Controlling device of compressor

Details Controlling device of compressor Controlling device of compressor

2002-09-16

2004-08-24

Sircus, Brian (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Compressor protective circuits

Reexamination Certificate

active

06781802

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of Japanese application serial no. 2001-333038, filed on Oct. 30, 2001.
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates in general to a controlling device of a compressor. A common mode noise (ground noise), which is generated inside a metal frame (the controlling device of a compressor) of an air conditioner etc for containing a compressor main body, suppresses the leakage current flowing from the frame to the ground by using the electrostatic (floating) capacitance between the compressor main body and the ground. In addition, the noise (namely, the noise terminal voltage) from the controlling device to the commercial AC power source through the power lines can be also suppressed.
2. Description of Related Art
Compressor used in the air conditioner etc, consists of a compressor mechanism, a DC brushless motor for providing a driving force to the compressor mechanism, and various protecting devices. Most of these devices are received in a compressor main body (namely, a metal case). The compressor executes a refrigerant compressing cycle, in which the compressor mechanism receives a driving force from the motor for compressing the refrigerant into the compressor main body, and then after the refrigerant is compressed and processed under high temperature and pressure, the refrigerant is exhausted out of the compressor main body. The refrigerant pipes that are connected to the compressor, the condenser or evaporator, etc, form a refrigerant loop of the air conditioner or the refrigerator, which is equivalent to a refrigerant cycling pump for heating or cooling the ambit air of the condenser or evaporator. In addition, recently, the limited use of the refrigerant (such as R-22, the old refrigerant, hereinafter) due to a concern of causing an ozone hole problem is actively replaced by a refrigerant (such as HFC containing R407 or R410A, the new refrigerant, hereinafter) that has no influence on the above said problem.
Examples of some of the compressors used are, a reciprocating compressor, a rotary compressor, and a scroll compressor. Recently, the rotary compressor or the scroll compressor has become the main product. In the compressor, because the compressed refrigerant is exhausted into the compressor main body (namely, the metal case), the refrigerant is exposed to the ambit air inside the case. Then, the high temperature and pressure, the refrigerant is exhausted out of the compressor main body through the refrigerant pipes (especially, the exhausting pipe) fixed on the case. The refrigerant cycling loop located behind the compressor is a general structure. In operation, because the interior of the compressor main body (the metal case) is filled with the compressed high-pressure refrigerant, the metal case is usually sealed.
As described, the motor in the sealed metal case can be a DC motor or an AC motor. In consideration of designing a compressor featuring a noise-free operation, easy controllability, and the compactness, an inverter driven DC motor is used. In addition, since the compressor main body is a sealed metal case, therefore it is preferable to use a brushless motor that is free from fixing or maintenance concerns. Recently, the DC brushless motor is most widely used.
FIG. 9
shows an example of a controlling device of a compressor having a driving circuit to drive an inverter driven DC brushless motor. The controlling device comprises a three-phase AC power source
1
, a driving circuit
2
for inverter driving a DC brushless motor, a compressor main body (i.e., a metal case)
9
, and a metal frame
10
forming a main body of an air conditioner for receiving the condenser, the fan and various controlling circuits (not shown). Metal pipes (not shown) are fixed on the compressor main body
9
by welding.
The driving circuit
2
has a main circuit consisting of a first noise filter
3
for decreasing (suppressing) a noise created by the machine itself and the ground noise (the common mode noise), created between power lines and the metal frame
10
or the ground, a rectifying diode bridge
4
for rectifying the three-phase AC power source to a DC power source, a second noise filter
6
, a rectifying capacitor
7
and a three-phase inverter circuit
8
.
The rectifying diode bridge
4
, the second noise filter
6
and the rectifier capacitor
7
smoothly converts an AC voltage to a DC voltage. In addition, the three-phase inverter circuit
8
switches the DC voltage from the rectifying capacitor
7
by a preset frequency (the switching frequency can be 5 kHz, for example), and then provides a driving power to the DC brushless motor. Furthermore, the compressor main body
9
and the metal frame
10
are respectively connected to the nodes among the second capacitors Cy
1
, Cy
2
, Cy
3
that are connected in series between the power lines of the three-phase AC power
1
. In addition, in view of a stable operation of the driving circuit
2
and safety for preventing the human body from the electric shock due to the possibility of touching the frame
10
, the compressor main body
9
and the metal frame
10
are grounded.
However, in the above situation, as the intermittent DC voltage, which is switched by the three-phase inverter circuit
8
with a high speed, is provided to the DC brushless motor, a DC current flows, and the power lines in the metal case
9
or the wirings (for specified, the wirings of the stator of the DC brushless motor) will have a coupling capacitance with the metal case
9
through the refrigerant sealed inside the compressor. In contrast to the old refrigerant, the coupling capacitance (the floating capacitance) created between the power lines and the case
9
through the new refrigerant, for example R410A, is larger. This is because the new refrigerant has a low resistance and a high dielectric constant with respect to the old refrigerant. Due to the influence of the resistance and the dielectric constant of the new refrigerant, the coupling capacitance becomes larger.
There are legal regulations for appliances to regulate the leakage current. In the appliance regulation, the regulation value for a leakage current should be below 1 mA. In particular, in the driving circuit
2
shown in
FIG. 9
, when the old refrigerant is replaced by the new refrigerant, the resulting leakage current is difficult to meet the regulation requirement (below 1 mA).
Consequently, there is a need to develop a leakage current suppressing circuit. One such circuit has been disclosed by a Japanese Laid Open publication number 11-146557 which uses a single-phase AC power source. However, when the three-phase AC power source shown in
FIG. 9
is used, the leakage current is definitely larger than that disclosed by the above disclosure, which describes using a single-phase AC power source. In recent years, the controlling device of the compressor, in which the economic factors were priorly considered, becomes more difficult to meet the requirement of the legal regulation values.
On the other hand, no matter what method is used in order to meet the legal regulation requirement for the leakage current, the noise terminal voltage, which shows the characteristic of the noise of the machine itself to powerlines, will increase. Therefore, the margin to meet the legal regulation requirement of the noise terminal voltage might become small. In the appliance regulation, the regulation value of the noise terminal voltage is below 56 dB at a frequency range from 526.5 kHz to 5 MHz, and is below 60 dB at a frequency range from 5 MHz to 30 MHz.
SUMMARY OF INVENTION
In the light of the foregoing description, an object of this invention is to provide a controlling device of a compressor. For example, even though the new refrigerant, such as R410A, and the three-phase AC power source are used, the leakage current can be reduced by a simple controlling device structure and the increase of the noise terminal voltage can be also suppressed at the same time. Furthermore, both of the

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