Power converter for AC load

Claim 2

1 . A power converter having a conversion circuit (12) connectible to an AC power source for converting AC power therefrom into DC power, a filter circuit comprising at least a capacitor (14) connected to the conversion circuit, and an inverter circuit (15) connected to the filter circuit for inversely converting the DC power into a second AC power, so as to drive an AC motor, the power converter comprising calculation means (62, 63) for calculating a torque current component of the AC motor from a three-phase terminal voltage and a three-phase terminal current of the AC motor; detection means (29) for detecting occurrence of an instantaneous interruption in the AC power source; command means (22) for commanding a frequency of said second AC power to be fed into the AC motor; control means (23) for controlling the terminal voltage of the AC motor in accordance with a signal relating to an output signal of said command means and a reference value; and first compensation means (64-67) for compensating the output signal of said command means so that the output signal of said calculation means (62, 63) is adjusted to be substantially zero in response to an output signal of said detection means (29).

Claim 3

The power converter according to claim 1, characterised in that said calculation means includes a first converter (71) for converting the three-phase terminal voltage of the AC motor into a two-phase voltage; a second converter (72) for converting the three-phase terminal current of the AC motor into a two-phase current; a first calculation circuit (73-81) for calculating a secondary flux vector of the AC motor from the output signals of said first converter and said second converter; a second calculation circuit (82) for calculating an absolute value from the secondary flux vector calculated within said first calculation circuit; a third calculation circuit (83) for calculating an instantaneous flux phase signal from the secondary flux vector and the absolute value thereof derived, respectively, from said first and second calculation circuits; and a fourth calculation circuit (86-88) for calculating a torque current component of the AC motor from the instantaneous flux phase signal calculated within said third calculation circuit and from the two-phase current derived within said second converter.

Claim 4

The power converter according to claim 1, characterised in the provision of second compensation means (121-123) for reducing the reference value of said control means to a certain specified value in response to the output signal of said detection means.

Claim 5

A power converter having a conversion circuit connectible to an AC power source for converting AC power therefrom into DC power, a filter circuit comprising at least a capacitor connected to the conversion circuit, and an inverter circuit connected to the filter circuit for inversely converting the DC power into a second AC power, so as to drive an AC motor, the power converter comprising first command means (34) for commanding a first torque current component of the AC motor on the basis of a speed reference of the AC motor and a speed of the AC motor; second command means (40) for commanding an exciting current component of the AC motor on the basis of a flux reference of the AC motor, and a three-phase terminal voltage and a three-phase terminal current of the AC motor; detection means (46) for detecting occurrence of an instantaneous interruption in the AC power source to produce a detection signal; first compensation means (141) for producing a compensated signal, the compensated signal is determined to be said first torque current component when the detection signal is not applied and to be substantially zero when the detection signal is applied; and third command means (41) for commanding an output voltage and a frequency of the inverter circuit on the basis of the compensated signal from said first compensation means and the exciting current component from said second command means.

Claim 6

A power converter having a conversion circuit connectible to an AC power source for converting AC power therefrom into DC power, a filter circuit comprising at least a capacitor connected to the conversion circuit, and an inverter circuit connected to the filter circuit for inversely converting the DC power into a second AC power, so as to drive an AC motor, the power converter comprising first command means (34) for commanding a first torque current component of the AC motor on the basis of a speed reference of the AC motor and a speed of the AC motor; second command means (40) for commanding an exciting current component of the AC motor on the basis of a flux reference of the AC motor, and a three-phase terminal voltage and a three-phase terminal current of the AC motor; detection means (46) for detecting occurrence of an instantaneous interruption in the AC power source to produce a detection signal; first compensation means (141) for producing a compensated signal, the compensated signal is determined to be said first torque current component when the detection signal is not applied and to be substantially zero when the detection signal is applied; and third command means (41) for commanding an output voltage and a frequency of the inverter circuit on the basis of the compensated signal from said first compensation means and the exciting current component from said second command means.

Claim 7

The power converter according to claim 4, further comprising second compensation means (142-144) for reducing the exciting current component to a certain specified value in response to the detection signal of said detection means.

Claim 8

The power converter according to claim 4, further comprising third compensation means (146-150) for calculating a second torque current component of the AC motor from three-phase terminal voltage and the three-phase terminal current of the AC motor; wherein said first compensation means further includes means for adding the first torque current component and the second torque current component to produce an added signal which is substantially zero; and means for producing said first torque current component as said compensated signal when the detection signal is not applied and said added signal as said compensated signal when said detection signal is applied.