Fukashi Ueda

Parallel-connections of pulsewidth modulated inverters using current sharing reactors

A technique of parallel connection of power devices by using current sharing reactors for pulsewidth modulated (PWM) inverters is reported in this paper. The proposed technique not only increases the current capacity but also decreases the output harmonic contents. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, thus it is anticipated that it will be difficult to analyze the output waveforms. For such waveforms, a frequency analysis approach is described, whose results are verified by experiments. >

A pulsewidth-modulated inverter with parallel connected transistors using current-sharing reactors

A technique for parallel connection of transistors by using current-sharing reactors for the pulse-width-modulated (PWM) transistor inverter is reported. The technique not only increases current capacity, but also decreases the output harmonic contents. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, and thus it is anticipated that it will be difficult to analyze the output harmonics. For such waveforms, a frequency analysis approach is described, and its results are verified by experiments. >

Application of parallel connected NPC-PWM inverters with multilevel modulation for AC motor drive

The neutral point clamped (NPC)-PWM inverters have been put into practical use for large capacity AC motor drives, because of their many advantages. With the increase in use, still larger capacity inverters are also expected. In this paper, a parallel connected NPC-PWM inverter is applied for AC motor drive. The conventional modulation techniques are extended to improve the inverter characteristics. To determine an optimum modulation for controlling the parallel connected NPC-PWM inverter, various modulation techniques are devised and discussed, whose results are verified by experiment.

Development of an on-line impedance meter to measure the impedance of a distribution line

In order to tackle the problem of harmonic elements in a distribution line system, it is important that we are able to measure the impedance of the distribution line in a simple way. In addition, it is desirable that we make the measurement without service interruption. The line impedance could be measured by a technique derived from fundamental measurement theory, in which only passive elements such as inductors or resistors are used. However, as the voltage and/or current being measured increases, the size of inductor or resistor would also need to be increased, so it would be very difficult for such a measurement system to be implemented. Under such circumstances, a novel measurement method for determining line impedance using an inverter circuit is proposed in this paper. In the case where we are determining the resistance, the result that we obtain also includes the circuit loss, so this needs to be measured in advance and subtracted from the result. In the case where we are determining the inductance, the line inductance can be measured relatively accurately.

Line Loss Minimum Control of Loop Distribution Systems Using UPFC

This paper presents an elaborated mathematical analysis of the line loss minimum condition of loop distribution systems. In order to achieve this condition, the unified power flow controller (UPFC), a typical FACTS (flexible AC transmission systems) device that is capable of instantaneous control of transmission and distribution power flow, is used. Also, the available control schemes of the UPFC to minimize the total line loss of the loop distribution system are presented. The authors propose the line inductance compensation control and the line voltage compensation control which can be applied to the loop distribution system according to the line parameters. The effectiveness of the proposed control scheme, line inductance compensation control, has been verified experimentally using laboratory prototype in a 200 V, 6 kVA system.

A technique of parallel-connections of pulsewidth modulated NPC inverters by and using current sharing reactors

A technique of parallel-connection of power devices by using current sharing reactors for the pulse-width modulated (PWM) inverters is reported in this paper. The proposed technique not only increases current capacity but also reduces output harmonic content. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, thus it is anticipated that it will be difficult to analyze these output waveforms. For such waveforms, a frequency analysis approach is described, whose results are verified by experiments.<<ETX>>

A novel PFC circuit for three-phase utilizing a single switching device

Nonlinear rectifier circuits, having capacitors or inductors, are generally used as rectifier circuits, such as those in consumer electronics and appliances. It is known that such rectifiers generate various harmonics in the power system. To reduce these harmonic problems, various original PFC (Power Factor Correction) circuits have been proposed. Amongst these, Prasad-Ziogas, et al, have proposed a PFC scheme using single switching device for three phase circuit applications. This method achieves a PFC effect by simultaneously creating three phase supplies by the use of a single switch through an inductor. On the basis of this scheme, we propose an alternative PFC circuit. This method attempts to improve the input current, approaching a nearly sinusoidal waveform, by using an intermediate capacitor circuit, with a method of operation analogous to the conventional method having capacitor filter, but is, nonetheless, original. Various fundamental operations have been considered and have been confirmed by computer simulation. Compared with the conventional Prasad-Ziogas circuits, the construction is a little more complicated, but the output power can be much increased, in addition to improved THD (Total Harmonic Distortion).

Power flow estimation and line-loss-minimization control using UPFC in loop distribution system

This paper presents the line loss minimization control using a UPFC (Unified Power Flow Controller) with power flow estimation in a loop distribution system. The minimization of line loss is realized by eliminating the circulating current using the UPFC in the loop system. In the control of the UPFC, all line current in the loop distribution system are necessary. Therefore, the condition and scheme for estimating the all line currents are derived. The effectiveness of the proposed control scheme has been verified by experiments using the laboratory prototype in the 200V-system.

On-line impedance meter to measure the impedance of a distribution line using inverter

To tackle the harmonic problem in a distribution line system, it is important that we are able to measure the impedance of the distribution line in a simple way. In addition, it is desirable that we make the measurement without service interruption. Under such circumstances, a novel measurement method for determining line impedance using an inverter circuit is proposed in this paper. In the case where we are determining the inductance, the line inductance can be measured relatively accurately. Moreover, we also propose the measurement method of the line capacitance. Finally, in the case where we are determining the resistance, the line impedance is measured by a technique derived from fundamental measurement theory, in which only passive elements such as inductors or resistors are used.

A novel PFC circuit using ladder type filter employing only passive devices

For various rectifier circuits such as those for consumer electronics and appliances, rectifier circuits of the capacitor input type are generally used. It is known that such rectifier generates various harmonics in the power system. To improve those harmonic problems, various PFC circuits have been proposed so far. Among these, Takahashi have proposed a PFC scheme using a LC filter without switching devices. This method makes a PFC effect by widening conduction period using the operations of capacitors and inductor. On the basis of this scheme, we propose another PFC circuit. This method attempts to improve the input current, towards satisfactory waveform by using a novel ladder type filter.