Tsuyoshi Funaki

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

Economic and Efficient Voltage Management Using Customer-Owned Energy Storage Systems in a Distribution Network With High Penetration of Photovoltaic Systems

The widespread installation of distributed generation systems is crucial for making optimal use of renewable energy. However, local distribution networks face voltage fluctuation problems if numerous photovoltaic (PV) systems are connected. Recently, energy storage systems that can be installed at commercial customers have been developed. This paper proposes a concept that solves the voltage fluctuation problem in distribution networks with high penetration of PV systems by using customer-side energy storage systems. The distribution network operator (DNO) is allowed to control the output of the energy storage systems of customers during a specific time period in exchange for a subsidy covering a portion of the initial cost of the storage system. The cost effectiveness of the cooperative operation for both customer and DNO is discussed by numerical simulations based on minute-by-minute solar irradiation data. Our results have clarified the possibilities of making voltage management more economical in distribution networks.

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.

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

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.

A Study on SiC Devices in Synchronous Rectification of DC-DC Converter

This paper shows the feasibility of synchronous rectification for SiC MOSFET in dc-dc converter applications. The SiC MOSFET is compared with the conventional Si MOSFET in dc characteristics to the gate voltage for forward and backward direction, at first. Then, their turn-on and turn-off switching characteristics are evaluated in single device operation. Finally, their operations in a practical circuit of dc-dc buck converter are experimented, and the feasibility of their operation in synchronous rectification are discussed. The body diode in SiC MOSFET shows less reverse recovery than the body diode in Si MOSFET. Then, SiC MOSFET gives superior performance in the synchronous rectification of high voltage dc-dc converter with fast switching. This paper also studies the effect of externally connected free-wheel SiC SBD in anti-parallel to MOSFET. The body diode of SiC MOSFET is comparable to the SiC SBD in the reverse recovery characteristics. The conduction loss in free-wheeling period can be reduced by the application of SiC SBD. They are confirmed in the dc characteristics and in the dc-dc buck converter operation.

A novel quasi-resonant DC-DC converter using phase-shift modulation in secondary side of high-frequency transformer

This paper presents a novel quasi-resonant DC-DC converter using phase-shift modulation (PSM) in the secondary side of a high-frequency transformer. The proposed DC-DC converter can easily achieve soft-switching operation under the low commutating current and no freewheeling current. As a result, the conduction losses caused by their currents is substantially reduced compared with the conventional soft-switching DC-DC converters. The operation principle and analysis are illustrated and discussed by means of simulation and experimental results.

Characterization of SiC JFET for Temperature Dependent Device Modeling

Silicon Carbide (SiC) is considered the wide band gap semiconductor material that can presently compete with silicon (Si) material for power switching devices. Compact circuit simulation models for SiC devices are of utmost importance for designing and analyzing converter circuits; in particular, if comparisons with Si devices will be performed. The SiC power switching device structure and composition inevitably differs from those of conventional Si devices so as to harness the superiority of the material. The operational characteristics of the device thus are different from those of conventional Si devices. These characteristics cannot be accurately predicted by current Si power device models. Hence, the motivation to develop circuit simulation models for SiC devices. Moreover, SiC transistors have not been characterized as thoroughly as diodes. This paper characterizes SiC JFETs for the purpose of modeling and parameter extraction which can then be utilized in circuit simulations. The characterization is based on the dc (current-voltage) characteristic measurements using a curve tracer and on the ac (capacitance [impedance] — voltage) measurements using an impedance analyzer. Noting that characterization data for SiC JFETs are only available up to an ambient temperature of 250°C, the device is characterized from room temperature to 450°C demonstrating the high temperature operation of SiC JFETs. To this end, the devices were packaged in dedicated high temperature packages, and measurement fixtures were specially fabricated to withstand high ambient temperatures. The body diode buried in the evaluated SiC JFET is also characterized for potential synchronous rectifier applications.

Simulation results of novel energy storage equipment series-connected to the traction inverter

We developed novel energy-storage equipment that is series-connected to DC side of traction inverter of DC electric railway vehicle. When a train is powering and braking at a high-speed and the equipment boosts an input voltage of the traction inverter, the motor torque increases. Consequently, the mechanical brake force, compensating the electric brake force, becomes less. That leads to less energy dissipation. During the powering period, the acceleration of the train becomes larger due to the boosting operation of the equipment. The equipment charges a part of regenerated energy when it boosts the voltage during braking period, and discharges the stored energy when it boosts the voltage during accelerating period. In this paper, we selected electric double layer capacitor (EDLC) for the energy storage device of the equipment. Firstly, we explain the operational principle of the energy storage equipment: how to boost voltage at a desired level; how to charge and discharges the energy of the EDLC. Next, we described the circuit configuration and the control algorithm. Finally, we present simulation results to evaluate the performance of the energy storage equipment. According to the simulation results, the equipment charged/discharged the regenerated energy smoothly, and controlled the input voltage of the traction inverter at a desired level.

Switching characteristics of SiC JFET and Schottky diode in high-temperature dc-dc power converters

This paper reports on SiC devices operating in a dc-dc buck converter under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky diodes in thermally stable packages and built a high-temperature inductor. The converter was tested at ambient temperatures up to 400°C. Although the conduction loss of the SiC JFET increases slightly with increasing temperatures, the SiC JFET and Schottky diode continue normal operation because their switching characteristics show minimal change with temperature. This work further demonstrates the suitability of the SiC devices for high-temperature power converter applications.