Cold air variable thrust control system and method

Abstract

The invention discloses a cold air variable thrust control system and method, and belongs to the technical field of aerospace propulsion. The system comprises a primary storage tank, a secondary storage tank, a stop valve, a first electromagnetic valve, a second electromagnetic valve, a first pressure detection part P1, a second pressure detection part P2, a flow control module and a spray pipe, a propellant is stored in the first-stage storage tank in a gas-liquid mixed state, and after vaporization and pressure stabilization are conducted through the second-stage storage tank, gas supplementation is controlled by the first electromagnetic valve, and gas injection is controlled by the second electromagnetic valve. According to the control method, on the basis of real-time pressure detection of P1 and P2, the switching frequency of the electromagnetic valve is adjusted in a closed-loop mode through threshold judgment and a pressure difference-flow model, and accurate flow control is achieved by introducing a PID algorithm. Through double-valve cooperation and a real-time feedback mechanism, under the condition that a traditional pressure reducing valve and a traditional air capacitor are omitted, the structure is remarkably simplified, light weight is achieved, and the beneficial effects of being fast in response, high in control precision, high in environmental adaptability and the like are achieved.

Description

Technical Field

[0001] This invention belongs to the field of aerospace propulsion technology, specifically relating to a low-power, high-precision, fast-response cold gas variable thrust control system and method suitable for micro and nano satellites. Background Technology

[0002] Small satellites are characterized by low launch costs, rapid development cycles, and wide applicability, making the option of launching multiple small satellites on a single rocket a widely adopted choice. Small satellites are defined as those weighing less than 10 kg. Since 2012, 1700 small satellites have been launched into orbit, with approximately 1000 more added in the past two years. It is projected that by 2025, 1000 small satellites will be launched into space annually. Due to their lower velocity variation requirements and smaller mass, the thruster needs are primarily focused on attitude control and orbital maneuvers with minimal velocity changes, necessitating the development of micro-Newton to millinewton thrust micro-propulsion systems.

[0003] Currently, propulsion systems used in space include cold gas propulsion, chemical propulsion, and electric propulsion. For microsatellites, the propulsion system is mainly used for orbit maintenance and attitude control, requiring small thrust and short operating time. Given that the payload space and total mass requirements are met, cold gas propulsion is the preferred choice for the space propulsion system of microsatellites.

[0004] Although various high-precision cold gas propulsion systems for different applications have been studied both domestically and internationally, these systems suffer from problems such as complex control, high power consumption, and low reliability.

[0005] In their paper "Preliminary Analysis of the Performance of Solid Cold Gas Propellants," Liang Zhenhua et al. designed two formulations of solid cold gas propellants using sodium azide (NaN3) as the gas-generating agent, lithium fluoride (LiF) as the condenser, and sodium silicate (Na2SiO3) as the binder. While this scheme achieves low-impurity, low-temperature, and stable thrust nitrogen generation, the solid-state propulsion system requires heating the working fluid, resulting in higher power consumption.

[0006] In their paper "Simulation Study on Dynamic Performance of Micro Ultra-High Pressure Cold Gas Propulsion System," Wang Lu et al. focused on the influence of cylinder pressure (60–120 MPa) on the system's response characteristics and thrust output. Although this scheme can achieve a stable thrust of approximately 200 mN, the high working fluid pressure of the ultra-high pressure cold gas propulsion system makes key components such as the pressure reducing valve and pressure stabilizing chamber prone to pressure shocks and oscillations during dynamic operation, affecting the stability and reliability of the system.

[0007] In their paper "Data-Driven PID Control Strategy for Micro-Proportional Thrust Modules," Wang Xudong et al. employed a data-driven PID control method. This involved establishing a strongly nonlinear model of current-valve opening, valve core motion, flow rate, and thrust, and constructing a current-thrust-flow rate database. While this approach effectively improves control response speed and meets the requirements for high-precision thrust adjustment, the control logic of the micro-proportional propulsion system is complex, involving multivariate coupling modeling, real-time database matching, and online parameter correction, making algorithm implementation and debugging challenging. Summary of the Invention

[0008] This invention addresses the technical problems of existing cold gas propulsion systems, such as large size, poor thrust stability, and high power consumption, by proposing a cold gas variable thrust control system and method.

[0009] The technical solution for achieving the present invention is as follows: a cold gas variable thrust control system, comprising a primary storage tank, a secondary storage tank, a shut-off valve, a first solenoid valve, a second solenoid valve, a first pressure detection element P1, a second pressure detection element P2, a flow control module, and a thruster nozzle outlet. The propellant is stored in the primary storage tank in a gas-liquid mixed state within the operating temperature range. A shut-off valve and a first solenoid valve are sequentially arranged between the primary and secondary storage tanks to achieve on / off control. A first pressure detection element P1 is arranged between the shut-off valve and the first solenoid valve after the primary storage tank. A second pressure detection element P2 is sequentially arranged after the secondary storage tank. A second solenoid valve is arranged between the second pressure detection element P2 and the thruster nozzle outlet. The first pressure detection element P1 and the second pressure detection element P2 are respectively connected to the flow control module.

[0010] A control method utilizing a cold gas variable thrust control system comprises the following steps:

[0011] Step 1: The flow control module acquires the real-time pressure of the first pressure sensor P1. and the real-time pressure of the second pressure detection element P2. Proceed to step 2.

[0012] Step 2: Determine the real-time pressure monitored by the second pressure detection element P2. With threshold Relationship:

[0013] when Below the threshold At that time, the first solenoid valve is opened to supply air to the secondary storage tank until... Reaching the threshold .

[0014] when Reaching the threshold At this time, the flow control module provides a conduction control signal to the second solenoid valve, opens the second solenoid valve, and proceeds to step 3.

[0015] Step 3: When the second solenoid valve opens, the propulsion pipeline is connected to the nozzle, and the propellant is ejected through the nozzle outlet to generate thrust, then proceed to step 4.

[0016] Step 4: Based on the parameters of the first solenoid valve, and in conjunction with the first pressure detection element P1... The second pressure detection element P2 The fitting relationship between pressure difference and flow rate is determined, where the pressure difference is the pressure difference measured by the first pressure sensor P1 and the second pressure sensor P2. - Proceed to step 5.

[0017] Step 5: Based on the obtained fitting relationship between pressure difference and flow rate, modify the parameters of the second solenoid valve to change or maintain the pressure at the desired level. At the same time, the accuracy and range of flow rate regulation can be changed by changing the parameters of the first solenoid valve to achieve finer regulation.

[0018] Compared with the prior art, the significant advantages of this invention are:

[0019] (1) The present invention significantly improves the flow control accuracy and environmental adaptability of the cold gas propulsion system by using a collaborative control architecture of the first solenoid valve and the second solenoid valve, combined with a real-time differential pressure flow model, without eliminating the traditional pressure reducing valve and gas capacity.

[0020] (2) To achieve thrust stability, the present invention introduces a closed-loop PID (proportional-integral-derivative) control mechanism based on flow feedback. This closed-loop control strategy effectively suppresses thrust fluctuations caused by factors such as upstream pressure pulsation, solenoid valve switching characteristics, and changes in space environment temperature, ensuring that the spacecraft has higher stationarity and stability when performing tasks such as attitude adjustment and orbit maintenance.

[0021] (3) While achieving high-performance control, the system structure is greatly simplified. The bulky pressure reducing valve and large-capacity gas cylinder are removed, making the pipeline layout more compact and reducing the number of parts. This achieves lightweight and low-power operation, and the overall performance is significantly better than that of traditional cold air propulsion systems. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the cold air propulsion flow control system of the present invention.

[0023] Figure 2 This is a schematic diagram of the PID control algorithm for the cold air propulsion flow control system of the present invention.

[0024] Figure 3 The figure shows the simulation results of this invention. Detailed Implementation

[0025] 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 a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0027] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0028] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixing," etc., should be interpreted broadly. For example, "fixing" can mean a fixed connection, a detachable connection, or an integral part; "connection" can mean a mechanical connection or an electrical connection. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible to those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0030] The following section will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention, using this design example as an example.

[0031] like Figure 1As shown, the cold gas variable thrust control system of the present invention includes a primary tank, a secondary tank, a shut-off valve, a first solenoid valve, a second solenoid valve, a first pressure sensor P1, a second pressure sensor P2, a flow control module, and a thruster nozzle outlet. The propellant is stored in the primary tank in a gas-liquid mixture state within the operating temperature range. A shut-off valve and a first solenoid valve are sequentially arranged between the primary and secondary tanks to achieve on / off control. A first pressure sensor P1 is arranged between the shut-off valve and the first solenoid valve after the primary tank. A second pressure sensor P2 is sequentially arranged after the secondary tank. A second solenoid valve is arranged between the second pressure sensor P2 and the thruster nozzle outlet. The first pressure sensor P1 and the second pressure sensor P2 are respectively connected to the flow control module.

[0032] The primary storage tank is used to store gas-liquid mixed propellant.

[0033] The secondary storage tank is used to vaporize and stabilize the pressure of the liquid propellant.

[0034] The shut-off valve controls the on / off state of the entire system.

[0035] The first solenoid valve controls the connection and disconnection between the primary and secondary storage tanks.

[0036] The second solenoid valve controls the connection and disconnection between the secondary storage tank and the propellant nozzle outlet.

[0037] In this invention, both the first and second solenoid valves are bang-bang valves (a type of relay control valve), which can adjust the switching frequency and the switching time each time.

[0038] The first pressure detection element P1 monitors the pressure of the primary storage tank.

[0039] The second pressure sensor P2 monitors the pressure of the secondary storage tank.

[0040] The flow control module provides on / off signals to the first and second solenoid valves.

[0041] The nozzle outlet of the propulsion unit is used to eject gas from the secondary storage tank.

[0042] A control method utilizing a cold gas variable thrust control system comprises the following steps:

[0043] Step 1: The flow control module acquires the real-time pressure of the first pressure sensor P1. and the real-time pressure of the second pressure detection element P2. Proceed to step 2.

[0044] Step 2: Determine the real-time pressure monitored by the second pressure detection element P2. With threshold Relationship:

[0045] when Below the threshold At that time, the first solenoid valve is opened to supply air to the secondary storage tank until... Reaching the threshold ;

[0046] when Reaching the threshold At this time, the flow control module provides a conduction control signal to the second solenoid valve, opens the second solenoid valve, and proceeds to step 3.

[0047] Step 3: When the second solenoid valve opens, the propulsion pipeline is connected to the nozzle, and the propellant is ejected through the nozzle outlet to generate thrust, then proceed to step 4.

[0048] Step 4: Based on the parameters of the first solenoid valve, and in conjunction with the first pressure detection element P1... The second pressure detection element P2 The fitting relationship between pressure difference and flow rate is determined, where the pressure difference is the pressure difference measured by the first pressure sensor P1 and the second pressure sensor P2. - Proceed to step 5.

[0049] Step 5: Based on the obtained fitting relationship between pressure difference and flow rate, modify the parameters of the second solenoid valve to change or maintain the pressure at the desired level. At the same time, the accuracy and range of flow rate regulation can be changed by changing the parameters of the first solenoid valve to achieve finer regulation.

[0050] In practical applications, to improve the accuracy of measurement and flow control, the relationship between the pressure difference between the pressures obtained by the first pressure sensor P1 and the second pressure sensor P2 and the actual flow rate can be calibrated. Typically, there is a certain nonlinear relationship between flow rate and pressure difference; therefore, calibration using experimental data and the introduction of a suitable flow calculation model are necessary.

[0051] In general engineering systems, the relationship between the pressure difference generated when a fluid passes through a pipe and the flow rate can be fitted using the following flow rate correction formula:

[0052] 1) Calculate the inlet mass flow rate of the secondary storage tank. :

[0053] ,

[0054] in, The flow coefficient of the first solenoid valve is... The effective flow area of ​​the first solenoid valve. The density of the liquid propellant. This refers to the real-time pressure of the first pressure sensor. This is the real-time pressure of the second pressure sensor.

[0055] 2) Calculate the flash evaporation ratio and flash vaporization rate in the secondary storage tank:

[0056] , ,

[0057] in, For dryness, The specific enthalpy of the liquid entering the secondary storage tank, The enthalpy of saturated liquid under the pressure of the secondary storage tank. The saturated vapor specific enthalpy at the pressure of the secondary storage tank. This refers to the vaporization mass flow rate.

[0058] 3) Calculate the propellant nozzle outlet flow rate :

[0059] ,

[0060] in, The nozzle flow coefficient is... This represents the area of ​​the nozzle throat. For specific heat ratio, The gas constant is... This is the current temperature.

[0061] 4) Update state variables:

[0062] Liquid mass reduction: , ,

[0063] Increase in gas volume: , ,

[0064] Pressure changes: , ,

[0065] in, The rate of change of liquid mass. For time step, The rate of change of gas volume. The volume occupied by the gas. This is the total volume of the secondary storage tank. The rate of change of pressure, The current temperature. For liquid mass.

[0066] The above equation is generally applicable to the steady, incompressible flow of fluids such as liquids and gases in pipelines. Essentially, the equation derives the flow rate by measuring the pressure difference generated in the pipeline, thus providing the fundamental data needed for pipeline design and flow monitoring.

[0067] In practical applications, due to the certain manufacturing tolerances and measurement errors of different pressure testing components, the measurement results of different pressure testing components may deviate. Therefore, pressure testing components can be calibrated before use.

[0068] Using the above flow correction fitting formula can eliminate the phenomenon that different pressure detection elements have numerical errors compared with the actual pressure.

[0069] In this invention, the calibration results described above can be combined with PID (proportional-integral-derivative) control for closed-loop flow control, achieving more accurate control results. Specifically, the following methods can be used:

[0070] like Figure 2 The diagram shown is a schematic of the PID control algorithm of the cold air propulsion flow control system of the present invention. Figure 2 Before performing flow control, the required set flow value is determined. Simultaneously, real-time output flow is collected from the downstream side of the second solenoid valve. The output flow is calculated and fitted using the detection data from the first pressure sensor P1 and the second pressure sensor P2, and then converted from analog to digital. Figure 2 After being converted into a digital signal by A / D conversion, it is input to the control unit. The difference between the digital signal and the set flow rate is calculated to obtain the corresponding deviation. If the deviation exceeds the valve setpoint, it is corrected by a PID algorithm. The corrected digital signal is then output and converted into a digital-to-analog converter. Figure 2 The signal is converted from a D / A converter to an analog signal or a PWM (pulse width modulation) signal, which in turn adjusts the parameters of the second solenoid valve.

[0071] The PID algorithm can effectively compensate for the hysteresis effect and poor repeatability of the second solenoid valve, reducing the difficulty of parameter control.

[0072] The system is monitored and dynamically adjusted in real time. After the output flow rate stabilizes, the system will periodically collect real-time pressure data through the first pressure sensor P1 and the second pressure sensor P2, calculate the real-time output flow rate, and compare it with the set flow rate value. If a deviation occurs, the parameters will be adjusted in time to ensure the accuracy and stability of the flow rate during long-term operation.

[0073] Example 1: Set the pressure setpoints to 200, 300, 400, 500, 600, and 700 kPa respectively, and the pressure changes are as follows: Figure 3As shown, the actual pressure fluctuates very little around the set value, and the response time is also very fast.

[0074] This invention's cold gas propulsion flow control system involves only primary and secondary storage tanks, two pressure sensors, and two solenoid valves, achieving a lightweight design that aligns with current trends in cold gas propulsion flow control systems. Furthermore, in terms of control methods, compared to traditional methods, this invention's cold gas propulsion flow control system achieves a lightweight design while maintaining an extremely wide flow adjustment range and high control accuracy. In practical applications, the satellite platform only needs to maintain a relatively constant ambient temperature; even without constant temperature, temperature calibration is possible, significantly simplifying the overall system complexity. Given that most current flow control systems require ground-based telemetry data to assess flow rate and continuously adjust parameters, this invention employs closed-loop control, greatly simplifying flow control complexity while improving accuracy. As solenoid valves and other components can experience performance degradation over time, leading to discrepancies between expected and actual flow rates, and as well as instability or increasing errors over time, the closed-loop control method in this invention can self-correct these issues.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cold gas variable thrust control system, characterized in that: The system includes a primary storage tank, a secondary storage tank, a shut-off valve, a first solenoid valve, a second solenoid valve, a first pressure sensor P1, a second pressure sensor P2, a flow control module, and a propellant nozzle outlet. The propellant is stored in the primary storage tank in a gas-liquid mixture state within the operating temperature range. A shut-off valve and a first solenoid valve are sequentially installed between the primary and secondary storage tanks to achieve on / off control. A first pressure sensor P1 is installed between the shut-off valve and the first solenoid valve after the primary storage tank. A second pressure sensor P2 is sequentially installed after the secondary storage tank. A second solenoid valve is installed between the second pressure sensor P2 and the propellant nozzle outlet. The first pressure sensor P1 and the second pressure sensor P2 are respectively connected to the flow control module.

2. The cold gas variable thrust control system according to claim 1, characterized in that: The primary storage tank is used to store gas-liquid mixed propellant; The secondary storage tank is used for vaporizing and stabilizing the pressure of the liquid propellant; A shut-off valve controls the on / off state of the entire system; The first solenoid valve controls the connection and disconnection between the primary and secondary storage tanks; The second solenoid valve controls the connection and disconnection between the secondary storage tank and the propellant nozzle outlet; The first pressure detection element P1 monitors the pressure of the primary storage tank. The second pressure sensor P2 monitors the pressure of the secondary storage tank. The flow control module provides on / off signals to the first and second solenoid valves; The propulsion nozzle is used to eject gas from the secondary storage tank.

3. A cold gas variable thrust control system according to claim 2, characterized in that: Both the first and second solenoid valves are bang-bang valves, used to adjust the switching frequency and the duration of each switching action.

4. A control method using the cold gas variable thrust control system as described in any one of claims 1 to 3, comprising the following steps: Step 1: The flow control module acquires the real-time pressure of the first pressure sensor P1. and the real-time pressure of the second pressure detection element P2. Proceed to step 2; Step 2: Determine the real-time pressure monitored by the second pressure detection element P2. With threshold Relationship: when Below the threshold At that time, the first solenoid valve is opened to supply air to the secondary storage tank until... Reaching the threshold ; when Reaching the threshold At this time, the flow control module provides a conduction control signal to the second solenoid valve, opens the second solenoid valve, and proceeds to step 3; Step 3: When the second solenoid valve opens, the propulsion line is connected to the nozzle, and the propellant is ejected through the nozzle outlet to generate thrust, then proceed to step 4. Step 4: Based on the parameters of the first solenoid valve, and in conjunction with the first pressure detection element P1... The second pressure detection element P2 The fitting relationship between pressure difference and flow rate is determined, where the pressure difference is the pressure difference measured by the first pressure sensor P1 and the second pressure sensor P2. - Proceed to step 5; Step 5: Based on the obtained fitting relationship between pressure difference and flow rate, modify the parameters of the second solenoid valve to change or maintain the pressure at the desired level. At the same time, the accuracy and range of flow rate regulation can be changed by changing the parameters of the first solenoid valve to achieve finer regulation.

5. The control method using a cold gas variable thrust control system according to claim 4, characterized in that, In step 2, the threshold Satisfy the following formula: ， in, Indicates real-time. , This is the time point for phase transition. , , These are the target pressure values ​​for different stages.

6. The control method using a cold gas variable thrust control system according to claim 4, characterized in that, In step 4, to improve the accuracy of measurement and flow control, a flow calculation model is introduced to calibrate the relationship between the pressure difference between the first pressure sensor P1 and the second pressure sensor P2 and the actual flow rate, as follows: The relationship between the pressure difference generated when fluid flows through a pipe and the flow rate is calibrated using the following flow rate calculation model: 1) Calculate the inlet mass flow rate of the secondary storage tank. : ， in, The flow coefficient of the first solenoid valve is... The effective flow area of ​​the first solenoid valve. The density of the liquid propellant. This refers to the real-time pressure of the first pressure sensor. This refers to the real-time pressure of the second pressure sensor. 2) Calculate the flash evaporation ratio and flash vaporization rate in the secondary storage tank: ， ， in, For dryness, The specific enthalpy of the liquid entering the secondary storage tank, The enthalpy of saturated liquid under the pressure of the secondary storage tank. The saturated vapor specific enthalpy at the pressure of the secondary storage tank. For vaporization mass flow rate; 3) Calculate the propellant nozzle outlet flow rate : ， in, The nozzle flow coefficient is... This represents the area of ​​the nozzle throat. For specific heat ratio, The gas constant is... The current temperature; 4) Update state variables: Liquid mass reduction: , , Increase in gas volume: , , Pressure changes: , , in, The rate of change of liquid mass. For time step, The rate of change of gas volume. The volume occupied by the gas. This is the total volume of the secondary storage tank. The rate of change of pressure, The current temperature. For liquid mass.

7. The control method using a cold gas variable thrust control system according to claim 6, characterized in that, The flow calculation model is applicable to stable, incompressible fluid flow of liquids and gases in pipes.

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