in series with two ends of the transmitting coil during the turn-off period of the transmitting current, and the resistance value of the power resistor is 200 to 500 times of that of the transmitting coil; during the turn-off period of the transmitting current, when a group of transient suppression diodes are connected in, the current in the transmitting coil breaks down the transient suppression diodes first and forms a loop, and when the energy in the transmitting coil is insufficient to maintain the breakdown state of the transient suppression diodes, the power resistor is connected in and forms a loop with the transmitting coil so as to absorb the residual energy in the transmitting coil and suppress the overshoot and tail oscillation of the transmitting current; during the turn-off period of the transmitting current, when the transient suppression diode is not connected, the power resistor and the transmitting coil form a loop, so that energy in the transmitting coil can be quickly absorbed, and the turn-off time of the transmitting current is shortened.

7. The method for controlling an electromagnetic emission system based on time domain three waveform combinations as claimed in claim 1, wherein: the RLC series resonance circuit is composed of a transmitting coil, a nonpolar capacitor and a magnetic ring inductor, wherein the resistor in the transmitting coil and the resistor in the inductor are used as resistors of the resonance circuit, the inductor in the transmitting coil and the magnetic ring inductor are used as inductors of the resonance circuit, and a plurality of high-voltage-resistant nonpolar capacitors which are connected in parallel are used as capacitors of the resonance circuit; the external power supply charges the polar energy storage capacitors, the on-off of the switch module is controlled by the main control circuit, and the two energy storage capacitors respectively supply power to the RLC series resonant circuit to generate bipolar half sine wave emission current; the inductance and capacitance in the RLC series resonant circuit determine the pulse width of the half sine wave transmit current.

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