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1. モデル誤差抑制補償器

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Hiroshi Okajima - リサーチマップ

Hiroshi Okajima (researchgate.net)

H Okajima [制御工学チャンネル] - YouTube (登録者8000名,制御工学)

Hiroshi Okajima - ORCID

Hiroshi Okajima - Google scholar

Hiroshi Okajima - Github(MATLAB code)

システム制御研究室の研究紹介動画（2時間，動画配信システム内でトピック選択可）

熊本大学 松永研究室 (System Integration Lab)

主要な研究論文 Main Research Articles about Control Theory

Hiroshi Okajima, Yusuke Fujimoto, Hiroshi Oku and Haruto Kondo, Cyclic Reformulation-Based System Identification for Periodically Time-Varying Systems | IEEE Journals & Magazine | IEEE Xplore , IEEE ACCESS (2025) (Open Access) 

Outline: This paper presents a novel system identification algorithm for linear periodically time-varying (LPTV) plants within a discrete-time framework. The algorithm integrates a cyclic reformulation with a state coordinate transformation of the cycled system to enable precise identification of LPTV dynamics. Specifically, subspace identification methods are applied to the cycled signals, allowing the extraction of Markov parameters, which form the basis for constructing the state-space model. Furthermore, the sparsity properties of the matrices derived from these Markov parameters are analyzed and utilized to design the coordinate transformation matrix, enhancing the representation and interpretability of the identified LPTV model. Unlike conventional methods that rely on specific periodic input signals, the proposed approach leverages the inherent periodic structure of the system, eliminating such requirements and improving flexibility in practical applications. Numerical simulations are conducted to demonstrate the algorithm’s effectiveness and accuracy in capturing the dynamic behavior of LPTV plants under realistic conditions, highlighting its potential for broad applicability.

Hiroshi Okajima, Yohei Hosoe and Tomomichi Hagiwara, State Observer under Multi-rate Sensing Environment and Its Design using l2 -Induced Norm, IEEE ACCESS (2023) (Open Access) 

Outline: The duration of a signal's sensing period typically relies on the sensor being used, and can vary even within a single control system that uses multiple sensors. This paper explores the design challenge of creating state observers for linear, time-invariant, discrete-time systems in a multi-rate sensing environment. We assume that the sensing periods of the plant's sensors have mutually rational ratios. First, we describe a state observer for a system with multi-rate sensing as a periodically time-varying state observer. Next, we examine the l2 performance analysis of state estimation errors using the given periodically changing state observer. A linear matrix inequality (LMI) condition is provided for this analysis. By expanding the LMI condition for analysis, we also offer a condition for multi-rate observer synthesis. We then demonstrate the effectiveness of our proposed multi-rate state observer through numerical examples. Notably, even when all sensors share the same period, sensing timing is not unique. As a result, we numerically investigate whether performance varies when the observation timing differs among multiple sensors. [MATLAB code]

Hiroshi Okajima, Yasuaki Kaneda and Nobutomo Matsunaga, State estimation method using median of multiple candidates for observation signals including outliers, SICE Journal of Control, Measurement, and System Integration, Volume 14 Issue 1 pages 257-267 (T&F, Open Access) 

Outline: This paper addresses the state estimation problem for systems with observation outputs that include outliers. The presence of outliers in observation outputs can significantly reduce the accuracy of state estimation. To tackle this issue, we propose a novel observer structure that employs multiple estimated state candidates. First, we generate multiple estimated state candidates, each using the sensing output value from a different detection timing. If outliers are rare, removing candidates affected by outliers helps maintain estimation accuracy. Our proposed observer then selects one estimated state candidate from the group using either a median or weighted median operation. This process ensures that the selected estimated state does not rely on outlier values. Furthermore, we present a method for designing observer gains for these estimated state candidates based on the reachable set of the estimated state error, using Lyapunov-based inequalities. The effectiveness of our proposed observer is demonstrated through numerical examples. [MATLAB Code]

H. Okajima, K. Fujinami, Estimation of Robust Invariant Set for Switched Linear Systems using Recursive State Updating and Robust Invariant Ellipsoid, SICE Journal of Control, Measurement, and System Integration, Volume 14 Issue 1 Pages 97-106 (2021) (T&F, Open Access) 

Outline: This paper presents an analysis method for robust invariant sets in discrete-time linear switched systems with peak-bounded disturbances. Analyzing the robust invariant set in switched linear systems is more challenging than in linear time-invariant systems. We introduce a novel approach to estimate a robust invariant set by combining recursive state updating and an invariant ellipsoid for a common Lyapunov function. The accuracy and effectiveness of our proposed method are demonstrated through numerical examples. [YouTube and  SupportPage] 

Ryuichiro Yoshida, Hiroshi Okajima and Takumi Sato, Model error compensator design for continuous- and discrete-time non-minimum phase systems with polytopic-type uncertainties, SICE Journal of Control, Measurement, and System Integration, Volume 15 Issue 2 pags 141-153 (2022) (T&F, Open Access) 

Outline: This paper introduces a design for a model error compensator combined with a parallel feedforward compensator for continuous- and discrete-time non-minimum phase multiple input multiple output (MIMO) plants. The model error compensator can readily enhance robustness in various control systems. By adding the compensator to the actual plant, the plant's output trajectory can closely follow that of the control system with the intended nominal model. Our previous research proposed a model error compensator design using particle swarm optimization and linear matrix inequalities based on the common Lyapunov function, addressing polytopic-type uncertainties in plants. However, designing the appropriate gain for the model error compensator becomes challenging when dealing with non-minimum phase MIMO systems. In this study, we attach a parallel feedforward compensator to the model error compensator to achieve minimum phase characteristics. With some assumptions, an evaluation system incorporating a parallel feedforward compensator can be derived as a system with polytopic uncertainties. This approach simplifies the gain design of the model error compensator, ensuring robust performance. We demonstrate the effectiveness of our proposed design through numerical examples. [MECpage] 

H. Okajima, K. Sawada and N. Matsunaga：Dynamic Quantizer Design Under Communication Rate Constraints, IEEE Transactions on Automatic Control, Vol.61, No.10, pp.3190-3196 (2016) 

Outline: Feedback-type dynamic quantizers, such as delta-sigma modulators, are often effective for converting high-resolution data into lower-resolution data. These dynamic quantizers consist of a filter and a static quantizer. When controlling under a communication rate constraint, the data rate of the quantizer output should be minimized appropriately through quantization. This technical note presents numerical methods for the comprehensive design of a type of dynamic quantizer, including the selection of all quantizer parameters to minimize a specific performance index while satisfying a communication constraint. We propose a design method for the dynamic quantizer using a particle swarm optimization (PSO) approach. Some initial quantizers in PSO are designed based on an invariant set analysis and an iteration algorithm. The effectiveness of the system employing the proposed quantizer is demonstrated through numerical examples. [SupportPage]

H. Okajima, H. Umei, N. Matsunaga and T. Asai：A Design Method of Compensator to Minimize Model Error, SICE Journal of Control, Measurement, and System Integration, Vol.6, No.4, pp.267-275 (2013) (T&F, Open Access) 

Outline: Robust control design methods have been widely studied in recent decades. A control system performs well under modeling errors and disturbances when the controller design is based on robust control methods. However, it is well known that control systems typically face a trade-off between control performance and robustness. To address this trade-off problem, an internal model-type compensator structure that minimizes the modeling gap between the nominal model and actual plant dynamics is proposed.   By employing the proposed compensator, the dynamics of the compensated system closely match those of the nominal model. Additionally, we introduce a design method for compensator parameters aimed at minimizing a set of plant dynamics. The proposed design method can be reduced to the standard µ design control problem. Using the proposed compensator for control systems instead of the plant itself may lead to improved output performance despite plant uncertainty. As the proposed compensator can be used for controlling not only linear but also nonlinear plants, it allows for the easy achievement of robust control in nonlinear systems. The effectiveness of our proposed method is demonstrated through numerical examples. [MECpage]  

H. Okajima and T. Asai：Performance Limitation of Tracking Control Problem for a Class of References, IEEE Transactions on Automatic Control, Vol.56, No.11, pp.2723-2727 (2011) 

Outline: This technical note focuses on the analysis of fundamental limitations in tracking control problems for single-input single-output (SISO) systems. Existing results analyze these limitations based on specific assumptions of reference signals, such as step, trigonometric signals, and others. In contrast, we define a class of reference signals in a more abstract but general way. For this general class of reference inputs, we provide an analytical solution for tracking performance limitations based on the achievable set of outputs, which are characterized by transfer functions. The analysis results clearly separate the contributions of the plant and the reference signal. [SupportPage and PDF]

岡島寛：状態のロバスト不変集合を用いた外れ値除去機能を有するMCVオブザーバの解析とオブザーバゲイン設計，計測自動制御学会論文集，Vol. 55, No. 12, pp. 823-829 (2019) 

岡島寛，細江陽平，萩原朋道: マルチレート系の状態推定のための周期時変状態オブザーバのl2誘導ノルム評価による設計，計測自動制御学会，Vol. 55, No. 12, pp. 792-799 (2019) 

岡島寛：有限整定条件下での不安定零点と最小アンダーシュート量の解析的表現，計測自動制御学会論文集，Vol. 55, No. 10, pp. 648-654 (2019) 

岡島寛，川脇治：制御システムを個性化するための制御系設計，システム制御情報学会論文誌，Vol. 31, No. 11, pp. 392-399 (2018）

岡島寛，西村悠樹，松永信智：モデル誤差抑制補償に基づく非線形システムのフィードバック線形化，計測自動制御学会論文集，Vol.50, No.12, pp.869-874 (2014) j-stage

鍋倉司樹，岡島寛，松永信智：プレフィルタとポストフィルタを含むAD/DA変換系の設計と音声信号圧縮系への適用，計測自動制御学会論文集，Vol.50, No.3, pp.295-302 (2014) j-stage

岡島寛，松永信智，澤田賢治：通信容量制約に基づく動的量子化器の量子化幅設計と性能解析，計測自動制御学会論文集，Vol.46，No.6，pp.327-335 (2010) j-stage 

岡島寛，松永信智，川路茂保：ニュートラルステア特性実現のための直接ヨーモーメント制御，計測自動制御学会論文集，Vol.45，No.3，pp.153-159 (2009) j-stage 

岡島寛，浅井徹，川路茂保：離散時間系に対する最適追従制御問題の解析解，計測自動制御学会論文集，Vol.44，No.10, pp.793-801 (2008) j-stage 

岡島寛，浅井徹，川路茂保：経路追従問題における最適速度制御，計測自動制御学会論文集，Vol.44，No.7，pp.566-574 (2008) j-stage 

岡島寛，浅井徹：「軌道の差」の評価に基づく軌道追従制御，システム制御情報学会論文誌，Vol.20，No.4，pp.133-143 (2007) j-stage