Masahito Shoyama

Phase-controlled DC-AC converter with high-frequency switching

An analysis of the phase-controlled DC-AC converter is presented. This converter has a pair of switches in each side of the primary and the secondary of the isolation transformer. The voltage conversion ratio is controlled by the phase difference between the two pairs of switches. The averaged equivalent circuit for low frequency operation is derived. The switching surge during commutation is much reduced by dividing the reactor into two parts. As a result, the transformer is miniaturized by increasing the switching frequency and the reactive energy can be easily recovered to the DC source. This DC-AC converter is especially suitable for small uninterruptible power supply systems. >

Balanced switching converter to reduce common-mode conducted noise

Because conventional switching converters have usually used 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 converters.

Efficiency improvement of piezoelectric-transformer DC-DC converter

Piezoelectric-transformers (PT) have a lot of merits in comparison with magnetic transformers. We have previously presented some types of piezoelectric-transformer DC-DC converters (PT-converters) for AC-adapters, but their efficiency was restricted. The maximum efficiency was less than 80%. Furthermore, the frequency characteristics of efficiency are not good due to the power loss generated in the input filter circuit of the PT. In this paper the improvement of the converter efficiency by using a different rectifier circuit topology and a synchronous-rectifier technique is described. Furthermore, the frequency characteristics of efficiency are improved by using a different topology of the input filter circuit and its optimum design. As a result, the converter efficiency has been increased up to 88% and the frequency characteristics of the efficiency is also improved.

Piezoelectric transformer converter with PWM control

A piezoelectric transformer (PT) converter with PWM is presented. The active-clamp technique makes it possible to control the output voltage with PWM even if the PT converter operates in a resonant fashion. The PT converter with PWM control was implemented on a printed circuit board. The line and load regulation was successfully achieved under the input-voltage variation of 20 to 30 V, Vo=5 V, Io=0-4 A, and fs=2.08 MHz. Maximum efficiency achieved 82%.

Dynamic analysis of parallel-module converter system with current balance controllers

Dynamic response and stability analyses of a parallel-module power converter system with current balance controllers are described. The state-space averaging method is used to obtain a small-signal model for the dynamic analysis. The root locus method is used to discuss the stability of the parallel system. As a result, instability of the parallel system is observed in the system composed of modules with different circuit parameters. Influence of module parameters on the stability of the parallel system is discussed. Analytical results are confirmed experimentally for a two-paralleled forward power converter system.<<ETX>>

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.

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.

Variable Step Size Maximum Power Point Tracker Using a Single Variable for Stand-alone Battery Storage PV Systems

The subject of variable step size maximum power point tracking (MPPT) algorithms has been addressed in the literature. However, most of the addressed algorithms tune the variable step size according to two variables: the photovoltaic (PV) array voltage (VPV) and the PV array current (I PV ). Therefore, both the PV array current and voltage have to be measured. Recently, maximum power point trackers that are based on a single variable (I PV or V PV ) have received a great deal of attention due to their simplicity and ease of implementation, when compared to other tracking techniques. In this paper, two methods have been proposed to design a variable step size MPPT algorithm using only a single current sensor for stand-alone battery storage PV systems. These methods utilize only the relationship between the PV array measured current and the converter duty cycle (D) to automatically adapt the step change in the duty cycle to reach the maximum power point (MPP) of the PV array. Detailed analyses and flowcharts of the proposed methods are included. Moreover, a comparison has been made between the proposed methods to investigate their performance in the transient and steady states. Finally, experimental results with field programmable gate arrays (FPGAs) are presented to verify the performance of the proposed methods.

Electronic ballast using piezoelectric transformers for fluorescent lamps

This paper proposes an electronic ballast utilizing piezoelectric transformers for fluorescent lamps. The electronic ballast composed of new-type piezoelectric transformers and a half-bridge parallel-resonant inverter was implemented. It enables a fluorescent lamp to be turned on stably, and achieves an efficiency over 80% in steady state.

Stability study of variable step size incremental conductance/impedance MPPT for PV systems

This paper proposes a variable step size maximum power point tracking MPPT based on incremental conductance/impedance INC method. In order to design the appropriate variable step size scaling factor, a small signal model for the overall system equipped with the PV model and the INC algorithm has been developed. The optimal value of the variable step size scaling factor has been designed using the root locus technique. The theoretical analysis and the design principle of the proposed stability analysis have been validated using PSIM simulation, and experimentally using digital signal processor DSP.