Electricity: motive power systems – Induction motor systems – Power-factor control
Reexamination Certificate
2001-08-27
2003-01-14
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Induction motor systems
Power-factor control
C318S438000, C363S037000, C363S038000, C363S039000, C363S040000, C363S041000, C363S074000
Reexamination Certificate
active
06507167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of controlling a voltage and a current inputted to an inverter driving a motor, and in particular to a power factor compensation device for a motor driving inverter which can compensate a power factor of a voltage and a current inputted to the motor driving inverter.
2. Description of the Background Art
Gradually, an inverter has been increasingly utilized to control a motor for home appliances due to reduction in energy consumption and easiness in output control. Various home appliances including a washing machine and a refrigerator have used an inverter for driving a motor.
FIG. 1
is a structure diagram illustrating a conventional motor driving inverter system. As shown therein, an inputted alternating current power
100
is full-wave rectified by a bridge diode
111
into a direct current voltage. The rectified voltage is smoothed through a choke coil
112
and a smoothing condenser
113
, and supplied to an inverter
120
. The smoothed direct current voltage is greater than a peak value of the alternating current power voltage. The inverter
120
converts the smoothed direct current voltage into a three phase alternating current power, and supplies it to a motor
130
. The motor
130
is driven by the converted three phase alternating current power.
FIG. 2
is a waveform diagram of each unit in the conventional art. A first waveform and a second waveform are voltage and current waveforms of the alternating current power, respectively. A time (t) is determined by a time constant by the choke coil
112
and the smoothing condenser
113
, and normally set to be approximately ⅕ of a period of the alternating current power. On the other hand, the peak value of the current is rapidly generated during the time (t). As a result, a noise takes place due to the peak value, and a loss happens due to unavailable power. The aforementioned disadvantage results from a power factor by a phase difference between the voltage and the current. A third waveform of
FIG. 2
shows an ideal current pattern of the alternating current power. As shown therein, when a current having an identical phase to a phase of the alternating current power voltage is applied to the inverter, a loss resulting from the unavailable power is removed.
In order to generate a current having such a waveform, a device having a power factor improvement function is shown in FIG.
3
.
FIG. 3
is a structure diagram illustrating a conventional power factor compensation device for the inverter system. Here, a power factor compensation unit
200
is further included in the configuration of FIG.
1
. The power factor compensation unit
200
includes: the choke coil
112
, an analog integrated circuit
210
, a plurality of resistances R
1
-R
13
, a plurality of condensers C
1
-C
3
and a plurality of diodes D
1
, D
2
.
FIG. 4
is a detailed circuit diagram illustrating the analog integrated circuit
210
. As shown therein, the analog integrated circuit
210
includes various logic circuits.
The direct current voltage outputted from a bridge diode
111
is divided by the resistances R
1
, R
2
of the power factor compensation unit
200
, and inputted to the integrated circuit
210
through a terminal {circumflex over (3)} VM
1
. The voltage applied to the choke coil
112
is inputted thereto through the resistance R
5
and a terminal {circumflex over (5)} ldet. The voltage of the choke coil
112
passing through the resistance R
4
and the diode D
1
and the voltage of the bridge diode
111
passing through the resistance R
3
become an inside power VCC of the integrated circuit
210
. In addition, the direct current voltage supplied to the inverter
120
through the choke coil
112
and the diode D
2
is divided by the resistances R
11
, R
12
, R
13
, and inputted to the integrated circuit
210
through a terminal {circumflex over (1)} INV. The voltage is inputted to a terminal {circumflex over (2)} COMP after the time constant is controlled by the resistances R
7
, R
8
and the condenser C
2
. In addition, a voltage corresponding to a current supplied to the inverter
120
, namely a voltage passing through the condenser C
3
is inputted to a terminal {circumflex over (4)} CS.
A voltage Vout having a predetermined duty rate is outputted through a terminal {circumflex over (7)} Vout by the various logic circuits in the integrated circuit
210
receiving the voltages, that is comparators
211
,
216
,
218
,
219
, a multiplexer
217
, an inverter I
1
, NAND gates
213
,
214
, a self-starter and a NOR gate
215
.
FIG. 5
shows waveforms of the voltages processed in the integrated circuit
210
. Reference mark ‘MO’ denotes a waveform of a voltage inputted from the multiplexer
217
to the comparator
216
, and ‘CS’ denotes a waveform of a voltage inputted to the comparator
216
through the terminal {circumflex over (4)} CS. As depicted in
FIG. 5
, MO and CS are compared, and the voltage Vout has a great duty at a portion where a sine wave is small (right and left sides in the drawing), and a small duty at a middle portion.
The voltage Vout is applied to a gate of a switching transistor Q
1
, and thus the switching transistor Q
1
repeatedly performs a switching operation, thereby removing a phase difference between the voltage and current inputted to the inverter
120
. Accordingly, the conventional power factor compensation device compensates the power factor by further including the power factor compensation unit, and thus removes the loss. However, there are disadvantages as follows.
Firstly, the power factor compensation unit must constantly receive the alternating current power voltage. Secondly, since the analog power factor compensation circuit is employed, an area for the circuit is increased. Accordingly, a cost thereof is also increased.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to compensate a power factor of a system by storing sine wave form voltage values corresponding to a voltage value of an utility alternating current power in advance, and switching a voltage supplied to an inverter in order to correspond to the stored sine wave form voltage values, in consideration of a phase of the utility alternating current power.
It is another object of the present invention to prevent noise from being generated from a voltage supplied to an inverter.
In order to achieve the above-described objects of the present invention, there is provided a power factor compensation device for a motor driving inverter system, including: an inverter connected to a motor; a microprocessor detecting a zero crossing point of an utility alternating current power, and sequentially outputting a driving signal corresponding to a plurality of sine wave form voltage values according to the detected result, in a state where the plurality of sine wave form voltage values corresponding to a voltage of the utility alternating current power and frequencies are internally stored; and a switching transistor connected in parallel to the inverter, and switched according to the driving signal, a duty of the driving signal being varied correspondingly to each of the plurality of sine wave form voltage values.
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Han Gyeong-Hae
Kim Jong-Ho
Lee Dong-Hyuk
Lee Hyung-Sang
Sim Keon
Fleshner & Kim LLP
Leykin Rita
LG Electronics Inc.
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