An AC-AC converter suitable for use in a cross-well electromagnetic transmission system

Abstract

The application discloses an AC-AC converter suitable for an interwell electromagnetic emission system and belongs to the technical field of interwell electromagnetic detection. The AC-AC converter comprises an FPGA control module, wherein the FPGA control module is connected with a power module and a driving circuit module; the power module is connected with an inverter module and the driving circuit module; the inverter module and the driving circuit module are connected with a full-bridge AC-AC converter module; and the full-bridge AC-AC converter module is connected with a coil load. According to the circuit characteristics of the full-bridge AC-AC converter module, a state space average model is established based on a state space average method, and the transfer function between a duty cycle signal and an output voltage signal, the transfer function between the duty cycle signal and an inductance current signal and the transfer function between the inductance current signal and the output voltage signal are separated and acquired to obtain a dynamic circuit state. The interwell electromagnetic emission system is controlled in combination with a current loop QPR controller and a voltage loop PI controller. The application greatly improves the overall control performance of the interwell electromagnetic emission system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cross-well electromagnetic detection, and particularly to an AC-AC converter suitable for a cross-well electromagnetic transmitting system. BACKGROUND

[0002] Cross-well electromagnetic method is a geophysical method for imaging and detecting the geological structure between wells by arranging electromagnetic wave transmitting devices and receiving devices in different boreholes respectively. This method has significant advantages such as large detection depth (up to thousands of meters) and strong penetration ability, and is widely used in the fields of oil exploration, mineral exploration and engineering geological survey.

[0003] At present, the cross-well electromagnetic transmitting system generally adopts the power supply mode on the well: a low-frequency alternating signal of a specific frequency is generated by a ground signal generator, amplified by a power amplifier, and then transmitted to the downhole transmitting coil by a long-distance cable. This scheme has the following inherent defects:

[0004] 1. Serious energy loss: the line loss of a high-power signal in a kilometer-level cable transmission is as high as 30%, which significantly reduces the system efficiency;

[0005] 2. Limited output voltage: due to the cable voltage drop, the actual voltage at the end of the downhole coil is less than 50% of the design value, which seriously restricts the detection depth;

[0006] 3. Poor waveform quality: the output of the traditional full-bridge inverter is mostly square wave signal, and its harmonic component (THD>40%) interferes with the extraction of target formation information, and the low-frequency square wave is easy to cause power tube short circuit;

[0007] 4. Difficulty in frequency / amplitude adjustment: the pulse stretching circuit needs to be redesigned or the matching network needs to be replaced, and it is impossible to realize the dynamic switching of multiple parameters in a single downhole process;

[0008] 5. Low power density: the switching frequency of the IGBT-based inverter is limited (<20kHz), resulting in a large volume of magnetic elements, which is difficult to meet the deployment requirements in the narrow space downhole.

[0009] Although some schemes attempt to use downhole DC / DC modules for power supply, the output voltage amplitude adjustment range is narrow (±10%), which cannot adapt to the differentiated requirements of complex strata for excitation signal amplitude-frequency characteristics. The accurate reconstruction of stratum information requires wide-range and high-precision independent adjustment of the frequency (5-20kHz) and amplitude (0-750V) of the transmitting signal in a single operation.

[0010] The prior art, such as Chinese invention patent-CN115441704B discloses a frequency amplitude adjustable interwell electromagnetic transmitting system, which adopts a bridge inverter module and an SPWM control technology, adjusts the modulation signal in real time through FPGA analysis of well communication instructions, and realizes adjustable output of frequency and amplitude. The system uses a well direct current power supply mode, reduces cable transmission loss, and uses SiC MOSFET to improve switching frequency and power density. However, it still has the following limitations: first, the system is based on a DC-AC inverter structure, which needs to convert direct current into alternating current signal, and there is a risk of efficiency loss and waveform distortion in the conversion process, especially in the high frequency band (such as above 20 kHz), it is difficult to ensure that the THD (total harmonic distortion) meets the demand; second, the control strategy depends on simple SPWM modulation, and an accurate circuit dynamic model (such as state space average model) is not established, resulting in slow system response speed, poor anti-interference ability, and inability to realize real-time impedance matching; third, the frequency adjustment range is limited, it is difficult to cover the wide frequency band (5-20 kHz) required for interwell detection, and there is a lack of adaptive control mechanism, which is prone to load mismatching in complex strata. Therefore, although the frequency amplitude adjustable interwell electromagnetic transmitting system has improved the basic frequency modulation and amplitude modulation, the overall control performance, waveform quality and adaptability are still insufficient.

[0011] Therefore, developing a downhole direct AC-AC conversion technology with high efficiency, high waveform quality, wide tuning range and compact structure has become a key path to break through the bottleneck of interwell electromagnetic detection. SUMMARY

[0012] The purpose of the present application is to overcome the shortcomings of the prior art and provide an AC-AC converter suitable for an interwell electromagnetic transmitting system.

[0013] The purpose of the present application is achieved by the following technical scheme: an AC-AC converter suitable for an interwell electromagnetic transmitting system, comprising a FPGA control module, the FPGA control module is connected with a power module and a driving circuit module, the power module is connected with an inverter module and the driving circuit module, the inverter module and the driving circuit module are connected with a full-bridge AC-AC converter module, and the full-bridge AC-AC converter module is connected with a coil load.

[0014] The FPGA control module is used for receiving a well communication signal and generating a bipolar SPWM signal sent to the driving circuit module.

[0015] The power module is used for converting well direct current power supply into system working voltage.

[0016] The driving circuit module is used for amplifying the bipolar SPWM signal to obtain an SPWM driving signal.

[0017] The full-bridge AC-AC converter module adopts a Cuk type topology, and is used for regulating and stably outputting a frequency-adjustable AC signal output by an inverter module according to a required amplitude, and transmitting the AC signal to both ends of a coil load for radiation.

[0018] According to the circuit characteristics of the full-bridge AC-AC converter module, a state space average model is established, and a transfer function between a duty cycle signal and an output voltage signal, a transfer function between the duty cycle signal and an inductor current signal, and a transfer function between the inductor current signal and the output voltage signal are separated and obtained to obtain a dynamic circuit state, and a current loop QPR controller and a voltage loop PI controller are combined to control the interwell electromagnetic transmission system.

[0019] Preferably, the full-bridge AC-AC converter module comprises power switch tubes S1, S2, S3, S4, an input inductor L1, an output inductor L2, a transmission capacitor C1, an output capacitor C2, and a resistor Ro; a first end of the input inductor L1 is connected to an input voltage u AC , a second end of the input inductor L1 is connected to a drain of the power switch tube S1 and a first end of the transmission capacitor C1; a second end of the transmission capacitor C1 is connected to a drain of the power switch tube S2 and a first end of the output inductor L2; a second end of the output inductor L2 is connected to the output capacitor C2 and a first end of the resistor Ro; a second end of the output capacitor C2 is connected to a second end of the resistor Ro, a drain of the power switch tube S4, a drain of the power switch tube S3, and the input voltage u AC ; a source of the power switch tube S1 is connected to a source of the power switch tube S3; a source of the power switch tube S2 is connected to a source of the power switch tube S4.

[0020] Preferably, the state space average model is established by the following steps:

[0021] Based on the state space average method, a current i L1 of the input inductor L1, a voltage u c1 of the transmission capacitor C1, a current i L2 of the output inductor L2, and a voltage u c2 of the output capacitor C2 are taken as a state vector to form a four-bit state vector x(t); an input voltage u AC is taken as an input variable to establish a state space average model in a CCM mode ignoring parasitic parameters:

[0022] ;

[0023] where is the differential operator; y is the output voltage; A avg is the state matrix, which is based on the duty cycle unification over the period of the AC supply; B avg is the input matrix, which is normalized;

[0024] , ;

[0025] where L 1 is the inductance value of the input inductor L1; L 2 is the inductance value of the output inductor L2; C 1 is the capacitance value of the transfer capacitor C1; C 2 is the capacitance value of the output capacitor C2; d is the duty cycle of the power switch; input voltage u AC is the AC current, which is processed in half cycle and introduced the sign function when modeling sgn ( u ) is normalized;

[0026] The state-space average model is linearized and separated to get the small-signal model of the full-bridge AC-AC converter module: ;

[0027] where the state vector ; the input disturbance ; is the control disturbance; the output = = ; A is the state matrix; B is the input matrix; C is the output matrix; E is the duty cycle disturbance matrix; is the state vector of the current of the input inductor L1; is the state vector of the voltage of the transfer capacitor C1; is the state vector of the current of the output inductor L2; is the state vector of the voltage of the output capacitor C2; is the voltage of the AC supply;

[0028] , , ;

[0029] where D is the duty cycle of the power switch S1; RC 2 is the time constant of the system; I L1The perturbation of the steady state current of the output inductor L2 for duty cycle calculation; I L2 The perturbation of the steady state current of the output inductor L2 for duty cycle calculation; U C1 The perturbation of the steady state voltage of the transmission capacitor C1 for duty cycle calculation;

[0030] The small signal model is Laplace transformed and separated to obtain the transfer function between the duty cycle signal and the output voltage signal, and the Laplace transformation and arrangement of the small signal model are as follows:

[0031] ;

[0032] Wherein is the Laplace transformation of , is a state vector; is the Laplace transformation of , is a control perturbation; the matrix is constructed as:

[0033] ; wherein s is the independent variable of the Laplace transformation; I is a unit matrix of the same order as A ;

[0034] The transfer function between the duty cycle signal and the output voltage signal is defined as:

[0035] , and the calculation is simplified to obtain:

[0036] ;

[0037] Wherein is the complex frequency domain voltage of the output capacitor C2; is the Laplace transformation of the control perturbation; the DC gain ; the right half plane zero point ; the output filter pole ; the output damping factor ; the input stage pole ; the resonance pole ; R is the load resistance;

[0038] Similarly, the transfer function between the duty cycle signal and the inductor current signal is defined as:

[0039] ;

[0040] Neglecting the dynamic effect of output capacitor C2, the analytical inverse is obtained as:

[0041] ;

[0042] If the parasitic capacitances (Cp1, Cp2) r L1 , r C2 and cross-coupling terms are considered, then we have:

[0043] where is the dynamic compensation term; is the dynamic damping correction term;

[0044] Similarly, the transfer function between the inductor current signal and the output voltage signal is defined as:

[0045] ;

[0046] From the power balance equation, considering the dynamics of the filter composed of output inductor L2 and output capacitor C2, we have: ;

[0047] If the parasitic capacitances (Cp1, Cp2) r L1 , r C2 and cross-coupling terms are considered, then we have: .

[0048] ​​​Preferably, the FPGA control module comprises a UART serial port receiving module, the UART serial port receiving module receives the wellhead communication signal, the output end of the UART serial port receiving module is connected with a decoder; the decoder is connected with a frequency / amplitude control module and a double closed loop control logic module; the frequency / amplitude control module is connected with the input end of a sine wave generator and a modulation signal generator; the input end of the sine wave generator is connected with the output end of a timer / counter module, the output end of the sine wave generator is connected with the modulation signal generator; the input end of the timer / counter module is connected with the output end of a GPS synchronization module; the double closed loop control logic module is connected with a voltage loop PI controller and a current loop QPR controller; the input end of the voltage loop PI controller is connected with an ADC interface module, the output end of the voltage loop PI controller is connected with the input end of the current loop QPR controller; the output end of the ADC interface module is connected with a feedforward compensation module, the current loop QPR controller and an overcurrent and overvoltage protection module; the feedforward compensation module is connected with the input end of the modulation signal generator; the output end of the current loop QPR controller and the modulation signal generator is connected with an SPWM pulse signal generation module; the input end of the SPWM pulse signal generation module is connected with a triangular carrier generator, the output end of the SPWM pulse signal generation module and the overcurrent and overvoltage protection module is connected with the input end of a dead zone generation module; the output end of the dead zone generation module is connected with a drive circuit module.

[0049] The UART serial port receiving module is used for receiving the communication instruction sent by the wellhead cabinet; the modulation signal generator is used for generating the sine modulation signal required to be set; the triangular carrier generator is used for generating the triangular carrier signal; the ADC interface module is used for managing the 4-way ADC acquisition; the overcurrent and overvoltage protection module is used for the real-time protection of overvoltage and overcurrent; the current loop QPR controller is used for tracking and eliminating the error in real time according to the dynamic difference of the magnetic field energy, solving the influence of high-frequency disturbance on the system; the voltage loop PI controller is used for eliminating the error according to the dynamic of the electric field energy, realizing the output steady-state precision; the SPWM pulse signal generation module is used for calculating and comparing the sine modulation signal and the triangular carrier signal to generate the SPWM pulse signal; the dead zone generation module is used for generating the dead zone in the SPWM pulse signal to protect the circuit and prevent the commutation problem of the simultaneous conduction or turn-off of the two groups of power switch tubes in the complementary conduction work of the full-bridge AC-AC converter module.

[0050] Preferably, the adaptive frequency control algorithm is used to realize the coupling between the full-bridge AC-AC converter module, the inverter module and the coil load.

[0051] Preferably, the adaptive frequency control algorithm comprises the following steps:

[0052] The disturbance signal is injected, the waveform of a complete disturbance period is synchronously collected, the impedance real part is extracted by decomposition, and thus the load impedance is identified in real time;

[0053] According to the result of dividing the load impedance real part identified in real time by the reference impedance value, the duty cycle is dynamically optimized through input voltage compensation, and adaptive control on the input frequency is realized through the control loop and anti-interference design.

[0054] The beneficial effects of the present application are:

[0055] 1) A four-order state space average model of the Cuk type full-bridge AC-AC converter module is established, the circuit dynamics can be more clearly and intuitively obtained, high-efficiency control is realized by combining the current loop QPR controller and the voltage loop PI controller, and the overall control performance of the interwell electromagnetic emission system is greatly improved;

[0056] 2) Through voltage and current double-loop control and high-frequency PWM modulation, wide-range accurate voltage regulation can be realized;

[0057] 3) Through QPR resonance control and dynamic feedforward compensation, high-frequency signal fidelity can be realized;

[0058] 4) The high-voltage-resistant SiC MOSFET is used as the switching tube of the interwell electromagnetic emission circuit and the adaptive bandwidth control, which can effectively increase the switching frequency, improve the overall response speed of the system, reduce the area of the emission circuit and improve the quality of the emission waveform;

[0059] 5) Relying on the adaptive frequency control algorithm, the real-time impedance matching in the well can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 It is the overall principle diagram of the present application;

[0061] Figure 2 It is the main circuit topology structure of the full-bridge AC-AC converter module;

[0062] Figure 3 It is the equivalent circuit diagram of the full-bridge AC-AC converter module in the working state;

[0063] Figure 4 It is the RC commutation circuit diagram of the full-bridge AC-AC converter module;

[0064] Figure 5 It is the principle diagram of the FPGA control module. DETAILED DESCRIPTION

[0065] The technical solutions of the present application will be described clearly and completely below in connection with the embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of the present application.

[0066] Referring to Figures 1-5 The present application provides a technical solution: an AC-AC converter suitable for an interwell electromagnetic emission system, comprising an FPGA control module, the FPGA control module is connected with a power module and a driving circuit module, the power module is connected with an inverter module and the driving circuit module, the inverter module and the driving circuit module are connected with a full-bridge AC-AC converter module, and the full-bridge AC-AC converter module is connected with a coil load.

[0067] The FPGA control module is used for receiving an uphole communication signal and generating a bipolar SPWM signal sent to the driving circuit module.

[0068] The power module is used for converting uphole direct current power supply into system working voltage.

[0069] The driving circuit module is used for amplifying the bipolar SPWM signal to obtain an SPWM driving signal.

[0070] The full-bridge AC-AC converter module adopts a Cuk type topology structure, is used for regulating and stabilizing the output of the frequency adjustable alternating current signal output by the inverter module according to the required amplitude, and sends the signal to the two ends of the coil load for radiation.

[0071] According to the circuit characteristics of the full-bridge AC-AC converter module, a state space average model is established based on the state space average method, and the transfer function between the duty cycle signal and the output voltage signal, the transfer function between the duty cycle signal and the inductance current signal, and the transfer function between the inductance current signal and the output voltage signal are separated to obtain the dynamic circuit state, and the interwell electromagnetic emission system is controlled in combination with the current loop QPR controller and the voltage loop PI controller.

[0072] In the present embodiment, the full-bridge AC-AC converter module adopts a Cuk type topology structure, and the power switch tube connection mode adopts a double-tube anti-series topology structure. In the positive half cycle of the power supply voltage, the switch tubes S3 and S4 are always turned off, and S1 and S2 are complementary on. In the negative half cycle of the power supply voltage, S1 and S2 are always turned off, and S3 and S4 are complementary on. At the same time, an RC commutation circuit can be added to provide a freewheeling loop for the conversion circuit.

[0073] The power module is composed of two DC / DC power chips 4812S and 4809S and their filter circuits, which can convert 48V DC voltage from the well into 12V and 9V DC voltage required by the FPGA control module and the driving circuit, so that the driving circuit module and the FPGA control module are in working condition.

[0074] Since the FPGA output high level voltage value is 3.3V and the low level is 0V, while the on voltage of SiC MOSFET is above 15V and the off voltage is below 0V, the control signal output by the FPGA is not enough to make the MOSFET in the AC-AC converter work, so the driving circuit module is designed to amplify the high level signal of the FPGA to 18V and the low level signal to-5V, so as to realize more accurate control. The driving circuit module in the embodiment uses isolated gate drive, converts the SPWM signal into optical signal through optical coupling, and then converts it into electrical signal output to the G and S ends of SiC MOSFET. This way can realize more stable and higher quality driving of SiC MOSFET in the bridge inverter module.

[0075] If the 5-20kHz adjustable frequency range of the inverter module of the interwell electromagnetic emission system needs to be coupled, and the output AC voltage effective value adjustable range of 0-750V is realized, the switching frequency of the Cuk type full-bridge AC-AC converter module can be set to 300kHz, the current inner loop bandwidth is set to 60kHz, and the voltage outer loop bandwidth is set to 3kHz; the four MOSFETs are selected as SiC MOSFET with a withstand voltage of 1200V; the input inductance L1 is selected as an inductance value of 6.8 ; the output inductance L2 is selected as an inductance value of 56 ; the transmission capacitor C1 is selected as 0.47 ; the output capacitor C2 is selected as 10 ; the capacitor Cs of the RC buffer circuit is selected as 3.3 ; the resistance Rs of the RC buffer circuit is selected as 6.8 Through the above parameters and selection design, 750V AC output at 20kHz frequency and THD less than 1% and full load efficiency not less than 95% can be realized.

[0076] In some embodiments, the full-bridge AC-AC converter module includes power switch tube S1, power switch tube S2, power switch tube S3, power switch tube S4, input inductance L1, output inductance L2, transmission capacitor C1, output capacitor C2 and resistance Ro; the first end of the input inductance L1 is connected to the input voltage u AC, the second end of the input inductor L1 is connected to the drain of the power switch S1 and the first end of the transfer capacitor C1; the second end of the transfer capacitor C1 is connected to the drain of the power switch S2 and the first end of the output inductor L2; the second end of the output inductor L2 is connected to the first end of the output capacitor C2 and the resistor Ro; the second end of the output capacitor C2 is connected to the second end of the resistor Ro, the drain of the power switch S4, the drain of the power switch S3 and the input voltage u AC ; the source of the power switch S1 is connected to the source of the power switch S3; the source of the power switch S2 is connected to the source of the power switch S4.

[0077] In the embodiment, taking the positive half cycle as an example, at t0-t1, the power switch S1 is turned on and the power switch S2 is turned off, and the equivalent circuit diagram of the full-bridge AC-AC converter module in working mode 1 is shown in Fig. (a). At t1-t2, the power switch S1 is turned off and the power switch S2 is turned on, and the equivalent circuit diagram of the full-bridge AC-AC converter module in working mode 2 is shown in Fig. (b). Figure 3 Figure 3

[0078] According to Figure 2 The increase of the inductive current of the inductors L1 and L2 can be calculated as:

[0079] ,

[0080] According to Figure 3 The increase of the inductive current of the inductors L1 and L2 in working mode 1 can be calculated as:

[0081] , wherein L 1 is the inductance value of the input inductor L1; L 2 is the inductance value of the output inductor L2; V i Vin is the input voltage; D D is the duty ratio of the power switch S1; T s T is a switching period; u c1 Vc is the voltage of the transfer capacitor C1; V o Vo is the output voltage; V L1 Vl is the voltage of the input inductor L1; V L2 V2 is the voltage of the output inductor L2; Vl1 is the L1 inductor voltage in working mode 1; V2 is the L2 inductor voltage in working mode 1.

[0082] Therefore, in​​DT s Within the time period V i Energy is stored in L1, while capacitor C1 discharges to the load and stores energy in inductor L2; in (1- D ) T s During the time period, inductor L1 charges C1, while inductor L2 supplies power to the load.

[0083] Since the current increment generated in inductors L1 and L2 is 0 during one switching cycle, that is:

[0084] It can be seen that by adjusting the duty cycle of the power switch... D It can achieve the ideal voltage output of the full-bridge AC-AC converter module, when D When the voltage is less than 0.5, the voltage reduction function can be achieved; when... D When the voltage is >0.5, the boost function can be achieved; when D When the voltage is 0.5, voltage regulation can be achieved. This allows for direct step-up / step-down adjustable output of the input AC voltage by controlling the duty cycle and using the transmission capacitor C1.

[0085] Furthermore, in Figure 2 The circuit structure consists of two sets of anti-tandem power switches connected in parallel with a commutation element RC, forming a freewheeling path for the inductive and non-resistive loads in the main circuit. Figure 4 As shown, a dead interval td is set for two sets of complementary bidirectional power switches to solve the commutation problem that inevitably occurs when the two sets of power switches are turned on or off simultaneously during the complementary conduction of power switches.

[0086] In some embodiments, the state-space averaging model is established through the following steps:

[0087] Based on the state-space averaging method, the current of the input inductor L1 is used as the starting point. i L1 Voltage of transfer capacitor C1 u c1 The current of output inductor L2 i L2 Voltage of output capacitor C2 u c2 As a state vector, a four-dimensional state vector x(t) is formed; the input voltage is taken. u AC For the input variables, establish a state-space averaged model in CCM mode, ignoring parasitic parameters:

[0088] ;

[0089] where is the differential operator; y is the output voltage; A avg is the state matrix, which is normalized based on the duty cycle over the period of the AC supply; B avg is the input matrix, which is normalized;

[0090] , ;

[0091] where L 1 is the inductance value of the input inductor L1; L 2 is the inductance value of the output inductor L2; C 1 is the capacitance value of the transmission capacitor C1; C 2 is the capacitance value of the output capacitor C2; d is the duty cycle of the power switch; input voltage u AC is the AC current, which is processed in half cycle and introduced the sign function when modeling sgn ( u ) is normalized;

[0092] The state-space average model is linearized and separated to get the small-signal model of the full-bridge AC-AC converter module: ;

[0093] where the state vector ; input disturbance ; is the control disturbance; output = = ; A is the state matrix; B is the input matrix; C is the output matrix; E is the duty cycle disturbance matrix; is the state vector of the current of the input inductor L1; is the state vector of the voltage of the transmission capacitor C1; is the state vector of the current of the output inductor L2; is the state vector of the voltage of the output capacitor C2; is the voltage of the AC supply;

[0094] , , ;

[0095] where D is the duty cycle of the power switch S1; RC 2 is the time constant of the system; I L1The perturbation of the steady-state current of the output inductor L2 for duty cycle calculation; I L2 The perturbation of the steady-state current of the output inductor L2 for duty cycle calculation; U C1 The perturbation of the steady-state voltage of the transmission capacitor C1 for duty cycle calculation;

[0096] The small signal model is Laplace-transformed and separated to obtain the transfer function between the duty cycle signal and the output voltage signal, and the Laplace-transformed and arranged small signal model is:

[0097] ;

[0098] Wherein is the Laplace transform of , is a state vector; is the Laplace transform of , is a control perturbation; the matrix is constructed as:

[0099] ; wherein s is the independent variable of the Laplace transform; I is a unit matrix of the same order as A ;

[0100] The transfer function between the duty cycle signal and the output voltage signal is defined as:

[0101] , and the calculation is simplified to obtain:

[0102] ;

[0103] Wherein is the complex frequency domain voltage of the output capacitor C2; is the Laplace transform of the control perturbation; the DC gain ; the right half plane zero ; the output filter pole ; the output damping factor ; the input stage pole ; the resonance pole ; R is the load resistance;

[0104] Similarly, the transfer function between the duty cycle signal and the inductor current signal is defined as:

[0105] ;

[0106] Neglecting the dynamic effect of output capacitor C2, the analytical inverse is obtained as:

[0107] ;

[0108] If the parasitic capacitance (C2p r L1 , r C2 ) and cross-coupling term are considered, the expression is:

[0109] where is the dynamic compensation term; is the dynamic damping correction term;

[0110] Similarly, the transfer function between inductor current signal and output voltage signal is defined as:

[0111] ;

[0112] From the power balance equation, considering the dynamics of the filter composed of output inductor L2 and output capacitor C2, the expression is: ;

[0113] If the parasitic capacitance (C2p r L1 , r C2 ) and cross-coupling term are considered, the expression is: .

[0114] In this embodiment, since the input voltage u AC is an alternating current, the modeling needs to be processed by half cycle and the sign function sgn ( u ) is introduced for normalization.

[0115] ​​​In some embodiments, the FPGA control module includes a UART serial port receiving module, the UART serial port receiving module receives the uphole communication signal, the output of the UART serial port receiving module is connected to a decoder; the decoder is connected to a frequency / amplitude control module and a double closed-loop control logic module; the frequency / amplitude control module is connected to the input of a sine wave generator and a modulation signal generator; the input of the sine wave generator is connected to the output of a timer / counter module, the output of the sine wave generator is connected to the modulation signal generator; the input of the timer / counter module is connected to the output of a GPS synchronization module; the double closed-loop control logic module is connected to a voltage loop PI controller and a current loop QPR controller; the input of the voltage loop PI controller is connected to an ADC interface module, the output of the voltage loop PI controller is connected to the input of the current loop QPR controller; the output of the ADC interface module is connected to a feedforward compensation module, the current loop QPR controller and an overcurrent and overvoltage protection module; the feedforward compensation module is connected to the input of the modulation signal generator; the output of the current loop QPR controller and the modulation signal generator is connected to an SPWM pulse signal generation module; the input of the SPWM pulse signal generation module is connected to a triangular carrier generator, the output of the SPWM pulse signal generation module and the overcurrent and overvoltage protection module is connected to the input of a dead zone generation module; the output of the dead zone generation module is connected to a drive circuit module.

[0116] The UART serial port receiving module is used to receive the communication instructions sent by the uphole cabinet; the modulation signal generator is used to generate the sine modulation signal required by the setting; the triangular carrier generator is used to generate the triangular carrier signal; the ADC interface module is used to manage the 4-way ADC acquisition; the overcurrent and overvoltage protection module is used for real-time protection of overvoltage and overcurrent; the current loop QPR controller is used to track and eliminate errors in real time according to the dynamic difference of magnetic field energy, and solve the influence of high-frequency disturbance on the system; the voltage loop PI controller is used to eliminate errors according to the dynamic of electric field energy, and realize the output steady-state precision; the SPWM pulse signal generation module is used to calculate and compare the sine modulation signal and the triangular carrier signal to generate the SPWM pulse signal; the dead zone generation module is used to generate the dead zone in the SPWM pulse signal to protect the circuit and prevent the commutation problem of the two groups of power switch tubes being turned on or turned off at the same time in the complementary conduction work of the full-bridge AC-AC converter module.

[0117] In this embodiment, in order to enable the full-bridge AC-AC converter module to achieve a stable target voltage output and meet the static and dynamic indicators required by the inter-well electromagnetic launch system, a voltage and current dual closed-loop control architecture is adopted. This architecture can perform hierarchical control based on the difference in dynamic characteristics between electric field energy and magnetic field energy. The current inner loop uses a current loop QPR controller to effectively solve the impact of high-frequency disturbances, while the voltage outer loop uses a PI controller to meet the steady-state accuracy requirements.

[0118] Ignoring the effects of PWM modulation, the simplified closed-loop model structure of the current loop after feedforward decoupling is obtained, as shown in the figure below. Figure 5 As shown in the block diagram, the transfer function of the current closed loop is calculated as follows:

[0119] ,

[0120] in Hi For the inner current loop feedback function; G QPR This is the QPR controller function for the current loop.

[0121] In engineering applications, the transfer function is often omitted for ease of design. Dynamic compensation item and current inner loop feedback function Hi The effect of this, when substituted into the current loop QPR controller function, yields: ;

[0122] Furthermore, the transfer function of the voltage closed loop is calculated as follows:

[0123] ;

[0124] in Hv For the voltage outer loop feedback function, G PI This is a function for a voltage loop PI controller.

[0125] In engineering applications, for ease of design, Treating the ideal state as 1, we simplify and omit parasitic capacitance and cross-coupling terms, as well as the voltage outer loop feedback function, in the transfer function. Hv The effect of this, when substituted into the voltage loop PI controller function, yields:

[0126] .

[0127] In some embodiments, an adaptive frequency control algorithm is used to couple the full-bridge AC-AC converter module, the inverter module, and the coil load.

[0128] In some embodiments, the adaptive frequency control algorithm includes the following steps:

[0129] The disturbance signal is injected, the waveform of the complete disturbance period is synchronously collected, the impedance real part is extracted, and thus the load impedance is identified in real time;

[0130] According to the result of dividing the load impedance real part identified in real time by the reference impedance value, the duty cycle is dynamically optimized through input voltage compensation, and adaptive control over the input frequency is realized in combination with the control loop and anti-interference design.

[0131] In the embodiment, the adaptive frequency control algorithm can realize efficient coupling between the Cuk-type full-bridge AC-AC converter module and the inverter module and the coil load of the interwell electromagnetic transmission system. The algorithm injects a disturbance signal, synchronously collects the waveform of the complete disturbance period, extracts the impedance real part, and thus identifies the load impedance in real time. According to the result of dividing the load impedance real part identified in real time by the reference impedance value, the duty cycle is dynamically optimized through input voltage compensation, and adaptive control over the input frequency is realized in combination with the control loop and anti-interference design.

[0132] The above description is only the preferred embodiment of the present application, and it should be understood that the present application is not limited to the form disclosed herein, and should not be considered as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein, through the above teaching or related technical or knowledge. Any modification and change made by those skilled in the art without departing from the spirit and scope of the present application shall be within the protection scope of the claims of the present application.

Claims

1. An AC-AC converter suitable for use in a cross-well electromagnetic launch system, characterized by: The application relates to a well electromagnetic transmission system, which comprises an FPGA control module, a power supply module, a driving circuit module, an inverter module, a full-bridge AC-AC converter module and a coil load. The FPGA control module is used for receiving an uphole communication signal and generating a bipolar SPWM signal sent to the driving circuit module. The power supply module is used for converting uphole direct current power supply into system working voltage. The driving circuit module is used for amplifying the bipolar SPWM signal to obtain an SPWM driving signal. The full-bridge AC-AC converter module adopts a Cuk type topology structure and is used for outputting a frequency-adjustable alternating current signal output by the inverter module after voltage regulation according to a required amplitude, and then radiating the signal to both ends of the coil load. According to the circuit characteristics of the full-bridge AC-AC converter module, a state space average model is established, and a transfer function between a duty cycle signal and an output voltage signal, a transfer function between the duty cycle signal and an inductance current signal and a transfer function between the inductance current signal and the output voltage signal are separated to obtain dynamic circuit states, and a current loop QPR controller and a voltage loop PI controller are combined to control the interwell electromagnetic transmission system. The adaptive frequency control algorithm is used for realizing coupling among the full-bridge AC-AC converter module, the inverter module and the coil load. The adaptive frequency control algorithm comprises the following steps: A disturbance signal is injected, a complete disturbance cycle waveform is synchronously collected, an impedance real part is extracted by decomposition, and thus the load impedance is identified in real time. According to a result of dividing the real-time identified load impedance real part by a reference impedance value, an input voltage compensation dynamic optimization duty cycle is realized, and then adaptive control is realized on the input frequency by combining a control loop and anti-interference design.

2. The AC-AC converter suitable for use in cross-well electromagnetic transmission systems according to claim 1, characterized in that: The full-bridge AC-AC converter module comprises power switch S1, power switch S2, power switch S3, power switch S4, input inductor L1, output inductor L2, transmission capacitor C1, output capacitor C2 and resistance Ro; the first end of the input inductor L1 is connected with input voltage u AC , the second end of the input inductor L1 is connected with the drain of the power switch S1 and the first end of the transmission capacitor C1; the second end of the transmission capacitor C1 is connected with the drain of the power switch S2 and the first end of the output inductor L2; the second end of the output inductor L2 is connected with the output capacitor C2 and the first end of the resistance Ro; the second end of the output capacitor C2 is connected with the second end of the resistance Ro, the drain of the power switch S4, the drain of the power switch S3 and the input voltage u AC ; the source of the power switch S1 is connected with the source of the power switch S3; the source of the power switch S2 is connected with the source of the power switch S4.

3. The AC-AC converter suitable for use in cross-well electromagnetic transmission systems according to claim 2, characterized in that: The state space average model is established by the following steps: Based on the state-space averaging method, the current of the input inductor L1 i L1 , the voltage of the transmission capacitor C1 u c1 , the current of the output inductor L2 i L2 , the voltage of the output capacitor C2 u c2 As a state vector, a four-bit state vector x(t) is composed; take the input voltage u AC As an input variable, the state-space average model ignoring parasitic parameters in CCM mode is established: ； wherein is the differential operator; y is the output voltage; A avg is the state matrix, based on the duty cycle in the form of a unity over the period of the AC supply; B avg For input matrix, make normalized uniform processing; ， ； wherein L 1 is the inductance value of the input inductor L1; L 2 is the inductance value of the output inductor L2; C 1 is the capacitance value of the transmission capacitor C1; C 2 is the capacitance value of the output capacitor C2; d is the duty cycle of the power switch; input voltage u AC is the alternating current, half-cycle processing is carried out when modeling and the sign function is introduced sgn ( u ) is normalized; Linearizing and separating the state-space averaged model, the small-signal model of the full-bridge AC-AC converter module is obtained: ; where the state vector ; input disturbance ; is the control disturbance; output = = ; A is the state matrix; B is the input matrix; C is the output matrix; E is the duty cycle disturbance matrix; is the state vector of the input inductor L1 current; is the state vector of the transmission capacitor C1 voltage; is the state vector of the output inductor L2 current; is the state vector of the output capacitor C2 voltage; is the AC supply voltage; ， ， ； wherein D Duty cycle of power switch S1 RC 2 Time constant of the system I L1 Small perturbation of the steady state current of input inductor L1 for duty cycle calculation I L2 a perturbation of the steady state current of the output inductor L2 for the duty cycle calculation; U C1 a perturbation of the steady state voltage of the transmission capacitor C1 for the duty cycle calculation; The small signal model is subjected to Laplace transformation and separation to obtain the transfer function between the duty cycle signal and the output voltage signal, and the small signal model Laplace transformation and arrangement are as follows: ； wherein is the Laplace transform of is a state vector; is the Laplace transform of is a control disturbance; the configuration matrix is: ; wherein s is the argument of the Laplace transform; I for A identity matrix of the same order; Transfer function between a duty cycle signal and an output voltage signal defined as: , the calculation is simplified to: ； wherein is the complex frequency domain voltage of the output capacitor C2; is the control perturbation Laplace transform; direct current gain ; right half plane zero ; output filter pole ; output damping factor ; input stage pole ; resonance pole ; R is the load resistance; Similarly, a transfer function between the duty cycle signal and the inductor current signal is defined as: is: ； The dynamic influence of an output capacitor C2 is ignored, and the following is obtained by analytical inversion: ； If parasitic capacitance is considered ( r L1 , r C2 ) and cross-coupling terms, then we get: wherein is a dynamic compensation term; is a dynamic damping correction term; By analogy, the transfer function between the inductor current signal and the output voltage signal is defined as: is: ； From the power balance equation, considering the filter dynamics of the output inductor L2 and the output capacitor C2, we have ; If parasitic capacitances (Cp) and cross-coupling terms are considered, r L1 , r C2 ) are taken into account, into , then we get .

4. The AC-AC converter suitable for use in cross-well electromagnetic transmission systems of claim 1, wherein: The FPGA control module comprises a UART serial port receiving module, the UART serial port receiving module receives an uphole communication signal, and an output end of the UART serial port receiving module is connected with a decoder; the decoder is connected with a frequency / amplitude control module and a double-closed-loop control logic module; the frequency / amplitude control module is connected with an input end of a sine wave generator and a modulation signal generator; an output end of the sine wave generator is connected with an output end of a timer / counter module, and an output end of the sine wave generator is connected with the modulation signal generator. The input end of the timer / counter module is connected with the output end of the GPS synchronization module; the double closed-loop control logic module is connected with the voltage loop PI controller and the current loop QPR controller; the input end of the voltage loop PI controller is connected with the ADC interface module, and the output end of the voltage loop PI controller is connected with the input end of the current loop QPR controller; the output end of the ADC interface module is connected with the feedforward compensation module, the current loop QPR controller and the overcurrent and overvoltage protection module; the input end of the feedforward compensation module is connected with the modulation signal generator; the output ends of the current loop QPR controller and the modulation signal generator are connected with the SPWM pulse signal generation module; the input end of the SPWM pulse signal generation module is connected with the triangular carrier generator, and the output ends of the SPWM pulse signal generation module and the overcurrent and overvoltage protection module are connected with the input end of the dead zone generation module; The output end of the dead zone generation module is connected with the drive circuit module; The UART serial port receiving module is used for receiving the communication instruction sent by the well box; The modulation signal generator is used for generating the sine modulation signal required to be set; The triangular carrier generator is used for generating the triangular carrier signal; The ADC interface module is used for managing the 4-way ADC acquisition; The overcurrent and overvoltage protection module is used for the real-time protection of overvoltage and overcurrent; the current loop QPR controller is used for tracking and eliminating errors in real time according to the dynamic difference of magnetic field energy, so as to solve the influence of high-frequency disturbance on the system; the voltage loop PI controller is used for error elimination according to the dynamic of electric field energy, so as to realize the output steady-state precision; The SPWM pulse signal generation module is used for calculating and comparing the sine modulation signal and the triangular carrier signal to generate the SPWM pulse signal; The dead zone generation module is used for generating the dead zone in the SPWM pulse signal, so as to protect the circuit and prevent the commutation problem of two groups of power switch tubes being turned on or turned off at the same time in the complementary conduction work of the full-bridge AC-AC converter module.

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