Shoji Iida

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.

Improved voltage source inverter with 18-step output waveforms

In this article, an improved voltage source inverter is proposed. This circuit is based on the NPC (neutral point clamped) inverter. By dividing the input DC source into four sections and adding four auxiliary switching elements, the proposed circuit can be performed as if an 18-step inverter as far as the harmonic components in the AC output voltages are concerned. The performances of the proposed circuit and the output AC voltage waveforms are discussed. Then the optimum conditions are determined by minimizing the distortion of the output waveform, and the effects for the harmonic reductions can be clarified by theoretical results. The ratings of circuit components, such as the separated DC sources and the switching devices, should be investigated. Moreover, we suggest the adjusting methods of the output voltages.

A method for reducing harmonics in output voltages of a double-connected inverter

A new method for reducing the harmonics involved in the output voltages of a double-connected inverter is proposed. By adding four auxiliary switching devices and an interphase transformer with a secondary winding to the conventional 12-step inverter, output voltages of the proposed circuit can produce almost the same waveforms as a conventional 36-step inverter. In this paper, circuit performances and output voltage waveforms are discussed, and optimum parameters are derived. The effects on harmonic reductions are then clarified by theoretical and experimental results, and the ratings of system components are investigated. >

A control scheme for a three-phase current source inverter in utility interactive photovoltaic system

A novel PWM control scheme for a three-phase current source inverter of a photovoltaic (PV) generation system connected to a utility is proposed. The PV-array output power can be adjusted by controlling the modulation factor in the proposed PWM pattern. The harmonic components of the output currents can be decreased sufficiently to satisfy the requirements of the Interactive Guidelines. Furthermore, a new Maximum Power Point Tracking control is proposed. The inverter output current should be detected, and the modulation factor may be controlled so as to obtain the maximum effective current. The inverter output power can be maintained at the maximum power point despite fluctuations of panel temperatures, insolation levels, and system voltages.

A method for reducing harmonics in output voltages of double connected inverter

A novel method for reducing harmonics involved in output voltage of double-connected inverter apparatus is proposed. by adding four auxiliary switching elements and an interphase power transformer with a secondary winding to the usual 12-step inverter, the proposed circuit decreases the harmonics in output voltages no less than the conventional 36-step inverter. The basic theory for the proposed inverter is discussed by analyzing the output voltage waveforms, and the optimum parameters are derived. Then, one can recognize the effects of harmonic reductions from theoretical and experimental results.<<ETX>>

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>>

Photovoltaic power system with simplified cascade boost choppers

Photovoltaic (PV) modules under different solar irradiances have generally the distinct maximum power points. In this paper, a circuit topology for obtaining the respective maximum powers from the above PV modules is investigated. Simplified double cascade boost choppers are proposed and a control scheme to derive the respective maximum output powers from individual PV modules is discussed. Furthermore, the Maximum Power Point Tracking controls on the starting operation, on the solar irradiance change and on the load fluctuation are confirmed by several experiments.

An AC-DC Converter with Power Compensator Functions for Single-Phase Three-Wire Distribution System

We have already proposed a power factor correction converter, composed of two half-bridge structures, connected to the single-phase three-wire distribution system. In this paper, by applying the above converter, we propose an AC-DC converter with several power compensator functions, as current balancer, static var generator and active filter, for the distribution system. As a result, even if every kind of loads are connected to the distribution system, the source currents can be balanced, their power factors can be maintained almost the unity and harmonic currents can be decreased effectively by the proposed converter, while itself outputs the DC power

An improved voltage source inverter with 18-step output waveforms

A new voltage source inverter with 18-step output waveforms is proposed in this paper in order to reduce harmonic components involved in the output voltages. Even though a conventional 18-step inverter employs three output transformers, the proposed circuit is no necessity for them. It is based on the neutral-point-clamped inverter composed of 12 switching devices. By dividing the DC voltage source into four pieces and adding four auxiliary switching devices, the proposed circuit can output almost the same waveforms as a conventional 18-step inverter. In this paper, the circuit performances are described and output waveforms are discussed. Then, the optimum parameters are derived and effects on harmonic reduction can be clarified by theoretical and experimental results. In addition, methods for adjusting output voltages are investigated.

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.