Published papers

In this chapter, we propose a calibration method for an array antenna, which includes electromagnetic coupling between antenna elements. Conventional methods such as the rotating element electric field vector (REV) method for elements of an array antenna do not take into account the electromagnetic coupling between elements. If the antenna calibration is not properly performed, the radiation pattern of the radio waves in the undesired directions will increase and interfere with the other satellites that are not intended. To overcome this drawback, a model of an array antenna including the mutual coupling between antenna elements has been constructed. Using this model, the estimation problem of the effect of the mutual coupling is formulated as a formulation problem. Finally, a calibration method based on the solution of the optimization problem is derived and shows the effectiveness of the method through some numerical examples.

© 2018 IEEE. This paper addresses a system identification problem for multiple isolated systems whose parameters are partially identical. An approach to the problem is a centralized identification; a single estimator collects all the input-output data from all of the systems to estimate their parameters at once. However, the approach can be practically infeasible when it is applied to a large number of systems due to the limitation of computational and communication resources. To solve the issue, we propose a method of a networked identification composed of two stages: 1) Multiple estimators collect the data from their own target systems to independently derive temporary estimates of their parameters and a covariance matrix of the estimates. 2) Then, with communicating the temporary estimates and the covariance matrix, they update their estimates. We also show the optimality of the proposed networked identification method with respect to the modeling accuracy, which is equivalently achieved by the centralized identification. Finally, we show the effectiveness of the proposed method in a numerical simulation.

© 2018 IEEE. In this paper, we address simultaneous estimation problems (SEPs) of state and physical parameters of rechargeable batteries. In general, the problems are transformed to state estimation of an augmented system whose state includes the parameters of the original system. Then, the SEPs are commonly solved by estimating the state of the augmented system. As a drawback of the solution, the simultaneous estimation fails for some types of the input currents. In this paper, we attempt to find input current conditions such that the SEPs are theoretically solved, through observability analysis of the augmented system.

© 2017 IEEE. In this paper, we investigate the reachability analysis and safety controller synthesis problem for linear discrete-Time systems under additive bounded disturbances. We consider the following problem; design a state feedback controller such that any state trajectories starting from an initial set can be robustly controlled towards a target one in finite time, while at the same time avoiding any prohibited regions. One of the potential disadvantages of existing reachability algorithms when external disturbances are taken into account, may be that the solution to guarantee reachability becomes conservative. Motivated by this, this paper provides a new controller synthesis framework based on the notion of tube-based control strategy, in which a suitable sequence of polytopes is generated according to a convex feasibility problem. An illustrative simulation validates the effectiveness of our proposed method.

© 2019 The Society of Instrument and Control Engineers - SICE. We propose a model-based state-of-charge (SOC) estimation method for rechargeable batteries which guarantees finite-time estimation error convergence. One of the most common approaches for the SOC estimation based on equivalent circuit model is to utilize the Kalman filter. The method has an asymptotic convergence property. From the practical standpoint, however, an estimation method that guarantees a finite-time estimation error convergence is desired. To this end, we employ the impulsive observer which achieves the finite-time estimation error convergence with the exact model. Furthermore, we analize the bounds of estimation errors in the case that the model used in the impulsive observer has errors. Finally, the effectiveness of the proposed method is illustrated through numerical experiments.

© 2018 IEEE. In recent years, event and self-triggered control have been proposed as energy-aware control strategies to expand the life-time of battery powered devices in Networked Control Systems (NCSs). In contrast to the previous works in which their control objective is to achieve stability, this paper presents a novel energy-aware control scheme for achieving high level specifications, or more specifically, temporal logic specifications. Inspired by the standard hierarchical strategy that has been proposed in the field of formal control synthesis paradigm, we propose a new abstraction procedure for jointly synthesizing control and communication strategies, such that the communication reduction in NCSs and the satisfaction of the temporal logic specifications are guaranteed. The benefits of the proposal are illustrated through a numerical example.

© 2018 IEEE. In this paper, we propose a frequency bandwidth allocation method for satellite communications (SATCOM) based on the Model Predictive Control (MPC) and a sparse optimization method. To utilize limited frequency bandwidth resources of SATCOM efficiently, control strategies for SATCOM system are studied. We treat the frequency bandwidth allocation problem for SATCOM as an optimal control problem. Then, based on the assumption that a time variation model of communication requests is obtained, we propose an optimal control method based on the MPC and the sparse optimization. By utilizing the proposed method, the limited frequency bandwidth is utilized efficiently. We verify the effectiveness of the proposed method in a numerical simulation by using actual data of aircraft.