– Three-phase multi-level voltage-fed converters operated by a two-phase PWM scheme offers relatively high ac voltage, low switching times, and low switching losses in comparison to that operated by a three-phase PWM scheme.However, the harmonics involved in the ac-side voltages and currents produced in the two-phase PWM scheme are distributed over a wide frequency range, which can be a significant drawback depending on its applications. To overcome this problem,the authors propose novel two-phase PWM scheme in which the harmonics appear in a frequency range as narrow as that in a the conventional three-phase PWM scheme. In this paper, the authors present the validity of the proposed PWM scheme from simulation and wavelet transform results.

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–We have already proposed the new control method for the bidirectional isolated dc/dc converter. This method is that the output terminals of two single phase bridge inverter A and B are connected through an isolated transformer, and the pulse width of the inverter of higher d.c. voltage is narrowed to make equal the fundamental a.c. voltage of both inverters. For example, to make the a.c. output voltage of both inverters same, the pulse width of the INV-A is 180 degree and the pulse width of INV-B is narrowed to 60 degree. In this paper, the control method that the efficiency improvement of dc/dc converter by a current power-factor control is proposed. In this control system, the function of phase difference and the pulse width control are used. Since sine wave current will be brought near by a straight with a low d.c.voltage, the zero-electric-current switching can be realized.

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– In recent years, the power conversion capability of grid-connected power supplies using the photovoltaic generation system have been introduced rapidly. The power conditioning system (PCS) of PV generation system operates the reactive and active power flow control in accordance with the line voltage regulation level. The reactive power flow control by using the PCS and/or SVC can effectively decrease the line voltage level, however, the voltage imbalance of high voltage distributed line become the cause that results simultaneously.
This paper describes the novel power flow controller which is installed near by the pole transformer, to maintain the voltage level the grid-connected distribution line and the voltage imbalance compensation at the high voltage distribution line. Simulation results using the Matlab/Simulink are demonstrating the effectiveness of the proposed power flow converter system.

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– Hybrid switches with metal contacts and semi-conductor devices for no-arc interruption are presented.

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We have already proposed the new control method of the bidirectional isolated DC/DC converter with a current resonant circuit which can perform the zero-current switching and the power factor improvement by means of the pulse width control. This method is that the pulse width of the inverter of the higher d.c. voltage is narrowed to make equal the fundamental a.c. voltage of both inverters. However,in this current resonant circuit, since the reactor becomes large and the resistance increases, there is a problem that the improvement of the efficiency is not so high. In this paper, in order to solve these problems, a new bidirectional isolated dc/dc converter using the NPC 3 level inverter will be proposed.

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This paper presents a new single-stage utility frequency ac-high frequency ac resonant power converter for high frequency induction heating applications.The newly-proposed ac-ac converter features a boost converter and full bridge resonant inverter integrated circuit with a source voltage sensorless control system.The experimental results of a 3.0kW-40kHz prototype are demonstrated on zero voltage soft switching(ZVS) operations and steady-state character-istics,then the validity of the proposed ac-ac converter is revealed from a practical point of view.

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This paper proposes an application of the Model Following Controlled (MFC) PWM inverter to grid-connected variable–speed wind generators using parallel-connected two-generator model in order that the wind generator system controlled by the grid connected MFC PWM inverter can behave as a synchronous generator. Simulation analysis is performed for evaluating the effectiveness of the proposed MFC PWM inverter and the wind generator system.

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This paper deals with a high-frequency chopper type step-down (buck) DC/DC converter system, which is designed for operating on the basis of a new conceptual delta-sigma modulation scheme developed by the authors. The novel typedelta-sigma modulator which consists of the prototype delta-sigma modulator and white noise-based multiplier is demonstrated specifically for this DC/DC converter. Large switching noise peaks suppression characteristics are illustrated and discussed by the spectrum analysis of the switched voltage of the buck type DC/DC converter. The spectrum of the converter is compared with those of prototype delta-sigma modulator and triangle carrier-based PWM generator.
And the output voltage of the DC/DC converter treated here can be controlled in the same manner as conventional PWM method.

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The Mild Hybrid has been mass-produced. It is equipped Motor-Generator in the vehicle, and is realized fuel efficiency improvement by deceleration energy recovery and Engine Assist.
In our laboratory, the Mild Hybrid system using an Alternator has been proposed. An alternator is automotive generator; it charges Battery and supplies power for electric component in the vehicle. Electric structure of an alternator is equivalent to a motor; therefore an alternator is able to control as Motor-Generator using Motor Driver Unit. In order to construct generic Mild Hybrid system, Authors conduct a study by installing proposed system to medium sized vehicle. For improvement of fuel efficiency, Assist-area is extended using higher battery voltage than that of general Mild Hybrid. And deceleration energy recovery is performed using Vector control. In proposed system, the alternator is controlled by using accelerator and Brake signal to assist the engine during acceleration, regenerate energy during deceleration, and otherwise charge the battery on constant voltage.
In this paper, authors report effectiveness of proposed system by simulation using M-G set and vehicle running test.

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This report introduces a 3 phase 3 wire 10kW photovoltaic power conditioner. LINE BACK αⅣthat uses an SiC device as the main circuit switching device. By using the SiC switching device, this power conditioner is able to greatly improve efficiency thus achieving a fanless, self-cooling and sealed structure. Furthermore, LINE BACK αⅣ is also equipped with functions like FRT, Output power control, new-type islanding operation detection that are required for grid stability.

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Power factor correction (PFC) converters are of three types, namely, boost- type, buck-boost-type, and buck-type.Out of these, boost-type is the standard type of PFC converter, which is used in a wide range of applications. Buck-boost-type converters, in contrast, are used for more specific applications. Although the buck-type converters have been rarely used previously, they have been used for applications such as LED drivers in recent years. Moreover, buck-type converters have some advantages: they are suitable for low output voltages, and are lighter and compact compared to buck-boost-type converters.Therefore, they should be used for a wider range of applications. In this paper, we propose a buck-type PFC converter using a novel control strategy, which realizes outstanding results for simple circuits. Furthermore, the operating principles of the control circuit and an evaluation of the results for a 100-W prototype are described in detail.

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– Three-phase current-fed inverters for line interactive systems operated by a two-phase PWM scheme offers relatively low switching times, and low switching losses in comparison to that operated by a three-phase PWM scheme.However, the harmonics involved in the ac-side currents produced in the two-phase PWM scheme are distributed over a wide frequency range, which can be a significant drawback depending on its applications. In this paper, compare the AC-side harmonics on the PWM schemes for the three-phase current-fed converter using a wavelet transform.

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– A single-phase 3-wired matrix converter connecting three-phase 4-wired micro-grid is used instead of transformers to improve the power quality on the Micro-grid. The switching harmonic analysis of the inverter circuit has been studied by former researchers. However, in MC systems, the harmonics of input current caused by switching operation has not been analyzed. MC is generally used for motor drive and the output currents of MC are smoothed by inner inductor in the motor.However, the series inductor used in the output filter is relatively small, so that the voltage drops due to the filter has small impact on the output current harmonics, which becomes large compared to the fundamental component and it influences the phase of the input fundamental current. In this paper, we formulate that the harmonics in output voltage finally effect the input current phase error of single-phase MC. The harmonics of input current caused by switching is calculated and confirmed by simulation.

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A multi-level inverter has advantages in high blocking voltages and reduced harmonics. However, it needs more complex technical challenges in the utilization of redundant switching vectors as its level is increased.This paper proposes a general space-vector (SV) modulation method for the optimal reduction of the switching losses in three-phase PWM inverter of an arbitrary n-level type. The proposed method consists of two steps. One is the general principle for generation of the SV map for an arbitrary n-level type. The other is the optimal selection of the SV pattern which minimizes the switching losses considering the three-phase currents based on the two-phase modulation method. Simulated examples controlled according to the proposed method are shown for some different levels.

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