Preface Before launch, it takes several hours to transport a certain type of satellite developed in China from the installation factory to the launch tower. As the electronic and optical instruments carried by the satellite become increasingly sophisticated, their requirements for environmental parameters also become increasingly stringent [1-2]. Therefore, there are strict requirements for the air quality inside the fairing containing the satellite during transportation. A special air conditioning system needs to be installed on the satellite transport vehicle to control its various parameters—temperature, humidity, pressure, and purification index—to meet the technical requirements of the air inside the satellite fairing. [b]1 Development Requirements and Device Characteristics[/b] 1.1 Development Requirements The satellite vehicle-mounted air conditioning system is used in areas with harsh climate conditions. The temperature controllable range is -20℃ to 35℃, and the relative humidity is 15% to 85%. The air inside the satellite fairing must be at a positive pressure of more than 50Pa and its cleanliness must reach Class 100,000. The vehicle air conditioning system must be safe, reliable, and have minimal temperature and humidity fluctuations during operation; the operating conditions inside the satellite enclosure should be adjustable within the specified temperature and relative humidity range; the temperature control accuracy should be ±0.5℃, and the relative humidity control accuracy should be ±4%; and the system should be able to quickly adjust from the initial state to any state within the specified range. 1.2 Characteristics of the Air Conditioning Unit Due to the special nature of this system, it is required to be reliable, cost-effective, and easy to operate. Through extensive calculations and analysis and comparison of various schemes [2-3], the air handling scheme shown in Figure 1 was determined to ensure that the air conditioning parameters inside the satellite enclosure meet the technical requirements. Fresh air is drawn into the fresh air duct by the fresh air fan through the fresh air inlet located on the roof. The fresh air then passes through a coarse filter and enters the air conditioning unit, where it mixes with the return air. After being cooled and dehumidified by the evaporator, heated and humidified by the heater and humidifier, and purified by the medium-efficiency filter and high-efficiency filter, the required air supply conditions are achieved. The cleanliness of the air inside the enclosure, the total volatile organic compounds, and the total amount of non-volatile residues must be tested. In addition, during operation, the vehicle air conditioning system needs to replenish the air leaked inside the enclosure, especially to ensure that the relative humidity reaches a minimum of 15%. Therefore, the return air system adopts a combination of primary and secondary return air. A secondary return air duct is installed in the air duct, and a variable frequency fan is used to regulate the airflow to achieve dehumidification and anti-frost purposes, ensuring stable operation. The air conditioning unit flow chart is shown in Figure 1. [b]2 Development of the Measurement and Control System[/b] 2.1 Overall Design Scheme The automatic monitoring system for satellite air conditioning units involves three control objects: return air temperature, return air humidity, and enclosure pressure. Due to the high accuracy requirements of the air conditioning environment control parameters and the absolute reliability of the system operation, the design focuses on high precision and reliability. For measuring operating parameters, high-quality, high-precision pressure and differential pressure transmitters and temperature and humidity sensors are used. After signal conversion and isolation, the signals are sent to the data acquisition instrument. The data acquisition instrument communicates with the computer via a data bus. Regarding operating condition regulation... The single-loop closed-loop regulation method is adopted, and the traditional PID control technology is introduced into the fuzzy controller [4] to give full play to the good robustness of fuzzy control and form a fuzzy-PID automatic regulation controller. In addition, in order to increase the reliability of the system and speed up the speed at which the air conditioning system parameters enter the control range, a set of manual control system is added. In terms of system equipment control, relay control is adopted due to the special requirements of the user. The software of this system is a computer measurement and control software developed based on the WINDOWS operating platform. Its function is not limited to simple data acquisition, but also includes post-processing functions such as management and data analysis; it can perform various tasks such as setting data acquisition channel parameters, system management and test history query, test result trend curve analysis, printing test record data and curves. The hardware structure of the measurement and control system is field sensors, transmitters and actuators, intelligent digital indicator controllers, and centralized computer acquisition and processing. Its structural flowchart is shown in Figure 2. 2.2 Dynamic characteristic analysis of the controlled object The controlled object of the air conditioning system is the satellite cover, and the related controlled variables are the temperature, relative humidity and pressure inside the cover. In general, the controlled object has two channels: control channel and disturbance channel, which can also be called internal disturbance channel and external disturbance channel. When temperature is the controlled variable, the controlled object is shown in Figure 3. There are two disturbance channels: one is the heat output N1(S) inside the satellite dome, mainly the heat converted from the power of the fan in the air handling unit, the heat leakage inside the dome and the air duct, and the heat of the satellite itself, with a dynamic characteristic of W1(S); the other is the cooling output N2(S) of the refrigeration unit, with a dynamic characteristic of W2(S). The controlled object also has a control channel, which is the heat output U(S) of the electric heater. Its magnitude is determined by the controller according to its built-in algorithm based on the deviation between the controlled variable and the set value, with a dynamic characteristic of W0(S). For the controlled variable of temperature inside the satellite dome, the set temperature can be obtained by adjusting U(S) to balance N1(S) and N2(S). Similarly, when relative humidity and pressure are used as controlled variables, the controlled object is analyzed as shown in Figure 3 when temperature is adjusted. 2.3 Engineering Self-Tuning of PID Fuzzy Controller From the analysis of the controlled object of the system above, it can be seen that the controlled object of this system is the temperature, humidity, and pressure of the air inside the satellite enclosure. Furthermore, the entire air conditioning system is a large inertia and large lag element with severe nonlinear characteristics, requiring the establishment of an accurate model of the air conditioning system. This poses a challenge to the air environment system controlled by PID, making the tuning of PID parameters largely dependent on experienced engineers, resulting in difficult debugging and unsatisfactory control effects. To address this situation, the parameter self-tuning Fuzzy-PID method is adopted to compensate for the lack of an accurate model for this type of air conditioning system, making it difficult to tune PID parameters. Because a fuzzy controller is used, it does not rely on an accurate mathematical model of the system, making it particularly suitable for complex systems (or processes) and fuzzy objects. It also possesses intelligence and self-learning capabilities, continuously learning and updating the knowledge representation, fuzzy rules, and synthetic reasoning in fuzzy control through expert knowledge or mature experience. The control system is robust and can effectively overcome uncertainties such as model parameter changes and nonlinearities in dynamic systems. Considering the actual situation involved in the device, only a single-loop control system will be discussed. Here, the optimization method of the digital regulator is used to perform self-optimization tuning of the PID parameters to achieve the goal of optimizing the objective function. Figure 4 shows one self-optimization control mode in the engineering tuning method. [align=left] 2.4 Actuators and Control Loops The actuator is an indispensable and important part of the automatic control system. It consists of an execution mechanism and a regulating mechanism. In this device, the actuators for controlling the temperature and relative humidity inside the enclosure are all three-phase power regulators. The three-phase power regulators adjust the power of the electric heater and the electric humidifier according to the control signal output by the PID regulator, so that the temperature and relative humidity inside the enclosure are controlled at the set value. The actuator for controlling the pressure inside the enclosure is a frequency converter. The frequency converter adjusts the frequency of the fan according to the control signal output by the PID regulator. As mentioned in the previous analysis, when the environment inside the enclosure is in a stable operating condition, all external disturbance inputs can be approximated as constants. In actual control, the external disturbances are indeed relatively small compared with the effect of the control channel. Therefore, a single-input single-output (SISO) control loop can be used. The temperature control loop inside the satellite enclosure consists of a temperature sensor, a PID controller, a three-phase power regulator, and an electric heater (see Figure 5); the relative humidity control loop consists of a humidity sensor, a PID controller, a three-phase power regulator, and a humidifier; the pressure control system consists of a pressure transmitter, a PID controller, a frequency converter, and a fan. [b]3. Debugging and Analysis of the Measurement and Control System[/b] Before debugging the controller, the initial parameters of the PID controller must be set, including signal I/O type, response time, maximum and minimum allowed input values, over-temperature and under-temperature alarm limits, and communication address. After setting the above parameters, the PID controller parameters should be self-tuned, that is, the process characteristics of the controller's automatic detection system should be fully understood, and the optimal PID parameters should be automatically calculated for debugging. 3.1 Temperature PID Controller Parameter Self-Tuning: With a set temperature of 20℃ and humidity of 38%, when the temperature and humidity inside the enclosure approach the set conditions, switch the humidity PID controller to manual mode to maintain a constant output to avoid interference with the system. Then, activate the temperature PID controller parameter self-tuning function. This will force the system to generate disturbances. The parameter self-tuning ends when the system parameters reach the third peak and automatically switches to automatic control. The greater the system inertia, the longer the self-tuning time will be. After tuning, stability tests under other operating conditions must be performed to verify the tuning effect. Figure 6 shows the temperature change over time when the temperature is set to 40℃ and the humidity to 38% after PID parameter self-tuning. As can be seen from Figure 6, although the temperature PID controller parameter self-tuning is performed at a temperature of 20℃, the adjustment effect is also very good at 40℃, with a very stable curve and a maximum fluctuation of no more than 0.2℃. 3.2 Humidity PID Controller Parameter Self-Tuning: Similar to the temperature PID controller, a parameter self-tuning test can be performed on the humidity PID controller. The set humidity condition during self-tuning was selected as 38%. The control effect after parameter self-tuning was then tested under different humidity conditions. It can be seen that under other conditions (set condition 20%, see Figure 7), the maximum humidity fluctuation does not exceed 2%, which meets the technical requirements. 3.3 Pressure PID Controller Parameter Self-Tuning: A parameter self-tuning test was performed on the pressure PID controller. The set pressure condition during self-tuning was selected as 50 Pa. Adjustment was then performed at a pressure of 100 Pa. As shown in Figure 8, after parameter self-tuning, the pressure curve is very stable, with a maximum fluctuation of about 7 Pa, which meets the technical requirements. **4. Conclusions** The analysis and parameter self-tuning results of the temperature, humidity, and pressure monitoring and control system of the air conditioning unit show that: 1. When the temperature, humidity, and pressure stabilize under stable operating conditions, they fluctuate within a range far below the specified limits. The designed fuzzy-PID control performs well, effectively solving the problem of air disturbance caused by sudden climate changes during satellite transportation and the resulting fresh air entering the enclosure. It also makes reasonable use of limited power, meeting the requirements for air environment control within the enclosure and achieving maximum energy saving. 2. The satellite vehicle-mounted air conditioning system has a high degree of automation, stable operation, convenient operation, short system stabilization time, and high measurement accuracy, receiving high praise from users during multiple satellite launches. The successful development of this project provides important reference value for the design and application of similar products.　**References** 1. Li Zhaojian. Air Conditioning Purification Design for Xichang Satellite Launch Tower. Heating, Ventilation & Air Conditioning [J], 2000, 30(5), 56-58. 2. Li Zhaojian, Wan Caida. Design of Air Conditioning Purification System for Satellite Battery Compartment [J]. Heating, Ventilation & Air Conditioning, 2003, 33(2), 62-643. 3. Lei Xintang, Xu Lie, Li Zhaoci. Design of Refrigeration and Vacuum System for Satellite Heat Pipe Heat Transfer Test Stand [J]. Journal of Shanghai Jiaotong University, 2003, 22(2), 102-104. 4. Li Jinchuan, Zheng Zhihui. Operation and Management of Air Conditioning Refrigeration Automatic Control System. Beijing: China Building Materials Industry Press, 2002. Editor: He Shiping