Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
1999-11-04
2001-09-18
Wayner, William (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C062S228300, C417S045000
Reexamination Certificate
active
06289680
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling an operation of a linear compressor, and more particularly, to an apparatus for controlling an operation of a linear compressor by which an unstable phenomenon caused due to a characteristics deviation of parts of a compressor is corrected to stabilize the operation of the system, thereby accomplishing an optimal operation, and to its method.
2. Description of the Background Art
A linear compressor is driven by a linear oscillating motor, without requiring a crank shaft which changes a rotational movement to a linear movement, so that there is little frictional loss. For this reason, the linear compressor is known to have a high efficiency compared to any other compressor.
Moreover, where the linear compressor is used for a refrigerator or an air-conditioner, since a compression ratio thereof can be varied by varying a stroke of a motor, it is suitably used for a variable cooling controlling.
The construction of a linear compressor in use for the refrigerator or the air-conditioner will now be described.
FIG. 1
is a schematic block diagram of an apparatus for controlling a linear compressor in accordance with a conventional art, which includes a linear oscillating motor
10
for controlling the strength of cooling air by varying a stroke relying on an up/down movement of a piston; an electric circuit unit
20
for controlling an alternate current power source in accordance with a gate control signal so as to control a power supplied to the linear oscillating motor
10
; and a control unit
30
for controlling a stroke command value according to inputted temperature information and a stroke estimated by a stroke voltage applied to the linear oscillating motor
10
, to be identical to each other, and providing a thusly obtained timer drive signal to the electric circuit unit
20
.
The control unit
30
includes a stroke command value determiner
31
for determining a stroke command value corresponding to a temperature upon receipt of the temperature information, and outputting it; a sensorless stroke estimator for receiving stroke voltages V
0
-V
3
provided by the linear oscillating motor, estimating its stroke value and outputting the estimated stroke value; a stroke controller for controlling in a way that the stroke estimated in the sensorless stroke estimator
32
is suitable to the stroke command value determined by the stroke command value determiner
31
, and accordingly outputting a timer command value; a zero-cross detector
34
for detecting a zero-cross point from an inputted voltage waveform and outputting a zero-cross signal; and a timer
35
for providing a gate drive signal in accordance with an estimated value estimated by the stroke controller
33
at the time when the zero-cross signal is outputted from the zero-cross detector
34
.
The operation of the apparatus for controlling a linear compressor in accordance with a conventional art constructed as described above will now be described.
A power supply voltage as shown in
FIG. 2A
is applied from a power supply voltage terminal, it is provided to the linear oscillating motor
10
through a current sensing resistance R, a triac Tr and a capacitor C of the electric circuit unit
20
, and that way, the current flows to the linear oscillating motor
10
. Thereafter, a piston
11
of the linear oscillating motor
10
performs a reciprocal movement, of which reciprocal stroke distance of the piston
11
refers to a stroke. A strength of cooling air can be varied by varying the stroke, that is the strength of cooling air of the refrigerator or the air-conditioner is controlled by varying the stroke.
When a user sets a temperature of the refrigerator or the air-conditioner, information relating to set temperature is received by the stroke command value determiner
31
of the control unit
30
. Upon receipt of the temperature information, the stroke command value determiner
31
determines a stroke command value corresponding to the set temperature and provides a signal of thusly determined stroke command value to the stroke controller
33
.
At this time, the sensorless stroke estimator
32
receives from the linear oscillating motor
10
the voltage V
0
between the current sensing resistance R and the power supply voltage terminal, the voltage V
1
between the current sensing resistance R and the triac Tr, the voltage V
2
supplied from the triac Tr to the linear oscillating motor
10
, and the voltage V
3
supplied to the linear oscillating motor
10
through the capacitor C, estimates stroke information and current information, and transmits thusly estimated information to the stroke controller
33
.
Thereafter, the stroke controller
33
controls in a manner that the stroke command value determined by the stroke command value determiner
31
to be identical to the estimated stroke value, and transmits the obtained timer command value to the timer
35
.
Then, the zero-cross detector
34
receives the voltage V
0
between the current sensing resistance R and the power supply voltage terminal, or the voltage V
4
, the one before passing the capacitor C starting from the power supply voltage terminal to detect a zero-cross point, and provides a detected zero-cross signal to the timer
35
.
Then, the timer
35
receives the zero-cross signal to a start terminal thereof. When the zero-cross signal is inputted to the start terminal, the timer
35
sets a time t1 as shown in
FIG. 2E
according to a timer command value provided by the stroke controller
33
.
After the time t1 is set, the timer
35
outputs a gate drive signal to the gate G of the triac Tr of the electric circuit unit
20
. In this respect, if the time t1 is short as shown in
FIG. 2C
, the gate drive signal is set to be short from the time point of the zero-cross as shown in
FIG. 2C
, so that a large current flows as shown in
FIG. 2D
, while, if the time t1 is long as shown in
FIG. 2E
, the gate drive signal is distanced from the zero-cross time point, so that a small current flows as shown in FIG.
2
F.
Therefore, as the gate drive signal is outputted to the gate G of the triac Tr of the electric circuit unit
20
, the triac Tr is turned on and the current is supplied to the linear oscillating motor
10
, and accordingly, the piston of the linear oscillating motor
10
moves upwardly and downwardly, thereby controlling the strength of cooling air of the refrigerator or the air-conditioner.
When the input current is applied as a periodic function, the movement of the piston has the same cycle, which has various shapes according to the pressure of suction and discharge.
FIG. 4
shows one example of it. Assuming that the cycle of the piston is ‘T’, since the stroke represents a maximum displacement within one cycle, it is defined by the following equation:
S(k)≡max({overscore (x)}(t)), (k−{fraction (1/2+L )})T≦t<(k+{fraction (1/2+L )})T where {overscore (x)} (t) is an estimated value by the senseless stroke estimator, there may exist an error between the estimated value and the real value as e(k)=x(k)−{overscore (x)}(t).
In case that the linear oscillating motor
10
makes a model as an R-L circuit having a back electromotive force as shown in
FIG. 3
, a theoretical basis for representing the movement of the piston can be expressed by the following two nonlinear simultaneous differential equation:
m
ⅆ
2
ⅆ
t
2
+
c
ⅆ
x
ⅆ
t
+
kx
=
α
i
-
Fp
(
x
)
(
1
)
L
ⅆ
i
ⅆ
t
+
(
R
+
r
)
i
+
1
C
∫
i
ⅆ
t
=
V
-
α
ⅆ
x
ⅆ
t
(
2
)
where x indicates a displacement of the piston, i indicates a current flowing to the motor, m indicates a mass of the piston, C indicates a damping coefficient, k indicates an equivalent spring constant, Fp indicates a force applied by the piston, &agr; indicates a back electromotive force constant, L indicates an equivalent inductance coefficient, R indicates an equivalent resista
Kim Joo Wan
Oh Ki Tae
LG Electronics Inc.
Ostrolenk Faber Gerb & Soffen, LLP
Wayner William
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