CN116094319A - Electric source high-current slow-turn-off emission control method based on direct-current chopping - Google Patents

Electric source high-current slow-turn-off emission control method based on direct-current chopping Download PDF

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CN116094319A
CN116094319A CN202211603168.2A CN202211603168A CN116094319A CN 116094319 A CN116094319 A CN 116094319A CN 202211603168 A CN202211603168 A CN 202211603168A CN 116094319 A CN116094319 A CN 116094319A
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turn
emission
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嵇艳鞠
邱仕林
王世鹏
李心源
黎东升
高全明
林君
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Jilin University
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Jilin University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

The invention relates to a direct-current chopping-based electric source high-current slow-turn-off emission control method. Before working, presetting current turn-off time and amplitude in a controller according to exploration requirements of different polaroids, and calculating reference currents at different moments during turn-off; in operation, the data of the emission current is collected by a Hall current sensor during the current turn-off period and fed back to the controller in a closed loop; the controller generates a driving signal of the switching device based on a direct current chopping technology, controls the period and the duty ratio of the switching device, and enables the emission current to drop to zero according to a constant slope. The invention aims to realize that the emission current falling edge of an electrical source emission system is controllable, and the turn-off time is changed aiming at different polarization effects, so that the observed polarization response is more obvious.

Description

Electric source high-current slow-turn-off emission control method based on direct-current chopping
Technical Field
The invention relates to the field of time domain electromagnetic exploration, in particular to an electric source high-current slow-turn-off emission control method based on direct-current chopping.
Background
In the field of time domain electromagnetic exploration, electrical source modes can provide larger emitted electric moment and detection depth, and are therefore widely used. Based on a time domain electromagnetic method of an electrical source, bipolar trapezoidal wave emission current is provided for the ground through a high-power electrical source emission system, primary magnetic field excitation is generated, and acquired secondary magnetic field (and change rate thereof) data comprise induction response and polarization response, so that resistivity and polarization rate can be extracted in a combined mode. The induction field at early stage is fast attenuated after the current is turned off, the induction field and the polarization field coexist, and the secondary magnetic field data is positive; the induction field in middle and late stages is almost absent and mainly polarized field, and the secondary magnetic field data is negative. Thus, the induced-polarization response curve has a sign inversion phenomenon, and polarization characteristics are generally represented by a sign inversion time and a maximum negative response amplitude. Wherein, the earlier the sign reversal moment is, the larger the maximum negative response amplitude is, and the more obvious the polarization characteristic is.
The off-time of the emission current affects the magnitude of the induced and polarized fields. The shorter the turn-off time, the stronger the induced field, the shorter the charging time of the polarized field, and the weaker the polarized field; the turn-off time is prolonged, the induction field is weakened, the charging time of the polarization field is increased, and the polarization field is enhanced; however, the turn-off time is too long, the energy of the primary magnetic field of excitation is too small, and both the induction field and the polarization field are difficult to observe. Since the magnitude of the polarization field is much smaller than that of the induced field, it is necessary to select a suitable off-time to make the polarization characteristics as pronounced as possible. Meanwhile, the requirements of different polarization targets on the turn-off time are different. Since the magnitude of the secondary magnetic field is proportional to the magnitude of the emission current, it is necessary to realize slow turn-off control of large current in an electric source mode.
CN108227011a discloses a dual trapezoidal wave transmitting system with controllable falling edge and a control method, which clamp voltages at two ends of a transmitting coil on a high level or a low level through a high-voltage transient suppression diode and a low-voltage transient suppression diode respectively, so that transmitting current is turned off quickly or turned off slowly. However, the method cannot be applied to the slow turn-off control of a high-power and high-current electrical source emission system due to the limited rated voltage of the transient suppression diode.
CN111769738B discloses a direct current chopper circuit control system, method and device, and timely control of output side load disturbance is achieved through output feedback. However, the reference current at the output side of the method is a constant value, and the purpose of the method is to realize constant-current constant-voltage control and to restrain input and output disturbance, and when a control system switching tube is turned off, the turn-off time of the output current cannot be controlled.
Disclosure of Invention
The invention aims to solve the technical problem of providing a direct-current chopping-based electric source heavy-current slow-turn-off emission control method, which solves the problem that the emission current turn-off time of a high-power heavy-current electric source emission system cannot be prolonged, ensures that the polarization characteristics in the acquired secondary magnetic field response data are more obvious, and improves the resolution and interpretation precision of an underground polarization target body.
The present invention has been achieved in such a way that,
an electric source high-current slow-turn-off emission control method based on direct-current chopping, which comprises the following steps:
1) According to the polarization parameters of the target body, calculating the optimal turn-off time t based on the mutual inductance relation between the grounding conductor and the equivalent eddy current loop of the target body o Presetting the turn-off time t of the emission current in the controller off ＝t o Reference currents I at different moments t during turn-off r According to the turn-off time t of preset emission current off And maximum current amplitude I m The calculation is performed such that,
Figure BDA0003996150920000021
the time t ranges from (0, t off ) During the off period after forward conductionThe reference current is positive, and the reference current in the turn-off period after reverse conduction is negative;
2) Starting a high-power electric source emission system, and adjusting the power supply voltage of a direct-current power supply to enable the amplitude of the actual emission current to be equal to that of the preset emission current;
3) The method comprises the steps that during the turn-off period of emission current, the magnitude of actual emission current is collected by a Hall current sensor and is fed back to a controller in a closed loop mode based on a direct current chopping technology, the period and the duty ratio of a driving signal of a switching device are changed, and the emission current is reduced to zero according to a constant slope;
the high-power electrical source transmitting system comprises a direct-current power supply, a transmitting bridge circuit, an impedance matching unit and a controller;
the direct current power supply provides stable direct current voltage, and outputs the stable direct current voltage to the transmitting bridge circuit or the impedance matching unit, and the impedance matching unit is connected with the transmitting bridge circuit in parallel;
the transmitting bridge is a bridge circuit formed by a switching device Q1, a switching device Q2, a switching device Q3 and a switching device Q4, when the switching device Q1 and the switching device Q4 are conducted, the system is conducted in the forward direction, and the transmitting current is positive; when the switching device Q2 and the switching device Q3 are conducted, the system is reversely conducted, and the emission current is negative; when all four switching devices are turned off, the emission current gradually decays to zero;
the transmitting bridge circuit inverts the direct-current voltage of the direct-current power supply into bipolar trapezoidal wave transmitting current which flows to the ground through the grounding wire;
the output of the transmitting bridge circuit is the series impedance of the grounding wire and the ground;
the impedance matching unit is formed by connecting a switching device Q5 and a matching load in series, and the impedance of the matching load is equal to the series impedance of the grounding wire and the ground;
the controller controls the on and off of five switching devices in the system, and when all the switching devices of the transmitting bridge are turned off, the switching device Q5 of the impedance matching unit is turned on.
Further, calculating the optimal turn-off time in step 1) refers to calculating the influence of different turn-off times on the polarization characteristic in the transient electromagnetic response curve based on the mutual inductance relationship between the grounding wire and the equivalent eddy current loop of the target body, and specifically includes the following steps:
1) Setting a grounding wire of a high-power electrical source emission system as a finite-length straight wire, enabling an underground target body to be equivalent to a polarized ring vortex loop, and calculating a mutual inductance M between the grounding wire and the equivalent vortex loop of the target body according to the relative position and the size of the grounding wire and the polarized ring vortex loop;
2) Establishing different off times t off Time domain expression I (t) of the oblique step emission current over time t as follows:
Figure BDA0003996150920000031
wherein I is m Maximum current amplitude, t on For a time when the emission current is stable on, approximately equal to one quarter of a period; u (t), u (t-t) on ) And u (t-t) on -t off ) Respectively the starting time is 0, t on And (t) on +t off ) Is a unit step signal of (a).
3) Calculating primary induced electromotive force emf generated by emission current in equivalent eddy current loop of target body 1 ，
Figure BDA0003996150920000032
4) Calculating transient electromagnetic response in the equivalent eddy current loop according to the polarization parameters of the target body, and analyzing the polarization characteristics of the response curve to obtain the optimal turn-off time t o The polarization parameters do not have resistivity ρ, polarization η, and time constant τ;
the polarization characteristic comprises a sign inversion time and a maximum negative response amplitude, and is most obvious when the turn-off time is equal to the optimal turn-off time, namely the sign inversion time is earliest and the corresponding maximum negative response amplitude is more than 90% of the maximum negative response amplitude under the zero turn-off time;
the preset off time ranges from 100 microseconds to 10 milliseconds, within which the preset off time is equal to the optimal off time.
Further, changing the period and duty cycle of the switching device driving signal based on the dc chopping technique in step 3) includes: after the forward conduction emission current starts to be turned off, calculating the difference value between the absolute value of the actual emission current and the absolute value of the reference current at each moment; when the difference is positive, the switching device Q1 and the switching device Q4 of the transmitting bridge circuit are turned off, the switching device Q5 of the impedance matching unit is turned on, and the transmitting current is reduced to be negative; when the difference is negative, the switching device Q1 and the switching device Q4 of the transmitting bridge are turned on, the switching device Q5 of the impedance matching unit is turned off, and the transmitting current rises until the difference is positive; when the emission current in the turn-off period is reduced to zero according to the preset turn-off time, the switching device Q5 of the impedance matching unit is turned on, and the switching device Q1 and the switching device Q4 of the emission bridge circuit are kept turned off to the next period; during this time, the switching devices Q2 and Q3 of the transmitting bridge are always turned off. When the reverse conduction emission current starts to be turned off, the control strategy is the same as that described above, and the switching devices Q2 and Q3 are interchanged with the switching devices Q1 and Q4.
Further, the emission current in step 3) decreases to zero according to a constant slope, which is the ratio of the amplitude of the emission current to the off time, means that the emission current decreasing during the off period based on the dc chopping technique is equivalent to the reference current of the ramp step.
Compared with the prior art, the invention has the beneficial effects that: the invention breaks through the voltage-resistant and current-resistant limitation of the voltage clamping device, solves the problem that the turn-off time of the emission current of the high-power high-current electrical source emission system cannot be prolonged, improves the control mode of the emission system and successfully realizes the controllable turn-off time of the high-power high-current electrical source emission system. Different turn-off times of output currents are preset according to parameters of different polarization mediums, and current reference values at different moments in the turn-off period are calculated. The switching device is controlled to be continuously turned on and off through current collection closed loop feedback, so that the output current of the transmitting system is reduced to zero according to a constant slope. The slow turn-off mode of the transmitting system enables the polarization characteristics in the acquired secondary magnetic field response data to be more obvious, is beneficial to extracting and inverting the polarization parameters of the underground target body, and improves the resolution and interpretation accuracy of the underground target body.
Drawings
FIG. 1 is a flow chart of a DC chopper-based control for large-current slow turn-off of an electrical source according to an embodiment of the present invention;
FIG. 2 is a block diagram of an electrical source emission system with slow turn-off control according to an embodiment of the present invention;
FIG. 3 is a timing diagram of driving signals for switching between normal off and slow off modes according to an embodiment of the present invention;
FIG. 4 is a diagram showing a measured slow off driving signal during an off period of an emission current according to an embodiment of the present invention;
FIG. 5 is a waveform of a measured current drop for slow off control according to an embodiment of the present invention;
FIG. 6 is a graph showing the response of the same polarizer to the induction-polarization at different turn-off times according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 1, the method for controlling the emission of the high-current slow turn-off of the electric source based on the direct-current chopping provided by the invention comprises the following steps:
1) Consult geological data, understand exploration needs, debug and connect with a high-power electrical source emission system,
the high-power electrical source emission system is composed of a direct-current power supply, an emission bridge circuit, an impedance matching unit and a controller, as shown in fig. 2;
the direct current power supply provides stable direct current voltage, and outputs the stable direct current voltage to the transmitting bridge circuit or the impedance matching unit, and the impedance matching unit is connected with the transmitting bridge circuit in parallel;
the transmitting bridge is composed of four switching devices (Q1, Q2, Q3 and Q4), load impedance is output and connected between the bridge, when the switching devices Q1 and Q4 are conducted, the system is conducted in the forward direction, and the transmitting current is positive; when the switching device Q2 and the switching device Q3 are conducted, the system is reversely conducted, and the emission current is negative; when all four switching devices are turned off, the emission current gradually decays to zero;
the transmitting bridge circuit inverts the direct-current voltage of the direct-current power supply into bipolar trapezoidal wave transmitting current which flows to the ground through the grounding wire;
the output of the transmitting bridge circuit is the series impedance of the grounding wire and the ground;
the impedance matching unit is formed by connecting a switching device Q5 and a matching load in series, and the impedance of the matching load is equal to the series impedance of the grounding wire and the ground;
the controller controls the on and off of five switching devices in the system, and when all the switching devices of the transmitting bridge are turned off, the switching device Q5 of the impedance matching unit is turned on, so that the output power of the system is ensured to be constant;
2) According to the polarization parameters of the target body, calculating the optimal turn-off time t based on the mutual inductance relation between the grounding conductor and the equivalent eddy current loop of the target body o Presetting the turn-off time t of the emission current in the controller off ＝t o Reference currents I at different moments t during turn-off r According to the turn-off time t of preset emission current off And maximum current amplitude I m The calculation is performed such that,
Figure BDA0003996150920000051
the time t ranges from (0, t off ) The reference current in the turn-off period after forward conduction is positive, and the reference current in the turn-off period after reverse conduction is negative;
further, calculating the optimal turn-off time refers to calculating the influence of different turn-off times on polarization characteristics in a transient electromagnetic response curve based on the mutual inductance relationship between the equivalent eddy current loop of the grounding wire and the target body, and specifically comprises the following steps:
firstly, setting a grounding wire of an electrical source emission system as a finite-length straight wire, enabling an underground target body to be equivalent to a polarized ring vortex loop, and calculating a mutual inductance M between the grounding wire and the equivalent vortex loop of the target body according to the relative position and the size of the grounding wire and the polarized ring vortex loop;
second, a different off time t is established off Time domain expression I (t) of the oblique step emission current over time t as follows:
Figure BDA0003996150920000061
wherein I is m Maximum current amplitude, t on For a time when the emission current is stable on, approximately equal to one quarter of a period; u (t), u (t-t) on ) And u (t-t) on -t off ) Respectively the starting time is 0, t on And (t) on +t off ) Is a unit step signal of (a).
Then, the primary induced electromotive force emf generated by the emission current in the equivalent eddy current loop of the target body is calculated 1 ，
Figure BDA0003996150920000062
Finally, calculating transient electromagnetic response in the equivalent eddy current loop according to the polarization parameters (resistivity rho, polarization rate eta and time constant tau) of the target body, and analyzing the polarization characteristics of the response curve to obtain the optimal turn-off time t o 。
The polarization characteristic comprises a sign inversion time and a maximum negative response amplitude, and is most obvious when the turn-off time is equal to the optimal turn-off time, namely the sign inversion time is earliest and the corresponding maximum negative response amplitude is more than 90% of the maximum negative response amplitude under the zero turn-off time;
the preset off time ranges from 100 microseconds to 10 milliseconds, within which the preset off time is equal to the optimal off time.
3) Starting a high-power electric source emission system, and adjusting the power supply voltage of a direct-current power supply to enable the amplitude of the actual emission current to be equal to that of the preset emission current;
4) The method comprises the steps that during the turn-off period of emission current, the magnitude of actual emission current is collected by a Hall current sensor and is fed back to a controller, the controller changes the period and the duty ratio of a driving signal of a switching device based on closed loop feedback of a direct current chopping technology, and the emission current is enabled to drop to zero according to a constant slope.
Referring to fig. 3, changing the period and duty ratio of the switching device driving signal based on the dc chopping technique means that, after the forward-on emission current starts to be turned off, the difference between the absolute value of the actual emission current and the absolute value of the reference current at each time is calculated; when the difference is positive, the switching device Q1 and the switching device Q4 of the transmitting bridge circuit are turned off, the switching device Q5 of the impedance matching unit is turned on, and the transmitting current is reduced to be negative; when the difference is negative, the switching device Q1 and the switching device Q4 of the transmitting bridge are turned on, the switching device Q5 of the impedance matching unit is turned off, and the transmitting current rises until the difference is positive; when the emission current in the turn-off period is reduced to zero according to the preset turn-off time, the switching device Q5 of the impedance matching unit is turned on, and the switching device Q1 and the switching device Q4 of the emission bridge circuit are kept turned off to the next period; during this time, the switching devices Q2 and Q3 of the transmitting bridge are always turned off. When the reverse conduction emission current starts to be turned off, the control strategy is the same as that described above, and the switching devices Q2 and Q3 are exchanged with the switching devices Q1 and Q4. The direct current chopper adopted by the invention has the advantages that the reference current in each current turn-off period changes along with time, and the turn-on and turn-off of the switching device needs to be adjusted at any time.
Wherein the emission current which is reduced based on the direct current chopping technique during the turn-off period can be equivalent to the reference current of the oblique step, and the slope is the ratio of the amplitude of the emission current and the turn-off time. The smaller the minimum period of the switching device driving signal, the smaller the ripple of the emission current which is turned off slowly, the better the excitation effect on the polarization effect, and the minimum switching period is limited by the actual power consumption and temperature rise of the switching device.
The method for controlling the large-current slow-turn-off emission of the electric source based on the direct-current chopping has been successfully realized and verified through field experiments. One set of verification cases is presented here, requiring a slow off control of 1.8 milliseconds to be implemented, depending on the induced-polarization characteristics of the polarized target under test. According to the slow turn-off emission control method provided by the invention, waveforms of the actually measured driving signal and the emission current falling edge in the turn-off period are respectively shown in fig. 4 and 5. As shown in fig. 5, the emission current amplitude of the electrical source emission system is 100 amperes, and the current turn-off time is 1.8 milliseconds. When the electrical source emission system adopts the normal turn-off of fig. 3, the emission current turn-off time of the electrical source emission system is 0.2 ms.
Referring to fig. 6, the induction-polarization response curves for excitation of the same polarizer are given for turn-off times of 0.2 ms and 1.8 ms, respectively. It can be seen that the polarization characteristics of the response curve corresponding to 1.8 ms are more pronounced than 0.2 ms. Not only is the sign inversion time advanced, but the maximum negative response amplitude is also increased by an order of magnitude. Obviously, the DC chopper-based electric source high-current slow-turn-off emission control method provided by the invention ensures that the polarization characteristics in the acquired secondary magnetic field response data are more obvious, is beneficial to extracting and inverting the polarization parameters of the underground target body, and improves the resolution and interpretation precision of the underground target body.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims (4)

1. The method for controlling the emission of the high-current slow-turn-off of the electrical source based on the direct-current chopping is characterized by comprising the following steps:
1) According to the polarization parameters of the target body, calculating the optimal turn-off time t based on the mutual inductance relation between the grounding conductor and the equivalent eddy current loop of the target body o Presetting the turn-off time t of the emission current in the controller off ＝t o Reference currents I at different moments t during turn-off r According to the turn-off time t of preset emission current off And maximum current amplitude I m The calculation is performed such that,
Figure FDA0003996150910000011
range of time tIs (0, t) off ) The reference current in the turn-off period after forward conduction is positive, and the reference current in the turn-off period after reverse conduction is negative;
2) Starting a high-power electric source emission system, and adjusting the power supply voltage of a direct-current power supply to enable the amplitude of the actual emission current to be equal to that of the preset emission current;
3) The method comprises the steps that during the turn-off period of emission current, the magnitude of actual emission current is collected by a Hall current sensor and is fed back to a controller in a closed loop mode based on a direct current chopping technology, the period and the duty ratio of a driving signal of a switching device are changed, and the emission current is reduced to zero according to a constant slope;
the high-power electrical source transmitting system comprises a direct-current power supply, a transmitting bridge circuit, an impedance matching unit and a controller;
the direct current power supply provides stable direct current voltage, and outputs the stable direct current voltage to the transmitting bridge circuit or the impedance matching unit, and the impedance matching unit is connected with the transmitting bridge circuit in parallel;
the transmitting bridge is a bridge circuit formed by a switching device Q1, a switching device Q2, a switching device Q3 and a switching device Q4, when the switching device Q1 and the switching device Q4 are conducted, the system is conducted in the forward direction, and the transmitting current is positive; when the switching device Q2 and the switching device Q3 are conducted, the system is reversely conducted, and the emission current is negative; when all four switching devices are turned off, the emission current gradually decays to zero;
the transmitting bridge circuit inverts the direct-current voltage of the direct-current power supply into bipolar trapezoidal wave transmitting current which flows to the ground through the grounding wire;
the output of the transmitting bridge circuit is the series impedance of the grounding wire and the ground;
the impedance matching unit is formed by connecting a switching device Q5 and a matching load in series, and the impedance of the matching load is equal to the series impedance of the grounding wire and the ground;
the controller controls the on and off of five switching devices in the system, and when all the switching devices of the transmitting bridge are turned off, the switching device Q5 of the impedance matching unit is turned on.
2. The method for controlling the emission of the high-current slow turn-off of the electric source based on the direct-current chopping according to claim 1, wherein the calculating of the optimal turn-off time in the step 1) means calculating the influence of different turn-off times on the polarization characteristics in the transient electromagnetic response curve based on the mutual inductance relation between the grounding wire and the equivalent eddy current loop of the target body, and specifically comprises the following steps:
1) Setting a grounding wire of a high-power electrical source emission system as a finite-length straight wire, enabling an underground target body to be equivalent to a polarized ring vortex loop, and calculating a mutual inductance M between the grounding wire and the equivalent vortex loop of the target body according to the relative position and the size of the grounding wire and the polarized ring vortex loop;
2) Establishing different off times t off Time domain expression I (t) of the oblique step emission current over time t as follows:
Figure FDA0003996150910000021
wherein I is m Maximum current amplitude, t on For a time when the emission current is stable on, approximately equal to one quarter of a period; u (t), u (t-t) on ) And u (t-t) on -t off ) Respectively the starting time is 0, t on And (t) on +t off ) Is a unit step signal of (a).
3) Calculating primary induced electromotive force emf generated by emission current in equivalent eddy current loop of target body 1 ，
Figure FDA0003996150910000022
4) Calculating transient electromagnetic response in the equivalent eddy current loop according to the polarization parameters of the target body, and analyzing the polarization characteristics of the response curve to obtain the optimal turn-off time t o The polarization parameters do not have resistivity ρ, polarization η, and time constant τ;
the polarization characteristic comprises a sign inversion time and a maximum negative response amplitude, and is most obvious when the turn-off time is equal to the optimal turn-off time, namely the sign inversion time is earliest and the corresponding maximum negative response amplitude is more than 90% of the maximum negative response amplitude under the zero turn-off time;
the preset off time ranges from 100 microseconds to 10 milliseconds, within which the preset off time is equal to the optimal off time.
3. The method for controlling the emission of a large-current slow-turn-off power source based on direct-current chopping according to claim 1, wherein the step 3) of changing the period and the duty ratio of the driving signal of the switching device based on the direct-current chopping technique comprises the steps of: after the forward conduction emission current starts to be turned off, calculating the difference value between the absolute value of the actual emission current and the absolute value of the reference current at each moment; when the difference is positive, the switching device Q1 and the switching device Q4 of the transmitting bridge circuit are turned off, the switching device Q5 of the impedance matching unit is turned on, and the transmitting current is reduced to be negative; when the difference is negative, the switching device Q1 and the switching device Q4 of the transmitting bridge are turned on, the switching device Q5 of the impedance matching unit is turned off, and the transmitting current rises until the difference is positive; when the emission current in the turn-off period is reduced to zero according to the preset turn-off time, the switching device Q5 of the impedance matching unit is turned on, and the switching device Q1 and the switching device Q4 of the emission bridge circuit are kept turned off to the next period; during this time, the switching devices Q2 and Q3 of the transmitting bridge are always turned off. When the reverse conduction emission current starts to be turned off, the control strategy is the same as that described above, and the switching devices Q2 and Q3 are interchanged with the switching devices Q1 and Q4.
4. The method for controlling the emission of a large-current slow-turn-off of an electrical source based on direct current chopping according to claim 1, wherein the emission current in the step 3) is reduced to zero according to a constant slope, which is the ratio of the amplitude of the emission current to the turn-off time, means that the emission current reduced based on the direct current chopping technique is equivalent to a reference current of a ramp step during the turn-off period.
CN202211603168.2A 2022-12-13 2022-12-13 Electric source high-current slow-turn-off emission control method based on direct-current chopping Pending CN116094319A (en)

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