Temperature protection system of inverter compressor

Abstract

The utility model provides a temperature protection system of an inverter compressor, which relates to the field of compressors and refrigeration equipment and comprises the inverter compressor, a metal mechanism is mounted on a shell of the inverter compressor, an NTC (negative temperature coefficient) temperature sensor is arranged in the metal mechanism, and a lead of the NTC temperature sensor is connected with a main control unit. The main control unit is connected with a frequency converter of the inverter compressor through a control signal wire, and the frequency converter is connected with the inverter compressor through a power transmission wire. According to the utility model, the metal mechanism is arranged on the shell of the inverter compressor, so that the NTC temperature sensor can well detect the temperature of the compressor and predict the temperature of the motor, and the NTC temperature sensor, the frequency converter and the main control unit controller form a protection system to protect the inverter compressor; the compressor can be reliably protected under abnormal working conditions such as refrigerant leakage and low-evaporation-temperature operation working conditions exceeding the operation range, namely under the condition that overcurrent protection is invalid.

Description

Technical Field

[0001] This utility model relates to the field of compressors and refrigeration equipment, and in particular to a temperature protection system for a variable frequency compressor. Background Technology

[0002] Under abnormal conditions such as low-quality power supply (unstable voltage or voltage exceeding ±10% of the rated voltage, phase loss, etc.), overload exceeding the operating range, refrigerant leakage in the refrigeration system leading to poor motor cooling, and lack of lubrication causing mechanical component damage and motor stalling, the motor windings may overheat and burn out. Therefore, protective devices must be installed.

[0003] Fixed-frequency compressors (rotary compressors and small scroll compressors, etc.) typically have Y-type windings. The motors are bundled and installed at the ends of the stator windings and connected to a temperature and current type protector (bimetallic contact type) at the neutral point to protect the compressor motor windings from overheating and overcurrent.

[0004] For high-horsepower fixed-frequency compressors (whose current exceeds the capacity range of temperature and current type protectors), as well as compressors for medium and low temperature refrigeration applications, a temperature switch or PTC temperature sensor is installed at the end of the motor winding. The signal is led out through the sealed terminal on the housing and directly connected to the compressor control circuit, or the control signal is sent to the compressor control circuit for protection after being judged by the logic of an external electronic controller.

[0005] Because variable frequency compressors use frequency converters to power their motors, the temperature and current protectors used in traditional fixed frequency compressors cannot meet the protection requirements of variable frequency compressors under multiple power supply frequencies and wide operating conditions. Furthermore, most modern variable frequency compressor motors have centralized windings, leaving no space for temperature and current protectors. Using temperature switches or PTC sensors also presents the same problem, requiring additional sealed terminals on the casing to output temperature signals, which also increases costs. Therefore, the industry currently uses a maximum operating current setting in the frequency converter to protect the compressor motor. However, this method only protects against motor overcurrent. While some methods predict compressor motor temperature based on the compressor discharge temperature for overheat protection, this is not sensitive for high-pressure compressors (where the motor is located in the discharge chamber). For low-pressure compressors (where the motor is located in the suction chamber), the discharge temperature is largely independent of the motor temperature, failing to provide effective overheat protection.

[0006] When refrigerant leaks in refrigeration equipment, the amount of refrigerant flowing through the motor decreases, the motor cooling deteriorates, and the temperature rises, but the current does not change significantly. In this case, relying solely on the frequency converter cannot effectively protect the motor.

[0007] When the compressor operates at a low frequency, the motor current is small, but at the same time, the amount of refrigerant cooling the motor also decreases. Especially when the compressor is operating at a low evaporation temperature, when there are voltage fluctuations, compressor mechanical failures, or when the compressor exceeds its allowable operating range, the motor operating current increases, but may still not exceed the current when the compressor is operating at high frequency. However, at this time, the motor cooling conditions are very poor, which may cause the motor temperature to be too high and burn out.

[0008] To address the problems existing in the prior art, a novel temperature protection system for variable frequency compressors is designed and researched to overcome these issues. Utility Model Content

[0009] This invention provides a temperature protection system for a variable frequency compressor, which solves the problem that existing compressor overheat protection systems cannot effectively protect the motor from overheating.

[0010] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0011] A temperature protection system for a variable frequency compressor includes a variable frequency compressor. A metal structure is installed on the casing of the variable frequency compressor. An NTC temperature sensor is disposed inside the metal structure. The wires of the NTC temperature sensor are connected to a main control unit. The main control unit is connected to the inverter of the variable frequency compressor via a control signal wire. The inverter is connected to the variable frequency compressor via a power transmission wire.

[0012] The metal mechanism is located on the outer casing corresponding to the center of the stator core and the upper end of the stator core of the motor.

[0013] Furthermore, the contact surface between the metal mechanism and the outer shell is arc-shaped, and it is connected to the outer shell by welding; the upper side of the metal mechanism is square or concave arc-shaped.

[0014] Furthermore, the temperature sensing portion of the NTC temperature sensor is axially parallel to the housing of the variable frequency compressor.

[0015] Furthermore, the variable frequency compressor is a rotary sealed compressor, and the motor is installed inside the variable frequency compressor housing by heat fitting or press fitting, with the stator core in close contact with the outer shell.

[0016] Furthermore, for an internal low-pressure rotary sealed compressor, the metal mechanism is located on the outer casing opposite to the suction pipe position of the variable frequency compressor; for an internal high-pressure rotary sealed compressor, the metal mechanism is located on the outer casing corresponding to the internal exhaust port of the variable frequency compressor.

[0017] Furthermore, the NTC temperature sensor is installed in the metal structure and is in close contact with the housing of the variable frequency compressor, and the outside of the metal structure is wrapped with insulation material.

[0018] The beneficial effects of this utility model are as follows:

[0019] This invention proposes a metal mechanism on the casing of a variable frequency compressor, enabling the NTC temperature sensor to accurately detect the compressor temperature and predict the motor temperature. This, together with the frequency converter and the main control unit controller, forms a protection system to protect the compressor. It can reliably protect the compressor under abnormal operating conditions such as refrigerant leakage, low evaporation temperature operation outside the operating range, and when overcurrent protection is ineffective.

[0020] This invention installs the temperature sensor outside the compressor housing. Compared with the traditional fixed-frequency compressor that installs the temperature sensor at the end of the motor winding, it solves the problem of installing the temperature sensor in the space of the variable frequency motor with centralized winding. At the same time, it eliminates the need for sealed wiring terminals to lead out the temperature signal and is easy to install.

[0021] Compared with the traditional mechanical contact temperature switch for compressors, this utility model can set an over-temperature warning for the compressor and control the frequency converter through the main control unit of the unit to adjust the frequency, reduce the motor load, thereby reducing the compressor temperature and preventing the compressor from stopping.

[0022] In summary, the technical solution of this utility model achieves overheat protection for the motor of a variable frequency compressor at a low cost, and is easy to install and implement, effectively solving the problem that variable frequency compressors in the industry cannot protect the temperature of the motor coil. Attached Figure Description

[0023] To more clearly illustrate the embodiments of this utility model or the technical solutions of the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the temperature protection system of the variable frequency compressor of this utility model.

[0025] Figure 2 This is a schematic diagram of the variable frequency compressor structure of this utility model.

[0026] Figure 3 This is a temperature-resistance characteristic curve of an NTC temperature sensor.

[0027] Explanation of icon numbers:

[0028] 1. Variable frequency compressor; 2. Housing; 3. Motor; 4. Stator winding; 5. Stator core; 6. Crankshaft assembly; 7. Secondary support assembly; 8. Main support assembly; 9. Moving scroll; 10. Stable scroll; 11. Sealed terminal block; 12. Motor terminal block; 13. Intake pipe; 14. Exhaust pipe; 15. Lubricating oil; 16. Metal structure; 17. NTC temperature sensor; 18. Air deflector; 19. Oil pump; 20. Main control unit; 21. Variable frequency drive. Detailed Implementation

[0029] It should be noted that, where there is no conflict, the embodiments and features in the embodiments of this utility model can be combined with each other. The present utility model will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this utility model or its application or use. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0033] In the description of this utility model, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this utility model and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this utility model. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0034] This utility model provides a technical solution: a temperature protection system for a variable frequency compressor 1, such as... Figure 1-3 As shown, the variable frequency compressor 1 has a metal housing 2 with an NTC temperature sensor 17 placed inside. The inverter 21 and main control unit 20 of the variable frequency compressor 1 refrigeration system constitute the motor 3 protection system of the variable frequency compressor 1.

[0035] The contact surface between the metal mechanism 16 and the outer shell 2 is arc-shaped and welded to the outer shell 2. The upper side is square or concave arc-shaped, which can produce sufficient deformation under pressure. After the NTC temperature sensor 17 is installed, the metal mechanism 16 exerts a squeezing force on it in the direction of the compressor.

[0036] The metal mechanism 16 is installed in the following positions: in the axial direction of the variable frequency compressor 1, it is located above the middle position of the stator core 5 of the motor 3, but not exceeding the upper end of the stator core 5; in the circumferential direction of the variable frequency compressor 1, it is located at the contact position between the stator core 5 and the outer casing 2.

[0037] After the NTC temperature sensor 17 is installed, its temperature sensing part is parallel to the outer casing 2 and is located in the corresponding area of ​​the stator core 5.

[0038] The variable frequency compressor 1 is a rotary sealed compressor. The stator of the motor 3 is heat-fitted or press-fitted into the compressor housing. The stator core 5 of the motor 3 is in direct and tight contact with the outer casing 2.

[0039] An arc-shaped or square metal mechanism 16 is welded to the outside of the contact point between the stator core 5 of the motor 3 and the outer casing 2 in the variable frequency compressor 1. For the variable frequency compressor 1 with low internal pressure (the motor 3 is located in the suction chamber of the variable frequency compressor 1), the metal mechanism 16 is located on the opposite side of the suction pipe 13 of the variable frequency compressor 1; for the variable frequency compressor 1 with high internal pressure (the motor 3 is located in the exhaust chamber of the variable frequency compressor 1), the metal mechanism 16 is located on the side of the internal exhaust pipe 14 of the compressor.

[0040] The NTC temperature sensor 17 is installed in the metal mechanism 16 and is in close contact with the housing 2. The metal mechanism 16 is wrapped with thermal insulation material to ensure that the NTC temperature sensor 17 can effectively sense the temperature.

[0041] Example 1

[0042] The working principle of this type of variable frequency compressor 1 and temperature protection system is explained using the internal low-pressure variable frequency compressor 1 as an example, but it is not limited to this type of variable frequency compressor 1.

[0043] When the variable frequency compressor 1 is working, the main control unit 20 on the refrigeration unit controls the inverter 21 to supply power to the variable frequency compressor 1. The current input sealed terminal 11 is connected to the terminal of the motor 3 inside the variable frequency compressor 1, and the motor 3 starts to work. The crankshaft assembly 6, which is fixed to the main support assembly 8 and the auxiliary support assembly 7, rotates, driving the moving scroll 9 to rotate. The moving scroll 9, in conjunction with the stationary scroll 10, compresses the refrigerant and discharges it from the variable frequency compressor 1 through the exhaust pipe 14. During this process, the oil pump 19 pumps the lubricating oil 15 from the lower part of the variable frequency compressor 1 into the moving scroll 9 through the internal channel of the crankshaft assembly 6, lubricating it and other moving parts.

[0044] The refrigerant continuously enters the variable frequency compressor 1 from the refrigeration system pipeline through the suction pipe 13. The flow direction is changed by the deflector 18, and all or part of it flows downward to the motor 3 to cool the motor 3. After passing the motor 3, it returns upward and enters the compression chamber formed by the moving scroll 9 and the fixed scroll 10 for compression. Finally, it is discharged through the exhaust pipe 14 and returns to the refrigeration system pipeline.

[0045] When the variable frequency compressor 1 is running, the inherent resistance of the stator winding 4 of the motor 3 causes copper loss and the iron loss generated by the stator core 5, which are converted into heat energy and raise the temperature of the motor 3. At the same time, the refrigerant flows through the motor 3 to cool it. However, the refrigerant does not cool the motor 3 uniformly. The temperature is lower on the side closer to the deflector 18 and higher on the side farther away from the deflector 18. According to the flow path characteristics of the refrigerant in the variable frequency compressor 1, the temperature of the upper part of the motor 3 is higher than that of the lower part.

[0046] The heat generated by the motor 3 due to losses is partly carried away by the refrigerant flowing through it, and partly transferred to the casing 2 of the inverter compressor 1 for heat dissipation to the surrounding environment. The main loss of the motor 3 is the copper loss generated by the stator winding 4 of the motor 3, and the secondary loss is the iron loss generated by the stator core 5 of the motor 3. Therefore, the temperature of the stator winding 4, Tcoil, is greater than the temperature of the stator core 5, Tcore, and the temperature of the casing 2 of the inverter compressor 1, Tcase. When the inverter compressor 1 is running normally, the temperature gradient of the above three components is within a certain range. Therefore, the temperature of Tcoil can be predicted based on Tcase. In order to obtain better results, Tcase should be the part of the stator core 5 that is in close contact with the casing 2 of the inverter compressor 1, located on the side away from the suction pipe 13 of the inverter compressor 1, and in the middle and above the motor 3. That is, the metal mechanism 16 is installed at this position, and the NTC temperature sensor 17 is inserted into it, which can measure Tcase well and thus predict Tcoil.

[0047] Based on the insulation class of the variable frequency compressor 1, the maximum allowable temperature Tw of the stator winding 4 of the motor 3 can be determined. Based on the temperature gradient ΔT, the protection temperature T2 of the NTC temperature sensor 17 can be obtained as Tw-ΔT. When the NTC temperature sensor 17 reaches T2, the main control unit 20 of the refrigeration unit detects its corresponding resistance value and sends a shutdown command to the frequency converter 21. The frequency converter 21 reduces the frequency until the variable frequency compressor 1 stops. At this time, the main control unit 20 of the refrigeration unit issues a fault alarm signal. It must be checked and manually cleared before it can continue to start up and run.

[0048] Before the casing 2 of the variable frequency compressor 1 reaches temperature T2, a warning temperature T1 is set, with a certain temperature difference ΔTt between it and T2, where T1 = T2 - ΔTt. When the NTC temperature sensor 17 reaches T1, the main control unit 20 of the refrigeration unit detects its corresponding resistance value and sends a shutdown command to the inverter 21. The inverter 21 reduces the frequency to allow the variable frequency compressor 1 to operate at a safe speed n. When the NTC temperature sensor 17 detects a temperature lower than T1-10℃, the main control unit 20 controls the inverter 21 to release the frequency reduction of the variable frequency compressor 1. When the NTC temperature sensor 17 detects a temperature lower than T1, the variable frequency compressor 1 operates normally.

[0049] The temperature-resistance characteristics of the NTC temperature sensor 17 designed in this invention are as follows: Figure 3 As shown, within its operating range, the resistance value decreases as the temperature increases, and there is a unique correspondence between the resistance value and the temperature value. In this invention, the warning temperature value T1 corresponds to its resistance value R1, and the protection temperature value T2 corresponds to its resistance value R2. The refrigeration unit controls the frequency converter 21 based on the detected resistance value compared with R1 and R2, thereby achieving the adjustment and protection of the variable frequency compressor 1.

[0050] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A temperature protection system for a variable frequency compressor, characterized in that, The system includes a variable frequency compressor (1), the outer casing (2) of the variable frequency compressor (1) is equipped with a metal mechanism (16), an NTC temperature sensor (17) is disposed inside the metal mechanism (16), the wire of the NTC temperature sensor (17) is connected to the main control unit (20), the main control unit (20) is connected to the inverter (21) of the variable frequency compressor (1) through a control signal wire, and the inverter (21) is connected to the variable frequency compressor (1) through a power transmission wire; The metal mechanism (16) is located on the corresponding outer shell (2) between the center of the stator core (5) of the motor (3) and the upper end of the stator core (5).

2. The temperature protection system for the variable frequency compressor according to claim 1, characterized in that, The contact surface between the metal mechanism (16) and the outer shell (2) is arc-shaped, and it is connected to the outer shell (2) by welding; the upper side of the metal mechanism (16) is square or concave arc-shaped.

3. The temperature protection system for the variable frequency compressor according to claim 1, characterized in that, The temperature sensing part of the NTC temperature sensor (17) is parallel to the housing (2) of the variable frequency compressor (1) along the axial direction.

4. The temperature protection system for the variable frequency compressor according to claim 1, characterized in that, The variable frequency compressor (1) is a rotary sealed compressor. The motor (3) is installed inside the casing of the variable frequency compressor (1) by heat fitting or press fitting. The stator core (5) is in close contact with the outer casing (2).

5. The temperature protection system for the variable frequency compressor according to claim 4, characterized in that, For an internal low-pressure rotary sealed compressor, the metal mechanism (16) is located on the outer casing (2) on the opposite side of the suction pipe (13) of the variable frequency compressor (1); for an internal high-pressure rotary sealed compressor, the metal mechanism (16) is located on the outer casing (2) corresponding to the internal exhaust port of the variable frequency compressor (1).

6. The temperature protection system for the variable frequency compressor according to claim 1, characterized in that, The NTC temperature sensor (17) is installed in the metal mechanism (16) and is in close contact with the housing (2) of the variable frequency compressor (1). The metal mechanism (16) is wrapped with insulation material.

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