Published papers

In this paper, load frequency control problem of a microgrid is discussed. The control is conducted to retain power demand supply balance by controling output of generators in power system. However, it becomes harder to retain the balance because of large-volume injection of renewable energy. For the problem, two approaches are considered in this research field. One is to use dispersion type power sources like batteries, and the other is to apply new control theories. Therefore, we focus on a microgrid which holds a wind turbine generator, a diesel generator and a battery, and propose a technique based a static H∞ control. In the beginning, we design the generalized plant considering the difference of the response speed of a diesel generator and a battery. Then, static H∞ control is applied to the generalized plant. Moreover, an LMI condition to avoid control gains to cause too big control input are combined with static H∞ control. In numerical simulation, we validate that the controller can suppress frequency deviation and deviation of residual capacity of the battery. Futhermore, we show that the approach can design controllers with lower dimensions, and avoid undesirable control gains. In experiment with a generator and a variable resistance, the effectiveness of the controller is also confirmed.

Ensuring cyber security of smart grid based on supervisory control and data acquisition using information and communications technology has been becoming a major challenge. Especially, a replay attack is a dangerous cyber attack affecting integrity and authorization. The goal of this paper is to detect replay attack that is one of cyber attacks on the sensors of a control system. We propose a detecting method adding intentional noise to sensors as code signal playing a time-stamping part. Replay attack can immediately be reflected by using fault diagnosis matrices that are composed of the estimator and observed values. Finally, we show simulation results to analyze effectiveness of the proposed method.

In this article, we deal with the optimal security investment problem for secure state estimation on cyber-physical systems. Toward effective secure state estimation, we aim to determine an optimal security investment that maximizes cost-effectiveness between the cost of the countermeasures and the effect of reinforcing the system resilience. Specifically, for each sensor, we decide whether to take costly security-aware action or inexpensive nonsecurity-aware action. In this article, we call the problem the optimal security investment problem, and we show that it is coNP-hard. Therefore, unless P = coNP, it is generally impossible to compute the optimal security investment in polynomial time. However, we also show a positive result that the optimal security investment can be solved in polynomial time if all the eigenvalues of the system matrix have geometric multiplicity 1. This article also presents the effect of improving the system resilience by adopting security-aware actions.

This paper considers the day-ahead market with batteries and accumulators to level power generation. First, we model consumers with batteries, generators with batteries, and accumulators, all of whom strive to maximize their own profit. An optimal pricing algorithm based on dual decomposition and the steepest descent method is derived and shown to be stable. Finally, the effectiveness of the algorithm is demonstrated by means of numerical simulations which indicate that it achieves demand–supply balance.

In this paper, a method for passivity- and robust integral of the sign of the error (RISE)-based control of a nonlinear teleoperation system with communication delays is proposed. This control strategy can accurately achieve coordinate positioning under conditions with viscous friction and unmodeled effects compensation errors, and its stability condition is independent of robot model parameter uncertainties and time delay. Using passivity-based stability analysis, the stability and tracking performance of this system are demonstrated, and experimental trials are performed to verify its effectiveness. © 2013 IEEE.

This study addresses the cooperative control of CAVs(Connected and Automated Vehicles) at Signal-free Intersection. The purpose is to reduce fuel consumption by crossing intersection without stopping as much as possible while ensuring safety. For this problem, We consider a two-stage control structure.The first stage is to calculate the merging time of each CAV by solving mixed integer linear programming (MILP). In the second stage, each CAV solves the optimal control problem and determines the input in time for the merging time. In this study, We propose an optimal control method using control barrier function considering more realistic scenario, and a speed regulation zone to cross the intersection at a pre-determined terminal speed. By using input corrections and trajectory tracking of speed and position, simulation results show that fuel consumption can be reduced while ensuring safety. Finally, compared to conventional research, the system achieves low fuel consumption, and demonstrating its superiority.

In this paper, we propose a new smart parking system that determines the optimal parking allocation in the long run. In this system, the demand situation is acquired earlier than the respective parking start time by motivating drivers to apply for early parking, and the system performs long-term optimization instead of optimization only for the current time. We propose three optimization methods focusing on the time axis. The first one ignores the time axis constraint, the second one has the time axis constraint but lacks driver motivation, and the third one is the proposed method that solves those problems. Finally, numerical simulations will be used to confirm the effectiveness of the proposed method.

本論文は磁気浮上系・磁気軸受における変位センサ支持板の共振と制御剛性に関して検討している．本稿ではセンサ支持板の変位を考慮した状態方程式を導出した．この式を基にセンサ支持板の共振周波数とフィードバックゲイン，およびロータ質量に関する不安定条件を導出し，これらのパラメータ空間上で不安定領域を明らかにした．またこの領域を避けることにより良好な実験結果が得られた．

本論文では磁気軸受の高剛性化を目的として，磁束密度フィードバックによる磁気軸受電磁石の応答速度改善に関して議論した．電流―電磁力伝達特性は，渦電流が無視出来ない高周波領域ではゲインが低下し，位相が遅れる．この問題を解決するために本稿では渦電流の作用を考慮した磁束密度フィードバック法を提案した．これにより電磁石の応答速度が改善し，磁気軸受を安定浮上回転させる際にロータの１次曲げモード共振周波数の減衰・消滅を達成した．

本論文ではH∞制御理論に基づくロバスト制御系設計法をロボットマニピュレータに適用した．リンク間の干渉とマニピュレータの重力項を構造的な不確かさとして取り扱い，その不確かさに対しても安定性と制御性能を保持する制御系の設計を行った．ロバスト安定性を保持するためにスモールゲイン定理に基づくH∞制御を用い，制御系解析の保守性を軽減するために定数スケーリング行列を導入した．最後に制御実験を行い，提案法の有効性を検証した．

This paper proposes a cooperative control of multi-agent system with disturbance. First, we introduce the sec- ond order model with disturbance for agent. The network topology among agents is undirected and connected, and information of reference is allowed to be available to at least one agent. Second, we propose the control law consists of graph theory, consensus algorithm and RISE. Graph theory and consensus algorithm are utilized to converge the states of agents to reference value, and RISE is utilized to suppress the disturbance. Then, we show the proposed control law guarantees the agents achieve synchronization, and derive the condition to achieve the control objective. Finally, simulation results show the effectiveness of the proposed control law.

This paper deals with a decentralized hierarchical control of power networks by using overlapping information. The control objective is to minimize the cost function of load frequency control problem. The control law is　constructed through three steps. In the 1st step, we make a hierarchical system with overlapping information. In the 2nd step, a relationship between the original system and the hierarchical system is confirmed. In the 3rd step, the hierarchical decentralized control for the hierarchical system is constructed and the decentralized hierarchical control law is contracted to the original system. Then, we show the effectiveness of the load frequency control by using the proposed control method.

本論文では分散型電源を導入した電力ネットワークに対して, 直線探索付き反復勾配法に基づく系統周波数制御を提案する. まず, ネットワーク構造を有する大規模システムを各サブシステムの結合系として状態遷移式で表現し, 状態と制御入力を考慮した評価関数を最小化する制御問題を定式化する. そしてこの制御問題に対して最適制御を計算する際に, 直線探索を付加した反復勾配法に基づく系統周波数制御を提案する. また, エネルギー/情報結合構造の変化に対してもフレキシブルに適応する事が可能である. 直線探索を行う際のステップ幅はArmijoとWolfe の規準の両方を満足しているため, 収束性を保証する事ができる. 最後に分散型電源を導入した電力ネットワークの負荷周波数制御(Lに対して提案制御則を適用する. そして提案制御則を用いることで, 従来制御則に対し評価関数の低減化や周波数変動の抑制など制御性能の向上が達成されていることをシミュレーションで示す.

This paper deals with H∞ filter－based short－term electric load prediction considering characteristics of load curve. We propose a predictive method to forecast a future electric load demand for 36 hours from 0 PM,and then evaluate the peak and bottom of load curves in the next day. We propose a load model, estimates unknown parameters of model via H∞ filter using the separated data from holiday and weekday, a same pattern of the previous data have been chosen and assigned to parameters for the model. The simulation results show the effectiveness of the proposed prediction methodology.

This paper deals with a sensor scheduling problem which considers state dependent noise and processing delay. A networked sensor system usually consists of a large number of sensors, which can be constructed with some different types of sensors. We propose a sensor scheduling algorithm based on the neighbor search algorithm nearby nodes for discrete time heterogeneous systems by minimization problem of assessment function. Finally experimental results show effectiveness of the proposed method.

This paper is one of the researches to countermeasure against disaster. This paper treats the short-term future prediction of gas concentration in a building for safer evacuation. Moreover, in order to treat disaster, such as re, failure of sensor installed in a building is assumed. Therefore, a fault-tolerant system against sensor's failure is designed. First, a concept of propagation coefficient is introduced, and a gas concentration model is constructed by propagation coefficient and amount of gas generation. And, in order to estimate these values, we apply Kalman Filter to this model. As this paper should consider sensor's failure, the fault-tolerant Kalman Filter is proposed. Then, by using the estimated result, the short-term future of gas concentration is predicted. Finally, we show experimental results to analyze effectiveness of the proposed method.