研究者詳細 - 瀨部　昇

論文 - 瀨部　昇

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Minimum-order exosystem-model-based disturbance observer and the relation among the disturbance observers 査読有り国際誌

Kana Shikada, Masakatsu Kawata, Noboru Sebe

SICE Journal of Control Measurement and System Integration 18 ( 1 ) 2025年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

The authors aim to show the relation among the disturbance observers. This paper considers disturbance observers, which are constructed to estimate the steady disturbance affecting the outputs of the plants with the same inputs and outputs. For such disturbance observers, Shikada and Sebe showed that the inverse-model-based disturbance observer could be realized as a full-order Luenberger-type observer for the nominal model. On the other hand, the exosystem-model-based disturbance observer is a full-order observer for the augmented system consisting of the nominal plant model and the exosystem model. Accordingly, the order of the exosystem-model-based disturbance observer is higher than that of the inverse-model-based disturbance observer. As a final remaining problem to clarify the relation of the disturbance observers, this paper constructs the minimum-order exosystem-model-based disturbance observer to fill the gap in their order. Furthermore, this paper also clarifies the one-to-one correspondence to the Luenberger-type disturbance observer for the nominal plant model. This correspondence shows that the minimum-order exosystem-model-based disturbance observer can achieve the same characteristics as the inverse-model-based disturbance observer. Finally, this paper summarizes the obtained relation among the disturbance observers in one inclusion relation. The obtained inclusion relation shows that all types of disturbance observers can be interpreted as one of the exosystem-model-based disturbance observers.

DOI： 10.1080/18824889.2025.2537505

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Minimum-Order Exosystem-Model-Based Disturbance Observer 査読有り国際誌

Kana Shikada, Masakatsu Kawata, Noboru Sebe

Proceedings of 2025 SICE International Symposium on Control Systems, SICE ISCS 2025 2A1-1, 8 pages 2025年03月

Realization of the inverse-model-based disturbance observer in the Luenberger-type observer form and its generalization 査読有り国際誌

Shikada K., Sebe N.

SICE Journal of Control, Measurement, and System Integration 18 ( 1 ) 2025年02月

記述言語：英語掲載種別：研究論文（学術雑誌）

This paper gives the state-space representation of the inverse-model-based disturbance observer. The inverse-model-based disturbance observer proposed by Ohishi et al. estimates the disturbance with the inverse model of the plant and a low-pass filter and cancels out the effect of the disturbance with the estimated disturbance. Generally, for non-minimum phase plants, the inverse-model-based disturbance observer is constructed with an approximate stable inverse model or adding a parallel filter. Furthermore, the inverse-model-based disturbance observer is commonly discussed with the transfer function, and the relation between the Luenbergar-type observer is not clear. This paper gives the state-space representation of the inverse-model-based disturbance observer in the Luenberger-type observer form. Furthermore, this paper focuses on the characteristics of the systems for estimating the disturbance and shows the conditions for the Luenberger-type observer to be a disturbance observer. The Luenberger-type disturbance observer that satisfies the condition can be used for non-minimum phase systems since it does not use the inverse system model.

DOI： 10.1080/18824889.2025.2463195

DOI： 10.1080/18824889.2025.2463195

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Sequential Overbounding Approximation Method for the scaled H-infinity control problem 査読有り国際誌

Yoshikami K., Sebe N.

2025 Australian and New Zealand Control Conference, ANZCC 2025 93 - 98 2025年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Australia Gold Coast 2025年01月30日 - 2025年01月31日

The H∞ control is a practical approach for designing robust control systems, notable for permitting frequency shaping within control systems. However, the design result tends to be conservative when parameter uncertainties are treated as unstructured, such as additive and multiplicative. The scaled H∞ control problem has been introduced to address parameter uncertainties. An effective numerical solution, the dual iteration method, has been proposed for the scaled H∞ control problem. While the dual iteration method enhances control performance efficiently, it introduces numerical instability due to the reverse application of the elimination lemma. Therefore, a numerically stable and highly efficient method is needed for the scaled H∞ problem. This paper proposes a numerical method for the scaled H∞ control problem based on the overbounding approximations of an inverse of a positive definite matrix and bilinear terms. The proposed method avoids eliminating the controller variables and achieves numerical stability. The effectiveness of the proposed method is illustrated through numerical examples.

DOI： 10.1109/ANZCC65042.2025.10873324

DOI： 10.1109/ANZCC65042.2025.10873324

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Fault Detection in Robust Control by Using Disturbance Observer and Test Signals 査読有り国際誌

Yuyama T., Tsuji I., Shikada K., Sebe N., Suyama K.

2025 Australian and New Zealand Control Conference, ANZCC 2025 111 - 116 2025年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Australia Gold Coast 2025年01月30日 - 2025年01月31日

It is important to design control systems that are robust against failures. Control systems that maintain control performance even in the presence of faults are called fault-tolerant control. Passive fault-tolerant control is one of the fault-tolerant controls without fault detection. However, it is desirable to detect faults for fault maintenance even if a control system is robust against faults. In general, the more robust control systems are, the less faults affect the signals in control systems. Thus, fault detection in robust control systems is difficult. To achieve robust control and easy fault detection, This paper proposes a fault detection method for robust control systems using a disturbance observer and test signals. In the proposed control system, the disturbance observer has the same generating model that generates the test signals. Numerical examples demonstrate the effectiveness of the proposed method.

DOI： 10.1109/ANZCC65042.2025.10872996

DOI： 10.1109/ANZCC65042.2025.10872996

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Observer-Structured PID Controller: Flight Controller Design Examples 査読有り国際誌

Sato M., Sebe N.

International Conference on Electrical, Computer, Communications and Mechatronics Engineering, ICECCME 2024 1 - 6 2024年11月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Maldives Male 2024年11月04日 - 2024年11月06日

This note shows two design examples of PID con-Trollers, whose state variables estimate the selected state vari-Ables of the controlled plant systems, for LTI Parametrically Dependent (LTIPD) systems. The authors have already proposed observer-structured controllers, whose structure is not the same as but is very similar to the well-established Luenberger observer-based controllers, and have also proposed a conversion method from a priori designed unstructured LTI or Linear Parameter-Varying (LPV) controllers to observer-structured LTI/LPV con-Trollers with the plant state estimation ability implemented. How-ever, the successful conversion has been reported only for full-order controllers. In this note, we show two examples, in which a priori designed LTI PID controllers are successfully converted to observer-structured PID controllers, and the designed observer-structured PID controllers well estimate the selected plant state variables in numerical simulations.

DOI： 10.1109/ICECCME62383.2024.10797124

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Similarities and differences between exosystem-model-based disturbance observer and model error compensator 査読有り国際誌

Shikada K., Sebe N.

SICE Journal of Control, Measurement, and System Integration 17 ( 1 ) 339 - 348 2024年09月

記述言語：英語掲載種別：研究論文（学術雑誌）

This paper clarifies the theoretical similarities and differences between the exosystem-model-based disturbance observer and the model error compensator. In 1972, Johnson proposed the exosystem-model-based disturbance observer. This observer is constructed against the augmented system model, which consists of nominal plant and disturbance-generating models. Ohnishi et al. proposed to cancel out the effect of uncertainties with its estimated disturbance. Furthermore, in 2013, Okajima et al. proposed the model error compensator, which compensates for the error between the output of the nominal plant model and the measurement outputs of the actual plant. The theoretical differences among these control structures have yet to be fully understood. Therefore, this paper theoretically investigates the relation and shows the superiority of the exosystem-model-based disturbance observer to the model error compensator in its freedom to assign the behavior of the uncontrollable modes. This superiority enables the exosystem-model-based disturbance observer to suppress output fluctuations against uncertainties effectively. This effect is shown by a numerical example.

DOI： 10.1080/18824889.2024.2391624

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A Design of H∞ Controllers Achieving Type 2 Sensitivity Characteristics in type 1 Servo Systems 査読有り国際誌

Kawakami R., Shikada K., Sebe N., Sato M.

2024 SICE Festival with Annual Conference, SICE FES 2024 973 - 979 2024年08月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Japan Kochi 2024年08月27日 - 2024年08月30日

This paper proposes an H∞ controller design method which realizes a two-degree-of-freedom (2-DOF) control system with lower sensitivity characteristics in the low-frequency range. A control system with a disturbance observer is a 2-DOF control system that can achieve low sensitivity characteristics in the specific low-frequency range. However, the design of a controller with a disturbance observer structure is a non-convex optimization problem if it is considered as an observer gain design problem. In addition, it has not yet been revealed whether a 2-DOF control system with the low sensitivity characteristics of the disturbance observer can be achieved by the H∞ controller design. Therefore, this paper proposes a design method for H∞ controllers that achieves the low-sensitivity characteristics of a type 2 servo system while maintaining the type 1 servo characteristics without specifying the disturbance observer structure. Numerical examples demonstrate the effectiveness of the proposed method.

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Estimation of Scheduling Parameters by Disturbance Observer 査読有り国際誌

Kamewari K., Shikada K., Sebe N., Sato M., Mizumoto I.

2024 SICE Festival with Annual Conference, SICE FES 2024 980 - 985 2024年08月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Japan Kochi 2024年08月27日 - 2024年08月30日

This paper proposes a method for estimating scheduling parameters using a disturbance observer. The input and output values of the scheduling parameters are estimated by a disturbance observer, and the scheduling parameters are estimated by calculating the ratio of these values. The effectiveness of the gain-scheduled control using the estimated values is verified by comparing the gain-scheduled control with actual scheduling parameters and the conventional robust control designed by the scaled H∞ control.

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A Numerical Method for Scaled H∞ Control Problems Based on Approximation of Inverse of Positive Definite Matrix 査読有り国際誌

Yoshikami K., Sebe N.

2024 SICE Festival with Annual Conference, SICE FES 2024 967 - 972 2024年08月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Japan Kochi 2024年08月27日 - 2024年08月30日

H∞ control is one of the effective design methods for robust control systems and is significant in that it allows frequency shaping in the control system, but the design results are conservative when dealing with parameter as multiplicative uncertainties. The scaled H∞ control problem has been proposed as an approach to handle this problem, and an effective numerical solution method is the dual iteration method. While the dual iteration method efficiently improves the control performance, it also leads to numerical instability. Accordingly, a numerical method for the scaled H∞ problem that has numerical stability and high efficiency is needed. This paper proposes a numerical method for the scaled H∞ control problem based on the approximation of inverse matrices. This paper also shows the effectiveness of the proposed method through a numerical example.

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Switching L2 Gain for Evaluating the Fluctuations Around an Output of a Specified Transfer Property 査読有り国際誌

Koichi Suyama, Noboru Sebe

2024 European Control Conference, ECC 2024 3306 - 3311 2024年06月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Sweden Stockholm 2024年06月25日 - 2024年06月28日

In this paper, we introduce the difference structure to pre- and post-switch systems, to propose a new switching L2 gain for evaluating the fluctuations around an output of a specified transfer property after a system switch. Moreover, we apply it to the initial state design of a newly-activated controller designed by model matching to establish its potential practicality as a design index.

DOI： 10.23919/ECC64448.2024.10591052

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Observer-structured controller for linear parametric plant 査読有り

Sato M., Sebe N.

Automatica 163 2024年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

It is well known that Luenberger observers are useful for the estimation of linear plant states; however, several papers have shown that there is no need to use the nominal state-space (s.s.) matrices of linear parametric plant systems for observer-based controllers to realize good control performance. Regarding observer-based controllers, when LTI controllers are considered for LTI plant systems, a method has been proposed to convert a priori designed unstructured LTI controllers to observer-based ones without altering control performance; however, the method has not been extended to the case of parametric plant systems. This note thus addresses the conversion problem of a priori designed unstructured controllers to observer-based ones for linear parametric plant systems. To this end, we first propose observer-structured controllers, which can be defined for linear parametric plant systems even if their nominal s.s. matrices are unspecified, as a structural extension of Luenberger observer-based controllers, and then show the parametrization of the s.s. matrices of the observer-structured controllers. Using the parametrization, a conversion method, which produces observer-structured controllers derived from the unstructured ones with minimal state estimation errors embedded, is proposed using state-transformation matrices obtained via parametrically dependent LMIs. A practical example (lateral-directional motion control around wing level flight of an airplane using a gain-scheduled controller) is included to demonstrate the usefulness and practicality of our propositions.

DOI： 10.1016/j.automatica.2024.111569

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State space analysis of the relation between two types of disturbance observers 査読有り国際誌

Shikada K., Sebe N.

Proceedings of 2024 SICE International Symposium on Control Systems, SICE ISCS 2024 2A1-1, 8 pages 2024年03月

Dissipativity-constrained learning of MPC with guaranteeing closed-loop stability 査読有り国際誌

Hara K., Inoue M., Sebe N.

Automatica ( The International Federation of Automatic Control ) 157 2023年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

This paper addresses the data-driven approximation of model predictive control (MPC) designed for nonlinear plant systems. MPC has high ability of handling complex system-specifications and of improving the control performance, while it requires high computational complexity. Aiming at reducing the complexity, this paper addresses the data-driven approximation of MPC. To this end, the control law in MPC is described by the Koopman operator, which is a linear operator defined on the infinite-dimensional lifted state space. Then, the problem of data-driven finite-dimensional approximation of the operator is addressed. The problem is formulated as an optimization problem subject to a specified dissipativity constraint, which guarantees closed-loop stability and is modeled by a set of matrix inequalities. This paper also presents a computationally efficient algorithm of solving the optimization problem. Finally, a numerical simulation of controller construction is performed. The approximated MPC control law shows the stability of the overall control system while demonstrating high control performance.

DOI： 10.1016/j.automatica.2023.111271

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A Variant of Extended LMI: Performance Analysis with Static Multiplier for Discrete-Time Lifted Systems 査読有り国際誌

Sato M., Sebe N.

IFAC-PapersOnLine 56 ( 2 ) 5825 - 5830 2023年07月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

This note revisits extended Linear Matrix Inequality (LMI) formulation of performance analysis, which incorporates static multiplier, for parametrically multi-affine discrete-time Linear Time-Invariant Parameter-Dependent (LTIPD) and Linear Periodically Time-Varying (LPTV) systems using lifting technique. Almost the same analysis conditions for parametrically affine discrete-time LTIPD/LPTV systems as the ones shown in this note have already been proposed in the literature, we thus focus on the simple derivations of the conditions using only Elimination lemma. To this end, a variant of extended LMI formulation, whose dimensional sizes are slightly larger than the conventional formulation with additional auxiliary matrices, is proposed in this note. It is also shown that our derived variant directly leads to a parametrically multi-affine extended LMI formulation for our addressed problem.

DOI： 10.1016/j.ifacol.2023.10.074

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Support technology for preventive maintenance of control systems based on fail-soft concept 査読有り国際誌

Suyama K., Sebe N.

IFAC-PapersOnLine 56 ( 2 ) 5566 - 5572 2023年07月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

In this paper, as a support technology for safely performing preventive maintenance of LTI control systems, we propose a safe shutdown process for a maintenance-object subsystem. The proposed process is based on the “fail-soft” concept that the subsystem gradually makes its way toward a complete stoppage and the overall control system is lead to a safe situation by using the remaining function in the overall system including the subsystem. The discussion in this paper can be applied to a return process to the normal operation.

DOI： 10.1016/j.ifacol.2023.10.458

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Robustness of disturbance observer based servo systems 査読有り国際誌

Shikada K., Sebe N., Sato M.

IFAC-PapersOnLine 56 ( 2 ) 11570 - 11577 2023年07月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

This paper gives a theoretical analysis of the robustness of servo systems with disturbance observers. The disturbance observers have been used as an easy way to enhance the robustness of servo systems because of their simple structure. However, the effectiveness has yet to be theoretically proved. Therefore, this paper aims to clarify the advantage of the disturbance observer. This paper considers the servo system consisting of a servo compensator and a disturbance observer. The servo system has robustness in suppressing the response variations against the system uncertainties. It is theoretically shown that the robustness comes from the systems having zeros of multiplicity two at s = 0, while the systems are type-1 servo systems. A numerical example is provided to confirm the theoretical result and to demonstrate the effectiveness of disturbance observers.

DOI： 10.1016/j.ifacol.2023.10.454

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Lower Bound Analysis of L<inf>p+</inf> Induced Norm for LTI Systems 査読有り国際誌

Ebihara Y., Sebe N., Waki H., Hagiwara T.

IFAC-PapersOnLine 56 ( 2 ) 2425 - 2430 2023年07月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

In this paper, we focus on the lower bounds of the Lp (p ∈ [1, ∞), p = ∞) induced norms of continuous-time LTI systems where input signals are restricted to be nonnegative. This induced norm, called the Lp+ induced norm, is particularly useful for the stability analysis of nonlinear feedback systems constructed from linear systems and static nonlinearities where the nonlinearities provide only nonnegative signals for the case p = 2. To have deeper understanding on the Lp+ induced norm, we analyze its lower bounds with respect to the standard Lp induced norm in this paper. As the main result, we show that the Lp+ induced norm of an LTI system cannot be smaller than the Lp induced norm scaled by 2(1−p)/p for ∈ [1, ∞) (scaled by 2−1 for p = ∞). On the other hand, in the case where p = 2, we further propose a method to compute better (larger) lower bounds for single-input systems via reduction of the lower bound analysis problem into a semi-infinite programming problem. The effectiveness of the lower bound computation method, together with an upper bound computation method proposed in our preceding paper, is illustrated by numerical examples.

DOI： 10.1016/j.ifacol.2023.10.1218

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Dependability management of control systems via controller design 査読有り国際誌

Suyama K., Miura R., Sebe N.

IFAC-PapersOnLine 56 ( 2 ) 5542 - 5547 2023年07月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

We propose dependability management of control systems via controller design under the authorization by international standards. We can obtain a controller achieving a given target value of availability and the optimal performance in the normal operation. Furthermore, we show quantitatively the existence of the trade-off between the availability target and control performance first time ever. This is meaningful for the further developments in fault-tolerant control.

DOI： 10.1016/j.ifacol.2023.10.451

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Switching L2 gain for analyzing successive system switches 査読有り

Suyama K., Sebe N.

2023 European Control Conference, ECC 2023 2239 - 2244 2023年06月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Romania Bucharest 2023年06月13日 - 2023年06月16日

In this paper, we consider a new switching L2 gain for evaluating the magnitude of successive system switches, and focus on its upper bound obtained simply as an analysis index. Furthermore, we simultaneously and simply design the initial states of newly-activated controllers at all system switches to establish the potential practicality as a design index of the upper bound. This is a novel approach to initial state design.

DOI： 10.23919/ECC57647.2023.10178211

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