Over-temperature protection method for variable frequency compressor

Abstract

The present application relates to the technical field of variable frequency compressor control, in order to realize the over-temperature protection of the motor of the variable frequency compressor, a kind of over-temperature protection method of variable frequency compressor is provided, comprising: step 1, the motor winding temperature T2 is detected in real time during the operation of variable frequency compressor;Step 2, judge whether the motor winding temperature T2 is greater than or equal to the maximum allowable operating temperature T of motor MAX , if yes, then enter step 3, if no, then the variable frequency compressor is normally operated according to the current state;Step 3, obtain the current speed n1 of variable frequency compressor, and judge whether n1 is greater than the rated speed n r of variable frequency compressor, if yes, then control the variable frequency compressor to reduce speed, and run according to η×n r , wherein η is proportional constant, and 1≥η>0;If no, then control the variable frequency compressor to stop running. The above steps can realize the over-temperature protection of the motor of the variable frequency compressor.

Description

Technical Field

[0001] This invention relates to the field of variable frequency compressor control technology, specifically a method for over-temperature protection of a variable frequency compressor. Background Technology

[0002] In actual operation, variable frequency compressors operate in harsh environments and under harsh refrigeration system conditions. Typically, before reaching the rated speed, the compressor is controlled in a constant torque mode, where the motor speed is proportional to the motor voltage and the motor current is relatively small. Once the rated speed is reached, it is controlled in a constant power mode, where the motor voltage and motor speed remain constant. If the motor wants to continue increasing its operating speed, it needs to use field weakening control, which will significantly increase the motor current. This will cause the motor winding temperature to rise continuously, potentially leading to motor burnout and compressor malfunction. Summary of the Invention

[0003] To address the aforementioned defects caused by overheating of the variable frequency compressor motor, this application provides a method for overheat protection of variable frequency compressors.

[0004] The technical solution adopted by the present invention to solve the above problems is:

[0005] Over-temperature protection methods for variable frequency compressors include:

[0006] Step 1: Monitor the motor winding temperature T2 in real time during the operation of the variable frequency compressor;

[0007] Step 2: Determine whether the motor winding temperature T2 is greater than or equal to the motor's maximum allowable operating temperature T. MAX If yes, proceed to step 3; otherwise, the inverter compressor will operate normally under its current condition.

[0008] Step 3: Obtain the current speed n1 of the variable frequency compressor and determine whether n1 is greater than the rated speed n of the variable frequency compressor. r If so, control the variable frequency compressor to reduce its speed and operate according to η×n. r If η is a proportional constant and 1 ≥ η > 0, then the variable frequency compressor is controlled to stop running.

[0009] Furthermore, in step 3, if n1-n r If τ > 1, then η is 1; otherwise, η is 85%-90%; where τ is the speed difference threshold.

[0010] Furthermore, τ is set to 600-900 rpm.

[0011] Furthermore, the rated speed n of the variable frequency compressor r The calculation steps are as follows: Measure the magnetic flux of the variable frequency compressor motor. According to magnetic flux Calculate the back electromotive force coefficient K of the variable frequency compressor motor E According to n r =U i ×δ / K E Calculate the rated speed of the variable frequency compressor, where U i δ is the power supply voltage, and δ is a constant.

[0012] Furthermore, δ is taken as 0.8 to 0.9.

[0013] Furthermore, the steps for obtaining T2 are as follows:

[0014] When the variable frequency compressor stops, the resistance R1 of the variable frequency compressor is obtained when the motor winding temperature T1 is obtained, where T1 is the ambient temperature;

[0015] Start the variable frequency compressor and monitor the motor resistance R2 in real time during the operation of the variable frequency compressor;

[0016] T2 is calculated using the formula T2 = K × (R2 - R1) / R1 + R2 × T1 / R1, where k is the temperature constant of the motor wire resistance.

[0017] The advantages of this invention compared to the prior art are: this method can not only accurately monitor whether the variable frequency compressor is overheating, but also achieve effective control and intelligent protection against overheating of the variable frequency compressor, which greatly reduces the risk of motor burnout and component damage of the variable frequency compressor, and improves the safety of the variable frequency compressor control system under overload and overheating. It has the advantages of reasonable design, simple use, high intelligence and strong safety, and can be widely applied to overheat protection of variable frequency compressors of any structure. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] Over-temperature protection methods for variable frequency compressors include:

[0020] Step 1: Monitor the motor winding temperature T2 in real time during the operation of the variable frequency compressor;

[0021] Step 2: Determine whether the motor winding temperature T2 is greater than or equal to the motor's maximum allowable operating temperature T. MAX If yes, proceed to step 3; otherwise, the inverter compressor will operate normally under its current condition.

[0022] Step 3: Obtain the current speed n1 of the variable frequency compressor and determine whether n1 is greater than the rated speed n of the variable frequency compressor.r If so, the variable frequency compressor is controlled to reduce its speed. In this embodiment, the variable frequency compressor reduces its speed at a constant deceleration rate, and according to η×n r If η is a proportional constant and 1 ≥ η > 0, then the variable frequency compressor is controlled to stop running.

[0023] Furthermore, in step 3, if n1-n r If τ > 1, then η is 1; otherwise, η is 85%-90%; where τ is the speed difference threshold, and τ can be 600-900 rpm.

[0024] Preferably, in addition to using the speed specified by the manufacturer, the rated speed of the variable frequency compressor can also be obtained independently to improve control accuracy. The rated speed n of the variable frequency compressor... r The calculation steps are as follows: Measure the magnetic flux of the variable frequency compressor motor using a digital flux meter. According to magnetic flux Calculating the back EMF coefficient K of the variable frequency compressor motor based on the mapping relationship with back EMF E K E =4.44×K N ×N×φ×P / 60, where K N U is the fundamental winding coefficient, N is the number of turns in series per phase of the stator winding, and P is the number of pole pairs of the motor; the variable frequency compressor and the frequency converter are connected to the compressor control system, and the power supply for the compressor control system is U. i According to n r =U i ×δ / K E Calculate the rated speed of the variable frequency compressor, where δ is a constant and can be taken as 0.8 to 0.9.

[0025] Besides direct detection, T2 can also be obtained through the following steps:

[0026] When the variable frequency compressor stops, the resistance R1 of the variable frequency compressor is obtained through the inverter software at the motor winding temperature T1, where T1 is the ambient temperature. In order to improve the detection accuracy of the resistance, the variable frequency compressor can be left to stand for t hours at the ambient temperature of T1 before measurement. In this embodiment, t is at least 24 hours.

[0027] Start the variable frequency compressor and monitor the motor resistance R2 in real time during the operation of the variable frequency compressor;

[0028] T2 is calculated according to T2=K×(R2-R1) / R1+R2×T1 / R1, where k is the temperature constant of the motor wire resistance, k is 235 for copper wire and 225 for aluminum wire.

[0029] The over-temperature protection method for a variable frequency compressor disclosed in this invention first collects the motor resistance of the variable frequency compressor during cold and hot operation using inverter software, and then monitors and calculates the motor winding temperature in real time. The acquired motor winding temperature is compared with a preset maximum allowable operating temperature of the motor to determine whether the variable frequency compressor is in an over-temperature operating state. Then, the inverter software collects the operating speed of the variable frequency compressor when it is in a hot state and compares the current speed with the rated speed. If the current speed is lower than the rated speed, the inverter input control signal is reset to zero, and the compressor stops directly for over-temperature protection. If the current speed exceeds the rated speed, the operating speed is reduced to decrease the motor operating current and lower the motor winding temperature for over-temperature protection. In this application, to achieve segmented precise control, the operating speed of the variable frequency compressor is reduced to the rated speed or below by comparing the speed difference between the current speed and the rated speed. This method can not only accurately monitor whether the variable frequency compressor is overheating, but also effectively control and intelligently protect the variable frequency compressor from overheating. It greatly reduces the risk of motor burnout and component damage in the variable frequency compressor, and improves the safety of the variable frequency compressor control system under overload and overheating conditions. It has the advantages of reasonable design, simple use, high intelligence and strong safety, and can be widely applied to overheat protection of variable frequency compressors of any structure.

Claims

1. A method for over-temperature protection of a variable frequency compressor, characterized in that, include: Step 1: Monitor the motor winding temperature T2 in real time during the operation of the variable frequency compressor; Step 2: Determine whether the motor winding temperature T2 is greater than or equal to the motor's maximum allowable operating temperature T. MAX If yes, proceed to step 3; otherwise, the inverter compressor will operate normally under its current condition. Step 3: Obtain the current speed n1 of the variable frequency compressor and determine whether n1 is greater than the rated speed n of the variable frequency compressor. r If so, control the variable frequency compressor to reduce its speed and operate according to η×n. r If η is a proportional constant and 1 ≥ η > 0, then the variable frequency compressor is controlled to stop running.

2. The over-temperature protection method for a variable frequency compressor according to claim 1, characterized in that, In step 3, if n1-n r If the value is greater than τ, then η is 1; otherwise, η is 85%-90%; where τ is the speed difference threshold.

3. The over-temperature protection method for a variable frequency compressor according to claim 2, characterized in that, Set the τ to 600-900 rpm.

4. The over-temperature protection method for a variable frequency compressor according to claim 1, characterized in that, The rated speed n of the variable frequency compressor r The calculation steps are as follows: Measure the magnetic flux of the variable frequency compressor motor. According to magnetic flux Calculate the back electromotive force coefficient K of the variable frequency compressor motor E ;according to Calculate the rated speed of the variable frequency compressor, where U i δ is the power supply voltage, and δ is a constant.

5. The over-temperature protection method for a variable frequency compressor according to claim 4, characterized in that, δ is taken as 0.8~0.

9.

6. The over-temperature protection method for a variable frequency compressor according to claim 1, characterized in that, The steps for obtaining T2 are as follows: When the variable frequency compressor stops, the resistance R1 of the variable frequency compressor is obtained when the motor winding temperature T1 is obtained, where T1 is the ambient temperature; Start the variable frequency compressor and monitor the motor resistance R2 in real time during the operation of the variable frequency compressor; according to Calculate T2, where K is the temperature constant of the motor wire resistance.