Excitation current interference identification method, device, equipment and medium

Abstract

The present application proposes a method, device, equipment and medium for identifying excitation current interference, which relates to the technical field of relay protection of main equipment in power systems. The method sets an open-circuit coil in the air gap magnetic field of the excitation motor to sense changes in the air gap magnetic flux. Regardless of whether the armature winding is normal or faulty, the reaction magnetic field of the armature winding rotates around the open-circuit coil, and the electromotive force induced in the open-circuit coil is a fractional harmonic induced electromotive force. When there is an interfering harmonic current in the excitation winding, a larger integer harmonic electromotive force will be induced in the open-circuit coil. Therefore, based on the relative change between the fractional harmonic induced electromotive force and the integer harmonic induced electromotive force in the open-circuit coil, the excitation current interference in the excitation winding can be accurately identified.

Description

Technical Field

[0001] The present application relates to the technical field of relay protection for main equipment in power systems, and in particular to a method, device, equipment, and medium for identifying excitation current interference. Background Art

[0002] The brushless excitation system is a crucial component of a generator set. Reliable monitoring of its status is crucial for ensuring the safe operation of the power generation system. However, compared to brushless excitation systems, the armature winding and rectifier are located on the rotor, making direct electrical measurement difficult. Therefore, current field current protection based on the stator excitation winding is widely used in actual engineering projects. This method uses the harmonics in the excitation current to diagnose internal faults in the brushless excitation system.

[0003] However, field operation experience shows that when the frequency of the fault harmonic is the same as the frequency of the interference harmonic in the excitation current (for example, externally introduced integer interference harmonics and fault harmonics caused by armature winding short circuit), this excitation current protection method is likely to misjudge the excitation current interference as an internal fault of the excitation system, thereby affecting production safety and efficiency.

[0004] Therefore, how to effectively distinguish between armature winding short-circuit faults and integer harmonic interference in the excitation current has become an urgent problem to be solved. Summary of the Invention

[0005] Based on this, it is necessary to provide an excitation current interference identification method, device, equipment and medium to address the above technical problems, so as to accurately identify integer harmonic interference in the excitation current, so as to effectively distinguish between armature winding short-circuit faults and integer harmonic interference in the excitation current.

[0006] In a first aspect, a method for identifying excitation current interference is proposed, the method comprising: obtaining the induced electromotive force generated by the air gap magnetic field of the excitation motor on the open coil; performing harmonic decomposition on the induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; calculating a first total effective value of the fractional harmonic induced electromotive force; calculating a second total effective value of the integer harmonic induced electromotive force; taking the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; if the interference characteristic value is less than a preset threshold, it is determined that excitation current interference exists.

[0007] In an embodiment of the present application, the open-circuit coil is arranged on a magnetic pole of the stator in the excitation motor.

[0008] In an embodiment of the present application, the calculation of the first total effective value of the fractional harmonic induced electromotive force includes: calculating the total effective value of the target fractional harmonic induced electromotive force to obtain the first total effective value; the target fractional harmonic induced electromotive force includes: a fractional harmonic induced electromotive force that does not exceed a preset number and does not belong to an inherent component; the fractional harmonic induced electromotive force of the inherent component is an induced electromotive force of m / P multiple harmonics, wherein m is the number of phases of the excitation motor, and P is the number of pole pairs of the excitation motor.

[0009] In the embodiment of the present application, the preset threshold is zero.

[0010] In an embodiment of the present application, calculating the second total effective value of the integer harmonic induced electromotive force includes: calculating the total effective value of the integer harmonic induced electromotive force not exceeding a preset number to obtain the second total effective value.

[0011] In an embodiment of the present application, the method further includes: when there is excitation current interference, performing a locking operation to disable the excitation current protection function of the brushless excitation system where the excitation motor is located; if the interference characteristic value is greater than or equal to the preset threshold, performing an unlocking operation to restore the excitation current protection function of the brushless excitation system.

[0012] In the embodiment of the present application, taking the logarithm of the ratio of the first total effective value to the second total effective value to obtain the interference characteristic value includes: calculating the interference characteristic value by the following formula:

[0013] ;

[0014] in, represents the interference characteristic value, represents the first total effective value, It represents the nth harmonic induced electromotive force, and n represents the order of the harmonic induced electromotive force.

[0015] In the second aspect, a device for identifying excitation current interference is proposed, which includes: an acquisition module for acquiring the induced electromotive force generated by the air gap magnetic field of the excitation motor on the open coil; a decomposition module for performing harmonic decomposition on the induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; a first calculation module for calculating a first total effective value of the fractional harmonic induced electromotive force; a second calculation module for calculating a second total effective value of the integer harmonic induced electromotive force; a third calculation module for taking the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; and a determination module for determining that there is excitation current interference if the interference characteristic value is less than a preset threshold.

[0016] In an embodiment of the present application, the first calculation module is used to: calculate the total effective value of the target fractional harmonic induced electromotive force to obtain the first total effective value; the target fractional harmonic induced electromotive force includes: the fractional harmonic induced electromotive force that does not exceed a preset number and does not belong to the inherent component; the fractional harmonic induced electromotive force of the inherent component is the induced electromotive force of the m / P multiple harmonic, wherein m is the number of phases of the excitation motor, and P is the number of pole pairs of the excitation motor.

[0017] In the embodiment of the present application, the preset threshold is zero.

[0018] In an embodiment of the present application, the second calculation module is used to calculate the total effective value of the integer harmonic induced electromotive force not exceeding a preset number to obtain the second total effective value.

[0019] In an embodiment of the present application, the device is also used to: when there is excitation current interference, perform a locking operation to disable the excitation current protection function of the brushless excitation system where the excitation motor is located; if the interference characteristic value is greater than or equal to the preset threshold, perform an unlocking operation to restore the excitation current protection function of the brushless excitation system.

[0020] In the embodiment of the present application, the third calculation module is used to calculate the interference characteristic value using the following formula: ;in, represents the interference characteristic value, represents the first total effective value, It represents the nth harmonic induced electromotive force, and n represents the order of the harmonic induced electromotive force.

[0021] In a third aspect, an electronic device is proposed, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for identifying excitation current interference described in any one of the above embodiments is implemented.

[0022] In a fourth aspect, a computer-readable storage medium is proposed, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the excitation current interference identification method described in any of the above embodiments is implemented.

[0023] In summary, the present application proposes a method, device, equipment and medium for identifying excitation current interference. The method first obtains the induced electromotive force generated by the air gap magnetic field of the excitation motor on the open coil; performs harmonic decomposition on the obtained induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; calculates the first total effective value of the fractional harmonic induced electromotive force; calculates the second total effective value of the integer harmonic induced electromotive force; takes the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; if the interference characteristic value is less than a preset threshold, it is determined that excitation current interference exists. In the present application, an open-circuit coil is set in the air-gap magnetic field of the excitation motor to sense the changes in the air-gap magnetic flux. Regardless of whether the armature winding is normal or faulty, the reaction magnetic field of the armature winding rotates around the open-circuit coil, and the electromotive force induced in the open-circuit coil is a fractional harmonic induced electromotive force. When there is an integer-order interfering harmonic current in the excitation winding, a larger integer-order harmonic induced electromotive force will be induced in the open-circuit coil. Therefore, based on the relative change between the fractional-order harmonic induced electromotive force and the integer-order harmonic induced electromotive force in the open-circuit coil, it is possible to accurately identify whether there is integer-order harmonic interference in the excitation current, thereby effectively distinguishing between an armature winding short-circuit fault and integer-order harmonic interference in the excitation current. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0025] Figure 1 is a flow chart of a method for identifying excitation current interference according to an exemplary embodiment of the present application;

[0026] Figure 2 is a schematic diagram of a multi-phase annular brushless excitation system according to an exemplary embodiment of the present application;

[0027] Figure 3 is a schematic diagram showing the position of an open-circuit coil according to another exemplary embodiment of the present application;

[0028] Figure 4 1 is an excitation current waveform with added interference harmonics according to an exemplary embodiment of the present application;

[0029] Figure 5 yes Figure 4 The harmonic results corresponding to the excitation current waveform shown;

[0030] Figure 61 is an excitation current waveform with added interference harmonics according to another exemplary embodiment of the present application;

[0031] Figure 7 yes Figure 6 The harmonic results corresponding to the excitation current waveform shown;

[0032] Figure 8 1 is an induced electromotive force waveform of an open-circuit coil when an interfering harmonic is added according to an exemplary embodiment of the present application;

[0033] Figure 9 yes Figure 8 The harmonic results corresponding to the induced electromotive force waveform shown;

[0034] Figure 10 1 is an induced electromotive force waveform of an open-circuit coil when an interfering harmonic is added according to another exemplary embodiment of the present application;

[0035] Figure 11 yes Figure 10 The harmonic results corresponding to the induced electromotive force waveform shown;

[0036] Figure 12 Response diagrams of the traditional excitation current protection mechanism and the air gap flux protection mechanism based on the excitation current interference identification method of the present application to excitation interference;

[0037] Figure 13 is a schematic block diagram of an excitation current interference identification device according to an exemplary embodiment of the present application;

[0038] Figure 14 It is a schematic block diagram of an electronic device according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. The embodiments described with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be understood as limiting this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0040] The excitation current interference identification method proposed in this application can be applied to a multi-phase toroidal brushless excitation system. By analyzing the changes in the air gap magnetic flux of the excitation system, it can detect and identify whether there is integer harmonic interference in the excitation current of the brushless excitation system, so as to avoid the excitation current protection mechanism from misjudging the integer harmonic interference as an internal fault of the excitation system.

[0041] Figure 1 The figure is a flow chart of a method for identifying excitation current interference according to an exemplary embodiment of the present application.

[0042] S101, obtaining the induced electromotive force generated on the open-circuit coil by the air gap magnetic field of the excitation motor.

[0043] As a major part of the excitation system, the excitation motor is used to provide the main generator with excitation current for generating a magnetic field, so that the required magnetic field is formed between the stator and rotor of the main generator, enabling the main generator to generate electricity normally.

[0044] Similarly, the excitation motor is mainly composed of two parts: the stator and the rotor. The stator winding transmits the excitation current required by the excitation system. The excitation current is used to generate a magnetic field in the air gap between the stator and the rotor of the excitation motor. The rotor rotates under the action of this magnetic field and induces the excitation current output to the main generator.

[0045] like Figure 2 The figure shows a schematic diagram of a multi-phase annular brushless excitation system. The system includes a multi-phase brushless exciter and a main generator. The rotating part of the multi-phase brushless exciter includes armature windings P1-Pm, for example, Figure 2 The armature windings P1, P2, P3, P4, P5, P6, P7, ..., Pm-1, Pm are arranged in a ring. A multi-phase brushless exciter field winding is located outside the armature winding. The excitation current input to the multi-phase brushless exciter is fed through a three-phase transformer and a three-phase rectifier. An automatic excitation regulator (AER) adjusts the excitation current input to the multi-phase brushless exciter field winding based on the current output by the main generator's armature winding. Each armature winding of the multi-phase brushless exciter is connected to the main generator's rotor (i.e., the main generator's excitation winding) through a fuse and a rectifier, outputting excitation current to the rotor. The armature winding is located outside the main generator's excitation winding, inducing current to generate electricity.

[0046] It should be noted that the excitation current interference identification method proposed in the embodiment of the present application is used to identify whether there is integer harmonic interference in the excitation current in the stator winding (i.e., excitation winding) of an excitation motor (for example, the above-mentioned multi-phase brushless exciter).

[0047] In an excitation motor, a magnetic field is generated in the air gap between the stator and the rotor. For the convenience of description, this embodiment refers to it as an air gap magnetic field.

[0048] An open coil can be set in the air gap magnetic field. The open coil can induce the magnetic flux change of the air gap magnetic field, thereby generating an induced electromotive force. However, since the open coil does not form a loop, there is no current in the open coil.

[0049] In some embodiments, the induced electromotive force in the open-circuit coil can be measured using a voltmeter, or by using an oscilloscope or other methods to obtain the induced electromotive force, which is not limited in this application.

[0050] In some embodiments, after the induced electromotive force in the open-circuit coil is obtained, the obtained induced electromotive force may be further filtered to reduce fluctuations and glitches in the induced electromotive force signal and extract a stable electromotive force signal for subsequent processing.

[0051] In some embodiments, the open coil may be disposed on a magnetic pole of a stator in an exciter motor.

[0052] like Figure 3 As shown in the figure, taking the 11-phase ring brushless excitation system as an example, the stator of the excitation motor serves as the excitation winding and the rotor serves as the armature winding. The stator has a total of 5 pairs of poles, with 90 turns per pole. A 10-turn open-circuit coil with a cross-sectional area of 1.23 mm² is installed on one of the magnetic poles, as shown in the figure. Figure 3 As shown in the figure, the air gap flux data of the excitation motor is extracted by analyzing the induced electromotive force of the open coil. The open coil is designed as an open-circuit structure without any operating current, so it does not affect the normal operation of the excitation motor. During normal operation, the excitation current in the excitation motor's excitation winding and the armature current in the excitation motor's armature winding generate a magnetic field in the air gap. The open coil is affected by this magnetic field, and when the magnetic flux passing through the open coil changes, the open coil can induce an induced electromotive force.

[0053] S102, performing harmonic decomposition on the induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force.

[0054] Frequency domain feature extraction is performed on the induced electromotive force obtained in the above step S101 to decompose the induced electromotive force at different frequencies. Based on the relationship with the fundamental frequency, the induced electromotive force can be divided into fractional harmonic induced electromotive force and integer harmonic induced electromotive force.

[0055] For example, the induced electromotive force signal acquired in step S101 is subjected to Fourier decomposition to extract the fractional harmonic induced electromotive force and the integer harmonic induced electromotive force.

[0056] S103, calculating a first total effective value of the fractional harmonic induced electromotive force.

[0057] Exemplarily, the first total effective value may be obtained by adding up the effective values of all fractional harmonic induced electromotive forces.

[0058] In some embodiments, the first total effective value of the fractional harmonic induced electromotive force may also be calculated by the following steps:

[0059] Calculating the total effective value of the target fractional harmonic induced electromotive force to obtain the first total effective value;

[0060] The target fractional harmonic induced electromotive force includes: a fractional harmonic induced electromotive force that does not exceed a preset order and does not belong to an inherent component; the fractional harmonic induced electromotive force of the inherent component is an induced electromotive force of a harmonic multiple of m / P, wherein m is the number of phases of the excitation motor and P is the number of pole pairs of the excitation motor.

[0061] For example, the first total effective value can be calculated by the following formula:

[0062] ;

[0063] in, represents the first total effective value, and Ui is the effective value of the i-th harmonic induced electromotive force in the open-circuit coil. Here, i is not an integer, does not exceed a preset number, and is not a multiple of m / P. For example, when m=11 and P=5, i≠1, 2, 11 / 5, 3, 4, 22 / 5, etc. The specific value of the preset number can be set as needed and is not limited by this application.

[0064] In this embodiment, the inherent component of the electromotive force that can always be induced by the open coil is removed when calculating the first total effective value, so that the magnitude of the first total effective value can accurately reflect the changes in the fractional harmonics in the air gap magnetic flux.

[0065] S104, calculating the second total effective value of the integer harmonic induced electromotive force.

[0066] Exemplarily, the first total effective value may be obtained by adding up the effective values of all integer harmonic induced electromotive forces.

[0067] In some embodiments, the second total effective value of the integer harmonic induced electromotive force can also be calculated by the following steps:

[0068] The total effective value of the integer harmonic induced electromotive force not exceeding a preset number is calculated to obtain the second total effective value.

[0069] For example, the second total effective value is calculated by the following formula:

[0070] ;

[0071] in, represents the second total effective value, It represents the effective value of the nth harmonic induced electromotive force, where n represents the order of the harmonic induced electromotive force, and the value of n can be an integer in [1, 6].

[0072] S105: Taking the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value.

[0073] For example, the interference characteristic value can be calculated by the following formula:

[0074] ;

[0075] in, represents the interference characteristic value, represents the first total effective value, It represents the nth harmonic induced electromotive force, n represents the order of the harmonic induced electromotive force, where n is a positive integer.

[0076] By taking the logarithm of the ratio between the first and second total effective values, we can use this logarithm to characterize the relative change between the first and second total effective values, making it easier to see the relative difference between the two, rather than just the absolute difference. This interference characteristic value allows us to better observe the relative changes in fractional and integer harmonics in the air gap flux, improving the accuracy of interference identification.

[0077] S106: If the interference characteristic value is less than a preset threshold, it is determined that there is excitation current interference.

[0078] In some embodiments, the preset threshold may be zero, that is, when the interference characteristic value is less than zero, it is determined that interference exists in the excitation current.

[0079] For ease of understanding, the principle of the 11-phase ring brushless excitation system is explained as an example:

[0080] The open-circuit coil is set on a magnetic pole of the stator, so the stator excitation winding is stationary relative to the open-circuit coil. The stable magnetic field of the stator excitation winding in normal operation will not induce an electromotive force on the open-circuit coil, while the armature reaction magnetic field rotates relative to the open-circuit coil, and will induce a harmonic induced electromotive force on the open-circuit coil under normal and fault conditions. The μ-order harmonic current of each phase armature winding will generate a v-order harmonic magnetic field in space, and the distribution of the spatial magnetic field generated by the k-phase armature winding along the rotor circumference is It can be expressed as:

[0081] (1)

[0082] Where, is the number of parallel turns of one-phase armature winding, is the winding coefficient of the one-phase armature winding of the excitation motor, μ is the number of current time harmonics, ω is the angular velocity, t is the time, P is the number of pole pairs, is the mechanical angle (radian) between two adjacent armature windings, λ is the air gap permeability coefficient, is the effective value of the μth harmonic current, γ is the electrical angle along the circumferential direction of the rotor, k is the phase number corresponding to the armature winding, and v is the number of harmonic magnetic fields generated by the μth harmonic current of the armature winding in the air gap space.

[0083] Among them, γ and stator space coordinates The following relationship exists:

[0084] (2)

[0085] Where γ is the electrical angle along the circumference of the rotor, is the stator space coordinate, ω is the angular velocity, and t is the time.

[0086] Substituting Equation (2) into Equation (1) and synthesizing the armature reaction magnetic field of each phase, the time-space expression of the spatial synthetic armature reaction magnetic field of the excitation motor relative to the stator coordinate can be obtained as follows:

[0087] (3)

[0088] Where, Represents the magnetic induction intensity of the spatial synthetic armature reaction magnetic field, Represents the positive and negative rotating components of the magnetic induction intensity of the spatially synthesized armature reaction field. The positive rotating component aligns with the direction of rotation of the excitation motor rotor, while the negative rotating component rotates in the opposite direction. It should be noted that the other symbols in this formula have the same meaning as in the preceding formula and are not repeated here.

[0089] The open-circuit coil is installed on the stator excitation winding, and its coordinate position on the stator remains unchanged. Therefore, when the air gap flux is measured with the open-circuit coil, the induced electromotive force is the derivative of the air gap flux with respect to time:

[0090] (4)

[0091] Where, is the number of turns of the open-circuit coil, is the cross-sectional area of the open-circuit coil, Represents the effective value of the induced electromotive force of the open-circuit coil. It should be noted that the other symbols in this formula have the same meaning as the same symbols in the above formula and will not be repeated here.

[0092] Combining equations (3) and (4), it can be seen that the open-circuit coil will induce a (μ±v) subharmonic induced electromotive force.

[0093] It is necessary to further explain that: 1) The spatial harmonics of the magnetic field during normal operation , used to express the adjustment coefficient between magnetic field harmonics and current harmonics. Therefore, since m and P do not have a common divisor, It is often in fractional form, so the induced electromotive force on the open-circuit coil presents fractional harmonic characteristics, that is, the induction result is fractional harmonic electromotive force;

[0094] 2) When an internal fault occurs in the excitation motor, the armature reaction magnetic field space harmonic v=n / P (n is an integer and n is not a multiple of P, for example, n=1, 2,..., n≠2P, 4P,...) times. After the fault, the open-circuit coil will also induce a (μ±v)th harmonic electromotive force, that is, a fractional harmonic induced electromotive force.

[0095] Since the open-circuit coil is an open-circuit structure, it does not induce harmonic currents and therefore does not affect the air gap magnetic field of the excitation motor. However, during normal operation, the excitation winding is a closed circuit, and during a fault, the excitation winding still flows with DC current, resulting in the presence of odd-order harmonic magnetic fields consistent with normal operation. In addition, the rotating armature magnetic field generated by the short-circuited armature winding after a fault will also induce a fault electromotive force and fault harmonic currents in the excitation winding, which will counteract the flux changes caused by the fault current.

[0096] The excitation winding is composed of 2P poles connected in series. The induced electromotive force on the excitation winding is actually the superposition of the induced electromotive force of the 2P pole coils. The open-circuit coil of the present invention is arranged on one magnetic pole of the excitation winding. Assuming it is the first magnetic pole, the induced electromotive force of the space magnetic field on the first magnetic pole is measured, that is, The above analysis shows that under normal conditions and armature winding short-circuit faults, the open-circuit coil will induce a (μ±v) subharmonic induced electromotive force. The electrical angle between adjacent magnetic poles is π, and the winding directions are opposite. The electromotive force induced on the entire excitation winding is for:

[0097] (5)

[0098] In the formula, k1 represents the number of magnetic poles. The other symbols in this formula have the same meaning as the same symbols in the above formula, and will not be repeated here. It can be seen that only when v is an odd number, It is not zero. Therefore, whether the brushless excitation system is operating normally or experiencing an internal fault, only integer harmonic currents are induced in the excitation winding, not fractional harmonic currents. These harmonic currents will affect the spatial magnetic field characteristics because they counteract the flux linkage changes of the v-order magnetic field generated by the fault current, while an open-circuited coil measures the flux changes through the magnetic poles. Therefore, the integer harmonic content in the open-circuited coil will not change much, or will remain essentially unchanged. Therefore, the fault component of the electromotive force induced by the open-circuited coil is mainly the fractional harmonic EMF.

[0099] When the excitation current in the excitation winding is subject to harmonic interference, the internal magnetic field does not induce fractional harmonic currents in the excitation winding. Therefore, traditional excitation current protection methods and mechanisms can identify interference containing fractional harmonic currents. However, if the frequency of the interfering harmonics matches the frequency of the fault harmonic current, the excitation current protection mechanism will malfunction. Therefore, the open-circuit coil mainly identifies the second type of interference, namely, integer-order interfering harmonics.

[0100] The open-circuit coil is directly installed on one of the magnetic poles of the excitation winding. The magnetic flux generated by the interference harmonics in the excitation winding will directly affect the However, the magnetic field generated by the excitation current does not rotate relative to the open-circuited coil. Therefore, the DC component of the excitation current will not induce an electromotive force in the open-circuited coil. The interfering harmonic current in the excitation winding will only induce a harmonic electromotive force in the open-circuited coil that is consistent with the interfering harmonic frequency. Therefore, the integer-order interfering harmonic current in the excitation current will not induce fractional harmonic electromotive forces in the open-circuited coil, but will only induce very obvious integer-order harmonic electromotive forces in the open-circuited coil. Based on this characteristic, it is completely possible to distinguish whether the excitation current is disturbed or the armature winding is short-circuited.

[0101] Therefore, the present invention primarily monitors and utilizes the fractional harmonic EMF of the open-circuit coil signal, minus the inherent component. Furthermore, since the integer-order induced EMF within the open-circuit coil is essentially zero during normal and fault conditions, and only when subjected to excitation interference does the open-circuit coil exhibit larger integer-order harmonic EMFs, the present invention utilizes the ratio of the fractional to integer harmonic EMFs to accurately distinguish between faults and interference.

[0102] Under normal operation and armature winding short-circuit faults, the interference characteristic value Bdet will be greater than 0dB. When the detection coil is disturbed by the excitation current, Udet is very small, while the effective value of the integer harmonic induced electromotive force is large, and Bdet will be significantly reduced. Because the integer harmonic induced electromotive force is extremely small under normal operation and armature winding short-circuit faults, the Bdet threshold value can be set to 0dB. Based on the value of Bdet, the direct impact of excitation interference harmonics can be avoided. This method complements the existing excitation current protection mechanism. The existing excitation current protection mechanism can identify interference containing fractional harmonics, while the open-circuit coil is immune to interference containing only integer harmonic currents, greatly improving the reliability of protection diagnosis.

[0103] In summary, the excitation current interference identification method proposed in this application first obtains the induced electromotive force generated by the air gap magnetic field of the excitation motor on the open coil; performs harmonic decomposition on the obtained induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; calculates the first total effective value of the fractional harmonic induced electromotive force; calculates the second total effective value of the integer harmonic induced electromotive force; takes the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; if the interference characteristic value is less than a preset threshold, it is determined that excitation current interference exists. In the present application, an open-circuit coil is set in the air-gap magnetic field of the excitation motor to sense the changes in the air-gap magnetic flux. Regardless of whether the armature winding is normal or faulty, the reaction magnetic field of the armature winding rotates around the open-circuit coil, and the electromotive force induced in the open-circuit coil is a fractional harmonic induced electromotive force. When there is an integer-order interfering harmonic current in the excitation winding, a larger integer-order harmonic induced electromotive force will be induced in the open-circuit coil. Therefore, based on the relative change between the fractional-order harmonic induced electromotive force and the integer-order harmonic induced electromotive force in the open-circuit coil, it is possible to accurately identify whether there is integer-order harmonic interference in the excitation current, thereby effectively distinguishing between an armature winding short-circuit fault and integer-order harmonic interference in the excitation current.

[0104] To verify the effectiveness of the proposed method, AC components at frequencies of fs (80 Hz) and 2fs (160 Hz) were added to the normal operating excitation current to test the proposed method's immunity to harmonic interference from the excitation current. During normal operation, the excitation current was approximately 2.5 A. The added 80 Hz harmonic current had an effective value of 0.19 A, and the 160 Hz harmonic current had an effective value of 0.1 A. Figure 4-Figure 7 The excitation current waveforms and harmonic results after adding interference harmonics of different frequencies are shown. It can be seen that the harmonic characteristics of the excitation current after interference are consistent with those during the fault, exhibiting integer harmonic characteristics. Traditional excitation current protection methods are completely unable to distinguish these harmonics and would mistakenly interpret the interference as an armature winding short-circuit fault, triggering a false protection operation.

[0105] However, no fractional harmonic electromotive force will appear on the open coil. Figure 8 and Figure 9 As shown in Figure 1, the induced electromotive force waveform and harmonic results of the open-circuit coil are when the excitation current is interfered by the harmonics of fs and 2fs. Figure 10 and 11 Figure 2 shows the induced EMF waveform and harmonic results of an open-circuited coil when the excitation current is disturbed by a 2fs harmonic. It can be seen that in addition to the 11 / 5 and 22 / 5 natural harmonic EMFs present during normal operation, the open-circuited coil also contains very large integer harmonic EMFs that coincide with the interfering harmonic frequency. This is the result of the induction of the interfering harmonics in the excitation current on the open-circuited coil, while it contains essentially no fractional harmonic EMFs.

[0106] When the excitation current is disturbed by 2fs harmonic, the excitation current characteristic quantity (i.e., Figure 12 The total effective value in) and the open-circuit coil Bdet (i.e., Figure 12 The change of the normalized amplitude in Figure 12 As shown in the figure, the traditional excitation current protection mechanism can malfunction under interference. However, the value of Bdet decreases significantly. At this point, the air gap flux protection mechanism based on the excitation current protection method of the present application can lock the excitation current protection function to prevent malfunction. Therefore, the method proposed in this invention can effectively immunize against excitation harmonic interference.

[0107] In some embodiments, the method may further include the following steps:

[0108] When there is excitation current interference, a locking operation is performed to disable the excitation current protection function of the brushless excitation system where the excitation motor is located; if the interference characteristic value is greater than or equal to the preset threshold, an unlocking operation is performed to restore the excitation current protection function of the brushless excitation system.

[0109] The excitation current protection function in this embodiment can be implemented through a traditional excitation current protection mechanism. On this basis, the excitation current interference method proposed in this application is applied in real time to determine whether there is excitation current interference in the stator winding. When excitation current interference exists, the lock is promptly executed to disable the excitation current protection function, thereby preventing the excitation current protection function from misjudging the excitation current interference as an internal fault of the excitation motor and triggering a shutdown. When the determined interference characteristic value is greater than or equal to the preset threshold, it can be determined that there is no excitation interference. At this time, the excitation current protection function can be unlocked to detect internal faults of the excitation motor based on this function. In this way, false protection operations caused by excitation current interference can be effectively avoided.

[0110] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0111] Figure 13 FIG. 1 is a block diagram of an excitation current interference identification device according to an exemplary embodiment of the present application. Figure 13 As shown, the apparatus 1300 includes: an acquisition module 1301 , a decomposition module 1302 , a first calculation module 1303 , a second calculation module 1304 , a third calculation module 1305 and a determination module 1306 .

[0112] An acquisition module 1301 is used to acquire the induced electromotive force generated on the open-circuit coil by the air gap magnetic field of the excitation motor;

[0113] A decomposition module 1302 is configured to perform harmonic decomposition on the induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force;

[0114] A first calculation module 1303 is used to calculate a first total effective value of the fractional harmonic induced electromotive force;

[0115] A second calculation module 1304 is configured to calculate a second total effective value of the integer harmonic induced electromotive force;

[0116] A third calculation module 1305 is configured to obtain an interference characteristic value by taking a logarithm of a ratio of the first total effective value to the second total effective value;

[0117] The determination module 1306 is configured to determine that there is excitation current interference if the interference characteristic value is less than a preset threshold.

[0118] In some embodiments, the first computing module is configured to:

[0119] Calculating the total effective value of the target fractional harmonic induced electromotive force to obtain the first total effective value;

[0120] The target fractional harmonic induced electromotive force includes: a fractional harmonic induced electromotive force that does not exceed a preset number and does not belong to an inherent component;

[0121] The fractional harmonic induced electromotive force of the inherent component is the induced electromotive force of the m / P multiple harmonic, wherein m is the number of phases of the excitation motor, and P is the number of pole pairs of the excitation motor.

[0122] In the embodiment of the present application, the preset threshold is zero.

[0123] In some embodiments, the second computing module is configured to:

[0124] The total effective value of the integer harmonic induced electromotive force not exceeding a preset number is calculated to obtain the second total effective value.

[0125] In some embodiments, the device is further configured to:

[0126] When there is an excitation current interference, a locking operation is performed to disable the excitation current protection function of the brushless excitation system where the excitation motor is located;

[0127] If the interference characteristic value is greater than or equal to the preset threshold, an unlocking operation is performed to restore the excitation current protection function of the brushless excitation system.

[0128] In some embodiments, the third computing module is configured to:

[0129] The interference characteristic value is calculated by the following formula:

[0130] ;

[0131] in, represents the interference characteristic value, represents the first total effective value, It represents the nth harmonic induced electromotive force, and n represents the order of the harmonic induced electromotive force.

[0132] In summary, the excitation current interference identification device proposed in this application first obtains the induced electromotive force generated by the air gap magnetic field of the excitation motor on the open coil; performs harmonic decomposition on the obtained induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; calculates the first total effective value of the fractional harmonic induced electromotive force; calculates the second total effective value of the integer harmonic induced electromotive force; takes the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; if the interference characteristic value is less than a preset threshold value, it is determined that excitation current interference exists. In the present application, an open-circuit coil is set in the air-gap magnetic field of the excitation motor to sense the changes in the air-gap magnetic flux. Regardless of whether the armature winding is normal or faulty, the reaction magnetic field of the armature winding rotates around the open-circuit coil, and the electromotive force induced in the open-circuit coil is a fractional harmonic induced electromotive force. When there is an interfering harmonic current in the excitation winding, a larger integer harmonic electromotive force will be induced in the open-circuit coil. Therefore, based on the relative change between the fractional harmonic induced electromotive force and the integer harmonic induced electromotive force in the open-circuit coil, the excitation current interference in the excitation winding can be accurately identified.

[0133] To implement the above embodiment, the embodiment of the present application also proposes an electronic device 1400, including a memory 1401, a processor 1402 and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the excitation current interference identification method in the above embodiment are implemented.

[0134] To implement the above embodiment, the embodiment of the present application further proposes a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps of the excitation current interference identification method are implemented.

[0135] Those skilled in the art will understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0136] Those skilled in the art will clearly understand that for the sake of convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0137] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for identifying excitation current interference, characterized in that: The method comprises: Obtain the induced electromotive force generated by the air gap magnetic field of the excitation motor on the open-circuit coil; Performing harmonic decomposition on the induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; Calculating a first total effective value of the fractional harmonic induced electromotive force; Calculating a second total effective value of the integer harmonic induced electromotive force; Taking the logarithm of the ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; If the interference characteristic value is smaller than a preset threshold, it is determined that excitation current interference exists.

2. The method according to claim 1, characterized in that The open coil is arranged on a magnetic pole of a stator in the excitation motor.

3. The method according to claim 2, characterized in that Calculating the first total effective value of the fractional harmonic induced electromotive force includes: Calculating the total effective value of the target fractional harmonic induced electromotive force to obtain the first total effective value; The target fractional harmonic induced electromotive force includes: a fractional harmonic induced electromotive force that does not exceed a preset number and does not belong to an inherent component; The fractional harmonic induced electromotive force of the inherent component is the induced electromotive force of the m / P multiple harmonic, wherein m is the number of phases of the excitation motor, and P is the number of pole pairs of the excitation motor.

4. The method according to claim 3, characterized in that The preset threshold is zero.

5. The method according to claim 1, wherein The calculating the second total effective value of the integer harmonic induced electromotive force comprises: The total effective value of the integer harmonic induced electromotive force not exceeding a preset number is calculated to obtain the second total effective value.

6. The method according to any one of claims 1 to 5, characterized in that The method further comprises: When there is an excitation current interference, a locking operation is performed to disable the excitation current protection function of the brushless excitation system where the excitation motor is located; If the interference characteristic value is greater than or equal to the preset threshold, an unlocking operation is performed to restore the excitation current protection function of the brushless excitation system.

7. The method according to any one of claims 1 to 5, characterized in that Taking the logarithm of the ratio of the first total effective value to the second total effective value to obtain the interference characteristic value includes: The interference characteristic value is calculated by the following formula: ； in, represents the interference characteristic value, represents the first total effective value, It represents the effective value of the nth harmonic induced electromotive force, where n represents the order of the harmonic induced electromotive force and is an integer.

8. An excitation current interference identification device, characterized in that: The device comprises: An acquisition module is used to acquire the induced electromotive force generated on the open-circuit coil by the air gap magnetic field of the excitation motor; A decomposition module is used to perform harmonic decomposition on the induced electromotive force to obtain fractional harmonic induced electromotive force and integer harmonic induced electromotive force; A first calculation module is used to calculate a first total effective value of the fractional harmonic induced electromotive force; A second calculation module is used to calculate the second total effective value of the integer harmonic induced electromotive force; a third calculation module, configured to take a logarithm of a ratio of the first total effective value to the second total effective value to obtain an interference characteristic value; The determination module is configured to determine that there is excitation current interference if the interference characteristic value is less than a preset threshold.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the excitation current interference identification method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the excitation current interference identification method according to any one of claims 1 to 7 is implemented.

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