Shota Miyairi

New Method for Reducing Harmonics Involved in Input and Output of Rectifier with Interphase Transformer

A new effective method for reducing harmonics involved in input ac line currents or output dc voltage of the thyristor rectifier apparatus with an interphase transformer is proposed. This method is based on the sophisticated utilization of several thyristors inserted in parallel between several taps equipped symmetrically for the midpoint of the interphase transformer and the terminal of the dc output circuit. The key point of this method can be understood easily when compared with conventional use of the interphase transformer, where the dc output circuit is taken from the midpoint of the interphase transformer directly. The features of this method are very simple and very economical in circuit construction. Their presentation will take the following form: 1) fundamental theory of the method; 2) analysis of waveforms of input ac line currents under optimum operation; 3) checking the validity of the theory by experiment using the six-phase 12-pulse thyristor polyphase rectifier apparatus; 4) various modifications of this method.

Study on magnetic noise caused by harmonics in output voltages of PWM inverter

Harmonic components included in the output waveform of inverter circuits cause magnetic noise from the output transformers or load motors. Functions are proposed for estimating the magnetic noise caused by the harmonics. By applying those functions, one can predict which of the waveforms is more noisy. The magnetic noise in several waveforms of PWM (pulsewidth-modulation) inverters is compared, and the output waveform is improved in order to reduce it.<<ETX>>

One method for selection of circuit parameters of a self-commutated rectifier

A method of selecting the circuit parameters of a self-commutated rectifier circuit which aims at improving the power factor is proposed.

Equivalence in Harmonics Between Cycloconverters and Bridge Converters

The similarity between a six-pulse three-phase cycloconverter operating in the circulating current-free mode and a six-pulse three-phase bridge converter is discussed analytically with regard to the rms value and the harmonics of the respective output voltages. A method is presented for calculating the rms voltage of a family of sideband frequencies which are generated in the output voltage of the cycloconverter. The results obtained from the analysis help to predict the amplitudes of subharmonics and beat frequencies with the cycloconverter and are essential for the design of the output filters. Analytical results are verified by comparison with those of experiment and digital computer simulation.