Electric compressor and method of operating compressor
By using magnetic bearings or electric brakes in electric compressors to generate heat at low temperatures, the starting problem caused by refrigerant migration is solved, the low-temperature operation range of the compressor is expanded, and a safer and simplified system design is achieved.
Patent Information
- Application Number
- CN202410910318.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-06-24
- Filing Date
- 2024-07-09
- Publication Date
- 2025-01-10
AI Technical Summary
When an electric refrigerant compressor starts in a low temperature environment, the refrigerant may migrate, resulting in an increase in starting torque, triggering motor current protection, and even leading to bearing damage, limiting the lower limit of the temperature range.
By using magnetic bearings or electric brakes to generate heat when the electric motor is not running, the migrated refrigerant is boiling and evaporating, or the electric motor acts as a heat source when the system is idle, ensuring that the refrigerant does not accumulate.
Effectively extend the operating temperature range of the electric compressor to lower, such as -32°C, avoiding start-up failures caused by refrigerant accumulation, simplifying system design, and avoiding additional complex supplementary systems.
Smart Images
Figure CN119288882A_ABST
Abstract
Description
[0001] Related Applications
[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 512,714, filed on July 10, 2023, the entire contents of which are incorporated herein by reference. Technical Field
[0003] The present application is directed to extending the operating range of an electric refrigerant compressor to lower ambient temperatures. Background Art
[0004] Refrigerant compressors are known and are used in many applications. One common use is in air handling systems, such as air conditioners or heat pumps. Air coolers are a common use.
[0005] The refrigerant circulates through the circuit. The refrigerant is compressed in the electric compressor and transferred to the condenser where the heat of the refrigerant is removed. The refrigerant then passes through the expansion device where the pressure of the refrigerant is reduced and the refrigerant becomes colder. The refrigerant then enters the evaporator where it cools another fluid, such as air. The refrigerant then returns to the electric compressor.
[0006] Electric compressors in such systems present challenges, particularly at low temperatures. As an example, when the electric compressor is shut down, refrigerant may migrate, creating challenges at start-up. As an example, if refrigerant has accumulated in the area of the shaft driven by the electric compressor, this may create challenges. As an example, it may significantly increase the starting torque to trigger the motor current protection, causing the compressor to fail at start-up. In fact, in extreme cases, this may add a large load on the shaft and cause the shaft to hit the bearings.
[0007] These challenges limit the lower end of the temperature range. Summary of the invention
[0008] In a characteristic embodiment, an electric compressor includes an electric motor including a rotor and a stator and a shaft that rotates with the rotor to drive a compressor impeller. A bearing supports the shaft. A housing encloses the impeller shaft, the bearing and the electric motor, and a sensor for sensing conditions within the housing. A controller for the electric motor receives information from the sensor indicating the likelihood of refrigerant migration when the electric motor is not running. The controller is operable to initiate a countermeasure to transfer heat into the housing to boil away the migrated refrigerant.
[0009] In another embodiment according to the preceding embodiment, the bearing is a magnetic bearing and the countermeasure is activating the magnetic bearing when the electric motor is not running.
[0010] In another embodiment according to any of the preceding embodiments, the countermeasure is controlling the electric motor to generate heat when the system is idle.
[0011] In another embodiment according to any of the preceding embodiments, the countermeasure is to operate the electric motor at a low speed when the system is idle so as to act as a heat source.
[0012] In another embodiment according to any of the foregoing embodiments, a check valve is positioned downstream of an impeller of the compressor and opens when the impeller of the compressor pressurizes the refrigerant to a sufficient pressure. The low speed is defined as operating the electric motor so that the compressor impeller does not pressurize the refrigerant enough to open the check valve.
[0013] In another embodiment according to any of the preceding embodiments, the countermeasure is to provide the rotor with an electric brake to act as a heat source when the system is idle.
[0014] In a further embodiment according to any of the preceding embodiments, the electric motor is an AC motor, and the electric brake is controlled by supplying a DC voltage to the electric motor.
[0015] In another embodiment according to any of the preceding embodiments, the countermeasure is initiated at least thirty seconds prior to an expected start of the electric compressor.
[0016] In a further embodiment according to any of the preceding embodiments, the countermeasure is cycled on and off.
[0017] In a further embodiment according to any of the preceding embodiments, the countermeasure is disabled if a threshold temperature is reached within the electric compressor.
[0018] In another feature embodiment, a method of operating a compressor includes the steps of determining that an electric motor for a compressor is not driving an impeller of the compressor, evaluating conditions within the housing to determine whether the conditions indicate the possible presence of migrated refrigerant when the electric motor is not driving the impeller, and taking countermeasures to boil away the migrated refrigerant within the housing when the electric motor is not driving the impeller.
[0019] In another embodiment according to any of the preceding embodiments, the electric motor includes a rotor, the rotor drives a shaft to drive the impeller, and the shaft is supported on magnetic bearings. The countermeasure includes activating the magnetic bearings to transfer heat into the housing when the electric motor is not driving the impeller.
[0020] In a further embodiment according to any of the preceding embodiments, the electric motor comprises a rotor provided with an electric brake, and the countermeasure comprises activating the electric brake when the electric motor is not driving the impeller.
[0021] In a further embodiment according to any of the preceding embodiments, the electric motor is an AC motor and the countermeasure is controlling the electric brake by supplying a DC voltage to the electric motor.
[0022] In another embodiment according to any of the preceding embodiments, the countermeasure is initiated at least thirty seconds prior to an expected start of the electric compressor.
[0023] In a further embodiment according to any of the preceding embodiments, the countermeasure causes the electric motor to operate at a low speed.
[0024] In another embodiment according to any of the preceding embodiments, a check valve is positioned downstream of an impeller of the compressor and opens when the compressor impeller pressurizes the refrigerant to a sufficient pressure. The low speed is defined as operating the electric motor so that the impeller of the compressor does not pressurize the refrigerant enough to open the check valve.
[0025] In another embodiment according to any of the preceding embodiments, the countermeasure is initiated at least thirty seconds prior to an expected start of the electric compressor.
[0026] In a further embodiment according to any of the preceding embodiments, the countermeasure is cycled on and off.
[0027] In a further embodiment according to any of the preceding embodiments, the countermeasure is disabled if a threshold temperature is reached within the electric compressor.
[0028] These and other features can be best understood from the following drawings and specification, the following of which is a brief description. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1A The refrigerant circuit is shown schematically.
[0030] Figure 1B Shows the challenges of such a circuit.
[0031] Figure 2 is a flow chart of a method included in the present disclosure. DETAILED DESCRIPTION
[0032] Figure 1A The example illustrates a refrigerant system 20. The refrigerant system 20 includes a main refrigerant loop or circuit 24 in communication with a compressor 22, a condenser 25, an evaporator 28, and an expansion device 26. For example, the refrigerant system 20 can be used in a chiller. In this example, a cooling tower can be in fluid communication with the condenser 25. Although a specific example of the refrigerant system 20 is shown, the application can be extended to other refrigerant system configurations, including configurations that do not include a chiller. For example, the main refrigerant loop 24 can include an economizer downstream of the condenser 16 and upstream of the expansion device 26.
[0033] The housing 31 surrounds the electric compressor 22. The inlet 32 delivers the refrigerant to the impeller 33. The impeller 33 delivers the compressed refrigerant to the outlet 23. From the outlet 23, the refrigerant reaches the condenser 25 through the circuit 24. As is well known, the refrigerant is cooled in the condenser.
[0034] The refrigerant then passes through an expansion device 26 which expands the refrigerant to a lower pressure and temperature. The refrigerant then passes through an evaporator 28 where it is allowed to cool a second fluid, such as air. The refrigerant then enters a passage 30 and returns to an inlet 32.
[0035] In the disclosed compressor 22, there are magnetic bearings 36 and 38 supporting the shaft 34. The motor rotor 42 rotates with the shaft 34. When powered, the motor stator 40 drives the rotor 42, and thus drives the shaft 34 and the impeller 33 to rotate. The motor is an AC motor. A controller 44 is shown in communication with the rotor 42, the stator 40, and the magnetic bearings 36 and 38. The controller 44 is also shown in communication with a sensor 46.
[0036] A discharge valve 35 is shown downstream of the impeller 33. As is well known, the discharge valve 35 may be a check valve that opens when the pressure of the refrigerant downstream of the impeller 33 exceeds a predetermined minimum value. The location and operation of the valve 35 may be known. Here, the valve 35 is shown schematically.
[0037] Figure 1B The problem discussed above is shown. As shown, the rotor 42, shaft 34, bearings 36 and 38, and stator 40 are all within the housing 31. Pooled refrigerant 48 is shown. The amount of pooled refrigerant may be exaggerated. Such a condition may occur when the compressor is in standby mode or is not operating at low ambient temperatures.
[0038] Figure 24 is a flow chart of the method and control according to the present disclosure. In step 50, it is asked whether the motor is running. If the answer is no, then step 52 asks whether the condition indicates potential refrigerant migration. Low ambient temperature is such an indicator. Such a condition will be provided to the controller 44 by the sensor 46. The sensor 46 can be a temperature sensor, or it can be a sensor that can sense such as Figure 1B A sensor for the presence of liquid refrigerant 48 is shown in FIG.
[0039] As an example, a prior art compressor 20 may have an operating range above -1° C. and below 51° C. Outside of this range, the compressor will typically not operate due to too much pooled refrigerant.
[0040] However, systems (such as Figure 1A Users of the refrigerant system shown in ) want to use such a system in many environments. Therefore, the -1°C range for current compressors is a limitation. Although various supplementary systems (such as the use of heaters) can be used to allow lower temperature operation, this complicates the system.
[0041] Returning to the flow chart at step 54, if step 52 determines that the conditions indicate potential refrigerant migration, then countermeasures are taken.
[0042] In one example, the controller 44 can energize the magnetic bearings 36 and 38. This transfers heat to the refrigerant 48, such as Figure 1B This will help boil off the refrigerant so that when the motor is powered on again, the above problems will be reduced or even eliminated. This measure will be taken when the motor is not running.
[0043] A second possible countermeasure, which can be done separately or in combination with the first, is to use the motor as a heat source rather than driving compression. One measure could be to run the motor at a low speed, which has the net effect of generating heat but no compression.
[0044] For purposes of this disclosure and interpreting the claims, the term “low speed” means operating the compressor at a speed such that the pressure of the refrigerant compressed by the impeller 33 is insufficient to open the valve 35 .
[0045] Another measure may be to implement an electric brake on the rotor 42. DC current may be delivered to the rotor 42 to prevent rotation under certain circumstances. By activating the brake, additional heat is transferred to the refrigerant 48 even when the motor is not running, such as Figure 1B As indicated by the arrow in .
[0046] To operate an electric motor as a DC brake, a fixed voltage is applied to the stator terminals. This induces a current through the windings, which generates a static magnetic field on the rotor magnets, aligning the two. The higher the voltage applied, the greater the current and the stronger the magnetic field. The resulting magnetic field has losses in the form of heat in the stator and rotor. These losses will heat the refrigerant and eventually boil it off. The larger the magnetic field generated, the higher the losses and the faster the refrigerant will boil off. The same principle can be used for magnetic bearings, whereby a fixed current can be supplied through the magnetic bearings, pushing the shaft in a static direction (not suspended in normal operation) and generating heat.
[0047] If this is done, logic can be included to disable intentional heating if certain thermal thresholds or time limits are reached on the motor or magnetic bearings. This will prevent internal heating of the bearings or motor windings from causing damage to the machine.
[0048] In an embodiment, similar to a home heater or air conditioning system, the countermeasure can be cycled on and off to regulate the liquid level. If there is too much liquid refrigerant accumulation, such as when the machine has been powered off for a period of time, the countermeasure can be cycled multiple times to convert all the liquid refrigerant to gas.
[0049] In an embodiment, the countermeasure will generally be used for a minimum time period. In one embodiment, the minimum time period is 30 seconds before the electric motor is powered on. In a more limited embodiment, the minimum time period will be at least one minute. In addition, in an embodiment, the maximum time period before the motor is started and the countermeasure is performed will be less than 10 minutes. Of course, in a cyclic operation as described above, after the countermeasure has been started, until the electric motor is started, this may be a relatively long period of time. However, in such a case, the countermeasure will not last more than 10 minutes.
[0050] By utilizing countermeasures as disclosed herein, the safe operating range of the compressor 22 may be significantly reduced, such as to approximately -32°C.
[0051] Back to Figure 2 After the countermeasure has taken place, in step 56, it is asked whether the condition has changed. One way to do this is whether the fluid level or the temperature from the sensor 46 is now acceptable.
[0052] If the condition has changed, the flow chart returns to step 52. At some point, the motor will be restarted to get the system running, and the present disclosure will ensure that the compressor will be able to start at that time.
[0053] While embodiments have been disclosed, those skilled in the art will recognize that modifications will fall within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.
Claims
1. An electric compressor comprising: an electric motor including a rotor and a stator and a shaft that rotates with the rotor to drive a compressor impeller; bearings supporting the shaft; a housing enclosing a shaft of the compressor impeller, the bearings, and the electric motor, and a sensor for sensing conditions within the housing; as well as A controller for the electric motor receives information from the sensor indicating the likelihood of refrigerant migration when the electric motor is not operating and is operable to initiate a countermeasure to transfer heat into the housing to boil off the migrated refrigerant.
2. The electric compressor according to claim 1, wherein: The bearing is a magnetic bearing, and the countermeasure is to activate the magnetic bearing when the electric motor is not running.
3. The electric compressor according to claim 1, wherein: The countermeasure is to control the electric motor to generate heat when the system is idle.
4. The electric compressor according to claim 3, wherein the countermeasure is to operate the electric motor at a low speed when the system is idle so as to act as a heat source.
5. The electric compressor according to claim 4, wherein: A check valve is positioned downstream of the compressor impeller and opens when the compressor impeller pressurizes the refrigerant to a sufficient pressure, and the low speed is defined to operate the electric motor so that the compressor impeller does not pressurize the refrigerant enough to open the check valve.
6. The electric compressor according to claim 3, wherein: The countermeasure is to provide the rotor with an electric brake to act as a heat source when the system is idle.
7. The electric compressor according to claim 6, wherein: The electric motor is an AC motor, and the electric brake is controlled by supplying a DC voltage to the electric motor.
8. The electric compressor according to claim 1, wherein: The countermeasure is initiated at least thirty seconds prior to an expected start-up of the electric compressor.
9. The electric compressor according to claim 1, wherein: The countermeasures are cycled on and off.
10. The electric compressor according to claim 1, wherein: If a threshold temperature is reached in the electric compressor, the countermeasure is disabled.
11. A method of operating a compressor, comprising the steps of: determining that an electric motor for a compressor is not driving an impeller of said compressor; evaluating conditions within the housing to determine whether the conditions indicate the possible presence of migrated refrigerant when the electric motor is not driving the impeller; as well as When the electric motor is not driving the impeller, countermeasures are taken to boil away the migrated refrigerant within the housing.
12. The method according to claim 11, wherein: The electric motor includes a rotor that drives a shaft to drive the impeller, and the shaft is supported on magnetic bearings, and the countermeasure includes activating the magnetic bearings to transfer heat into the housing when the electric motor is not driving the impeller.
13. The method according to claim 11, wherein: The electric motor includes a rotor provided with an electric brake, and the countermeasure includes activating the electric brake when the electric motor is not driving the impeller.
14. The method according to claim 13, wherein: The electric motor is an AC motor, and the countermeasure is to control the electric brake by supplying a DC voltage to the electric motor.
15. The method according to claim 14, wherein: The countermeasure is initiated at least thirty seconds prior to an expected start-up of the electric compressor.
16. The method according to claim 11, wherein: The countermeasure causes the electric motor to operate at a low speed.
17. The method according to claim 16, wherein: A check valve is positioned downstream of the compressor impeller and opens when the compressor impeller pressurizes the refrigerant to a sufficient pressure, and the low speed is defined as operating the electric motor so that the compressor impeller does not pressurize the refrigerant enough to open the check valve.
18. The method according to claim 11, wherein: The countermeasure is initiated at least thirty seconds prior to an expected start-up of the electric compressor.
19. The method according to claim 11, wherein: The countermeasures are cycled on and off.
20. The method according to claim 11, wherein: If a threshold temperature is reached in the electric compressor, the countermeasure is disabled.