Takashi Hikihara

Power Conversion With SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

An experimental study on stabilization of unstable periodic motion in magneto-elastic chaos

Abstract Some experimental results of controlling chaos on a magneto-elastic beam system, which is described by the Duffing equation, are discussed. We adopt a delayed feedback control method proposed by Pyragas to stabilize an unstable periodic attractor embedded in a chaotic attractor. This is a negative feedback control using the gained error between the output of the chaotic system and the periodically delayed one. It is shown that unstable periodic motion in magneto-elastic chaos can be stabilized experimentally. The effectiveness of the control method is confirmed for two types of the Duffing system. Numerical considerations for the typical Duffing equation are also given.

In-Home Power Distribution Systems by Circuit Switching and Power Packet Dispatching

Renewable, natural, and distributed power sources have been adopted in order to reduce consumption of fossil fuels. These new energy sources have fluctuations in the amount of output power, frequency, and voltage. Similar situation arises at the regulation of power flow in-home. Thus, suppression of the fluctuation is required for avoiding disturbance in power grid. In this paper, two types of in-home power distribution systems are proposed. One is a circuit switching system, and the other is a power packet dispatching system. The experiments show the possibilities of new power management.

Measuring Terminal Capacitance and Its Voltage Dependency for High-Voltage Power Devices

The switching behavior of semiconductor devices responds to charge/discharge phenomenon of terminal capacitance in the device. The differential capacitance in a semiconductor device varies with the applied voltage in accordance with the depleted region thickness. This study develops a C - V characterization system for high-voltage power transistors (e.g., MOSFET, insulated gate bipolar transistor, and JFET), which realizes the selective measurement of a specified capacitance from among several capacitances integrated in one device. Three capacitances between terminals are evaluated to specify device characteristics-the capacitance for gate-source, gate-drain, and drain-source. The input, output, and reverse transfer capacitance are also evaluated to assess the switching behavior of the power transistor in the circuit. Thus, this paper discusses the five specifications of a C -V characterization system and its measurement results. Moreover, the developed C -V characterization system enables measurement of the transistor capacitances from its blocking condition to the conducting condition with a varying gate bias voltage. The measured C -V characteristics show intricate changes in the low-bias-voltage region, which reflect the device structure. The monotonic capacitance change in the high-voltage region is attributable to the expansion of the depletion region in the drift region. These results help to understand the dynamic behavior of high-power devices during switching operation.

A Coupled Dynamical Model of Redox Flow Battery Based on Chemical Reaction, Fluid Flow, and Electrical Circuit

The redox (Reduction-Oxidation) flow battery is one of the most promising rechargeable batteries due to its ability to average loads and output of power sources. The transient characteristics are well known as the remarkable feature of the battery. Then it can also compensate for a sudden voltage drop. The dynamics are governed by the chemical reactions, fluid flow, and electrical circuit of its structure. This causes the difficulty of the analysis at transient state. This paper discusses the transient behavior of the redox flow battery based on chemical reactions. The concentration change of vanadium ions depends on the chemical reactions and the flow of electrolysis solution. The chemical reaction rate is restricted by the attached external electric circuit. In this paper, a model of the transient behavior is introduced. The validity of the derived model is examined based on experiments for a tested micro-redox flow battery system.

Coherent Swing Instability of Power Grids

We interpret and explain a phenomenon in short-term swing dynamics of multi-machine power grids that we term the Coherent Swing Instability (CSI). This is an undesirable and emergent phenomenon of synchronous machines in a power grid, in which most of the machines in a sub-grid coherently lose synchronism with the rest of the grid after being subjected to a finite disturbance. We develop a minimal mathematical model of CSI for synchronous machines that are strongly coupled in a loop transmission network and weakly connected to the infinite bus. This model provides a dynamical origin of CSI: it is related to the escape from a potential well, or, more precisely, to exit across a separatrix in the dynamical system for the amplitude of the weak nonlinear mode that governs the collective motion of the machines. The linear oscillations between strongly coupled machines then act as perturbations on the nonlinear mode. Thus we reveal how the three different mode oscillations—local plant, inter-machine, and inter-area modes—interact to destabilize a power grid. Furthermore, we present a phenomenon of short-term swing dynamics in the New England (NE) 39-bus test system, which is a well-known benchmark model for power grid stability studies. Using a partial linearization of the nonlinear swing equations and the proper orthonormal decomposition, we show that CSI occurs in the NE test system, because it is a dynamical system with a nonlinear mode that is weak relative to the linear oscillatory modes.

Power Conversion with SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

Control of microcantilevers in dynamic force microscopy using time delayed feedback

It has been recently shown that microcantilever sensors in dynamic force microscopes possibly exhibit chaotic oscillations due to the nonlinear tip-sample interaction force. In this article, we propose elimination of the chaotic oscillations using the time delayed feedback control method, which has an ability to stabilize unstable periodic orbits embedded in chaotic attractors. An extended operating range of the microscopes is numerically estimated by stability analysis of the target periodic oscillation. We also discuss an improved transient response of oscillation, which allows us to accelerate the scanning rate of the microscopes without reducing their force sensitivity.

Levitation drift of a magnet supported by a high-Tc superconductor under vibration

Abstract Since the discovery of high- T c superconductors, many kinds of applications have been proposed. Among them, the high- T c superconducting bearing is considered to be one of the most possible applications. The bearing depends on the supporting force between a permanent magnet and a superconductor, caused by the flux pinning of high- T c superconductors. In this paper, the stability of levitation is discussed experimentally under external vibration. Then it shows the levitation drift for sintered YBaCuO, melt-quenched YBaCuO and melt-powder-melt-growth BiSrCaCuO. The characteristics of drift are explained as a relation with the force-displacement hysteresis. A dynamical model of the magnet and high- T c superconductor is also proposed to give the drift a physical meaning numerically.

A Study of Output Terminal Voltage Modeling for Redox Flow Battery Based on Charge and Discharge Experiments

The vanadium reduction oxidation (redox) flow battery is one type of rechargeable batteries. The battery has abilities of high-speed response and overload operation. Characteristics of the redox flow battery have been experimentally and numerically discussed for periodical operation and transient states, at many institutes and companies. This paper focuses on the modeling of redox flow battery near practical operating setups. In particular, the equivalent series resistance and the overpotential at cell are estimated based on the experimental results.