Variable thrust cold air propulsion system, control method thereof and valve element position calibration method

Abstract

The invention relates to the technical field of spacecraft propulsion systems, in particular to a variable thrust cold air propulsion system and a control method and a valve element position calibration method thereof. The system comprises a gas cylinder, a high-pressure pressure sensor, a micro pressure module, a low-pressure pressure sensor, a buffer gas capacitor, a micro-Newton-level cold air variable thrust module and a variable thrust control circuit box. And the micro-Newton-level cold air variable thrust module is integrated with a piezoelectric driving valve, a displacement sensor and a spray pipe. According to the method, instruction thrust and pressure signals are received, and a thrust-valve element opening degree conversion model is used for calculating a valve element opening degree target value; according to the actual displacement, measured by the displacement sensor, of the valve element and the pre-calibrated valve element position parameters, the current valve element opening degree is calculated; closed-loop control is carried out with the target value as the set value and the current opening degree as the feedback value, the piezoelectric driving valve is driven to generate accurate thrust, and the method has the advantages of being short in response time, high in adjustment resolution, wide in output range and simpler in structure and control logic.

Description

Technical Field

[0001] This invention relates to the field of spacecraft propulsion system technology, and in particular to a variable thrust cold gas propulsion system and its control method and valve core position calibration method. Background Technology

[0002] Ultra-high precision space science exploration spacecraft (such as space gravitational wave detectors and Earth gravity field measurement spacecraft) require micro-Newton level thrusters to achieve ultra-high precision drag-free or pointing control. Among them, micro-Newton level cold gas propulsion systems, which have the characteristics of wide range, high precision, and low noise, are an ideal solution.

[0003] Variable thrust control is a key technology for such systems. Currently, most variable thrust control systems employ flow feedback regulation. However, flow sensors suffer from problems such as acquisition time delay and zero-point drift during long-term operation, limiting further improvements in system response speed and accuracy. Although existing technologies employ complex schemes that introduce an inner displacement loop to assist the outer flow loop, these schemes have complex system structures, cumbersome control logic, and fail to fundamentally avoid dependence on flow feedback or the delays it introduces.

[0004] Therefore, there is an urgent need in this field for a variable thrust control scheme with a wide output range, faster response, higher adjustment resolution, and simpler structure and control. Summary of the Invention

[0005] One objective of this invention is to overcome the shortcomings of the prior art and provide a variable thrust cold gas propulsion system and its control method. The system utilizes displacement and pressure sensors as sensors and employs valve core opening for feedback adjustment, which has the advantages of fast response time, high adjustment resolution, wide output range, and simpler structure and control logic.

[0006] Another objective of this invention is to provide a valve core position calibration method for calibrating the aforementioned variable thrust cold gas propulsion system.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a variable thrust cold gas propulsion system, including a gas cylinder, a high-pressure sensor, a low-pressure sensor, a micro-Newton level cold gas variable thrust module, and a variable thrust control circuit box. The micro-Newton level cold air variable thrust module includes a piezoelectric driven valve, a displacement sensor, and a nozzle; The variable thrust control circuit box is configured as follows: Receive command thrust and pressure signal from the low-pressure sensor; Based on the command thrust and the pressure signal, the target value of the valve core opening is calculated using the thrust-valve core opening conversion model. Receive the actual displacement signal of the valve core from the displacement sensor; The current valve opening degree is calculated based on the actual displacement signal of the valve core, the pre-calibrated valve core opening point position, and the valve core maximum opening position. Using the target value of the valve core opening as the set value and the current valve core opening as the feedback value, a closed-loop control calculation is performed to generate a drive signal and output it to the piezoelectric drive valve.

[0008] Optionally, the variable thrust control circuit box is configured to calculate the current valve spool opening using the following formula: Where A is the current valve core opening. This refers to the value corresponding to the actual displacement signal of the valve core, which is collected in real time by the displacement sensor. The displacement sensor reading obtained during pre-calibration when the valve core just opens represents the valve core opening point position. The displacement sensor reading obtained from the pre-calibration is when the valve core reaches its maximum opening, i.e., the position of the valve core at its maximum opening.

[0009] Optionally, when the commanded thrust ranges from 0.1 to 10 μN, the thrust-valve opening conversion model is as follows: When the commanded thrust ranges from 10 to 1000 μN, the thrust-valve opening conversion model is as follows: in, The command thrust is P, the low-pressure sensor reading is A, the current valve opening is A, and k0, k1, k2, k3, k4, h0, h1, h2, h3 are coefficients obtained from ground calibration; and / or The closed-loop control operation employs a PID control algorithm.

[0010] Optionally, the system further includes a micro pressure module, which integrates a first high-pressure solenoid valve, a second high-pressure solenoid valve, a pressure reducing component, and a pressure stabilizing component, and is connected to the gas cylinder and the micro-Newton level cold air variable thrust module through a pipeline, wherein the first high-pressure solenoid valve and the second high-pressure solenoid valve are connected in parallel, and the pressure reducing component and the pressure stabilizing component are connected in series and located downstream of the first high-pressure solenoid valve and the second high-pressure solenoid valve.

[0011] Optionally, the micro-Newton level cold air variable thrust module further includes a heater and a temperature measuring resistor. The variable thrust control circuit box is connected to the heater and the temperature measuring resistor and is configured to perform temperature compensation on the thrust-valve opening conversion model based on the signal from the temperature measuring resistor.

[0012] Optionally, the system uses nitrogen, xenon, or helium as the working medium.

[0013] In a second aspect, the present invention also provides a variable thrust control method, applied to the variable thrust cold gas propulsion system described in any one of the first aspects, comprising the following steps: Receives commands from thrust and pressure sensor signals; Based on the commanded thrust and the low-pressure sensor signal, the target value of the valve core opening is calculated using the thrust-valve core opening conversion model. Acquire the actual displacement signal of the valve core detected by the displacement sensor; The current valve opening degree is calculated based on the actual displacement signal of the valve core, the pre-calibrated valve core opening point position, and the valve core maximum opening position. Using the target value of the valve core opening as the set value and the current valve core opening as the feedback value, closed-loop control is performed to generate a drive signal to drive the piezoelectric drive valve.

[0014] Optionally, in the second aspect, the following formula may be used in the step of calculating the current valve core opening: Where A is the current valve core opening. This refers to the value corresponding to the actual displacement signal of the valve core, which is collected in real time by the displacement sensor. The displacement sensor reading obtained during pre-calibration when the valve core just opens represents the valve core opening point position. The displacement sensor reading obtained from the pre-calibration is when the valve core reaches its maximum opening, i.e., the position of the valve core at its maximum opening.

[0015] Thirdly, the present invention also provides a valve core position calibration method for calibrating the variable thrust cold gas propulsion system described in any one of the first aspects, and includes the following steps: A sequence of driving voltages that gradually increases from an initial voltage is applied to the piezoelectric driven valve; During the application of the driving voltage sequence, the readings of the displacement sensor and the flow readings of the flow sensor are acquired simultaneously. Calculate the change in flow rate reading under adjacent drive voltages, wherein the change in flow rate is calculated using the following formula: ; in, This represents the change in flow rate; For flow sensor readings; When the flow rate change value first exceeds a preset threshold, the corresponding displacement sensor reading is determined, and this displacement value is recorded as the valve core opening point position.

[0016] Optionally in the third aspect, the driving voltage sequence is a voltage sequence that gradually increases from 0.1V to 100V in steps of 0.1V, and the duration of each voltage value is 1 second.

[0017] The above-described technical solution of the present invention has the following advantages: The variable thrust cold gas propulsion system provided by this invention integrates pressure sensors, flow sensors, displacement sensors, and temperature sensors, providing comprehensive measurement capabilities. It also features high integration; the miniature pressure module integrates a solenoid valve, pressure reducing components, and pressure stabilizing components, while the micro-Newton-level cold gas variable thrust module integrates a flow sensor, piezoelectric valve, displacement sensor, and temperature sensor, resulting in a small size and easy installation. Furthermore, the displacement sensor directly measures the valve core position, avoiding the delay problem of the flow sensor; using the valve core opening degree as a control parameter achieves rapid response and high-precision control, offering advantages such as fast response time, high adjustment resolution, wide output range, and simpler structure and control logic.

[0018] The displacement-mode variable thrust control method proposed in this invention is the first to propose a control method that uses valve core opening as the target value for feedback adjustment. It uses displacement and pressure sensors as sensors, and directly measures the valve core position through the displacement sensor, avoiding the delay problem of the flow sensor. By using valve core opening as the control parameter, it achieves fast response and high-precision control.

[0019] The valve core position calibration method proposed in this invention is the first to provide a calibration method for the valve core position. It effectively identifies the valve core opening position and is applicable to both ground testing and on-orbit operation, demonstrating good versatility. Attached Figure Description

[0020] The accompanying drawings are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not be consistent with the actual product.

[0021] Figure 1 This is a schematic block diagram of a variable thrust cold gas propulsion system according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the principle of a variable thrust control method in an embodiment of the present invention.

[0022] In the picture: 1: Gas cylinder; 2: High-pressure sensor; 3: Miniature pressure module; 31: First high-pressure solenoid valve; 32: Second high-pressure solenoid valve; 33: Pressure relief component; 34: Voltage regulator components; 4: Damping orifice; 5: Low-pressure sensor; 6: Buffer gas capacity; 7: Micro-Newton level cold air variable thrust module; 71: Flow sensor; 72: Piezoelectrically driven valve; 73: Displacement sensor; 74: Nozzle; 75: Heater; 76: Temperature measuring resistor; 8: Variable thrust control circuit box. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 like Figure 1 As shown in the figure, an embodiment of the present invention provides a variable thrust cold gas propulsion system, including a gas cylinder 1, a high-pressure sensor 2, a micro pressure module 3, a damping orifice 4, a low-pressure sensor 5, a buffer gas container 6, a micro-Newton level cold gas variable thrust module 7, and a variable thrust control circuit box 8.

[0025] The gas cylinder 1 is used to store propellant and is compatible with various working media, including but not limited to nitrogen, xenon, and helium. The high-pressure sensor 2 is used to monitor the outlet pressure of the gas cylinder.

[0026] The miniature pressure module 3 adopts a modular design, including a first high-pressure solenoid valve 31, a second high-pressure solenoid valve 32, a pressure reducing component 33, and a pressure regulating component 34. The first high-pressure solenoid valve 31 and the second high-pressure solenoid valve 32 are connected in parallel, while the pressure reducing component 33 and the pressure regulating component 34 are connected in series downstream of the first high-pressure solenoid valve 31 and the second high-pressure solenoid valve 32. This design improves the reliability of the system; if one solenoid valve fails, the other can still operate normally.

[0027] The pressure reducing component 33 and the voltage stabilizing component 34 cooperate with the damping orifice 4 to reduce vibration and noise caused by airflow impact.

[0028] The micro-Newton level cold air variable thrust module 7 adopts a modular design, including a flow sensor 71, a piezoelectric driven valve 72, a displacement sensor 73, a nozzle 74, a heater 75, and a temperature measuring resistor 76. This highly integrated design makes the system small in size and easy to install.

[0029] The variable thrust control circuit box 8 includes a control board, a data acquisition board, a piezoelectric drive board, an interface board, and a chassis, and is responsible for the overall control and data processing of the system.

[0030] This embodiment achieves high system integration through modular design, reducing system size and improving installation convenience; improves system reliability through parallel solenoid valve design; and enhances system adaptability by being compatible with multiple working media.

[0031] In this embodiment, the variable thrust control circuit box 8 is configured to perform the following operations: Receive command thrust and pressure signal from the low-pressure sensor; Based on the commanded thrust Fc and the pressure signal P, the target value Am of the valve core opening is calculated using the thrust-valve core opening conversion model. Receive the actual displacement signal of the valve core from the displacement sensor 73; The current valve opening degree is calculated based on the actual displacement signal of the valve core, the pre-calibrated valve core opening point position, and the valve core maximum opening position. Using the target value Am of the valve core opening as the setpoint and the current valve core opening A as the feedback value, closed-loop control calculations are performed to generate a drive signal and output it to the piezoelectric drive valve 72. This embodiment directly measures the valve core position using a displacement sensor, avoiding the delay problem of the flow sensor. Employing the valve core opening as the core control parameter, and based on current high-precision piezoelectric drive and displacement detection technology (with a displacement detection range of 10nm to 1000μm and a resolution down to the nanometer level), the system achieves rapid response and high-precision control. This direct control strategy eliminates the complex flow closed-loop adjustment stage, making the system structure and control logic simpler compared to schemes relying on flow feedback. Simultaneously, by precisely controlling the valve core at any position within its full stroke range (from near-closed micrometer / nanometer-level opening to maximum opening), the system can achieve an extremely wide thrust output ranging from micronewtons to millinewtons.

[0032] In one example, the variable thrust control circuit box is configured to calculate the current valve spool opening using the following formula: Where A is the current valve core opening. This refers to the value corresponding to the actual displacement signal of the valve core, which is collected in real time by the displacement sensor. The displacement sensor reading obtained during pre-calibration when the valve core just opens represents the valve core opening point position. The displacement sensor reading obtained from the pre-calibration is when the valve core reaches its maximum opening, i.e., the position of the valve core at its maximum opening.

[0033] In one example, the thrust-valve opening conversion model is a mathematical model established based on the relationship between thrust and valve opening, which can be obtained by fitting ground test data. In this embodiment, the model can be segmented, for example: "Preferably, the thrust-valve opening conversion model is segmented according to the working range of the commanded thrust to adapt to the differences in the nonlinear characteristics of the thrust-valve opening relationship under different thrust ranges." In a specific implementation: When the commanded thrust ranges from 0.1 to 10 μN, the thrust-valve opening conversion model is the following high-order polynomial model: Where Fc is the commanded thrust, P is the low-pressure sensor reading, A is the current valve opening, and k0, k1, k2, k3, and k4 are coefficients obtained from ground calibration. When the commanded thrust ranges from 10 to 1000 μN, the thrust-valve opening conversion model adopts the following low-order polynomial model: Where Fc is the command thrust, P is the low-pressure sensor reading, A is the current valve core opening, and h0, h1, h2, and h3 are coefficients obtained from ground calibration.

[0034] This piecewise model comprehensively considers the complex nonlinear relationship between pressure, fluid characteristics and valve core opening under different thrust ranges.

[0035] The advantages of using a piecewise model are as follows: In the low thrust range (approaching the valve core closed state), fluid behavior is significantly affected by nonlinear effects (such as viscous forces, surface tension, and discontinuous flow effects in minimal flow channels), and the relationship between thrust and valve core opening is extremely complex and highly nonlinear. Using a fourth-order polynomial model, due to its more coefficients and higher curve fitting flexibility, it can better capture and approximate these complex nonlinear characteristics, thereby achieving ultra-high precision control in the critical range approaching zero thrust.

[0036] In the higher thrust range (larger valve opening): gas flow tends to be more stable, the relationship between thrust and opening is relatively smooth, and the degree of nonlinearity is reduced. At this point, a third-order polynomial is sufficient to describe the corresponding relationship with high accuracy. Using a lower order can reduce the amount of computation, improve the response speed of the control system, and avoid overfitting and numerical instability problems that may occur in high-order models in sparse data regions.

[0037] For propulsion systems covering a wide thrust range from 0.1μN to 1000μN, a segmented model is adopted, which can achieve the extremely high control accuracy required for nanometer-level resolution in the ultra-low thrust range approaching zero thrust, while maintaining efficient and stable output in the conventional thrust range. Thus, it fully realizes the comprehensive benefits of fast response, high resolution and wide output range.

[0038] In one example, a closed-loop control operation is performed using the target value of the valve spool opening as the setpoint and the current valve spool opening as the feedback value. The closed-loop control operation employs a PID control algorithm. The PID control algorithm ensures the stability and dynamic performance of the system.

[0039] In one example, the micro-Newton level cold air variable thrust module 7 also includes a heater 75 and a temperature measuring resistor 76. The variable thrust control circuit box 8 is connected to the heater 75 and the temperature measuring resistor 76 and is configured to perform temperature compensation on the thrust-valve opening conversion model based on the signal from the temperature measuring resistor 76.

[0040] The specific compensation method is as follows: based on the temperature value measured by the temperature measuring resistor 76, adjust the parameters in the thrust-valve opening conversion model to compensate for the impact of temperature changes on thrust output.

[0041] In this example, the temperature compensation mechanism effectively eliminates the impact of temperature changes on thrust accuracy, thereby improving the thrust output accuracy and stability of the system under different ambient temperatures.

[0042] In this embodiment, the pneumatic components of the variable thrust cold gas propulsion system are connected via pipelines, all using threaded connections for easy installation; the sealing method involves a hard seal between a metal ball head and a metal conical surface, ensuring good airtightness. This embodiment employs threaded connections and hard metal seals, guaranteeing both ease of installation and system airtightness.

[0043] The electronic components of the variable thrust cold gas propulsion system are connected by cables. The connection relationship is as follows: the variable thrust control circuit box 8 is connected to the high-pressure sensor 2, the low-pressure sensor 5, the first high-pressure solenoid valve 31, the second high-pressure solenoid valve 32, the flow sensor 71, the piezoelectric actuated valve 72, the displacement sensor 73, the heater 75, and the temperature measuring resistor 76. The reasonable cable connection design ensures the reliability of signal transmission.

[0044] It is worth noting that in this embodiment, the valve core opening is the space between the valve core (valve needle) and the valve orifice (nozzle 74). The nozzle 74 is the terminal component that generates thrust in the variable thrust cold gas propulsion system. It is directly connected downstream of the piezoelectric drive valve through the internal flow channel of the module, receives gas with precise flow control, and accelerates it out to generate the required microNewton thrust.

[0045] Example 2 like Figure 2 As shown, this embodiment provides a variable thrust control method, applied to any of the variable thrust cold gas propulsion systems in Embodiment 1 above, including the following steps: like Figure 2 As shown, this embodiment provides a variable thrust control method, applied to the variable thrust cold gas propulsion system described in any of the above embodiments, including the following steps: Step S1: Receive the command thrust Fc and the pressure signal P from the low-pressure sensor; Step S2: Based on the commanded thrust Fc and pressure signal P, calculate the target value Am of the valve core opening through the thrust-valve core opening conversion model; Step S3: Obtain the actual displacement signal of the valve core detected by the displacement sensor; Step S4: Based on the actual displacement signal of the valve core and the pre-calibrated valve core opening point position. and the valve core maximum opening position Calculate the current valve core opening A: Step S5: Using the target value Am of the valve core opening as the set value and the current valve core opening A as the feedback value, perform closed-loop control (e.g., using a PID control algorithm) to generate a drive signal to drive the piezoelectric drive valve.

[0046] This method directly controls the valve core opening, resulting in a fast response speed; closed-loop control ensures control accuracy; and it is suitable for high-precision control requirements of micro-Newton level thrust.

[0047] In one example, the following formula is used in the step of calculating the current valve spool opening: Where A is the current valve core opening. This refers to the value corresponding to the actual displacement signal of the valve core, which is collected in real time by the displacement sensor. The displacement sensor reading obtained during pre-calibration when the valve core just opens represents the valve core opening point position. The displacement sensor reading obtained from the pre-calibration is when the valve core reaches its maximum opening, i.e., the position of the valve core at its maximum opening.

[0048] Example 3 This embodiment provides a valve core position calibration method for calibrating any variable thrust cold gas propulsion system in Embodiment 1 above, including the following steps: Step 1: Apply a sequence of driving voltages that gradually increases from an initial voltage to the piezoelectric driven valve; Step 2: During the application of the driving voltage sequence, the readings of the displacement sensor and the flow readings of the flow sensor are collected simultaneously; Step 3: Calculate the change in flow rate reading under adjacent drive voltages, wherein the change in flow rate is calculated using the following formula: ; in, This represents the change in flow rate; For flow sensor readings; Step 4: Determine the displacement sensor reading corresponding to the first time the flow rate change value exceeds the preset critical value, and record this displacement value as the valve core opening point position.

[0049] This calibration method provides an accurate and reliable valve core position calibration scheme, which can accurately identify the valve core opening point and maximum opening position, providing a basis for precise control; it is applicable to both ground testing and on-orbit calibration.

[0050] In a preferred example, after step one, i.e. after the system is powered on, it is preheated for 30 minutes. After preheating, a sequence of driving voltages that gradually increases from the initial voltage is applied to the piezoelectric drive valve.

[0051] In one example, the driving voltage sequence is a voltage sequence that increases gradually from 0.1V to 100V in 0.1V increments, and the duration of each voltage value is 1 second.

[0052] The valve core position calibration method in this embodiment is mainly performed before the variable thrust cold gas propulsion system operates for the first time.

[0053] This embodiment also provides a method for powering on and off a variable thrust cold gas propulsion system.

[0054] The power-on sequence of the variable thrust cold gas propulsion system includes: 1. Power on the variable thrust control circuit box; 2. Pressure sensor power is on; 3. Flow sensor power on; 4. Displacement sensor power on; 5. Power on the piezoelectric drive board.

[0055] The power-off sequence of the variable thrust cold gas propulsion system is the reverse of the power-on sequence, including: 1. Power off the piezoelectric drive board; 2. Displacement sensor power off; 3. Flow sensor power off; 4. Pressure sensor power off; 5. The variable thrust control circuit box is de-energized.

[0056] By setting a reasonable power-on and power-off sequence, it is possible to ensure that there is no mutual interference between different types of secondary power supplies, thereby improving the stability and reliability of the system.

[0057] The complete workflow of the variable thrust cold gas propulsion system is further described below: System initialization: Power on each component of the system in the power-on sequence and preheat for 30 minutes; Valve spool position calibration: Execute the valve spool position calibration procedure as needed to obtain the valve spool opening point position. and maximum opening position ; Receive thrust command: Receive thrust command Fc from the spacecraft control system; Acquire sensor data: Acquire the low-pressure sensor signal P and the displacement sensor signal L; Calculate the target valve opening: Calculate the target valve opening value Am based on the thrust-valve opening conversion model; Calculate the current opening degree: Calculate the current valve core opening degree A based on the displacement sensor signal and calibration parameters; Closed-loop control: Using Am as the setpoint and A as the feedback value, PID closed-loop control is performed to generate drive signals; Thrust output: The drive signal is sent to the piezoelectric drive valve to generate the corresponding thrust; Continuous monitoring: Throughout the entire operation, continuously monitor the data from each sensor and perform temperature compensation and parameter adjustments as necessary.

[0058] Any aspects of this invention not described in detail are common knowledge or existing technology in the field.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution, and in the absence of conflict between solutions, the various technical features mentioned in each embodiment can be combined in any way to form other implementation methods that can be understood by those skilled in the art.

[0060] Furthermore, without departing from the scope of the present invention, modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some of the technical features, shall not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A variable thrust cold gas propulsion system, comprising a gas cylinder, a high-pressure sensor, a low-pressure sensor, a micro-Newton level cold gas variable thrust module, and a variable thrust control circuit box, characterized in that: The micro-Newton level cold air variable thrust module includes a piezoelectric driven valve, a displacement sensor, and a nozzle; The variable thrust control circuit box is configured as follows: Receive command thrust and pressure signal from the low-pressure sensor; Based on the command thrust and the pressure signal, the target value of the valve core opening is calculated using the thrust-valve core opening conversion model. Receive the actual displacement signal of the valve core from the displacement sensor; The current valve opening degree is calculated based on the actual displacement signal of the valve core, the pre-calibrated valve core opening point position, and the valve core maximum opening position. Using the target value of the valve core opening as the set value and the current valve core opening as the feedback value, a closed-loop control calculation is performed to generate a drive signal and output it to the piezoelectric drive valve.

2. The variable thrust cold gas propulsion system according to claim 1, characterized in that: The variable thrust control circuit box is configured to calculate the current valve opening using the following formula: Where A is the current valve core opening. This refers to the value corresponding to the actual displacement signal of the valve core, which is collected in real time by the displacement sensor. The displacement sensor reading obtained during pre-calibration when the valve core just opens represents the valve core opening point position. The displacement sensor reading obtained from the pre-calibration is when the valve core reaches its maximum opening, i.e., the position of the valve core at its maximum opening.

3. The variable thrust cold gas propulsion system according to claim 1 or 2, characterized in that: When the commanded thrust ranges from 0.1 to 10 μN, the thrust-valve opening conversion model is as follows: When the commanded thrust ranges from 10 to 1000 μN, the thrust-valve opening conversion model is as follows: Where Fc is the commanded thrust, P is the low-pressure sensor reading, A is the current valve opening, and k0, k1, k2, k3, k4, h0, h1, h2, h3 are coefficients obtained from ground calibration; and / or The closed-loop control operation employs a PID control algorithm.

4. The variable thrust cold gas propulsion system according to claim 1 or 2, characterized in that: The system also includes a micro pressure module, which integrates a first high-pressure solenoid valve, a second high-pressure solenoid valve, a pressure reducing component, and a pressure stabilizing component. It is connected to the gas cylinder and the micro-Newton level cold air variable thrust module through pipelines. The first high-pressure solenoid valve and the second high-pressure solenoid valve are connected in parallel, and the pressure reducing component and the pressure stabilizing component are connected in series and located downstream of the first high-pressure solenoid valve and the second high-pressure solenoid valve.

5. The variable thrust cold gas propulsion system according to claim 1 or 2, characterized in that: The micro-Newton level cold air variable thrust module also includes a heater and a temperature measuring resistor. The variable thrust control circuit box is connected to the heater and the temperature measuring resistor and is configured to perform temperature compensation on the thrust-valve opening conversion model based on the signal from the temperature measuring resistor.

6. The variable thrust cold gas propulsion system according to claim 1 or 2, characterized in that: The system uses nitrogen, xenon, or helium as the working medium.

7. A variable thrust control method, characterized in that: The method, when applied to the variable thrust cold gas propulsion system as described in any one of claims 1-6, includes the following steps: Receives commands from thrust and pressure sensor signals; Based on the commanded thrust and the low-pressure sensor signal, the target value of the valve core opening is calculated using the thrust-valve core opening conversion model. Acquire the actual displacement signal of the valve core detected by the displacement sensor; The current valve opening degree is calculated based on the actual displacement signal of the valve core, the pre-calibrated valve core opening point position, and the valve core maximum opening position. Using the target value of the valve core opening as the set value and the current valve core opening as the feedback value, closed-loop control is performed to generate a drive signal to drive the piezoelectric drive valve.

8. The method according to claim 7, characterized in that: The following formula is used in the step of calculating the current valve spool opening: Where A is the current valve core opening. This refers to the value corresponding to the actual displacement signal of the valve core, which is collected in real time by the displacement sensor. The displacement sensor reading obtained during pre-calibration when the valve core just opens represents the valve core opening point position. The displacement sensor reading obtained from the pre-calibration is when the valve core reaches its maximum opening, i.e., the position of the valve core at its maximum opening.

9. A method for calibrating the position of a valve core, characterized in that: The method is used to calibrate the variable thrust cold gas propulsion system as described in any one of claims 1-6, and includes the following steps: A sequence of driving voltages that gradually increases from an initial voltage is applied to the piezoelectric driven valve; During the application of the driving voltage sequence, the readings of the displacement sensor and the flow readings of the flow sensor are acquired simultaneously. Calculate the change in flow rate reading under adjacent drive voltages, wherein the change in flow rate is calculated using the following formula: ； in, This represents the change in flow rate; For flow sensor readings; When the flow rate change value first exceeds a preset threshold, the corresponding displacement sensor reading is determined, and this displacement value is recorded as the valve core opening point position.

10. The method according to claim 9, characterized in that: The driving voltage sequence is a voltage sequence that increases gradually from 0.1V to 100V in 0.1V increments, and the duration of each voltage value is 1 second.

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