A method for controlling the high current slow shutdown emission of an electric source based on DC chopping

Abstract

The present invention relates to a method for controlling the large current slow shutdown emission of an electric source based on DC chopping. The high-power electric source emission system is composed of a DC power supply, an impedance matching unit, an emission bridge and a controller. The emission bridge is used to provide a bipolar trapezoidal wave emission current to the underground, and the impedance matching unit is used to ensure the stability of the system output power. Before work, according to the exploration needs of different polarization bodies, the current shutdown time and amplitude are preset in the controller, and the reference current at different times during the shutdown period is calculated; during work, during the current shutdown period, the Hall current sensor is used to collect the emission current data and feedback it to the controller in a closed loop; the controller generates a driving signal of the switching device based on the DC chopping technology, controls the period and duty cycle of the switching device, and makes the emission current drop to zero at a constant slope. The purpose of the present invention is to achieve controllable emission current falling edge of the electric source emission system, change the shutdown time according to different polarization effects, and make the observed polarization response more obvious.

Description

Technical Field

[0001] The present invention relates to the field of time domain electromagnetic exploration, and in particular to a method for controlling a large current slow shutdown emission of an electrical source based on direct current chopping. Background Art

[0002] In the field of time-domain electromagnetic exploration, the electrical source method can provide a larger transmitting moment and detection depth, so it is widely used. The time-domain electromagnetic method based on the electrical source provides a bipolar trapezoidal wave transmitting current to the earth through a high-power electrical source transmitting system to generate a primary magnetic field excitation. The collected secondary magnetic field (and its rate of change) data contains the induction response and polarization response, which can be used to jointly extract the resistivity and polarizability. After the current is turned off, the early induction field decays rapidly, the induction field and the polarization field coexist, and the secondary magnetic field data is positive; in the middle and late stages, there is almost no induction field, which is mainly a polarization field, and the secondary magnetic field data is negative. Therefore, there is a sign reversal phenomenon in the induction-polarization response curve, and the polarization characteristics are usually represented by the sign reversal moment and the maximum negative response amplitude. Among them, the earlier the sign reversal moment, the larger the maximum negative response amplitude, and the more obvious the polarization characteristics.

[0003] The turn-off time of the emission current affects the size of the induction field and the polarization field. The shorter the turn-off time, the stronger the induction field, the shorter the charging time of the polarization field, and the weaker the polarization field; the longer the turn-off time, the weakened induction field, the longer the charging time of the polarization field, and the enhanced polarization field; but if the turn-off time is too long, the energy of the excited primary magnetic field 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 induction field, it is necessary to select a suitable turn-off time to make the polarization characteristics as obvious as possible. At the same time, different polarization targets have different requirements for the size of the turn-off time. Since the size of the secondary magnetic field is proportional to the amplitude of the emission current, it is necessary to realize slow shutdown control of large currents under the electrical source mode.

[0004] CN108227011A discloses a dual trapezoidal wave transmitting system and control method with controllable falling edge, which clamps the voltage at both ends of the transmitting coil at a high level or a low level through a high-voltage transient suppression diode and a low-voltage transient suppression diode, respectively, so that the transmitting current is quickly shut down or slowly shut down. However, due to the limited rated voltage of the transient suppression diode, this method cannot be applied to the slow shutdown control of the high-power and high-current electrical source transmitting system.

[0005] CN111769738B discloses a DC chopper circuit control system, method and device, which realizes timely control of output side load disturbance through output feedback. However, the output side reference current of this method is a constant value, and its purpose is to realize constant current and constant voltage control and suppress input and output disturbances. When the control system switch tube is turned off, the output current off time cannot be controlled. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a DC chopping-based electric source large current slow shutdown emission control method, which solves the problem that the emission current shutdown time of the high-power and high-current electric source emission system cannot be extended, makes the polarization characteristics in the collected secondary magnetic field response data more obvious, and improves the resolution and interpretation accuracy of underground polarization targets.

[0007] The present invention is achieved in this way.

[0008] A method for controlling a large current slow shutdown emission of an electric source based on direct current chopping, the method comprising:

[0009] 1) According to the polarization parameters of the target, the optimal shutdown time t is calculated based on the mutual inductance relationship between the grounding wire and the equivalent eddy current loop of the target o , the emission current off time t is preset in the controller off =t o , the reference current I at different times t during the shutdown period r According to the preset emission current off time t off and the maximum current amplitude I m calculate, The range of time t is (0, t off ), the reference current during the off period after forward conduction is positive, and the reference current during the off period after reverse conduction is negative;

[0010] 2) Start the high-power electrical source emission system and adjust the supply voltage of the DC power supply so that the actual emission current is equal to the amplitude of the preset emission current;

[0011] 3) During the period when the emission current is turned off, the actual emission current is collected by the Hall current sensor and sent to the controller. The controller changes the cycle and duty cycle of the switch device drive signal based on the closed-loop feedback of the DC chopping technology, so that the emission current decreases to zero at a constant slope;

[0012] Wherein, the high-power electrical source transmitting system includes a DC power supply, a transmitting bridge, an impedance matching unit and a controller;

[0013] The DC power supply provides a stable DC voltage, and the output is a transmitting bridge circuit or an impedance matching unit, and the impedance matching unit is connected in parallel with the transmitting bridge circuit;

[0014] The transmitting bridge is a bridge composed of a switch device Q1, a switch device Q2, a switch device Q3 and a switch device Q4. When the switch device Q1 and the switch device Q4 are turned on, the system is forward-conducted, and the magnitude of the transmitting current is positive; when the switch device Q2 and the switch device Q3 are turned on, the system is reverse-conducted, and the magnitude of the transmitting current is negative; when all four switch devices are turned off, the transmitting current gradually decays to zero;

[0015] The transmitting bridge circuit inverts the DC voltage of the DC power supply into a bipolar trapezoidal wave transmitting current, which flows to the ground through the grounding wire;

[0016] The output of the transmitting bridge circuit is the series impedance of the grounding wire and the earth;

[0017] The impedance matching unit is composed of a switch device Q5 and a matching load connected in series, and the impedance of the matching load is equal to the series impedance of the grounding wire and the earth;

[0018] The controller controls the on and off of five switch devices in the system. When all the switch devices of the transmitting bridge are turned off, the switch device Q5 of the impedance matching unit is turned on.

[0019] Further, the calculation of the optimal turn-off time in step 1) refers to calculating the influence of different turn-off times on the polarization characteristics 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 the specific steps are as follows:

[0020] 1) Assume that the grounding wire of the high-power electrical source transmission system is a finite-length straight wire, and the underground target is equivalent to a polarization ring eddy current loop. Calculate the mutual inductance M between the grounding wire and the equivalent eddy current loop of the target based on their relative position and size;

[0021] 2) Establish different off-times t off The time domain expression of the ramp step emission current with time t, I(t), is as follows:

[0022]

[0023] Among them, I m is the maximum current amplitude, t on is the time for the emission current to be stably turned on, which is approximately equal to one quarter of a cycle; u(t), u(tt on ) and u(tt on -t off ) are the starting time 0 and t on and (t on +t off ) is a unit step signal.

[0024] 3) Calculate the primary induced electromotive force emf generated by the emission current in the equivalent eddy current loop of the target body 1 ,

[0025] 4) Calculate the transient electromagnetic response in the equivalent eddy current circuit according to the polarization parameters of the target body, analyze the polarization characteristics of the response curve, and obtain the optimal shutdown time t o, the polarization parameters are resistivity ρ, polarizability η, and time constant τ;

[0026] Among them, the polarization characteristics include the sign reversal time and the maximum negative response amplitude. The polarization characteristics are most obvious when the turn-off time is equal to the optimal turn-off time, that is, the sign reversal time is the earliest and the corresponding maximum negative response amplitude is greater than 90% of the maximum negative response amplitude under zero turn-off time;

[0027] The preset off-time ranges from 100 microseconds to 10 milliseconds, and within this range the preset off-time is equal to the optimal off-time.

[0028] Furthermore, in step 3), the period and duty cycle of the switch device drive signal are changed based on the DC chopping technology, including: when the forward-conducting emission current begins to turn off, the difference between the absolute value of the actual emission current and the absolute value of the reference current at each moment is calculated; when the difference is positive, the switch device Q1 and the switch device Q4 of the emission bridge are turned off, the switch device Q5 of the impedance matching unit is turned on, and the emission current drops to a negative difference; when the difference is negative, the switch device Q1 and the switch device Q4 of the emission bridge are turned on, the switch device Q5 of the impedance matching unit is turned off, and the emission current rises to a positive difference; when the emission current during the shutdown period drops to zero according to the preset shutdown time, the switch device Q5 of the impedance matching unit is turned on, and the switch devices Q1 and Q4 of the emission bridge remain turned off until the next cycle; during this period, the switch devices Q2 and Q3 of the emission bridge are always turned off. When the reverse-conducting emission current begins to shut down, the control strategy is the same as above, and the switching devices Q2 and Q3 are interchanged with the switching devices Q1 and Q4.

[0029] Furthermore, in step 3), the emission current decreases to zero at a constant slope, which means that the emission current decreased based on the DC chopping technology during the shutdown period is equivalent to the reference current of the ramp step, and the slope is the ratio of the amplitude of the emission current to the shutdown time.

[0030] Compared with the prior art, the present invention has the following beneficial effects: the present invention breaks through the voltage and current resistance limitations of the voltage clamp device, solves the problem that the emission current shutdown time of the high-power and high-current electric source emission system cannot be extended, and improves and successfully realizes the controllable shutdown time of the high-power and high-current electric source emission system in the control mode of the emission system. Different output current shutdown times are preset for parameters of different polarization media, and current reference values ​​at different times during the shutdown period are calculated. The continuous on and off of the switching device is controlled by current acquisition closed-loop feedback, so that the output current of the emission system drops to zero at a constant slope. The slow shutdown mode of this emission system makes the polarization characteristics in the collected secondary magnetic field response data more obvious, which is conducive to the extraction and inversion of the polarization parameters of the underground target body, and improves the resolution and interpretation accuracy of the underground target body. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A control flow chart of a large current slow shutdown of an electrical source based on DC chopping provided in an embodiment of the present invention;

[0032] Figure 2 A structural diagram of an electrical source emission system with slow shutoff control provided by an embodiment of the present invention;

[0033] Figure 3 A timing diagram of a driving signal for switching between normal shutdown mode and slow shutdown mode provided by an embodiment of the present invention;

[0034] Figure 4 The measured slow shutdown driving signal during the shutdown period of the emission current provided by the embodiment of the present invention;

[0035] Figure 5 The actual measured current drop process waveform of the slow shutdown control provided by the embodiment of the present invention;

[0036] Figure 6 The induction-polarization response curves of the same polarizer with different turn-off times provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] See also Figure 1 As shown, the DC chopping-based electric source large current slow shutdown emission control method provided by the present invention includes the following steps:

[0039] 1) Consult geological data, understand exploration needs, debug and connect high-power electrical source transmission systems,

[0040] The high-power electrical source transmission system is composed of a DC power supply, a transmission bridge, an impedance matching unit and a controller. Figure 2 As shown;

[0041] The DC power supply provides a stable DC voltage, and the output is a transmitting bridge circuit or an impedance matching unit, and the impedance matching unit is connected in parallel with the transmitting bridge circuit;

[0042] The transmitting bridge is a bridge composed of four switching devices (Q1, Q2, Q3 and Q4), and the output of the bridge is connected to the load impedance. When the switching device Q1 and the switching device Q4 are turned on, the system is forward-conducted, and the magnitude of the transmitting current is positive; when the switching device Q2 and the switching device Q3 are turned on, the system is reverse-conducted, and the magnitude of the transmitting current is negative; when all four switching devices are turned off, the transmitting current gradually decays to zero;

[0043] The transmitting bridge circuit inverts the DC voltage of the DC power supply into a bipolar trapezoidal wave transmitting current, which flows to the ground through the grounding wire;

[0044] The output of the transmitting bridge circuit is the series impedance of the grounding wire and the earth;

[0045] The impedance matching unit is composed of a switch device Q5 and a matching load connected in series, and the impedance of the matching load is equal to the series impedance of the grounding wire and the earth;

[0046] The controller controls the on and off of five switch devices in the system. When all the switch devices of the transmitting bridge are turned off, the switch device Q5 of the impedance matching unit is turned on to ensure that the output power of the system is constant.

[0047] 2) According to the polarization parameters of the target, the optimal shutdown time t is calculated based on the mutual inductance relationship between the grounding wire and the equivalent eddy current loop of the target o , the emission current off time t is preset in the controller off =t o , the reference current I at different times t during the shutdown period r According to the preset emission current off time t off and the maximum current amplitude I m calculate, The range of time t is (0, t off ), the reference current during the off period after forward conduction is positive, and the reference current during the off period after reverse conduction is negative;

[0048] Further, calculating the optimal turn-off time means calculating the influence of different turn-off times on the polarization characteristics 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. The specific steps are as follows:

[0049] Firstly, the grounding wire of the electric source emission system is assumed to be a finite length straight wire, and the underground target is equivalent to a polarization ring eddy current loop. The mutual inductance coefficient M between the grounding wire and the equivalent eddy current loop of the target is calculated according to the relative position and size of the two.

[0050] Secondly, establish different off-times t off The time domain expression of the ramp step emission current with time t, I(t), is as follows:

[0051]

[0052] Among them, I m is the maximum current amplitude, t on is the time for the emission current to be stably turned on, which is approximately equal to one quarter of a cycle; u(t), u(tton ) and u(tt on -t off ) are the starting time 0 and t on and (t on +t off ) is a unit step signal.

[0053] Then, calculate the primary induced electromotive force emf generated by the emission current in the equivalent eddy current loop of the target body 1 ,

[0054] Finally, the transient electromagnetic response in the equivalent eddy current circuit is calculated according to the polarization parameters of the target body (resistivity ρ, polarizability η, time constant τ), the polarization characteristics of the response curve are analyzed, and the optimal shutdown time t is obtained. o .

[0055] Among them, the polarization characteristics include the sign reversal time and the maximum negative response amplitude. The polarization characteristics are most obvious when the turn-off time is equal to the optimal turn-off time, that is, the sign reversal time is the earliest and the corresponding maximum negative response amplitude is greater than 90% of the maximum negative response amplitude under zero turn-off time;

[0056] The preset off-time ranges from 100 microseconds to 10 milliseconds, and within this range the preset off-time is equal to the optimal off-time.

[0057] 3) Start the high-power electrical source emission system and adjust the supply voltage of the DC power supply so that the actual emission current is equal to the amplitude of the preset emission current;

[0058] 4) During the period when the emission current is turned off, the actual emission current is collected by the Hall current sensor and sent to the controller. The controller uses closed-loop feedback based on the DC chopping technology to change the period and duty cycle of the switching device drive signal so that the emission current decreases to zero at a constant slope.

[0059] See also Figure 3As shown, changing the cycle and duty cycle of the switch device driving signal based on the DC chopping technology means that when the forward-conducting emission current begins to turn off, the difference between the absolute value of the actual emission current and the absolute value of the reference current at each moment is calculated; when the difference is positive, the switch devices Q1 and Q4 of the emission bridge are turned off, the switch device Q5 of the impedance matching unit is turned on, and the emission current drops to a negative difference; when the difference is negative, the switch devices Q1 and Q4 of the emission bridge are turned on, the switch device Q5 of the impedance matching unit is turned off, and the emission current rises to a positive difference; when the emission current during the off period drops to zero according to the preset off time, the switch device Q5 of the impedance matching unit is turned on, and the switch devices Q1 and Q4 of the emission bridge remain off until the next cycle; during this period, the switch devices Q2 and Q3 of the emission bridge are always off. When the reverse-conducting emission current begins to turn off, the control strategy is the same as above, and the switch devices Q2 and Q3 are interchanged with the switch devices Q1 and Q4. In the DC chopping adopted by the present invention, the reference current during each current cut-off period varies with time, and the on and off of the switch device needs to be adjusted at any time.

[0060] Among them, the emission current that decreases based on the DC chopping technology during the shutdown period can be equivalent to the reference current of the ramp step, and the slope is the ratio of the amplitude of the emission current to the shutdown time. The smaller the minimum cycle of the switch device drive signal, the smaller the ripple of the slow-turnoff emission current, and the better the excitation effect on the polarization effect. The minimum switching cycle is limited by the actual power consumption and temperature rise of the switch device.

[0061] The DC chopping-based electric source large current slow shutdown emission control method provided by the present invention has been successfully implemented and verified through field experiments. Here is a set of verification cases. According to the inductive-polarization characteristics of the polarized target body under test, a 1.8 millisecond slow shutdown control needs to be implemented. According to the slow shutdown emission control method proposed by the present invention, the measured drive signal during the shutdown period and the emission current falling edge waveform are respectively as follows: Figure 4 and Figure 5 As shown. Figure 5 As shown, the emission current amplitude of the electric source emission system is 100 amperes, and the current cut-off time is 1.8 milliseconds. Figure 3 When the power source emission system is normally shut down, the emission current shut-off time is 0.2 milliseconds.

[0062] See also Figure 6As shown, the induction-polarization response curves for the excitation of the same polarized body when the shutdown time is 0.2 milliseconds and 1.8 milliseconds respectively are given. It can be seen that compared with 0.2 milliseconds, the polarization characteristics of the response curve corresponding to 1.8 milliseconds are more obvious. Not only is the sign reversal moment advanced, but the maximum negative response amplitude is also increased by an order of magnitude. Obviously, the DC chopping-based electrical source large current slow shutdown emission control method provided by the present invention makes the polarization characteristics in the collected secondary magnetic field response data more obvious, which is beneficial to the extraction and inversion of the polarization parameters of the underground target body, and improves the resolution and interpretation accuracy of the underground target body.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling the slow shutdown of a large current source of an electric source based on DC chopping. It is characterized in that The method includes: 1) According to the polarization parameters of the target, the optimal shutdown time t is calculated based on the mutual inductance relationship between the grounding wire and the equivalent eddy current loop of the target o , the emission current off time t is preset in the controller off =t o , the reference current I at different times t during the shutdown period r According to the preset emission current off time t off and the maximum current amplitude I m calculate, The range of time t is (0, t off ), the reference current during the off period after forward conduction is positive, and the reference current during the off period after reverse conduction is negative; 2) Start the high-power electrical source emission system and adjust the supply voltage of the DC power supply so that the actual emission current is equal to the amplitude of the preset emission current; 3) During the period when the emission current is turned off, the actual emission current is collected by the Hall current sensor and sent to the controller. The controller changes the cycle and duty cycle of the switch device drive signal based on the closed-loop feedback of the DC chopping technology, so that the emission current decreases to zero at a constant slope; Wherein, the high-power electrical source transmitting system includes a DC power supply, a transmitting bridge, an impedance matching unit and a controller; The DC power supply provides a stable DC voltage, and the output is a transmitting bridge circuit or an impedance matching unit, and the impedance matching unit is connected in parallel with the transmitting bridge circuit; The transmitting bridge is a bridge composed of a switch device Q1, a switch device Q2, a switch device Q3 and a switch device Q4. When the switch device Q1 and the switch device Q4 are turned on, the system is forward-conducted, and the magnitude of the transmitting current is positive; when the switch device Q2 and the switch device Q3 are turned on, the system is reverse-conducted, and the magnitude of the transmitting current is negative; when all four switch devices are turned off, the transmitting current gradually decays to zero; The transmitting bridge circuit inverts the DC voltage of the DC power supply into a 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 earth; The impedance matching unit is composed of a switch device Q5 and a matching load connected in series, and the impedance of the matching load is equal to the series impedance of the grounding wire and the earth; The controller controls the on and off of five switch devices in the system, and when all the switch devices of the transmitting bridge are turned off, the switch device Q5 of the impedance matching unit is turned on; The period and duty cycle of the switch device drive signal are changed based on the DC chopping technology, including: when the forward-conducting emission current begins 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 moment is calculated; when the difference is positive, the switch device Q1 and the switch device Q4 of the emission bridge are turned off, the switch device Q5 of the impedance matching unit is turned on, and the emission current drops to a negative difference; when the difference is negative, the switch device Q1 and the switch device Q4 of the emission bridge are turned on, the switch device Q5 of the impedance matching unit is turned off, and the emission current rises to a positive difference.

2. The method for controlling the large current slow shutdown emission of an electric source based on DC chopping according to claim 1, It is characterized in that Calculating the optimal off-time in step 1) means calculating the influence of different off-times on the polarization characteristics 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. The specific steps are as follows: 1) Assume that the grounding wire of the high-power electrical source transmission system is a finite-length straight wire, and the underground target is equivalent to a polarization ring eddy current loop. Calculate the mutual inductance M between the grounding wire and the equivalent eddy current loop of the target based on their relative position and size; 2) Establish different off-times t off The time domain expression of the ramp step emission current with time t, I(t), is as follows: Among them, I m is the maximum current amplitude, t on is the time for the emission current to be stably turned on, which is equal to one quarter of a cycle; u(t), u(tt on ) and u(tt on -t off ) are the starting time 0 and t on and (t on +t off ) is a unit step signal; 3) Calculate the primary induced electromotive force emf generated by the emission current in the equivalent eddy current loop of the target body 1 , 4) Calculate the transient electromagnetic response in the equivalent eddy current circuit according to the polarization parameters of the target body, analyze the polarization characteristics of the response curve, and obtain the optimal shutdown time t o , the polarization parameters are resistivity ρ, polarizability η, and time constant τ; Among them, the polarization characteristics include the sign reversal time and the maximum negative response amplitude. The polarization characteristics are most obvious when the turn-off time is equal to the optimal turn-off time, that is, the sign reversal time is the earliest and the corresponding maximum negative response amplitude is greater than 90% of the maximum negative response amplitude under zero turn-off time; The preset off-time ranges from 100 microseconds to 10 milliseconds, and within this range the preset off-time is equal to the optimal off-time.

3. The DC chopping-based high current slow-off emission control method for an electric source according to claim 1, It is characterized in that In step 3), when the emission current during the shutdown period drops to zero according to the preset shutdown time, the switch device Q5 of the impedance matching unit is turned on, and the switch devices Q1 and Q4 of the emission bridge remain turned off until the next cycle; during this period, the switch devices Q2 and Q3 of the emission bridge are always turned off; when the reverse-conducting emission current begins to turn off, the control strategy is the same as above, and the switch devices Q2 and Q3 are interchanged with the switch devices Q1 and Q4.

4. The method for controlling the large current slow shutdown emission of an electric source based on DC chopping according to claim 1, It is characterized in that In step 3), the emission current decreases to zero at a constant slope, which means that the emission current decreased based on the DC chopping technology during the shutdown period is equivalent to the reference current of the ramp step, and the slope is the ratio of the amplitude of the emission current to the shutdown time.

Images