A method and system for diagnosing combined faults of eccentricity and demagnetization of a flywheel energy storage system

Abstract

The present invention discloses a method and system for diagnosing a combined fault of eccentricity and demagnetization in a flywheel energy storage system. The method is applied to the field of energy storage technology. A detection device is installed in a permanent magnet synchronous motor, and a test platform is constructed. The magnetic field signals of at least four points symmetrically located on the center of the stator cross section measured by the detection device are used to reflect the change in the air gap magnetic flux density of the permanent magnet synchronous motor. The magnetic field signals are subjected to time-frequency analysis and root mean square value calculation respectively. The components of the signal frequency and the size of the root mean square value are used as the basis for judging the working condition, and the fault is judged as normal operation, static eccentricity fault, dynamic eccentricity fault, demagnetization fault, static eccentricity and demagnetization combined fault, or dynamic eccentricity and demagnetization combined fault. The present invention discloses a method and system for diagnosing a combined fault of eccentricity and demagnetization in a flywheel energy storage system, which provides an effective reference for the timely repair and maintenance of the motor of the flywheel energy storage system, thereby improving the operational reliability and safety of the energy storage system.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and more particularly to a method and system for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system. Background Art

[0002] As a highly efficient and fast-responding energy storage method, flywheel energy storage systems hold enormous potential for energy storage and grid frequency regulation. The permanent magnet synchronous motor, the core drive element of a flywheel energy storage system, performs the crucial task of converting mechanical energy into electrical energy. However, in actual operation, the flywheel's rotor system and the permanent magnet synchronous motor may experience various faults, leading to system performance degradation or even downtime. Eccentricity and demagnetization are two common fault types, which can cause system performance degradation, power loss, and even equipment damage, posing a threat to the safety and stability of the energy storage system.

[0003] Eccentricity faults occur when a flywheel rotor system deviates from its central axis of rotation, while demagnetization refers to the weakening or disappearance of the magnetic field strength of the motor's permanent magnets. Currently, researchers focus on single fault diagnosis, but in reality, flywheel energy storage systems often experience multiple faults simultaneously. Diagnosing complex faults is more challenging than single faults because different types of faults may produce similar or overlapping characteristics, further complicating the diagnostic process. Accurately and promptly diagnosing complex faults has become a current research focus.

[0004] To address this problem, this patent proposes a magnetic field-based flywheel energy storage system eccentricity and demagnetization composite fault diagnosis method, which provides an effective reference basis for the timely repair and maintenance of the flywheel energy storage system motor, and improves the operating reliability and safety of the energy storage system. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, so as to solve the problems in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In one aspect, the present invention discloses a method for diagnosing a combined eccentricity and demagnetization fault of a flywheel energy storage system, comprising:

[0008] Install detection devices into permanent magnet synchronous motors and build a test platform;

[0009] According to the magnetic field signals of at least four points symmetrically located at the center of the stator cross section measured by the detection device, the change of the air gap magnetic flux density of the permanent magnet synchronous motor is reflected;

[0010] The magnetic field signal is subjected to time-frequency analysis and root mean square value calculation respectively. The signal frequency components and the size of the root mean square value are used as the basis for judging the working condition, and it is judged as normal operation, static eccentricity fault, dynamic eccentricity fault, demagnetization fault, static eccentricity and demagnetization combined fault, and dynamic eccentricity and demagnetization combined fault.

[0011] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, the working condition judgment is based on the following formula:

[0012]

[0013] Among them, F r,μ is the rotor μ subharmonic magnetomotive force amplitude, μ is the rotor harmonic order, φ μ is the initial phase angle of the rotor μ subharmonic magnetomotive force; F s,υ is the stator harmonic magnetomotive force amplitude, υ is the stator harmonic order, φ υ is the initial phase angle of the stator subharmonic magnetomotive force, θ is the mechanical position angle, ω=2πf, f=50Hz is the electrical frequency, p is the number of motor pole pairs; g0 is the air gap length which is a constant; δ s is the static eccentricity of the rotor, δ d is the rotor dynamic eccentricity; Λ0 is the magnetic permeability constant per unit area of ​​the air gap.

[0014] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, the specific steps for determining the working condition judgment basis are as follows:

[0015] According to the air gap magnetomotive force of the permanent magnet synchronous motor under normal conditions and after the demagnetization fault occurs, the air gap magnetomotive force of the permanent magnet synchronous motor under various working conditions is calculated;

[0016] The air gap permeability under various working conditions is calculated using the air gap length distribution after eccentricity and the air gap permeability before and after eccentricity;

[0017] The air gap magnetic flux density is obtained by multiplying the air gap magnetic potential and the air gap magnetic permeance, and the air gap magnetic flux density is calculated;

[0018] Different working conditions are determined based on the frequency components of the air gap magnetic flux and the magnetic flux amplitude at each location.

[0019] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, different working conditions are judged according to the frequency components of the air gap magnetic flux and the magnetic flux amplitudes at various locations as follows:

[0020] Normal working condition: The magnetic flux density frequency component is only the fundamental frequency, and the magnetic flux density amplitude is consistent at all locations;

[0021] Static eccentricity fault condition: The magnetic flux density frequency component is only the fundamental frequency, the magnetic flux density amplitude is different at different locations, and the eccentricity direction is the side with larger magnetic flux density;

[0022] Dynamic eccentricity fault condition: The magnetic flux density frequency component has the fundamental frequency plus and minus rotation frequency components, and the magnetic flux density amplitude at each location is consistent and basically the same as under normal conditions;

[0023] Demagnetization fault condition: The magnetic flux density frequency component has fractional frequency components, and the magnetic flux density amplitude is consistent at all locations and is smaller than that under normal conditions;

[0024] Static eccentricity and demagnetization combined fault condition: The magnetic flux density frequency component has fractional frequency components, the magnetic flux density amplitude is different at different locations, and the eccentricity direction is the side with larger magnetic flux density;

[0025] Dynamic eccentricity and demagnetization combined fault condition: The magnetic flux density frequency component shows fractional frequency components, and the magnetic flux density amplitude is consistent at all locations and is smaller than that under normal conditions;

[0026] The specific frequency amplitude is calculated by Fourier transform, and the magnetic density amplitude at a certain point is represented by the root mean square value of the point over a period of time.

[0027] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, under normal circumstances, the expression for the air gap magnetomotive force of the permanent magnet synchronous motor is:

[0028]

[0029] Where: F r,μ is the rotor μ subharmonic magnetomotive force amplitude, μ is the rotor harmonic order, φ μ is the initial phase angle of the rotor μ subharmonic magnetomotive force; F s,υ is the stator harmonic magnetomotive force amplitude, υ is the stator harmonic order, φ υ is the initial phase angle of the stator subharmonic magnetomotive force, θ is the mechanical position angle, ω = 2πf, f = 50 Hz is the electrical frequency;

[0030] After the demagnetization fault occurs, the magnetic potential expression is:

[0031]

[0032] Where: F dn is the reverse magnetomotive force amplitude, and n is a natural number.

[0033] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, the air gap magnetomotive force of the permanent magnet synchronous motor under various working conditions is calculated as:

[0034]

[0035] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, the distribution of the air gap length after eccentricity is expressed as follows:

[0036]

[0037] Where: δ s is the static eccentricity of the rotor, δ d is the rotor dynamic eccentricity; g0 is the air gap length under normal conditions, which is a constant value; θ is the mechanical position angle, ω r is the rotor rotation angular velocity, φ0 is the initial position of the minimum air gap length.

[0038] The expression of air gap permeability before and after eccentricity is:

[0039]

[0040] Where Λ0 is the constant part of the air gap permeance.

[0041] Preferably, in the above-mentioned method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system, the air gap magnetic permeability under each working condition is:

[0042]

[0043] On the other hand, the present invention discloses a flywheel energy storage system eccentricity and demagnetization composite fault diagnosis system, which applies the above method and includes:

[0044] A flywheel (1) and a permanent magnet synchronous motor (2), a detection device (3) is arranged in an air gap at one end of the permanent magnet synchronous motor (2), the detection device is connected to a data acquisition device (4), and the data acquisition device (4) is connected to a computer (5);

[0045] The axial position of the detection device (3) is consistent with that of the permanent magnet synchronous motor (2), and the detection device (3) is evenly distributed along the circumference of the air gap at one end of the motor; the flywheel energy storage system is adjusted to a state to be tested, and the measurement channel is balanced and cleared.

[0046] Preferably, in the above-mentioned flywheel energy storage system eccentricity and demagnetization composite fault diagnosis system, the detection device is a Hall sensor, there are at least four Hall sensors, and the feet of the Hall sensors are installed in the stator slots of the permanent magnet synchronous motor.

[0047] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method and system for diagnosing a combined fault of eccentricity and demagnetization in a flywheel energy storage system, which provides an effective reference basis for the timely repair and maintenance of the flywheel energy storage system motor, thereby improving the operational reliability and safety of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0049] Figure 1 A flowchart of the fault diagnosis steps provided by an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of the connection of a fault diagnosis system according to an embodiment of the present invention, in which: 1. flywheel; 2. permanent magnet synchronous motor; 3. Hall sensor; 4. data acquisition instrument; 5. computer;

[0051] Figure 3 A schematic diagram of the distribution of Hall sensors provided in an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of eccentricity and demagnetization faults provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0054] The embodiment of the present invention discloses a method for diagnosing a combined fault of eccentricity and demagnetization of a flywheel energy storage system. Figure 1 Shown, including:

[0055] Install detection devices into permanent magnet synchronous motors and build a test platform;

[0056] According to the magnetic field signals of at least four points symmetrically located at the center of the stator cross section measured by the detection device, the change of the air gap magnetic flux density of the permanent magnet synchronous motor is reflected;

[0057] The magnetic field signal is subjected to time-frequency analysis and root mean square value calculation respectively. The signal frequency components and the size of the root mean square value are used as the basis for judging the working condition, and it is judged as normal operation, static eccentricity fault, dynamic eccentricity fault, demagnetization fault, static eccentricity and demagnetization combined fault, and dynamic eccentricity and demagnetization combined fault.

[0058] Figure 2 A schematic diagram of a fault diagnosis system connection provided by an embodiment of the present invention is shown in FIG. Figure 2As shown, the flywheel energy storage system mainly includes a flywheel (1) and a permanent magnet synchronous motor (2), eight Hall sensors (3) are arranged in the air gap at one end of the permanent magnet synchronous motor (2), the Hall sensors are connected to a data acquisition device (4), and the data acquisition device (4) is connected to a computer (5);

[0059] Further, such as Figure 3 As shown, the axial position of the Hall sensor (3) is consistent with that of the permanent magnet synchronous motor (2), and the eight Hall sensors (3) are evenly distributed along the circumference of the air gap at one end of the motor.

[0060] At the beginning of the experiment, the flywheel system is first adjusted to the state to be tested, and then the measurement channel is balanced and cleared. Preferably, balancing and clearing are performed before each measurement.

[0061] Each set of data includes 8 Hall sensor signals, and time-frequency analysis and RMS value calculation are performed on them respectively. The analysis results can be used as a basis for judging the working conditions, as follows:

[0062] 1. The signal frequency only has the fundamental frequency component, and the RMS values ​​of the signals at the eight locations are equal, indicating that the flywheel energy storage system is working normally.

[0063] 2. The signal frequency only has the fundamental frequency component, and the RMS values ​​of the eight signals are different. The flywheel energy storage system has a static eccentricity fault, and the eccentricity direction is the side with the larger RMS value of the signal. The greater the difference in the RMS values, the greater the degree of the static eccentricity fault.

[0064] 3. The signal frequency shows fundamental frequency plus and minus rotation frequency components. The RMS values ​​of the eight signals are equal and similar to normal conditions. A dynamic eccentricity fault occurs in the flywheel energy storage system. The larger the amplitude of the fundamental frequency plus and minus rotation frequency components, the greater the degree of the dynamic eccentricity fault.

[0065] 4. Fractional frequency components appear in the signal frequency, and the RMS values ​​of the signals at 8 locations are equal and smaller than normal, indicating a demagnetization fault in the flywheel energy storage system. The larger the amplitude of the fractional frequency component, the greater the degree of the demagnetization fault.

[0066] 5. The signal frequency exhibits fractional frequency components, and the RMS values ​​of the eight signals are not equal. This indicates a combined static eccentricity and demagnetization fault in the flywheel energy storage system, with the eccentricity direction being the side with the larger RMS value. The methods for determining the degree of static eccentricity and demagnetization faults are shown in Cases 2 and 4, respectively.

[0067] 6. Fractional frequency components appear in the signal frequency, and the RMS values ​​of the signals at 8 locations are equal and smaller than normal. This indicates a combined fault of dynamic eccentricity and demagnetization in the flywheel energy storage system. The methods for determining the degree of dynamic eccentricity and demagnetization faults are as shown in Cases 3 and 4, respectively.

[0068] The theoretical analysis is as follows:

[0069] The eccentricity and demagnetization of the flywheel energy storage system are the eccentricity and demagnetization of the permanent magnet synchronous motor. The fault diagram is as follows Figure 4 shown.

[0070] The permanent magnet demagnetization failure mainly affects the air gap magnetomotive force of the motor and has no effect on the air gap magnetic permeability.

[0071] Under normal circumstances, the expression of the motor air gap magnetomotive force is:

[0072]

[0073] Where: F r,μ is the rotor μ subharmonic magnetomotive force amplitude, μ is the rotor harmonic order, φ μ is the initial phase angle of the rotor μ subharmonic magnetomotive force; F s,υ is the stator harmonic magnetomotive force amplitude, υ is the stator harmonic order, φ υ is the initial phase angle of the stator subharmonic magnetomotive force, θ is the mechanical position angle, ω = 2πf (f = 50 Hz, electrical frequency), and p is the number of motor pole pairs.

[0074] After the demagnetization fault occurs, the magnetic potential generated by the demagnetized permanent magnet decreases, which is equivalent to adding a reverse magnetic potential at that position, such as Figure 4 As shown, the magnetic potential expression is:

[0075]

[0076] The eccentricity of the flywheel rotor system has no effect on the air gap magnetomotive force of the motor, but mainly affects the air gap magnetic permeability.

[0077] Under normal circumstances, the air gap length is a constant value g0. After eccentricity, the air gap length distribution changes, and its expression is:

[0078]

[0079] Where: δ s is the static eccentricity of the rotor, δ d is the rotor dynamic eccentricity.

[0080] Therefore, the expression of air gap permeability before and after eccentricity is:

[0081]

[0082] In summary, the air gap magnetic potential under each working condition is:

[0083]

[0084] The air gap permeability under each working condition is:

[0085]

[0086] Therefore, the air gap magnetic flux density under each working condition is:

[0087]

[0088] As shown in the above formula, under normal circumstances, the magnetic density has only fundamental frequency components, static eccentricity fault does not change the magnetic density frequency components, dynamic eccentricity fault increases the fundamental frequency plus or minus conversion frequency components, demagnetization fault increases the magnetic density fractional multiple frequency components of the fundamental frequency divided by the pole logarithm, demagnetization and static eccentricity combined fault magnetic density frequency components are consistent with demagnetization fault, demagnetization and dynamic eccentricity combined fault magnetic density frequency components include fractional multiple frequency components and fundamental frequency plus or minus conversion frequency components, but it is worth noting that the fundamental frequency plus or minus conversion frequency components are included in the fractional multiple frequency components.

[0089] In addition, static eccentricity fault will change the distribution of magnetic flux density. The magnetic flux density amplitude will decrease where the air gap length increases, and the magnetic flux density amplitude will increase where the air gap length decreases. Dynamic eccentricity fault will change the amplitude of the fundamental frequency plus or minus rotation frequency components. The greater the degree of dynamic eccentricity, the greater the amplitude of the fundamental frequency plus or minus rotation frequency components. Demagnetization fault will change the amplitude of the fundamental frequency of magnetic flux density. The greater the degree of demagnetization, the smaller the amplitude of the fundamental frequency of magnetic flux density.

[0090] In summary, the magnetic flux density under different working conditions is as follows:

[0091] Normal working condition: The magnetic flux density frequency component is only the fundamental frequency, and the magnetic flux density amplitude is consistent at all locations;

[0092] Static eccentricity fault condition: The magnetic flux density frequency component is only the fundamental frequency, the magnetic flux density amplitude is different at different locations, and the eccentricity direction is the side with larger magnetic flux density;

[0093] Dynamic eccentricity fault condition: The magnetic flux density frequency component has the fundamental frequency plus and minus rotation frequency components, and the magnetic flux density amplitude at each location is consistent and basically the same as under normal conditions;

[0094] Demagnetization fault condition: The magnetic flux density frequency component has fractional frequency components, and the magnetic flux density amplitude is consistent at all locations and is smaller than that under normal conditions;

[0095] Static eccentricity and demagnetization combined fault condition: The magnetic flux density frequency component has fractional frequency components, the magnetic flux density amplitude is different at different locations, and the eccentricity direction is the side with larger magnetic flux density;

[0096] Dynamic eccentricity and demagnetization combined fault condition: The magnetic flux density frequency component shows fractional frequency components, and the magnetic flux density amplitude is consistent at all locations and is smaller than that under normal conditions;

[0097] The specific frequency amplitude is calculated by Fourier transform, and the magnetic density amplitude at a certain point is represented by the root mean square value of the point over a period of time.

[0098] Hall sensors measure magnetic field information, reflecting changes in the motor's air gap flux density, and can be used for fault diagnosis. The more pronounced the fault signature, the greater the severity of the fault. The motor's air gap flux density is used for time-frequency analysis and RMS value calculation. The signal analysis results are used to determine the fault type and severity.

[0099] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0100] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for diagnosing a combined fault of eccentricity and demagnetization in a flywheel energy storage system, characterized in that: include: Install detection devices into permanent magnet synchronous motors and build a test platform; According to the magnetic field signals of at least four points symmetrically located at the center of the stator cross section measured by the detection device, the change of the air gap magnetic flux density of the permanent magnet synchronous motor is reflected; Performing time-frequency analysis and root mean square value calculation on the magnetic field signal, respectively; judging the working condition as normal operation, static eccentricity fault, dynamic eccentricity fault, demagnetization fault, static eccentricity and demagnetization combined fault, or dynamic eccentricity and demagnetization combined fault based on the signal frequency components and the magnitude of the root mean square value; The working condition judgment formula is as follows: Among them, F r,μ is the rotor μ subharmonic magnetomotive force amplitude, μ is the rotor harmonic order, φ μ is the initial phase angle of the rotor μ subharmonic magnetomotive force; F s,υ is the stator harmonic magnetomotive force amplitude, υ is the stator harmonic order, φ υ is the initial phase angle of the stator subharmonic magnetomotive force, θ is the mechanical position angle, ω=2πf, f=50Hz is the electrical frequency, p is the number of motor pole pairs; g0 is the air gap length which is a constant; δ s is the static eccentricity of the rotor, δ d is the rotor dynamic eccentricity; Λ0 is the air gap permeability constant per unit area; B(θ,t) is the air gap magnetic flux density; F dn is the reverse magnetomotive force amplitude, ω r is the rotor rotational angular velocity.

2. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to claim 1, characterized in that: The specific steps to determine the basis for working condition judgment are as follows: According to the air gap magnetomotive force of the permanent magnet synchronous motor under normal conditions and after the demagnetization fault occurs, the air gap magnetomotive force of the permanent magnet synchronous motor under various working conditions is calculated; The air gap permeability under various working conditions is calculated using the air gap length distribution after eccentricity and the air gap permeability before and after eccentricity; The air gap magnetic flux density is obtained by multiplying the air gap magnetic potential and the air gap magnetic permeance, and the air gap magnetic flux density is calculated; Different working conditions are determined based on the frequency components of the air gap magnetic flux and the magnetic flux amplitude at each location.

3. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to claim 2, characterized in that: The different working conditions are judged according to the frequency components of the air gap magnetic flux and the magnetic flux amplitude at each location as follows: Normal working condition: The magnetic flux density frequency component is only the fundamental frequency, and the magnetic flux density amplitude is consistent at all locations; Static eccentricity fault condition: The magnetic flux density frequency component is only the fundamental frequency, the magnetic flux density amplitude is different at different locations, and the eccentricity direction is the side with larger magnetic flux density; Dynamic eccentricity fault condition: The magnetic flux density frequency component has the fundamental frequency plus and minus rotation frequency components, and the magnetic flux density amplitude at each location is consistent and basically the same as under normal conditions; Demagnetization fault condition: The magnetic flux density frequency component has fractional frequency components, and the magnetic flux density amplitude is consistent at all locations and is smaller than that under normal conditions; Static eccentricity and demagnetization combined fault condition: The magnetic flux density frequency component has fractional frequency components, the magnetic flux density amplitude is different at different locations, and the eccentricity direction is the side with larger magnetic flux density; Dynamic eccentricity and demagnetization combined fault condition: The magnetic flux density frequency component shows fractional frequency components, and the magnetic flux density amplitude is consistent at all locations and is smaller than that under normal conditions; The specific frequency amplitude is calculated by Fourier transform, and the magnetic density amplitude at a certain point is represented by the root mean square value of the point over a period of time.

4. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to claim 2, characterized in that: Under normal circumstances, the expression of the air gap magnetomotive force of the permanent magnet synchronous motor is: Where: F r,μ is the rotor μ subharmonic magnetomotive force amplitude, μ is the rotor harmonic order, φ μ is the initial phase angle of the rotor μ subharmonic magnetomotive force; F s,υ is the stator harmonic magnetomotive force amplitude, υ is the stator harmonic order, φ υ is the initial phase angle of the stator subharmonic magnetomotive force, θ is the mechanical position angle, ω = 2πf, f = 50 Hz is the electrical frequency; After the demagnetization fault occurs, the magnetic potential expression is: Where: F dn is the reverse magnetomotive force amplitude, and n is a natural number.

5. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to claim 4, characterized in that: The air gap magnetomotive force of the permanent magnet synchronous motor under various working conditions is calculated as follows:

6. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to claim 2, characterized in that: The distribution of air gap length after eccentricity is expressed as: Where: δ s is the static eccentricity of the rotor, δ d is the rotor dynamic eccentricity; g0 is the air gap length under normal conditions, which is a constant value; θ is the mechanical position angle, ω r is the rotor rotation angular velocity, φ0 is the initial position of the minimum air gap length; The expression of air gap permeability before and after eccentricity is: Where Λ0 is the constant part of the air gap permeance.

7. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to claim 6, characterized in that: The air gap permeability under each working condition is:

8. A flywheel energy storage system eccentricity and demagnetization combined fault diagnosis system, using the flywheel energy storage system eccentricity and demagnetization combined fault diagnosis method according to any one of claims 1 to 7, characterized in that: include: A flywheel (1) and a permanent magnet synchronous motor (2), a detection device (3) is arranged in an air gap at one end of the permanent magnet synchronous motor (2), the detection device is connected to a data acquisition device (4), and the data acquisition device (4) is connected to a computer (5); The axial position of the detection device (3) is consistent with that of the permanent magnet synchronous motor (2), and the detection device (3) is evenly distributed along the circumference of the air gap at one end of the motor; the flywheel energy storage system is adjusted to a state to be tested, and the measurement channel is balanced and cleared.

9. A flywheel energy storage system eccentricity and demagnetization composite fault diagnosis system according to claim 8, characterized in that: The detection device is a Hall sensor, and there are at least four Hall sensors. The feet of the Hall sensors are installed in the stator slots of the permanent magnet synchronous motor.

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