Seiichi Shin

Synthesis of dynamic quantizers for quantized feedback systems within invariant set analysis framework

This paper focuses on quantized feedback systems which consist of the linear system and the dynamic quantizer. From the perspective of the invariant set analysis, we discuss the effectiveness and the limitation of our quantizer synthesis condition considering several performances. If the all transmission zeros of the given system are stable, the proposed quantizer gives an optimal output approximation property. Otherwise, our method can design a stable suboptimal quantizer guaranteed with infinite time control performance. The numerical examples show that our quantizer can achieve the coarsely-quantized signal, while avoiding the excess performance deterioration.

Synthesis of continuous-time dynamic quantizers for LFT type quantized feedback systems

This paper focuses on analysis and synthesis methods of continuous-time dynamic quantizers for LFT type quantized control systems. Our aim is to propose a numerical optimization design method of multiple (decentralized) quantizers such that a given linear system is optimally approximated by the given linear system with the multiple quantizers. Our method is based on the invariant set analysis and the LMI technique. In addition, we clarify that our proposed method naturally extends to multiobjective control problems similar to linear control. For implementation, this paper presents an analysis condition of the applicable interval of switching process of quantizer. Finally, it is pointed out that the proposed method is helpful through a numerical example.

Synthesis of decentralized dynamic quantizer within invariant set analysis framework

Abstract This paper focuses on the synthesis of decentralized dynamic quantizers for linear systems with discrete-valued signal in terms of invariant set analysis. We derive the synthesis condition that can be recast as parameter dependent linear matrix inequalities and has a closed-form solution under some circumstances. In the case of minimum phase systems, our method can provide an optimal decentralized dynamic quantizer in the sense that the quantizer gives an optimal output approximation property. Also, in the case of non-minimum phase systems, our method can provide a suboptimal stable decentralized dynamic quantizer. As a result, this paper gives a unified design method of the dynamic quantizer based on the invariant set analysis.

Model following control for continuous-time discrete-valued input systems

This paper considers a model following control problem for continuous-time discrete-valued input systems, i.e., systems including the signal quantization such as networked control systems. The constraints we address is the quantized accuracy and switching speed of the signal quantization. This paper considers the two constraints simultaneously, while most of the existing results consider them separately or either of them. Our analysis and synthesis conditions are derived in terms of invariant set and BIBO stability. Especially, the synthesis condition is recast as a set of matrix inequalities based on a non-common Lyapunov variable technique of linear matrix inequality-based multi-objective control. Moreover, we clarify the effectiveness of the proposed method through a numerical example.

INPUT-OUTPUT RELATION OF LINEAR SYSTEMS BY USING COMPLEX WAVELET PACKET TRANSFORM

This paper is concerned with an input-output relation of linear systems when using the complex wavelet packet transform. In general, the linear relation between input-output is guaranteed by the following two conditions: (1) the mother wavelet has a better frequency resolution, and (2) the real and imaginary parts in the mother wavelet consist of a Hilbert transform pair. The complex wavelet satisfying the above conditions has been used for demonstrating the linear relation. In this paper, a complex wavelet packet transform is applied for improving the frequency resolution. The validity of our approach is shown through a numerical experiment.

A fallback control study of networked control systems for cybersecurity

Recent control systems of critical infrastructures are networked systems, which are exposed to the infection of the computer malwares. This paper considers a cybersecurity technology of networked control systems in terms of availability. Architecture of fallback control is proposed, which consists of the remote controller and the local controller. The former achieves the high control performance and the latter guarantees the minimum required control performance. If the malicious behavior of the remote controller is detected by the local controller, the local controller breaks the network communication between the plant and the remote controller and takes over the plant control. This framework aims to prevent the spread of the damage caused by the infection of the computer malwares. As a first step of the research, a prototype fallback control system is applied to a simple automation system simulating the defective discriminator.

Simultaneous optimization of dispatching and routing for OHT systems via hybrid system modeling

This paper proposes a new static simultaneous optimization of dispatching and conflict-free routing for unidirectional Overhead Hoist Transport (OHT) systems. Our objective is to minimize the entire transportation time where the given transportation tasks are finished. A hybrid system modeling is applied for OHT system that is constituted by the OHT vehicles at the lower level and governed by the upper level scheduler. In the proposed modeling, it is clarified that the simultaneous optimization problems are recast as a binary integer linear problem by using model predictive control. This paper presents a numerical example and discusses limitation of proposed modeling.

Numerical Optimization Design of Dynamic Quantizer via Matrix Uncertainty Approach

In networked control systems, continuous-valued signals are compressed to discrete-valued signals via quantizers and then transmitted/received through communication channels. Such quantization often degrades the control performance; a quantizer must be designed that minimizes the output difference between before and after the quantizer is inserted. In terms of the broadbandization and the robustness of the networked control systems, we consider the continuous-time quantizer design problem. In particular, this paper describes a numerical optimization method for a continuous-time dynamic quantizer considering the switching speed. Using a matrix uncertainty approach of sampled-data control, we clarify that both the temporal and spatial resolution constraints can be considered in analysis and synthesis, simultaneously. Finally, for the slow switching, we compare the proposed and the existing methods through numerical examples. From the examples, a new insight is presented for the two-step design of the existing continuous-time optimal quantizer.

Security enhancements of networked control systems using RSA public-key cryptosystem

To enhance the security of networked control systems, we propose the concept of secured control rules that is defined as a method that achieves concealing both signals over communication channels and parameters within controllers. Our method proposed in this study uses the homomorphism of the RSA cryptosystem to determine control signals directly from encrypted feedback signals and control parameters without performing any decryption processes. A numerical simulation confirms that the proposed method contributes to the improvement of security.

Model following output feedback controller synthesis for discrete-valued input systems

This paper considers an output feedback control for discrete-valued input systems. Our controller achieves model following control for networked control systems and embedded devices with low-resolution AD/DA converters. The synthesis problem we address is the simultaneous synthesis of the nominal controller and the delta-sigma modulator (where the modulators are called the dynamic quantizers). Our approach is based on the invariant set analysis and the LMI technique. First, this paper considers a controller structure for model following control. Second, this paper proposes a controller analysis condition for quantized feedback systems. Third, we provide a simultaneous synthesis condition that is recast as a set of matrix inequalities.