Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Reexamination Certificate
2001-09-26
2003-02-18
Freay, Charles G. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
C417S053000, C417S044100, C417S417000, C417S045000, C417S018000, C417S212000
Reexamination Certificate
active
06520746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for controlling operation of a reciprocating compressor operating a compressor by being inputted a certain stroke command value, and in particular to an apparatus and a method for controlling operation of a reciprocating compressor which is capable of operating a reciprocating compressor stably by detecting a phase difference of a current and a voltage and a phase difference of a current and a velocity and using an inflection point of the phase difference.
2. Description of the Prior Art
Generally, a compressor is for pressurizing refrigerant vapor (compressing refrigerant vapor) in order to make condensing of refrigerant vapor evaporated in a vaporizer easier. By the operation of the compressor, heat can be transmitted from a cold side to a warm side by a refrigerant circulating inside a refrigerating apparatus while repeating a condensing and a vaporizing processes.
These days various types of compressors are used, among them a reciprocating compressor is generally used. The reciprocating compressor pressurizes vapor by a piston moving up and down inside a cylinder, particularly when the reciprocating compressor is used for a refrigerator or an air conditioner, a pressure ratio can be varied by varying a stroke voltage applied to the reciprocating compressor, accordingly it is advantageous to a variable refrigerating capacity control.
FIG. 1
is a block diagram illustrating a construction of an apparatus for controlling operation of a reciprocating compressor in accordance with the prior art. As depicted in
FIG. 1
, an apparatus for controlling operation of a reciprocating compressor includes a voltage/current detecting unit
13
detecting a voltage and a current generated in a reciprocating compressor, a stroke calculating unit
11
calculating a stroke (a distance between a top dead center and a bottom dead center of a piston) by using the voltage and the current detected in the voltage/current detecting unit
13
and outputting it, a comparator
10
comparing the calculated stroke with a certain stroke command value inputted by a user and outputting a comparison signal according to the comparison result, a stroke controller
12
increasing or decreasing a stroke voltage according to the comparison signal from the comparator
10
and outputting it, a microcomputer
14
outputting a switching control signal according to the stroke voltage outputted from the stroke controller
12
, and an electric circuit unit
15
applying a certain voltage to the reciprocating compressor according to a switching control signal of the microcomputer
14
.
The control operation of the reciprocating compressor in accordance with the prior art will be described.
In the reciprocating compressor, when a stroke voltage is outputted by being inputted a certain stroke command value from a user, a stroke (a distance between a top dead center and a bottom dead center of the piston) is varied by an up and down motion of a piston of a cylinder, a refrigerating gas inside the cylinder is transmitted to a condenser through a discharge valve, accordingly a refrigerating capacity can be adjusted.
Herein, as depicted in
FIG. 2
, according to the increase of the stroke by the stroke voltage, when the voltage and the current generated in the reciprocating compressor are detected and applied to the stroke calculating unit
11
as shown at step ST
10
, the stroke calculating unit
11
calculates a stroke by using the voltage and the current detected from the voltage/current detecting unit
13
as shown at step ST
11
. Accordingly, the comparator
10
is inputted, compares the stroke command value with the stroke calculated in the stroke calculating unit
11
and applies a comparison value to the stroke controller
12
as shown at step ST
12
, and the stroke controller
12
varies the stroke voltage according to the comparison value and applies it to the microcomputer
14
as shown at step ST
13
. After, the microcomputer
14
outputs a switching control signal by the voltage applied from the stroke controller as shown at step ST
14
and operates the reciprocating compressor as shown at step ST
15
.
Herein, when the stroke value calculated in the stroke calculating unit
11
is smaller than the stroke command value, the stroke controller
12
increases a stroke voltage, when the stroke value calculated in the stroke calculating unit
11
is larger than the stroke command value, the stroke controller
12
decreases a stroke voltage and applies it to the microcomputer
14
.
Herein, the stroke calculating unit
11
is inputted a motor constant &agr; (constant for converting an electric power into a mechanical power), R
ac
(a loss value due to resistance such as a copper loss or an iron loss), a voltage V
M
between both ends of a motor, etc. and calculates a velocity of a piston and a stroke by below equations.
Velocity=V
M
−R
ac
i−L di/di
Stroke=
1
/&agr;∫(Velocity)
dt
In the meantime, a stroke of a triac of the electric circuit unit
15
is increased by lengthening a turn on cycle according to a switching control signal of the microcomputer
14
, herein the voltage and the current generated in the reciprocating compressor are separately detected in the voltage/current detecting unit
13
and are applied to the stroke calculating unit
11
.
Then, the stroke calculating unit
11
calculates a stroke by using the voltage and the current detected from the voltage/current detecting unit
13
, the calculated stroke is compared with the stroke command value in the comparator
10
the comparison result is outputted to the stroke controller
12
, the stroke controller
12
increases or decreases the stroke voltage, the microcomputer
14
is inputted the stroke voltage outputted from the stroke controller
12
and outputs a switching control signal for controlling a reciprocating compressor to the reciprocating compressor.
In more detail, when the calculated stroke is smaller than the stroke command value, the microcomputer
14
increases a stroke voltage applied to the reciprocating compressor by outputting a switching control signal for lengthening an turn on cycle of the triac, when the calculated stroke is larger than the stroke command value, the microcomputer
14
decreases a stroke voltage applied to the reciprocating compressor by outputting a switching control signal for shortening a turn on cycle of the triac.
In the meantime, the microcomputer
14
detects a load (the outdoor temperature or a condenser temperature, etc.) by installing a sensor at the circumstances of a compressor or a circuit unit of a refrigerator and uses it as basic information for precision control of a refrigerator. For example, the microcomputer
14
detects the temperature through a sensor installed at the surface of the condenser and detects a load.
However, the apparatus and the method for controlling operation of the reciprocating compressor in accordance with the prior art has a serious nonlinearity in the mechanical motion characteristic aspect due to difficulties in measuring accurate current and voltage caused by loss such as a motor constant or a copper loss or an iron loss, it is impossible to perform a precise control with the control method not considering the nonlinearity, in load detecting for precise control of the compressor, the outdoor temperature or a temperature of a condenser is measured through a sensor installed on the surface, after examining each load condition different control algorithm has to be applied according to each condition, accordingly a time delay occurs and the load can not be accurately detected due to the time delay.
In addition, because a reciprocating compressor is controlled with a fixed stroke, a TDC (Top Dead Center) is varied according to increase or decrease of load of a refrigerator. And, because the reciprocating compressor is operated by a quantitative control (control using a constant value required for converting an electric power into a m
Kim Hyung Jin
Kwon Kye Si
Yoo Jae Yoo
LG Electronics Inc.
Rodriguez W
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