阅读说明：本技术 基于宽配谐的短死区磁共振发射装置及控制方法 (Short dead zone magnetic resonance emission device based on wide harmonic matching and control method ) 是由 林婷婷 李苏杭 张洋 万玲 滕飞 于 2019-10-10 设计创作，主要内容包括：本发明涉及地球物理勘探设备领域,具体而言,涉及一种基于宽配谐的短死区磁共振发射装置及控制方法,PC上位机,主控模块,根据上位机的指令,控制DC-DC变换器为储能电容充电,充电能量来源为蓄电池；通过发送PWM波控制H桥发射模块及线圈进行双极性脉冲发射,发射能量来源为储能电容；以及通过控制第一开关驱动模块控制第一开关的通断,通过控制第二开关驱动模块控制第二开关的通断,通过控制第三开关驱动模块从而控制钳位模块的钳位电压；通过取反电路,用于将主控模块的开关控制信号取非,对第一开关和第二开关导通信号进行互补。解决信号本身幅度较低,经能释时间衰减后几乎完全淹没在噪声中,为后续数据处理及反演带来极大困难,严重影响探测效果的问题,能够有效缩短发射系统的关断时间,减小磁共振探测的死区时间,从而提高信号幅度。(The invention relates to the field of geophysical exploration equipment, in particular to a short dead zone magnetic resonance emission device based on wide harmonic matching and a control method thereof, wherein a PC (personal computer) upper computer and a main control module are used for controlling a DC-DC (direct current-direct current) converter to charge an energy storage capacitor according to the instruction of the upper computer, and a charging energy source is a storage battery; the method comprises the steps that a PWM wave is sent to control an H-bridge transmitting module and a coil to carry out bipolar pulse transmission, and a transmitting energy source is an energy storage capacitor; the on-off of the first switch is controlled by controlling the first switch driving module, the on-off of the second switch is controlled by controlling the second switch driving module, and the clamping voltage of the clamping module is controlled by controlling the third switch driving module; and the negation circuit is used for negating the switch control signal of the main control module and complementing the conducting signals of the first switch and the second switch. The problems that the amplitude of a signal is low, the signal is almost completely submerged in noise after energy release time attenuation, great difficulty is brought to subsequent data processing and inversion, and the detection effect is seriously influenced are solved, the turn-off time of a transmitting system can be effectively shortened, the dead time of magnetic resonance detection is reduced, and the signal amplitude is improved.)

1. A short dead zone magnetic resonance emission device based on wide tuning for a magnetic resonance detection system, the device comprising: a PC upper computer, a main control module, a DC-DC converter, a storage battery, an energy storage capacitor, a first switch driving module, a second switch driving module, a third switch driving module, a first switch, a second switch, an H-bridge transmitting module, a coil, a clamping module and an inverting circuit,

the PC upper computer sends the transmission parameters and the control instructions to the main control module through the PC upper computer and displays the working state of the system;

the main control module controls the DC-DC converter to charge the energy storage capacitor according to an instruction of the upper computer, and the charging energy source is a storage battery; the method comprises the steps that a PWM wave is sent to control an H-bridge transmitting module and a coil to carry out bipolar pulse transmission, and a transmitting energy source is an energy storage capacitor; the on-off of the first switch is controlled by controlling the first switch driving module, the on-off of the second switch is controlled by controlling the second switch driving module, and the clamping voltage of the clamping module is controlled by controlling the third switch driving module;

the first switch is used for controlling the on-off of the energy storage capacitor, the H-bridge transmitting module and the coil;

the second switch is used for controlling the connection and disconnection of the H-bridge transmitting module and the coil and clamping module;

the clamping module is used for clamping voltage so as to achieve the purpose of quick turn-off;

and the negation circuit is used for negating the switch control signal of the main control module and complementing the conducting signals of the first switch and the second switch.

2. The apparatus of claim 1 wherein said H-bridge transmit module and coil comprises a bridge of 4 IGBT devices and a diode in parallel with each IGBT and a transmit coil between the 4 IGBT devices.

3. The apparatus of claim 1, wherein the clamping module comprises a plurality of clamping diodes connected in series and a controllable switch connected in parallel with each clamping diode.

4. The apparatus of claim 1, wherein the main control module determines a clamping voltage value according to the excitation current and the excitation voltage, determines the number of clamping diodes connected into the loop according to the clamping voltage value, and controls the on/off of the controllable switches in the clamping modules through the third switch driving module to adjust the number of clamping diodes connected into the loop in series.

5. The apparatus of claim 1, wherein the main control module transmits the PWM signal to the H-bridge transmission module according to a transmission timing sequence, and the main control module controls the first switch through the first switch driving module and the second switch through the second switch driving module according to the transmission timing sequence, so as to perform the excitation of the bipolar pulse through the coil, and the specific control process includes:

setting the control signal of the H-bridge emission module as Q, the first switch control signal as S1 and the second switch control signal as S2, carrying out bipolar pulse emission once in a period T, wherein T is an excitation pulse period, and satisfying the following conditions:

(1) in time t1, the PWMA signals of the IGBTQ1 and the IGBTQ4 are controlled to be effective, the signal of the first switch is controlled to be effective, the PWMB signals of the IGBTQ2 and the IGBTQ3 and the signal of the second switch are controlled to be ineffective, the IGBTQ1 and the IGBTQ4 are conducted at the moment, the IGBTQ2 and the IGBTQ3 are cut off, the first switch is conducted, the second switch is disconnected, the transmitting coil, the IGBTQ1, the IGBTQ4, the first switch and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, the current in the coil is gradually increased, and the current direction in the coil is set to be a forward direction at the moment;

(2) during time t2, the signals controlling the second switch are active, the signals controlling the first switch and the signals controlling the PWMA and PWMB of the IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are inactive, at this time, the IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are cut off, the first switch is cut off, the second switch is turned on, the diode D2 connected with the transmitting coil in parallel with the IGBTQ2, the diode D3 connected with the IGBTQ3 in parallel, the second switch and the clamping module form a loop, the transmitting coil discharges electricity through the loop, and the current in the transmitting coil gradually decreases;

(3) in time t3, the PWMB signals of IGBTQ2 and IGBTQ3 are controlled to be effective, the signal of the first switch is controlled to be effective, the PWMA signals of IGBTQ1 and IGBTQ4 and the signal of the second switch are controlled to be ineffective, at the moment, IGBTQ2 and IGBTQ3 are conducted, IGBTQ1 and IGBTQ4 are cut off, the first switch is conducted, the second switch is disconnected, the coil, IGBTQ2, IGBTQ3, the first switch and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, and the current in the coil is reversely and gradually increased;

(4) at time t4, the signals controlling the second switch are active, and the signals controlling the first switch and the PWMA and PWMB signals controlling IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are inactive, at this time, IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are turned off, the first switch is turned off, the second switch is turned on, the emitting coil, the diode D1 parallel to IGBTQ1 and the diode D4 parallel to IGBTQ4, the second switch and the clamp module form a loop, the emitting coil discharges through the loop, the current amplitude in the emitting coil gradually decreases, and the direction is reverse.

6. A short dead zone magnetic resonance emission control method based on wide tuning is characterized by comprising the following steps:

a. setting parameters: PC host computer conveys emission parameter and control signal to master control module, includes: excitation current I, excitation voltage U, excitation frequency f, preset excitation time t, excitation pulse duty ratio d and superposition times k;

b. adjusting the clamping voltage: the main control module determines a clamping voltage value according to the excitation current and the excitation voltage, determines the number of clamping diodes connected into a loop according to the clamping voltage value, controls the on-off of a controllable switch in the clamping module through a third switch driving module, and adjusts the number of the clamping diodes connected into the loop in series;

c. charging an energy storage capacitor: the main control module controls the DC-DC converter module to work according to the excitation voltage and charges the energy storage capacitor module;

d. emission of monocycle excitation pulse: the main control module transmits PWM signals to the H-bridge transmitting module and the coil according to a transmitting time sequence, and controls a first switch through the first switch driving module and a second switch through the second switch driving module according to the transmitting time sequence, so that bipolar pulse excitation is carried out through the coil;

e. and (3) judging completion of single emission: and f, continuing to enter the next step f after the single pulse transmission is finished, otherwise returning to the step d, and judging whether the single pulse transmission is finished according to the following steps: and (3) finishing the emission of the single-period excitation pulse of m periods, wherein the value of m is determined by the preset excitation time and satisfies the following conditions:

t＝mT,m∈Z

t is an excitation pulse period, and satisfies the following conditions:

f. and (3) judging the completion of superposition transmission: and (e) after the superposition transmission is finished, continuing to enter the next step (g), otherwise, returning to the step (c), wherein the judgment basis of the completion of the superposition transmission is as follows: completing k times of single emission;

g. waiting for entering the next work cycle: parameter setting, clamping voltage adjustment, energy storage capacitor charging, single-period excitation pulse emission, single emission completion judgment and superposition emission completion judgment until detection is finished.

7. The control method according to claim 6, wherein the main control module transmits the PWM signal to the H-bridge transmission module according to a transmission timing sequence, and the main control module controls the first switch through the first switch driving module and the second switch through the second switch driving module according to the transmission timing sequence, so as to perform the excitation of the bipolar pulse through the coil, and the specific control process comprises:

setting the control signal of the H-bridge emission module as Q, the first switch control signal as S1 and the second switch control signal as S2, carrying out bipolar pulse emission once in a period T, wherein T is an excitation pulse period, and satisfying the following conditions:

(1) in time t1, the PWMA signals of the IGBTQ1 and the IGBTQ4 are controlled to be effective, the signal of the first switch is controlled to be effective, the PWMB signals of the IGBTQ2 and the IGBTQ3 and the signal of the second switch are controlled to be ineffective, the IGBTQ1 and the IGBTQ4 are conducted at the moment, the IGBTQ2 and the IGBTQ3 are cut off, the first switch is conducted, the second switch is disconnected, the transmitting coil, the IGBTQ1, the IGBTQ4, the first switch and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, the current in the coil is gradually increased, and the current direction in the coil is set to be a forward direction at the moment;

(2) during time t2, the signals controlling the second switch are active, the signals controlling the first switch and the signals controlling the PWMA and PWMB of the IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are inactive, at this time, the IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are cut off, the first switch is cut off, the second switch is turned on, the diode D2 connected with the transmitting coil in parallel with the IGBTQ2, the diode D3 connected with the IGBTQ3 in parallel, the second switch and the clamping module form a loop, the transmitting coil discharges electricity through the loop, and the current in the transmitting coil gradually decreases;

(3) in time t3, the PWMB signals of IGBTQ2 and IGBTQ3 are controlled to be effective, the signal of the first switch is controlled to be effective, the PWMA signals of IGBTQ1 and IGBTQ4 and the signal of the second switch are controlled to be ineffective, at the moment, IGBTQ2 and IGBTQ3 are conducted, IGBTQ1 and IGBTQ4 are cut off, the first switch is conducted, the second switch is disconnected, the coil, IGBTQ2, IGBTQ3, the first switch and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, and the current in the coil is reversely and gradually increased;

(4) at time t4, the signals controlling the second switch are active, and the signals controlling the first switch and the PWMA and PWMB signals controlling IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are inactive, at this time, IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are turned off, the first switch is turned off, the second switch is turned on, the emitting coil, the diode D1 parallel to IGBTQ1 and the diode D4 parallel to IGBTQ4, the second switch and the clamp module form a loop, the emitting coil discharges through the loop, the current amplitude in the emitting coil gradually decreases, and the direction is reverse.

Technical Field

The invention relates to the field of geophysical exploration equipment, in particular to a short dead zone magnetic resonance emission device based on wide resonance matching and a control method.

Background

The surface Magnetic Resonance (MRS) technology is the only geophysical method for non-invasive underground water detection at present, and is widely used in underground water detection. When the magnetic resonance water detecting system detects underground water, firstly a transmitter transmits bipolar pulses for a certain time through a load coil to excite hydrogen protons in the underground water, then the excitation pulses are removed, and a receiver receives induced Free Induction Decay (FID) signals through the same coil, so that the hydrogeological condition is obtained through inversion.

The MRS effective signal is nV grade, so the receiving system meets the characteristic of a weak signal acquisition system. Because the load coil is inductive, a large amount of energy can be stored during transmission, and when the same coil is adopted for receiving and transmitting, the receiver can be burnt down even if the effective MRS signal cannot be distinguished. Therefore, after the end of the excitation pulse and before the start of the signal reception, a period of time is required for the coil to release energy, which is called the release time, also called the dead time of the instrument.

For traditional magnetic resonance detection, a capacitor with a proper capacitance value is connected in series in a transmitting loop during transmitting so as to achieve the purpose of matching resonance, and after the matching resonance capacitor is added, the loop is in an underdamping state. After the excitation pulse is finished, the current in the coil vibrates and attenuates, so that the energy in the coil is slowly released, and the dead time is extremely long. For a coil of 100 x 100m, the off-time tr is about 10ms at an excitation current of 50A. However, after the excitation signal is removed, hydrogen protons in the groundwater immediately start to release a free decay signal, and the signal is in an exponential decay form, and the dead time of the current magnetic resonance system is generally 20ms, so that a large amount of effective MRS signals are lost in the release time, and the signal-to-noise ratio of the received signals is low. Particularly in shallow detection application, the signal amplitude is low, and the signal is almost completely submerged in noise after energy release time attenuation, so that great difficulty is brought to subsequent data processing and inversion, and the detection effect is seriously influenced.

Disclosure of Invention

The invention aims to solve the technical problem of providing a short dead zone magnetic resonance emission device based on wide harmonic matching and a control method thereof, and solves the problems that the amplitude of a signal is low, the signal is almost completely submerged in noise after energy release time attenuation, great difficulty is brought to subsequent data processing and inversion, and the detection effect is seriously influenced.

The present invention is achieved in such a way that,

a short dead-zone magnetic resonance emission apparatus based on wide-band resonance for a magnetic resonance detection system, the apparatus comprising: a PC upper computer, a main control module, a DC-DC converter, a storage battery, an energy storage capacitor, a first switch driving module, a second switch driving module, a third switch driving module, a first switch, a second switch, an H-bridge transmitting module, a coil, a clamping module and an inverting circuit,

the PC upper computer sends the transmission parameters and the control instructions to the main control module through the PC upper computer and displays the working state of the system;

the main control module controls the DC-DC converter to charge the energy storage capacitor according to an instruction of the upper computer, and the charging energy source is a storage battery; the method comprises the steps that a PWM wave is sent to control an H-bridge transmitting module and a coil to carry out bipolar pulse transmission, and a transmitting energy source is an energy storage capacitor; the on-off of the first switch is controlled by controlling the first switch driving module, the on-off of the second switch is controlled by controlling the second switch driving module, and the clamping voltage of the clamping module is controlled by controlling the third switch driving module;

the first switch is used for controlling the on-off of the energy storage capacitor, the H-bridge transmitting module and the coil;

the second switch is used for controlling the connection and disconnection of the H-bridge transmitting module and the coil and clamping module;

the clamping module is used for clamping voltage so as to achieve the purpose of quick turn-off;

and the negation circuit is used for negating the switch control signal of the main control module and complementing the conducting signals of the first switch and the second switch.

Further, the H-bridge transmitting module and the coil comprise a bridge circuit formed by 4 IGBT devices and diodes connected with each IGBT in parallel, and a transmitting coil between the 4 IGBT devices.

Further, the clamping module comprises a plurality of clamping diodes connected in series and a controllable switch connected in parallel with each clamping diode.

Furthermore, the main control module determines a clamping voltage value according to the excitation current and the excitation voltage, determines the number of clamping diodes connected into the loop according to the clamping voltage value, controls the on-off of a controllable switch in the clamping module through a third switch driving module, and adjusts the number of clamping diodes connected into the loop in series.

A short dead zone magnetic resonance emission control method based on wide tuning comprises the following steps:

a. setting parameters: PC host computer conveys emission parameter and control signal to master control module, includes: excitation current I, excitation voltage U, excitation frequency f, preset excitation time t, excitation pulse duty ratio d and superposition times k;

b. adjusting the clamping voltage: the main control module determines a clamping voltage value according to the excitation current and the excitation voltage, determines the number of clamping diodes connected into a loop according to the clamping voltage value, controls the on-off of a controllable switch in the clamping module through a third switch driving module, and adjusts the number of the clamping diodes connected into the loop in series;

c. charging an energy storage capacitor: the main control module controls the DC-DC converter module to work according to the excitation voltage and charges the energy storage capacitor module;

d. emission of monocycle excitation pulse: the main control module transmits PWM signals to the H-bridge transmitting module and the coil according to a transmitting time sequence, and controls a first switch through the first switch driving module and a second switch through the second switch driving module according to the transmitting time sequence, so that bipolar pulse excitation is carried out through the coil;

e. and (3) judging completion of single emission: and f, continuing to enter the next step f after the single pulse transmission is finished, otherwise returning to the step d, and judging whether the single pulse transmission is finished according to the following steps: and (3) finishing the emission of the single-period excitation pulse of m periods, wherein the value of m is determined by the preset excitation time and satisfies the following conditions:

t＝mT,m∈Z

t is an excitation pulse period, and satisfies the following conditions:

f. and (3) judging the completion of superposition transmission: and (e) after the superposition transmission is finished, continuing to enter the next step (g), otherwise, returning to the step (c), wherein the judgment basis of the completion of the superposition transmission is as follows: completing k times of single emission;

g. waiting for entering the next work cycle: parameter setting, clamping voltage adjustment, energy storage capacitor charging, single-period excitation pulse emission, single emission completion judgment and superposition emission completion judgment until detection is finished.

Further, master control module transmits the PWM signal to H bridge emission module according to the transmission time sequence, and master control module passes through first switch drive module control first switch, controls the second switch through second switch drive module according to the transmission time sequence to carry out bipolar pulse excitation through the coil, specific control process includes:

setting the control signal of the H-bridge emission module as Q, the first switch control signal as S1 and the second switch control signal as S2, carrying out bipolar pulse emission once in a period T, wherein T is an excitation pulse period, and satisfying the following conditions:

the period T sequentially comprises T1, T2, T3 and T4 time periods, wherein,

(1) in time t1, the PWMA signals of the IGBTQ1 and the IGBTQ4 are controlled to be effective, the signal of the first switch is controlled to be effective, the PWMB signals of the IGBTQ2 and the IGBTQ3 and the signal of the second switch are controlled to be ineffective, the IGBTQ1 and the IGBTQ4 are conducted at the moment, the IGBTQ2 and the IGBTQ3 are cut off, the first switch is conducted, the second switch is disconnected, the transmitting coil, the IGBTQ1, the IGBTQ4, the first switch and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, the current in the coil is gradually increased, and the current direction in the coil is set to be a forward direction at the moment;

(2) during time t2, the signals controlling the second switch are active, the signals controlling the first switch and the signals controlling the PWMA and PWMB of the IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are inactive, at this time, the IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are cut off, the first switch is cut off, the second switch is turned on, the diode D2 connected with the transmitting coil in parallel with the IGBTQ2, the diode D3 connected with the IGBTQ3 in parallel, the second switch and the clamping module form a loop, the transmitting coil discharges electricity through the loop, and the current in the transmitting coil gradually decreases;

(3) in time t3, the PWMB signals of IGBTQ2 and IGBTQ3 are controlled to be effective, the signal of the first switch is controlled to be effective, the PWMA signals of IGBTQ1 and IGBTQ4 and the signal of the second switch are controlled to be ineffective, at the moment, IGBTQ2 and IGBTQ3 are conducted, IGBTQ1 and IGBTQ4 are cut off, the first switch is conducted, the second switch is disconnected, the coil, IGBTQ2, IGBTQ3, the first switch and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, and the current in the coil is reversely and gradually increased;

(4) at time t4, the signals controlling the second switch are active, and the signals controlling the first switch and the PWMA and PWMB signals controlling IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are inactive, at this time, IGBTQ1, IGBTQ4, IGBTQ2 and IGBTQ3 are turned off, the first switch is turned off, the second switch is turned on, the emitting coil, the diode D1 parallel to IGBTQ1 and the diode D4 parallel to IGBTQ4, the second switch and the clamp module form a loop, the emitting coil discharges through the loop, the current amplitude in the emitting coil gradually decreases, and the direction is reverse.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention adopts a wide-harmonic-matching emission mode to replace the traditional harmonic matching, can effectively shorten the turn-off time of an emission system, and reduce the dead time of magnetic resonance detection, thereby improving the signal amplitude;

(2) according to the invention, passive clamp switching-off is adopted, and the clamp voltage value is adjusted through the controllable switch so as to adapt to different emission currents, thereby further reducing dead time and improving the amplitude of a detection signal;

(3) the invention adopts a whole-period turn-off method, turns off in the dead time of the excitation pulse, replaces the traditional fixed-time excitation mode, removes the ineffective excitation pulse, further shortens the dead time, improves the working efficiency and improves the detection effect.

Drawings

FIG. 1 is a schematic diagram of a short dead zone magnetic resonance emitting device based on wide tuning;

FIG. 2 shows a short dead-zone magnetic resonance emission timing diagram based on wide-tuning;

FIG. 3 shows a short dead-zone magnetic resonance emission workflow diagram based on wide-tuning;

figure 4 illustrates conventional detuning magnetic resonance emission current turn-off and short dead-zone magnetic resonance emission current turn-off simulation waveforms based on wide detuning, for one embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in fig. 1, a short dead zone magnetic resonance emitting device based on wide tuning for a magnetic resonance detection system, the device comprises: the device comprises a PC upper computer 1, a main control module 2, a DC-DC converter 3, a storage battery 4, an energy storage capacitor 5, a first switch driving module 6, a second switch driving module 7, a third switch driving module 8, a first switch 9, a second switch 10, an H-bridge transmitting module and coil 11, a clamping module 12 and an inverting circuit 13.

The H-bridge transmitting module and coil 11 includes a bridge circuit composed of 4 IGBT devices Q1-Q4 and diodes D1-D4 connected in parallel with each IGBT, and a transmitting coil which can be equivalent to a series connection of an inductor L and a resistor R. The IGBTQ1 is connected with the IGBTQ3 and then connected with the first switch S1 in series at two poles of the energy storage capacitor 5. IGBTQ2 is connected with IGBTQ4 and then connected with a first switch S1 in series at two poles of the energy storage capacitor 5. The IGBTQ1 and IGBTQ3 were previously connected with the transmit coil between IGBTQ2 and IGBTQ 4.

The clamp module 12 includes a plurality of clamp diodes DZ 1-DZn and switches SZ 1-SZn in parallel with each diode.

The PC upper computer 1 is used for carrying out man-machine interaction, and an experimenter sends transmission parameters and control instructions to the main control module 2 through the PC upper computer 1 and displays the working state of the system;

the main control module 2 interacts with an upper computer and controls the DC-DC conversion module 3 to charge the energy storage capacitor 5, and the charging energy source is a storage battery 4;

the main control module 2 controls the H-bridge transmitting module and the coil 11 to transmit bipolar pulses by sending PWM waves, and the transmitting energy source is the energy storage capacitor 5;

the main control module 2 controls the on-off of the first switch 9 by controlling the first switch driving module 6, controls the on-off of the second switch 10 by controlling the second switch driving module 7, and controls the clamping voltage of the clamping module 12 by controlling the third switch driving module 8;

the first switch 9 is used for controlling the on-off of the energy storage capacitor 5, the H-bridge transmitting module and the coil 11;

the second switch 10 is used for controlling the on-off of the H-bridge transmitting module, the coil 11 and the clamping module 12;

and the clamping module 12 is used for clamping voltage so as to achieve the purpose of quick turn-off.

And the inverting circuit 13 is used for negating the switch control signals so as to ensure that the conducting signals of the first switch 9 and the second switch 10 are strictly complementary.

As shown in fig. 3, a short dead zone magnetic resonance emission control method based on wide tuning includes the following steps:

a. setting parameters: PC host computer 1 transmits transmission parameter and control signal to host control module 2, includes: excitation current I, excitation voltage U, excitation frequency f, preset excitation time t, excitation pulse duty ratio d and superposition times k;

b. adjusting the clamping voltage: the main control module determines a clamping voltage value according to the excitation current and the excitation voltage, and determines the number of clamping diodes connected into the loop according to the clamping voltage value. The main control module 2 controls the on-off of the controllable switches SZ 1-SZn in the clamping module 12 through the third switch driving module 8, so as to adjust the number n of clamping diodes connected in series into the loop, and the relation between the clamping voltage value and the number n of diodes satisfies:

V_r＝nV_th,n∈Z

wherein, V_rTo clamp the voltage value, V_thA clamping voltage value of a single clamping diode;

c. charging an energy storage capacitor: the main control module 2 controls the DC-DC converter module 4 to work according to the excitation voltage to charge the energy storage capacitor 5;

d. emission of monocycle excitation pulse: the main control module 2 transmits PWM signals to the H-bridge transmitting module according to a transmitting time sequence, and the main control module 2 controls the first switch through the first switch driving module and controls the second switch through the second switch driving module according to the transmitting time sequence, so that bipolar pulse excitation is carried out through the coil.

As shown in fig. 2, the H-bridge transmitting module control signal is Q (PWMA, PWMB), the first switch 9 (switch S1) control signal is S1, and the second switch 10 (switch S2) control signal is S2. In a period T, bipolar pulse emission is carried out once, wherein T is an excitation pulse period and satisfies the following conditions:

the specific control process and steps of the part are as follows:

(1) in time t1, the PWMA signals of IGBTQ1 and IGBTQ4 are controlled to be effective, the signal of a control switch S1 is controlled to be effective, the PWMB signals of IGBTQ2 and IGBTQ3 and the signal of a control second switch S2 are controlled to be ineffective, at the moment, the IGBTQ1 and IGBTQ4 are conducted, the IGBTQ2 and IGBTQ3 are cut off, a first switch S1 is conducted, a second switch S2 is cut off, the coil, the IGBTQ1, the IGBTQ4, the first switch S1 and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, the current in the coil gradually increases, and the current direction in the coil is set to be positive at the moment;

(2) during time t2, the signal for controlling the second switch S2 is active, the PWMA and PWMB signals for controlling IGBTQ 1-Q4 and the signal for controlling the first switch S1 are inactive, at this time, IGBTQ 1-Q4 are turned off, the first switch S1 is turned off, the second switch S2 is turned on, the coil and the diodes D2, D3, S2 and DZ 1-DZn form a loop, the coil discharges electricity through the loop, and the current in the coil gradually decreases;

(3) in time t3, the PWMB signals of IGBTQ2 and IGBTQ3 are controlled to be effective, the signal of the first switch S1 is controlled to be effective, the PWMA signal of IGBTQ1IGBTQ4 and the signal of the second switch S2 are controlled to be ineffective, at the moment, IGBTQ2 and IGBTQ3 are conducted, IGBTQ1 and IGBTQ4 are cut off, the first switch S1 is conducted, the first switch S2 is disconnected, the coil, the IGBTQ2, IGBTQ3, the first switch S1 and the energy storage capacitor form a loop, the energy storage capacitor charges the transmitting coil, and the current in the coil is reversely and gradually increased;

(4) during time t4, the signal for controlling the switch S2 is active, the PWMA and PWMB signals for controlling IGBTQ 1-Q4 and the signal for controlling the first switch S1 are inactive, at this time, IGBTQ 1-Q4 are turned off, the first switch S1 is turned off, the first switch S2 is turned on, the coil forms a loop with the diode D1, the diode D4, the second switches S2 and DZ 1-DZn, the coil discharges electricity through the loop, the amplitude of the current in the coil gradually decreases, and the direction is reverse;

e. and (3) judging completion of single emission: and (e) completing the single pulse transmission, continuing to enter the next step f, and otherwise returning to the step d. The judgment basis of whether the single emission is finished is as follows: and (3) completing the emission of a monocycle excitation pulse with m periods, wherein the value of m is determined by the preset excitation time and satisfies the following conditions:

t＝mT,m∈Z

f. and (3) judging the completion of superposition transmission: and (e) after the superposition transmission is finished, continuing to enter the next step g, and otherwise, returning to the step c. The judgment basis of the completion of the superposition transmission is as follows: completing k times of single emission;

g. waiting for entering the next work cycle: parameter setting, clamping voltage adjustment, energy storage capacitor charging, single-period excitation pulse emission, single emission completion judgment and superposition emission completion judgment until detection is finished.