空间环境模拟器液氮系统数学模型

大型空间环境模拟器的液氮系统庞大复杂，为满足确定控制方案、建立故障诊断模型、技术改造等的需要，建立液氮系统的数学模型是十分必要的。以某空间环境模拟器的液氮系统为例，建立了液氮系统的数学模型；分析了系统输入参数对系统输出参数影响；最后，应用这个模型，得到了一些有益的结论，提出了一种调节阀的准稳态控制方法。

MATHEMATICAL MODEL OF LIQUID NITROGEN SYSTEM OF SPACE ENVIRONMENTAL SIMULATOR

A mathematical model of liquid nitrogen system of a space environmental simulator is introduced and a quasi-stationary control method is developed in this paper. The variables describing the system characteristics include pressure, temperature, height of liquid, flow, etc. The input variables to the system include travel of valve, heating power, pressure of liquid nitrogen in cooler, heat load, etc. For convenience, a single-phase hermetic cycle system is divided into three blocks: cooler block, pump block and cryogenic sink block. The equations describing pressure and temperature of the three blocks are obtained, and then the mathematical model is built. The pressure, temperature and flow at each critical point in the system are obtained by solving the equations. The regulating valves of the liquid nitrogen system are typical nonlinearity elements, so the control of coupling loops is difficult. Two types of quasi-stationary control method of the regulating valves are developed in this paper, namely absolute regulating method and relative regulating method. The first method depends on the measurement of the flow of each pipe. The secondmethod does not require it and can be used in the nonlinearity control of the valves. The result shows that relative regulating method has many advantages: small overshoot, short regulating time and simple algorithm, which are needed for the control of liquid nitrogen system.