Objective As space infrared technology advances towards high quantification, higher requirements are demanded for the precision of blackbody temperature control. Simultaneously, as spacecraft functionality becomes more complex, integrated design is necessary to reduce power consumption and weight. Traditional blackbody temperature control systems based on CPU or DSP are unable to meet the demands of high integration and high precision. To address this issue, this paper presents the design of a high-precision temperature control system for on-board blackbodies based on FPGA.
Methods Temperature acquisition and control are performed using an FPGA as the core control unit, enabling multifunctional high-speed parallel processing. The blackbody temperature measurement module adopts a three-wire Wheatstone bridge to minimize the influence of wire resistance. In the signal conditioning section, a three-stage active filtering and amplification, composed of integrated operational amplifiers, is employed to achieve low-noise amplification of the electrical output. Compared to traditional instrumentation amplifiers combined with passive filtering, this method exhibits stronger interference suppression capabilities. Additionally, to address the non-linear error between platinum resistor resistance and temperature, as well as circuit errors in the temperature measurement system, a hierarchical fitting correction method based on polynomial models and least squares theory is proposed to further improve temperature measurement accuracy. The temperature control module incorporates a novel fuzzy control and incremental PID (FIPID) combination to reduce overshoot, accelerate convergence speed, and achieve high-precision temperature control.
Results and Discussions Based on the measurement results using precision standard resistors, the temperature measurement accuracy of the system within the range of 247-375 K is 0.035 K, which is a 90.9% improvement compared to the uncorrected accuracy of 0.383 K (Tab.4). Temperature control simulation experiments demonstrate that compared to PID control, the FIPID algorithm achieves zero overshoot, while the PID algorithm has a 12.4% overshoot. Furthermore, the FIPID algorithm exhibits a 64% improvement in convergence speed (Fig.6). Ground thermal vacuum and on-orbit temperature control experiments indicate that the measured temperature control accuracy within the range of 256-367 K is 0.039 K, with a steady-state deviation not exceeding 0.018 K, and a temperature rise stabilization time of less than 10 minutes for a 10 K increase (Tab.5-6).
Conclusions Traditional blackbody temperature control systems based on CPU or DSP cannot meet the requirements for high integration and high precision. To address this issue, this paper presents the design of a high-precision integrated temperature control system for on-board blackbodies based on FPGA. The approach uses a three-wire Wheatstone bridge to minimize the influence of wire resistance and introduces three-stage active filtering and amplification to improve the system's interference suppression capabilities. To mitigate temperature measurement errors, a hierarchical fitting correction method based on polynomial models and least squares theory is proposed. Additionally, a novel fuzzy control PID temperature control algorithm is introduced in the temperature control module to achieve high-precision temperature control. Experimental results demonstrate that the temperature measurement accuracy of the system is 0.035 K, which is a 90.9% improvement compared to the pre-optimized accuracy. Temperature control simulation experiments show that this method achieves a 64% improvement in convergence speed compared to traditional PID control, with zero overshoot, while the PID algorithm exhibits a 12.4% overshoot. Ground thermal vacuum and on-orbit temperature control experiments indicate that the measured temperature control accuracy within the range of 256-367 K is 0.039 K, meeting the requirements for on-orbit high-precision calibration and high integration. The system has been successfully applied to an on-orbit infrared camera of a specific model. The system possesses the advantages of high temperature measurement and control accuracy, wide dynamic range, and ease of integration, making it suitable for widespread application in other high-precision active temperature control systems in space.
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