Shigeo Masukawa

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.

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.

Development of quasi 24-step voltage source hybrid diode rectifier by injection harmonics

A new method for reducing harmonics involved in input voltages of a three-phase voltage source diode rectifier is proposed. It is applied to the conventional 6-step diode rectifier with a three-phase autotransformer. By injecting harmonics to the neutral point of the autotransformer from an auxiliary circuit, input voltages of the proposed diode rectifier can be almost the same as a conventional 36-step diode rectifier. In this paper, circuit performances and input voltage waveforms are discussed, and the optimum parameters are determined by taking effect of harmonic reductions. Then, characteristics of the proposed rectifier can be clarified by simulation results.

Development of quasi 24-step voltage source inverter

A new method for reducing harmonics involved in output voltages of a three-phase voltage source inverter is proposed. It is applied to the conventional 6-step inverter with a three-phase autotransformer. By injecting harmonics to the neutral point of the autotransformer from an auxiliary circuit, output voltages of the proposed inverter can be almost the same as a conventional 36-step inverter. In this paper, circuit performances and output voltage waveforms are discussed, and the optimum parameters are determined by taking effect of harmonic reductions. Then, characteristics of the proposed inverter can be clarified by simulation results and experimental results.

A Method for Reducing Harmonics in Input Current of Double Connected Three-Phase Hybrid Rectifier without Input Transformers

In this paper, a double connected three-phase hybrid rectifier employing thyristors and self-turn-off devices without input transformers is proposed. Two three-phase bridge rectifiers with auxiliary circuit injecting harmonic currents are connected in parallel. This system can be performed as the conventional 24-step rectifier on the optimum conditions. In this paper, circuit performances of the proposed method are discussed by graphical analysis, and optimum parameters are derived. Then, effects on harmonics reduction can be clarified by simulations.

A simplified 24-step inverter without output transformers

In this paper, we propose an improved multi-level voltage source inverter whose output harmonic components can be effectively reduced regardless of simple construction. It is based on the neutral-point-clamped (NPC) inverter. The input DC source is divided into six sections and an auxiliary circuit composed of six switching devices and four clamping diodes are added into the conventional NPC inverter. By controlling the auxiliary circuit appropriately, quasi 24-step voltage waveforms can be outputted from the proposed inverter though it has no output transformers. In this paper, the circuit performances are described and the output voltage waveforms are derived theoretically. The circuit constants and the control parameters for decreasing the output harmonics are discussed. It is made clear that the proposed inverter can be performed with the same output distortions approximately as the conventional 24-step inverter with 24 switching devices and the heavy output transformers. Moreover, in order to adjust the output voltages, the step width control and the PWM control are investigated theoretically and experimentally.