arXiv subjects

Takashi Hikihara

Publications and source records attributed to Takashi Hikihara.

28 records · Page 2Linked to original sources

arXiv2018

Structural Analysis and Control of a Model of Two-site Electricity and Heat Supply

This paper introduces a control problem of regulation of energy flows in a two-site electricity and heat supply system, where two Combined Heat and Power (CHP) plants are interconnected via electricity and heat flows. The control problem is motivated by recent development of fast operation of CHP plants to provide ancillary services of power system on the order of tens of seconds to minutes. Due to the physical constraint that the responses of the heat subsystem are not necessary as fast as those of the electric subsystem, the target controlled state is not represented by any isolated equilibrium point, implying that stability of the system is lost in the long-term sense on the order of hours. In this paper, we first prove in the context of nonlinear control theory that the state-space model of the two-site system is non-minimum phase due to nonexistence of isolated equilibrium points of the associated zero dynamics.Instead, we locate a one-dimensional invariant manifold that represents the target controlled flows completely. Then, by utilizing a virtual output under which the state-space model becomes minimum phase, we synthesize a controller that achieves not only the regulation of energy flows in the short-term regime but also stabilization of an equilibrium point in the long-term regime. Effectiveness of the synthesized controller is established with numerical simulations with a practical set of model parameters.

math.OC↗

arXiv2017

High-Speed Gate Driver Using GaN HEMTs for 20-MHz Hard Switching of SiC MOSFETs

In this paper, we investigated a gate driver using a GaN HEMT push-pull configuration for the high-frequency hard switching of a SiC power MOSFET. Low on-resistance and low input capacitance of GaN HEMTs are suitable for a high-frequency gate driver from the logic level, and robustness of SiC MOSFET with high avalanche capability is suitable for a valve transistor in power converters. Our proposed gate driver consists of digital isolators, complementary Si MOSFETs, and GaN HEMTs. The GaN HEMT push-pull stage has a high driving capability owing to its superior switching characteristics, and complementary Si MOSFETs can enhance the control signal from the digital isolator. We investigated limiting factors of the switching frequency of the proposed gate driver by focusing on each circuit component and proposed an improved driving configuration for the gate driver. As a result, 20-MHz hard switching of a SiC MOSFET was achieved using the improved gate driver with GaN HEMTs.

eess.SP↗

arXiv2017

Transient Behavior of Redox Flow Battery Connected to Circuit Based on Global Phase Structure

A Redox Flow Battery (RFB) is one of the promising energy storage systems in power grid. An RFB has many advantages such as a quick response, a large capacity, and a scalability. Due to these advantages, an RFB can operate in mixed time scale. Actually, it has been demonstrated that an RFB can be used for load leveling, compensating sag, and smoothing the output of the renewable sources. An analysis on transient behaviors of an RFB is a key issue for these applications. An RFB is governed by electrical, chemical, and fluid dynamics. The hybrid structure makes the analysis difficult. To analyze transient behaviors of an RFB, the exact model is necessary. In this paper, we focus on a change in a concentration of ions in the electrolyte, and simulate the change with a model which is mainly based on chemical kinetics. The simulation results introduces transient behaviors of an RFB in a response to a load variation. There are found three kinds of typical transient behaviors including oscillations. As results, it is clarified that the complex transient behaviors, due to slow and fast dynamics in the system, arise by the quick response to load.

eess.SP↗

arXiv2017

Power packet transferability via symbol propagation matrix

Power packet is a unit of electric power transferred by a power pulse with an information tag. In Shannon's information theory, messages are represented by symbol sequences in a digitized manner. Referring to this formulation, we define symbols in power packetization as a minimum unit of power transferred by a tagged pulse. Here, power is digitized and quantized. In this paper, we consider packetized power in networks for a finite duration, giving symbols and their energies to the networks. A network structure is defined using a graph whose nodes represent routers, sources, and destinations. First, we introduce symbol propagation matrix (SPM) in which symbols are transferred at links during unit times. Packetized power is described as a network flow in a spatio-temporal structure. Then, we study the problem of selecting an SPM in terms of transferability, that is, the possibility to represent given energies at sources and destinations during the finite duration. To select an SPM, we consider a network flow problem of packetized power. The problem is formulated as an M-convex submodular flow problem which is known as generalization of the minimum cost flow problem and solvable. Finally, through examples, we verify that this formulation provides reasonable packetized power.

eess.SY↗

arXiv2017

On the Spectral Equivalence of Koopman Operators through Delay Embedding

We provide one theorem of spectral equivalence of Koopman operators of an original dynamical system and its reconstructed one through the delay-embedding technique. The theorem is proved for measure-preserving maps (e.g. dynamics on compact attractors) and provides a mathematical foundation of computing spectral properties of the Koopman operators by a combination of extended dynamic mode decomposition and delay-embedding.

math.DS↗

arXiv2017

Applied Koopman Operator Theory for Power Systems Technology

Koopman operator is a composition operator defined for a dynamical system described by nonlinear differential or difference equation. Although the original system is nonlinear and evolves on a finite-dimensional state space, the Koopman operator itself is linear but infinite-dimensional (evolves on a function space). This linear operator captures the full information of the dynamics described by the original nonlinear system. In particular, spectral properties of the Koopman operator play a crucial role in analyzing the original system. In the first part of this paper, we review the so-called Koopman operator theory for nonlinear dynamical systems, with emphasis on modal decomposition and computation that are direct to wide applications. Then, in the second part, we present a series of applications of the Koopman operator theory to power systems technology. The applications are established as data-centric methods, namely, how to use massive quantities of data obtained numerically and experimentally, through spectral analysis of the Koopman operator: coherency identification of swings in coupled synchronous generators, precursor diagnostic of instabilities in the coupled swing dynamics, and stability assessment of power systems without any use of mathematical models. Future problems of this research direction are identified in the last concluding part of this paper.

eess.SY↗

arXiv2015

Active and reactive power in stochastic resonance for energy harvesting

A power allocation to active and reactive power in stochastic resonance is discussed for energy harvesting from mechanical noise. It is confirmed that active power can be increased at stochastic resonance, in the same way of the relationship between energy and phase at an appropriate setting in resonance.

physics.soc-ph↗

arXiv2015

Security of Power Packet Dispatching Using Differential Chaos Shift Keying

This paper investigates and confirms one advantageous function of a power packet dispatching system, which has been proposed by authors' group with being apart from the conventional power distribution system. Here is focused on the function to establish the security of power packet dispatching for prohibiting not only information but also power of power packet from being stolen by attackers. For the purpose of protecting power packets, we introduce a simple encryption of power packets before sending them. Encryption scheme based on chaotic signal is one possibility for this purpose. This paper adopts the Differential Chaos Shift Keying (DCSK) scheme for the encryption, those are partial power packet encryption and whole power packet encryption.

cs.IT↗

arXiv2014

Logic-Memory Device of a Mechanical Resonator

We report multifunctional operation based on the nonlinear dynamics in a single microelectromechanical system (MEMS) resonator. This Letter focuses on a logic-memory device that uses a closed loop control and a nonlinear MEMS resonator in which multiple states coexist. To obtain both logic and memory operations in a MEMS resonator, we examine the nonlinear dynamics with and without control input. Based on both experiments and numerical simulations, we develop a novel device that combines an OR gate and memory functions in a single MEMS resonator.

cond-mat.mes-hall↗

arXiv2013

Counter operation in nonlinear micro-electro-mechanical resonators

This paper discusses a logical operation of multi-memories that consist of coupled nonlinear micro-electro-mechanical systems (MEMS) resonators. A MEMS resonator shows two coexisting stable states when nonlinear responses appear. Previous studies addressed that a micro- or nano-electrical-mechanical resonator can be utilized as a mechanical 1-bit memory or mechanical logic gates. The next phase is the development of logic system with coupled multi-resonators. From the viewpoint of application of nonlinear dynamics in coupled MEMS resonators, we show the first experimental success of the controlling nonlinear behavior as a 2-bit binary counter.

cond-mat.mes-hall↗