High-precision non-magnetic thermal control system for magnetic measurement optical platform of geomagnetic measurement satellite

Abstract

The invention discloses a high-precision non-magnetic thermal control system for a magnetic measurement optical platform of a geomagnetic measurement satellite. The high-precision non-magnetic thermal control system comprises a non-magnetic thermal control assembly, a non-magnetic heater and a temperature sensor, the temperature sensor uses a Pt1000 platinum resistor and adopts a constant current source four-wire system temperature measurement technology to complete high-precision temperature acquisition of the optical platform. The non-magnetic heater is made of a low-magnetic material and adopts a double-layer four-loop demagnetization design, so that non-magnetic heating of the optical platform is completed. The non-magnetic thermal control assembly heats the heater according to a temperature value collected by the temperature sensor and a preset temperature control strategy by using a PID temperature control algorithm through sine wave amplitude modulation heating and square wave duty ratio adjustment heating, high-precision temperature closed-loop control over the optical platform is completed, and the temperature stability reaches + / -0.2 DEG C. The non-magnetic thermal control system adopts a non-magnetic temperature measurement and control technology, a high-stability temperature environment is provided for the optical platform, meanwhile, the non-magnetic requirement of the optical platform is met, and the high-precision magnetic field measurement requirement of the vector magnetometer is guaranteed.

Description

Technical Field

[0001] The invention relates to a high-precision non-magnetic thermal control system for a magnetic measurement optical platform of a geomagnetic measurement satellite. Background Art

[0002] The Earth's magnetic field is one of the most important physical fields on Earth. Conducting precise observations and research on the Earth's magnetic field is a major fundamental scientific topic. Geomagnetic satellites are essential tools for geomagnetic measurements. Compared to other geomagnetic measurement methods, they offer all-weather, all-day coverage and a wide range of observations. They can acquire high-precision, high-resolution geomagnetic data, meeting the needs of geophysical and space physics research.

[0003] Geomagnetic measurement satellites are usually equipped with a high-precision magnetic measurement optical platform, on which a vector magnetometer and a star sensor are installed. The vector magnetometer is responsible for measuring the vector magnetic field at the satellite's location, and the star sensor is responsible for determining the satellite's own attitude and longitude and latitude. Through the transfer matrix conversion from the vector magnetometer to the star sensor, accurate vector magnetic field data in inertial space can be obtained.

[0004] To further improve magnetic field measurement accuracy, it is necessary to maximize the stability of the transfer matrix from the vector magnetometer to the star sensor and reduce its fluctuations with space temperature. To achieve this, the optical platform thermal control must ensure that the optical platform structure operates within a well-defined temperature range and has good thermal stability. Since the vector magnetometer is integrated within the optical platform, this also requires that the optical platform thermal control must not produce significant magnetic interference with the vector magnetometer's magnetic field measurements.

[0005] Currently, due to the different missions of satellites, conventional satellite thermal control systems do not specifically design and control the magnetic interference caused by thermal control materials, thermal control measurement and temperature control, etc. Therefore, it is particularly necessary to design a non-magnetic thermal control system for magnetic measurement optical platforms to meet the mission requirements of high-precision magnetic measurement for geomagnetic measurement satellites. Summary of the Invention

[0006] The technical problem solved by the present invention is: in response to the demand for high-precision magnetic measurement of geomagnetic measurement satellites, the deficiency that existing conventional thermal control means do not specifically design and control the magnetic interference generated by thermal control materials, thermal control measurement and temperature control, etc., is overcome, and a non-magnetic thermal control system for a magnetic measurement optical platform is designed to control the residual magnetism of the thermal control material. Non-magnetic or low-magnetic materials are used, and a demagnetization design is adopted. Non-magnetic measurement and temperature control technology is adopted to minimize the magnetic interference generated when the thermal control temperature measurement circuit and the heating circuit are working, thereby solving the problem of high-precision non-magnetic thermal control of the magnetic measurement optical platform.

[0007] The technical solution of the present invention is: a high-precision non-magnetic thermal control system for a magnetic measurement optical platform of a geomagnetic measurement satellite, comprising a non-magnetic thermal control component, a non-magnetic heater, and a temperature sensor;

[0008] Temperature sensors are attached to different temperature measurement points on the thermal control cabin of the magnetic measurement optical platform to measure the temperature of the thermal control cabin;

[0009] The non-magnetic heater is attached to different parts of the thermal control cabin and heats the thermal control cabin by driving current;

[0010] The non-magnetic thermal control component uses the PID temperature control algorithm according to the temperature value collected by the temperature sensor and the preset temperature control strategy. It controls the heating of the non-magnetic heater through sinusoidal wave amplitude modulation heating and square wave duty cycle heating to achieve temperature control of the thermal control cabin.

[0011] Furthermore, the temperature sensor uses a Pt1000 platinum resistor and an MF601 thermistor; the temperature measurement point is collected with high precision through the Pt1000 platinum resistor;

[0012] Among them, the Pt1000 platinum resistor adopts a four-wire component, including power supply C1+, power supply C2-, acquisition P1+, and acquisition P2-; power supply C1+ and power supply C2- are set in adjacent positions, and the lead wires of the Pt1000 platinum resistor power supply C1+ and C2- are twisted, and the distance between adjacent twisting points is not more than 20mm; the lead wires of the acquisition P1+ and P2- are twisted, and the distance between adjacent twisting points is not more than 25mm.

[0013] Furthermore, the non-magnetic heater adopts a thin film electric heater and a cable electric heater;

[0014] Film type electric heaters and cable type electric heaters use 6J8 manganese copper foil / wire to make electric heating lines and electric heating wires;

[0015] The thin-film electric heater uses a double-layer four-circuit design for magnetic field offset. The thin-film electric heater includes two layers of heating plates, the lower layer of which includes a first main circuit and a first backup circuit. The first main circuit includes outlet points A1 and A1', and the first backup circuit includes outlet points B1 and B1'. The upper layer of the heating plate includes a second main circuit and a second backup circuit. The second main circuit includes outlet points A2 and A2', and the second backup circuit includes outlet points B2 and B2'.

[0016] After the upper and lower heating plates are bonded, the heating wires of the first main circuit and the second main circuit are required to overlap up and down, and the heating wires of the first backup circuit and the second backup circuit are required to overlap up and down; the upper and lower heating plates have a total of four outlet points arranged crosswise; all circuit leads are twisted pair cables.

[0017] Furthermore, the non-magnetic thermal control component includes a sinusoidal heating module, a square wave heating module, an acquisition module, a control module and a power supply module; the sinusoidal heating module generates several sinusoidal waves with adjustable amplitudes, and the square wave heating module generates several square waves with adjustable duty cycles, which respectively perform sinusoidal wave heating and square wave heating on the non-magnetic heater; the acquisition module controls the temperature sensor to collect temperature at the temperature measuring points; the control module uses the PID control algorithm to complete closed-loop heating control of the heating plate based on the collected optical platform temperature measurement data; the power supply module provides the heating drive voltage required by the sinusoidal heating module and the square wave heating module.

[0018] Furthermore, the sinusoidal heating module includes a sinusoidal wave frequency control circuit, a sinusoidal wave generating circuit, a power amplifying circuit and an exchange subcircuit;

[0019] The sine wave frequency control circuit receives a control signal and several square wave signals sent by the control module, and outputs a DA control signal and a square wave signal required by the sine wave generating circuit. The square wave signal sent by the control module is set with four timing sequences. The four square wave signals are divided into two groups, each group containing two square wave signals. The two square wave signals in each group have a phase difference of 180°, and the square wave signals between the two groups have a phase difference of 90°. Under the control of the control signal sent by the control module, the sine wave frequency control circuit selects one of the square wave signals with different timing sequences to output to the sine wave generating circuit.

[0020] The sine wave generating circuit converts the square wave signal into an amplitude-adjustable sine wave signal;

[0021] The power amplifier circuit amplifies the power and amplitude of the sinusoidal signal generated by the sinusoidal wave generating circuit, and outputs the sinusoidal wave signal with power and amplitude amplification to the switching sub-circuit;

[0022] The switching subcircuit switches and outputs the collected sinusoidal voltage analog quantities to the control module.

[0023] Furthermore, the square wave heating module includes a square wave control circuit, a power amplification circuit and a switching subcircuit;

[0024] The square wave control circuit receives the control signals sent by the control module, including the DIR control signal, the data line control signal, the address line control signal, and the board selection signal control signal. After decoding and latching, it outputs the control signals required by the power amplifier circuit LMD18200, including the DIR control signal, the PWM control signal, and the BRAKE control signal.

[0025] The power amplifier circuit includes N LMD18200 circuits and a transformer, and uses LMD18200 to amplify the amplitude and power of the square wave signal;

[0026] The switching subcircuit uses a multi-channel analog switch and adopts a patrol acquisition method to send the collected current signals and power-off status analog signals of N-channel LMD18200 circuits to the control module in a time-sharing manner after gating control.

[0027] Furthermore, the acquisition module includes a constant current source circuit and an acquisition circuit;

[0028] The constant current source circuit provides a constant 0.1mA current as an excitation signal for the Pt1000 platinum resistor temperature measurement circuit. After being selected by the multi-channel analog switch of the switching sub-circuit, it is sent to each Pt1000 platinum resistor as the power input. The constant current source circuit is equipped with an internal platinum resistor simulation circuit to simulate the voltage of the platinum resistor at a fixed resistance value at different temperatures, providing an internal reference for the platinum resistor temperature curve at different temperatures.

[0029] The acquisition circuit completes the temperature acquisition of the thermistor and the platinum resistor; the acquisition circuit includes two ADs, one for conventional temperature acquisition and the other for high-precision temperature acquisition; when the temperature at the Pt1000 platinum resistor meets the range of -30℃~30℃, the high-precision temperature acquisition is started under the control of the control module; otherwise, the conventional temperature acquisition of the MF601 thermistor and the Pt1000 platinum resistor is started.

[0030] Furthermore, the control module controls the acquisition module to complete the temperature acquisition of the Pt1000 platinum resistor and the MF601 thermistor, and at the same time outputs the control signals required by the sinusoidal wave heating module and the square wave heating module; the temperature of the non-magnetic heater is controlled according to the collected temperature value and the preset temperature control strategy. When the collected temperature enters the high-precision temperature measurement range, the high-precision temperature measurement and control function is started, and temperature control under different temperature control mechanisms and accuracies is achieved through sinusoidal wave amplitude modulation and square wave duty cycle adjustment.

[0031] Furthermore, the temperature control mode of the control module includes closed-loop temperature control, open-loop stop heating, and open-loop heating;

[0032] The control parameters of each temperature control loop can be set from the ground through injection commands. The injection parameters include: temperature control point selection and modification, temperature control target value modification, integral adjustment parameter Ki modification, proportional adjustment parameter Kp modification, and temperature control mode modification. The downlink telemetry parameters include four-wire platinum resistance measurement temperature, heating circuit duty cycle, heating circuit control mode, and heating circuit temperature control parameters.

[0033] In the open-loop temperature control circuit, the working state of the open-loop temperature control circuit is set by the ground injection command, and the command setting is the heater heating state or the heater stopping heating state;

[0034] The closed-loop temperature control adopts a switching and incremental PI control algorithm. PI control is used within the temperature control threshold range, and switching control is used outside the temperature control threshold. The specific processes of the switching and incremental PI control algorithms are as follows:

[0035] Step1: Obtain the temperature value T(k) of the controlled point at the k-th sampling moment;

[0036] Step2: Calculate the temperature deviation e(k) = Tsp - T(k); Tsp is the controlled target temperature;

[0037] Step3: When T(k) > Tup or T(k) < Tlow, adopt switching control; if T(k) < Tlow, the non-magnetic heater is turned on for heating, and the heating duration t(k) of the non-magnetic heater is set to Ts, where Ts is the temperature control period; if T(k) > Tup, the non-magnetic heater is turned off for heating, and the heating duration t(k) of the non-magnetic heater is set to 0; go to Step6;

[0038] Step4: When Tlow ≤ T(k) ≤ Tup, according to the incremental PI control algorithm, obtain the heating duration increment value △t(k) of the non-magnetic heater and calculate the heating duration t(k) of the non-magnetic heater within the time period from k*Ts to (k + 1)*Ts as follows:

[0039] △t(k) = Kp * [e(k) - e(k - 1)] + Ki * e(k);

[0040] t(k) = t(k - 1) + △t(k);

[0041] Step5: Before the controller outputs, perform a threshold judgment on the heating duration t(k) of the non-magnetic heater: if t(k) < 0, set t(k) = 0; if t(k) > Ts, set t(k) = Ts;

[0042] Step6: Calculate the heating duty cycle w(k) of the non-magnetic heater = (Us / Uf) * INT((t(k) / Ts) * 100);

[0043] where, Us represents the nominal bus voltage, Uf represents the actual bus voltage; INT() represents taking the integer;

[0044] Step7: Return to Step1 and wait for the next control cycle.

[0045] Furthermore, at a position where the distance vector magnetometer ≤ 400 mm, sinusoidal amplitude modulation heating is adopted; at a position where the distance vector magnetometer > 400 mm, square wave duty cycle modulation heating is adopted.

[0046] The advantages of the present invention compared with the prior art are as follows:

[0047] To meet the high temperature stability and non-magnetic requirements of the magnetic measurement optical platform, a special high-precision non-magnetic thermal control system was designed. Using a PID temperature control algorithm, high-precision non-magnetic temperature closed-loop control of the optical platform is achieved. At a distance close to the vector magnetometer (this system recommends no more than 400mm), a sinusoidal wave amplitude modulation heating method is used to reduce the magnetic interference generated by the heater on the magnetometer during operation. At a distance far from the vector magnetometer (this system recommends no less than 400mm), a more efficient square wave duty cycle heating method is used to reduce the power demand on the satellite. At the same time, the heater improves the traditional copper foil / wire material and uses low-magnetic manganese copper foil / wire. It also adopts a double-layer four-circuit demagnetization design to reduce the residual magnetic interference generated by the heater on the vector magnetometer during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a typical schematic diagram of a magnetic measurement optical platform system;

[0049] Figure 2 This is a schematic diagram of the high-precision non-magnetic thermal control system of the magnetic measurement optical platform;

[0050] Figure 3 This is a schematic diagram of the leads of a four-wire platinum resistor assembly;

[0051] Figure 4 This is a schematic diagram of the wiring method of the upper and lower layers of a double-layer four-circuit heating plate;

[0052] Figure 5 This is a schematic diagram of the heating circuit wiring design;

[0053] Figure 6 This is a schematic diagram of the sinusoidal wave heating module;

[0054] Figure 7 It is a schematic diagram of four square wave timing designs;

[0055] Figure 8 This is a schematic diagram of the square wave heating module;

[0056] Figure 9 This is a schematic diagram of the acquisition module;

[0057] Figure 10 It is a closed-loop temperature control flow chart. DETAILED DESCRIPTION

[0058] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments:

[0059] like Figure 1As shown in the figure, a typical magnetic measurement optical platform consists of an extension rod, a carbon fiber arm, kinematic supports, a star-sensing bracket, a thermal control cabin, a vector magnetometer, and three star sensors. The vector magnetometer is typically a spherical sensor mounted at the front end of the carbon fiber arm. The star sensor is mounted on the star-sensing bracket, and the carbon fiber arm and star-sensing bracket are assembled together by gluing. The entire vector magnetometer, carbon fiber arm, star sensor, and star-sensing bracket constitute the main optical platform. The main optical platform is mounted on the extension rod via kinematic supports. An enclosed thermal control cabin is installed outside the carbon fiber arm, star-sensing bracket, and vector magnetometer. By coating the thermal control cabin with multiple layers of thermal control, active thermal control measures are implemented to provide a stable temperature environment for the entire optical platform, ensuring its thermal stability and, therefore, the measurement accuracy of the vector magnetometer.

[0060] like Figure 2 As shown in the figure, the non-magnetic thermal control system for an optical platform consists of a high-precision non-magnetic thermal control assembly, a non-magnetic heater, and a temperature sensor. The temperature sensors, primarily Pt1000 platinum resistors and MF601 thermistors, are attached to various temperature measurement points in the thermal control chamber to measure the temperature. Non-magnetic heaters are attached to various locations in the thermal control chamber and drive current to heat the chamber. The non-magnetic thermal control assembly controls the temperature sensor to acquire the chamber's temperature. A PID temperature control algorithm is then used to control the heating of the non-magnetic heater, completing the closed-loop temperature control of the optical platform.

[0061] In theory, a sinusoidal-wave driven heating circuit only generates an alternating magnetic field with a single drive frequency. If the alternating magnetic field frequency exceeds the bandwidth of the vector magnetometer (typically no more than 30 Hz), it will not affect the operation of the vector magnetometer. Therefore, at a relatively close distance from the vector magnetometer (this system recommends no more than 400 mm), the heater is heated using a sinusoidal-wave heating method with a sinusoidal operating frequency of 100 kHz. Sine-wave operation generates significant additional heat loss. Considering the limited energy supply capacity of the satellite, at a relatively long distance from the vector magnetometer (this system recommends more than 400 mm), the magnetic field generated by the heating current decays rapidly with distance, essentially having no impact on the normal operation of the vector magnetometer. Instead, a square-wave drive with lower additional heat loss and higher heating efficiency is used to heat the heater at a square-wave operating frequency of 200 kHz.

[0062] The Pt1000 platinum resistor uses a constant current source four-wire temperature measurement technology. The non-magnetic thermal control component's constant current source circuit provides a 0.1mA current as an excitation signal. The Pt1000 resistor converts the temperature into a standard voltage analog value, completing high-precision temperature acquisition at the optical platform's measurement points. This is then fed to the non-magnetic thermal control component for high-precision closed-loop temperature control of the optical platform. The Pt1000 platinum resistor operates within a temperature range of -30°C to +50°C, with a temperature measurement accuracy better than ±0.1°C. Temperature stability is better than ±0.05°C in the -10°C to +10°C range and better than ±0.1°C in other temperature ranges.

[0063] like Figure 3 As shown, the Pt1000 resistor uses a four-wire assembly, including power supply C1+, power supply C2-, and data acquisition P1+ and P2-. To reduce magnetic interference generated by the resistor's operating current, the loop area formed by power supply C1+ and power supply C2- must be as small as possible. C1+ and C2- are designed to be adjacent. The resistor's lead wires, C1+ and C2-, are twisted, with the distance between adjacent twist points no greater than 20mm. P1+ and P2- are twisted, with the distance between adjacent twist points no greater than 25mm.

[0064] MF601 is mainly used for temperature measurement of other parts on optical platforms that do not require high-precision temperature measurement. Its operating temperature range is -30℃ to +30℃, with temperature measurement accuracy better than ±0.2℃ and temperature measurement stability better than ±0.2℃.

[0065] The heaters are either thin-film or cable-type. Cable-type heaters are primarily used for heating the optical platform's kinematic support legs. Thin-film heaters are affixed to other areas of the optical platform. Thin-film heaters consist of a heating strip and upper and lower insulation layers, while cable-type heaters consist of a central heating wire and an outer insulation layer. Conventional heating strips and wires are made of Constantan foil / wire. Constantan foil contains over 30% nickel, resulting in significant residual magnetism. To meet the residual magnetism requirements of non-magnetic heaters, the heating strips and wires were made of 6J8 manganese copper foil / wire, which is essentially nickel-free.

[0066] like Figure 4 As shown, the thin-film electric heater adopts a double-layer four-circuit magnetic field offset design to minimize the interference of the magnetic field generated by the working current of the electric heater on the vector magnetometer when the electric heater is working.

[0067] The thin-film electric heater includes two layers of heating plates, the lower layer of which includes a first main circuit and a first backup circuit. The first main circuit includes an A1 outlet point and an A1' outlet point, and the first backup circuit includes a B1 outlet point and a B1' outlet point. The upper layer of the heating plate includes a second main circuit and a second backup circuit. The second main circuit includes an A2 outlet point and an A2' outlet point, and the second backup circuit includes a B2 outlet point and a B2' outlet point.

[0068] After bonding the upper and lower heating sheets, the heating wires of the first and second main circuits must overlap vertically, and the heating wires of the first and second backup circuits must overlap vertically. The two lead-out points of each circuit (including the upper main circuit, upper backup circuit, lower main circuit, or lower backup circuit) must be as close as possible while meeting process requirements. The four lead-out points of the upper and lower main circuits and the four lead-out points of the backup circuits must be as close as possible. The four lead-out points of the upper and lower main circuits and the backup circuits must be arranged as close as possible. The four lead-out points of the upper and lower heating sheets are arranged in a cross pattern. All circuit leads are twisted-pair wires to eliminate magnetic fields on the circuit traces.

[0069] The resulting heating circuit is usually composed of multiple thin film electric heaters connected in series, such as Figure 5 As shown, taking two thin-film electric heaters connected in series as an example, the current flows as follows: A1 outlet point of the lower heating plate of the first heater → A1' outlet point of the lower heating plate of the first heater → A1 outlet point of the lower heating plate of the second heater → A1' outlet point of the lower heating plate of the second heater → A2' outlet point of the upper heating plate of the second heater → A2 outlet point of the upper heating plate of the second heater → A2' outlet point of the upper heating plate of the first heater → A2 outlet point of the upper heating plate of the first heater.

[0070] The non-magnetic temperature control component is responsible for completing the high-precision temperature acquisition and temperature control tasks of the optical platform. Figure 2 As shown, the non-magnetic thermal control assembly includes a sinusoidal heating module, a square-wave heating module, an acquisition module, a control module, and a power module. The sinusoidal heating module generates multiple 100kHz sine waves with adjustable amplitude, while the square-wave heating module generates multiple 200kHz square waves with adjustable duty cycles, respectively implementing sinusoidal and square-wave heating of the non-magnetic heater. The acquisition module provides the 0.1mA constant current required by the Pt1000 platinum resistor, controlling the Pt1000 platinum resistor and the MF601 thermistor to acquire temperatures at the optical platform measurement points. The control module uses a PID control algorithm based on the collected optical platform temperature data to achieve closed-loop heating control of the heater. The power module provides the ±12V and +13.2V heating drive voltages required by the heating module.

[0071] The sinusoidal heating module mainly generates multiple 100kHz sine waves with adjustable amplitude to complete the sinusoidal drive control of the heating circuit. At the same time, it collects the working voltage of the sinusoidal wave and sends it to the control module after conditioning. Figure 6 As shown, the sinusoidal heating module consists of a sinusoidal wave frequency control circuit, a sinusoidal wave generating circuit, a power amplifying circuit and an exchange sub-circuit.

[0072] like Figure 6 As shown, the sine wave frequency control circuit receives the control signal and four 100kHz square wave signals sent by the control module, and outputs the DA control signal and 100kHz square wave signal required by the sine wave generating circuit. Figure 7 As shown, to reduce the power demand of the sine wave on the power supply, the square wave signal sent by the control module is designed with four timings. The four square wave signals are divided into two groups, each containing two square wave signals. The two square wave signals in each group are 180° out of phase, and the square wave signals between the two groups are 90° out of phase. Under the control of the control signal, the sine wave control circuit selects one of the sine wave signals to output to the sine wave generation circuit.

[0073] The sine wave generator circuit converts the square wave signal into an amplitude-adjustable sine wave signal. Figure 6 As shown, the sine wave transmission circuit consists of a bandpass filter, a DA, a multiplier, and an amplifier circuit. The bandpass filter circuit conditions the 0-5V, 100kHz square wave signal sent from the sine wave control circuit into a 100kHz sine wave with a peak-to-peak value of approximately 5V. The multiplier multiplies two analog signal factors, multiplying the sine wave output from the bandpass filter by the DA output. The multiplier's output is equal to the product of the two input factors divided by 10. The DA's maximum output amplitude is 2.5V, so the multiplier's maximum output is 1.25V (2.5V × 5V ÷ 10 = 1.25V). To effectively drive the heater, an amplifier is designed after the multiplier. It uses in-phase proportional amplification with an amplification factor of approximately 8, amplifying the sine wave's amplitude to 10V.

[0074] like Figure 6 As shown, the power amplifier circuit consists of a power amplifier and a transformer. The power amplifier circuit amplifies the power and amplitude of the 10V, 100kHz sinusoidal signal generated by the sine wave generator circuit, ultimately outputting a 40V, 100kHz sinusoidal signal. The switching subcircuit switches the analog sine wave voltages collected from each heating circuit and outputs them to the control module.

[0075] The square wave heating module primarily generates multiple 200kHz square waves with adjustable duty cycles to control the square wave drive of the heating circuit. It also collects the square wave operating voltage, conditions it, and sends it to the control module. Square wave heating uses an H-bridge circuit to generate bidirectional square wave drive, controlling the heater's on and off state. The H-bridge circuit driver chip utilizes the LMD18200, a specialized H-bridge component for motion control. The LMD18200 amplifies the 0-5V input signal into an AC square wave with a voltage range of -13.2V to 13.2V. This is then isolated and boosted using a transformer, resulting in a final output voltage of no less than 40V. The DIR control signal controls the output frequency of the 200kHz AC square wave, while the PWM and Brake control signals adjust the duty cycle for temperature control. The duty cycle is designed to be 5kHz with 40 adjustable steps.

[0076] like Figure 8 As shown, the square wave heating module consists of a square wave control circuit, a power amplifier circuit, and a switching subcircuit. The square wave control circuit receives control signals such as the DIR signal, data line, address line, and board select signal from the control module. After decoding and latching, it outputs the DIR signal, PWM signal, and BRAKE signal required by the LMD18200 power amplifier circuit. The power amplifier circuit contains N LMD18200 circuits and a transformer, using the LMD18200 to amplify the amplitude and power of the square wave signal. The switching subcircuit uses a multi-channel analog switch and a polling acquisition method to collect analog signals such as current and power-on / off status from the N LMD18200 circuits. After gating, it transmits them to the control module in a time-sharing manner.

[0077] The acquisition module mainly realizes the temperature acquisition of Pt1000 platinum resistance and MF601 thermistor. Figure 9 As shown, the acquisition module consists of a constant current source circuit and an acquisition circuit. The constant current source circuit provides a constant 0.1mA current as an excitation signal to the Pt1000 platinum resistor temperature measurement circuit. After selection by the switching subcircuit's multi-channel analog switch, it is supplied to each Pt1000 platinum resistor as its power input. The constant current source circuit incorporates an internal platinum resistor simulation circuit to simulate the voltage measured when the platinum resistor has a fixed resistance at different temperatures, providing an internal reference for the platinum resistor temperature curve at different temperatures. The acquisition circuit primarily acquires the temperature of the thermistor and platinum resistor. The acquisition circuit incorporates two ADs, one for routine temperature acquisition and the other for high-precision temperature acquisition of the platinum resistor. When the platinum resistor temperature falls between -30°C and 30°C, high-precision temperature acquisition is initiated under the control of the control module. Otherwise, routine temperature acquisition is performed for the MF601 thermistor and platinum resistor.

[0078] The control module mainly controls the acquisition module's exchanger and AD to complete the temperature acquisition of the Pt1000 platinum resistor and MF601 thermistor, and simultaneously outputs the control signals required by the sine wave heating module and the square wave heating module. The control module controls the temperature of the heating plate based on the collected temperature value and the preset temperature control strategy (the control mode and related parameters of the heating plate can be injected through the upstream path, including the temperature control cycle, thermistor channel number, upper and lower temperature control limits, PID value, etc.). When the collected temperature enters the high-precision temperature measurement range, the high-precision temperature measurement function is activated, and high-stability temperature control under different temperature control mechanisms and accuracies is achieved through sinusoidal wave amplitude modulation and square wave duty cycle adjustment.

[0079] The power module converts the 28V bus voltage into the +5V and ±12V voltages required by the non-magnetic thermal control assembly's internal control circuits. It also converts the 28V heating bus voltage into the ±12V required by the sine-wave heating circuit and the +13.2V required by the square-wave heating circuit. The 28V bus and the 28V heating bus are independent and isolated.

[0080] like Figure 10 As shown, the workflow of the high-precision temperature control of the present invention is as follows:

[0081] After power-on or reset, the program is initialized. The initialization content includes: running the original PROM program and using the program default parameters; power-on self-test; initializing the lower computer hardware environment; initializing software operating parameters; watchdog enable and timer reset; setting and initializing the data storage area; all temperature control loops are set to the default state (open loop closed).

[0082] After initialization is complete, periodic automatic acquisition of temperature parameters is initiated and stored in the data area. Temperature measurement employs software filtering to reduce measurement errors caused by transient interference. The temperature acquisition cycle is ≤ 5 seconds. The functional relationship between the temperature measurement component and the temperature value is shown in the following equation.

[0083]

[0084] Where: R0 is the resistance value of the platinum resistor at a temperature of 0°C; Rt is the resistance value of the platinum resistor at a temperature of t; A and B are coefficients fitted according to the calibration data.

[0085] The optical platform's temperature control modes include closed-loop temperature control, open-loop heating stop, and open-loop heating. All temperature control loops have the ability to modify the temperature control mode through indirect commands. The control parameters of each temperature control loop can be set from the ground through injected commands. Injected parameters include: temperature control point selection and modification, temperature control target value modification, temperature control parameter (Ki, Kp) modification, temperature control mode modification (closed-loop temperature control, open-loop off, open-loop on), and other parameters. In order to reflect the status of the software and hardware, the corresponding telemetry parameters are designed to be transmitted, including four-wire platinum resistance temperature measurement, heating circuit duty cycle, heating circuit control mode, heating circuit temperature control parameters, etc.

[0086] In the open-loop temperature control circuit, there is no need to judge the temperature measurement value of the temperature measuring resistor. The working state of the open-loop temperature control circuit is completely set by the ground injection instruction, and the instruction setting is whether the heater is heating or the heater stops heating.

[0087] Closed-loop temperature control utilizes an on-off + incremental PI control algorithm. PI control is used within the temperature control threshold range, and on-off control is used outside the threshold range. The Kp and Ki parameters for PI control are calculated based on the thermal model of the controlled object and verified through experimental verification. The upper and lower temperature control thresholds, Kp, and Ki parameters can be modified online.

[0088] The main parameters of the switch + incremental PI control algorithm include:

[0089] 1) p: proportion;

[0090] 2) i: integral;

[0091] 3) Kp parameter: proportional adjustment coefficient, affecting the response speed of the system;

[0092] 4) Ki parameter: integral adjustment parameter, affecting the steady-state error of the system;

[0093] 5) Ts: temperature control period;

[0094] 6) Tup: upper limit of temperature control threshold;

[0095] 7) Tlow: upper limit of temperature control threshold;

[0096] 8) Us: nominal bus voltage (40(V));

[0097] 9)Uf: Actual bus voltage (V).

[0098] The specific process of the switch + incremental PI control algorithm is as follows:

[0099] Step 1: The temperature value of the controlled point obtained at the kth sampling moment is T(k);

[0100] Step 2: Calculate the temperature deviation e(k) = Tsp (controlled target temperature) - T(k);

[0101] Step 3: When T(k) > Tup or T(k) < Tlow, adopt on-off control. If T(k) < Tlow, the non-magnetic heater starts heating, and set the heating duration of the non-magnetic heater t(k) = Ts (control temperature cycle); if T(k) > Tup, the non-magnetic heater stops heating, and the heating duration of the non-magnetic heater t(k) = 0; go to Step 6;

[0102] Step 4: When Tlow ≤ T(k) ≤ Tup, based on the incremental PI control algorithm, obtain the heating duration increment value of the non-magnetic heater during the period from k*Ts to (k + 1)*Ts as △t(k), and the heating duration of the non-magnetic heater is t(k). The calculations of △t(k) and t(k) are as follows:

[0103] △t(k) = Kp * [e(k) - e(k - 1)] + Ki * e(k);

[0104] t(k) = t(k - 1) + △t(k)

[0105] Step 5: Before the controller outputs, perform a threshold judgment on t(k): if t(k) < 0, then set t(k) = 0; if t(k) > Ts, then set t(k) = Ts;

[0106] Step 6: Calculate the duty cycle of the non-magnetic heater w(k) = (Us / Uf) * INT((t(k) / Ts) * 100); INT() represents taking the integer;

[0107] Step 7: Return to Step 1 and wait for the next control cycle.

[0108] The on-off control of the non-magnetic heater adopts a grouping method, which staggers the control switch timings of each heater circuit, avoids multiple heaters from switching on and off simultaneously, reduces the fluctuating current, and thus reduces the magnetic field interference generated by the heating current.

[0109] When each closed-loop temperature control loop corresponds to multiple temperature measuring resistors, the selection principle of the temperature measuring resistors used in the control algorithm is as follows: for the heating circuit controlled by a specified resistor, the default resistor is initially selected as the temperature reference for temperature control; a certain temperature measuring resistor can be forcibly selected as the temperature reference for temperature control through ground data injection. For the heating circuit controlled by the minimum value, it is initially set to select the minimum value of the temperatures measured by multiple temperature measuring resistors as the temperature reference for temperature control; the temperature control mode can be changed to specified resistor control through ground data injection, and a certain temperature measuring resistor can be forcibly selected as the temperature reference for temperature control.

[0110] The closed-loop temperature control circuit is designed with a corresponding safety mode, which makes a numerical safety judgment on the temperature reference selected for temperature control: for a heating circuit with specified resistance temperature control, when the measured temperature value exceeds the specified normal range (-30 to +30°C) and the exceedance duration exceeds 10 seconds, the temperature control circuit selects the backup temperature control reference four-wire platinum resistance component; if the measured temperature value still exceeds the specified normal range (-30 to +30°C) after switching to the backup four-wire platinum resistance component and the exceedance duration exceeds 10 seconds, the heating circuit is switched to the open-loop state to stop heating.

[0111] The non-magnetic thermal control system can achieve a temperature stability of ±0.2°C, and the magnetic field interference generated at a distance of 3 cm from the vector magnetometer is no more than 0.1nT.

[0112] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform, characterized by: Including non-magnetic thermal control components, non-magnetic heaters, and temperature sensors; Temperature sensors are attached to different temperature measurement points on the thermal control cabin of the magnetic measurement optical platform to measure the temperature of the thermal control cabin; The non-magnetic heater is attached to different parts of the thermal control cabin and heats the thermal control cabin by driving current; The non-magnetic thermal control component uses the PID temperature control algorithm according to the temperature value collected by the temperature sensor and the preset temperature control strategy. It controls the heating of the non-magnetic heater through sinusoidal wave amplitude modulation heating and square wave duty cycle heating to achieve temperature control of the thermal control cabin.

2. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 1, characterized in that: The temperature sensor uses a Pt1000 platinum resistor and an MF601 thermistor; the temperature measurement point is collected with high precision through the Pt1000 platinum resistor; Among them, the Pt1000 platinum resistor adopts a four-wire component, including power supply C1+, power supply C2-, acquisition P1+, and acquisition P2-; power supply C1+ and power supply C2- are set in adjacent positions, and the lead wires of the Pt1000 platinum resistor power supply C1+ and C2- are twisted, and the distance between adjacent twisting points is not more than 20mm; the lead wires of the acquisition P1+ and P2- are twisted, and the distance between adjacent twisting points is not more than 25mm.

3. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 2, characterized in that: The non-magnetic heater adopts a thin film electric heater and a cable electric heater; Film type electric heaters and cable type electric heaters use 6J8 manganese copper foil / wire to make electric heating lines and electric heating wires; The thin-film electric heater uses a double-layer four-circuit design for magnetic field offset. The thin-film electric heater includes two layers of heating plates, the lower layer of which includes a first main circuit and a first backup circuit. The first main circuit includes outlet points A1 and A1', and the first backup circuit includes outlet points B1 and B1'. The upper layer of the heating plate includes a second main circuit and a second backup circuit. The second main circuit includes outlet points A2 and A2', and the second backup circuit includes outlet points B2 and B2'. After the upper and lower heating plates are bonded, the heating wires of the first main circuit and the second main circuit are required to overlap up and down, and the heating wires of the first backup circuit and the second backup circuit are required to overlap up and down; the upper and lower heating plates have a total of four outlet points arranged crosswise; all circuit leads are twisted pair cables.

4. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 3, characterized in that: The non-magnetic thermal control component includes a sinusoidal heating module, a square wave heating module, an acquisition module, a control module and a power module. The sinusoidal heating module generates several sinusoidal waves with adjustable amplitudes, and the square wave heating module generates several square waves with adjustable duty cycles, respectively performing sinusoidal wave heating and square wave heating on the non-magnetic heater. The acquisition module controls the temperature sensor to collect temperature at the temperature measurement point. The control module uses a PID control algorithm to complete closed-loop heating control of the heating plate based on the collected optical platform temperature measurement data. The power module provides the heating drive voltage required by the sinusoidal heating module and the square wave heating module.

5. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 4, characterized in that: The sinusoidal heating module includes a sinusoidal wave frequency control circuit, a sinusoidal wave generating circuit, a power amplifying circuit and an exchange subcircuit; The sine wave frequency control circuit receives a control signal and several square wave signals sent by the control module, and outputs a DA control signal and a square wave signal required by the sine wave generating circuit. The square wave signal sent by the control module is set with four timing sequences. The four square wave signals are divided into two groups, each group containing two square wave signals. The two square wave signals in each group have a phase difference of 180°, and the square wave signals between the two groups have a phase difference of 90°. Under the control of the control signal sent by the control module, the sine wave frequency control circuit selects one of the square wave signals with different timing sequences to output to the sine wave generating circuit. The sine wave generating circuit converts the square wave signal into an amplitude-adjustable sine wave signal; The power amplifier circuit amplifies the power and amplitude of the sinusoidal signal generated by the sinusoidal wave generating circuit, and outputs the sinusoidal wave signal with power and amplitude amplification to the switching sub-circuit; The switching subcircuit switches and outputs the collected sinusoidal voltage analog quantities to the control module.

6. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 4, characterized in that: The square wave heating module includes a square wave control circuit, a power amplifier circuit and an exchange subcircuit; The square wave control circuit receives the control signals sent by the control module, including the DIR control signal, the data line control signal, the address line control signal, and the board selection signal control signal. After decoding and latching, it outputs the control signals required by the power amplifier circuit LMD18200, including the DIR control signal, the PWM control signal, and the BRAKE control signal. The power amplifier circuit includes N LMD18200 circuits and a transformer, and uses LMD18200 to amplify the amplitude and power of the square wave signal; The switching subcircuit uses a multi-channel analog switch and adopts a patrol acquisition method to send the collected current signals and power-off status analog signals of N-channel LMD18200 circuits to the control module in a time-sharing manner after gating control.

7. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 6, characterized in that: The acquisition module includes a constant current source circuit and an acquisition circuit; The constant current source circuit provides a constant 0.1mA current as an excitation signal for the Pt1000 platinum resistor temperature measurement circuit. After being selected by the multi-channel analog switch of the switching sub-circuit, it is sent to each Pt1000 platinum resistor as the power input. The constant current source circuit is equipped with an internal platinum resistor simulation circuit to simulate the voltage of the platinum resistor at a fixed resistance value at different temperatures, providing an internal reference for the platinum resistor temperature curve at different temperatures. The acquisition circuit completes the temperature acquisition of the thermistor and the platinum resistor; the acquisition circuit includes two ADs, one for conventional temperature acquisition and the other for high-precision temperature acquisition; when the temperature at the Pt1000 platinum resistor meets the range of -30℃~30℃, the high-precision temperature acquisition is started under the control of the control module; otherwise, the conventional temperature acquisition of the MF601 thermistor and the Pt1000 platinum resistor is started.

8. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 7, characterized in that: The control module controls the acquisition module to complete the temperature acquisition of the Pt1000 platinum resistor and the MF601 thermistor, and simultaneously outputs the control signals required for the sine wave heating module and the square wave heating module; it controls the temperature of the non-magnetic heater according to the acquired temperature value and the preset temperature control strategy. When the acquired temperature enters the high-precision temperature measurement range, it starts the high-precision temperature measurement and control function, and realizes the temperature control under different temperature control mechanisms and precisions through sine wave amplitude modulation and square wave duty cycle modulation.

9. The high-precision non-magnetic thermal control system for a geomagnetic measurement satellite magnetic optical platform according to claim 8, characterized in that: The temperature control modes of the control module include closed-loop temperature control, open-loop stop heating, and open-loop heating. The control parameters of each temperature control loop can be set by the ground through injection commands; the uploaded parameters include: selection and modification of the temperature control point, modification of the temperature control target value, modification of the integral regulation parameter Ki, modification of the proportional regulation parameter Kp, and modification of the temperature control mode; the downlinked telemetry parameters include the temperature measured by the four-wire platinum resistor, the duty cycle of the heating loop, the control mode of the heating loop, and the temperature control parameters of the heating loop. In the open-loop temperature control loop, the working state of the open-loop temperature control loop is set by the ground upload command, and it is set through the command whether the heater heats or the heater stops heating. Closed-loop temperature control adopts the switch and incremental PI control algorithms. PI control is used within the temperature control threshold range, and switch control is used outside the temperature control threshold; the specific processes of the switch and incremental PI control algorithms are as follows: Step1: Obtain the temperature value T(k) of the controlled point at the kth sampling moment. Step2: Calculate the temperature deviation e(k) = Tsp - T(k); Tsp is the controlled target temperature. Step3: When T(k) > Tup or T(k) < Tlow, adopt switch control; if T(k) < Tlow, the non-magnetic heater starts heating, and set the heating duration t(k) of the non-magnetic heater = Ts, where Ts is the temperature control period; if T(k) > Tup, the non-magnetic heater stops heating, and the heating duration t(k) of the non-magnetic heater = 0; go to Step6. Step4: When Tlow ≤ T(k) ≤ Tup, according to the incremental PI control algorithm, obtain the heating duration increment value △t(k) of the non-magnetic heater and the calculation of the heating duration t(k) of the non-magnetic heater within the time period k*Ts~(k + 1)*Ts are as follows: △t(k) = Kp * [e(k) - e(k - 1)] + Ki * e(k); t(k) = t(k - 1) + △t(k); Step5: Before the controller outputs, perform a threshold judgment on the heating duration t(k) of the non-magnetic heater: if t(k) < 0, set t(k) = 0; if t(k) > Ts, set t(k) = Ts. Step6: Calculate the heating duty cycle w(k) of the non-magnetic heater = (Us / Uf) * INT((t(k) / Ts) * 100); where, Us represents the nominal bus voltage, Uf represents the actual bus voltage; INT() represents taking the integer. Step7: Return to Step1 and wait for the next control cycle.

10. The high-precision non-magnetic thermal control system for a magnetic measurement optical platform of a geomagnetic measurement satellite according to claim 9, characterized in that: When the distance from the vector magnetometer is ≤400mm, sinusoidal wave amplitude modulation heating is adopted; when the distance from the vector magnetometer is greater than 400mm, square wave duty cycle modulation heating is adopted.

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