Background
With the rapid development of railways and the wide application of power electronic technology, sensor technology and information processing technology, ac transmission electric locomotives have become mainstream. At present, the CRH1, CRH2, CRH2-300, CRH3 and CRH5 motor train units which are commonly used in China form a traction transmission system which mainly comprises a traction transformer, a grid-side pulse rectifier, a motor-side inverter, a traction motor (namely a three-phase asynchronous motor) and the like. Compared with a direct current locomotive, the alternating current transmission electric locomotive has greater advantages in a railway traction system: (1) the traction performance is better, and the voltage regulation and frequency regulation characteristics in a frequency conversion speed regulation system can be utilized to enable the electric locomotive and the motor train unit to generate larger starting torque. (2) The phase of the input current of the power grid is adjusted through a PWM method, so that the power factor of the input current becomes high (close to 1), and harmonic interference is effectively suppressed. (3) The asynchronous motor has large power and light weight, and the unit mass power kW/kg of the asynchronous motor is 3 times that of a direct current motor. (4) The structure is simple, the manufacture is easy, and the commutator and the electric brush device do not exist in the inner part, so that the operation is more reliable. (5) The dynamic performance and the adhesion utilization are good.
Asynchronous machines rely on electromagnetic induction to generate an induced current in the rotor windings, thereby generating an electromagnetic torque, also known as induction machines. The structure of the magnetic motor mainly comprises a stator and a rotor, and an air gap is arranged between the stator and the rotor. In addition, the parts such as end covers, bearings, bases and the like are also arranged. The main faults of asynchronous machines can be divided into four categories, namely: stator winding faults, air gap eccentric faults, rotor bar breakage or end ring faults, bearing faults and the like; the stator winding fault accounts for the major part of the stator fault, accounts for about 30-40% of the motor fault, and is mainly in the form of short circuit between two adjacent turns of coils of the same-phase winding, and is usually short circuit faults with different expression forms caused by transient overvoltage, vibration caused by bearing electromagnetic force, insulation aging, long-term overload, high temperature and high pressure or insulation skin damage caused by a severe working environment in the switching process of the stator winding fault. Stator winding faults can be further classified into inter-turn short circuits, inter-phase short circuits, ground short circuits, and the like, wherein inter-turn short circuit faults are the most common fault and can cause other faults.
The common diagnosis of the stator winding turn-to-turn short circuit fault of the asynchronous motor can be divided into a diagnosis method based on a model, a diagnosis method based on knowledge and a diagnosis method based on signal processing. (1) The diagnosis method based on the model is realized by carrying out circuit on an asynchronous motor,Magnetic circuit and other researches are carried out to establish a more accurate mathematical model of a diagnosed object, and the analysis of the fault characteristics can be divided into: parameter estimation, state estimation, and equivalent space. Stocks published in Proceedings of the Conference, ofhe 2007IEEE Conference on control applications: the method for detecting the short circuit fault of the stator of the asynchronous motor by the On-line insulation electric parameters in the insulation mechanisms to the stator is carried out through parameters, and the method is influenced by strong coupling and the like and is difficult to realize. (2) Knowledge-based diagnostic methods: many documents use artificial neural network methods for fault diagnosis. The method further comprises: fuzzy logic methods, expert systems, genetic algorithms, fault trees, and the like. (3) Signal processing based diagnostic methods: common fault characteristics are torque, power, voltage, current, etc. Stator current spectral analysis (MSCA) is most commonly used because the current signal is most readily available. When the stator winding of the asynchronous motor fails, the symmetry of three-phase stator current is usually affected, which is also the basic basis for detection by the MSCA method. However, the initial degree of the fault is relatively light, the characteristic quantity is not obvious, and parameter changes such as the terminal voltage of the three-phase stator and the power frequency exist, so that the detection of the stator winding fault is usually ignored or misjudged to some extent. The authors are in articles with Wangbing: research on an analysis method and a detection method for common faults of the asynchronous motor indicates that 5 th harmonic waves and 7 th harmonic waves in stator current of the asynchronous motor are obviously increased when the asynchronous motor has short-circuit faults between stator winding containers, so that the harmonic wave content in three-phase stator current can be analyzed to be used as a method for detecting the faults. Stavrou, H.G.Sedding et al in IEEE Transactions on Energy Conversion by analyzing whether three-phase stator currents contain currents with frequencies of approximately f1/p、2f1/p、3f1P (p is the number of pole pairs, f)1Power supply frequency) to achieve short circuit fault detection. The detection method is rough and is easily influenced by inherent harmonic content in an alternating-current transmission system, so that a more accurate stator short-circuit fault detection method needs to be foundThe method is carried out.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to overcome the defects in the prior art and provide a method for judging the turn-to-turn short circuit fault of the stator winding of the asynchronous motor.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
a method for judging turn-to-turn short circuit fault of stator winding of asynchronous motor includes following steps:
(1) obtaining three-phase stator current and three-phase stator voltage i of asynchronous motor to be fault detectedsa、isb、isc、usa、usb、usc;
(2) Converting the obtained current and voltage to a two-phase stationary alpha beta 0 coordinate system to obtain isα、isβ、usα、usβ;
(3) Separating the positive and negative sequence components of the stator current under the two-phase static coordinate system by using Hilbert transformation
And
(4) will be provided with
And
respectively inverse transforming to ABC coordinate system to obtain positive sequence component and negative sequence component of stator current in three-phase coordinate system
(5) Determining stator voltage imbalance factor
Whether the result is true or not;
Unand UpRespectively a negative sequence component and a positive sequence component of the stator voltage,
KTis a specified standard;
(6) judging whether the current negative sequence component amplitude caused by the turn-to-turn short circuit fault reaches a fault early warning value, if so, judging whether the asynchronous motor to be subjected to fault detection has the stator winding turn-to-turn short circuit fault, and judging the severity of the fault:
|ΔIn|=|In-In0|
Inand In0The actual value and the inherent value of the negative sequence component of the stator current are respectively.
Preferably, the step (2) comprises the following specific steps:
(201)isα、isβthe following equation was used to obtain:
(202)usα、usβthe following equation was used to obtain:
preferably, the step (3) comprises the following specific steps:
(301)isαand isβObtained by Hilbert transform
H is a Hilbert operator;
(302)
and
is obtained by the following formula:
preferably, the step (4) comprises the following specific steps:
(401)
calculated from the following formula:
(402)
calculated from the following formula:
compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. compared with the traditional detection method based on the sensor, the method has the advantages of convenience in detection, good real-time performance and simple algorithm;
2. the detection method is very suitable for online real-time detection in the frequency converter, only uses voltage and current signals, does not need additional sensors, and is very suitable for embedded development in the frequency converter;
3. the fault characteristic signal of the detection method is very obvious, and after the asynchronous motor has a stator turn-to-turn short circuit, the difference between the negative sequence current component of the stator current due to the turn-to-turn short circuit and the inherent negative sequence current component of the asynchronous motor is very large;
4. the method is simple and easy to implement, low in cost and suitable for popularization and application.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
the first embodiment is as follows:
in this embodiment, referring to fig. 1 and fig. 2, a method for determining an inter-turn short circuit fault of a stator winding of an asynchronous motor includes the following steps:
(1) obtaining three-phase stator current and three-phase stator voltage i of asynchronous motor to be fault detectedsa、isb、isc、usa、usb、usc;
(2) Converting the obtained current and voltage to a two-phase stationary alpha beta 0 coordinate system to obtain isα、isβ、usα、usβ;
(3) Separating the positive and negative sequence components of the stator current under the two-phase static coordinate system by using Hilbert transformation
And
(4) will be provided with
And
respectively inverse transforming to ABC coordinate system to obtain positive sequence component and negative sequence component of stator current in three-phase coordinate system
(5) Determining stator voltage imbalance factor
Whether the result is true or not;
Unand UpRespectively a negative sequence component and a positive sequence component of the stator voltage,
KTis a specified standard;
(6) judging whether the current negative sequence component amplitude caused by the turn-to-turn short circuit fault reaches a fault early warning value, if so, judging whether the asynchronous motor to be subjected to fault detection has the stator winding turn-to-turn short circuit fault, and judging the severity of the fault:
|ΔIn|=|In-In0|
Inand In0The actual value and the inherent value of the negative sequence component of the stator current are respectively.
Compared with the traditional detection method based on the sensor, the detection method has the advantages of convenience in detection, good real-time performance and simple algorithm.
Example two:
this embodiment is substantially the same as the first embodiment, and is characterized in that:
in this embodiment, referring to fig. 1 and fig. 2, the step (2) specifically includes:
(201)isα、isβthe following equation was used to obtain:
(202)usα、usβthe following equation was used to obtain:
in this embodiment, the step (3) specifically includes the steps of:
(301)isαand isβObtained by Hilbert transform
H is a Hilbert operator;
(302)
and
is obtained by the following formula:
in this embodiment, the step (4) specifically includes the following steps:
(401)
calculated from the following formula:
(402)
calculated from the following formula:
compared with the traditional detection method based on the sensor, the method has the advantages of convenience in detection, good real-time performance and simple algorithm. The detection method is very suitable for online real-time detection in the frequency converter, only uses voltage and current signals, does not need additional sensors, and is very suitable for embedded development in the frequency converter. The fault characteristic signal of the detection method of the embodiment is very obvious, and after the asynchronous motor has a stator turn-to-turn short circuit, the difference between the negative sequence current component of the stator current due to the turn-to-turn short circuit and the inherent negative sequence current component of the asynchronous motor is very large.
Example three:
this embodiment is substantially the same as the above embodiment, and is characterized in that:
in this embodiment, whether a stator turn-to-turn short circuit occurs is determined by the magnitude of a negative sequence component of a stator current in a three-phase asynchronous motor, and a mathematical model of the turn-to-turn short circuit asynchronous motor is given below:
the structure of the motor is asymmetric due to the turn-to-turn short circuit fault of the stator winding of the three-phase asynchronous motor, as shown in fig. 1, if the three-phase winding of the stator is Y-connected, the turn-to-turn short circuit fault occurs on the A-phase winding of the stator, and the A-phase winding is divided into a normal winding part sa1And short-circuiting the winding section sa2Let the short-circuit winding coefficient be μ ═ lsa2/(lsa1+lsa2) Wherein l issa1、lsa2The lengths of the normal winding part and the short-circuit winding part, respectively, the mathematical model of the asynchronous motor in this fault state can be expressed as follows:
voltage equation:
wherein the stator voltage us=[usa1 usa2 usb usc]TStator current is=[isa(isa-if)isb isc]TRotor current if=[ira irb irc]TStator resistance Rs=Rsdiag[1-μμ11]Rotor resistance Rr=Rrdiag[111];
In the formula usa1、usa2、usb、uscCorresponding to the instantaneous values of the stator voltages of the A-phase normal winding part, the A-phase fault winding part, the B-phase stator and the C-phase stator respectively;
isa、if、isb、iscrespectively corresponding to instantaneous values of A-phase short-circuit current, B-phase stator current and C-phase stator current;
ira、irb、irccorresponding to the instantaneous values of the rotor currents of the a phase, the b phase and the c phase respectively;
Rsresistance of each phase winding of the stator;
Rris the rotor winding resistance per phase.
The flux linkage equation:
stator flux linkage psis=[ψsa1ψsa2ψsbψsc]T;
Rotor flux linkage psir=[ψraψrbψrc]T;
Self inductance of stator
Stator-rotor mutual inductance
θrIs the rotor angular displacement.
By adding the first two terms of the equation (1) and the equation (2), the voltage equation of the fault motor can be expressed as:
the flux linkage equation:
in the formula: u. ofs'=[usa usb usc]T
ψs'=[ψsa ψsb ψsc]T
is'=[isa isb isc]T
A1=[-R s 0 0]T
A2=[-(Lls+Lms) Lms/2 Lms/2]T
A3=-Lms[cosθr cos(θr+120°) cos(θr-120°)]T
For short-circuit winding sa2The voltage and flux linkage equation can be expressed as
usa2=μRs(isa-if)+pψsa2=Rfif (5)
ψsa2=-μA2 Tis'-μA3 Tir-μ(Lls+μLms)if (6)
Electromagnetic torque equation:
in the formula: n ispThe number of pole pairs of the motor is shown.
In order to simplify the mathematical model of the asynchronous machine in the fault state, the fault model is transformed from a three-phase stationary coordinate system to a two-phase stationary coordinate system in order to eliminate electromagnetic coupling between the two-phase windings.
Transformed voltage equation:
in the formula: omegarIs the motor speed.
The flux linkage equation:
for a shorted winding, the voltage and flux linkage equation can be expressed as:
usa2=Rfif=μRs(isα-if)+pψsa2 (10)
fig. 2 is a flowchart of a method for determining a turn-to-turn short circuit fault of a stator winding of an asynchronous motor according to the present invention, and the method includes the following steps:
step 1: the method comprises the following steps of obtaining three-phase current and three-phase voltage of a stator, and when an asynchronous motor stator winding generates turn-to-turn short circuit fault, the three-phase current is distorted so as to generate a series of harmonic components, wherein the three-phase current expression is as follows:
step 2: converting the fault current into a two-phase stationary alpha beta 0 coordinate system
And step 3: and separating the positive sequence component and the negative sequence component of the stator current by using the frequency phase shift generated by Hilbert conversion. Where H is the Hilbert operator, isαAnd isβObtained by Hilbert transform
By combining formula (13) with formula (14),
i under the ABC coordinate systemsα +、isβ +As a positive sequence component of current isα -、isβ -For the negative sequence component of the current, willAnd respectively carrying out inverse transformation on the three-phase stator current and the three-phase stator current to an ABC coordinate system to obtain a positive sequence component and a negative sequence component of the three-phase stator current. The transformation matrix is as follows
And 4, step 4: when the asynchronous motor has no fault, part of fixed negative sequence components still exist in the current due to self factors such as the motor, control and the like. This component varies with the stator voltage imbalance. In order to avoid misjudgment caused by non-fault factors, a stator voltage unbalance factor is judged firstly:
in the formula of UnAnd UpThe stator voltage negative sequence and positive sequence components are respectively.
If K<KTIf so, executing the step 5, otherwise, returning to the step 1.
And 5: when K is<KTWhen (wherein K)TAnd the voltage is a specified standard), the three-phase voltage symmetry of the asynchronous motor is good, and the negative sequence current of the stator caused by the voltage unbalance is negligible. The diagnosis is carried out according to the negative sequence current deviation value, and the fault degree is expressed as follows:
in the formula InAnd In0The actual value and the inherent value of the negative sequence component of the stator current are respectively.
A fault motor open-loop system simulation model built on Matlab/Simulink simulation software is shown in fig. 3, a detection method is built according to the design steps, a fault motor is compiled by the fault motor mathematical model, and parameters of an asynchronous motor are shown in the following table:
TABLE 1 basic parameters of asynchronous machines
Fig. 4 to 7 show simulation results when the winding short-circuit coefficient μ is 0, 0.01, 0.02, and 0.05, respectively. The results show that: when turn-to-turn short circuit occurs in the stator winding, the amplitude of the short-circuit phase current is increased, the three-phase current balance is damaged, and the amplitude of a negative sequence component extracted by the three-phase stator current through Hilbert transformation is increased along with the aggravation of the fault degree.
To sum up, the method for determining turn-to-turn faults of the stator winding of the asynchronous motor in the embodiment includes the following steps: acquiring three-phase voltage and three-phase current of a stator of an asynchronous motor to be fault identified; transforming the obtained voltage and current to a static two-phase coordinate system; carrying out positive and negative sequence separation on the stator current and voltage by using Hilbert conversion; respectively inversely transforming the positive sequence current and the negative sequence current to a three-phase coordinate system; in order to avoid misjudgment caused by non-fault factors, firstly, the stator voltage unbalance factor K is judged to be Un/UpWhether or not less than KTIf so, judging whether the current negative sequence component amplitude reaches a fault early warning value, and if so, judging that the asynchronous motor to be subjected to fault judgment has a stator winding turn-to-turn short circuit fault. Compared with the prior art, the method has the advantages of convenience in detection, good real-time performance and simple algorithm.
The embodiments of the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and various changes and modifications can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitutions, as long as the purpose of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the present invention.