Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2000-09-20
2001-11-20
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C363S098000
Reexamination Certificate
active
06320775
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for converting input ac power into dc power and further converting the dc power into desired ac power, or an apparatus for converting input dc power into desired ac power.
BACKGROUND OF THE INVENTION
FIG. 46
is a circuit diagram showing a first known example of the above type of power conversion apparatus. This apparatus includes a single-phase ac power supply
101
, reactor
102
, converter
201
for shaping the waveform of input current into a sinusoidal wave having a high power factor, smoothing capacitor
202
provided in a dc intermediate circuit, and a three-phase voltage type inverter
231
for driving an induction motor
501
at variable speeds. In
FIG. 46
, the induction motor
501
is represented by its equivalent circuit.
In the converter
201
shown in
FIG. 46
, an ac power supply voltage applied through the reactor
102
is short-circuited by semiconductor switches, to thus form a suitable waveform of input current. As a result, ac power generated from the ac power supply
101
is converted into dc power, and the waveform of the input current is controlled to be in the shape of a sinusoidal wave. On the other hand, the inverter
231
consists of a three-phase voltage type PWM inverter, or the like, which includes three pairs of upper and lower arms each consisting of a self-commutated semiconductor switching element, such as IGBT, and a diode that is connected in reverse parallel to the switching element. The operation of this three-phase voltage type PWM inverter is well-known in the art, and therefore will not be explained in detail. The inverter
231
may operate in a selected one of six switching patterns established by controlling the conduction states of the six arms so as to control voltage between respective lines of the three phases, and two switching patterns associated with a zero-voltage vector, which are established by conducting all of the upper arms or all of the lower arms, so that all of the voltages between the lines of the three phases are made equal to zero level.
In the following description of other known circuits, the same reference numerals as used in
FIG. 46
will be used for identifying functionally corresponding components or elements.
FIG. 47
is a circuit diagram showing a second known example of the above-described type of power conversion apparatus. The apparatus includes a dc power supply
103
, and a converter (two-quadrant chopper)
204
which consists of one pair of upper and lower arms and serves to control the voltage applied to the inverter
231
.
In this known circuit, dc power supply voltage applied through the reactor
102
is short-circuited by semiconductor switches, so that some energy is stored in the reactor
102
. When the semiconductor switches are turned off, the energy of the reactor
102
is supplied, together with energy from the dc power supply
103
, to the smoothing capacitor
202
, so that the dc voltage of the smoothing capacitor
202
becomes higher than the power supply voltage.
In the power conversion apparatus shown in FIG.
46
and
FIG. 47
, the capacitance of the smoothing capacitor
202
is made sufficiently large, so that switching operations of the converter
201
or converter
204
, and the inverter
231
can be freely performed independently of each other.
FIG. 48
is a circuit diagram showing a third known example of the above type of power conversion apparatus, wherein reference numeral
104
denotes a single-phase, full-wave rectifier circuit consisting of a diode bridge, and reference numeral
205
denotes a converter in which the upper arm consists solely of a diode.
In the apparatus shown in
FIG. 48
, ac power supply voltage is subjected to full-wave rectification by the full-wave rectifier circuit
104
, and the resulting dc voltage applied through the reactor
102
is short-circuited by semiconductor switches, thereby to form a suitable waveform of input current. In this manner, ac power generated from the ac power supply
101
can be converted into dc power, and the waveform of the input current can be controlled to be in the shape of a sinusoidal wave.
FIG. 49
is a circuit diagram showing a fourth known example of the above type of power conversion apparatus. This circuit diagram is disclosed in a paper titled “715 Reduction in Capacitance of Capacitor of Single-phase PWM Converter Having DC Active Filter Function” printed in 1996 National Convention Record I.E.E. Japan.
The apparatus shown in
FIG. 49
includes a single-phase ac power supply
101
, reactor
102
, converter
201
, inverter
231
, two-quadrant chopper
401
, smoothing capacitor
202
provided in a dc intermediate circuit, reactor
403
and capacitor
404
used for filters, and an induction motor
501
.
While the operation of this circuit will not be described in detail, its basic operation is such that the converter
201
performs PWM control so as to keep a sinusoidal waveform of ac input current, while controlling the input power factor to 1. In order to absorb power ripple arising at the dc output side of the converter
201
and having a frequency that is twice as high as the power supply frequency, the two-quadrant chopper
401
controls the voltage of the capacitor
404
so as to supply and receive energy, thereby to reduce the capacitance of the smoothing capacitor
202
.
FIG. 50
is a circuit diagram showing a fifth known example of the above-described type of power conversion apparatus. This circuit diagram is disclosed in a paper titled “One Measure to Reduce DC Voltage Ripple of Single-phase PWM Converter” printed in the Transactions of I.E.E. J. A Publication of Industry Applications Society published in 1993 (vol. 113-D, No. 9, p. 1106-p. 1107).
FIG. 51
is a circuit diagram showing a sixth known example of the above type of power conversion apparatus. This circuit diagram is disclosed in a paper titled “79 Method for Reducing Power Ripple of Single-phase Voltage Type PWM Converter” printed in 1996 National Convention Record I.E.E.J. Industry Applications Society.
In
FIG. 50
, reference numeral
405
denotes a LC filter in the form of a series resonance circuit that is coupled to a dc intermediate circuit. In
FIG. 51
, reference numeral
406
denotes a reactor.
While the operations of these circuits will not be described in detail, their basic operations are such that power ripple arising at the dc output side of the converter
201
and having a frequency that is twice as high as the power supply is absorbed by the LC filter
405
of
FIG. 50
or the reactor
406
of
FIG. 51
having the same resonance frequency, so that the capacitance of the smoothing capacitor
202
can be reduced.
In any case of the known circuits shown in FIG.
46
through
FIG. 51
, the reactor
102
needs to be provided on the input side of the converter
201
,
204
or
205
, for the purpose of absorbing the ripple that arises upon switching of the converter, and therefore the overall size and cost of the power conversion apparatus cannot be reduced as desired.
In the known circuits shown in FIG.
49
through
FIG. 51
, the reactor (reactor of the LC filter
405
or reactor
406
) is used for absorbing the power ripple, and therefore the size and cost of the power conversion apparatus cannot be reduced as desired.
In the known circuits shown in FIG.
49
and
FIG. 51
, one pair of upper and lower arm (two-quadrant chopper
401
) needs to be added to the dc intermediate circuit, and therefore the size and cost of the power conversion apparatus cannot be reduced as desired. Also, the known circuit as shown in
FIG. 50
suffers from a problem that the breakdown voltage of the capacitor of the LC filter
405
becomes twice as high as the intermediate dc voltage.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a power conversion apparatus which has a simple circuit configuration, and permits reduction in its size and cost.
To accomplish the above object, there is provided according the first aspect of the present invention a
Fujita Koetsu
Ito Jun-ichi
Fuji Electric & Co., Ltd.
Laxton Gary L.
Rossi & Associates
Wong Peter S.
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