A method and apparatus for detecting demagnetization of a permanent magnet motor

Abstract

This invention discloses a method and apparatus for detecting demagnetization of a permanent magnet motor. The method includes: acquiring the real-time back EMF coefficient during the operation of the permanent magnet motor; comparing the real-time back EMF coefficient with an initial back EMF coefficient; determining that the permanent magnet motor exhibits a demagnetization trend when the real-time back EMF coefficient is less than the initial back EMF coefficient; and adjusting the control parameters of the frequency converter until the demagnetization trend disappears. This solution solves the problem of the inability to detect demagnetization in a timely manner, achieving the technical effect of timely and efficient detection of permanent magnet motor demagnetization and providing demagnetization protection.

Description

Technical Field

[0001] This invention relates to the field of generator set testing technology, and more specifically, to a method and apparatus for detecting the demagnetization of a permanent magnet motor. Background Technology

[0002] With the continuous development of frequency converter technology, permanent magnet synchronous motors are increasingly being used in compressors. However, after years of use or in certain extreme environments, permanent magnet motors may experience demagnetization of the permanent magnets. The main reasons for motor demagnetization include excessive current and excessively high temperature. Demagnetization will lead to a significant reduction in the motor's output torque, and in severe cases, the motor may even become unusable.

[0003] However, current control systems generally only perform demagnetization checks, lacking protective measures against demagnetization. Furthermore, most demagnetization checks rely on offline measurements, which not only fail to provide demagnetization protection but also fail to detect demagnetization in a timely manner.

[0004] There is currently no effective solution to the above problems. Summary of the Invention

[0005] This invention provides a method and apparatus for detecting demagnetization of a permanent magnet motor, in order to solve the problem that the existing technology cannot detect and protect against demagnetization of the unit in real time.

[0006] To address the aforementioned technical problems, this invention provides a demagnetization detection method for a permanent magnet motor. The method includes: acquiring a real-time back EMF coefficient during permanent magnet motor operation; comparing the real-time back EMF coefficient with an initial back EMF coefficient; determining that the permanent magnet motor exhibits a demagnetization trend when the real-time back EMF coefficient is less than the initial back EMF coefficient; and adjusting the control parameters of the frequency converter until the demagnetization trend disappears when the permanent magnet motor exhibits a demagnetization trend.

[0007] Further, adjusting the control parameters of the frequency converter until the demagnetization trend disappears includes: increasing the switching frequency of the permanent magnet motor according to a preset ratio; determining whether there is a demagnetization trend after increasing the switching frequency; and if it is determined that there is still a demagnetization trend, continuing to increase the switching frequency until the demagnetization trend disappears.

[0008] Further, determining whether there is a demagnetization trend after increasing the switching frequency includes: obtaining the result of summing the previous predetermined harmonics of the permanent magnet motor after increasing the switching frequency as the real-time total harmonic current value; comparing the real-time total harmonic current value with the initial total harmonic current value; and determining that the permanent magnet motor still has a demagnetization trend if the real-time total harmonic current value is less than the initial total harmonic current value.

[0009] Furthermore, before obtaining the real-time back EMF coefficient during the operation of the permanent magnet motor, the process includes: determining whether the permanent magnet motor is running for the first time; if it is determined that the permanent magnet motor is running for the first time, controlling the permanent magnet motor to operate in a mode where the current component on the d-axis is 0; and obtaining the back EMF coefficient and total harmonic current value of the permanent magnet motor in the current mode as the initial back EMF coefficient and initial total harmonic current value.

[0010] Furthermore, obtaining the real-time back EMF coefficient during permanent magnet motor operation includes: determining the real-time back EMF coefficient according to the following formula:

[0011]

[0012] Where, λ af i represents the real-time back electromotive force coefficient. q T represents the voltage component on the q-axis. e i represents the torque of a permanent magnet motor. s denoted as stator current amplitude, and P as the number of pole pairs of the permanent magnet motor.

[0013] Furthermore, the above method also includes: detecting the real-time ambient temperature of the permanent magnet motor; and increasing the opening degree of the electronic expansion of the cooling winding in the permanent magnet motor when the real-time ambient temperature exceeds a preset temperature threshold.

[0014] Furthermore, obtaining the real-time back EMF coefficient during the operation of the permanent magnet motor includes: controlling the permanent magnet motor to restart; and after restarting, calling the motor demagnetization detection program to obtain the real-time back EMF coefficient during the operation of the permanent magnet motor.

[0015] The present invention also provides a demagnetization detection device for a permanent magnet motor, the device comprising:

[0016] The acquisition module is used to acquire the real-time back EMF coefficient during the operation of the permanent magnet motor;

[0017] The comparison module is used to compare the real-time back EMF coefficient with the initial back EMF coefficient;

[0018] The determination module is used to determine that the permanent magnet motor has a demagnetization trend when the real-time back EMF coefficient is less than the initial back EMF coefficient;

[0019] The adjustment module is used to adjust the control parameters of the frequency converter until the demagnetization trend disappears when it is determined that the permanent magnet motor is showing a demagnetization trend.

[0020] The present invention also provides a variable frequency compressor device, including the demagnetization detection device for the permanent magnet motor described above.

[0021] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described above.

[0022] The present invention also provides an electronic device, comprising: one or more processors; and a storage device for storing one or more programs, which, when executed by the one or more processors, cause the one or more processors to perform the method as described above.

[0023] By applying the technical solution of this invention, the real-time back EMF coefficient of the permanent magnet motor in the unit is obtained, and compared with the initial back EMF coefficient to determine whether a demagnetizing trend exists. If a demagnetizing trend exists, the control parameters of the frequency converter are adjusted until the demagnetizing trend disappears. This solution solves the problem of the inability to detect demagnetizing in a timely manner, achieving the technical effect of timely and efficient detection of permanent magnet motor demagnetization and providing demagnetization protection. Attached Figure Description

[0024] Figure 1 This is a flowchart of a demagnetization detection method for a permanent magnet motor according to an embodiment of the present invention;

[0025] Figure 2 This is a flowchart of the operation of an air conditioning system according to an embodiment of the present invention;

[0026] Figure 3 This is a flowchart illustrating a demagnetization scheme according to an embodiment of the present invention;

[0027] Figure 4 This is a structural block diagram of a demagnetization detection device for a permanent magnet motor according to an embodiment of the present invention;

[0028] Figure 5 This is a schematic diagram of the architecture of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0031] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0032] Depending on the context, the words “if” or “suppose” as used here can be interpreted as “when” or “in response to determination” or “in response to detection.” Similarly, depending on the context, the phrases “if determination” or “if detection (of the stated condition or event)” can be interpreted as “when determination” or “in response to determination” or “when detection (of the stated condition or event)” or “in response to detection (of the stated condition or event).”

[0033] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0034] The optional embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] Example 1

[0036] Figure 1 This is a flowchart of a demagnetization detection method for a permanent magnet motor according to an embodiment of the present invention, as shown below. Figure 1 As shown, the method includes the following steps:

[0037] Step S101: Obtain the real-time back EMF coefficient during the operation of the permanent magnet motor;

[0038] Step S102: Compare the real-time back EMF coefficient with the initial back EMF coefficient;

[0039] Step S103: If the real-time back EMF coefficient is determined to be less than the initial back EMF coefficient, it is determined that the permanent magnet motor has a demagnetization trend.

[0040] Step S104: If it is determined that the permanent magnet motor is showing a demagnetizing trend, adjust the control parameters of the frequency converter until the demagnetizing trend disappears.

[0041] In the example above, by acquiring the real-time back EMF coefficient of the permanent magnet motor during operation, and comparing the real-time back EMF coefficient with the initial back EMF coefficient, it is determined whether there is a demagnetization trend. If a demagnetization trend exists, the control parameters of the frequency converter are adjusted until the demagnetization trend disappears. This solution solves the problem of the inability to detect demagnetization in a timely manner, achieving the technical effect of timely and efficient detection of permanent magnet motor demagnetization and demagnetization prevention protection.

[0042] Specifically, considering that the main causes of motor demagnetization are current and temperature, if demagnetization is detected, an appropriate switching frequency can be selected for current control. This involves determining whether the maximum input current to the motor has decreased, as the switching frequency determines the magnitude of the harmonic currents input to the motor. Excessive harmonic current will result in larger harmonic currents at each order. Therefore, when adjusting the inverter's control parameters until the demagnetization trend disappears, the switching frequency of the permanent magnet motor can be increased by a preset ratio. It can then be determined whether a demagnetization trend persists after increasing the switching frequency. If a demagnetization trend still exists, the switching frequency can be increased further until it disappears. In other words, by increasing the switching frequency, harmonics are reduced, and the current components at each order are decreased, thereby eliminating or preventing the demagnetization trend.

[0043] During implementation, determining whether there is a demagnetization trend after increasing the switching frequency can be achieved by obtaining the sum of the previous predetermined harmonics of the permanent magnet motor after increasing the switching frequency as the real-time total harmonic current value; comparing the real-time total harmonic current value with the initial total harmonic current value; if the real-time total harmonic current value is less than the initial total harmonic current value, it is determined that the permanent magnet motor still has a demagnetization trend. That is, after adjusting the control coefficient, the magnitude of the back EMF of the current is detected again. If the back EMF no longer shows a demagnetization trend, the motor is operated according to this parameter; if the back EMF shows a decreasing trend, the switching frequency is further increased to reduce the harmonic current.

[0044] The initial back EMF coefficient and initial total harmonic current value mentioned above can be detected during the first startup. That is, before obtaining the real-time back EMF coefficient of the permanent magnet motor during operation, it can be determined whether the permanent magnet motor is running for the first time. If it is determined that the permanent magnet motor is running for the first time, the current of the permanent magnet motor is controlled to run in a mode where the component of the current on the d-axis is 0. The back EMF coefficient and total harmonic current value of the permanent magnet motor in the current mode are obtained as the initial back EMF coefficient and initial total harmonic current value.

[0045] When obtaining the real-time back EMF coefficient during the operation of a permanent magnet motor, the real-time back EMF coefficient can be determined according to the following formula:

[0046]

[0047] Where, λaf i represents the real-time back electromotive force coefficient. q T represents the voltage component on the q-axis. e i represents the torque of a permanent magnet motor. s denoted as stator current amplitude, and P as the number of pole pairs of the permanent magnet motor.

[0048] Regarding demagnetization, the effects are due to both current and temperature. For temperature-related issues, the real-time ambient temperature of the permanent magnet motor can be monitored. If the ambient temperature exceeds a preset temperature threshold, the opening of the electronic expansion valve in the cooling winding of the permanent magnet motor can be increased. For example, the motor winding temperature can be monitored simultaneously in real time. If the winding temperature becomes too high during operation, for example, exceeding 90 degrees Celsius, an electronic expansion valve controlling the motor cooling system can be added to prevent permanent demagnetization caused by excessively high motor temperatures.

[0049] To obtain the real-time back EMF coefficient of a permanent magnet motor during operation, the permanent magnet motor can be restarted. After restarting, a motor demagnetization detection program is invoked to obtain the real-time back EMF coefficient. Specifically, after running for a period of time, upon restarting, the motor demagnetization detection program is invoked to re-detect the motor's back EMF coefficient and total harmonic current data, comparing them with those from the initial startup. If the back EMF coefficient is consistent, it indicates that the motor has not demagnetized. If the back EMF coefficient begins to decrease, the inverter control parameters are adjusted to increase the switching frequency, reduce harmonics, and decrease the current components of each order.

[0050] The demagnetization detection method for permanent magnet motors described above can be applied to air conditioners, as well as to the control methods for permanent magnet motors in refrigerators and washing machines.

[0051] Example 2

[0052] The above method will be described below with reference to a specific embodiment. However, it is worth noting that this specific embodiment is only for better illustration of this application and does not constitute an improper limitation of this application.

[0053] This example proposes a method for detecting the back EMF coefficient of a permanent magnet motor after a change in operating mode. The detected back EMF coefficient is then analyzed, and control modulation is implemented when partial demagnetization occurs to prevent further demagnetization. Specifically, the control algorithm of the permanent magnet motor is adjusted online via a frequency converter to determine the motor's demagnetization status. Simultaneously, the back EMF coefficient value of the motor is acquired online. When a demagnetization trend is detected, the control method is analyzed and improved, and appropriate control parameters are selected to prevent further demagnetization. This method allows for the detection of the motor's back EMF coefficient without stopping the motor, and further demagnetization can be prevented by adjusting the control parameters.

[0054] Based on this, this example proposes an online detection method for whether a permanent magnet motor has demagnetized. When demagnetization is detected, the method has the ability to adjust and modify the control parameters to prevent further demagnetization of the motor, thereby protecting the air conditioner compressor from demagnetization.

[0055] First, check if the permanent magnets of the motor have demagnetized: Considering that air conditioner motors generally use a maximum torque / current ratio control strategy to achieve maximum torque control, under normal control, the current of the permanent magnet motor is divided into i d i q Components, i of motor torque and current d i q The component is related, and its specific formula can be expressed as:

[0056] Mathematical model of a permanent magnet synchronous centrifuge in the dq synchronous rotating coordinate system:

[0057]

[0058]

[0059]

[0060] Among them, i d i q u d u q These are the components of the stator current and voltage on the d-axis and q-axis, respectively. d L q These are direct-axis synchronous inductors and quadrature-axis synchronous inductors, respectively, T e Let P be the torque of the motor, P be the number of pole pairs of the motor, and λ be the torque of the motor. af Let ω be the back electromotive force constant of the motor. e Let ω be the electric angular velocity of the motor. e =P×ω r (P is the number of pole pairs of the motor, ω) r (This refers to the mechanical angular velocity of the motor).

[0061] Therefore, to detect the back potential constant λ af Therefore, a dedicated control method is needed to achieve this, because the current i d The component does not affect the motor torque; therefore, we can let i... d =0, at i d =0:

[0062]

[0063] Among them, i sLet i be the stator current amplitude. From this formula, it can be seen that under the same air conditioning operating conditions, such as (nominal operating conditions at a frequency of 300Hz), the motor's back EMF coefficient is inversely proportional to the current. If the air conditioner is in i... d If the current increases by 20% under the same operating conditions in 0 mode, it indicates that the rotor back EMF coefficient has decreased by 20%. During online operation, by measuring the frequency and current and comparing the current data under stable air conditioning conditions, it can be determined whether the back EMF coefficient has decreased and by how much.

[0064] Meanwhile, the main causes of motor demagnetization are current and temperature. If demagnetization is detected, the program selects an appropriate switching frequency to determine whether the maximum value of the current input to the motor has decreased. This is because the switching frequency determines the magnitude of the harmonic current input to the motor. When the harmonic current is too large, each harmonic current will be relatively large. Therefore, by detecting the input current and analyzing its harmonic currents, the program extracts and sums the first 40 harmonic currents. After doubling the switching frequency, the program sums the harmonic currents again and compares whether the sum of the harmonic currents has decreased. Finally, the program checks again to see if the motor still shows signs of demagnetization.

[0065] Furthermore, if the ambient temperature is detected to be too high, the opening of the electronic expansion of the motor cooling winding is increased to control the flow rate of the motor cooling refrigerant, thereby achieving motor cooling.

[0066] Specifically, this may include the following steps:

[0067] Step 1: When the air conditioner inverter system is started for the first time, the program runs the motor demagnetization detection program, using the motor current i d =0 control method to save the initial back EMF coefficient and initial total harmonic current value of the motor. After saving, exit the demagnetization detection program and run according to the normal control program. At the same time, the motor winding temperature is monitored in real time. When the winding temperature is too high during operation, for example, exceeding 90 degrees, the motor cooler control electronic expansion valve is added to prevent the motor from being permanently demagnetized due to excessive motor temperature.

[0068] Step 2: After running for a period of time, when restarting, call the motor demagnetization detection program to check the motor back EMF coefficient and total harmonic current data again and compare them with those at the first startup. If the back EMF coefficient is consistent, it means that the motor has not demagnetized. If the motor back EMF coefficient starts to become smaller, adjust the inverter control parameters, increase the switching frequency, reduce harmonics, reduce each current component, run the control program again, and compare it with the harmonic current value saved at the initial startup to determine whether the total current value has decreased.

[0069] Step 3: After adjusting the control coefficient, check the magnitude of the back EMF of the current again. If the back EMF no longer shows a demagnetizing trend, then operate according to this parameter. If the back EMF shows a decreasing trend again, then continue to increase the switching frequency to reduce the harmonic current.

[0070] Specifically, for air conditioners, it can be done according to the following: Figure 2 The process shown includes:

[0071] S1: The generator unit is powered on via AC;

[0072] S2: Determine if this is the first run. If it is the first run, execute S3; otherwise, execute S5.

[0073] S3: Operates in back EMF coefficient detection mode;

[0074] S4: Determine whether the back EMF detection is complete. If it is complete, proceed to S5; otherwise, proceed to S3.

[0075] S5: Operate in normal control mode.

[0076] Regarding the demagnetization adjustment scheme, it can be followed as follows: Figure 3 The process shown includes:

[0077] S1: Run i d =0 control mode, start back EMF coefficient detection;

[0078] S2: Determine whether the current is consistent under the same operating conditions. If it is consistent, proceed to S7; if it is inconsistent, proceed to S3.

[0079] S3: Calculate the back EMF coefficient;

[0080] S4: Adjust the control switch frequency;

[0081] S5: Calculate the harmonic current and determine if the harmonic current is smaller than the original current. If so, execute S4; if not, execute S6.

[0082] S6: Adjustment confirmed;

[0083] S7: Confirm that the motor has not demagnetized.

[0084] The above-mentioned method for online detection of whether a permanent magnet motor has demagnetized can be applied to air conditioners, as well as to the control methods for permanent magnet motors in refrigerators and washing machines.

[0085] Example 3

[0086] Corresponding to Figure 1 The demagnetization detection method for permanent magnet motors introduced in this embodiment provides a demagnetization detection device for permanent magnet motors, such as... Figure 4 The diagram shown depicts the structural block diagram of a demagnetization detection device for a permanent magnet motor. The device includes:

[0087] The acquisition module 401 is used to acquire the real-time back EMF coefficient during the operation of the permanent magnet motor;

[0088] The comparison module 402 is used to compare the real-time back EMF coefficient with the initial back EMF coefficient;

[0089] The determination module 403 is used to determine that the permanent magnet motor has a demagnetization trend when the real-time back EMF coefficient is less than the initial back EMF coefficient;

[0090] The adjustment module 404 is used to adjust the control parameters of the frequency converter until the demagnetization trend disappears when it is determined that the permanent magnet motor has a demagnetization trend.

[0091] In one embodiment, the adjustment module 404 can be specifically used to increase the switching frequency of the permanent magnet motor according to a preset ratio; determine whether there is a demagnetization trend after increasing the switching frequency; and if it is determined that there is still a demagnetization trend, continue to increase the switching frequency until the demagnetization trend disappears.

[0092] In one embodiment, the determining module 403 can be specifically used to obtain the result of summing the previous predetermined harmonics of the permanent magnet motor after increasing the switching frequency as the real-time total harmonic current value; compare the real-time total harmonic current value with the initial total harmonic current value; and determine that the permanent magnet motor still has a demagnetizing trend if the real-time total harmonic current value is less than the initial total harmonic current value.

[0093] In one embodiment, the demagnetization detection device for the permanent magnet motor is further used to determine whether the permanent magnet motor is running for the first time before acquiring the real-time back EMF coefficient during operation; if it is determined that the permanent magnet motor is running for the first time, control the permanent magnet motor to operate in a mode where the current component on the d-axis is 0; acquire the back EMF coefficient and total harmonic current value of the permanent magnet motor in the current mode as the initial back EMF coefficient and initial total harmonic current value.

[0094] In one embodiment, the acquisition module 401 can specifically determine the real-time back EMF coefficient according to the following formula:

[0095]

[0096] Where, λ af i represents the real-time back electromotive force coefficient. q T represents the voltage component on the q-axis. e i represents the torque of a permanent magnet motor. s denoted as stator current amplitude, and P as the number of pole pairs of the permanent magnet motor.

[0097] In one embodiment, the demagnetization detection device of the permanent magnet motor is also used to detect the real-time ambient temperature of the permanent magnet motor; when the real-time ambient temperature exceeds a preset temperature threshold, the opening degree of the electronic expansion of the cooling winding in the permanent magnet motor is increased.

[0098] In one embodiment, the acquisition module 401 can specifically control the permanent magnet motor to restart; after restarting, it calls the motor demagnetization detection program to obtain the real-time back EMF coefficient of the permanent magnet motor during operation.

[0099] Example 4

[0100] like Figure 5 As shown, this embodiment provides an electronic device 10, which may include one or more (only one is shown in the figure) processors 02 (processors 02 may include, but are not limited to, microprocessors MCUs or programmable logic devices FPGAs, etc.), a memory 04 for storing data, and a transmission module 06 for communication functions. Those skilled in the art will understand that... Figure 5 The structure shown is for illustrative purposes only and does not limit the structure of the electronic device described above. For example, electronic device 10 may also include... Figure 5 The more or fewer components shown, or having the same Figure 5 The different configurations shown.

[0101] The memory 04 can be used to store software programs and modules for application software, such as the program instructions / modules corresponding to the demagnetization detection method for a permanent magnet motor in this embodiment. The processor 02 executes various functional applications and data processing by running the software programs and modules stored in the memory 04, thereby implementing the aforementioned application program for the demagnetization detection method for a permanent magnet motor. The memory 04 may include high-speed random access memory and may also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 04 may further include memory remotely located relative to the processor 02, and these remote memories can be connected to the electronic device 10 via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0102] The transmission module 06 is used to receive or send data via a network. Specific examples of the network described above may include a wireless network provided by the communication provider of the electronic device 10. In one example, the transmission module 06 includes a Network Interface Controller (NIC), which can connect to other network devices via a base station to communicate with the Internet. In another example, the transmission module 06 may be a Radio Frequency (RF) module, used for wireless communication with the Internet.

[0103] Example 5

[0104] This invention provides software for executing the technical solutions described in the above embodiments and preferred embodiments.

[0105] This invention provides a non-volatile computer storage medium storing computer-executable instructions that can execute the demagnetization detection method for a permanent magnet motor in any of the above method embodiments.

[0106] The aforementioned storage medium stores the aforementioned software, and the storage medium includes, but is not limited to, optical discs, floppy disks, hard disks, and rewritable memory.

[0107] The above-described product can execute the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0108] The electronic devices of this invention exist in various forms, including but not limited to:

[0109] (1) Mobile communication devices: These devices are characterized by their mobile communication capabilities and primarily aim to provide voice and data communication. These terminals include: smartphones (e.g., iPhones), multimedia phones, feature phones, and low-end phones, etc.

[0110] (2) Ultra-mobile personal computer devices: These devices fall under the category of personal computers, possessing computing and processing capabilities, and generally also have mobile internet access features. These terminals include PDAs, MIDs, and UMPCs, such as the iPad.

[0111] (3) Portable entertainment devices: These devices can display and play multimedia content. This category includes audio and video players (such as iPods), handheld game consoles, e-book readers, as well as smart toys and portable car navigation devices.

[0112] (4) Server, a device that provides computing services. The components of a server include processor, hard disk, memory, device bus, etc. Servers are similar to general computer architectures, but because they need to provide highly reliable services, they have higher requirements in terms of processing power, stability, reliability, security, scalability and manageability.

[0113] (5) Other electronic devices with data interaction functions, such as televisions and in-vehicle screens.

[0114] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0115] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of detecting demagnetization of a permanent magnet motor, characterized by, The method comprises: acquiring a real-time back EMF coefficient of the permanent magnet motor during operation; comparing the real-time back EMF coefficient with an initial back EMF coefficient; determining that the permanent magnet motor has a demagnetization trend if the real-time back EMF coefficient is less than the initial back EMF coefficient; adjusting control parameters of a frequency converter until the demagnetization trend disappears if it is determined that the permanent magnet motor has a demagnetization trend, which comprises: increasing a switching frequency of the permanent magnet motor according to a preset proportion; determining whether there is a demagnetization trend after the switching frequency is increased; and continuously increasing the switching frequency until the demagnetization trend disappears if it is determined that there is still a demagnetization trend.

2. The method of claim 1, wherein, Determining whether there is a demagnetization trend after the switching frequency is increased comprises: acquiring a result of a pre-determined sum of harmonics of the permanent magnet motor after the switching frequency is increased as a real-time total harmonic current value; comparing the real-time total harmonic current value with an initial total harmonic current value; determining that the permanent magnet motor still has a demagnetization trend if the real-time total harmonic current value is less than the initial total harmonic current value.

3. The method of claim 2, wherein, Before acquiring the real-time back EMF coefficient of the permanent magnet motor during operation, the method further comprises: determining whether the permanent magnet motor is operated for the first time; controlling the permanent magnet motor to operate in a mode in which a component of a current of the permanent magnet motor on a d-axis is 0 if it is determined that the permanent magnet motor is operated for the first time; acquiring a back EMF coefficient and a total harmonic current value of the permanent magnet motor in the current mode as an initial back EMF coefficient and an initial total harmonic current value.

4. The method of claim 1, wherein, Acquiring the real-time back EMF coefficient of the permanent magnet motor during operation comprises: determining the real-time back EMF coefficient according to the following formula: where λ af represents the real-time back EMF coefficient, i q represents the component of the voltage on the q-axis, T e represents the torque of the permanent magnet motor, i s is the stator current amplitude, and P is the pole pair number of the permanent magnet motor.

5. The method of claim 1, wherein, The method further comprises: detecting a real-time ambient temperature of the permanent magnet motor; increasing an opening degree of electronic expansion of a cooling machine winding of the permanent magnet motor if the real-time ambient temperature exceeds a preset temperature threshold.

6. The method according to any one of claims 1 to 5, characterized in that, Acquiring the real-time back EMF coefficient of the permanent magnet motor during operation comprises: controlling the permanent magnet motor to restart operation; calling a motor demagnetization detection program to acquire the real-time back EMF coefficient of the permanent magnet motor during operation after the permanent magnet motor restarts operation.

7. A demagnetization detection device of a permanent magnet motor for implementing the demagnetization detection method of the permanent magnet motor according to any one of claims 1 to 6, characterized by The device comprises: an acquisition module configured to acquire a real-time back EMF coefficient of the permanent magnet motor during operation; a comparison module configured to compare the real-time back EMF coefficient with an initial back EMF coefficient; a determination module configured to determine that the permanent magnet motor has a demagnetization trend if the real-time back EMF coefficient is less than the initial back EMF coefficient; an adjustment module configured to adjust control parameters of a frequency converter until the demagnetization trend disappears if it is determined that the permanent magnet motor has a demagnetization trend.

8. A variable frequency compressor apparatus, characterized by, The device comprises the permanent magnet motor of claim 7.

9. A computer readable storage medium having stored thereon a computer program, characterized in that, The program causes a processor to implement the method of any one of claims 1 to 6 when the program is executed by the processor.

10. An electronic device, comprising: The device comprises: one or more processors; a storage device configured to store one or more programs, which cause the one or more processors to implement the method of any one of claims 1 to 6 when the one or more programs are executed by the one or more processors.

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