Shinji Sato

Single-chip microcomputer control of the inverter by the magnetic flux control PWM method (machine control)

Single-chip microcomputer control of a pulsewidth-modulated (PWM) inverter for motor drive applications is presented. The PWM pattern generation and the system control of the inverter are achieved by software of the 8-bit single-chip microcomputer. The single-chip microcomputer has a low processing speed and small memory capacity, disadvantages that can be overcome by the magnetic flux control PWM method. The PWM pattern is generated every 90 mu s. The memory capacity of the PWM look-up table is less than 2 kbytes. Experimental results show that the motor performances are the same as that of the multichip triangular-sinewave PWM inverter. >

High efficiency, unity power factor VVVF drive system of an induction motor

A high-efficiency, unity-power-factor VVVF (variable voltage, variable frequency) drive scheme for an induction motor is presented. A unity-power-factor PWM (pulsewidth modulated) converter regulates DC voltage. An inverter circuit with the magnetic flux control PWM method generates VVVF PWM waveforms. The modulation factor of the inverter PWM control with controllable DC link DC voltage is studied. As a result, the distortion factor and the switching frequency are reduced by over-modulation with low DC link voltage. A high-efficiency and unity-power-factor VVVF induction motor drive has been achieved using the control strategy. >

New single-phase unity power factor PWM converter-inverter system

A single-phase, unity power factor converter-inverter is presented for an induction motor drive. The converter circuit, which delivers sinusoidal input current, regulates DC voltage. The inverter, which uses the magnetic flux control PWM (pulse-width-modulation) method, generates a variable-voltage, variable-frequency PWM waveform in order to minimize the output voltage distortion factor. The experimental result shows that the motor efficiency is as high as that of the sinusoidal output voltage. As a result, the system efficiency and the power factor are improved.<<ETX>>

Relationship between electrode surface roughness and impulse breakdown voltage in vacuum gap of Cu and Cu-Cr electrodes

The relationship between the impulse breakdown voltage of vacuum gaps and electrode surface roughness was investigated for the purpose of controlling the surface roughness on HV conductors. The roughness of mechanically polished Cu and Cu-Cr electrodes was measured with a roughness meter, and the relationship between the breakdown voltage and surface roughness was obtained for plate-to-plate gaps. The discharge-conditioning effect increased with reduction in the surface roughness. The breakdown voltage depended not only on the roughness of the cathode but also on the anode surfaces. Reducing the surface roughness was found not to be an effective way to increase the breakdown voltage for non-uniform field gaps after discharge conditioning.

Restrike characteristics on capacitive current breaking in vacuum

Restrike characteristics on a capacitive current breaking in a vacuum have been investigated. In a small capacitive current breaking test, double voltage from commercial voltage (peak) would be applied between contacts of a VI. The configuration of contacts and the current conditioning dependence of VI practical samples with axial magnetic field contacts were investigated under a simulated capacitive current breaking test. Minimum restrike voltage decreased and voltage dispersion was high due to the presence of slits on the contacts. On the other hand, the minimum restrike voltage increased and restrike voltage dispersion was low due to current conditioning. By practical tests and standardized tests, a new 72 kV VI and dry air insulated VCB has been developed.

Voltage modulation factor of the magnetic flux control PWM method for inverter

The voltage modulation factor of the magnetic flux control pulse-width modulation (PWM) method is discussed. The modulation factor is derived from a theoretical study on the flux locus produced from the inverter output voltage. The derivation is based on the fact that the fundamental component of the inverter output voltage is proportional to the radius of the flux locus. It is shown theoretically that the voltage modulation factor is expressed by the content of a zero vector in one cycle of the selected PWM pattern of the space vector expression. The modulation factor of the magnetic flux control PWM method is calculated. The modulation factor can be varied from zero to 12/ pi /sup 2/. The output voltage of the magnetic flux control PWM method can be controlled by the modulation factor linearly from zero up to overmodulation. The simulation and experimental results are also shown. >

Effect of mechanical polish of electrode on several breakdown characteristics of vacuum gap

For the purpose of controlling conductor surface roughness, relationships between breakdown voltage of vacuum gaps and electrode surface roughness were discussed The roughness of mechanically polished Cu and CuCr electrodes were measured by a roughness meter. Experimental formula between breakdown voltage and surface roughness were obtained for plate-to-plate gaps of both Cu and CuCr electrodes. It was shown that the discharge conditioning effect increased with reducing the value of surface roughness. The breakdown voltage depended on not only cathode surface but also anode. Moreover, for nonuniform field gaps after treating the discharge conditioning, it was found that improvement in surface roughness was not effective on increasing breakdown voltage.

Behavior of conductive microparticles under electric field in vacuum and their influence on breakdown characteristics

Impulse breakdown voltage (BDV) for the gap which was injected with copper microparticles with a diameter from 7 to 500 /spl mu/m is measured. Electrode materials are copper, stainless steel, and an alloy of copper and chromium. In the short gap (approximately <5 mm), the BDV does not depend on the particle size or electrode material. However, in the long gap (>5 mm), the BDV varies according to the particle size and electrode material. Compared with the short gap, incrementation of the BDV with an increase in gap length is gradual. For both gap ranges, the BDV under negatively charged particles is lower than the BDV under positive polarity. The effectiveness of electrode surface roughness on the BDV is small compared with the clear gap. Further, AC voltages are applied to a rod-plate gap which was injected in the particles in order to observe their dynamic behavior. The particles begin to move when the upper direction electrostatic force originated by the AC field competes to the gravity force acting on the particles, and are finally removed from the area where the electrostatic force exceeds the gravity force as a result of reflection movements between electrodes.

Flashover voltage of alumina ceramic contaminated by metal vapor in vacuum interrupters

We have discussed the influence of metal vapor contamination for ceramic surface of vacuum interrupters (VIS) on surface flashover characteristics. Firstly, using the metal vapor emission fmm CuCr contacts, we produced disk-shape alumina (A1203,) ceramic samples with surface resistivity (p) of 102-1015 Ω, and measured their surface flashover voltages. It was identified that lightening impulse flashover voltage decreased as p reduced and that both the conditioning effect and scattering of the flashover voltage became small when pwas below 1012 Ω. Secondly, we produced two types of VIS, with CuCr spiral contacts and CuCr axial magnetic field contacts respctively, to conduct forty times of short-circuit current interruptions with 20-40 kArms. It was specified that p f o r the ceramic of the VI with spiral contacts reduced down to 104 Ω, and that breakdown vokage between terminals of the VI also decreased. pand breakdown voltage for the VI with AMF contacts did not decreased.