An auxiliary power supply device, system and method for downhole generator of water injection well

Abstract

This disclosure relates to the field of oil and gas extraction and downhole tool power supply technology, specifically to an auxiliary power supply device, system, and method for a downhole generator in a water injection well. The device may include: a leakage protection module, a bidirectional DC-DC converter, a supercapacitor module, and a controller. The controller is configured to: in response to determining that the voltage value is higher than a first threshold but not higher than a safety threshold, control the bidirectional DC-DC converter to store electrical energy from the DC bus in the supercapacitor module; in response to determining that the voltage value is higher than the safety threshold, transfer the electrical energy from the DC bus to the load branch and release it through the load resistor; in response to determining that the voltage value is lower than a second threshold, control the bidirectional DC-DC converter to supply the electrical energy stored in the supercapacitor module to the DC bus. This technical solution enables the DC bus voltage value to remain within a very narrow fluctuation range and reliably clamped even under fluctuations in water injection volume.

Description

Technical Field

[0001] This disclosure relates to the field of oil and gas extraction and downhole tool power supply technology, specifically to an auxiliary power supply device, system and method for a downhole generator in a water injection well. Background Technology

[0002] In oil and gas field development, water injection wells are a key means of maintaining reservoir pressure and achieving stable and increased production. With the development of intelligent oilfield technology, various downhole sensors, actuators, and data acquisition and transmission units are widely used. The stable operation of these downhole instruments directly determines the effectiveness of the water injection process and the safety of the wellbore. Because water injection wells are located in an extreme environment of high temperature, high pressure, and confined space, it is difficult to directly supply power from the surface via wiring. Therefore, utilizing the kinetic energy of the water flow to drive a turbine generator to generate electricity has become the main power source for downhole instruments and equipment.

[0003] Existing downhole power supply systems mostly use turbine generators as power conversion devices. In actual operations, the flow rate of injection wells is often subject to random fluctuations due to surface control commands and wellbore flow characteristics, resulting in uncertainty in the generator's power output. Current power regulation schemes employ a parallel power supply mode with chemical batteries and generators, utilizing the batteries for power buffering.

[0004] However, achieving high dynamic response, long life and high reliability of downhole auxiliary power supply in high temperature and variable flow environments remains one of the directions for technological development in this field. Summary of the Invention

[0005] This disclosure provides, in a first aspect, an auxiliary power supply device for a downhole generator in a water injection well, comprising a leakage protection module and a bidirectional DC-DC converter connected in parallel to a DC bus, a supercapacitor module connected to the output of the converter, and a core controller. The leakage protection module integrates a full-bridge circuit, a transformer, and a load branch including rectifier diodes and load resistors, while the bidirectional DC-DC converter includes power transistors and an energy storage inductor. The controller monitors the DC bus voltage in real time and compares it with preset first, safety, and second thresholds to switch between different operating modes: When the bus voltage is higher than the first threshold but not exceeding the safety threshold, the controller drives the bidirectional DC-DC converter to store the bus energy in the supercapacitor module via the energy storage inductor; if the bus voltage exceeds the safety threshold, the controller enables the energy leakage protection module, allowing excess energy to be transferred to the load branch through the full-bridge circuit and transformer, where it is consumed by the rectifier diodes and load resistors; when the bus voltage is lower than the second threshold, the controller controls the bidirectional DC-DC converter to operate in reverse, feeding back the energy stored in the supercapacitor module to the DC bus through the energy storage inductor to achieve energy compensation and voltage stabilization.

[0006] This disclosure, in a second aspect, provides an auxiliary power supply system for a downhole generator in a water injection well, comprising: based on the first aspect, further integrating a power generation, phase number reconstruction, and rectification and voltage regulation module. The power generation module converts the energy generated by downhole water injection into three-phase AC power. Subsequently, a three-phase to two-phase converter reconstructs the phase number of the electrical energy output from the eddy current generator, converting it into two-phase AC power. The rectification module converts the two-phase AC power into DC power, and the DC voltage regulation module performs voltage stabilization processing, thereby achieving stable electrical energy output and dynamic compensation from the original mechanical energy harvesting.

[0007] This disclosure provides a method for auxiliary power supply of a downhole generator in a water injection well. By real-time monitoring of the DC bus voltage and logically comparing it with preset first, safety, and second thresholds, the system's energy state can be dynamically adjusted. During operation, if the DC bus voltage is higher than the first threshold but not higher than the safety threshold, the system drives a bidirectional DC-DC converter, allowing the DC bus's electrical energy to be stored in a supercapacitor module via an energy storage inductor. When the voltage rises further and exceeds the safety threshold, the system controls a full-bridge circuit to transmit the bus's electrical energy to the load branch via a transformer, utilizing rectifier diodes and load resistors for energy release to ensure system safety. When the DC bus voltage is lower than the second threshold, the system controls the bidirectional DC-DC converter to operate in reverse, feeding back the stored energy in the supercapacitor module to the DC bus via the energy storage inductor, effectively compensating for the bus voltage and providing power support. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of a water injection well power generation scenario provided in this disclosure; Figure 2 The curves showing the changes in water injection volume and water injection pressure provided in this disclosure; Figure 3 A publicly available diagram showing the DC voltage fluctuation of the power generation system in the injection well. Figure 4 This is a comparison chart of the charge and discharge response times of batteries and supercapacitors provided in this disclosure; Figure 5 This is a structural diagram of an auxiliary power supply device for a downhole generator in a water injection well, provided in this disclosure. Figure 6 The output voltage waveform diagram of the auxiliary power supply device for the downhole generator in the water injection well provided in this disclosure; Figure 7 This disclosure provides an internal circuit diagram of an auxiliary power supply device for a downhole generator in a water injection well. Figure 8 This is a structural diagram of an auxiliary power supply system for a downhole generator in a water injection well, as provided in this disclosure. Detailed Implementation

[0009] The technical solutions in this disclosure will now be clearly and completely described with reference to the accompanying drawings.

[0010] Figure 1 This is a schematic diagram of a water injection well power generation scenario provided in this public disclosure, including: a surface water injection system 110, an injection water flow 120, a turbine 130, a generator 140, and an electrical load 150.

[0011] Specifically, the surface water injection system 110 applies an injection water flow 120 to the well via a wellhead device. The injection water flow 120 flows downward within the wellbore, forming a fluid medium with a certain kinetic energy.

[0012] At a predetermined layer downhole, water flow 120 flows through turbine 130. Turbine 130, driven by fluid kinetic energy, generates rotational mechanical energy, which in turn drives generator 140, coaxially connected to it, to generate electricity. Generator 140 converts mechanical energy into raw electrical energy output. Due to random fluctuations in the flow rate and pressure of the injected water flow caused by surface regulation and downhole operating conditions, the raw electrical energy output by generator 140 typically exhibits unstable voltage and frequency characteristics.

[0013] The electrical load 150 is typically composed of highly integrated microelectronic components, high-precision sensors, and electromagnetic actuators. It is used to perform tasks such as monitoring water injection parameters, regulating water injection production, and data communication. It has strict requirements on the static stability and transient response characteristics of the power supply.

[0014] Specifically, the analog signal processing circuits (such as high-precision analog-to-digital converters) in the electrical load 150 require extremely low voltage ripple to ensure data accuracy and signal-to-noise ratio during the acquisition of physical quantities such as pressure, flow rate, and temperature. Excessive fluctuations in the power supply voltage will directly lead to increased measurement errors or data failure.

[0015] However, the injection volume and injection pressure in water injection wells typically fluctuate significantly, such as... Figure 2 As shown, Figure 2 This is a graph showing the changes in water injection volume and pressure provided in this disclosure. In the early stage of water injection, the injection pressure is relatively high (e.g., 14 MPa), but due to the poor water absorption of the formation, the water injection volume is relatively low (e.g., 4 L / min). In the later stage of water injection, as the blockage in the well is reopened or the fractures are opened, the water absorption of the formation becomes stronger, and a very high injection pressure is not required. An injection flow of 120 km / h is sufficient to inject water into the well, thus the water injection volume becomes higher (e.g., 14 L / min).

[0016] The water injection rate is a key factor affecting the turbine's input power. A higher flow rate results in greater momentum of the injected water impacting the turbine blades, leading to a greater driving torque, higher turbine blade speed, and consequently, higher generator output voltage. Figure 3 As shown, Figure 3This is a publicly available diagram showing the DC voltage fluctuations in the underground power generation system of a water injection well. Due to changes in the amount of water injected, the output DC voltage experiences large fluctuations (e.g., from 45V to 92V), severely affecting the stability of the underground power supply.

[0017] Existing technologies include a power supply mode that uses a chemical battery connected in parallel with a generator, utilizing the battery for energy buffering. Please refer to [link to relevant documentation]. Figure 4 , Figure 4 It is a publicly available comparison chart of the charge and discharge response times of batteries and supercapacitors.

[0018] Figure 4 The dashed line represents the response curve of a chemical battery commonly used in existing technologies. It can be seen that, limited by the electrochemical reaction rate, the battery requires a relatively long settling time (typically over 5 ms) from receiving a charging command to reaching a steady-state voltage (normalized value 1.0), and there is also a significant voltage lag during the discharge phase. This slow dynamic response speed is difficult to match the response speed of water injection wells due to random fluctuations in water flow (e.g., ...). Figure 3 The instantaneous voltage spikes or drops (as shown) can lead to poor energy buffering and make the bus voltage prone to overshoot.

[0019] In contrast, the solid line in the figure represents the response curve of the supercapacitor used in this disclosure. Because the supercapacitor stores energy based on the double-layer physical charge separation mechanism and does not involve complex chemical reactions, its charging and discharging transient response is extremely fast, reaching the target voltage level within 1 ms. This millisecond-level response characteristic enables the device to compensate for high-frequency fluctuations on the DC bus in real time, ensuring instantaneous power throughput even under extreme conditions of drastic changes in water injection volume, thereby providing a higher quality, lower-ripple power environment for the subsequent electrical load 150.

[0020] In such Figure 2 In the event of large fluctuations in the water injection volume, this disclosure provides an auxiliary power supply device for a downhole generator in a water injection well to maintain the power supply voltage within a narrow and stable preset range. Figure 5 This is a schematic diagram of the structure of an auxiliary power supply device for a downhole generator in a water injection well, as disclosed in this publication. Figure 5 Includes: 500 auxiliary power supply device for generator in water injection well and 510 DC bus.

[0021] The DC bus 510 includes a positive DC bus 511 and a negative DC bus 512.

[0022] The auxiliary power supply device 500 for the downhole generator in the water injection well includes a leakage protection module 520, a bidirectional DC converter 530, a supercapacitor module 540, and a controller 550.

[0023] The energy leakage protection module 520 is connected between the positive and negative terminals of the DC bus and includes a full-bridge circuit, a transformer, and a load branch. The transformer is connected to the full-bridge circuit, and the load branch is connected to the secondary winding of the transformer. The full-bridge circuit can be composed of four high-frequency power switching transistors, which convert the energy of the DC bus 510 into alternating magnetic field energy through the alternating conduction of the switching transistors. The load branch includes unidirectional conductive elements (such as rectifier diodes) and load resistors. The load resistor, as an energy dissipation element, can be a high-power wire-wound resistor with high temperature resistance (e.g., operating temperature range -55℃ to +250℃, rated power 100W to 500W, temperature coefficient ≤ ±200ppm / ℃, insulation resistance ≥1000MΩ, high temperature conductivity ceramic package) to dissipate excess electrical energy as heat.

[0024] The bidirectional DC-DC converter 530 is connected between the positive and negative terminals of the DC bus 510. As the core energy conversion unit connecting the DC bus 510 and the supercapacitor module 540, its structure includes a first power transistor, a second power transistor, and an energy storage inductor. The bidirectional DC-DC converter 530 can dynamically switch between buck and boost modes according to the voltage fluctuations of the DC bus 510, thereby realizing bidirectional power flow and refined management.

[0025] When the bidirectional DC-DC converter 530 operates in buck mode, it reduces the input voltage to the target voltage value and outputs it by controlling the on and off states of its internal switching devices. When the bidirectional DC-DC converter 530 operates in boost mode, it boosts the power on the low-voltage side to the required voltage level on the high-voltage side. The two operating modes can be switched according to the voltage relationship between the two sides and the direction of power delivery, maintaining a stable output voltage during the switching process. Throughout operation, the converter maintains its preset structural characteristics of either electrical isolation or non-isolation and sustains energy conversion efficiency over a wide voltage range.

[0026] The supercapacitor module 540 includes at least one supercapacitor connected to the output terminal of the bidirectional DC-DC converter. The supercapacitor module 540 can be composed of multiple supercapacitor cells connected in series. A supercapacitor is an energy storage element intermediate between a traditional electrostatic capacitor and an electrochemical battery. Its core energy storage mechanism is based on physical charge separation through a double layer formed at the interface between a high-specific-surface-area porous carbon electrode and the electrolyte, without involving chemical reactions. Compared to batteries, supercapacitors offer higher power density and cycle life, maintain excellent stability even in high-temperature environments downhole (up to 150°C), and do not require frequent replacement, making them suitable for special scenarios requiring constant maintenance and replacement in downhole environments.

[0027] For example, a supercapacitor can be selected with a rated voltage of 2.85V and a capacity of 400F. Twelve cells can be connected in series to form a module with a withstand voltage of about 28V and a capacity of 33F. This single supercapacitor can operate in a high-temperature environment of 150℃ and has a diameter of only 35mm, which can adapt to the high temperature and confined space environment downhole.

[0028] The controller in this disclosure may include one or more of the following components: a processor and a memory.

[0029] Optionally, the processor connects various parts of the controller using various interfaces and lines, and performs various functions and processes data by running or executing instructions, programs, code sets, or instruction sets stored in memory, and by calling data stored in memory. Optionally, the processor can be implemented using at least one hardware form of Digital Signal Processing (DSP), Field-Programmable Gate Array (FPGA), or Programmable Logic Array (PLA). The processor can integrate one or a combination of several of the following: Central Processing Unit (CPU), Neural-network Processing Unit (NPU), and baseband chip. The CPU primarily handles the operating system and applications; the NPU is used to implement Artificial Intelligence (AI) functions; and the baseband chip is used for wireless communication. It is understood that the baseband chip can also be implemented as a separate chip without being integrated into the processor.

[0030] The memory may include random access memory (RAM) or read-only memory (ROM). Optionally, the memory may include non-transitory computer-readable storage medium. The memory may be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function, instructions for implementing the various method embodiments described above, etc.; the data storage area may store data created according to the use of the controller, etc.

[0031] In addition, those skilled in the art will understand that the structure of the controller shown in the above figures does not constitute a limitation on the controller. The controller may include more or fewer components than shown, or combine certain components, or have different component arrangements. For example, the controller may also include radio frequency circuits, input units, sensors (such as accelerometers, angular velocity sensors, etc.), power supplies, Bluetooth modules, etc., which will not be described in detail here.

[0032] The controller 550 monitors the voltage value of the DC bus 510 in real time and compares it with preset first threshold, safety threshold, and second threshold to achieve hierarchical logic control of the bidirectional DC converter 530 and the leakage protection module. The safety threshold is a pre-stored upper voltage limit value within the controller 550, representing the highest voltage allowed for the DC bus 510. The following relationship exists: second threshold < first threshold < safety threshold. The specific control strategy of the controller 550 is as follows: (1) Energy storage mode (first threshold < voltage value ≤ safety threshold) When the voltage of DC bus 510 is higher than the first threshold but not higher than the safety threshold, controller 550 triggers this mode. In this state, controller 550 drives bidirectional DC converter 530 to enter buck mode, converting the electrical energy of DC bus 510 through energy storage inductor and storing it in supercapacitor module 540.

[0033] (2) Energy leakage protection mode (voltage value > safety threshold) When the voltage of DC bus 510 exceeds the safety threshold, controller 550 enables energy leakage protection module 520. By controlling the operation of the full-bridge circuit, the electrical energy of DC bus 510 is coupled to the load branch through the transformer, and finally dissipated by the load resistor through the rectifier diode, so as to ensure that the system voltage is within the safe range.

[0034] (3) Energy feedback mode (voltage value < second threshold) When the voltage of DC bus 510 falls below the second threshold, controller 550 triggers this mode. In this state, controller 550 drives bidirectional DC-DC converter 530 into boost mode. At this time, controller 550 regulates bidirectional DC-DC converter 530 so that the electrical energy stored in supercapacitor module 540 is fed back to DC bus 510 via energy storage inductor, thereby achieving voltage feedback to DC bus 510.

[0035] When the second threshold is less than or equal to the voltage value and less than or equal to the first threshold, the controller 550 does not perform any of the above control actions. Within this range, the voltage of the DC bus 510 is within the system's preset normal operating range, requiring neither energy storage through the supercapacitor module 540 nor energy dissipation through the load branch, and also requiring no energy feedback from the supercapacitor module 540.

[0036] Figure 5 The technical solution shown achieves "peak shaving and valley filling" of the DC bus 510 voltage, ensuring that the voltage value of the DC bus 510 remains within a very narrow range even with fluctuations in water flow. Furthermore, under extreme operating conditions (such as sudden load shedding or a surge in water flow), the surge voltage that could potentially break down the circuit is forcibly dissipated across the load resistor, achieving reliable voltage clamping.

[0037] Figure 5 The technical effects produced by the technical solution shown can be derived from Figure 6 Visual representation. For example... Figure 6 As shown, Figure 6 This is a waveform diagram of the output voltage of the auxiliary power supply device for the downhole generator in the water injection well provided in this disclosure. When, for example, the voltage of the DC bus 510 fluctuates around 24V, the output voltage waveform is stabilized within a narrow range (as shown in 600A) and the output voltage ripple is <2% (as shown in 600B) by the adjustment of the auxiliary power supply device for the downhole generator in the water injection well provided in this disclosure.

[0038] for Figure 5 The technical solution, in some possible implementations, such as Figure 7 As shown, Figure 7 This disclosure provides an internal circuit diagram of an auxiliary power supply device for a downhole generator in a water injection well. The full-bridge circuit includes a first bridge arm and a second bridge arm; the primary winding of the transformer is connected between the midpoint of the first bridge arm and the negative terminal 512 of the DC bus, and the secondary winding of the transformer is connected between the midpoint of the second bridge arm and the negative terminal 512 of the DC bus; the load branch is connected between the midpoint of the second bridge arm and the negative terminal 512 of the DC bus. Specifically, Figure 7 Includes: The DC bus 510 includes a positive DC bus 511 and a negative DC bus 512.

[0039] The energy leakage protection module 520 includes power switches 711, 712, 713, and 714. Power switches 711 and 713 form the first bridge arm, with their connection point at the midpoint 715; power switches 712 and 714 form the second bridge arm, with their connection point at the midpoint 716. The transformer 720 includes a primary winding 721 and a secondary winding 722. The load branch includes unidirectional conductive elements 717 and 718 and a load resistor 723. The primary winding 721 of the transformer 720 is connected between the midpoint 715 and the negative terminal of the DC bus 512, and the secondary winding 722 is connected between the midpoint 716 and the negative terminal of the DC bus 512.

[0040] Understandably, the energy leakage protection module may also include a capacitor 724 connected in parallel to the DC bus 510.

[0041] Capacitor 724 is used to limit voltage spikes caused by leakage inductance and provides a freewheeling path for the leakage inductance current of transformer 720 when power switches 711, 712, 713 and 714 are all turned off.

[0042] It is understandable that the load branch may also include a capacitor 719 connected in parallel with the load resistor 723.

[0043] Capacitor 719 filters out high-frequency ripple during the charging and discharging process, making the voltage flowing through the load resistor 723 more stable. Furthermore, since the load resistor 723 is typically a high-power resistor, instantaneous high-voltage surges can cause drastic current fluctuations. Capacitor 719 acts as an energy buffer, making the energy dissipation process more linear and stable, preventing unnecessary stress on the resistor due to instantaneous current overload. Finally, the presence of capacitor 719 ensures that the resistor continues to dissipate energy even during the minute gaps (dead time, etc.) when the switching transistor is turned off.

[0044] The bidirectional DC-DC converter 530 includes a power switch 731, a power switch 732, a unidirectional conductive element 734, a unidirectional conductive element 735, and an energy storage inductor 736.

[0045] The supercapacitor module 540 includes at least one supercapacitor 743, an equivalent series resistance 741 of the supercapacitor 743, and, understandably, also includes a capacitor 742.

[0046] Increasing the capacitance of the supercapacitor 743 or reducing the equivalent series resistance 741 can effectively improve the system's ability to suppress large low-frequency fluctuations. Furthermore, the equivalent series resistance 741 also plays a role in limiting inrush current and suppressing high-frequency oscillations, making the energy exchange process smoother and improving the reliability and safety of system operation.

[0047] The introduction of capacitor 742 prevents excessive switching stress from directly driving the supercapacitor during energy discharge and absorbs high-frequency voltage ripple. The equivalent series resistance 741 of supercapacitor 743 is typically very small, but its frequency characteristics are not as good as those of the smaller capacitor 742. Capacitor 742 effectively absorbs high-frequency noise generated by the high-frequency switching action of the power transistor.

[0048] The controller 550 can control the energy leakage protection module 520 according to the following strategy: First, power switches 711 and 714 are turned on, while power switches 712 and 713 are turned off. At this time, the current flow is as follows: DC bus positive terminal 511 → power switch 711 → midpoint 715 → primary winding 721 (induction) → secondary winding 722 → midpoint 716 → power switch 714 → DC bus negative terminal 512.

[0049] Subsequently, power switches 712 and 713 are turned on, while power switches 711 and 714 are turned off. At this time, the current flow is as follows: DC bus positive terminal 511 → power switch 712 → midpoint 716 → secondary winding 722 (induction) primary winding 721 → midpoint 715 → power switch 713 → DC bus negative terminal 512.

[0050] The alternating switching of the two modes causes the primary winding 721 of the transformer 720 to generate an alternating square wave voltage, which transfers the energy on the DC bus 510 to the secondary winding 722 in a magnetic coupling manner, and then converts it into heat energy consumption on the load resistor 723.

[0051] The controller 550 can control the bidirectional DC-DC converter 530 according to the following strategy: (1) During the step-down charging process, the bidirectional DC converter 530 operates in BUCK mode. When the generator 140 outputs excess energy, causing the voltage of the DC bus 510 to rise, the controller 550 drives the bidirectional DC converter 530 to enter step-down mode, storing the energy from the bus into the supercapacitor module 540.

[0052] The controller 550 drives the power switch 731 to conduct. At this time, current flows from the DC bus 510 through the power switch 731 and the energy storage inductor 736 to the supercapacitor 743 to charge the supercapacitor 743. Meanwhile, the energy storage inductor 736 stores magnetic field energy.

[0053] When the power switch 731 is turned off, since the inductor current cannot change abruptly, the controller 550 turns on the power switch 732 after the dead time. The energy storage inductor 736 releases energy, and the current continues to charge the supercapacitor 743 through the loop formed by 732.

[0054] (2) During the boost discharge process, the bidirectional DC converter 530 operates in BOOST mode. When the output energy of the generator 140 decreases or the downhole load suddenly increases, causing the voltage of the DC bus 510 to drop, the controller 550 drives the bidirectional DC converter 530 to enter boost mode, feeding the energy of the supercapacitor 743 back to the DC bus 510.

[0055] The controller 550 turns off the power switch 731 and turns on the power switch 732. At this time, the current of the supercapacitor 743 flows through the energy storage inductor 736 and the power switch 732 back to the negative terminal of the DC bus 512, and the energy storage inductor 736 begins to store energy.

[0056] When the power switch 732 is turned off, the energy storage inductor 736 generates an induced electromotive force, the voltage of which is superimposed on the voltage of the supercapacitor 743. After the dead time, the controller 550 turns on the power switch 731, and the superimposed high-voltage current flows back to the DC bus 510 through the power switch 731.

[0057] In the above technical solution, the energy storage inductor 736 plays the role of energy storage and filtering in boost mode, smoothing the charging current; and plays the role of energy pumping in buck mode.

[0058] for Figure 5 In some possible implementations of the technical solution, the controller 550 acquires the real-time capacity data of the supercapacitor (e.g., through ADC sampling) and uses this as the basis for determining the logic enable of the bidirectional DC-DC converter 530. When the bidirectional DC-DC converter 530 is in buck mode and the controller 550 detects that the real-time capacity of the supercapacitor 743 exceeds a preset third threshold, the controller will automatically trigger protection logic to disable the bidirectional DC-DC converter 530 and stop the charging process. Correspondingly, when the bidirectional DC-DC converter 530 switches to boost mode, the controller 550 continuously compares the real-time capacity with a preset fourth threshold; if the real-time capacity drops below the fourth threshold, the controller will immediately stop the enable signal of the bidirectional DC-DC converter 530 and prevent the supercapacitor 743 from continuing to discharge by interrupting its boost output.

[0059] The controller 550 limits the operating capacity range of the supercapacitor 743 to between the fourth and third thresholds. In buck mode, the converter is only allowed to charge if the real-time capacity does not exceed the third threshold; in boost mode, the converter is only allowed to discharge if the real-time capacity does not fall below the fourth threshold. Once the corresponding threshold boundary is reached, the controller immediately disables the converter, thereby achieving overcharge and over-discharge protection for the supercapacitor.

[0060] for Figure 5In some possible implementations of the technical solution, the controller 550 is configured to output two complementary pulse width modulation (PWM) signals with dead time to drive the full-bridge circuit. A dead time exists between these two PWM signals to prevent the upper and lower switches of the same bridge arm of the full-bridge circuit from conducting simultaneously. The controller monitors the DC bus voltage in real time and compares this voltage value with a preset safety threshold.

[0061] When the controller 550 detects that the voltage of the DC bus 510 is higher than the safety threshold, the controller 550 initiates voltage clamping control. Specifically, the controller 550 controls the on-time of the switching transistors in the full-bridge circuit by adjusting the duty cycle of the two pulse width modulation signals output to the full-bridge circuit. The change in duty cycle directly changes the average voltage output from the full-bridge circuit to the load branch, thereby changing the power of the energy-consuming components in the load branch, i.e., changing the energy dissipation rate of the load resistor 723. The controller 550 dynamically adjusts the duty cycle value according to the degree to which the voltage of the DC bus 510 exceeds the safety threshold: when the voltage of the DC bus 510 is high, the controller 550 increases the duty cycle, causing the energy-consuming components to operate at higher power, thereby accelerating energy dissipation and causing the voltage of the DC bus 510 to drop rapidly; when the voltage of the DC bus 510 is close to the safety threshold, the controller decreases the duty cycle, causing the energy-consuming components to operate at lower power and dissipate energy at a slower rate.

[0062] Through the above adjustment process, the controller 550 maintains and limits the voltage of the DC bus 510 within a preset range, ensuring that the voltage of the DC bus 510 does not continuously exceed the safety threshold, nor does it drop to an excessively low level due to over-discharge, thereby achieving the voltage clamping function of the DC bus 510. Throughout the clamping process, the controller 550 continuously compares the bus voltage with the safety threshold and continuously adjusts the duty cycle until the voltage of the DC bus 510 stabilizes within the preset range.

[0063] for Figure 5 In some possible implementations of the technical solution, the controller 550 drives and controls the full-bridge circuit by outputting two complementary pulse-width modulation (PWM) signals configured with dead times. During operation, the controller 550 calculates the difference between the voltage sample value of the DC bus 510 and the preset safety threshold in real time, and dynamically adjusts the duty cycle of the PWM signal based on the magnitude of this difference. By adjusting the duty cycle to change the equivalent conduction time of the full-bridge circuit, the controller can precisely control the current flowing through the load branch, thereby effectively regulating the energy dissipation rate of the load branch and ensuring that the DC bus 510 can be discharged in a timely and controlled manner under overvoltage conditions.

[0064] Specifically, the controller 550 outputs two complementary pulse-width modulation (PWM) signals with dead time to drive the full-bridge circuit. These two PWM signals are 180 degrees out of phase; when one signal is high, the other is low, and a dead time is inserted between them to prevent simultaneous conduction of the upper and lower switches on the same bridge arm, which could cause a shoot-through short circuit. The controller 550 uses these two signals to control the on / off state of two diagonal switches in the full-bridge circuit, thereby generating an alternating voltage waveform at the output of the full-bridge circuit. This voltage is filtered and then applied to the load branch.

[0065] The controller 550 acquires the voltage value of the DC bus 510 in real time and compares it with a preset safety threshold. When the DC bus voltage exceeds the safety threshold, energy discharge needs to be initiated; when the DC bus voltage is below the safety threshold, discharge stops. The controller 550 calculates the difference between the DC bus 510 voltage value and the safety threshold. This difference reflects the degree to which the current voltage exceeds the safe range: the larger the difference, the more severe the overvoltage, requiring a faster rate of energy dissipation; the smaller the difference, the closer the overvoltage is to the critical point, requiring only a slower rate of energy dissipation.

[0066] Based on the magnitude of this difference, the controller adjusts the duty cycle of the pulse width modulation signal. The duty cycle refers to the proportion of the high-level time in the pulse width modulation signal to the entire cycle. The larger the duty cycle, the longer the conduction time of the switching transistors in the full-bridge circuit, the higher the average voltage obtained in the load branch, and the larger the current flowing through the energy-consuming components, thus the faster the energy dissipation rate; conversely, the smaller the duty cycle, the shorter the conduction time, and the slower the energy dissipation rate. The controller 550 can use a linear or piecewise proportional relationship to map the difference to the duty cycle value: when the difference is large, a larger duty cycle is output, causing the load resistor 723 to work at higher power and quickly pull down the voltage value of the DC bus 510; when the difference is small, a smaller duty cycle is output, causing the load resistor 723 to work at lower power and maintaining the voltage value of the DC bus 510 near the safety threshold; when the voltage value of the DC bus 510 is lower than the safety threshold, the difference is zero or negative, the controller adjusts the duty cycle to zero, at which time the pulse width modulation signal is continuously low, the full bridge circuit stops working, and the load branch no longer dissipates energy.

[0067] The controller 550 dynamically adjusts the duty cycle of the pulse width modulation signal according to the degree to which the voltage of the DC bus 510 exceeds the safety threshold, thereby continuously adjusting the power dissipation rate of the load branch and realizing closed-loop regulation and overvoltage protection of the DC bus 510.

[0068] for Figure 5In some possible implementations of the technical solution, the controller 550 outputs two complementary pulse width modulation signals with dead time to drive the full-bridge circuit. It should be noted that the bidirectional DC-DC converter 530 includes an upper transistor and a lower transistor, referring to the two switching transistors on the same bridge arm of the full-bridge circuit. The upper transistor is connected to the positive terminal of the high-voltage side, and the lower transistor is connected to the negative terminal of the high-voltage side or ground.

[0069] The controller 550 applies different driving strategies to the upper and lower transistors respectively according to the current operating mode of the bidirectional DC-DC converter 530.

[0070] When the bidirectional DC-DC converter 530 operates in buck mode, energy is transferred from the high-voltage side to the low-voltage side, and the controller 550 drives the upper MOSFET to perform chopping operation. Specifically, the controller outputs a pulse-width modulation signal to the control terminal of the upper MOSFET, causing the upper MOSFET to periodically turn on and off with a certain duty cycle. During the upper MOSFET's on period, the input voltage is applied to the energy storage inductor 736 through the upper MOSFET, the inductor current rises linearly, and energy is transferred to the load and stored in the capacitor; during the upper MOSFET's off period, the input voltage is cut off. At the same time, the controller 550 drives the lower MOSFET to conduct complementary freewheeling. The drive signal of the lower MOSFET is complementary to that of the upper MOSFET, that is, the lower MOSFET is on when the upper MOSFET is off, but a dead time is inserted between them to avoid shoot-through. During the lower MOSFET's on period, the energy storage inductor 736 forms a closed loop through the lower MOSFET, and the energy stored in the inductor continues to be released to the load through the lower MOSFET, and the inductor current decreases linearly through the lower MOSFET's freewheeling. Through the cooperation of the upper MOSFET's chopping and the lower MOSFET's complementary freewheeling, voltage bucking is achieved.

[0071] When the bidirectional DC-DC converter operates in boost mode, energy flows back from the low-voltage side to the high-voltage side, and the controller 550 drives the lower transistor to perform switching operations. Specifically, the controller outputs a pulse-width modulation signal to the control terminal of the lower transistor, causing it to periodically turn on and off with a certain duty cycle. During the lower transistor's conduction period, the low-voltage side power supply forms a loop through the energy storage inductor and the lower transistor, and the inductor current rises linearly, storing energy. During the lower transistor's turn-off period, the inductor current cannot change abruptly; instead, it outputs to the high-voltage side through the upper transistor. The energy released by the inductor is superimposed on the input voltage, resulting in a boosted voltage on the high-voltage side. Simultaneously, the controller 550 drives the upper transistor to perform complementary rectification. The drive signals for the upper and lower transistors are complementary, meaning the upper transistor turns on when the lower transistor turns off, with a dead time inserted between them. During the upper transistor's conduction period, the inductor current flows through the upper transistor to the high-voltage side load and capacitor, achieving rectification and energy output. Through the coordination of the lower transistor's switching and the upper transistor's complementary rectification, voltage boosting is achieved.

[0072] The controller 550 assigns the upper transistor as a chopper and the lower transistor as a freewheeling transistor, or the lower transistor as a switch and the upper transistor as a rectifier, depending on whether the voltage is buck or boost, so that the same full-bridge circuit can work normally in both operating modes.

[0073] Based on the description of specific devices applicable to downhole water injection wells, this disclosure further provides a downhole generator auxiliary power supply system 800 for water injection wells including such devices. Figure 8 This disclosure provides a structural diagram of an auxiliary power supply system for a downhole generator in a water injection well, comprising: a downhole generator auxiliary power supply system 800, an injection water flow 120, a turbine 130, a generator 140, and an electrical load 160. The downhole generator auxiliary power supply system 800 further includes: a three-phase to two-phase converter 810, a rectifier module 820, an auxiliary power supply device for the downhole generator 500, and a DC voltage regulator module 830.

[0074] The three-phase to two-phase converter 810 does not reconstruct the phase relationship of the three-phase AC power. Instead, it arbitrarily selects two phases (such as phases A and B, or phases B and C, or phases C and A) from the three-phase AC power output from the generator and outputs them to the subsequent rectifier module 820. The phase difference between the selected two phases maintains the original phase relationship of the generator output. This phase selection method requires no passive components, introduces no additional losses, and does not change the original phase relationship. It is suitable for low-power downhole scenarios where circuit simplification and minimization are required.

[0075] After the three-phase to two-phase conversion, the subsequent rectifier module 820 can use a simpler single-phase full-bridge rectifier circuit (4 diodes). This results in a simpler circuit structure, occupies less space, and is suitable for the confined spaces of underground wells. Furthermore, the output power of generators in water injection wells is typically low, often ranging from tens to hundreds of watts. In low-power scenarios, the high current capacity of three-phase rectification is not required; two-phase rectification is sufficient to meet power supply needs without wasting the capacity of power devices.

[0076] The input terminal of rectifier module 820 is connected to the output terminal of three-phase to two-phase module 810 to receive two-phase AC power. Rectifier module 820 performs full-bridge rectification on this two-phase AC power, converting it into pulsating DC power. Since two-phase rectification only requires a full-bridge rectifier circuit consisting of four diodes, compared to the six diodes required for three-phase rectification, the number of power devices is reduced, lowering the probability of failure in the high-temperature, high-pressure environment underground, while also reducing the circuit's footprint.

[0077] The output of the rectifier module 820 is connected to the input of the auxiliary power supply device 500 for the downhole generator in the water injection well. The auxiliary power supply device 500 receives the DC power output from the rectifier module 820 and performs voltage regulation and overvoltage protection based on the system's operating status. Specifically, the device includes a leakage protection module 520, a bidirectional DC-DC converter 530, a supercapacitor module 540, and a controller 550. When the output voltage of the rectifier module 820 is too high, the auxiliary power supply device 500 dissipates excess energy through the load branch and performs energy buffering, maintaining the DC bus 510 within a safe range, thus achieving peak shaving and valley filling of the DC bus voltage.

[0078] The DC voltage regulator module 830 is connected to the output terminal of the auxiliary power supply device 500 for the downhole generator in the water injection well. It is used to stabilize the wide-range fluctuating DC voltage output by the device to the target voltage required by the load. Because the output power of the downhole generator in the water injection well fluctuates significantly with changes in water flow, and the DC voltage after the aforementioned stages of conversion has a wide input range, this DC voltage regulator module actually employs a voltage regulator circuit with wide input adaptability. Specifically, the DC voltage regulator module 830 can output a stable target voltage (e.g., 12V or 24V) within a wide input voltage range (e.g., from 10V to 60V). This module can utilize a wide-input-range buck, boost, or buck-boost DC-DC converter topology, such as a single-ended primary-inductor converter (SEPIC) circuit, to adapt to the wide fluctuations in downhole power.

[0079] The three-phase to two-phase module 810, the rectifier module 820, and the auxiliary power supply device 500 for the downhole generator in the water injection well are connected in sequence to form a complete auxiliary power supply link from the downhole generator to the downhole load.

[0080] Based on the same inventive concept, the following describes the auxiliary power supply method for the downhole generator in the water injection well, which achieves hierarchical control by collecting the DC bus voltage and comparing it with multiple thresholds.

[0081] First, the voltage value of the DC bus is acquired. The voltage sampling terminal of the controller is connected between the positive and negative terminals of the DC bus, and the instantaneous voltage value of the DC bus is acquired in real time at a preset sampling period. This analog quantity is then converted into a digital quantity for internal comparison and judgment.

[0082] Then, the acquired voltage value is compared with the first threshold, the safety threshold, and the second threshold. The controller has three pre-stored threshold parameters: the first threshold, the safety threshold, and the second threshold. The first threshold is lower than the safety threshold and is used to determine whether to initiate supercapacitor charging; the safety threshold is the highest permissible voltage value of the DC bus, determined by the system's withstand voltage rating and component selection; the second threshold is lower than the first threshold and is used to determine whether to initiate supercapacitor discharging. The controller compares the real-time acquired DC bus voltage value with each of these three thresholds to determine the current voltage range.

[0083] Next, different control actions will be executed based on the comparison results: When the controller determines that the DC bus voltage is higher than the first threshold but not higher than the safety threshold, the controller controls the bidirectional DC-DC converter to operate in buck mode, allowing the electrical energy from the DC bus to be stored in the supercapacitor module via the energy storage inductor. In this state, the DC bus voltage is in the normal slightly high range and has not yet reached the overvoltage threshold. Storing excess energy in the supercapacitor achieves both energy recovery and reduces the discharge pressure on subsequent load branches. Specifically, the controller outputs a pulse-width modulation signal to drive the upper transistor in the bidirectional DC-DC converter to chop, causing current to flow from the DC bus through the upper transistor and the energy storage inductor to charge the supercapacitor.

[0084] When the controller determines that the DC bus voltage is higher than the safety threshold, it activates the full-bridge circuit to transfer energy from the DC bus to the load branch via the transformer, where it is released through the rectifier diodes and load resistors. In this state, the DC bus voltage has exceeded the system's safety limit, indicating that the supercapacitor lacks sufficient charging capacity or its charging rate is insufficient to suppress the voltage rise. The controller immediately activates the full-bridge circuit, transferring excess energy to the load branch via the transformer's electromagnetic coupling. The rectifier diodes in the load branch rectify the AC voltage output from the transformer, and the load resistor dissipates the energy as heat, thus rapidly lowering the DC bus voltage.

[0085] When the controller determines that the DC bus voltage is below the second threshold, it controls the bidirectional DC-DC converter to operate in boost mode, allowing the energy stored in the supercapacitor module to be supplied to the DC bus via the energy storage inductor. In this state, if the DC bus voltage is too low, it indicates that the generator output power is insufficient to maintain the normal operating voltage of the bus. The controller then switches the bidirectional DC-DC converter to boost mode, driving the lower transistor to switch, allowing the pre-stored energy in the supercapacitor to be boosted via the energy storage inductor and fed back to the DC bus. This compensates for and supports the bus voltage, preventing downstream loads from shutting down abnormally due to undervoltage.

[0086] Through the above steps, the controller executes three different control strategies—energy storage charging, energy dissipation, and energy feedback—based on the different ranges of the DC bus voltage, dynamically maintaining the DC bus voltage between the second threshold and the safety threshold. This method achieves hierarchical management of the DC bus voltage, prioritizing energy buffering through supercapacitors and only activating energy-consuming circuits when the supercapacitors are insufficient to suppress overvoltage, thus balancing energy utilization efficiency and system safety.

Claims

1. An auxiliary power supply device for downhole generator of water injection well, characterized in that, include: A leakage protection module is connected in parallel with the DC bus. The leakage protection module includes a full-bridge circuit, a transformer, and a load branch. The full-bridge circuit is connected between the DC bus and the transformer. The load branch is connected to the output side of the transformer and includes a rectifier diode and a load resistor. A bidirectional DC-DC converter is connected in parallel with the DC bus, and the bidirectional DC-DC converter includes a first power transistor, a second power transistor, and an energy storage inductor. A supercapacitor module, comprising at least one supercapacitor, wherein the supercapacitor module is connected to the output terminal of the bidirectional DC-DC converter; and The controller, electrically connected to the energy leakage protection module and the bidirectional DC-DC converter, is configured to: Based on the comparison results between the voltage value of the DC bus and the first threshold, the safety threshold and the second threshold, the bidirectional DC converter and the energy leakage protection module are selectively controlled. In response to determining that the voltage value is higher than the first threshold and not higher than the safety threshold, the bidirectional DC-DC converter is controlled to store electrical energy from the DC bus into the supercapacitor module via the energy storage inductor. In response to determining that the voltage value is higher than the safety threshold, the full-bridge circuit is controlled to transfer electrical energy from the DC bus to the load branch via the transformer and release it through the load resistor; and In response to determining that the voltage value is lower than the second threshold, the bidirectional DC-DC converter is controlled to supply the electrical energy stored in the supercapacitor module to the DC bus via the energy storage inductor.

2. The apparatus according to claim 1, characterized in that, The full-bridge circuit includes a first bridge arm and a second bridge arm. The primary winding of the transformer is connected between the midpoint of the first bridge arm and the negative terminal of the DC bus, and the secondary winding of the transformer is connected between the midpoint of the second bridge arm and the negative terminal of the DC bus. The load branch is connected between the midpoint of the second bridge arm and the negative terminal of the DC bus.

3. The apparatus of claim 1, wherein, The supercapacitor module also includes a capacitor connected in parallel with the supercapacitor.

4. The apparatus of claim 1, wherein, The load branch also includes a capacitor connected in parallel with the load resistor.

5. The apparatus according to claim 1, characterized in that, The controller is configured to: Monitor the real-time capacity of the supercapacitor; In response to the bidirectional DC-DC converter operating in buck mode and the real-time capacitance of the supercapacitor being greater than a third threshold, the controller disables the bidirectional DC-DC converter. In response to the bidirectional DC-DC converter operating in boost mode and the real-time capacity of the supercapacitor being less than a fourth threshold, the controller disables the bidirectional DC-DC converter.

6. The apparatus according to claim 1, characterized in that, The controller is configured to output two complementary pulse-width modulated signals with dead time to drive the full-bridge circuit; and, In response to the DC bus voltage being higher than the safety threshold, the duty cycle of the pulse width modulation signal is adjusted to clamp the DC bus voltage within a preset range.

7. The apparatus according to claim 1, characterized in that, The controller outputs two complementary pulse width modulation signals with dead time to drive the full-bridge circuit. The controller adjusts the duty cycle of the pulse width modulation signal based on the difference between the voltage of the DC bus and the safety threshold, so as to control the power dissipation rate of the load branch.

8. The apparatus according to claim 1, characterized in that, The controller is configured to output two complementary pulse-width modulated signals with dead time to drive the full-bridge circuit; and, The bidirectional DC-DC converter includes an upper transistor and a lower transistor; In response to the bidirectional DC-DC converter operating in buck mode, the controller drives the upper transistor to perform chopping and drives the lower transistor to perform complementary freewheeling. In response to the bidirectional DC-DC converter operating in boost mode, the controller drives the lower transistor to switch and drives the upper transistor to conduct complementary rectification.

9. An auxiliary power supply system for a downhole generator in a water injection well, characterized in that, include: The three-phase to two-phase module reconfigures the three-phase AC power output from the generator into two-phase AC power. The rectifier module converts the two-phase AC power into DC power. The device as described in any one of claims 1 to 8 has its input terminal connected to the rectifier module to regulate the voltage of the DC power. A DC voltage regulator module is connected to the output terminal of the device and outputs the target voltage.

10. A method for auxiliary power supply from a downhole generator in a water injection well, characterized in that, include: Obtain the voltage value of the DC bus; The voltage value is compared with the first threshold, the safety threshold, and the second threshold, respectively. In response to determining that the voltage value is higher than the first threshold and not higher than the safety threshold, the bidirectional DC-DC converter is controlled to store electrical energy from the DC bus into the supercapacitor module via the energy storage inductor. In response to determining that the voltage value is higher than the safety threshold, the full-bridge circuit is controlled to transfer electrical energy from the DC bus to the load branch via the transformer, and release it through the load resistor in the load branch; and In response to determining that the voltage value is lower than the second threshold, the bidirectional DC-DC converter is controlled to supply the electrical energy stored in the supercapacitor module to the DC bus via the energy storage inductor.

Images