Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-12-18
2002-09-24
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C318S116000, C417S011000
Reexamination Certificate
active
06456508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive apparatus which is used in conjunction with a vibrating-type compressor and is configured to supply electrical power to the compressor by use of an inverter, and, more particularly, to a drive apparatus for a vibrating-type compressor which enables use of both AC and DC power sources without use of a mechanical changeover unit.
2. Description of the Related Art
Conventionally, an AC/DC power supply apparatus as shown in
FIG. 14
(from Japanese Patent Applications Laid-Open (kokai) No. 7-111781) has been used as a drive apparatus for a vibrating-type compressor. In
FIG. 14
, reference numeral
1
denotes a vibrating-type compressor which is used as part of a refrigerator and operates upon receipt of a low AC voltage of, for example, 12 V or 24 V. Reference numeral
2
denotes a DC power source such as a battery which is mounted on a vehicle and which outputs a DC voltage of 12 V or 24 V.
Alternating current from a commercial AC power source
10
is converted to direct current by an AC/DC converter
8
in order to obtain a DC voltage equal to the DC voltage E obtained from the battery
2
. One of the DC voltage E output from the battery and the DC voltage output from the AC/DC converter
8
is selected by an automatic changeover unit and is converted to an AC voltage by an inverter
6
. The thus-obtained AC voltage is supplied to the vibrating-type compressor
1
. The inverter
6
includes a first transistor
52
and a second transistor
53
. These transistors
52
and
53
are turned on alternately in order to generate the AC voltage.
The voltage E output from the battery
2
or the AC/DC converter
8
is applied to the first transistor
52
, whereas a voltage -E output from a polarity inversion circuit
3
is applied to the second transistor
53
. The polarity inversion circuit
3
includes a transistor
11
, a pulse generation circuit
12
, a choke coil
13
, a diode
14
, and a capacitor
15
and outputs a DC voltage −E, whose polarity is opposite the DC voltage E with respect to ground.
A control unit
7
variably controls the AC voltage output from the inverter
6
by means of changing the duty ratios of respective output waveforms of the first and second transistors
52
and
53
, to thereby change the frequency of the AC voltage applied to the vibrating-type compressor
1
.
The resonance frequency of the vibrating-type compressor
1
changes depending not only on variation in load but also on the environment in which the vibrating-type compressor
1
is used. Therefore, if the frequency of the AC voltage supplied to the vibrating-type compressor
1
is maintained constant, the efficiency of the vibrating-type compressor
1
is low. In view of this problem, there has conventionally been used a technique for controlling the frequency in order to minimize the difference between the first-half peak and the second-half peak within each period of the waveform of current flowing through the vibrating-type compressor
1
, to thereby maximize the efficiency of the vibrating-type compressor
1
.
A frequency following circuit
24
shown in
FIG. 14
compares the average value of current flowing through a shunt resistor
20
during a first half of a single waveform period of an oscillation signal output from an oscillator
21
and that during a second half of the period and outputs a control signal for variably controlling the oscillation frequency of the oscillator
21
such that the difference assumes a predetermined value. Accordingly, the oscillator
21
generates a pulse signal of a frequency corresponding to the control signal, which pulse signal is then subjected to frequency division effected by a frequency divider
22
. A pulse signal output from the frequency divider
22
is supplied to a transistor control circuit
23
in order to control the first and second transistors
52
and
53
. Therefore, the power supply apparatus can generate AC voltage whose frequency follows variation in resonance frequency caused by variation in the load of the vibrating-type compressor
1
, and thus can drive the vibrating-type compressor
1
at maximum efficiency.
However, such a conventional drive apparatus may break, because it has mechanical contacts within the automatic changeover unit. Further, during AC input, conversion of AC→DC→DC→AC is performed, conversion efficiency is low, and therefore a relatively large amount of electrical power is consumed.
The inverter of the conventional drive apparatus outputs voltage which assumes a square waveform such that the signal assumes an on level potential during a first 180°-phase period within each period of the waveform and an off level potential during a second 180°-phase period within each period of the waveform. Since the voltage applied to the vibrating-type compressor
1
assumes not a sinusoidal waveform but a square waveform having a 180° positive period and a 180° negative period, the operation efficiency of the vibrating-type compressor
1
has been low.
When the above-described power supply apparatus is used, an AC voltage signal whose potential changes between positive and negative with respect to the zero potential is applied to the vibrating-type compressor. Therefore, one terminal of the vibrating-type compressor can be grounded, thereby enabling a cord to be connected to the casing itself of the vibrating-type compressor. However, a polarity inversion circuit as described has been required, in order to enable connection of a cord to the casing.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a drive apparatus for a vibrating-type compressor which solves the above-described problem.
Specifically, a first object of the present invention is to provide a drive apparatus for a vibrating-type compressor which employs a configuration which eliminates a mechanical changeover unit for effecting changeover between AC and DC and in which a commercial AC power source is connected to an inverter unit via an AC/DC converter and a diode OR circuit in order to eliminate mechanical contacts from the power system to thereby decrease failure rate; i.e., to improve reliability.
A second object of the present invention is to provide a drive apparatus for a vibrating-type compressor in which in place of conversion of AC→DC→DC→AC, conversion of AC→DC→AC is effected during AC input in order to improve conversion efficiency and reduce power consumption.
A third object of the present invention is to provide a drive apparatus for a vibrating-type compressor in which FETs disposed in the upper and lower arms of the inverter are turned on alternately such that each FET is in an on state over a 100° to 140° phase angle, whereby as compared with 180° alternating supply of electricity, a wave closer to a sinusoidal wave is supplied to the vibrating-type compressor to thereby improve the operation efficiency of the vibrating-type compressor itself.
A fourth object of the present invention is to provide a drive apparatus for a vibrating-type compressor in which the on period over a 100° to 140° phase angle is slightly changed on the basis of the detected ambient temperature of the vibrating-type compressor, whereby the efficiency is improved further, and a valve-hitting phenomena peculiar to vibrating-type compressors is prevented.
A fifth object of the present invention is to provide a drive apparatus for a vibrating-type compressor which can cope with a wide range of input voltage, including AC 100 V, AC 200, DC 12 V, and DC 24 V, and which can detect a drop in the power source voltage regardless of the input voltage changing in the wide range.
A sixth object of the present invention is to provide a drive apparatus for a vibrating-type compressor which enables one end of the vibrating-type compressor to be grounded without provision of a polarity inversion circuit for generating a negative power source.
A seventh object of the present invention is to provide a drive
Akazawa Naoki
Namai Masao
McGlew and Tuttle , P.C.
Patel Rajnikant B.
Sawafuji Electric Co. Ltd.
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