Hitachi, Ltd.

Other

Teiichi Furukawa

Hiroyuki Tomita

Toshiaki Okuyama

Junji Kato

Kinya Nakatsu

Masahiro Hiraga

Keijiro Sakai

Seiji Ishida

Tetsuya Kimura

An inverter apparatus for converting a DC power converted from an input AC power to an output AC power of a variable frequency and a variable electric power to drive an induction motor at a variable speed. The inverter apparatus includes a rectifying unit, a filter capacitor, an inverter unit having an input connected across the filter capacitor, an input current detector and a gate circuitry for driving the inverter unit. An excitation current detection unit detects an excitation current of the induction motor from an output signal of the input current detector, a gate signal for driving the gate circuitry and a reference phase command. A setting unit sets a limitation level of the excitation current, a torque boost voltage command unit produces a torque boost voltage command, and a torque boost voltage compensation unit changes the torque boost voltage command so that the detected excitation current value is smaller than or equal to the limitation level.

Inverter apparatus

Induction voltage command Em* is obtained from inverter's primary frequency command &ohgr; * and torque boost voltage commander produces torque boost voltage command &Dgr;Vz* in accordance with &ohgr; * while integrator produces reference phase command &thgr;d*. uvw/dq converter detects motor excitation current Id (equivalent of no-load current). Next, deviation of excitation current limitation level command Idmax* and detected Id is inputted to limiter processing unit to produce torque boost voltage compensation value &Dgr;Vc for varying &Dgr;Vz* so that Id is smaller than or equal to Idmax*. Inverted &Dgr;Vz* is set up as a lower limiter value of the limiter processing unit. Next, &Dgr;Vc and &Dgr;Vz* are added to produce final compensated torque boost voltage command &Dgr;Vt* and &Dgr;Vt* and Em* are added to produce q-axis voltage command Vq* of the inverter output voltage.

PWM inverter with long carrier wave insertion

AC current detecting device for inverter apparatus and AC current detecting method therefor

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Narashino, Japan

Teiichi Furukawa