Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2000-01-18
2001-01-30
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S089000
Reexamination Certificate
active
06181583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply device which converts an alternating current into a DC, and reduces a harmonic distortion of an input current so as to improve a power factor.
2. Description of the Related Art
Conventionally, a capacitor input type rectifier circuit has been used as an AC-to-DC converter circuit in various fields. The capacitor input type rectifier circuit inputs an AC voltage to a diode rectifier circuit so as to obtain a ripple voltage output, and smoothens the ripple voltage output by a capacitor so as to obtain a DC voltage. However, in the capacitor input type rectifier circuit, a conduction period of an input current becomes narrow, and then, a power factor is worsened, and further, a reactive power is much. For this reason, it is not possible to effectively use a power, and the input current contains much harmonic distortions; as a result, there is a problem of fault to equipment connected to the identical power supply device. In order to solve the above problem, conventionally, a power supply device having a circuit configuration as shown in
FIG. 31A
has been developed as a technique for improving a power factor to reduce a harmonic distortion.
As shown in
FIG. 31B
, when a rectifier circuit
103
converts an AC voltage Vin from an AC power supply
101
into a ripple output voltage, the power supply device can relieve a rush of the input current Iin by an inserted reactor
102
. As a result, the conduction period becomes widened, and thereby it is possible to improve a power factor and to reduce a harmonic distortion contained in the input current Iin.
As described above, the conventional power supply device shown in
FIG. 31
has been used in various apparatuses because only passive components having a simple construction are inserted so as to improve a power factor.
In recent years, a power supply device as shown in
FIG. 32A
has been developed, which improves a power factor using active elements. The power supply device shown in
FIG. 32A
will be described below. In
FIG. 32A
, a control circuit
109
generates and outputs a signal for turning on and off a switching element
107
at a high frequency so as to form an input current into a shape of a sine wave. A reactor
106
is a high-frequency compliant reactor for forming the input current into a shape of sine wave together with the switching element
107
. A diode
108
prevents an electric change changed to a smoothing capacitor
104
from reversely flowing when the switching element
107
is in an on state.
The following is a description on an operation of the above power supply device. The control circuit
109
compares a detection current from an input current detecting circuit (not shown) with a sine wave-shaped reference waveform prepared based on a power supply voltage waveform, and then, generates and outputs a pulse signal for controlling an on/off of the switching element
107
so as to form the input current into a shape of a sine wave. The switching element
107
makes an on/off operation in accordance with the pulse signal to cause the reactor
106
to be in a short circuit or in an open circuit repeatedly so that the input current is brought close to the reference waveform. As a result, as shown in
FIG. 32B
, it is possible to obtain a sine wave-shaped input current substantially similar to the alternating voltage Vin of the AC power supply
101
, and thus, to bring a power factor close to 1. Further, it is possible to greatly reduce a harmonic distortion contained in the input current Iin.
Moreover, there is a power supply device which remarkably simplifies a switching control so as to improve a power factor, as disclosed in Japanese Patent Laid-open Publication No. 9-266674, 10-174442, or Japanese Patent No. 2-763479.
These power supply devices will be described below with reference to
FIGS. 33 and 34
.
In a power supply device shown in
FIG. 33A
, a reactor
102
is used for a low frequency. A control circuit
110
outputs a pulse signal for turning on the switching element
107
for a predetermined time in synchronous with a zero cross point of the AC power supply
101
. Whereby a current for short-circuiting the AC power supply
101
flows via the rectifier circuit
103
, the reactor
102
and the switching element
107
, and thereby, the input current flows from the zero cross point of the AC power supply
101
. Then, when the switching element
107
becomes an off state, a current flows through the rectifier circuit
103
, the reactor
102
, a reverse-current blocking rectifier element
108
and the smoothing capacitor
104
. As a result, it is possible to be make wide a conduction period to improve a power factor. Further, the control circuit
110
can output the pulse signal for turning on the switching element
107
after a delay of predetermined time from the zero cross point of the AC power supply
101
. The delay time may be set in accordance with a magnitude of load, and thereby, it is possible to obtain an optimum power factor for each load.
A power supply device shown in
FIG. 34A
includes capacitors
120
a
and
120
b
for improving a power factor. A control circuit
111
outputs a pulse signal for turning on a bi-directional signal
115
for a predetermined time in the vicinity of the zero cross point of the AC power supply
101
. Thus a charging current flows to the capacitor
120
a
or
120
b
via a reactor
102
and a rectifier circuit
103
. A phase of the charging current is advanced, it is therefore possible to make early a rise of the input current. Then, when the bi-directional switch
115
becomes off, an input current flows through the reactor
102
, the rectifier circuit
103
and a smoothing circuit
104
. Consequently, a conduction period of the input current can be widened to improve a power factor.
Moreover, in the power supply device shown in
FIG. 34A
, the control circuit
111
can change an output voltage value by changing a pulse width of the pulse signal. More specifically, the power supply device shown in
FIG. 34A
is operated as a full-wave rectifier circuit when the bi-directional switch is off, and is operated as a voltage doubler rectifier circuit when the bi-directional switch is in an on state.
Therefore, by changing a pulse width of the pulse signal, the control circuit
111
can change an output voltage within a range which is more than a voltage obtained a full-wave rectification, and is lower than a voltage obtained by a voltage doubler rectification.
However, in the above power supply device shown in
FIG. 31A
, its improvement effect is low although the power supply device can improve a power factor with a simple construction and a sufficient power factor can not be obtained. Since a reactor value must be made large in order to obtain high power factor with the circuit construction, it causes a problem that components would be made into a large size and a loss would simultaneously increase.
Even though the above power supply device shown in
FIG. 32A
can form the input current into a shape of sine wave and control a power factor to approximately 1, the power supply device has the following problems. More specifically, the control becomes complicate, and a loss in the switching element
107
is increased due to high frequency switching accompanying with waveform shaping, and further, a switching noise increases. Therefore a powerful filter circuit is required for restricting the aforesaid loss. This causes a cost increase, an increase of loss in the filter circuit, and finally efficiency deterioration as a whole.
The above power supply device shown in
FIG. 33A
has the following problems although it can remarkably simplify a switching control. More specifically, in particular, a current waveform becomes a non-continuous state as shown in
FIG. 33B
in a low load, or is too advanced; for this reason, a sufficient power factor can not obtained. Further, an output timing of the pulse signal is delayed for a predetermined time from the zero cross point of th
Ogawa Masanori
Okui Hiroshi
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Nguyen Matthew
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