CN108334659B - Calibration method for piston displacement relative to pressure wave phase angle in linear compressor - Google Patents

Calibration method for piston displacement relative to pressure wave phase angle in linear compressor Download PDF

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CN108334659B
CN108334659B CN201711430900.XA CN201711430900A CN108334659B CN 108334659 B CN108334659 B CN 108334659B CN 201711430900 A CN201711430900 A CN 201711430900A CN 108334659 B CN108334659 B CN 108334659B
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displacement
pressure
phase angle
piston
back pressure
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尤晓宽
邱利民
陶希军
段超祥
王建军
植晓琴
姜晓
赵钦宇
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Zhejiang University ZJU
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Abstract

The invention provides a method for calibrating the angle of piston displacement relative to pressure wave in a linear compressor, which comprises the steps of respectively measuring the amplitude of the piston displacement of the linear compressor, the amplitude of the pressure wave of a compression cavity and a back pressure cavity and the phase angle between the pressure wave and the displacement by using a pressure sensor and a displacement sensor, calibrating the measured original phase angle by using a displacement calculation formula of a compressor mass gas spring model, and verifying the calibrated phase angle by using two modes of compressor energy distribution calculation and compressor heat dissipation amount measurement, wherein the calibration is correct. The method provided by the invention calibrates the angle between the displacement and the pressure wave, and has important significance for measuring and calculating the output sound work and energy distribution of the compressor.

Description

Calibration method for piston displacement relative to pressure wave phase angle in linear compressor
Technical Field
The invention relates to the technical field of linear compressors, in particular to a method for calibrating a phase angle of piston displacement relative to pressure waves in a linear compressor.
Background
The linear compressor combines the key technologies of a linear motor, a plate spring, gap sealing and the like, has the advantages of long service life, no friction, low vibration, low noise and the like, and is widely applied to the fields of low-temperature refrigerators, low-temperature refrigerators and the like. When the linear compressor is applied to a low-temperature refrigerator such as a pulse tube refrigerator, the output sound power is a key parameter related to the efficiency of the pulse tube refrigerator. The value of the pulse tube refrigerating machine directly reflects the electro-acoustic conversion efficiency of the compressor and influences the overall efficiency of the pulse tube refrigerating machine. Therefore, how to more accurately measure the acoustic work output by the linear compressor is critical for pulse tube refrigerators.
The acoustic work is calculated by measuring the gas pressure wave, the piston displacement, and the phase angle between the two. However, the pressure wave and piston displacement are measured by two different types of sensors, making the phase angle measurement inaccurate due to the inherent delays caused by the measurement. The current common way is to use the back pressure cavity pressure phase to calculate the acoustic work, which is considered to be 180 degrees from the displacement phase angle. However, this approach has the disadvantage that the assumption is not entirely true, that the phase angle between the back pressure chamber pressure and displacement is not exactly 180 degrees, and that the assumption is such that the back pressure chamber acoustic work is zero and no energy is dissipated. When the sound power of the compressor is calculated, the calculated value may be large. Therefore, it remains a problem how to calibrate the angle between the pressure wave and the displacement so that it can be applied to the acoustic work calculation.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for calibrating the phase angle of the piston displacement relative to the pressure wave in the linear compressor, which can calculate the acoustic power more accurately and provide a basis for the design of the compressor and the pulse tube refrigerator.
A method of calibrating piston displacement relative to pressure wave phase angle in a linear compressor comprising the steps of:
step 1, respectively measuring the amplitude of the displacement of a piston of the linear compressor and the pressure amplitude p of a compression cavity by using a displacement sensor and a pressure sensorcPressure amplitude p of the back pressure chamberbThe angular difference theta between the compression chamber pressure sensor and the displacement1Back pressure chamber pressure sensor and displacement2；
Step 2, assuming that the fixed delay between the pressure sensor and the displacement sensor is t, wherein-2 pi/omega < t <2 pi/omega, and omega is angular frequency;
and 3, obtaining a delay phase angle delta theta between the pressure sensor and the displacement sensor as omega t according to the fixed delay t, and obtaining a phase angle theta between the pressure of the compression cavity and the displacement as thetac＝θ1+ Δ θ, phase angle between back pressure chamber pressure and displacement is θb＝θ2+Δθ；
Step 4, substituting the obtained data into a displacement formula of the mass gas spring model to obtain piston displacement;
step 5, calculating the deviation between the piston displacement and the measured piston displacement amplitude, if the deviation is greater than 10%, assuming the time t again, returning to the step 3, and if the deviation is less than 10%, executing the step 6;
and 6, completing correction, and further verifying the result.
In step 1, the displacement sensor is a Micro-epsilon displacement sensor or other type of displacement sensor capable of measuring alternating motion; the pressure sensor is an Endevco pressure sensor or other type of pressure sensor that can measure alternating pressure.
In step 4, the displacement formula of the mass gas spring model is as follows:
Figure BDA0001524895000000021
wherein x is piston displacement, α is motor specific thrust coefficient, I is working current, f is working frequency, RmIs a mechanical damping coefficient, ksIs spring rate, m is piston dynamic mass, gamma is adiabatic index, pmFor the working pressure, A is the piston area, VcTo compress the chamber volume, VbIs the back pressure cavity product, thetacFor the phase angle between compression chamber pressure and displacement, θbThe phase angle between the back pressure chamber pressure and the displacement.
In step 5, the specific method for re-assuming the time t is as follows: and comparing the piston displacement with the measured piston displacement amplitude, if the calculated piston displacement is larger than the measured piston displacement, increasing t, otherwise, decreasing t.
In the step 6, two verification modes are mainly adopted, the first verification method is that the energy distribution of the compressor is calculated by using the calibrated angle, the energy distribution comprises the sound power of a compression cavity and the sound power of a back pressure cavity, in addition, the joule heat and the damping loss are calculated, the sum of the four energies is equal to the input electric power, and the angle calibration is proved to be correct.
The calculation formula of the sound power of the compression cavity is as follows:
Figure BDA0001524895000000031
the back pressure cavity acoustic power calculation formula is as follows:
Figure BDA0001524895000000032
the joule heat calculation formula is as follows:
Wi＝I2R
the damping loss calculation formula is as follows:
Figure BDA0001524895000000033
wherein, WpV1For compressing the acoustic work of the chamber, WpV2Is the back pressure cavity acoustic power, WiIs Joule heat, WdFor damping losses, pcIn order to compress the magnitude of the chamber pressure,
Figure BDA0001524895000000034
for compression of chamber volume flow amplitude, pbIs the amplitude of the back pressure chamber pressure,
Figure BDA0001524895000000035
is the magnitude of back pressure chamber flow, θcFor the phase angle between compression chamber pressure and displacement, θbIs the phase angle between the pressure and the displacement of the back pressure cavity, omega is the angular frequency, x is the displacement of the piston, A is the area of the piston, I is the working current, R is the resistance, R is the pressure of the back pressure cavitymIs the mechanical damping coefficient.
The second verification method is to calculate the back pressure cavity sound power of the compressor by the calibrated angle, and calculate the joule heat and the damping loss to obtain the sum of the three. The heat dissipation capacity of the shell of the compressor is calculated by measuring the flow and the temperature rise of a cooling water pipe on the shell of the compressor. Because the compression cavity can also radiate a part of heat to the shell, the heat radiation quantity of the shell of the compressor is more than or equal to the sum of the three, and if the heat radiation quantity is more than 10 percent of the calculated value, the correct angle calibration is also proved.
The invention starts from a mass gas spring model of the compressor, analyzes and calculates the problem that the phase angles of the displacement sensor and the pressure sensor are inaccurate when the displacement sensor and the pressure sensor are respectively adopted to measure the displacement and the pressure, calibrates the angle between pressure wave and the displacement, verifies whether the calibrated angle is correct through the energy distribution of the compressor, and verifies whether the calibrated angle is correct on the other hand through measuring the heat dissipation of the compressor. The verification shows that the angle calibration is correct, and a foundation is provided for the subsequent calculation of the sound power of the compressor and the design of the refrigerating machine.
Drawings
FIG. 1 is a schematic flow chart of the present invention.
Detailed Description
The following describes embodiments of the present invention with reference to the drawings.
As shown in fig. 1, a method for calibrating piston displacement with respect to pressure wave phase angle in a linear compressor comprises the following steps:
step 1, respectively measuring the amplitude of the displacement of the piston of the linear compressor, the amplitude of pressure waves of a compression cavity and a back pressure cavity and a phase angle between the pressure waves and the displacement by using a pressure sensor and a displacement sensor. The embodiment measures the angular difference theta between the compression cavity pressure sensor and the displacement by taking the displacement phase as a reference value when the frequency is 45Hz1Is 17 degrees, and the angle difference between the pressure sensor of the back pressure cavity and the displacement is theta2Is 189 deg.
And 2, assuming that the fixed delay t between the pressure sensor and the displacement sensor is-0.03.
Step 3, according to the fixed extensionAnd delaying t, and obtaining a delay phase angle delta theta-t-8.5 between the pressure sensor and the displacement sensor, and a phase angle theta between the pressure of the compression cavity and the displacementc＝θ1+ Δ θ is 8.5, and the phase angle between the back pressure chamber pressure and the displacement is θb＝θ2+Δθ＝180.5。
Step 4, obtaining thetacAnd thetabSubstituting the displacement formula of the mass gas spring model to obtain the piston displacement;
and 5, calculating the deviation 13.6% between the piston displacement and the measured piston displacement amplitude, and if the deviation is more than 10%, assuming that the time t is-0.023 again, returning to the step 3, sequentially calculating the deviation 8.3% between the piston displacement and the measured piston displacement amplitude, and if the deviation is less than 10%, and performing the step 6.
And 6, completing correction, and further verifying the result.
In this embodiment, θ is calculatedcAnd thetab10.6 deg. and 2.6 deg., respectively. In step 6, whether the angle calibration is correct is verified, the energy distribution of the compressor is calculated according to the calibrated angle, including the sound power of the compression cavity and the sound power of the back pressure cavity, and the joule heat and the damping loss are calculated, in the embodiment, the calculated values are 837W, 144W, 576W and 70W respectively, the sum of the four values is 1627W, the measured electric power is 1537W, and the error of the two values is 6%, so that the angle calibration is correct.
The angular calibration is verified in another way. And calculating the sound work of the back pressure cavity of the compressor by using the calibrated angle, and additionally calculating the joule heat and the damping loss, wherein the calculated values of the three are 144W, 576W and 70W respectively, and the sum of the three is 790W. The flow of a cooling water pipe on the shell of the compressor is measured to be 0.392m3The temperature rise was 1.9K, and the calculated heat dissipation of the compressor housing was 890W. The error is 13%, since the compression chamber also dissipates a portion of the heat to the housing, so the error is positive, proving that the angular alignment is correct.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.

Claims (6)

1. A method for calibrating piston displacement relative to pressure wave phase angle in a linear compressor, comprising the steps of:
step 1, respectively measuring the amplitude of the displacement of a piston of the linear compressor and the pressure amplitude p of a compression cavity by using a displacement sensor and a pressure sensorcPressure amplitude p of the back pressure chamberbThe angular difference theta between the compression chamber pressure sensor and the displacement1Back pressure chamber pressure sensor and displacement2；
Step 2, assuming that the fixed delay between the pressure sensor and the displacement sensor is t, wherein-2 pi/omega < t <2 pi/omega, and omega is angular frequency;
and 3, obtaining a delay phase angle delta theta between the pressure sensor and the displacement sensor as omega t according to the fixed delay t, and obtaining a phase angle theta between the pressure of the compression cavity and the displacement as thetac＝θ1+ Δ θ, phase angle between back pressure chamber pressure and displacement is θb＝θ2+Δθ；
Step 4, substituting the obtained data into a displacement formula of the mass gas spring model to obtain piston displacement;
step 5, calculating the deviation between the piston displacement and the measured piston displacement amplitude, if the deviation is greater than 10%, assuming the time t again, returning to the step 3, and if the deviation is less than 10%, executing the step 6;
and 6, completing correction, and further verifying the result.
2. The method for calibrating piston displacement with respect to pressure wave phase angle in a linear compressor according to claim 1, wherein in step 4, the displacement formula of the mass gas spring model is as follows:
Figure FDA0001524894990000011
wherein x is piston displacement, α is motor specific thrust coefficient, I is working current, f is working frequency, RmIs a mechanical damping coefficient, ksIs spring rate, m is piston dynamic mass, gamma is adiabatic index, pmFor the working pressure, A is the piston area, VcTo compress the chamber volume, VbIs the back pressure cavity product, thetacFor the phase angle between compression chamber pressure and displacement, θbThe phase angle between the back pressure chamber pressure and the displacement.
3. The method for calibrating piston displacement with respect to pressure wave phase angle in linear compressor according to claim 1, wherein in step 5, the specific method for re-assuming time t is as follows: and comparing the piston displacement with the measured piston displacement amplitude, if the calculated piston displacement is larger than the measured piston displacement, increasing t, otherwise, decreasing t.
4. The method for calibrating piston displacement relative to pressure wave phase angle in a linear compressor according to claim 1, wherein in step 6, the calibration is verified by calculating the compression chamber acoustic power, back pressure chamber acoustic power, joule heating and damping loss of the compressor at the calibrated angle, and if the sum of the four is equal to the input electric power, the angle calibration is verified to be correct.
5. The method for calibrating piston displacement with respect to pressure wave phase angle in a linear compressor according to claim 4, wherein said compression chamber acoustic work is calculated by the formula:
Figure FDA0001524894990000021
the back pressure cavity acoustic power calculation formula is as follows:
Figure FDA0001524894990000022
the joule heat calculation formula is as follows:
Wi＝I2R
the damping loss calculation formula is as follows:
Figure FDA0001524894990000023
wherein, WpV1For compressing the acoustic work of the chamber, WpV2Is the back pressure cavity acoustic power, WiIs Joule heat, WdFor damping losses, pcIn order to compress the magnitude of the chamber pressure,
Figure FDA0001524894990000024
for compression of chamber volume flow amplitude, pbIs the amplitude of the back pressure chamber pressure,
Figure FDA0001524894990000025
is the magnitude of back pressure chamber flow, θcFor the phase angle between compression chamber pressure and displacement, θbIs the phase angle between the pressure and the displacement of the back pressure cavity, omega is the angular frequency, x is the displacement of the piston, A is the area of the piston, I is the working current, R is the resistance, R is the pressure of the back pressure cavitymIs the mechanical damping coefficient.
6. The method for calibrating piston displacement relative to pressure wave phase angle in a linear compressor according to claim 1, wherein in step 6, the calibration is performed by calculating the back pressure cavity acoustic power, joule heat and damping loss of the compressor at the calibrated angle, calculating the heat dissipation capacity of the compressor shell by measuring the flow rate and temperature rise of the cooling water pipe on the compressor shell, and if the heat dissipation capacity of the compressor shell is greater than or equal to the sum of the three, the angle calibration is verified to be correct.
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