Control Method of Variable Frequency Compressor

Abstract

The control method of the variable-frequency compressor of the present invention relates to the technical field of compressor control. By obtaining the minimum value Tbase of the condenser outlet temperature Tcond, the compressor motor winding temperature Tmotor, and the temperature at the bottom of the compressor housing during the operation of the compressor min , calculate the temperature Tbase at the bottom of the compressor housing according to the compressor motor winding temperature Tmotor. Compare Tbase≤Tbase once every period of time min , when Tbase≤Tbase min , increase the operating frequency △F of the compressor. When Tbase>Tbase min , the operating frequency of the compressor operates according to the actual required frequency. In this way, the determination conditions for refrigerant deposition and oil dilution are increased, and the frequency increase control is carried out in advance, solving the problems of refrigerant deposition and oil dilution existing in the air-conditioning oil return control in the prior art. The present invention is applicable to compressor control.

Description

Technical Field

[0001] The present invention relates to the technical field of compressor control, and particularly to a control method for a variable-frequency compressor. Background Art

[0002] A compressor operates by the rotation of an electric motor driving a crankshaft, a connecting rod device, and other components. Lubricating oil forms an oil film on the surfaces of these transmission components to reduce wear of the components. Therefore, the lubricating oil is closely related to the operating performance and service life of the compressor.

[0003] To ensure the reliable operation of the compressor, the compressor control specification generally clearly stipulates the lower limit of the temperature at the bottom of the housing (oil temperature). Because low temperature causes the viscosity of the lubricating oil to increase, reducing the lubrication effect and increasing compressor wear. And since both the compressor housing and the condenser are on the high-pressure side of the system, if the internal temperature of the housing is lower than the condensation temperature, it means that high-pressure gaseous refrigerant will condense inside the compressor housing, that is, the so-called "refrigerant deposition and oil dilution" problem. When the compressor operates at low frequency for a long time, the deposition of refrigerant at the bottom gradually increases, and the low-temperature state at the bottom of the housing continues to intensify. Seriously, the temperature at the bottom of the housing is much lower than the condensation temperature of the internal refrigerant. After the oil is diluted, it seriously affects the performance of the oil film. If the compressor works in this low-temperature state for a long time, it will cause the compressor to fail prematurely. To prevent the "refrigerant deposition and oil dilution" problem, the compressor specification requires that the housing temperature be higher than the condensation temperature of the system refrigerant.

[0004] Currently, in order to prevent the "refrigerant deposition and oil dilution" problem, in the control scheme, air-conditioning manufacturers will increase the compressor frequency to the medium frequency band after the compressor operates at low frequency for a certain period of time, operate for a certain period of time, and then allow the compressor to operate at low frequency again, that is, oil return control. The frequency of this air conditioner fluctuates greatly, which will affect the comfort of the air conditioner. And because the temperature at the bottom of the housing cannot be detected, this oil return control by increasing the fixed frequency cannot ensure that the temperature requirements of the lubricating oil can be met under all operating conditions of the air conditioner. Summary of the Invention

[0005] The technical problem to be solved by the present invention: Provide a control method for a variable-frequency compressor to solve the problem of refrigerant deposition and oil dilution existing in the oil return control of air conditioners in the prior art.

[0006] The technical solution adopted by the present invention to solve the above technical problem: A control method for a variable-frequency compressor, comprising the following steps:

[0007] S01. Obtain the minimum value Tbase of the temperature Tcond at the outlet of the condenser, the temperature Tmotor of the compressor motor winding, and the temperature at the bottom of the compressor housing during the operation of the compressor min ;

[0008] S02. Calculate the bottom temperature Tbase of the compressor housing based on the compressor motor winding temperature Tmotor. The calculation formula is: Tbase = Tmotor - T, where T is greater than the maximum value of the temperature difference between the bottom temperature of the compressor housing and the condensation temperature under each working condition;

[0009] S03. Compare Tbase ≤ Tbase once every period of time min ;

[0010] When Tbase ≤ Tbase min , increase the compressor operating frequency ΔF. The ΔF = K * (Tbase - Tbase min ) + B, where K and B are constants;

[0011] When Tbase > Tbase min , the compressor operating frequency operates according to the actual required frequency.

[0012] Further, the condenser outlet temperature Tcond is collected by a temperature sensor.

[0013] Further, K is 1.5 and B is 2.

[0014] Further, the period of time is 2 minutes.

[0015] Advantages of the present invention: The control method of the variable-frequency compressor of the present invention, by obtaining the minimum value Tbase of the condenser outlet temperature Tcond, the compressor motor winding temperature Tmotor and the bottom temperature of the compressor housing during the operation of the compressor min , calculate the bottom temperature Tbase of the compressor housing based on the compressor motor winding temperature Tmotor, compare Tbase ≤ Tbase once every period of time min , when Tbase ≤ Tbase min , increase the compressor operating frequency ΔF, when Tbase > Tbase min , the compressor operating frequency operates according to the actual required frequency. In this way, the determination conditions for refrigerant deposition and oil dilution are increased, and frequency increase control is carried out in advance, solving the problems of refrigerant deposition and oil dilution in the existing air-conditioning oil return control. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 is a schematic flow chart of the control method of the variable-frequency compressor of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The control method of the variable-frequency compressor of the present invention, as shown in the attached Figure 1 , includes the following steps:

[0018] S01. Obtain the minimum value Tbase of the condenser outlet temperature Tcond, the compressor motor winding temperature Tmotor, and the temperature at the bottom of the compressor housing during the operation of the compressor. min ;

[0019] Specifically, the condenser outlet temperature Tcond is collected by a temperature sensor; the compressor motor winding temperature Tmotor can be obtained by the motor winding temperature calculation method disclosed in the invention patent with the patent number ZL201910249866.9, and during the R & D stage, it can be detected and obtained by arranging thermocouples; the minimum value Tbase of the temperature at the bottom of the compressor housing min can be obtained according to the requirements in the compressor specification.

[0020] S02. Calculate the temperature Tbase at the bottom of the compressor housing based on the compressor motor winding temperature Tmotor. The calculation formula is: Tbase = Tmotor - T, where T is greater than the maximum value of the temperature difference between the temperature at the bottom of the compressor housing and the condensation temperature under various working conditions;

[0021] Specifically, through testing the operating compressor, it is found that the temperature difference between the temperature at the bottom of the compressor housing and the compressor motor winding temperature basically does not change with the working conditions. For example, for a certain compressor under various working conditions, the temperature difference between the temperature at the bottom of the compressor housing and the condensation temperature is between 8.4 °C and 14.1 °C. Therefore, in order to increase the control margin, T is set to 15 °C, or it can also be set to values such as 16 °C. Based on this, no matter what working condition the compressor is in, the calculated temperature Tbase at the bottom of the compressor housing is lower than the actual value of the temperature at the bottom of the compressor housing. Using Tbase as the judgment basis improves the control margin.

[0022] S03. Compare Tbase ≤ Tbase every once in a while. min ,

[0023] When Tbase ≤ Tbase min , increase the compressor operating frequency △F, where △F = K * (Tbase - Tbase min ) + B, where K and B are constants;

[0024] When Tbase > Tbase min , the compressor operating frequency operates at the actual required frequency.

[0025] Specifically, a period of time is usually set to 2 minutes, which can be set according to actual needs. Since the calculated temperature Tbase at the bottom of the compressor housing is lower than the actual value of the temperature at the bottom of the compressor housing, when Tbase is equal to Tbase min , the actual value of the temperature at the bottom of the compressor housing is higher than Tbase min, therefore, controlling the compressor in advance can increase the control margin. Based on this, the problems of refrigerant deposition and oil dilution are solved, and the reliability of the compressor operation is improved. The specific control method is as follows: increase the operating frequency of the compressor by an amount of △F. The calculation formula is: △F = K * (Tbase - Tbase min ) + B, where K and B are constants, and the values of K and B are related to the power and can be obtained through matching during the product development stage. For example, for a 1.5P air conditioner, K is 1.5 and B is 2. Increasing the frequency of the compressor by the △F method is a step-by-step frequency increase. Compared with the prior art where the frequency directly rises from low to medium frequency, the frequency fluctuation is relatively small, ensuring the comfort of the air conditioner while also ensuring the oil return effect.

Claims

1. A control method for a variable frequency compressor, characterized in that, Including the following steps: S01. Obtain the minimum value Tbase of the condenser outlet temperature Tcond, the compressor motor winding temperature Tmotor, and the temperature at the bottom of the compressor housing during compressor operation min ; S02. Calculate the temperature Tbase at the bottom of the compressor housing according to the temperature Tmotor of the compressor motor winding. The calculation formula is: Tbase = Tmotor - T, where T is greater than the maximum value of the temperature difference between the temperature at the bottom of the compressor housing and the condensation temperature under various working conditions; S03. Compare Tbase ≤ Tbase every once in a while min ; When Tbase ≤ Tbase min , increase the compressor operating frequency △F, where △F = K * (Tbase - Tbase min ) + B, where K and B are constants; When Tbase > Tbase min , the compressor operating frequency runs at the actual required frequency.

2. The control method of the variable-frequency compressor according to claim 1, characterized in that The temperature Tcond at the outlet of the condenser is collected by a temperature sensor.

3. The control method of the variable-frequency compressor according to claim 1, wherein K is 1.5 and B is 2.

4. The control method of the variable frequency compressor according to claim 1, characterized in that Said period of time is 2 minutes.

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