Tohru Koyashiki

Characteristics of a high-frequency link resonant inverter

The authors describe the configuration and operation of a high frequency link resonant inverter. In this inverter, a resonant link high frequency voltage generated in a primary resonant inverter is isolated by a high frequency transformer, then directly converted into a resonant link low-frequency voltage by a cycloconverter. The switching losses and surge voltage levels can be reduced by making all switches in the primary inverter and the cycloconverter operate at zero voltage. The relationship between the characteristic impedance of the resonant circuit and the conversion efficiency, and the output voltage characteristics are discussed by comparing analytical and experimental results.<<ETX>>

A Low-Power Constant-Current Converter with HIC Techniques and its Circuit Simplification

A low-power constant-current converter that is required to be small and inexpensive, is developed. The most effective means for size and cost reduction is to introduce hybrid IC (HIC) techniques and to mount as large a number of circuit elements as possible on the HIC substrate. Application of a circuit with a simple configuration is important for the HIC techniques. A flyback type converter that has a small number of parts is utilized, and circuit simplification techniques are developed. The driving transformer for isolation between the input and output in the control loop is replaced by a photocoupler, and the power supply for the transformer secondary circuit is improved to miniaturize the converter. A control circuit to compensate for phase-lag in the photocoupler is studied and a simple method is proposed. Both a method for simplifying the circuits and the analysis and design of the phase-compensation circuit for the constant-current converter are described. The converter is miniaturized to 9.2 cm3/W by application of the HIC technique. The size of the converter corresponding to one subscriber can be reduced to 1/5 compared with that of the conventional multi-output converter.

A resonant DC link inverter with low-noise and high-output power

A resonant DC link inverter that provides high efficiency with low noise for uninterruptible power supplies has been developed. This paper describes the noise radiation, efficiency, and output voltage characteristics of a prototype resonant DC link inverter. It has 300 V DC input, and 200 V (1/spl phi/) and 10 kVA AC output. The noise radiation level meets the CISPR Pub. 22 standard and its efficiency and output voltage characteristics make it usable for practical applications.<<ETX>>

Improving Input Current Waveforms in a Switching Mode Rectifier with a High Frequency Transformer

In recent years, switching mode rectifiers (SMRs) which are composed of a capacitor input type rectifier and a DC-DC converter have been used to supply DC power to various electronic systems. Despite their desirable features such as small-size, light-weight, and high-efficiency, there is a disadvantage in that their input current waveforms include many harmonic components, which could severely influence other systems that AC power lines in common with the SMR. Conventional method to improve the waveforms uses bidirectional switch modules or three full bridge conversion circuits. However, this method cannot decrease the size, because the number of the switching devices increase.To solve this problem, a novel SMR with a high frequency transformer has been studied. In it, input 3-phase AC voltage is directly converted into high frequency AC, then rectified. Futhermore, low order harmonics in the input current waveforms can be eliminated by controlling the conduction intervals of switches, proportional to the instantaneous input line to line voltage.This paper describes the configuration of the novel SMR and its operating principle for obtaining sinusoidal input current waveforms as well as discusses the distortion factor characteristics of the input current waveforms.