Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
2000-05-16
2001-04-10
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S282000
Reexamination Certificate
active
06215287
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on application No. 11-135297 filed in Japan, the contents of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply apparatus which can supply a regulated (stabilized) DC voltage to electronic apparatuses for industry and livelihood.
2. Description of the Related Art
In recent years, electric and industrial apparatuses have come into wide use, and with this wise use, a high harmonic current is introduced into a power apparatus. This has caused problems such as heating of various apparatuses, malfunction and the like. In order to solve these problems, a suitable measure to the high harmonic is required in various apparatuses. Thus, an AC-to-DC converter has been used as a power supply apparatus built in these apparatuses. The AC-to-DC converter makes use of an energy storage effect by an operation of a reactor and a switching element, and corrects a power factor so as to raise an output voltage.
Japanese Patent Laid-open Publication No. 59-198873 has disclosed a control of the AC-to-DC converter.
As described in the Publication, the control is carried out in the following manner. AC voltage signal is multiplied by a voltage difference between a DC voltage and a target value thereof. Then, a conductive ratio is determined in accordance with the value obtained by the multiply to correct the power factor.
FIG. 10
is a circuit diagram showing a construction of the aforesaid conventional power supply apparatus.
An output of an AC power supply
1
is rectified by a rectifier circuit
2
comprising a diode bridge, and then the rectified voltage is switched by a switching element
4
via a reactor
3
. Further, voltage across terminals of the switching element
4
is smoothened by a smoothing capacitor
6
via a diode
5
so that a DC voltage is supplied to a load
7
. An operation of the switching element
4
is controlled by a switching operation controller
11
. The control flow is as follows.
First, a DC voltage value obtained by a DC voltage detecting section
10
is smoothened by a low-pass filter
110
. A voltage comparator
112
calculates a voltage difference between the smoothened value and a target value of DC voltage from a target voltage calculating section
111
. On the other hand, a target current calculating section
113
calculates a target current by multiplying the voltage difference by a voltage obtained from an input voltage detecting section
9
. Next, a current comparator
114
calculates a difference between the target current value calculated by target current calculating section
113
and the current value obtained by the current detecting section
8
. Then, in accordance with the difference thus calculated, a conductive ratio of the switching element
4
is determined by a PWM duty calculating section
115
. The switching element
4
is switched according to the conductive ratio.
In that AC-to-DC converter, when a load connected to the output terminal becomes large or heavy, as shown in
FIG. 11
, a ripple having a frequency of two times as much as a voltage
13
of an AC power supply in a DC voltage
14
. Therefore, it is general to use a value obtained by passing through a low-pass filter
110
having a slow response speed (with a fixed cut-off frequency of about 1 Hz as shown in
FIG. 12
) as a DC voltage value to be used for calculating a voltage difference value.
However, in the conventional AC-to-DC converter having the above construction, when a DC voltage raises in a small or light load state in which a load connected to an output terminal is small or light, since a DC voltage passing through a low-pass filter with a slow response speed is used to calculate a voltage difference between the DC voltage and a target value, that is, to determine a conductive ratio of the switching element, there is a problem that the DC voltage continues to raise.
In order to solve this problem, when the DC voltage value raises more than a threshold value which is pre-determined based on a target value, there is a control such that an operation of the switching element is temporarily stopped until the DC voltage value becomes the target value. However, according to such a control, as shown in
FIG. 13
, there is a problem that a DC voltage
16
is hunting between a target value
18
and a threshold value
19
(In
FIG. 13
, a waveform
17
shows a rectified voltage value after passing through the low-pass filter.).
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the above problem in the prior art. It is, therefore, an object of the present invention to provide a power supply apparatus which can prevent hunting from being generated in a DC voltage of an AC-to-DC converter even in a low load state.
In order to solve the problem, the present invention provides a power supply apparatus which comprises an AC-to-DC converter, a current detecting section, an input voltage detecting section, a DC voltage detecting section, a switching operation controller and a low-pass filter.
The AC-to-DC converter converts a DC voltage from an AC power supply to supply the DC voltage, and comprises at least a switching element, a reactor and a diode.
The current detecting section detects a current value of the AC power supply. The input voltage detecting section detects a voltage value of the AC power supply. The DC voltage detecting section detects a DC voltage value outputted from the AC-to-DC converter. The switching operation controller corrects a power factor based on each value obtained by the current detecting section, the input voltage detecting section and the DC voltage detecting section. The switching operation controller controls an operation of the switching element so that the DC value becomes a predetermined target value. The low-pass filter for smoothening the DC voltage form the DC voltage detecting section is included in the switching operation controller and has a cut-off frequency which is variable. The cut-off frequency may be varied in accordance with at least one of a detected value by the current detecting section, a detected value by the input voltage detecting section, and a detected value by the DC voltage detecting section, or a load state obtained based on those values.
With the above construction, it is possible to prevent hunting from being generated in a DC voltage of an AC-to-DC converter even in a low load state, and to perform a stable power factor correction and a boost operation even in the case where a load becomes high.
REFERENCES:
patent: 4688162 (1987-08-01), Mutch et al.
patent: 5793623 (1998-08-01), Kawashima et al.
patent: 5798635 (1998-08-01), Hwang et al.
patent: 5949229 (1999-09-01), Choi et al.
patent: 6034513 (2000-03-01), Farrington et al.
patent: 0695024 (1996-01-01), None
patent: 59-198873 (1984-11-01), None
patent: 8-33392 (1996-02-01), None
patent: 8168255 (1996-06-01), None
patent: 8182329 (1996-07-01), None
Matsushiro Hideo
Ogawa Masanori
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Nguyen Matthew
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