This paper analyzes the first-order and first-order time-delayed systems control approaches, focusing mainly on unstable systems. First, it discusses asymmetries between the disturbance observer-based (DOB) control with decoupled tracking and the disturbance rejection responses, stressing applications to stable and unstable plants. The paper analyzes some DOB-based control solutions for unstable systems which do not use internal closed-loop stabilization. The novelty of the paper is thorough study accompanied with a comprehensive explanation of the differences between two distinct approaches: the transfer-function- and the closed-loop-based feedforward control approach from the point of view of control constraints. It is clearly illustrated that the main cause of instability of DOB-based approaches, applied to unstable systems, is given by their effort to impose on the system the unstable dynamics of the chosen nominal process model. It is also shown that the closed-loop stability of the DOB-based control, applied to the unstable systems, can be restored by using the supervising reference model control (RMC). The main novelty of the proposed approach is that its eliminates the mentioned stability problems while maintaining the full functionality of the chosen control structures. RMC has so far only been implemented for generating a setpoint feedforward signal. However, by generalization of this approach for disturbance rejection, the methodology of DOB design, based on nominal models, can be extended to the control of unstable systems. Without the use of disturbance reference models, the interactions of the master stabilizer with disturbance compensation cannot be eliminated. Without the internal stabilization, the stable transients can only be achieved by designing controllers based on stable models, instead of unstable ones. The existing modifications of DOB-based schemes for unstable plants, proposed in some references, are shown to lead to traditional Proportional-Integrative (PI) control, thus losing all the advantages over the PI controllers. In all the considered structures, the role of integrating models is also emphasized.

中文翻译：

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稳定和不稳定一阶电厂扰动补偿方法的不对称性

本文分析了一阶和一阶时滞系统的控制方法，主要关注不稳定系统。首先，它讨论了具有解耦跟踪的基于干扰观测器 (DOB) 的控制与干扰抑制响应之间的不对称性，强调了对稳定和不稳定设备的应用。本文分析了一些针对不使用内部闭环稳定的不稳定系统的基于 DOB 的控制解决方案。本文的新颖之处在于深入研究，并从控制约束的角度全面解释了两种不同方法之间的差异：基于传递函数和基于闭环的前馈控制方法。清楚地表明，应用于不稳定系统的基于 DOB 的方法不稳定的主要原因，由他们努力将所选标称过程模型的不稳定动态强加给系统。还表明，应用于不稳定系统的基于 DOB 的控制的闭环稳定性可以通过使用监督参考模型控制 (RMC) 来恢复。所提出的方法的主要新颖之处在于它消除了提到的稳定性问题，同时保持了所选控制结构的全部功能。迄今为止，RMC 仅用于生成设定值前馈信号。然而，通过这种抗扰方法的推广，基于标称模型的 DOB 设计方法可以扩展到不稳定系统的控制。在不使用干扰参考模型的情况下，主稳定器与干扰补偿的相互作用无法消除。如果没有内部稳定，稳定的瞬态只能通过基于稳定模型而不是不稳定模型设计控制器来实现。一些参考文献中提出的针对不稳定设备的基于 DOB 的方案的现有修改被证明会导致传统的比例积分 (PI) 控制，从而失去了与 PI 控制器相比的所有优势。在所有考虑的结构中，还强调了集成模型的作用。显示会导致传统的比例积分 (PI) 控制，从而失去与 PI 控制器相比的所有优势。在所有考虑的结构中，还强调了集成模型的作用。显示会导致传统的比例积分 (PI) 控制，从而失去与 PI 控制器相比的所有优势。在所有考虑的结构中，还强调了集成模型的作用。