Method for judging whether to return oil or not by detecting current of compressor

Abstract

The invention provides a method for judging whether oil is returned or not by detecting the current of a compressor, and the method comprises the steps that the standard input current I standard of the compressor is calculated according to the calculation formula P = 1.732 * U * I standard * cosphi of three-phase electricity, P is the actual input power of the compressor, U is the effective input voltage of the compressor, cosphi is the power factor, and the output current I standard of the compressor is calculated according to the calculation formula P = 1.732 * U * I standard * cosphi. And if the current I < current > of the compressor is detected to be larger than 1.5 * I < standard >, the compressor is judged to be in a mixed lubrication state, and the system needs to return oil. According to the method, the oil quantity state and the oil return time of the compressor can be monitored in real time, the situation that the compressor frequently enters the oil return state due to inaccurate judgment is avoided, a user can better experience the refrigerating and heating effects, and meanwhile the reliability of the compressor is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of air conditioners, and in particular to a method for judging whether oil is returned by detecting compressor current. Background Art

[0002] At present, most multi-split air conditioners will enter the oil return after a certain period of cumulative operation to ensure the reliability of the compressor. The conditions for entering the oil return are generally based on the compressor operation time or oil discharge volume. These are the most reliable oil return entry conditions calculated under the worst conditions based on the oil discharge characteristics of the compressor unit provided by the compressor manufacturer. Generally, the refrigeration oil return will increase the compressor frequency, increase the valve opening of the indoor unit, and suck the oil back through the flow rate. The heating oil return will be switched to the cooling mode through the four-way valve reversing, and the oil will be brought back through the liquid. Frequent entry into the refrigeration oil return will increase the valve opening of the indoor unit, increase the compressor frequency, and generate refrigerant flow sound and compressor noise. Frequent entry into the heating oil return will cause the air conditioner to switch to the cooling mode, the indoor unit will not blow hot air, and the indoor temperature will drop, affecting the user's use effect. Summary of the invention

[0003] The present invention provides a method for judging whether there is oil return by detecting the compressor current, so as to solve the problem that the oil return of the multi-split air conditioner generates noise during refrigeration and does not blow hot air during heating, which affects the user experience as a whole.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0005] A method for determining whether oil is returned by detecting the compressor current, the method is based on the calculation formula P of the three-phase electricity 实际 =1.732*U*I 标 *cosφ, calculate the standard input current I of the compressor 标 , where P 实际 is the actual input power of the compressor, U is the effective input voltage of the compressor, cosφ is the power factor, if the current current I of the compressor is detected 当前 >1.5*I 标 , it is determined that the compressor is in a mixed lubrication state and the system needs to return oil.

[0006] Furthermore, the actual input power P of the compressor 实际 It is calculated by the theoretical input power P of the compressor 理论 obtained by the ratio of isentropic efficiency;

[0007] The theoretical input power P of the compressor 理论 =M r *(enthalpy value at point P2 - enthalpy value at point P1) / 1000, M ris the mass flow rate of the air conditioner refrigerant, the difference between the enthalpy value at the reference point P2 and the enthalpy value at the reference point P1 is the enthalpy difference, which is obtained by querying the thermodynamic pressure-enthalpy diagram of the air conditioner;

[0008] The isentropic efficiency ratio is obtained by querying the isentropic efficiency curve of the air conditioner.

[0009] Furthermore, the mass flow rate of the air conditioning refrigerant in is the cooling capacity of the air conditioner, and q0 is the enthalpy difference.

[0010] The above solution of the present invention includes at least the following beneficial effects:

[0011] A new judgment condition for the compressor to enter the oil return state is proposed, which can monitor the oil level status and oil return timing of the compressor in real time, avoiding the compressor frequently entering the oil return state due to inaccurate judgment, allowing users to have a better experience of cooling and heating effects, while ensuring the reliability of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a thermodynamic pressure-enthalpy diagram provided by an embodiment of the present invention.

[0013] Figure 2 yes Figure 1 Numerical graph of enthalpy values ​​at various reference points in .

[0014] Figure 3 This is a calculation data diagram of a compressor with a displacement of 85cc and a frequency of 55HZ provided in an embodiment of the present invention.

[0015] Figure 4 This is the isentropic efficiency curve with a condensing temperature of 49.9° C. and an evaporating temperature of 10.2° C. provided in an embodiment of the present invention;

[0016] Figure 5 This is a volumetric efficiency curve with a condensing temperature of 49.9° C. and an evaporating temperature of 10.2° C. provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in a form and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0018] For variable frequency rotor compressors or scroll compressors used in multi-split air conditioners, a large part of the input power of the compressor is done by the friction pair between the rotor and the stator. The friction pair is lubricated by compressor oil to ensure the reliability of the compressor. The friction coefficient of the friction pair depends on the state of the oil between the friction pairs. It can be specifically divided into fluid lubrication, mixed lubrication, and boundary lubrication. Boundary lubrication has the highest friction coefficient. A high friction coefficient means a large input power and input current at the same frequency, and vice versa. By detecting the current of the compressor, it is possible to determine what stage the compressor is in, and thus determine whether the compressor needs to return oil.

[0019] like Figure 1-5 As shown, the embodiment of the present invention proposes a method for determining whether oil is returned by detecting the compressor current. The method is based on the calculation formula P of the three-phase electricity. 实 =1.732*U*I 标 *cosφ, calculate the standard input current I of the compressor 标 , where P 实际 is the actual input power of the compressor, U is the effective input voltage of the compressor, cosφ is the power factor, if the current current I of the compressor is detected 当前 >1.5*I 标 , the compressor is judged to be in mixed lubrication state, and the system needs to return oil. The current I 当前 Detected by current transformer.

[0020] The actual input power of the compressor P 实际 It is calculated by the theoretical input power P of the compressor 理论 It is obtained by the ratio of isentropic efficiency.

[0021] Theoretical input power of compressor P 理论 =M r *(enthalpy value at point P2 - enthalpy value at point P1), M r is the mass flow rate of the air conditioner refrigerant, and the enthalpy values ​​at point P2 and P1 are obtained by querying the thermodynamic pressure-enthalpy diagram of the air conditioner. The pressure-enthalpy diagram is drawn based on the condensing temperature, evaporating temperature, subcooling, superheating, and cooling capacity. Figure 1 It is based on the pressure-enthalpy diagram with a cooling capacity of 30KW, a condensing temperature of 49.9℃, an evaporating temperature of 10.2℃, a superheat of 3℃, and a subcooling of 7℃.

[0022] Mass flow rate of air conditioning refrigerant in is the cooling capacity of the air conditioner, and q0 is the enthalpy difference.

[0023] Figure 1 The pressure-enthalpy diagram is drawn based on the cooling capacity of 30KW, condensing temperature of 49.9℃, evaporating temperature of 10.2℃, superheat of 3℃, and subcooling of 7℃.

[0024]

[0025] Theoretical input power of compressor P 理论 =M r *(enthalpy value at point P2 - enthalpy value at point P1) = 0.1927*(455.45-427.24) = 5.44KW.

[0026] The actual input power of the compressor P 实际 = Theoretical input power of compressor P 理论 / isentropic efficiency ratio. Under different compressor frequencies, different condensing and evaporating pressures, different subcooling and superheating, and when the friction pair is lubricated by fluid, what is the isentropic efficiency and volumetric efficiency? Generally, compressor manufacturers will conduct experiments to determine the isentropic characteristic curve and volumetric efficiency characteristic curve of the compressor and write them into the air conditioner baseboard program. Figure 4 , 5 The isentropic efficiency curve and volumetric efficiency curve of a compressor with a displacement of 85cc at a condensing temperature of 49.9℃ and an evaporating temperature of 10.2℃ are shown in Figure 1. Figure 2 The isentropic efficiency ratio can be queried by calculating the compressor frequency.

[0027] In this embodiment, the compressor frequency F=V r *1000000 / (H*L*3600), where V r is the suction volume flow rate, H is the compressor exhaust volume, and L is the volumetric efficiency. The compressor exhaust volume of this embodiment is 85cc and the volumetric efficiency is 1. The suction volume flow rate can be calculated by Figure 1-3 The pressure-enthalpy diagram shown in FIG. 1 shows that the suction volume flow rate of this embodiment is 16.85 m 3 / s,

[0028] Compressor frequency F = 16.85*1000000 / 85*1*3600 = 55.06 Hz.

[0029] according to Figure 4 The isentropic efficiency curve of the compressor shows that the isentropic efficiency ratio corresponding to 55.06 Hz is 0.75. The actual input power of the compressor is P = 5.44 / 0.75 = 7.25 KW.

[0030] According to P = 1.732 * U * I 标 *cosφ, the effective input voltage U of the compressor in this embodiment is 410V, and the power factor is 0.93, so I 标 =10.98A, if the current I 当前 >1.5*I 标 , that is I当前 >16.5A, the press is judged to be in mixed lubrication state and the system needs to return oil.

[0031] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for judging whether oil is returned by detecting the compressor current, characterized in that: The method is based on the calculation formula P of three-phase electricity 实际 =1.732*U*I 标 *cosφ, calculate the standard input current I of the compressor 标 , where P 实际 is the actual input power of the compressor, U is the effective input voltage of the compressor, cosφ is the power factor, if the current current I of the compressor is detected 当前 >1.5*I 标 , it is determined that the compressor is in a mixed lubrication state and the system needs to return oil.

2. The method for judging whether oil is returned by detecting compressor current according to claim 1, characterized in that: The actual input power P of the compressor 实际 It is calculated by the theoretical input power P of the compressor 理论 obtained by the ratio of isentropic efficiency; The theoretical input power P of the compressor 理论 =M r *(enthalpy value at point P2 - enthalpy value at point P1) / 1000, M r is the mass flow rate of the air conditioner refrigerant, the difference between the enthalpy value at the reference point P2 and the enthalpy value at the reference point P1 is the enthalpy difference, which is obtained by querying the thermodynamic pressure-enthalpy diagram of the air conditioner; The isentropic efficiency ratio is obtained by querying the isentropic efficiency curve of the air conditioner.

3. The method for judging whether oil is returned by detecting compressor current according to claim 2, characterized in that: The mass flow rate of the air conditioning refrigerant in is the cooling capacity of the air conditioner, and q0 is the enthalpy difference.

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