Tamotsu Ninomiya

Piezoelectric transformer converter with frequency control

An efficient piezoelectric transformer (PT) power converter with frequency control is presented. The optimum-designed reactance components are able to keep power efficiency high while controlling the output voltage for some load variation. An implemented PT power converter with frequency control achieves an efficiency higher than 75% at V/sub o/=5 V, I/sub o/=0.5-2 A, and switching frequency of around 2 MHz. Furthermore, a means to improve the voltage control characteristic over a wide range is also added.

High-efficiency high-power dc-dc converter for energy and space saving of power-supply system in a data center

This paper presents the power density developments of high-power isolated dc-dc converter to be utilized in a higher voltage direct-current (HVDC) power-supply system of a data center. This technique results in a prototype of dc-dc converter unit which is smaller by factor of ten when compared with the conventional one, and the area of power-supply system becomes much smaller than before. Consequently, the cooling power for this power-supply system is saved and both the energy and the space saving are available. In order to realize a prototype of the high-power isolated dc-dc converter, the switching power devices composed of a hybrid pair of Si-CoolMOS and SiC-SBD are utilized and operated in a driving pattern of hard switching with a frequency of 200kHz. As a result, an isolated dc-dc converter with the input/output voltage of 400V/400V, a rating power of 5kW, and a high power density of 10W/cm3 has been fabricated. The experimental confirmation was reported and the surge problems due to diode recovery difficulties mentioned before was solved.

FPGA-Based Spread-Spectrum Schemes for Conducted-Noise Mitigation in DC–DC Power Converters: Design, Implementation, and Experimental Investigation

This paper proposes a family of spread-spectrum schemes, several of which are new, for conducted-noise reduction in dc-dc converters. The schemes use three randomized parameters to generate the switching signals: carrier frequency, duty ratio, and pulse position. The increasing performance and cost reduction of field-programmable gate array (FPGA) technology have made the application of these schemes possible in this field. A theoretical framework for a general representative scheme is provided. Then, the proposed schemes are designed and implemented using an FPGA-based controller. Furthermore, the effect of using the proposed controller on common-mode, differential-mode, and total conducted-noise characteristics of the dc-dc converter is experimentally investigated. In addition, the three randomization parameters are swept to determine the values that best achieve the conducted-noise spectrum spread. All studied cases are designed, implemented, and experimentally investigated. Then, the conducted-noise spectra are compared. The experimental results show that the use of the proposed controller with the determined randomization values significantly improves the conducted-noise spectrum and effectively reduces the noise peaks at both high- and low-frequency ranges.

Analytical considerations on power loss in a three-arm-type uninterruptible power supply

The power efficiency of a three-arm-type UPS has been examined. In this UPS configuration, the center arm, called the common arm, operates in both PWM rectifier mode and PWM inverter mode. In this paper, a basic steady-state analysis and analytical considerations on power loss are described, and these analysis are confirmed by experiments.

PWM-controlled current-mode resonant converter using an active-clamp technique

A novel resonant power converter is proposed. The combination of an active-clamp technique and resonant circuit makes it possible to control the output voltage of the resonant power converter with PWM. This new resonant power converter was implemented and has achieved a good controllability.

Input Current-Ripple Consideration for the Pulse-link DC-AC Converter for Fuel Cells by Small Series LC Circuit

This paper mentions the input current ripple reduction method of the Pulse-link DC-AC Converter for Fuel Cells. The conventional DC-AC converter for fuel cells is interpolated large capacitor between boost converter stage and PWM inverter stage. That capacitor disturbs the size reduction of this unit. To overcome this problem, authors have proposed a novel topology called as Pulse-link DC-AC converter. The proposed topology provides boosted-voltage pulse directly to PWM inverter. This topology does not require large capacitor between two stages. Instead, small values of inductor and capacitor are connected series and inserted between two stages in parallel. This paper examines the relationship between the inductor and capacitor values and input current-ripple. As the result, inductor value has the relationship with current-ripple.

Power-density development of a 5MHz-switching DC-DC converter

This paper presents the power-density development of a high-frequency isolated DC-DC converter for ICT equipments. This technique results in a prototype of a 5MHz DC-DC converter module. In order to realize a prototype of the high-frequency isolated DC-DC converter, its topology is selected to be a half-bridge type current-mode resonant converter, and switching power devices of GaN-FET and Si-SBD and the transformer composed of a nickel-zinc ferrite core are utilized. As a result, a 5MHz isolated DC-DC converter with the input/output voltages of 48V/12V and the power rating of 120W has been fabricated, and the high power-density of 14W/cm3 has been performed.

Balanced switching converter to reduce common-mode conducted noise

Because conventional switching converters have been usually using unbalanced circuit topologies, parasitic capacitance between the drain/collector of an active switch and the frame ground through its heat sink may generate the common-mode conducted noise. This paper proposes a balanced switching converter circuit, which is an effective way to reduce the common-mode conducted noise. As an example, a boost converter version of the balanced switching converter is presented, and the mechanism of the common-mode noise reduction is explained using an equivalent circuit. This good feature is confirmed by experimental results. The concept of the balanced switching converter is applied to some other types of switching converter.

Operation analysis of the push-pull piezoelectric inverter

Operation of the push-pull inverter with a piezoelectric transformer is analyzed. The piezoelectric transformer is used in the third-order longitudinal vibration mode to produce a high output voltage to light up a cold cathode fluorescent lamp. The load characteristics of the inverter are analyzed using an equivalent circuit of the piezoelectric transformer. The ZVS conditions are derived using simplified equivalent circuits to determine the ZVS operation region. These analytical results are confirmed by experiments.

A Novel Implementation of an FPGA-Based Controller for Conducted-Noise Reduction in Randomly Switched DC-DC Converters

This paper proposes a novel implementation of an FPGA-Based controller for conducted-noise reduction in dc-dc converters. The switching noise produced by the converter has been reduced by randomly varying the switching frequency of the converter. Traditionally, the implementation of the switching-mode power supply (SMPS) has been accomplished using analog control circuits. However, the field-programmable gate array (FPGA) is much flexible than analog control circuits, becoming lower cost, and applicable for power supply applications. The implementation of the SMPS has been accomplished using FPGA-based digital controller. Moreover, breadboard has been built-up for testing the effect of using the proposed FPGA-based digital controller for noise reduction in dc-dc converters. Experimental results show that the conducted-noise spectrum has been significantly improved and the noise level has been effectively reduced.