Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2000-09-11
2001-05-29
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S080000, C363S053000
Reexamination Certificate
active
06239992
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electric power unit with a condenser input type rectification circuit which converts an alternating current power source to a direct current voltage, and more particularly, to an electric power unit for inverter-controlled refrigerators, etc.
PRIOR ART
While a condenser input type rectification circuit has been widely used to convert an alternating current to a direct current in inverters of refrigerating systems such as refrigerators, air conditioners and the like, or in switching power sources, etc., a current waveform of the condenser input type rectification circuit is not a sine wave, but includes many higher harmonics, particularly higher harmonic components of odd orders of a fundamental frequency, thus causing various troubles. For lessening the current of higher harmonics, therefore, more and more development has been proceeded, one of which is realized as a passive filter. The passive filter is adapted generally to soften the current waveform with the use of a reactor thereby to suppress higher harmonics. However, the reactor of the passive filter should be of a considerably large capacity in order to completely suppress the higher harmonics only thereby. In the meantime, another type of proposals has been made to control the higher harmonics, in which an auxiliary means is employed. For instance, Unexamined Japanese Patent Laid-Open Publication No. H7-274515 describes an effective method for the purpose.
BACKGROUND TECHNOLOGY OF THE INVENTION AND ITS PROBLEM
In order to understand features of the present invention, an electric power unit adopting a conventional higher harmonics control method will be described with reference to
FIGS. 19 and 20
.
FIG. 19
is a circuit diagram of an example of a conventionally used electric power unit. An electric power unit
100
in
FIG. 19
is constituted of an alternating current power source
101
which is, for example, a commercial power source of 100V 50 Hz to general household, a bridge-type rectifier
102
for rectifying the alternating current power source
101
, a first reactor
103
, a diode
104
, a second reactor
105
, a capacitor
106
and a smoothing capacitor
107
. The bridge-type rectifier
102
consists of four diodes D
101
, D
102
, D
103
, D
104
in bridge connection.
The first reactor
103
has its one end connected to a + output of the bridge-type rectifier
102
and the other end connected to an anode of the diode
104
. The second reactor
105
has its one end connected to the + output of the bridge-type rectifier
102
and the other end connected to one end of the capacitor
106
. A cathode of the diode
104
is connected with the other end of the capacitor
106
, and connected also to one end of the smoothing capacitor
107
. The other end of the smoothing capacitor
107
is connected to a − output of the bridge-type rectifier
102
. A load
108
of the power unit
100
is connected to both ends of the smoothing capacitor
107
.
Now, the operation of the electric power unit
100
will be described.
FIG. 20
is a diagram of waveforms of a half cycle in the electric power unit
100
shown in FIG.
19
. An input voltage Vin from the alternating current power source
101
is a sine wave as indicated in
FIG. 20. A
current I
101
running in the first reactor
103
shows a bent waveform because a charging current to the smoothing capacitor
107
is smoothed at the first reactor
103
. A current I
102
running in the second reactor
105
shows a waveform oscillating with a resonant frequency of the second reactor
105
and capacitor
106
. An input current Iin becomes a sum of I
101
and I
102
, assuming a waveform as shown in FIG.
20
. Since the waveform of the input power is softened and a peak value of the current is lowered as above, higher harmonics are suppressed further.
The aforementioned arrangement has drawbacks, though. As described hereinabove, in the prior art, such current is supplied that supplements higher harmonics with the utilization of the resonance of the second reactor
105
and capacitor
106
and consequently, the resonant frequency is required to be set at three times a frequency of the power source. For example, when the power source has a frequency of 50 Hz, the resonant frequency should be set to approximately 150 Hz. The second reactor
105
should be approximately 10 mH supposing that the capacitor
106
has a capacity of 100 &mgr;F. In the conventional arrangement, both the second reactor
105
and the capacitor
106
should have large capacities in order to suppress the higher harmonics. The first reactor
103
alike should have a large current capacity to cope with a large current in case of a large load. From these reasons, the conventional electric power unit is disadvantageously bulky in size and is expensive.
SUMMARY OF THE INVENTION
The present invention is devised to solve the above-discussed problems and has for its object to provide an electric power unit which, with using smaller parts, sufficiently effectively suppresses higher harmonics in reduced size and cost.
In order to achieve the aforementioned objective, according to the present invention, an electric power unit for feeding electric power to a load comprises an alternating current power source, a bridge-type rectification circuit having an input from the alternating current power source and formed of diodes in bridge connection, an auxiliary capacitor connected in parallel to an output of the bridge-type rectification circuit, a series circuit consisting of a reactor and a diode which is connected between one output of the bridge-type rectification circuit and the load so as to feed a load current in a forward direction, and a smoothing capacitor connected in parallel to the load. Because of the auxiliary capacitor of a small capacity set at the output of the bridge-type rectification circuit, and since a charging current is sent to the auxiliary capacitor before the smoothing capacitor is charged, the charging current to the auxiliary capacitor is utilized as a supplementary current.
An electric power unit according to the present invention for feeding electric power to a load consists of an alternating current power source, a bridge-type rectification circuit of diodes in bridge connection with having an input from the alternating current power source, an auxiliary reactor having one end connected to one output of the bridge-type rectification circuit, an auxiliary capacitor connected between the other end of the auxiliary reactor and the other output of the bridge-type rectification circuit, a series circuit of a reactor and a diode connected between the other end of the auxiliary reactor and the load so as to feed a load current in a forward direction, and a smoothing capacitor connected in parallel to the load. The auxiliary reactor of a small capacity connected between the bridge-type rectification circuit and the auxiliary capacitor controls a charging current to the auxiliary capacitor not to rise sharply.
An electric power unit of the present invention feeds electric power to a load, which comprises an alternating current power source, a bridge-type rectification circuit formed of diodes in bridge connection with having an input from the alternating current power source, a reactor with a middle tap which has one end connected to one output of the bridge-type rectification circuit, an auxiliary capacitor connected between the middle tap of the reactor and the other output of the bridge-type rectification circuit, a diode connected between the other end of the reactor and the load so as to feed a load current in a forward direction, and a smoothing capacitor connected in parallel to the load. Because of the reactor constituted of a reactor with a middle tap, a count of parts of the electric power unit is reduced while the suppression effect to higher harmonics is maintained.
An electric power unit according to the present invention feeds electric power to a load, which comprises an alternating current power source, a bridge-ty
Endo Katsumi
Hamaoka Koji
Kurimoto Kazunori
Matsushita Refrigeration Company
Vu Bao Q.
Wenderoth , Lind & Ponack, L.L.P.
Wong Peter S.
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