Electricity: electrical systems and devices – Safety and protection of systems and devices – Compressor protective circuits
Reexamination Certificate
1999-05-20
2001-01-30
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Compressor protective circuits
Reexamination Certificate
active
06181539
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power conversion apparatus and an air conditioner using the same and, more particularly, to a power conversion apparatus for rectifying and smoothing an AC voltage supplied from an AC power supply, converting the AC voltage into a DC voltage, reconverting the DC voltage into an AC voltage, and supplying the obtained AC voltage to a load, and an air conditioner using the same.
BACKGROUND ART
A large-capacity power conversion apparatus for converting an AC voltage supplied from an AC power supply into a DC voltage, further converting the DC voltage into a pulse-width-modulated (PWM) voltage, and supplying the PWM voltage to a load has conventionally been known.
For example, as a power conversion apparatus for 400 W to 5 kW, a passive filter power conversion apparatus is available in which a reactor is connected to an AC power supply line, and an AC voltage obtained via the reactor is rectified by a voltage doubling/rectifying circuit in order to increase the power factor and reduce the harmonic component of the power supply (distortion of the power supply waveform).
FIG. 17
is a circuit diagram showing the arrangement of an inverter apparatus used in an air conditioner using an AC power supply voltage in 100V class, i.e., a conventional passive filter power conversion apparatus for controlling the ability of a refrigeration cycle drive motor.
As shown in
FIG. 17
, one terminal of a reactor Lin is connected to one terminal of an AC power supply Vin.
The other terminal of the reactor Lin is connected to the connection point between series-connected diodes DH and DL.
The series circuit made up of the diodes DH and DL is parallel-connected to the series circuit made up of diodes D
1
and D
2
and the series circuit made up of capacitors CH and CL.
The other terminal of the AC power supply Vin is connected to the connection point of the diodes D
1
and D
2
and to the connection point of the capacitors CH and CL called voltage doubling capacitors.
A smoothing capacitor CD is connected between the two terminals of the series circuit made up of the capacitors CH and CL.
The voltage across the smoothing capacitor CD is supplied to an inverter
50
.
When the inverter
50
is connected to a load of about 1.8 kW, a reactor Lin having an inductance of 6.2 mH, voltage doubling capacitors CL and CH each having a capacitance of 360 pF, and a smoothing capacitor CD having a capacitance of 1,600 &mgr;F are employed.
In the positive half cycle of the AC power supply Vin, the capacitor CH is charged via the diode DH; in the negative half cycle, the capacitor CL is charged via the diode DL.
The sum of the capacitor CH charge voltage and the capacitor CL charge voltage is applied to the smoothing capacitor CD, and thus the voltage twice the AC power supply Vin is supplied to the inverter
50
.
The diode D
1
forms a discharge circuit so as not to reversely charge the capacitor CH at the start of charge.
The diode D
2
forms a discharge circuit so as not to reversely charge the capacitor CL at the start of charge.
The diodes DH, DL, D
1
, and D
2
, the voltage doubling capacitors CH and CL, and the smoothing capacitor CD shown in
FIG. 17
constitute a conversion section (to be described later) according to the present invention. The inverter
50
constitutes an inversion section (to be described later) according to the present invention.
That is, this conversion section includes a voltage doubling/rectifying circuit
45
and the voltage doubling capacitors CH and CL.
When a compressor drive motor (not shown) serving as a load is driven using the conventional power conversion apparatus, a harmonic component is generated in the power supply, as indicated by the current value in FIG.
18
.
FIG. 18
shows a current I (Lin) together with a current I (IEC) in class E standard by IEC (International Electrotechnical Commission). Comparing the current I (Lin) with the current I (IEC), the third harmonic component of I (Lin) exceeds that of I (IEC).
The third harmonic component can be reduced using a reactor having a larger inductance. In this case, however, the apparatus becomes bulky.
In the power conversion apparatus shown in
FIG. 17
, the power factor of the power supply is as relatively low as about 93%. As the load increases, an AC input current may increase, and the current value may reach a predetermined limit value. For this reason, the rotational speed and the like of the compressor drive motor (not shown) serving as a load are often limited.
FIG. 19
is a circuit diagram showing the arrangement of an inverter apparatus used in an air conditioner using an AC power supply voltage in 200V class, i.e., a passive filter power conversion apparatus for controlling the ability of a refrigeration cycle drive motor.
As shown in
FIG. 19
, the series circuit made up of diodes D
3
and D
4
is parallel-connected between the two terminals of the series circuit made up of diodes D
1
and D
2
to form a known full-wave rectifying circuit
40
.
One terminal of an AC power supply Vin is connected to the connection point between the diodes D
1
and D
2
, whereas the other terminal is connected to the connection point between the diodes D
3
and D
4
.
A power factor improvement capacitor CP is connected between the two terminals of the series-connected diode circuit, and a smoothing capacitor CD is also connected between them via a reactor Lin and a reverse-flow prevention diode DB.
The voltage across the smoothing capacitor CD is supplied to an inverter
50
.
The full-wave rectifying circuit
40
by the diodes D
1
, D
2
, D
3
, and D
4
, and the smoothing capacitor CD shown in
FIG. 19
constitute a conversion section (to be described later) according to the present invention. The inverter
50
constitutes an inversion section (to be described later) according to the present invention.
That is, this conversion section includes the full-wave rectifying circuit
40
and the smoothing capacitor CD.
FIG. 20
shows the voltage and current waveforms of one cycle in the power conversion apparatus shown in FIG.
19
.
As shown in
FIG. 20
, even a conduction angle of 110° leads to a power factor of only 90%. Compared to an AC power supply voltage in 100V class, an AC input current hardly reaches a limit value for the same input power.
However, the power factor is lower than in the power supply in 100V class. To increase the power factor, a reactor having a larger inductance must be used, resulting in a bulky apparatus.
DISCLOSURE OF INVENTION
The present invention has been made to solve the above drawbacks, and has as its object to provide a power conversion apparatus capable of increasing the power factor of the power supply and making the harmonic component of the power supply match or very closer to the IEC standard.
It is another object of the present invention to provide an air conditioner using the power conversion apparatus capable of increasing the power factor of the power supply and making the harmonic component of the power supply match or very closer to the IEC standard.
To achieve the above objects, according to the first aspect of the present invention, there is provided a power conversion apparatus characterized by comprising;
a conversion section for rectifying and smoothing an AC voltage supplied from an AC power supply and converting the AC voltage into a DC voltage,
an inversion section for converting the DC voltage converted by the conversion section into an AC voltage and supplying the AC voltage to a load,
a reactor series-connected to the AC power supply side in the conversion section the reactor having an inductance of 4 to 20 mH,
a booster for forcibly short-circuiting the AC power supply via the reactor, and
a controller for controlling a short-circuiting conduction time of the AC power supply by the booster, within a range of 1.5 to 3.5 msec so as to optimize a power factor of the AC power supply.
To achieve the above objects, according to the second aspect of the present invention, there is provided a power conversion apparatus defined in the
Igarashi Tadayuki
Kato Yuji
Maejima Akihiro
Jackson Stephen W.
Kabushiki Kaisha Toshiba
Pillsbury Madison & Sutro LLP
Polk Sharon
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