| 摘要 |
PCT No. PCT/JP89/00889 Sec. 371 Date Apr. 24, 1990 Sec. 102(e) Date Apr. 24, 1990 PCT Filed Aug. 30, 1989 PCT Pub. No. WO90/02442 PCT Pub. Date Mar. 8, 1990.A current transformer (4) detects the output currents of a voltage-type inverter (INV), and comparators (6) check whether the outputs from the current transformer exceed a predetermined limit value. The detected output currents are fed to a vector analyzer (8) to determine the location of the output current vector. A zone determining circuit (9) determines the location of the current vector in the zones. An output pattern generating circuit (10) responds to the output from the zone determining circuit (9) and provides a switching pattern corresponding to the voltage vector nearest to a vector having the direction opposite to that of the output current vector. A selector (2), being controlled by the comparator (6), selects a switching pattern from the output pattern generating circuit and provides it to the inverter (INV), when the comparator (6) detects that the magnitude of the current vector exceeds the predetermined limit value. The rate of change of the output current vector works so as to reduce the current regardless of whether the motor (IM) (a load of the inverter) is to be driven or braked, regardless of the location of the counter-electromotive force vector or the location of the voltage vector selected at that timing when the current limit enters into action. This ensures that the output current of the inverter (INV) will be reduced.
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