压缩式制冷系统的内模控制策略研究

发布时间：2018-06-14 12:15

本文选题：压缩机变频 + 鲁棒控制　；参考：《天津大学》2014年硕士论文

【摘要】：压缩式制冷系统通常按照最大冷、热负荷量进行设计。实际运行时，制冷系统因外界环境影响，长期工作在非额定工况下，产生冷量大于实际所需冷量，，因而造成浪费。为了保证制冷系统能够准确的“按需供给”和“逐点优化”，设计了基于内模结构的制冷系统控制策略，并通过仿真研究，验证了该策略的有效性。首先，根据实际制冷系统的实验数据，分析了制冷系统的内部特性，主要包括制冷系统主要参数变化的影响因素和变化趋势，制冷系统组件输入输出变量间的耦合关系，以及部分输出变量响应滞后的现象及原因。此外，对本研究小组提出的制冷系统六阶非线性模型进行了特点分析，说明了该模型区别于以往模型的优势，能够较为全面的体现制冷系统的主要特性，并为控制策略设计提供了依据。其次，为消除制冷系统因耦合和滞后等特性给系统运行带来的不良影响，设计出了制冷系统内模解耦控制策略。在设计时，在线辨识了制冷系统带时滞的二阶线性数学模型，并分析了该模型是否为稳态非奇异矩阵和模型逆是否存在复右半平面（RHP）极点的问题。利用分析结果，对制冷系统构建了内模控制结构，并将解耦控制纳入了控制策略设计中。另外，采用最小稳定过热度曲线优化了过热度设定点，从而设计和完善了制冷系统内模解耦控制策略。通过鲁棒性分析，给出了该策略能够保证制冷系统鲁棒稳定性的条件。在仿真实验中，分时段加入了阶跃输入信号和阶跃干扰信号，将该制冷系统内模解耦控制策略与双回路PID控制策略和带Simth预估器的解耦控制策略的控制效果进行对比，直观的展示了该策略在解耦能力和抑制扰动方面的优势。在上述仿真实验假设条件下，又加入了三种典型的不确定性条件，再次对比三种策略下的制冷系统输出响应曲线，验证了该制冷系统内模解耦控制策略在提高系统鲁棒性方面优于其他控制策略。最后，由于该制冷系统内模解耦控制策略所采用的线性模型不能完全真实地体现制冷系统的复杂性，因此提出了基于上述制冷系统六阶非线性模型的非线性内模控制策略。为了利于控制策略的设计，将上述模型简化为仿射非线性形式，并采用反馈线性化方法将其变换为伪线性形式。针对变换后的伪线性系统构建了内模控制结构，从而完成了非线性内模控制策略的设计。通过系统性能分析和鲁棒性分析，从理论上证明了该策略的有效性，并给出了保证系统鲁棒稳定性的条件。同时，仿真结果验证了该策略具有较强的解耦能力、抗扰性和鲁棒性。
[Abstract]:Compression refrigeration systems are usually designed according to maximum cooling and heat loads. In the actual operation, the refrigeration system works under non-rated working conditions for a long time because of the influence of external environment, and the cooling rate is larger than the actual required cooling rate, thus causing waste. In order to ensure the accurate "on-demand" and "point-by-point optimization" of refrigeration system, the control strategy of refrigeration system based on internal model structure is designed, and the effectiveness of the strategy is verified by simulation. Firstly, according to the experimental data of the actual refrigeration system, the internal characteristics of the refrigeration system are analyzed, including the influencing factors and the changing trend of the main parameters of the refrigeration system, and the coupling relationship between the input and output variables of the refrigeration system components. And the phenomenon and reason of partial output variable response lag. In addition, the characteristics of the sixth-order nonlinear model of refrigeration system proposed by this research group are analyzed, which shows that the model is different from the previous model and can fully reflect the main characteristics of the refrigeration system. It also provides the basis for the design of control strategy. Secondly, the decoupling control strategy of internal model of refrigeration system is designed in order to eliminate the bad effect of coupling and hysteresis on the operation of refrigeration system. In the design, the second order linear mathematical model with time delay for refrigeration system is identified online, and the problem of whether the model is a steady state nonsingular matrix and whether there exists a complex right half plane (RHP) pole in the model inverse is analyzed. Based on the analysis results, the internal model control structure of the refrigeration system is constructed, and the decoupling control is incorporated into the design of the control strategy. In addition, the minimum stable superheat curve is used to optimize the setting point of superheat, so as to design and perfect the decoupling control strategy of internal model of refrigeration system. Through the robustness analysis, the condition that the strategy can guarantee the robust stability of the refrigeration system is given. In the simulation experiment, step input signal and step interference signal are added into the simulation experiment, and the control effect of the internal model decoupling control strategy of the refrigeration system is compared with that of the double loop pid control strategy and the decoupling control strategy with Simth predictor. The advantages of the strategy in decoupling ability and disturbance suppression are demonstrated intuitively. Under the assumption of the simulation experiment above, three kinds of typical uncertainty conditions are added, and the output response curves of the refrigeration system under the three strategies are compared again. It is verified that the decoupling control strategy of internal model of refrigeration system is superior to other control strategies in improving the robustness of the system. Finally, because the linear model used in the decoupling control strategy of the refrigeration system can not fully reflect the complexity of the refrigeration system, a nonlinear internal model control strategy based on the sixth-order nonlinear model of the refrigeration system is proposed. In order to facilitate the design of control strategy, the above model is simplified to affine nonlinear form, and the feedback linearization method is used to transform it into pseudo linear form. The internal model control structure is constructed for the transformed pseudo linear system, and the nonlinear internal model control strategy is designed. Through the system performance analysis and robustness analysis, the effectiveness of the strategy is proved theoretically, and the conditions to ensure the robust stability of the system are given. At the same time, the simulation results show that the strategy has strong decoupling ability, immunity and robustness.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657

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