A method for determining inter-turn short-circuit fault of stator winding of asynchronous motor

Abstract

The present invention discloses a method for determining an inter-turn fault of an asynchronous motor stator winding. The method comprises the following steps: obtaining a three-phase voltage and a three-phase current of an asynchronous motor stator to be identified; transforming the obtained voltage and current into a stationary two-phase coordinate system; performing positive and negative sequence separation of the stator current and voltage by using Hilbert transformation; inversely transforming the positive and negative sequence currents into a three-phase coordinate system respectively; first determining a stator voltage unbalance factor K=U to avoid misjudgment caused by non-fault factors; n / U p Is it less than K? T If yes, it is determined whether the amplitude of the negative sequence component of the current reaches the fault warning value. If it reaches the fault warning value, the asynchronous motor to be judged for fault has a stator winding turn-to-turn short circuit fault. Compared with the prior art, the present invention has the advantages of convenient detection, good real-time performance and simple algorithm.

Description

Technical Field

[0001] The invention belongs to the field of fault diagnosis and monitoring of motors, and relates to a fault diagnosis method for short-circuit between turns of stator windings of an asynchronous motor. Background Art

[0002] With the rapid development of railways and the widespread application of power electronics technology, sensor technology, and information processing technology, AC drive electric locomotives have become the mainstream. At present, the traction drive systems of CRH1, CRH2, CRH2-300, CRH3, and CRH5 EMUs commonly used in my country are mainly composed of traction transformers, grid-side pulse rectifiers, motor-side inverters, and traction motors (i.e., three-phase asynchronous motors). Compared with DC locomotives, AC drive electric locomotives have greater advantages in railway traction systems: (1) They have better traction performance and can utilize the voltage and frequency regulation characteristics of the variable frequency speed regulation system to enable electric locomotives and EMUs to generate larger starting torques. (2) The PWM method is used to adjust the grid input current phase to increase its power factor (close to 1), thereby effectively suppressing harmonic interference. (3) The asynchronous motor has high power and light weight, and its unit mass power kW / kg is three times that of the DC motor. (4) The structure is simple and easy to manufacture, and there is no commutator or brush device inside, making its operation more reliable. (5) The dynamic performance and adhesion utilization are good.

[0003] Asynchronous motors rely on electromagnetic induction to generate induced current in the rotor winding, thereby generating electromagnetic torque. They are also called induction motors. Their structure mainly consists of two parts: the stator and the rotor, with an air gap between them. In addition, there are components such as end covers, bearings, and machine bases. The main faults of asynchronous motors can be divided into four categories, namely: stator winding fault, air gap eccentricity fault, rotor bar or end ring fault, bearing fault, etc. Among them, stator winding fault accounts for the main part of stator faults, accounting for about 30% to 40% of motor faults. The main form is a short circuit between two adjacent turns of the same-phase winding. It is usually caused by transient overvoltage generated during the switching process, vibration caused by electromagnetic force, insulation aging, long-term overload, high temperature and high pressure, or insulation skin damage caused by harsh working environment. Stator winding faults can be divided into turn-to-turn short circuit, phase-to-phase short circuit, ground short circuit, etc. Among them, turn-to-turn short circuit faults are the most common and can cause other faults.

[0004] Commonly used asynchronous motor stator winding inter-turn short-circuit fault diagnosis can be divided into three categories: model-based diagnosis method, knowledge-based diagnosis method, and signal processing-based diagnosis method. (1) Model-based diagnosis method By studying the circuit and magnetic circuit of the asynchronous motor, a more accurate mathematical model of the object to be diagnosed is established, and its fault characteristics are analyzed based on this model. Specifically, it can be divided into: parameter estimation method, state estimation method, and equivalent space method. The author M. Stocks published an article in the Proceedings of the 2007 IEEE Conference on Control Applications: On-line estimation of electrical parameters in induction machines subject to stator fault. The detection method of asynchronous motor stator short-circuit fault is based on parameters. This method is affected by strong coupling and is difficult to implement. (2) Knowledge-based diagnosis method: Many literatures use artificial neural network method for fault diagnosis. In addition, this method also includes: fuzzy logic method, expert system, genetic algorithm, fault tree, etc. (3) Signal processing-based diagnosis method: Commonly used fault characteristic quantities include torque, power, voltage, current, etc. Since current signals are the easiest to obtain, stator current spectrum analysis (MSCA) is the most commonly used method. When an asynchronous motor has a stator winding fault, it usually affects the symmetry of the three-phase stator current, which is also the basic basis for MSCA detection. However, due to the relatively mild severity of the initial fault, the lack of obvious characteristic quantities, and the presence of changes in parameters such as the three-phase stator terminal voltage and power supply frequency, the detection of stator winding faults is usually ignored or misjudged to a certain extent. The author Wang Bingfeng pointed out in the article: Analysis Methods and Detection Methods of Common Faults of Asynchronous Motors that when an asynchronous motor has a short circuit fault between the stator winding tubes, the 5th and 7th harmonics in its stator current increase significantly, so the above harmonic content in the three-phase stator current can be analyzed as a method for detecting faults. In the article Current monitoring for detecting inter-turn short circuits in induction motors published by A. Stavrous, HG Sedding et al. in IEEE Transactions on Energy Conversion, short circuit fault detection is achieved by analyzing whether the three-phase stator current contains components with frequencies approximately f1 / p, 2f1 / p, 3f1 / p (p is the number of pole pairs, f1 is the power supply frequency). The above detection method is relatively rough and easily affected by the inherent harmonic content in the AC drive system, so it is necessary to seek a more accurate stator short circuit fault detection method. Summary of the invention

[0005] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for determining the inter-turn short-circuit fault of the stator winding of an asynchronous motor. The present invention has the advantages of convenient detection, good real-time performance and simple algorithm.

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

[0007] A method for determining an inter-turn short circuit fault of an asynchronous motor stator winding comprises the following steps:

[0008] (1) Obtain the three-phase stator current and three-phase stator voltage i of the asynchronous motor to be detected sa 、i sb 、i sc 、u sa 、u sb 、u sc ;

[0009] (2) The current and voltage obtained above are transformed into the two-phase stationary αβ0 coordinate system to obtain i sα 、i sβ 、u sα 、u sβ ;

[0010] (3) Using Hilbert transform, the positive and negative sequence components of the stator current in the two-phase stationary coordinate system are separated to obtain and

[0011] (4) and By inversely transforming to the ABC coordinate system respectively, we can get the positive sequence component and negative sequence component of the stator current in the three-phase coordinate system.

[0012] (5) Determine the stator voltage unbalance factor whether it is established;

[0013] U n with U p are the negative and positive sequence components of the stator voltage respectively,

[0014] K T to a prescribed standard;

[0015] (6) Determine whether the amplitude of the negative sequence component of the current caused by the inter-turn short-circuit fault reaches the fault warning value. If so, the asynchronous motor to be detected has a stator winding inter-turn short-circuit fault, and the severity of the fault is:

[0016]

[0017] |ΔIn |=|I n -I n0 |

[0018] I n with I n0 They are the actual value and inherent value of the negative sequence component of the stator current respectively.

[0019] Preferably, the specific steps of step (2) are:

[0020] (201)i sα 、i sβ Use the following formula to obtain:

[0021]

[0022] (202)u sα 、u sβ Use the following formula to obtain:

[0023]

[0024] Preferably, the specific steps of step (3) are:

[0025] (301)i sα and i sβ After Hilbert transformation, we get

[0026]

[0027] H is the Hilbert operator;

[0028] (302) and It is obtained from the following formula:

[0029]

[0030] Preferably, the specific steps of step (4) are:

[0031] (401) Calculated by the following formula:

[0032]

[0033] (402) Calculated by the following formula:

[0034]

[0035] Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

[0036] 1. Compared with the traditional sensor-based detection method, the method of the present invention has the advantages of convenient detection, good real-time performance and simple algorithm;

[0037] 2. The detection method of the present invention is very suitable for online real-time detection in the frequency converter. It only uses voltage and current signals and does not require additional sensors. It is very suitable for embedded development in the frequency converter.

[0038] 3. The fault characteristic signal of the detection method of the present invention is very obvious. After the stator turn-to-turn short circuit occurs in the asynchronous motor, the negative sequence current component in the stator current caused by the turn-to-turn short circuit is very different from the inherent negative sequence current component of the asynchronous motor;

[0039] 4. The method of the present invention is simple, easy to implement, low in cost, and suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the inter-turn short circuit fault model of phase A winding of asynchronous motor.

[0041] Figure 2 The present invention is a flow chart of a method for determining an inter-turn short-circuit fault of a stator winding of an asynchronous motor.

[0042] Figure 3 It is a matlab / simulink simulation model of the three-phase asynchronous motor stator winding turn-to-turn short-circuit fault detection system.

[0043] Figure 4 The simulation results are as follows when μ=0. Figure 4 (a) is the three-phase stator current waveform when μ=0; Figure 4 (b) is the negative sequence current waveform of phase A extracted by Hilbert transform (μ=0).

[0044] Figure 5 This is the simulation result when μ=0.01. Figure 5 (a) is the three-phase stator current waveform when μ=0.01; Figure 5 (b) is the A-phase negative-sequence current waveform extracted by Hilbert transform (μ=0.01).

[0045] Figure 6 This is the simulation result when μ=0.02. Figure 6 (a) is the three-phase stator current waveform when μ=0.02; Figure 6 (b) is the negative sequence current waveform of phase A extracted by Hilbert transform (μ=0.02).

[0046] Figure 7 This is the simulation result when μ=0.05. Figure 7 (a) is the three-phase stator current waveform when μ=0.05; Figure 7(b) is the A-phase negative-sequence current waveform extracted by Hilbert transform (μ=0.05). DETAILED DESCRIPTION

[0047] The above scheme is further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0048] Embodiment 1:

[0049] In this embodiment, see Figure 1 and Figure 2 A method for determining an inter-turn short circuit fault of a stator winding of an asynchronous motor comprises the following steps:

[0050] (1) Obtain the three-phase stator current and three-phase stator voltage i of the asynchronous motor to be detected sa 、i sb 、i sc 、u sa 、u sb 、u sc ;

[0051] (2) The current and voltage obtained above are transformed into the two-phase stationary αβ0 coordinate system to obtain i sα 、i sβ 、u sα 、u sβ ;

[0052] (3) Using Hilbert transform, the positive and negative sequence components of the stator current in the two-phase stationary coordinate system are separated to obtain and

[0053] (4) and By inversely transforming to the ABC coordinate system respectively, we can get the positive sequence component and negative sequence component of the stator current in the three-phase coordinate system.

[0054] (5) Determine the stator voltage unbalance factor whether it is established;

[0055] U n with U p are the negative and positive sequence components of the stator voltage respectively,

[0056] K T to a prescribed standard;

[0057] (6) Determine whether the amplitude of the negative sequence component of the current caused by the inter-turn short-circuit fault reaches the fault warning value. If so, the asynchronous motor to be detected has a stator winding inter-turn short-circuit fault, and the severity of the fault is:

[0058]

[0059] |ΔI n |=|I n -I n0 |

[0060] I n with I n0 They are the actual value and inherent value of the negative sequence component of the stator current respectively.

[0061] Compared with the traditional sensor-based detection method, the detection method of this embodiment has the advantages of convenient detection, good real-time performance and simple algorithm.

[0062] Embodiment 2:

[0063] This embodiment is basically the same as the first embodiment, except that:

[0064] In this embodiment, see Figure 1 and Figure 2 , the specific steps of step (2) are:

[0065] (201)i sα 、i sβ Use the following formula to obtain:

[0066]

[0067] (202)u sα 、u sβ Use the following formula to obtain:

[0068]

[0069] In this embodiment, the specific steps of step (3) are:

[0070] (301)i sα and i sβ After Hilbert transformation, we get

[0071]

[0072] H is the Hilbert operator;

[0073] (302) and It is obtained from the following formula:

[0074]

[0075] In this embodiment, the specific steps of step (4) are:

[0076] (401) Calculated by the following formula:

[0077]

[0078] (402) Calculated by the following formula:

[0079]

[0080] Compared with the traditional sensor-based detection method, the method of this embodiment has the advantages of convenient detection, good real-time performance and simple algorithm. The detection method of this embodiment is very suitable for online real-time detection in the frequency converter. It only uses voltage and current signals and does not require additional sensors. It is very suitable for embedded development in the frequency converter. The fault characteristic signal of the detection method of this embodiment is very obvious. After the stator inter-turn short circuit occurs in the asynchronous motor, the negative sequence current component in the stator current caused by the inter-turn short circuit is very different from the inherent negative sequence current component of the asynchronous motor.

[0081] Embodiment three:

[0082] This embodiment is basically the same as the above embodiment, with the following features:

[0083] In this embodiment, whether a stator turn-to-turn short circuit occurs is determined by measuring the magnitude of the negative sequence component of the stator current in the three-phase asynchronous motor. The mathematical model of the turn-to-turn short circuit asynchronous motor is given below:

[0084] The short-circuit fault between the turns of the stator winding of the three-phase asynchronous motor makes the motor structure asymmetric, such as Figure 1 As shown in the figure, assuming that the stator three-phase winding is Y-connected, a turn-to-turn short circuit fault occurs in the stator A phase winding, and the A phase winding is divided into the normal winding part s a1 And short-circuited winding parts a2 , assuming the short-circuit winding coefficient is μ = l sa2 / (l sa1 +l sa2 ), where l sa1 , l sa2 are the lengths of the normal winding part and the short-circuited winding part respectively. The mathematical model of the asynchronous motor under this fault state can be expressed as follows:

[0085] Voltage equation:

[0086]

[0087] Among them, the stator voltage u s =[u sa1 u sa2 u sb u sc ] T , stator current i s =[i sa(i sa -i f )is b is c ] T , rotor current i f =[i ra i rb i rc ] T , stator resistance R s =R s diag[1-μμ11], rotor resistance R r =R r diag

[111] ;

[0088] Where u sa1 、u sa2 、u sb 、u sc They correspond to the instantaneous values ​​of the stator voltages of the normal winding part of phase A, the faulty winding part of phase A, phase B, and phase C respectively;

[0089] i sa 、i f 、i sb 、i sc They correspond to the instantaneous values ​​of phase A, phase A short-circuit current, phase B, and phase C stator current respectively;

[0090] i ra 、i rb 、i rc They correspond to the instantaneous values ​​of the rotor currents of phases a, b and c respectively;

[0091] R s is the stator winding resistance per phase;

[0092] R r is the resistance of each phase winding of the rotor.

[0093] Magnetic flux equation:

[0094]

[0095] Stator flux ψ s =[ψ sa1 ψ sa2 ψ sb ψ sc ] T ;

[0096] Rotor flux ψ r =[ψ ra ψ rb ψ rc ] T ;

[0097] Stator self-inductance

[0098]

[0099] Rotor self-inductance

[0100] Stator and rotor mutual inductance

[0101]

[0102] θ r is the rotor angular displacement.

[0103] By adding the first two terms of equation (1) and equation (2), the voltage equation of the faulty motor can be expressed as:

[0104] Magnetic flux equation:

[0105]

[0106] Where: u s '=[u sa u sb u sc ] T

[0107] ψ s '=[ψ sa ψ sb ψ sc ] T

[0108] i s '=[i sa i sb i sc ] T

[0109] A1=[-R s 0 0] T

[0110] A2=[-(L ls +L ms ) ms / 2 L ms / 2] T

[0111] A3=-L ms [cosθ r cos(θ r +120°) cos(θ r -120°)] T

[0112]

[0113]

[0114] For short-circuited windings a2 , its voltage and flux equations can be expressed as

[0115] u sa2 =μR s (i sa -i f )+pψ sa2 =R f i f (5)

[0116] ψ sa2 =-μA2 T i s '-μA3 T i r -μ(L ls +μL ms )i f (6)

[0117] Electromagnetic torque equation:

[0118]

[0119] Where: n p is the number of motor pole pairs.

[0120] In order to simplify the mathematical model of the asynchronous motor under fault conditions, the fault model is transformed from a three-phase stationary coordinate system to a two-phase stationary coordinate system to eliminate the electromagnetic coupling between the two-phase windings.

[0121] The transformed voltage equation is:

[0122]

[0123] Where: r is the motor speed.

[0124] Magnetic flux equation:

[0125]

[0126] For a short-circuited winding, the voltage and flux equation can be expressed as:

[0127] u sa2 =R f i f =μR s (i sα -i f )+pψ sa2 (10)

[0128]

[0129] like Figure 2 The flowchart of the method for determining the short-circuit fault of the stator winding of an asynchronous motor according to the present invention is shown. The method comprises the following steps:

[0130] Step 1: Obtain the stator three-phase current and three-phase voltage. When an inter-turn short circuit fault occurs in the stator winding of the asynchronous motor, the three-phase current is distorted, thereby generating a series of harmonic components. The three-phase current expression is:

[0131]

[0132] Step 2: Transform the above fault current to the two-phase stationary αβ0 coordinate system:

[0133]

[0134] Step 3: Use the frequency phase shift generated by Hilbert transform to separate the positive and negative sequence components of the stator current. sα and i sβ After Hilbert transformation, we get

[0135]

[0136] Combining formula (13) and formula (14), we can get:

[0137]

[0138] In the ABC coordinate system, i sα + 、i sβ + is the positive sequence component of current, i sα - 、i sβ - is the negative sequence component of the current. By inversely transforming them to the ABC coordinate system, we can get the positive sequence component and negative sequence component of the three-phase stator current. The transformation matrix is ​​as follows:

[0139]

[0140] Step 4: When the asynchronous motor has no faults, there are still some fixed negative sequence components in the current due to the motor and control factors. This component changes with the stator voltage imbalance. In order to avoid misjudgment caused by non-fault factors, the stator voltage imbalance factor should be determined first:

[0141]

[0142] Where U n with U pThey are the negative and positive sequence components of the stator voltage respectively.

[0143] If K <K T If yes, go to step 5, otherwise go back to step 1.

[0144] Step 5: When K <K T When (K T For a certain specified standard), the three-phase voltage symmetry of the asynchronous motor is good, and the stator negative sequence current caused by voltage imbalance can be ignored. At this time, diagnosis is performed based on the deviation value of the negative sequence current, and the fault degree is expressed as follows:

[0145] |ΔI n |=|I n -I n0 |

[0146] In the formula, I n with I n0 They are the actual value and inherent value of the negative sequence component of the stator current respectively.

[0147] The fault motor open-loop system simulation model built on Matlab / Simulink simulation software is as follows Figure 3 As shown, the detection method is built according to the design steps introduced above. The faulty motor is written using the faulty motor mathematical model introduced above. The parameters of the asynchronous motor are shown in the following table:

[0148] Table 1 Basic parameters of asynchronous motor

[0149]

[0150] Figure 4 to Figure 7 These are the simulation results when the winding short-circuit coefficient μ is 0, 0.01, 0.02, and 0.05. The results show that when a short circuit occurs between turns in the stator winding, the amplitude of the short-circuit phase current increases, the balance of the three-phase current is destroyed, and the amplitude of the negative sequence component extracted by the Hilbert transform of the three-phase stator current increases, and increases with the severity of the fault.

[0151] In summary, the method for determining the inter-turn fault of the stator winding of the asynchronous motor in the above embodiment includes the following steps: obtaining the three-phase voltage and three-phase current of the stator of the asynchronous motor to be identified; transforming the obtained voltage and current into a stationary two-phase coordinate system; using Hilbert transformation to separate the positive and negative sequence of the stator current and voltage; inversely transforming the positive and negative sequence currents into a three-phase coordinate system respectively; in order to avoid misjudgment caused by non-fault factors, first determine the stator voltage unbalance factor K=U n / U p Is it less than K? TIf yes, it is determined whether the amplitude of the negative sequence component of the current reaches the fault warning value. If it reaches the fault warning value, the asynchronous motor to be judged for fault has a stator winding turn-to-turn short circuit fault. Compared with the prior art, the present invention has the advantages of convenient detection, good real-time performance and simple algorithm.

[0152] The above describes the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent replacement methods. As long as they meet the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the protection scope of the present invention.

Claims

1. A method for determining an inter-turn short-circuit fault of an asynchronous motor stator winding, characterized in that: The steps include: (1) Obtain the three-phase stator current and three-phase stator voltage i of the asynchronous motor to be detected sa 、i sb 、i sc 、u sa 、u sb 、u sc ; (2) The current and voltage obtained above are transformed into the two-phase stationary αβ0 coordinate system to obtain i sα 、i sβ 、u sα 、u sβ ; (3) Using Hilbert transform, the positive and negative sequence components of the stator current in the two-phase stationary coordinate system are separated to obtain and (4) and By inversely transforming to the ABC coordinate system respectively, we can get the positive sequence component and negative sequence component of the stator current in the three-phase coordinate system. (5) Determine the stator voltage unbalance factor whether it is established; U n with U p are the negative and positive sequence components of the stator voltage respectively, K T to a prescribed standard; (6) Determine whether the amplitude of the negative sequence component of the current caused by the inter-turn short-circuit fault reaches the fault warning value. If so, the asynchronous motor to be detected has a stator winding inter-turn short-circuit fault, and the severity of the fault is: |ΔI n |=|I n -I n0 | I n with I n0 They are the actual value and inherent value of the negative sequence component of the stator current respectively.

2. The method for determining an inter-turn short-circuit fault of an asynchronous motor stator winding according to claim 1, characterized in that: The specific steps of step (2) are: (201)i sα 、i sβ Use the following formula to obtain: (202)u α 、u β Use the following formula to obtain:

3. The method for determining an inter-turn short-circuit fault of an asynchronous motor stator winding according to claim 1, characterized in that: The specific steps of step (3) are: (301)i sα and i sβ After Hilbert transformation, we get H is the Hilbert operator; (302) and It is obtained from the following formula:

4. The method for determining an inter-turn short-circuit fault of an asynchronous motor stator winding according to claim 1, characterized in that: The specific steps of step (4) are: (401) Calculated by the following formula: (402) Calculated by the following formula:

Images