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为保证安全性与快速性,大型超导磁体预冷过程中需要通过冷热氦气混合来严格控制温差与压降。大型氦低温系统中这一冷热氦气混合过程具有双变量强耦合、非线性以及迟延等难控特性。为实现其自动控制,通过过程的动态特性、系统关联以及控制逻辑分析,设计了分阶段的解耦控制方案。根据相对增益计算,得出弱耦合阶段的变量匹配控制方案;强耦合阶段采用非线性乘法解耦器、不同频率的采样调节器、带有死区的非线性PID控制算法及增益调度进行解耦控制。该方案在DCS中易于实现,可用于超导磁体的降温与回温控制。实际运行结果表明,解耦后系统有较好的稳定性与鲁棒性,温差控制及时且超调量小,在确保冷却装置安全的同时又保证了降温速率,很好地满足了降温实验需求。
In order to ensure safety and rapidity, large superconducting magnets need to be strictly controlled temperature and pressure drop through the mixing of hot and cold helium during the pre-cooling process. The large helium cryogenic system has the characteristics of two variables, such as strong coupling, non-linearity and delay. In order to realize its automatic control, a decoupled control scheme is designed through the dynamic characteristics of the process, system correlation and control logic analysis. According to the relative gain calculation, we get the variable matching control scheme in the weak coupling stage. In the strong coupling stage, the nonlinear multiplicative decoupler, the sampling regulator with different frequencies, the nonlinear PID control algorithm with dead zone and the gain scheduling are decoupled control. The program is easy to implement in DCS and can be used for cooling and temperature control of superconducting magnets. The actual operation results show that the decoupled system has good stability and robustness, temperature control is timely and small overshoot, while ensuring the cooling device safety while ensuring the cooling rate, well meet the cooling needs .