Abstract: 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.

Abstract: Induction voltage command Em* is obtained from inverter's primary frequency command &ohgr;1* and torque boost voltage commander produces torque boost voltage command &Dgr;Vz* in accordance with &ohgr;1* 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.

Abstract: In calculation 3 phase AC output current Iu, Iv,Iw of an inverter based on the input DC current Idc of the inverter, it is difficult to detect the DC current Idc when the line-to-line voltage pulse width is narrow, thereby the DC current Idc pulse width becomes narrower. The frequency Fc of the carrier wave C is lowered in a phase whose line-to-line voltage is high, thereby the DC current Idc pulse width is set wider. As a result, the current detection is enabled.

Abstract: Establishing a current detection system good in accuracy allows implementation of a reduction in the size of an inverter apparatus good in current detection accuracy, even if the number of current sensors is reduced. A current sensor of a DC section and a current sensor corresponding to one phase of an output AC current are used, and means for determining switching patterns of DC main elements and determining a current component of Idc or means for detecting a maximum value of Idc is used, thereby determining an AC current value and a power factor angle.

Abstract: 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.

Abstract: In calculation 3 phase AC output current Iu, Iv,Iw of an inverter based on the input DC current Idc of the inverter, it is difficult to detect the DC current Idc when the line-to-line voltage pulse width is narrow, thereby the DC current Idc pulse width becomes narrower.

Abstract: Establishing a current detection system good in accuracy allows implementation of a reduction in the size of an inverter apparatus good in current detection accuracy, even if the number of current sensors is reduced.

Abstract: Induction voltage command Em* is obtained from inverter's primary frequency command &ohgr;1* and torque boost voltage commander produces torque boost voltage command &Dgr;Vz* in accordance with &ohgr;1* 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.