Electricity: motive power systems – Positional servo systems – Pulse-width modulated power input to motor
Reexamination Certificate
2001-08-30
2003-12-02
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
Pulse-width modulated power input to motor
C318S811000, C388S804000
Reexamination Certificate
active
06657412
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pulse width modulation system, and in particular, to a pulse width modulation system for controlling a power converter.
FIG. 18
shows an example of a power converter using a pulse width modulation system. In
FIG. 18
, the reference numeral
1
refers to AC power supply,
2
to a rectifier circuit,
3
to a smoothing capacitor,
4
to a motor,
5
to a current detector,
6
to a PWM control unit,
7
to a current detection unit,
8
to a motor control unit, Qu, Qv, Qw, Qx, Qy and Qz to switching elements, and
10
to the power converter. Voltage supplied from the AC power supply
1
is rectified by the rectifier circuit
2
, and further, smoothed by the smoothing capacitor
3
, to be converted to DC voltage. By switching the switching elements Qu, Qv, Qw, Qx, Qy and Qz, the DC voltage is converted to a U-phase voltage, a V-phase voltage and a W-phase voltage connected to the motor
4
.
Further, the current detector
5
detects a DC current Idc that flows from the switching elements Qx, Qy and Qz to the smoothing capacitor
3
. And, the current detection unit
7
detects a U-phase motor current Iu, a V-phase motor current Iv and a W-phase motor current Iw based on the DC current Idc detected by the current detector
5
and from gate signals Gu, Gv, Gw, Gx, Gy and Gz outputted by the PWM control unit
6
.
Based on the detected motor currents Iu, Iv and Iw and a speed command Fr* given from the outside, the motor control unit
8
outputs a U-phase AC voltage command Eu, a V-phase AC voltage command Ev, and a W-phase AC voltage command Ew. And, based on the AC voltage commands Eu, Ev and Ew, the PWM control unit
6
outputs the gate signals Gu, Gv, Gw, Gx, Gy and Gz that instruct respective switching elements Qu, Qv, Qw, Qx, Qy and Qz. Here, the power converter
10
comprises the rectifier circuit
2
, the smoothing capacitor
3
, the current detector
5
, the PWM control unit
6
, the current detection unit
7
, the motor control unit
8
, and the switching elements Qu, Qv, Qw, Qx, Qy and Qz.
FIG. 19
shows a configuration of the PWM control unit
6
. The PWM control unit
6
comprises a carrier generation unit
601
, a U-phase comparing unit
602
, a V-phase comparing unit
603
, a W-phase comparing unit
604
, and reversing units
605
,
606
and
607
. The carrier generation unit
601
outputs a carrier C as a triangular wave of a frequency Fc, based on a carrier frequency command Fc. The U-phase comparing unit
602
, which outputs the gate signal Gu, compares the U-phase AC voltage command Eu with the carrier C, and outputs an H level when the U-phase AC voltage command Eu is larger, and outputs an L level when smaller. Further, the reversing unit
605
, which outputs the gate signal Gx, outputs the H level when the gate signal Gu is L level, and outputs the L level when the gate signal Gu is H level. Similarly, the V-phase comparing unit
603
, which outputs the gate signal Gv, compares the V-phase AC voltage command Ev with the carrier C, and outputs the H level when the V-phase AC voltage command Ev is larger, and outputs L level when smaller. Further, the reversing unit
606
, which outputs the gate signal Gy, outputs the H level when the gate signal Gv is L level, and outputs the L level when the gate signal Gv is H level. Further, the W-phase comparing unit
604
, which outputs the gate signal Gw, compares the W-phase AC voltage command Ew with the carrier C, and outputs the H level when the W-phase AC voltage command Ew is larger and L level when smaller. Further, the reversing unit
607
, which outputs the gate signal Gz, outputs the H level when the gate signal Gw is L level and outputs the L level when the gate signal Gw is H level.
Next, operation of the PWM control unit
6
will be described.
FIG. 20
is a waveform chart for various parts including the PWM control unit, and its horizontal axis is a time axis. Each waveform will be described in turn from the top. In
FIG. 20
, (a) shows waveforms of the AC voltage commands Eu, Ev and Ew and a waveform of the carrier C for pulse width modulation of the AC voltage commands Eu, Ev and Ew.
In
FIG. 20
, (b) shows a waveform of the gate signal Gu obtained by comparing the U-phase AC voltage command Eu with the carrier C. The waveform becomes H level when the U-phase AC voltage command Eu is larger than the carrier C, and becomes L level when the U-phase AC voltage command Eu is smaller than the carrier C. When the gate signal Gu is H level, the gate signal Gx becomes L level, and at that time, the switching element Qu becomes on and the switching element Qx becomes off. On the other hand, when the gate signal Gu is L level, the gate signal Gx becomes H level, and at that time, the switching element Qu becomes off and the switching element Qx becomes on.
In
FIG. 20
, (c) shows a waveform of the gate signal Gv that is obtained by comparing the V-phase AC voltage command Ev with the carrier C. That waveform becomes H level when the V-phase AC voltage command Ev is larger than the carrier C, and becomes L level when the V-phase AC voltage command Ev is smaller than the carrier C. A relation between the gate signals Gv and Gy, and operations of the switching elements Qv and Qy are similar to the relation between the gate signals Gu and Gx and the operation of the switching elements Qu and Qx, respectively.
In
FIG. 20
, (d) shows a waveform of the gate signal Gw that is obtained by comparing the W-phase AC voltage command Ew and the carrier C. The waveform becomes H level when the W-phase AC voltage command Ew is larger than the carrier C, and becomes L level when the W-phase AC voltage command Ew is smaller than the carrier C. A relation between the gate signals Gw and Gz, and operation of the switching elements Qw and Qz are similar to the relation between the gate signals Gu and Gx and the operation of the switching elements Qu and Qx, respectively.
In
FIG. 20
, (e) shows a waveform of a line voltage Vuv between a U-phase output to which the switching element Qu is connected and a V-phase output to which the switching element Qv is connected, out of line voltages as outputs of the power converter.
In
FIG. 20
, (f) shows waveforms of currents that flow from the power converter
10
to the motor
4
. Here, the symbol Iu refers to the U-phase motor current, Iv to the V-phase motor current, and Iw to the W-phase motor current. The U-phase motor current Iv, the V-phase motor current Iv and the W-phase motor current Iw correspond to the U-phase output to which the switching element Qu is connected, the V-phase output to which the switching element Qv is connected, and the W-phase output to which the switching element Qw is connected, respectively.
In
FIG. 20
, (g) shows a waveform of the DC current Idc. By turning on and off the switching elements, based on the gate signals, the outputs of the power converter, i.e., the U-phase voltage, the V-phase voltage and the W-phase voltage with respect to the lower terminal (cathode) of the smoothing capacitor
3
have waveforms similar to the gate signals Gu, Gv and Gw, respectively. As a result, the line voltage Vuv of the motor becomes the voltage shown in the figure. As described above, the PWM control unit
6
outputs the gate signals Gu, Gv and Gw, by comparing the carrier C with the AC voltage commands Eu, Ev and Ew, respectively.
Next, referring to
FIG. 21
, a method of detecting the motor currents Iu, Iv and Iw in the current detection unit
7
will be described.
FIG. 21
shows details of the period T
1
in FIG.
20
. In
FIG. 21
, the horizontal axis indicates time, and the vertical axis indicates the gate signal Gu, the gate signal Gv, the gate signal Gw, the line voltage Vuv, a line voltage Vvw between the V-phase output and the W-phase output, a line voltage Vwu between the W-phase output and the V-phase output, and the DC current Idc, in turn from the top. As shown in
FIG. 20
, the sign of the V-phase motor current Iv is plus, and the signs of the U-phase motor current Iu and the W-phase motor current I
Ando Tatsuo
Fujii Hiroshi
Ishida Seiji
Kimura Hideo
Okuyama Toshiaki
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Masih Karen
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