A method for detecting a stator inter-turn short circuit fault of a multiphase permanent magnet motor

Abstract

The present application belongs to the field of motor system fault diagnosis, and relates to a kind of multi-phase permanent magnet motor stator inter-turn short circuit fault detection method, the method includes analyzing and calculating the space harmonic generated in air gap after the stator inter-turn short circuit fault of multi-phase permanent magnet motor occurs;According to the space harmonic generated after the calculation to determine the detection coil structure and arrangement position, and according to the detection coil structure and arrangement position, the detection coil induction voltage signal is collected.According to the induction voltage signal of the detection coil collected, it is processed as the stator inter-turn short circuit fault diagnosis variable;Set the reference value of diagnostic variable, and compare the stator inter-turn short circuit fault diagnosis variable with the reference value of diagnostic variable, and judge whether the stator inter-turn short circuit fault of multi-phase permanent magnet motor occurs according to the comparison result, while realizing the distinction of winding open circuit fault.The present application can accurately realize the on-line diagnosis of the stator inter-turn short circuit fault of multi-phase permanent magnet motor and distinguish from winding open circuit fault.

Description

Technical Field

[0001] This invention belongs to the field of motor fault diagnosis and relates to a method for detecting inter-turn short-circuit faults in the stator of a multiphase permanent magnet motor. Background Technology

[0002] During long-term operation, multiphase permanent magnet motor systems are affected by thermal stress, electrical stress, and mechanical stress, which can lead to aging and damage of the winding insulation layer, making them highly susceptible to inter-turn short-circuit faults in the stator windings. Stator inter-turn short-circuit faults in multiphase permanent magnet motors are often more dangerous than other electrical or mechanical faults. This is because a stator inter-turn short-circuit fault creates a short-circuit loop in the stator winding, generating a large short-circuit current. If the stator inter-turn short-circuit fault cannot be diagnosed and isolated quickly and accurately, the large short-circuit current in the short-circuited turn will further deteriorate the surrounding insulation, leading to other serious faults such as coil-to-coil, phase-to-phase, and phase-to-ground faults, causing severe damage to the motor. Therefore, rapid and accurate diagnosis of early inter-turn short-circuit faults in multiphase permanent magnet motors is crucial.

[0003] Scholars dedicated to diagnosing stator inter-turn short-circuit faults in motors have been focusing on feature extraction, data analysis, and comparative diagnostic effectiveness. While most model- and current-signal-based diagnostic strategies are simple and quick, the extracted fault features are often not unique to stator inter-turn short-circuit faults. For example, they may include second-harmonic pulsations and negative-sequence components on the direct and quadrature axes. These fault features can also occur after current sensor failures or open-circuit faults in motor windings, making misdiagnosis highly likely. Furthermore, these faults differ in severity from stator inter-turn short-circuit faults, requiring different isolation and fault-tolerance methods after diagnosis. Failure to quickly and accurately identify the fault type and select an appropriate fault-tolerant control strategy can severely damage the motor system.

[0004] Therefore, optimizing the detection accuracy and diagnostic indicators of stator inter-turn short circuit faults in multiphase permanent magnet motors, enabling online rapid diagnosis of stator inter-turn short circuit faults and parallel winding open circuit faults, and providing a basis for selecting appropriate online switching fault-tolerant control strategies are urgent problems to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a method for detecting stator inter-turn short circuit faults in multiphase permanent magnet motors. This method can detect stator inter-turn short circuit faults online and avoid false detection of winding open circuit faults, thus solving the problem of misdiagnosis in the above-mentioned technical issues.

[0006] To achieve the aforementioned objectives, this invention starts with a stator inter-turn short-circuit fault model for multiphase permanent magnet motors. For ease of analysis, the mathematical model in the natural coordinate system after a stator inter-turn short-circuit fault occurs is first derived. By analyzing the important fault characteristic of introducing spatial harmonics into the air gap magnetic field after a stator inter-turn short-circuit fault occurs, several detection coils are installed at the stator slots of the motor. Finally, diagnostic variables are extracted from the induced voltage of the detection coils. Based on the extracted diagnostic variables, stator inter-turn short-circuit faults in multiphase permanent magnet motors can be diagnosed online, and winding open-circuit faults can be distinguished. The specific process steps are as follows:

[0007] Step (1): Analyze and calculate the spatial harmonics generated in the air gap after a stator inter-turn short circuit fault occurs in a multiphase permanent magnet motor;

[0008] Step (2): Determine the structure and arrangement of the detection coil based on the spatial harmonics generated after the fault is calculated, and collect the induced voltage signal of the detection coil based on the structure and arrangement of the detection coil.

[0009] Step (3): Process the induced voltage signal of the collected detection coil as a variable for stator inter-turn short circuit fault diagnosis;

[0010] Step (4): Set the reference value of the diagnostic variable, and compare the stator inter-turn short circuit fault diagnostic variable with the reference value of the diagnostic variable. Based on the comparison result, determine whether a stator inter-turn short circuit fault of a multiphase permanent magnet motor has occurred, and at the same time realize the differentiation of winding open circuit fault.

[0011] Compared with the prior art, the present invention has the following advantages: First, the detection coil arranged in the method is a single-turn open-circuit coil, which has low installation cost and no current is generated in the coil, so it will not affect the normal operation of the motor; Second, it can accurately diagnose inter-turn short circuit faults in multi-phase permanent magnet motors while distinguishing winding open circuit faults; Third, the fault characteristics extracted by the induced voltage of the detection coil are not affected by load changes, making it more suitable for applications with large load changes. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the motor winding structure involved in the present invention.

[0013] Figure 2 This is a schematic diagram of an inter-turn short-circuit fault in the stator winding involved in the present invention.

[0014] Figure 3 This is a schematic diagram of the air gap magnetomotive force generated by a single coil carrying current, as per the present invention.

[0015] Figure 4 The present invention relates to the air gap harmonic content under different fault levels.

[0016] Figure 5This is a schematic diagram of the detection coil structure involved in the present invention.

[0017] Figure 6(a) shows the end connection lines of each detection coil involved in the present invention (at one end of the stator core).

[0018] Figure 6(b) shows the lead wires at the ends of each detection coil involved in the present invention (at the other end of the stator core).

[0019] Figure 7(a) shows the phase current and induced voltage signal of the detection coil before and after the stator inter-turn short circuit fault involved in this invention.

[0020] Figure 7(b) shows the harmonic content of the induced voltage of the detection coil involved in this invention.

[0021] Figure 8 The present invention relates to the phase current winding and the induced voltage signal of the detection coil before and after an open-circuit fault in the winding. Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0023] This embodiment uses a semi-symmetrical six-phase permanent magnet motor with an open winding (such as...). Figure 1 As shown) A stator inter-turn short circuit fault occurred in winding a1 (e.g.) Figure 2 As shown in the figure), taking the open circuit fault of phase a1 winding as an example, the specific fault diagnosis process is as follows:

[0024] (1) Analyze the stator turn-to-turn short circuit fault of a multiphase permanent magnet motor, and derive and calculate the spatial harmonics generated in the air gap after the fault. Specifically, it can be divided into:

[0025] (1A) Constructing a mathematical model of a six-phase permanent magnet motor in the natural coordinate system after a stator inter-turn short-circuit fault occurs:

[0026] Voltage equation:

[0027] Magnetic flux linkage equation:

[0028] In the formula, u s R is the stator phase voltage matrix. s Let i be the stator resistance matrix. s Let ψ be the stator phase current matrix. s Let L be the stator flux linkage matrix. s For the stator inductance matrix, ψ f d represents the flux linkage amplitude of the rotor permanent magnet, t represents the differential sign, and F represents time. s (θ) is the permanent magnet flux linkage matrix, and θ is the rotor position angle.

[0029] coefficient matrix F s (θ) is defined as:

[0030]

[0031] In the formula, T is the matrix transpose symbol, μ is the inter-turn short-circuit ratio (the ratio of the number of short-circuit coil turns in one phase winding to the total number of turns in one phase winding), and F... s (θ) is the permanent magnet flux linkage matrix, and θ is the rotor position angle.

[0032] The stator phase voltage matrix is:

[0033]

[0034] In the formula, u s For stator phase voltage, u ax a x Phase voltage, u bx b x Phase voltage, u cx c x Phase voltages (x=1, 2), T is the matrix transpose symbol.

[0035] The stator phase current matrix is:

[0036]

[0037] In the formula, i s For stator phase current, i ax a x Phase current, i bx b x Phase current, i cx c x Phase current (x=1, 2), i f For short-circuit current of short-circuit coil (e.g.) Figure 2 As shown in the figure, T is the matrix transpose symbol.

[0038] The resistance matrix is:

[0039]

[0040] In the formula, R s R is the stator resistance. f μ is the external contact resistance of the short-circuit coil, μ is the inter-turn short-circuit ratio, and μR is the short-circuit resistance of the coil. s The short-circuit coil resistance is -μR. s -R f Taking the negative sign means that the short-circuit current flowing through the short-circuit coil resistor and the short-circuit coil external contact resistor are opposite to the specified positive direction.

[0041] The inductor matrix is:

[0042]

[0043] In the formula, L m For stator mutual inductance, L ls For stator leakage inductance, γ = π / 6, μ is the inter-turn short-circuit ratio, μ 2 The square of the inter-turn short-circuit ratio, μL m For the mutual inductance of the short-circuit coils, μ 2 L ls For short-circuit coil leakage inductance, μ 2 L m For the self-inductance of the short-circuit coil, -μL m -μ 2 L ls -μ 2 L m Taking the negative sign means that the short-circuit current flowing through the short-circuit coil is in the opposite direction to the specified positive direction.

[0044] (1B) Analysis of the air gap space magnetomotive force after a stator inter-turn short circuit fault occurs.

[0045] When an inter-turn short circuit fault occurs in motor winding a1, the winding diagram is as follows: Figure 2 As shown, i f For short-circuit current, R f For short-circuit resistance, a s1 For phase a1, which is a non-fault winding, a s2 It is a short-circuit winding composed of short-circuit coils.

[0046] When an inter-turn short circuit occurs in the a1 phase winding, the winding will become two parts. One part is a metal short circuit formed by direct contact between the short-circuit coil turns or a short circuit loop formed by a certain external contact resistance. This part of the winding is called the short-circuit winding. The other part is the part of the a1 phase winding that is not short-circuited. This part of the winding is called the non-fault winding of the a1 phase.

[0047] At this point, the short-circuit loop formed by the short-circuit coil is equivalent to a single coil. The short-circuit current flowing through the short-circuit coil will introduce a new magnetomotive force into the air gap, such as... Figure 3 As shown.

[0048] Setting sub-coil AA ’ A current i is passed through, generating a rectangular wave magnetomotive force as shown in the figure. Fourier decomposition of the rectangular wave yields a result in a value within the entire air gap circumference in the range [-pπ, pπ].

[0049] n=1,2,…

[0050] In the formula, F(θ) is the rectangular wave magnetomotive force, p is the number of pole pairs, θ is the electrical angle along the circumference of the motor, n is the harmonic order, and a n It represents the amplitude of the nth harmonic magnetomotive force.

[0051] Due to the rectangular wave magnetomotive force on coil AA ’ Since the axis is symmetrical, the above equation only contains a cosine term.

[0052]

[0053] In the formula, n is the harmonic order, a n Let F(θ) be the amplitude of the nth harmonic magnetomotive force, F(θ) be the rectangular wave magnetomotive force, p be the number of pole pairs, β be the coil short-pitch ratio, and ω be the amplitude of the nth harmonic magnetomotive force. k θ is the number of coil turns, θ is the electrical angle along the circumference of the motor, i is the current flowing through it, π is pi, and d is the differential symbol.

[0054] It can be seen that the fractional and low-order harmonics are very strong in the rectangular magnetomotive force generated by a current flowing through a single coil.

[0055] Using a space wave with a period of 2π electrical angle as the fundamental wave, the above equation is rearranged to obtain:

[0056]

[0057] In the formula, F(θ) is the rectangular wave magnetomotive force, p is the number of pole pairs, θ is the electrical angle along the circumference of the motor, k is the order of the new additional magnetic field, and F k The amplitude of the kth harmonic magnetomotive force is given.

[0058] The new additional magnetic fields generated in the air gap magnetic field are mainly of the order 1 / p, 2 / p, ... Taking a six-phase permanent magnet motor with four pole pairs as an example, the harmonic content in the air gap after a stator inter-turn short-circuit fault is as follows: Figure 4 As shown.

[0059] (2) Determine the structure and location of the detection coil based on the spatial harmonics generated after the fault;

[0060] (2A) Structure and detection principle of the detection coil.

[0061] Under normal circumstances or when the motor experiences an external fault, the air gap magnetic field is mainly dominated by the fundamental wave. In (1B), it is described that when the motor experiences an inter-turn short circuit fault in the stator winding, the new additional magnetic field generated in the air gap mainly has the following frequencies: 1 / p, 2 / p, ...

[0062] The detection coil is fixed at the slot on the inner circle of the stator and is a single coil with a pitch of 2τ (τ is the pole pitch). Integer-order spatial harmonic magnetic fields are distributed in an integer number of periods within this detection coil. Therefore, the total magnetic flux linkage generated by the fundamental spatial magnetic field and a small number of higher-order odd-order harmonic magnetic fields in this detection coil is 0. Thus, under normal operation and external fault conditions, the induced voltage of the detection coil is theoretically 0. Only the fractional-order harmonic magnetomotive force generated by a stator inter-turn short-circuit fault will produce alternating magnetic flux linkage and induced voltage in the detection coil. Therefore, a stator inter-turn short-circuit fault will cause an increase in the induced voltage of the detection coil, thus constituting the diagnostic criterion for stator inter-turn short-circuit faults. A schematic diagram of the detection coil structure is shown below. Figure 5 As shown.

[0063] (2B) The location of the detection coil.

[0064] This method takes a six-phase permanent magnet motor with 4 pole pairs and 48 slots as an example to arrange the detection coils. The specific location diagrams are shown in Figure 6(a) and Figure 6(b).

[0065] The detection coils 1 through 3 are all single coils with a pitch of 1 pole pair (i.e., 12 slot pitch) and a number of turns of 1.

[0066] The two coil sides of the No. 1 detection coil are placed at the openings of slots No. 1 and No. 13, respectively;

[0067] The two coil sides of the No. 2 detection coil are placed in the slot openings of slots No. 10 and No. 22, respectively;

[0068] The two coil sides of the No. 3 detection coil are placed in the slots of No. 16 and No. 28, respectively.

[0069] (3) Extract fault characteristics using the induced voltage of the detection coil and calculate diagnostic variables.

[0070] (1B) describes how a turn-to-turn short-circuit fault in the stator winding of a multiphase permanent magnet motor induces a fractional harmonic magnetic field in the air gap magnetic field. The rotational speed n of the v-th fractional spatial harmonic magnetic field generated by the μ-th current harmonic is described. v It is μ / v times the rotational speed n of the fundamental magnetic field generated by the fundamental current.

[0071] The rotational speed of the fractional harmonic magnetic field in the air gap is expressed as:

[0072]

[0073] In the formula, μ is the stator current harmonic order, v is the magnetic field harmonic order, f is the fundamental frequency, p is the number of pole pairs of the motor, and n v Let v be the rotational speed of the fractional-order spatial harmonic magnetic field, and n be the rotational speed of the fundamental magnetic field generated by the fundamental current.

[0074] Therefore, the frequency of the voltage induced by the v-th space harmonic in the detection coil is:

[0075]

[0076] In the formula, μ is the stator current harmonic order, v is the magnetic field harmonic order, f is the fundamental frequency, p is the number of pole pairs of the motor, and n v Let f be the rotational speed of the v-th fractional spatial harmonic magnetic field. v The frequency of the vth spatial harmonic is given.

[0077] The fractional harmonics v caused by the stator inter-turn short circuit fault are 1 / p, 2 / p, ... From the above formula, it can be seen that the harmonic order of the induced voltage in the detection coil is related to the harmonic order of the stator current. Therefore, theoretically, the frequency of the induced voltage in the detection coil caused by the fractional spatial harmonics generated by the stator current after the fault is the fundamental frequency and the odd harmonics.

[0078] Therefore, diagnostic variables are defined as follows:

[0079]

[0080] In the formula, U sc U is a diagnostic variable. d,1 To detect the effective value of the fundamental component of the induced voltage in the detection coil, U d,3 To detect the effective value of the third harmonic component of the induced voltage in the detection coil, U d,2k+1 The effective value of the 2k+1th harmonic component of the induced voltage of the detection coil (k is a natural number).

[0081] In theory, as long as the diagnostic variable U is detected... sc A value greater than 0 indicates a short circuit fault between stator turns in the motor. However, during normal motor operation, due to factors such as manufacturing process errors, the detection coil also has an inherent voltage with a very small amplitude. To avoid misdiagnosis due to the inherent voltage of the detection coil during normal motor operation, a diagnostic threshold U is usually set. set Only when U sc >U set The system can detect stator inter-turn short circuit faults in real time.

[0082] First, when the motor is running normally, measure the total effective value U of the inherent voltage of the detection coil. d.normal and the corresponding rotational speed n normal Then, what is the diagnostic threshold U for stator inter-turn short-circuit faults under any operating condition? set.1 :

[0083]

[0084] In the formula, n is the actual operating speed of the motor, and U set.1 U is the diagnostic threshold for stator inter-turn short-circuit faults under arbitrary operating conditions. d.normalTo detect the total effective value of the inherent voltage of the coil, n normal K represents the corresponding speed under the corresponding operating conditions. tol.1 For the reliability coefficient, we can take 1.1 ≤ K. tol.1 ≤2.

[0085] (4) Detect the stator turn short circuit fault of the multiphase permanent magnet motor and distinguish the winding open circuit fault according to the diagnostic variable defined by the induced voltage of the detection coil.

[0086] (4A) When a stator inter-turn short circuit fault occurs in a multiphase permanent magnet motor, according to the description in (3), the fractional spatial harmonics introduced by the short-circuit ring in the air gap will generate induced voltage signals of fundamental and odd harmonics in the detection coil. Before the fault, it contains only a very small inherent voltage (theoretical value is 0). By defining the diagnostic threshold, stator inter-turn short circuit diagnosis can be realized. After the stator inter-turn short circuit fault occurs, the phase current, the induced voltage of the detection coil, and the Fourier decomposition are shown in Figure 7.

[0087] (4B) When an open-circuit fault occurs in phase a1 of the motor winding, the combined magnetomotive force generated by the currents of the other five phases will not induce a voltage signal in the detection coil proposed in this invention. The phase current and the induced voltage of the detection coil during an open-circuit fault in the motor winding are as follows: Figure 8 As shown.

[0088] This invention uses the induced voltage signal from a detection coil as a diagnostic variable to accurately detect inter-turn short-circuit faults in the stator of a multiphase permanent magnet motor and distinguish between winding open-circuit faults. Compared with existing technologies, it avoids misdiagnosis due to the lack of uniqueness of the selected fault characteristics, which could lead to misdiagnosis of winding open-circuit faults. It allows for rapid online fault type determination, providing a basis for selecting appropriate fault-tolerant control strategies.

Claims

1. A method for detecting inter-turn short-circuit faults in the stator of a multiphase permanent magnet motor, characterized in that, Includes the following steps: Step (1): Analyze and calculate the spatial harmonics generated in the air gap after the stator inter-turn short circuit fault of the multiphase permanent magnet motor, and take the fractional spatial harmonics introduced into the air gap magnetic field after the stator inter-turn short circuit fault as the fault characteristics. Step (2): Determine the structure and arrangement of the detection coil based on the spatial harmonics generated after the fault is calculated, and collect the induced voltage signal of the detection coil according to the structure and arrangement of the detection coil. The detection coil is arranged at the stator slot, with a pitch of one pair of poles and a number of turns of 1. Step (3): Process the induced voltage signal of the collected detection coil as a diagnostic variable for stator inter-turn short circuit fault. Therefore, define the diagnostic variable: In the formula, U sc U is a diagnostic variable. d,1 To detect the effective value of the fundamental component of the induced voltage in the detection coil, U d,3 To detect the effective value of the third harmonic component of the induced voltage in the detection coil, U d,2k+1 The effective value of the 2k+1th harmonic component of the induced voltage of the detection coil is given, where k is a natural number. Step (4): Set reference values ​​for diagnostic variables, and compare the stator inter-turn short circuit fault diagnostic variables with the reference values ​​for diagnostic variables. Based on the comparison results, determine whether a stator inter-turn short circuit fault has occurred in a multiphase permanent magnet motor, and simultaneously distinguish between winding open circuit faults. Then, the diagnostic threshold U for stator inter-turn short circuit faults under any operating condition is... set.1 : In the formula, n is the actual operating speed of the motor, and U set.1 U is the diagnostic threshold for stator inter-turn short-circuit faults under arbitrary operating conditions. d.normal To detect the total effective value of the inherent voltage of the coil, n normal K represents the corresponding speed under the corresponding operating conditions. tol.1 For the reliability coefficient, we can take 1.1 ≤ K. tol.1 ≤2.

2. The method for detecting inter-turn short-circuit faults in the stator of a multiphase permanent magnet motor according to claim 1, characterized in that, The reference value for the diagnostic variable is the inherent voltage signal of the detection coil when the motor is running normally.

3. The method for detecting inter-turn short-circuit faults in the stator of a multiphase permanent magnet motor according to any one of claims 1 to 2, characterized in that, The permanent magnet motor has multiple phases.

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