Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Reexamination Certificate
2002-07-24
2004-06-08
Yu, Justine R. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
C417S053000, C417S416000, C417S417000, C318S607000, C318S606000, C318S433000
Reexamination Certificate
active
06746211
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reciprocating compressor, and more particularly, to an operation control method of a reciprocating compressor that is capable of stably driving a compressor when a motor is overloaded.
2. Description of the Background Art
In general, a reciprocating compressor is a device that variably controls a cooling capacity discharged therefrom by varying a compression ratio according to a stroke voltage applied thereto.
The general reciprocating compressor will now be described with reference to FIG.
1
.
FIG. 1
is a block diagram of the construction of an operation control apparatus of the general reciprocating compressor.
As shown in
FIG. 1
, an operation control apparatus of the general reciprocating compressor includes: a reciprocating compressor (R.COMP)
12
for receiving a stroke voltage provided to an internal motor (not shown) according to a stroke reference value set by a user to control a vertical movement of an internal piston (not shown); a voltage detecting unit
30
for detecting a voltage applied to the reciprocating compressor
12
as the stroke is varied; a current detecting unit
20
for detecting a current applied to the reciprocating compressor as the stroke is varied; a microcomputer
40
for calculating a stroke by using the voltage and the current detected from the voltage detecting unit
30
and the current detecting unit
20
, comparing the calculated stroke value with the stroke reference value, and outputting a corresponding switching control signal; and an electric circuit unit
10
for switching on/off an AC power with a triac (Tr
1
) according to the switching control signal of the microcomputer
40
so as to control a size of the stroke voltage applied to the reciprocating compressor
12
.
The operation of the operation control apparatus of the conventional reciprocating compressor constructed as described above will now be explained.
In the reciprocating compressor
12
, a piston is vertically moved by a stroke voltage inputted from the motor (not shown) according to a stroke reference value set by a user, and accordingly, a stroke is varied to thereby control a cooling capacity.
The stroke signifies a distance that the piston is reciprocally moved in the reciprocating compressor
12
.
A turn-on period of the triac (Tr
1
) of the electric circuit unit
10
is lengthened by the switching control signal of the microcomputer
40
, and as the turn-on period is lengthened, a stroke is increased.
At this time, the voltage detecting unit
30
and the current detecting unit
20
detect a voltage and a current applied to the reciprocating compressor
12
and apply them to the microcomputer
40
, respectively,
The microcomputer
40
calculates a stroke by using the voltage and the current detected by the voltage detecting unit
30
and the current detecting unit
20
, compares the calculated stroke with the stroke reference value, and outputs a corresponding switching control signal.
If the calculated stroke is smaller than the stroke reference value, the microcomputer
40
outputs a switching control signal to length the ON-period of the triac (Tr
1
) to thereby increase the stroke voltage applied to the reciprocating compressor
12
.
If, however, the calculated stroke is greater than the stroke reference value, the microcomputer
40
outputs a switching control signal to shorten the ON-period of the triac (Tr
1
) to thereby reduce the stroke voltage applied to the reciprocating compressor
12
.
As for the motor (not shown) installed in the reciprocating compressor
12
, a coil is evenly wound thereon at a certain coil winding ratio, so that when a current according to the stroke voltage is applied to the coil, a magnetic pole is generated at the electromagnet in the coil of the motor and a magnetic flux is generated at the coil.
The reciprocating compressor is mechanically resonated at a rated driving frequency.
For example, if a rated frequency of the reciprocating compressor is 60 Hz, a resonance frequency is designed to be also 60 Hz at a rated current.
In case of a rated load of the reciprocating compressor, the resonance frequency (a rated driving frequency) is obtained by the sum of an inertia force (M{umlaut over (X)}(t)), a damping force (c{dot over (X)}(t))and a restitution (kX(t))of a spring.
f
(
t
)=&agr;
i
(
t
)=
M{dot over (x)}
(t)+
c{dot over (x)}
(
t
)+
kx
(
t
) (1)
k=ks+kg
(2)
wherein f(t) is a force applied to the motor, &agr; is a motor constant, I(t) is current, x(t) is displacement, ‘M’ is a moving mass, ‘c’ is a damping constant, ‘k’ is a spring constant, ks is a machine spring, and kg is a gas spring.
The spring constant (k) is a sum of the machine spring (ks) connected to a mass moving by the motor so as to adjust a resonance point of the reciprocating compressor and the gas spring (kg) varied depending on a load of the reciprocating compressor.
The displacement (x(t)) is a distance that the magnet is moved from the center of the coil.
By Laplace transforming equation (1), a relation between the current and the displacement of the reciprocating compressor can be obtained.
The reciprocating compressor is designed such that the resonance frequency and the driving frequency are the same with each other at a rated load.
Equation (1) can be expressed as the frequency domain as follows:
F
(
j
ω
)
=
-
M
ω
2
X
(
jω
)
+
c
j
ω
X
(
jω
)
+
kX
(
j
ω
)
(
3
)
X
(
j
ω
)
F
(
j
ω
)
=
1
-
M
ω
2
+
k
+
j
ω
c
(
4
)
f
n
=
1
2
π
k
M
(
5
)
ω
=
2
π
f
=
k
M
(
6
)
M
ω
2
=
k
(
7
)
X
(
jω
)
F
(
j
ω
)
=
1
j
ω
c
=
-
j
1
c
ω
(
8
)
wherein &ohgr; is a driving frequency (rad/s), ‘f’ is a driving frequency (Hz), ‘j’ is an imaginary number, and f
n
is a resonance frequency.
At this time, F(j&ohgr;) is a value obtained by Fourier transforming f(t) of equation (q) and XO(j&ohgr;) is a value obtained by Fourier transforming x(t).
By applying equation (5) related to the resonance frequency (rated driving frequency) of the reciprocating compressor to equation (4) related to the force and the displacement of the reciprocating compressor, a force and a displacement according to the resonance frequency of the reciprocating compressor can be obtained.
Thus, as shown in equation (8), a force and a displacement exhibits a 90° phase difference. In addition, since the force and the phase of current are the same, a magnetic flux of the core generated by the current shows 90° phase difference from the magnetic flux generated due to the displacement of the magnet.
This will now be described in detail with reference to FIG.
2
.
FIG. 2
illustrates waveforms showing a relation between the current applied to the reciprocating compressor and a displacement in resonating at a rated load.
As shown in
FIG. 2
, when current is applied to the motor in resonating at a rated load, current is applied to the coil of the motor and a magnetic flux is generated at the coil in a direction that the current is applied.
As indicated by ‘a’ shown in
FIG. 2
, when current is inputted counterclockwise, N pole is generated from the right side of the coil while S pole is generated from the left side of the coil. At this time, a magnetic flux generated by the current is maximized. When the magnetic flux by the current is maximized, the magnetic flux by the current and the magnetic flux according to the displacement of the magnet have the 90° phase difference, so that the magnet is positioned at the center of the coil and the magnetic flux of the core by the magnet is minimized.
Subsequently, as indicated by ‘b’ sho
Kim Hyung-Jin
Kwon Kye-Si
Lee Hyuk
Birch & Stewart Kolasch & Birch, LLP
LG Electronics Inc.
Sayoc Emmanuel
Yu Justine R.
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