Diode open circuit fault detection method and device for multi-phase brushless exciter

Abstract

The present invention relates to a diode open circuit fault detection method and device for a multi-phase brushless exciter, and the diode open circuit fault detection method comprises: a sampling step: real-time sampling of the excitation current of the stator excitation winding; a processing step: filtering the sampled excitation current to obtain a processed current signal; an analysis step: extracting the time domain characteristics of the current signal, and judging whether a diode open circuit fault occurs based on the extracted time domain characteristics. By implementing the technical solution of the present invention, this online detection method is simple, effective, and has a high accuracy rate, which ensures the power generation safety of the unit and improves the operation reliability of the unit.

Description

Technical Field

[0001] The invention relates to the field of power systems, and in particular to a diode open circuit fault detection method and device for a multi-phase brushless exciter. Background Art

[0002] The excitation system is an important component of large-scale generators. An excitation system with excellent performance and high reliability is the basis for ensuring the safety of generators and the stable operation of power systems. Compared with static excitation, the brushless excitation system eliminates the carbon brushes and slip rings of the generator, significantly improving the reliability of the excitation system and becoming the preferred excitation method for large-capacity nuclear power units. The multi-phase brushless excitation system can not only reduce the requirements of the high-power excitation system for the capacity of a single diode, but also improve the quality of the rectified voltage and the fault tolerance of the system.

[0003] In the multi-phase brushless excitation system, since the rectifier diode is in a high-speed rotating state and only one fuse is installed at the outlet of each bridge arm, open circuit faults caused by diode damage often occur in actual operation. In the early stage of open circuit fault, the exciter can still provide normal current to the main generator, but if the fault is allowed to continue to deteriorate, it will seriously affect the normal operation of the main generator and cause serious consequences.

[0004] For rotating rectifier failures, the brushless excitation systems currently operating on site generally use the DNC (Diode Non-conduction Detection System) system that is standard when the rotating rectifier leaves the factory for monitoring. Its false operation and refusal to operate also occur frequently on site (especially for units with long operating time). Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and device for detecting a diode open circuit fault of a multi-phase brushless exciter in view of the defect that the accuracy of diode open circuit fault detection in the prior art is low.

[0006] The technical solution adopted by the present invention to solve the technical problem is: constructing a diode open circuit fault detection method for a multi-phase brushless exciter, comprising:

[0007] Sampling steps: real-time sampling of the excitation current of the stator excitation winding;

[0008] Processing steps: filtering the sampled excitation current to obtain a processed current signal;

[0009] Analysis step: extracting the time domain features of the current signal, and determining whether a diode open circuit fault occurs based on the extracted time domain features.

[0010] Preferably, the analyzing step comprises:

[0011] Step S31. Calculate the average current value of the current signal in one electrical cycle;

[0012] Step S32. According to the average current value, determine whether the current signal has a fault distortion point within the electrical cycle. If so, execute step S33;

[0013] Step S33. Determine the number and position of the fault distortion points in the electrical cycle, and determine the fault type and fault position according to the number and position, wherein the fault type includes: diode-tube open circuit fault; diode-phase open circuit fault.

[0014] Preferably, the step S33 comprises:

[0015] It is determined whether the number of fault distortion points in the electrical cycle is 1. If so, it is determined that a diode open circuit fault occurs.

[0016] Preferably, the step S33 comprises:

[0017] Determine whether the number of fault distortion points in the electrical cycle is 2;

[0018] If the number of fault distortion points in the electrical cycle is 2, it is determined whether the time interval between two fault distortion points in the electrical cycle is half of the electrical cycle. If so, it is determined that a single-phase open-circuit fault of the diode occurs.

[0019] Preferably, the step S32 includes:

[0020] Determine whether the current signal has a fault data segment within the electrical cycle, wherein the fault data segment satisfies: a duration in which the current value in the current signal is less than the average current value is greater than a preset time;

[0021] If there is a fault data segment, determine the minimum value point in the fault data segment, and judge whether the minimum value point is within a preset range;

[0022] If it is within the preset range, the minimum value point is taken as the fault distortion point.

[0023] Preferably, whether the minimum value point is within a preset range is determined according to the following formula:

[0024]

[0025] Among them, i min is the minimum point, i f0 is the average current value, ξ1 and ξ2 are the preset lower threshold value and upper threshold value respectively.

[0026] The present invention also constructs a diode open circuit fault detection device for a multi-phase brushless exciter, comprising:

[0027] A sampling module is used to sample the excitation current of the stator excitation winding in real time;

[0028] A processing module, used for filtering the sampled excitation current to obtain a processed current signal;

[0029] The analysis module is used to extract the time domain features of the current signal and determine whether a diode open circuit fault occurs according to the extracted time domain features.

[0030] Preferably, the analysis module comprises:

[0031] A calculation unit, used for calculating an average current value of the current signal in one electrical cycle;

[0032] A first judgment unit, configured to judge whether the current signal has a fault distortion point within the electrical cycle according to the average current value;

[0033] The second judgment unit is used to determine the number and position of the fault distortion point in the electrical cycle when there is a fault distortion point, and determine the fault type and fault position according to the number and position, wherein the fault type includes: a diode-tube open circuit fault; a diode-phase open circuit fault.

[0034] Preferably, the second judgment unit is used to judge whether the number of fault distortion points in the electrical cycle is 1 when there is a fault distortion point, and if so, determine that a diode open circuit fault occurs.

[0035] Preferably, the second judgment unit is used to judge whether the number of fault distortion points in the electrical cycle is 2 when there is a fault distortion point, and when the number of fault distortion points in the electrical cycle is 2, judge whether the time interval between two fault distortion points in the electrical cycle is half of the electrical cycle. If so, it is determined that a single-phase open circuit fault of the diode has occurred.

[0036] Preferably, the first judgment unit is used to determine whether there is a fault data segment in the current signal within the electrical cycle, and when there is a fault data segment, determine the minimum point in the fault data segment, and determine whether the minimum point is within a preset range. If it is within the preset range, the minimum point is used as the fault distortion point; wherein the fault data segment satisfies: the duration of the current value in the current signal being less than the average current value is greater than the preset time.

[0037] The technical solution provided by the present invention determines whether a diode open circuit fault occurs by sampling the excitation current of the stator excitation winding and performing time domain characteristic analysis. This online detection method is simple, effective, and highly accurate, which ensures the power generation safety of the unit and improves the operating reliability of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0039] Figure 1 It is a flow chart of a first embodiment of a method for detecting a diode open circuit fault of a multi-phase brushless exciter of the present invention;

[0040] Figure 2 It is a flow chart of the first embodiment of the analysis step in the diode open circuit fault detection method of the multi-phase brushless exciter of the present invention;

[0041] Figure 3 It is a schematic diagram of the structure of the 11-phase brushless exciter and rotating rectifier;

[0042] Figure 4 yes Figure 3 Schematic diagram of the diode conduction sequence;

[0043] Figure 5 for Figure 3 Schematic diagram of the excitation current time domain waveform of the exciter in normal operation, diode-one tube open circuit fault and diode-one phase open circuit fault;

[0044] Fig. 6A , 6B They are Figure 3 The experimental waveform diagram of the excitation current of the exciter in normal operation and when one phase of the diode is open circuit fault;

[0045] Figure 7 It is a schematic diagram of extracting time domain features of excitation current signal;

[0046] Figure 8 It is a logical structure diagram of the first embodiment of the diode open circuit fault detection device of the multi-phase brushless exciter of the present invention. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Since the brushless excitation rectifier (composed of diodes) rotates together with the rotor of the exciter, the open circuit fault of the rectifier cannot be directly monitored. In view of this technical problem, the present application constructs a diode open circuit fault detection method, which collects the stator excitation current, obtains the time domain characteristics of the current according to a certain method, and judges the fault according to the time domain characteristics. The method can be used to effectively monitor and protect the diode open circuit fault of the multi-phase angle brushless exciter online.

[0049] Figure 1 1 is a flow chart of a first embodiment of a method for detecting a diode open circuit fault of a multi-phase brushless exciter according to the present invention. The method for detecting a diode open circuit fault of the first embodiment comprises the following steps:

[0050] Sampling step S10: real-time sampling of the excitation current of the stator excitation winding;

[0051] Processing step S20: filtering the sampled excitation current to obtain a processed current signal;

[0052] Analysis step S30: extracting time domain features of the current signal, and determining whether a diode open circuit fault occurs based on the extracted time domain features.

[0053] In this embodiment, it is first explained that the working principle of the brushless exciter is: when the excitation current is provided to the stator excitation winding of the exciter, its rotor armature winding will generate alternating current, and the alternating current is used to supply power to the rotor excitation winding of the main generator after passing through the rotating rectifier. When a diode open circuit fault occurs in the rotating rectifier, within an electrical cycle, for the moment when the faulty diode is not involved in the operation, the excitation current of the exciter and each armature current are consistent with the normal operation moment; for the moment when the faulty diode is involved in the operation, the armature current will be distorted, and the armature reaction magnetic field will induce harmonic potential in the stator winding, thereby affecting the time domain waveform of the stator excitation current. Therefore, it is possible to determine whether a diode open circuit fault occurs by sampling the excitation current of the stator excitation winding and analyzing the time domain characteristics. Moreover, this online detection method is simple and effective, which ensures the power generation safety of the unit and improves the operation reliability of the unit.

[0054] Further, in an optional embodiment, in combination Figure 2 , the analysis step S30 specifically includes:

[0055] Step S31. Calculate the average current value of the current signal in one electrical cycle;

[0056] Step S32. According to the average current value, determine whether the current signal has a fault distortion point within the electrical cycle. If so, execute step S33;

[0057] Step S33. Determine the number and position of the fault distortion points in the electrical cycle, and determine the fault type and fault position according to the number and position, wherein the fault type includes: diode-tube open circuit fault; diode-phase open circuit fault.

[0058] In this embodiment, since the diodes at both ends of the armature winding with the largest line voltage are turned on when the exciter is operating normally, the diode open circuit fault will only affect the working state related to it. When the faulty diode is not involved in the operation, the excitation current and each armature current of the exciter are consistent with the normal operation time. The diode open circuit fault will cause the rectifier to fail. When the exciter runs to the moment when the faulty diode is turned on, the armature current will be distorted, and the corresponding position of the excitation current time domain waveform will also be distorted for a certain period of time. Since the diodes are turned on in turn, the number and duration of distortion on the excitation current time domain waveform in the same electrical cycle are related to the number and relative position of the faulty diodes. Therefore, after obtaining the filtered excitation current signal (the relationship between current and time), the current average value within an electrical cycle is first calculated, and then it is determined whether there is a fault distortion point within the electrical cycle. If so, the fault type and fault location are determined according to the number and location of the fault distortion points.

[0059] In a specific embodiment, in step S33, it is determined whether the number of fault distortion points in the electrical cycle is 1. If so, it is determined that a diode open circuit fault occurs.

[0060] In a specific embodiment, in step S33, it is determined whether the number of fault distortion points within the electrical cycle is 2; if the number of fault distortion points within the electrical cycle is 2, it is determined whether the time interval between two fault distortion points within the electrical cycle is half of the electrical cycle, and if so, it is determined that a single-phase open circuit fault of the diode has occurred.

[0061] In a specific embodiment, step S32 includes:

[0062] Determine whether the current signal has a fault data segment within the electrical cycle, wherein the fault data segment satisfies: a duration in which the current value in the current signal is less than the average current value is greater than a preset time;

[0063] If there is a fault data segment, determine the minimum value point in the fault data segment, and judge whether the minimum value point is within a preset range;

[0064] If it is within the preset range, the minimum value point is taken as the fault distortion point.

[0065] Furthermore, whether the minimum value point is within a preset range can be determined according to the following formula:

[0066]

[0067] Among them, i min is the minimum point, i f0 is the average current value, ξ1 and ξ2 are the preset lower threshold value and upper threshold value respectively.

[0068] In this embodiment, in order to improve the accuracy of fault detection, when determining the fault distortion point, first define the duration t in the current signal s The current values ​​are all less than the average current value i f0 The data segment is the fault data segment, and then find the minimum value point i of the data segment. min , and when the following conditions are met, the minimum point is regarded as a valid fault distortion point:

[0069] t s >δ

[0070]

[0071] Among them, δ is the preset time, and the values ​​of δ, ξ1 and ξ2 should ensure that the unbalanced components under various working conditions during normal operation can be reliably avoided.

[0072] The following takes an 11-phase ring brushless exciter as an example to illustrate the diode open circuit fault detection method:

[0073] like Figure 3 As shown, in the 11-phase annular brushless exciter, the rotating rectifier adopts a full-bridge rectification method, and the two diodes corresponding to the maximum line voltage are turned on at all times. The 11-phase armature windings r1, r2, r3, r4, r5, r6, r7, r8, r9, r10, and r11 of the exciter adopt an end-to-end annular structure, and the maximum line voltage is the sum of the phase voltages of the armature windings in series. According to the arrangement of the 11-phase armature windings, the adjacent two-phase armature windings differ in space by 4π / 11 electrical angles, and the phase voltages of the adjacent two-phase armature windings also differ in time by 4π / 11 electrical angles. Assume that the phase voltage of the k-th phase armature winding is:

[0074]

[0075] Among them, U is the amplitude of the armature winding phase voltage, ω is the rotor angular frequency, t is time, and k is the number of phases (k=1, 2, ..., 11).

[0076] Moreover, the series voltage of adjacent j (j=1, 2, ..., 10) phases is:

[0077]

[0078] It can be seen from formula (2) that when j=3, the amplitude of the j-phase series voltage reaches the maximum value, that is, the three-phase series voltage is the maximum line voltage. Therefore, the two diodes corresponding to the three-phase series armature winding are turned on at every moment.

[0079] It can be seen that as time changes, the 22 diodes will be turned on in turn as the phase sequence of the synthetic maximum electromotive force changes. When the exciter is operating normally, the conduction sequence of the upper and lower bridge arm diodes of the rotating rectifier is as follows: Figure 4 shown.

[0080] When the exciter is operating normally, the diodes at both ends of the armature winding with the largest line voltage are turned on. The diode failure will only affect the related working state. When the faulty diode is not involved in the operation, the exciter's excitation current and each armature current are consistent with the normal operation. When the exciter runs to the moment when the faulty diode is turned on, the armature current will be distorted, and the corresponding position of the excitation current time domain waveform will be distorted for a certain period of time. Since the diodes are turned on in turn, the number and duration of distortion on the excitation current time domain waveform in the same electrical cycle are related to the number and relative position of the faulty diodes.

[0081] Depend on Figure 5 It can be seen that according to the conduction order of the diodes of the rotating rectifier, each diode continues to conduct for 2π / 11, and when the conduction ends, it switches to the next diode to continue conducting. From theoretical analysis, it can be seen that during normal operation, the excitation current will be modulated into 22 pulses by the diode, and since there is no fault component at this time, the excitation current will not be distorted.

[0082] When a diode opens, only the working state connected to the open diode will be affected. Figure 5 As shown in the figure, when the diode D1 fails to open circuit, the working state from point a to point f will change. According to the phase change sequence of the diodes in the figure, the diode D13 will continue to conduct until it is closed due to the reverse voltage, and then directly commutate to the diode D11. Correspondingly, the waveform of the excitation current corresponding to the point a to f segment will be distorted, and the distortion duration is equal to the conduction time of the diode D1, 2π / 11. 2π is used to represent the period of the stator excitation current, and n is used to represent the period of the stator excitation current. distortion Indicates the number of distortion points in one cycle of the stator excitation current, expressed as t distortionrepresents the duration of a distortion. Therefore, it can be obtained that when a tube open circuit fault occurs, the time domain characteristic of the stator excitation current is n distortion =1,t distortion =2π / 11.

[0083] In addition, since fuses are often used in practical projects to protect diodes from overcurrent, such as Figure 3 As shown in the figure, when the connecting fuse between the armature winding and the rotating rectifier is blown, a phase open circuit fault will occur. Since a phase diode includes an upper bridge arm diode and a lower bridge arm diode, when a phase diode has an open circuit fault, two distortions with a duration of 2π / 11 and an interval of π electrical angle will appear in the excitation current waveform. Figure 5 As shown in the figure, when the first phase fuse blows, it is equivalent to the diodes D0 and D1 having open circuit faults at the same time. Δt is used to represent the time interval between two distortions in one cycle of the stator excitation current. When a single-phase open circuit fault occurs, the time domain characteristics of the stator excitation current are:

[0084] n distortion =2,t distortion =2π / 11, Δt=π

[0085] The analysis results show that in the case of a single-phase open-circuit fault of the diode, the stator excitation current will be greatly distorted. Two distortions with a duration of 2π / 11 and a half-cycle interval will appear in one cycle of the excitation current. Since the distortion is only affected by the number and relative position of the diode faults, this time domain feature is a unique time domain feature of the single-phase open-circuit fault of the diode. Therefore, the position and interval time of the fault distortion in the excitation current time domain waveform can be used to diagnose the single-phase open-circuit fault of the diode. Extract the number of distortions n in the excitation current time domain waveform distortion , distortion duration t s The distortion interval time Δt is used as the basis for fault protection judgment, which has high reliability and provides an effective way for monitoring and protecting one-phase open-circuit fault of diode.

[0086] The effective extraction of time domain features is the prerequisite for fault diagnosis. Fig. 6A , 6B The experimental waveforms of the excitation current of the 11-phase brushless exciter in normal operation and when one phase of the diode is open circuit fault are shown. It can be found that the excitation current time domain waveform is obviously distorted after the one phase of the diode is open circuit fault. If the experimental sampling rate is 20kS / s, when a one phase of the diode is open circuit fault, the excitation current is defined as continuous t s Time less than i f0 The data segment is the fault data segment, and the minimum value point i of the data segment is found. min ,

[0087]

[0088] When the above two conditions are met at the same time, this data segment is defined as a valid distortion. It can be seen that the excitation current of the 11-phase brushless exciter contains two valid distortions in one cycle, and at the same time, it meets:

[0089] Δt=T / 2 (4)

[0090] Then the operating state of the exciter is judged: when the number of effective distortions n of the excitation current in a continuous electrical cycle distortion When it is 2 and the interval between the extreme points of the distorted waveform differs by T / 2, it is judged that a diode open-circuit fault occurs in one phase of the exciter.

[0091] If the experimental excitation fundamental frequency is 80Hz and the period is 12.5ms, based on the above time domain feature extraction method, the experimental excitation current time domain characteristics of the 11-phase brushless excitation motor prototype with a diode one-phase open circuit fault are shown in Table 1. In fact, due to the time constant of the winding inductance, t s It is larger than the theoretical value, but the number of effective distortions and Δt are consistent with the theoretical analysis.

[0092] <![CDATA[n distortion ]]> <![CDATA[t s ]]> Δt Normal operation 0 0 0 Theoretical characteristics 2 1.14ms 6.25ms Dynamic prototype experiment 2 2.20ms 6.25ms

[0093] Table 1

[0094] Through the above calculation and analysis, it is shown that the number of distortions n in the time domain waveform of the excitation current distortion , distortion duration t distortion And the distortion interval time Δt can fully reflect the characteristics brought by the diode open circuit fault, and can distinguish between the normal operation of the exciter and the diode open circuit fault. Therefore, the fault judgment method is simple and effective, and has extremely high reliability.

[0095] Figure 8 It is a logical structure diagram of the first embodiment of the diode open circuit fault detection device of the multi-phase brushless exciter of the present invention. The diode open circuit fault detection device of this embodiment includes: a sampling module 10, a processing module 20, and an analysis module 30, wherein the sampling module 10 is used to sample the excitation current of the stator excitation winding in real time; the processing module 20 is used to filter the sampled excitation current to obtain a processed current signal; the analysis module 30 is used to extract the time domain characteristics of the current signal, and determine whether a diode open circuit fault occurs based on the extracted time domain characteristics.

[0096] Furthermore, the analysis module includes: a calculation unit, a first judgment unit, and a second judgment unit, wherein the calculation unit is used to calculate the average current value of the current signal within an electrical cycle; the first judgment unit is used to judge whether there is a fault distortion point in the current signal within the electrical cycle based on the average current value; the second judgment unit is used to determine the number and position of the fault distortion points within the electrical cycle when there are fault distortion points, and determine the fault type and fault position based on the number and position, wherein the fault types include: a diode-tube open circuit fault; a diode-phase open circuit fault.

[0097] Further, the second judgment unit is used to judge whether the number of fault distortion points in the electrical cycle is 1 when there is a fault distortion point, and if so, determine that a diode open circuit fault occurs.

[0098] Furthermore, the second judgment unit is used to judge whether the number of fault distortion points within the electrical cycle is 2 when there is a fault distortion point, and when the number of fault distortion points within the electrical cycle is 2, judge whether the time interval between two fault distortion points within the electrical cycle is half of the electrical cycle. If so, it is determined that a single-phase open circuit fault of the diode has occurred.

[0099] Furthermore, the first judgment unit is used to determine whether there is a fault data segment in the current signal within the electrical cycle, and when there is a fault data segment, determine the minimum point in the fault data segment, and determine whether the minimum point is within a preset range. If it is within the preset range, the minimum point is used as a fault distortion point; wherein the fault data segment satisfies: the duration of the current value in the current signal being less than the average current value is greater than a preset time.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A method for detecting a diode open circuit fault of a multi-phase brushless exciter, characterized in that: include: Sampling steps: real-time sampling of the excitation current of the stator excitation winding; Processing steps: filtering the sampled excitation current to obtain a processed current signal; Analysis step: extracting time domain features of the current signal, and determining whether a diode open circuit fault occurs according to the extracted time domain features; The analysis steps include: Step S31. Calculate the average current value of the current signal in one electrical cycle; Step S32. According to the average current value, determine whether the current signal has a fault distortion point within the electrical cycle. If so, execute step S33; Step S33. Determine the number and position of the fault distortion points in the electrical cycle, and determine the fault type and fault position according to the number and position, wherein the fault type includes: diode-tube open circuit fault; diode-phase open circuit fault.

2. The diode open circuit fault detection method of a multi-phase brushless exciter according to claim 1, characterized in that: The step S33 comprises: It is determined whether the number of fault distortion points in the electrical cycle is 1. If so, it is determined that a diode open circuit fault occurs.

3. The diode open circuit fault detection method of a multi-phase brushless exciter according to claim 1, characterized in that: The step S33 comprises: Determine whether the number of fault distortion points in the electrical cycle is 2; If the number of fault distortion points in the electrical cycle is 2, it is determined whether the time interval between two fault distortion points in the electrical cycle is half of the electrical cycle. If so, it is determined that a single-phase open-circuit fault of the diode occurs.

4. The diode open circuit fault detection method of a multi-phase brushless exciter according to any one of claims 1 to 3, characterized in that: The step S32 comprises: Determine whether the current signal has a fault data segment within the electrical cycle, wherein the fault data segment satisfies: a duration in which the current value in the current signal is less than the average current value is greater than a preset time; If there is a fault data segment, determine the minimum value point in the fault data segment, and judge whether the minimum value point is within a preset range; If it is within the preset range, the minimum value point is taken as the fault distortion point.

5. The diode open circuit fault detection method of a multi-phase brushless exciter according to claim 4, characterized in that: Determine whether the minimum value point is within the preset range according to the following formula: in, i min is the minimum point, i f0 is the average current value, , They are respectively the preset lower threshold value and the upper threshold value.

6. A diode open circuit fault detection device for a multi-phase brushless exciter, characterized in that: include: A sampling module is used to sample the excitation current of the stator excitation winding in real time; A processing module, used for filtering the sampled excitation current to obtain a processed current signal; An analysis module, used to extract time domain features of the current signal and determine whether a diode open circuit fault occurs according to the extracted time domain features; The analysis module comprises: A calculation unit, used for calculating an average current value of the current signal in one electrical cycle; A first judgment unit, configured to judge whether the current signal has a fault distortion point within the electrical cycle according to the average current value; The second judgment unit is used to determine the number and position of the fault distortion point in the electrical cycle when there is a fault distortion point, and determine the fault type and fault position according to the number and position, wherein the fault type includes: a diode-tube open circuit fault; a diode-phase open circuit fault.

7. The diode open circuit fault detection device for a multi-phase brushless exciter according to claim 6, characterized in that: The second judgment unit is used to judge whether the number of fault distortion points in the electrical cycle is 1 when there is a fault distortion point, and if so, determine that a diode open circuit fault occurs.

8. The diode open circuit fault detection device for a multi-phase brushless exciter according to claim 6, characterized in that: The second judgment unit is used to judge whether the number of fault distortion points in the electrical cycle is 2 when there is a fault distortion point, and to judge whether the time interval between two fault distortion points in the electrical cycle is half of the electrical cycle when the number of fault distortion points in the electrical cycle is 2. If so, it is determined that a single-phase open circuit fault of the diode has occurred.

9. The diode open circuit fault detection device for a multi-phase brushless exciter according to any one of claims 6 to 8, characterized in that: The first judgment unit is used to judge whether there is a fault data segment in the current signal within the electrical cycle, and when there is a fault data segment, determine the minimum point in the fault data segment, and judge whether the minimum point is within a preset range. If it is within the preset range, the minimum point is used as the fault distortion point; wherein the fault data segment satisfies: the duration of the current value in the current signal being less than the average current value is greater than the preset time.

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