KR100742041B1 - Method of controlling a compressor, piston position monitoring system and compressor - Google Patents

Abstract

The present invention relates to a method of controlling the compressor (1), in particular to a method of preventing the piston (5) from colliding with the valve plates (8, 9) provided therein, which means that the piston (5) is a valve plate ( The stroke of the piston (5) of the linear compressor (1), which can advance to the end of its mechanical stroke under extreme conditions of the load, is controlled without causing it to collide with 8,9). With a piston 5 and a linear motor 2, the piston 5 moves along the stroke and is driven by the motor 2, and the average voltage Vm is applied to the motor 2 while the piston ( A method of controlling a compressor (1), such as a linear compressor, adapted to control the movement of 5), the method comprising: measuring the duration of the piston (5); Comparing the duration with the expected time; If the duration is different from the expected time, changing the average voltage (Vm) such that the estimated time is a time at which the movement of the piston (5) reaches a maximum point (M); (M) is located close to the end of the piston stroke. The present invention provides a system for monitoring the position of the piston (5) of the linear compressor (1) as well as the compressor (1).

Description

Compressor control method and piston position monitoring system and compressor

The present invention relates to a method of controlling a compressor, in particular a method of preventing a piston from colliding with a valve system installed therein, a system for monitoring the position of a piston of a compressor, and a compressor equipped with a piston position monitoring system.

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Linear compressors are known from the prior art and consist of a mechanism in which the piston reciprocates, and in most cases there is an elastic means for interconnecting the cylinder and the piston, giving resonance to the reciprocating motion. Will be supplied.
In a known technique (see US Patent No. 5,704,771 to Sawafuji Electric), the stroke of the piston is essentially proportional to the voltage value applied to the linear motor of the stationary magnet and the moving coil. The mechanism of this technique is that the relationship between the diameter of the piston and the range of stroke is so deep that the change in the end position reached by the piston during reciprocation due to the change in supply voltage and load is a characteristic of the capacity and efficiency of cooling the compressor. Does not significantly affect

The mechanism of this technique is that if the piston exceeds the predetermined maximum stroke in its reciprocating motion, for example when an excessive voltage is applied to the motor, the piston will contact the discharge valve, which will advance the piston slightly. And a discharge valve configured to prevent collision with the valve plate.

In other known techniques (see B: Sunpower, Inc., U.S. Patent 4,602,174), the stroke of the piston is essentially proportional to the voltage applied to the linear motor consisting of the movable magnet and the stationary coil.

The structure of the mechanism in this technique does not have a mechanical limit on the piston stroke and is not sized to withstand the excessive impact of the piston against the valve plate. Due to the optimized structure in terms of efficiency, the relationship between the diameter and the stroke of the piston is not important, which makes the performance of the compressor more dependent on the change in the piston stroke. For example, the process of releasing gas occurs in a very small part of the stroke, which is about 5% of the total.

Another effect that occurs with this type of compressor is that the midpoint of the reciprocating motion moves, which has the effect of moving the piston away from the discharge valve. This is due to the elastic deformation of the resonant mechanical system formed by the piston and the spring when there is a pressure difference between the two sides of the piston. The movement of the midpoint of the reciprocating motion is proportional to the pressure difference between the discharge and the suction.

For the same reason as above, it is necessary to use a control device for controlling the piston stroke in this technique. The control device controls the voltage applied to the linear motor based on the information returned again, basically relating to the piston position obtained from the information of the current supplied to the motor and the voltage introduced into the terminal of the motor (Technology C: US Patent 5,342,176, 5,496,153, 5,450,521, 5,592,073).

Another process used to send back to this voltage control device is that a collision of the piston against the valve plate is detected by a shock detection microphone or accelerometer (Technology D) that issues a command to reduce the voltage applied to the motor and the piston stroke. To see if it is possible.

In technique (A), the piston stroke is uncontrolled and the structure in which the voltage and load can be changed without any damage to the mechanism, but this limits the efficiency. In addition, in this technique, the impact of the piston on the discharge valve will increase the noise even if the reliability of the product is not compromised.

In the technique (C), the piston stroke is controlled with reference to the measured position of the piston calculated from the current and voltage at the terminal of the motor, but this is caused by an error due to the change of the structure of the motor, the change of temperature and load, and so on. Precise control is hampered and limits efficiency and operation under extreme conditions of cooling capacity.

Another disadvantage of this technique is that the calculation of the movement of the midpoint of the reciprocating motion is inaccurate, which is basically caused by the average difference between the suction and discharge pressures and the elastic modulus of the spring of the resonant system.

In technique (D), the maximum piston stroke is controlled by keeping the voltage applied to the motor just below the level causing the collision, which is achieved by slightly reducing the applied voltage based on the information obtained while detecting the collision.

A disadvantage of this technique is the collision itself, which is necessary to inform the piston of the approach to the valve plate since it causes noise and some mechanical damage that reduces the useful life of the product.

Another disadvantage is the relatively slow response of this type of control, which often reduces the overall cooling capacity and prevents collisions during periods of sudden power supply ramp up in the public grid.

These limitations on precise control of piston strokes greatly limit the performance of this type of compressor. Ideally, the piston should be as close as possible to the valve plate without collision. Controls known in the art do not allow this proximity to occur because of the inaccuracy in measuring the position of the piston, preventing the compressor from pumping gas at high outlet pressures and maximizing due to dead volume. It is necessary to maintain a long safety distance which reduces the allowable efficiency.

The object of the present invention,

-Control the stroke of the piston of the linear compressor so that the piston will advance to the end of its mechanical stroke, even under extreme load conditions, without causing the piston to hit the valve system;

Controls the stroke of the linear compressor's piston so that the piston advances to the end of its mechanical stroke, even under extreme conditions of the load, even if there is excessive variation from the energy supply chain,

To control the stroke of the piston of the linear compressor without requiring information about the displacement of the midpoint of the piston reciprocation,

It is to control the size of the reciprocating stroke of the linear compressor to control the cooling capacity of the compressor.

This object is directed to a control method of a compressor, such as a linear compressor, having a piston and a linear motor, the piston moving along a stroke and driven by the motor, the average voltage being applied to the motor to control the movement of the piston. Accomplished by
The method comprises the steps of measuring the travel time of the piston; Comparing the travel time with the expected travel time; And if the travel time is different from the expected travel time, changing the voltage such that the estimated travel time is a time at which the movement of the piston reaches a maximum point.

A system for monitoring the position of the piston of the compressor is also provided for the purpose of preventing the piston from colliding with the valve plate located at the end of the piston stroke. This object is achieved by a position monitoring system of a piston, such as a piston of a linear compressor, in which a piston moves along a stroke and is driven by a motor, the motor being driven by a voltage.
The system includes an electronic circuit that monitors the movement of the piston as it passes through the reference point, the reference point being located farther from the end of the piston stroke than the maximum point, the electronic circuit being referred to by the piston. Measure the duration of stay over the point and compare this duration with the desired expected time, which is shorter than or equal to the maximum stroke time when the piston reaches its maximum point, and the electronic circuitry If the time is longer than the expected time, the voltage is reduced. If the duration is shorter than the expected time, the voltage is increased.

It is also an object of the present invention to provide a compressor with a monitoring system which prevents the piston from advancing to the end of the mechanical stroke even under extreme conditions of the load without causing the piston to collide with the valve system. This object is achieved by a compressor, such as a linear compressor, having a piston and a valve plate and a linear motor, the piston moving along a stroke and driven by the motor.
The compressor has an electronic circuit which measures the duration the piston has stayed past the reference point and compares this duration with the desired expected time, which is the maximum stroke time of the maximum stroke when the piston reaches its maximum point. Shorter or equal, the reference point is located further away from the valve plate than the maximum point.

The invention will be explained in more detail with reference to the embodiment shown in the drawings.

1 is a schematic diagram of a linear compressor to which the method of the present invention is applied,

Figure 2 is a graph showing the response of the piston of the compressor shown in Figure 1, and the response of the voltage applied to the motor controlling it,

3 is a block diagram of a method according to the invention,

4 is a graph showing the correlation between the displacement of the piston and the voltage applied to the linear motor,

5 is a schematic diagram of an inverter for controlling a motor;

6 is a block diagram illustrating how a sensor operates on an inverter by a microcomputer.

1 schematically shows a linear compressor 1 with a piston 5 housed in a block 6 in which stroke and movement are defined and driven by a linear motor 2. The piston 5 is a reciprocating motion of the resonant flow by the operation of the spring 4, the control of the movement is made by the electronic circuit 40 including the inverter 50 and the microcontroller 41, The inverter 50 may change the size of the piston stroke. In the case of external fluctuations that change the movement of the piston 5, the valve plates 8, 9, which cause the piston 5 to collide, are near the end of the piston stroke.

The control and change of the stroke size are made by the resupply 31 measured at the reference point R physically formed in the block 6 along the stroke of the piston 5 as shown in FIG. 3. In particular, an object of the present invention is to provide information on the duration of the piston 5 past the reference point R near the end of the maximum point M of the maximum possible stroke for the piston 5 and the complete cycle. Information on the maximum stroke time (tom) corresponding to the maximum point (M) of the piston (5) shown by the cycle time (tc) and the curve (Pm) of Fig. 2, and the average voltage (Vm) applied to the motor Is increased if the duration of the piston past the reference point is shorter than the expected time tod, and decreased if it is vice versa, so that the compressor 1 supplies a predetermined cooling capacity of the system in which it is used. The displacement P of is maintained.

The duration to of the piston 5 is the average of the final measurements of the durations to (n), to (n-1), ..., and the preferred expected time (tod, estimated travel time) is at most It is shorter than point M and corresponds to the time the piston 5 has stayed past the reference point R for the preferred stroke P. The preferred stroke P is determined by the requirements of the refrigeration by the system.

In addition to the control of the average voltage Vm, the average of the cycle time tc the piston has passed at the reference point R and the previous cycle times tc (n), tc (n-1), ... The time difference between the expected calculation time (projected tc) at the moment defined and expected to pass the reference point (R) is the voltage V1 applied to the motor that differs from the desired voltage (V2) during the cycle. The correction value dV is required. In particular, during the time when the piston 5 passes through the reference point R and during the moment when it is expected to pass through the point P of the maximum size, the path of the cycle is modified to make the stroke P2 the preferred stroke P3. Is very close to the piston 5, which can occur if the path of the piston 5 is continuous as shown by the curves P1 and P4 from the beginning of the fluctuation D of FIG. The collision with the valve plates 8 and 9 is prevented.

The maximum point M is usually very close to the valve plates 8, 9, leaving a distance of several tens of micrometers.

The reference point R is normally located close to the valve plates 8 and 9 with a distance of 1 to 2 mm.

For example, assuming that the compressor 1 has a resonant frequency of 50 Hz, the stroke of the piston 5 is approximately 16 mm, and the reference point R is located about 2 mm away from the valve plates 8, 9, Depending on the cooling capacity it has a duration (to) that varies from 0 to a maximum stroke time (tom) of about 3.9 ms. The estimated output time (output tc) is 20 ms (1/50 ms), and the cycle time (tc (n)) is usually changed to 5% of the expected output time (output tc), which is in the range of 5% This is because of the variation of (35).

Measurement of these times is typically performed using a temporizer, which can be physically a "timer" in the microcontroller 41. For example, in the measurement of the duration to, the logic value from the sensor 10 installed at the reference point R may change from 0 to 1 indicating that the piston 5 is in the zone past the reference point R. At the beginning of the measurement of the duration to, which ends when the sensor 10 changes from 1 to 0, indicating that the piston 5 has returned to the position opposite the reference point R. do. Similarly, the second temporizer is between the moment when the piston 5 advances past the reference point R of the current cycle and between the moment when the piston 5 passes the reference point again in the next cycle. The elapsed time is measured, which is the cycle time tc (n).

The preferred tod should be determined according to the required cooling capacity, and there is a maximum allowable value for this preferred tod, which is the maximum stroke time when the piston 5 is at its maximum stroke. Corresponds to). The longer the desired tod, the greater the cooling capacity, and a corresponding table between the cooling capacity and the value of the desired tod should be established for each model of the compressor. In addition, the preferred estimated time tod may be expressed as "k" times the maximum stroke time (tom), for example, tod = k.tom. Preferred expected time tod varies as needed and ranges from zero to the same value as the maximum stroke time, so that "k" also varies from zero to one.

The method according to the invention, as well as the system for monitoring the piston 5, enables to assess the magnitude of the reciprocating motion of the piston 5 much more precisely in each cycle, and to compensate for slow changes in cooling capacity. Rapid control of the electronic control to allow the reaction, to maintain the average size of the stroke of the piston 5 to a desired value, such as "P", and to cancel the sudden change in the operating state caused by the fluctuations in the voltage of the supply chain 35 In addition to allowing the reaction, this correction must be made in each cycle of the reciprocating motion to modify the size of the stroke of the piston 5 at the end of the path after passing through the physical reference point R.

In the case where the voltage rises rapidly, the correction of the stroke is performed by the voltage V applied to the motor at a correction value dV proportional to the difference between the cycle time tc (n) and the expected calculation time (output tc). This is achieved by increasing or decreasing the value of the average voltage Vm.

When the requirements of the compressor 1 change or the electricity supply chain changes slowly, if the duration to which the piston 5 stays past the reference point R is different from the desired expected time, The average voltage (Vm) is changed. If the duration (to) is shorter than the expected time (tod), the average voltage (Vm) is increased, and if the duration (to) is longer than the expected time (tod), the average applied Reduce the voltage (Vm).

As can be seen in FIGS. 5 and 6, the electronic circuit 40 including the inverter 50 controls the motor 2 to a value of the average voltage Vm, and the sensor 10 installed in the compressor 1. ), The resupply 31 is received, and the movement of the piston 5 is controlled.

A preferred method of raising and lowering the value of the average voltage Vm is to control the keys Q1, Q2, Q3, Q4 by varying the controllable voltage values at the terminals of the linear motor 2 to change the operating cycle of regulation. Some use PWM control to apply. Typically, a frequency of about 5 Hz is used for PWM regulation of the voltage of the motor 2. An embodiment of this type of circuit is shown in FIG. 5.

The PWM cycle is changed to perform control of the correction value dV, which passes rapidly from 80% of the "operation cycle" to 50% of the operating cycle for a small number of regulation cycles, for example during a few seconds of change from the supply chain. The piston stroke will be corrected after a sharp change in.

Control of the inverter 50 is carried out by the sensor 10, which is activated by starting a temporizer that measures the duration to (n) and the cycle time tc (n). The calculation of the average value of the last cycle and other comparison operations between the times calculated by the estimated calculation time (calculation tc) and the maximum stroke time (tom) stored therein are performed by the microcontroller 41. The result of these calculations is the value of the cycle of applying the average voltage Vm to the motor 2 to obtain the required cooling capacity. In addition, the result of these calculations is a sudden and temporary change in the PWM cycle that corrects the voltage to compensate for a sudden change in voltage, such as a transient that occurs when the motor is turned off in the vicinity of the electricity supply network 35.

The method and system and the compressor 1 are advantageous in that they do not need to be judged based on the voltage and current applied to the motor 2, and thus the temperature, the structure of the motor 2, and the side surfaces of the piston 5 are advantageous. There is no error due to secondary changes such as the movement of the midpoint of the reciprocating motion of the piston 5 due to the average pressure difference, and it reacts quickly and corrects in each cycle. In addition, it is possible to maintain effective control over the stroke of the piston 5 independently of the required cooling capacity, even if there is a sudden fluctuation caused by natural fluctuations in voltage in the supply chain 35 of electrical energy. Mechanical collision of the piston 5 against (8, 9) can be prevented.

As shown by way of example in FIG. 4, a voltage V1 lower than the voltage V2 is required to achieve the same amplitude of the piston 5, respectively, when the load C2 is greater than the load C1.

Detecting the passage of the piston 5 through the physical reference point R consists of a physical sensor 10 installed in the compressor 1, which may be contact, optical, inductive, or equivalent. Can be. This sensing may also be made by adding a magnetic variation to the voltage at the terminal of the motor 2, which may be caused, for example, by a component of the magnetic circuit of the motor.

While the preferred embodiments have been described, the scope of the invention is not limited to the content of the claims, including corresponding examples, but includes other possible variations.

Claims (17)

With a piston 5 and a linear motor 2, the piston 5 moves along the stroke and is driven by the motor 2, and the average voltage Vm is applied to the motor 2 while the piston ( In the method of controlling the compressor (1) adapted to control the movement of 5), The method comprises the steps of measuring the duration of movement of the piston (to); Comparing the measured duration with a predetermined expected time; Changing the average voltage (Vm) if the measured duration is different from the estimated time (tod), the time at which the movement of the piston (5) reaches the maximum point (M); Compressor control method. 2. The measured duration of claim 1, wherein the measured duration is a duration (to) in which the piston (5) stays past a reference point (R) located along the stroke of the piston (5). Located at a position farther from the end of the stroke of the piston 5 than the point M, The estimated time is a predetermined preferred estimated time (tod), The method reduces the average voltage (Vm) if the duration (to) is longer than the desired expected time (tod), the preferred expected time (tod) is shorter or equal to the maximum stroke time (tom), and the maximum stroke time. tom is the time when the piston 5 reaches the maximum point M; And increasing the average voltage (Vm) if the duration (to) is shorter than the expected time (tod). 3. The maximum stroke time (tom) is the time elapsed between a first pass and a second pass where the piston (5) passes the reference point (R) when the piston (5) reaches the end of the stroke. Compressor control method, characterized in that less than time. 4. The first pass according to claim 3, wherein the piston (5) passes the reference point (R) occurs when the piston (5) moves towards the end of the piston stroke, The second passage of the piston (5) occurs when the piston (5) moves in the opposite direction at the end of the piston stroke and following the moment of the first passage. The method of claim 1, wherein the duration is a cycle time tc (n) which is a duration of a complete piston cycle, the estimated time is an expected calculation time (output tc), and the cycle time tc (n in the comparing step. )) And the estimated output time (output tc), The expected calculation time (calculation tc) is a time at which the piston 5 is expected to pass the reference point R and has a minimum value that prevents the piston 5 from colliding at the end of the stroke, and the reference point R ) Is located at a point farther from the end of the stroke of the piston 5 than the maximum point M, and in the changing step, if the cycle time tc (n) is shorter than the expected calculation time (output tc), the average voltage Vm Compressor control method, characterized in that to reduce). 6. The compressor control method according to claim 5, wherein in the changing step, the average voltage (Vm) is reduced when the piston (5) passes the reference point (R). The method of claim 6, wherein in the changing step, the average voltage (Vm) is changed by the correction value (dV) applied to the voltage (V), the correction value (dV) is the cycle time (tc (n)) and the expected calculation A compressor control method, characterized in that it is proportional to the difference between time (output tc). The compressor control method according to claim 1, further comprising the step of measuring the position of the piston (5) at the reference point (R). In a system in which the piston 5 moves along a stroke and is driven by a motor 2, which monitors the position of the piston 5 to be driven by an average voltage Vm, The system includes an electronic circuit 40 for monitoring the movement of the piston 5 as the piston 5 passes at the reference point R, the reference point R being a piston (rather than the maximum point M). Is located at a further distance from the end of the stroke of 5), The electronic circuit 40 compares this duration (to) with the desired expected time (tod) by measuring the duration (to) of the piston 5 staying past the reference point (R), tod) is shorter than or equal to the maximum stroke time of the maximum stroke when the piston 5 reaches the maximum point M, The electronic circuit 40 decreases the average voltage Vm if the duration to is longer than the expected time tod, and decreases the average voltage Vm if the duration to is shorter than the expected time tod. Piston position monitoring system, characterized in that for increasing. 10. The electronic circuit 40 measures the cycle time tc (n), which is the duration of the complete cycle of the piston 5, to determine the cycle time tc (n) and the expected calculation time (calculation). tc) is compared, but this estimated output time (output tc) is the time when the piston 5 is expected to pass the reference point (R), And the system reduces the average voltage (Vm) if the cycle time (tc (n)) is shorter than the expected calculation time (calculation tc). The piston position monitoring system according to claim 10, wherein the reference point (R) is located at a position farther from the end of the stroke of the piston (5) than the maximum point (M). 12. The electronic circuit (40) according to claim 11, wherein the electronic circuit (40) includes a microcontroller (41) and an inverter (50), wherein the microcontroller (41) has a duration (to) and a cycle time (tc (n)). And the inverter 50 changes the average voltage (Vm). In the compressor (1) having a piston (5) and valve plates (8, 9) and a linear motor (2), the piston (5) moves along a stroke and is driven by the motor (2), The compressor 1 comprises an electronic circuit 40 which measures the duration to which the piston 5 has stayed past the reference point R and compares this duration to the desired expected time tod. In addition, the preferred estimated time (d) is shorter than or equal to the maximum stroke time (tom) of the maximum stroke when the piston (5) reaches the maximum point (M), the reference point (R) is the maximum point Compressor, characterized in that located in a position farther from the valve plate (8,9) than (M). 14. The electronic circuit 40 according to claim 13, wherein the electronic circuit 40 reduces the average voltage Vm if the duration to is longer than the expected time tod, and if the duration to is shorter than the expected time tod. Compressor, characterized in that to increase the average voltage (Vm). The electronic circuit 40 measures the cycle time tc (n), which is the duration of the complete cycle of the piston 5, and calculates the cycle time tc (n) and the expected calculation time (calculation). tc) is compared, but this estimated output time (output tc) is the time when the piston 5 is expected to pass the reference point (R), And the electronic circuit (40) reduces the average voltage (Vm) if the cycle time (tc (n)) is shorter than the expected calculation time (calculation tc). 15. The electronic circuit (40) according to claim 14, wherein the electronic circuit (40) comprises a microcontroller (41) and an inverter (50), wherein the microcontroller (41) has a duration (to) and a cycle time (tc (n)). And the inverter (50) changes the average voltage (Vm). 16. The compressor as claimed in claim 15, wherein the duration to and cycle time tc (n) are averages of a plurality of measured values.

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