Diagnosis device for electric motor

Abstract

To detect the occurrence of a layer short with high accuracy.SOLUTION: A diagnosis device 1 comprises: a current detection circuit 5 for detecting a current of an electric motor 2; a voltage detection circuit 6 for detecting a voltage of the electric motor 2; and a processing unit 7 configured to execute various processes for diagnosing a layer short of the electric motor 2 on the basis of the current and the voltage of the electric motor 2 detected by the current detection circuit 5 and the voltage detection circuit 6. The processing unit 7 executes: an acquisition process of calculating and acquiring a negative-phase current vector based on a voltage phase by using the current of the electric motor 2 and the voltage of the electric motor 2; a setting process of setting a reference value based on the negative-phase current vector acquired during a predetermined first period in a normal state; a calculation process of calculating a difference vector, which is a difference between the negative-phase current vector acquired during operation and the reference value; and a diagnosis process of diagnosing that a layer short has occurred in the electric motor 2 when the difference vector becomes greater than or equal to a predetermined threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a diagnostic device for an electric motor.

Background Art

[0002] For example, electric motors such as induction motors are widely used as equipment in many factories, and particularly in chemical plants, power plants, etc., a large number of induction motors are being used. Conventionally, in order to monitor the states of such a large number of electric motors being used, regular maintenance such as having skilled workers perform maintenance on each one regularly has been carried out. However, against the backdrop of a shortage of skilled workers, increased efficiency and IoT implementation of equipment operation, etc., state monitoring of electric motors by sensors has been increasingly demanded.

[0003] Typical sensors include vibration sensors, thermal sensors, etc. However, in state monitoring using these sensors, there is a problem that the cost increases as the number of monitoring targets increases. Also, it is conceivable to perform state monitoring of an electric motor using a switchboard that centrally manages the operation of the electric motor, such as a control center. However, in that case, there is a problem that installation becomes difficult because the wiring increases. For such reasons, a diagnostic method that utilizes the power supply line for supplying power to the electric motor has been proposed.

[0004] One of the causes of electric motor failure is a rare short circuit where a short circuit occurs between the coils of the stator winding. Since a relatively large current flows through the short circuit part in a rare short circuit, if discovery is delayed, there is a risk of winding burnout, and therefore early detection is required. Also, when a rare short circuit occurs, the balance of the currents flowing in the three phases deteriorates due to the current flowing through the short circuit part, and the reverse-phase current increases. It is conceivable to detect a rare short circuit of the electric motor by such a reverse-phase current. However, in the method of detecting a rare short circuit by only monitoring the magnitude of the reverse-phase current, there may be a case where only the phase changes and the magnitude of the reverse-phase current does not change. As a result, the change in the reverse-phase current cannot be surely captured, and thus there was a problem that the detection accuracy of the rare short circuit could not be sufficiently increased.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, a diagnostic device for an electric motor that can accurately detect the occurrence of a rare short circuit is provided.

Means for Solving the Problems

[0007] The diagnostic device for an electric motor according to the present embodiment includes a current detection circuit that detects the current of the electric motor, a voltage detection circuit that detects the voltage of the electric motor, and a processing unit that executes various processes for diagnosing a rare short circuit of the electric motor based on the current and voltage of the electric motor detected by the current detection circuit and the voltage detection circuit. The processing unit executes an acquisition process of calculating and acquiring an inverse-phase current vector based on the voltage phase using the current of the electric motor and the voltage of the electric motor, a setting process of setting a reference value based on the inverse-phase current vector acquired during a predetermined first period in a normal state, a calculation process of calculating a difference vector that is the difference between the inverse-phase current vector acquired during operation and the reference value, and a diagnosis process of diagnosing that a rare short circuit has occurred in the electric motor when the difference vector is equal to or greater than a predetermined threshold value.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, a plurality of embodiments will be described with reference to the drawings. In each embodiment, substantially the same configurations are denoted by the same reference numerals and the description thereof is omitted. (First Embodiment) Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 7.

[0010] <Configuration of Diagnostic Device> As shown in Fig. 1, the diagnostic device 1 for an electric motor according to this embodiment diagnoses the electric motor 2 for driving a mechanical equipment (not shown). In the following, the diagnostic device for the electric motor may be abbreviated as the diagnostic device. In the diagnostic device 1, a transformer 4 for detecting the load current of the main circuit 3 is provided in the main circuit 3 of the power supply drawn from the power system.

[0011] The transformer 4 is, for example, a current transformer or the like. Although not shown in the figure, a wiring circuit breaker and an electromagnetic contactor are also provided in the main circuit 3. Further, the main circuit 3 is connected to the electric motor 2 which is a load. The electric motor 2 is, for example, a three-phase induction motor. In this case, the three phases of the electric motor 2 are assumed to be the R phase, the S phase, and the T phase.

[0012] The diagnostic device 1 includes a current detection circuit 5 for detecting the current of the electric motor 2, a voltage detection circuit 6 for detecting the voltage of the electric motor 2, a processing unit 7, a display unit 8, a communication circuit 9, and the like. The current detection circuit 5 converts the load current of the main circuit 3 detected via the transformer 4 into a predetermined signal such as the phase current or magnitude of the electric motor 2 to detect the current of the electric motor 2 and outputs it to the processing unit 7. The voltage detection circuit 6 detects the line voltage of the main circuit 3 connected to the electric motor 2, converts it into a predetermined signal such as the phase voltage or magnitude of the electric motor 2 to detect the voltage of the electric motor 2, and outputs it to the processing unit 7.

[0013] Each output of the current detection circuit 5 and the voltage detection circuit 6 is input to the processing unit 7. The processing unit 7 can execute various processes for diagnosing the rare short circuit of the electric motor 2 based on the current and voltage of the electric motor 2 detected by the current detection circuit 5 and the voltage detection circuit 6. The processing unit 7 is configured by an arithmetic processing device including a CPU, a RAM, a ROM, and the like.

[0014] The processing unit 7 includes functional blocks such as an acquisition processing unit 11, a setting processing unit 12, a calculation processing unit 13, and a diagnosis processing unit 14. Each of these functional blocks is realized by the CPU included in the processing unit 7 executing a computer program stored in a ROM or the like to execute processing corresponding to the computer program, that is, realized by software. Note that at least a part of each functional block may be realized by hardware.

[0015] The acquisition processing unit 11 executes an acquisition process of calculating and acquiring a reverse-phase current vector based on a voltage phase using the current of the electric motor 2 and the voltage of the electric motor 2. The setting processing unit 12 executes a setting process of setting a reference value based on the reverse-phase current vector acquired during a predetermined first period in a normal state. The calculation processing unit 13 executes a calculation process of calculating a difference vector that is the difference between the reverse-phase current vector acquired during operation and the reference value. The diagnosis processing unit 14 executes a diagnosis process of diagnosing that a rare short circuit has occurred in the electric motor 2 when the difference vector becomes equal to or greater than a predetermined threshold value. Since the reference value is a vector, in the following description and drawings, the reference value may be referred to as a reference vector.

[0016] The display unit 8 is composed of, for example, a 7-segment LED, a display, etc., and performs a display for notifying the user to that effect when it is diagnosed by the processing unit 7 that a rare short circuit has occurred in the electric motor 2. The communication circuit 9 is for communicating with an external monitoring device 10. The monitoring device 10 is provided in a control center that centrally manages the operation of a plurality of electric motors including the electric motor 2, and monitors the operation status of the diagnostic device 1.

[0017] <Method for diagnosing rare short circuit> Next, the specific content of the method for diagnosing a rare short circuit of the electric motor 2 by the diagnostic device 1 will be described with reference to FIGS. 2 and 3. As the diagnostic procedure, first, an "initial setting flow" is executed, and then a "diagnosis flow" is executed.

[0018] [1] Recording of initial state The initial setting flow is a record of the initial state. For example, it obtains the sum ΣIsn of the reverse-phase current vectors during a first period, which is a fixed period such as one week or ten days, and sets a reference vector μ based on this. Specifically, the initial setting flow is a process with the content as shown in, for example, FIG. 2. The initial setting flow is executed during normal operation when there is no abnormality such as a rare short circuit in the motor 2.

[0019] In step S101, the operating current, which is the current of the motor 2, and the voltage of the motor 2 are measured. In step S102, based on the measurement results of step S101, the effective value of the current and various powers, specifically the active power, reactive power, and apparent power, are calculated. In step S103, based on the effective value of the current, it is determined whether the motor 2 is in an operating state. Here, if the motor 2 is not in an operating state, in step S103, it becomes "NO" and returns to step S101. On the other hand, if the motor 2 is in an operating state, in step S103, it becomes "YES" and proceeds to step S104.

[0020] In step S104, the reverse-phase current vector Isn is calculated based on the effective value of the current. As the calculation formula in this case, for example, the following formula (1) can be adopted. However, Ir is the R-phase current vector, Is is the S-phase current vector, and It is the T-phase current vector. Also, these Ir, Is, and It are current vectors based on the voltage reference. In addition, in each formula and each drawing including formula (1), a dot is attached above Isn, Ir, Is, and It, but the dot is omitted in the description in this specification. Also, "a" in formula (1) is a rotation vector, that is, a rotation operator, and is represented by formula (2).

[0021]

Equation

[0022] The calculation formula of the reverse-phase current vector Isn is not limited to the above formula (1), and any formula that can represent a vector is acceptable. For example, the reverse-phase current vector Isn can also be calculated by a formula such as multiplying the scalar values of the R-phase current, S-phase current, and T-phase current by terms of active power and reactive power, or by terms of active power and R-phase voltage, i.e., the power supply voltage, to convert them back to vectors. By calculating the reverse-phase current in this way, a reverse-phase current vector based on the voltage vector can be calculated, so that it is possible to make a determination using not only the magnitude of the reverse-phase current but also the information on the phase of the reverse-phase current.

[0023] In step S105, it is determined whether the first period has elapsed. Here, if the first period has not elapsed, the result in step S105 is "NO", and the process returns to step S101. On the other hand, if the first period has elapsed, the result in step S105 is "YES", and the process proceeds to step S106. In step S106, the sum ΣIsn of the reverse-phase current vectors Isn is calculated, and the value obtained by dividing the sum ΣIsn by N is set as the reference vector μ. The calculation formula of the reference vector μ is as shown in the following formula (3). Here, N is the number of times the reverse-phase current vector Isn is obtained, i.e., the number of measurement points.

[0024]

Equation

[0025] After the execution of step S106, the initial setting flow ends. Among the respective processes in the above-described initial setting flow, steps S101 to S104 correspond to the acquisition processes executed by the acquisition processing unit 11, and steps S105 to S106 correspond to the setting processes executed by the setting processing unit 12.

[0026] [2] Diagnosis Flow The diagnostic flow is executed during the operation of the equipment. Specifically, it is a process with the content as shown in, for example, Fig. 3. In step S201, the operating current, which is the current of the motor 2, and the voltage of the motor 2 are measured. In step S202, based on the measurement results of step S201, the effective value of the current, active power, reactive power, and apparent power are calculated. In step S203, based on the effective value of the current, it is determined whether the motor 2 is in the operating state. Here, if the motor 2 is not in the operating state, in step S203, it becomes "NO" and returns to step S201. On the other hand, if the motor 2 is in the operating state, in step S203, it becomes "YES" and proceeds to step S204.

[0027] In step S204, the inverse-phase current vector Isn is calculated based on the effective value of the current. The calculation formula for the inverse-phase current vector Isn is the same as that for the initial setting flow. By executing step S204, the inverse-phase current vector Isn during the operation of the motor 2 is obtained. In step S205, the difference vector, which is the difference between the inverse-phase current vector Isn obtained during operation and the reference vector μ, is calculated, and that difference vector is set as the evaluation value Δ. That is, in step S205, the evaluation value Δ is calculated and set based on the following formula (4).

[0028]

Equation

[0029] In step S206, it is determined whether the evaluation value Δ is greater than or equal to a predetermined threshold α. Here, if the evaluation value Δ is less than the threshold α, in step S206, it becomes "NO" and returns to step S201. On the other hand, if the evaluation value Δ is greater than or equal to the threshold α, in step S206, it becomes "YES" and proceeds to step S207. In step S207, it is diagnosed that a rare short circuit has occurred in the motor 2, that is, the winding short circuit determination is performed. After executing step S207, the diagnostic flow ends.

[0030] Note that the threshold value α is determined by considering either one or both of the reverse-phase current measured when the motor 2 is operated at the assumed voltage unbalance rate and the reverse-phase current measured when a rare short circuit occurs. Also, due to the difference in the number of short-circuited turns according to the structure, capacity, etc. of the motor 2, the ease of occurrence of the reverse-phase current changes. Therefore, it is necessary to set the threshold value α in consideration of the structure, capacity, etc. of the motor 2. Among the respective processes in the above-described diagnosis flow, steps S201 to S204 correspond to the acquisition process executed by the acquisition processing unit 11, step S205 corresponds to the calculation process executed by the calculation processing unit 13, and steps S206 to S207 correspond to the diagnosis process executed by the diagnosis processing unit 14.

[0031] According to the present embodiment described above, a reverse-phase current vector based on the voltage phase is calculated and acquired using the current and voltage of the motor 2, a reference value is set based on the reverse-phase current vector acquired during a predetermined first period during normal operation, a difference vector that is the difference between the reverse-phase current vector acquired during operation and the reference value is calculated, and when the difference vector becomes equal to or greater than a predetermined threshold value, it is diagnosed that a rare short circuit has occurred in the motor 2. Thus, according to the present embodiment, by performing monitoring in terms of vectors, an effect that the detection accuracy of a rare short circuit can be improved is obtained.

[0032] Hereinafter, the effects obtained by such a present embodiment will be described in detail. First, the distribution of the reverse-phase current of the motor 2 is as shown in FIG. 4. In FIG. 4, the measurement points are represented by black triangular marks, and the vector of the average value and the determination range are shown. In FIG. 4, the one-dot chain line represents the determination range, the dashed arrow represents the occurrence of a winding short circuit, the solid arrow represents the reference value, that is, the average value during normal operation, and the dotted arrow represents the amount changed due to the winding short circuit. Also, the vertical axis of FIG. 4 is the imaginary part of the reverse-phase current, and the horizontal axis of FIG. 4 is the real part of the reverse-phase current.

[0033] When a winding short circuit, i.e., a rare short, occurs in the electric motor 2, the reverse-phase current changes. However, as shown by the dotted arrow in Fig. 4, there are cases where only the phase changes and the magnitude of the reverse-phase current remains unchanged. In such cases, the change cannot be detected by a method that monitors only the magnitude of the reverse-phase current. However, if vector calculation is performed as in the diagnostic method of the present embodiment, it becomes possible to detect it, and as a result, the detection accuracy of the rare short can be improved. The effect obtained by such the present embodiment becomes clearer when compared with the case where the reverse-phase current is calculated as a scalar.

[0034] Therefore, hereinafter, while comparing the present embodiment in which the reverse-phase current is calculated as a vector with a comparative example in which the reverse-phase current is calculated as a scalar with reference to Figs. 5 and 6, the effect obtained by the present embodiment will be explained in more detail. In Figs. 5 and 6, the left figure shows the comparative example, and the right figure shows the present embodiment. Also, in Figs. 5 and 6, the dotted arrow represents the reverse-phase current vector in the normal state, the dotted arrow represents the reverse-phase current vector due to the rare short, the solid arrow represents the composite vector, the range surrounded by the dotted line represents the normal range during scalar calculation, and the range surrounded by the solid line represents the normal range during vector calculation. Further, the vertical axis in Figs. 5 and 6 is the imaginary part of the reverse-phase current, and the horizontal axis in Figs. 5 and 6 is the real part of the reverse-phase current.

[0035] In the case of the comparative example, the presence or absence of a rare short is determined by the amount of change in the magnitude of the reverse-phase current. The normal range in this case is a donut-shaped circle centered on the origin, as shown by the slanted lines in the left figures of Figs. 5 and 6. On the other hand, in the case of the present embodiment, the rare short can be detected by the composite vector. The normal range in this case is a circle centered on the end point of the reverse-phase current vector in the normal state, as shown by the slanted lines in the right figures of Figs. 5 and 6. In the present embodiment, compared with the comparative example, the area of the normal range is clearly smaller, which means that the rare short can be detected with high detection sensitivity.

[0036] As shown in Fig. 5, when the reverse-phase current vector generated by the rare short circuit has the same phase as the reverse-phase current vector in the normal state, the composite vector of the reverse-phase current vectors in the normal state and due to the rare short circuit exceeds the normal range shown by the hatching in both the comparative example and the present embodiment, and it can be seen that it can be detected by any method.

[0037] On the other hand, as shown in Fig. 6, when the reverse-phase current vector generated by the rare short circuit has a different phase from the reverse-phase current vector in the normal state, in the comparative example, since the change in phase cannot be captured, the composite vector remains within the normal range, and the rare short circuit cannot be detected. In contrast, in the present embodiment, since the composite vector exceeds the normal range, the rare short circuit can be detected. As is clear from such an example, by performing vector calculation as in the present embodiment, even when a reverse-phase current having a different phase from the reverse-phase current vector in the normal state occurs, the rare short circuit can be detected with high sensitivity.

[0038] Also, according to the present embodiment, the following effect can also be obtained. That is, the direction, that is, the phase of the reverse-phase current vector when a rare short circuit occurs in the electric motor 2 is determined by the configuration of the coils of the electric motor 2. Therefore, by performing vector calculation as in the present embodiment, it is possible to determine which phase winding among the plurality of phases has become abnormal. For example, when the configuration of the coils of the electric motor 2 is a star connection, as shown in Fig. 7, the phase in which the rare short circuit has occurred can be specified according to the position of the reverse-phase current vector.

[0039] (Second Embodiment) Hereinafter, the second embodiment will be described with reference to Figs. 8 to 11. <Configuration of Diagnostic Device> As shown in FIG. 8, the diagnostic apparatus 21 of the present embodiment is different from the diagnostic apparatus 1 of the first embodiment in that it includes a processing unit 22 instead of the processing unit 7. The processing unit 22 is different from the processing unit 7 of the first embodiment in that a functional block called an update processing unit 23 is added. The update processing unit 23 executes an update process for updating a reference value based on a value obtained by averaging the inverse-phase current vectors acquired during operation for each predetermined second period.

[0040] <Diagnosis method for rare short circuit> Next, specific details of the diagnosis method for the rare short circuit of the electric motor 2 by the diagnostic apparatus 21 will be described with reference to FIG. 9. In this case, since the initial setting flow is the same as that of the first embodiment, the description thereof will be omitted. The diagnostic flow is specifically a process having the content as shown in FIG. 9, for example. The diagnostic flow of the present embodiment shown in FIG. 9 is different from the diagnostic flow of the first embodiment shown in FIG. 3 in that steps S221 to S224 are added.

[0041] In this case, after the execution of step S204, step S221 is executed. In step S221, the sum ΣIsn of the inverse-phase current vectors Isn is calculated. In step S222, it is determined whether or not the specified number of times N has elapsed. The specified number of times N is the number of times the inverse-phase current vector Isn is obtained, that is, the number of measurement points. Here, when the specified number of times N has not elapsed, "NO" is obtained in step S222, and the process proceeds to step S205. On the other hand, when the specified number of times N has elapsed, "YES" is obtained in step S222, and the process proceeds to step S223.

[0042] In step S223, the value obtained by dividing the sum ΣIsn by N is stored. After the execution of step S223, the process proceeds to step S224, where the reference vector μ is replaced with the value stored in step S223, that is, the reference vector μ is updated. After the execution of step S224, the process proceeds to step S205. In this case, the time required for the number of measurement points of the inverse-phase current vector Isn to reach the specified number N corresponds to the second period. Among the processes in the above-described diagnosis flow, steps S221 to S224 correspond to the update process executed by the update processing unit 23. According to the diagnosis method of this embodiment, the average value of the inverse-phase current vector is obtained for each second period, which is a certain period, and the reference vector μ is updated so that the value becomes the reference vector μ.

[0043] For example, as shown in FIG. 10, the reference value μ is obtained based on the data of the measurement points in section [1], and the obtained reference value μ is used as the reference value μ1 for the determination in the subsequent section [2]. In the further subsequent section [3], the reference value μ obtained based on the data of the measurement points in section [2] is adopted as the new reference value μ2, and the reference value is updated in this way. In FIG. 10, the vertical axis represents the inverse-phase current, and the horizontal axis represents time. Also, in FIG. 10, for the convenience of explaining the change of the reference value μ on the time axis, the reference value is represented as a scalar instead of a vector. Note that the method of updating such a reference value is merely an example, and various methods can be used to update the reference value, such as a method of setting the reference value while overlapping the average intervals, a method of constantly updating using a moving average, and the like.

[0044] According to the embodiment described above, the reference value is updated based on the value obtained by averaging the inverse-phase current vector acquired during operation for each predetermined second period, and the difference vector, which is the difference between the updated reference value and the inverse-phase current vector acquired during operation, is calculated. When the difference vector becomes equal to or greater than a predetermined threshold value, it is diagnosed that a rare short circuit has occurred in the motor 2. Thus, according to this embodiment, by updating the reference value for each second period, which is a certain period, the normal range can be kept narrow, and thus the effect of further improving the detection accuracy of the rare short circuit can be obtained.

[0045] The effects obtained by such an embodiment become clearer when compared with the case of fixing the reference vector. Therefore, hereinafter, while comparing the present embodiment in which the reference vector is updated with reference to FIG. 11 showing an example of the inverse-phase current measured every fixed period and a comparative example in which the reference vector is fixed, the effects obtained by the present embodiment will be described in more detail. In FIG. 11, the measurement points are represented by black triangular marks. In FIG. 11, the solid line represents the normal range in the present embodiment, and the dashed-dotted line represents the normal range in the comparative example. In FIG. 11, the vertical axis represents the inverse-phase current, and the horizontal axis represents time.

[0046] Even when the electric motor 2 is in a normal state, for example, on a factory holiday, if the operating state of the load in the same electrical system changes, the three-phase balance of the power supply voltage changes, and as a result, the inverse-phase current also changes. When the inverse-phase current has a distribution as shown in the example of FIG. 11, if the specification is to determine the determination range by learning for a certain period at the start of operation, it is necessary to set a large normal range as shown by the dashed-dotted line in FIG. 11. However, if there is a device to update the reference vector every fixed period as in the present embodiment, the normal range can be kept narrow as shown by the solid line in FIG. 11, so an improvement in the detection accuracy of rare shorts can be expected.

[0047] (Third Embodiment) Hereinafter, the third embodiment will be described with reference to FIGS. 12 and 13. <Configuration of Diagnostic Device> As shown in FIG. 12, the diagnostic device 31 of the present embodiment is different from the diagnostic device 1 of the first embodiment in that, for example, it includes a processing unit 32 instead of the processing unit 7. The processing unit 32 is different from the processing unit 7 of the first embodiment in that a functional block called a statistical processing unit 33 is added, and a diagnostic processing unit 34 is provided instead of the diagnostic processing unit 14.

[0048] The statistical processing unit 33 executes statistical processing to statistically obtain the value of the standard deviation of the reverse-phase current based on the variation of the reverse-phase current vector in the first period. The diagnostic processing unit 34 uses, as a threshold value, a value obtained by multiplying the value of the standard deviation obtained by the statistical processing by a predetermined value. Note that the predetermined value is a positive integer such as 3, 5, etc.

[0049] <Diagnosis Method for Rare Short Circuit> Next, the specific content of the diagnosis method for the rare short circuit of the motor 2 by the diagnostic device 31 will be described with reference to FIG. 13. In this case, since the diagnostic flow is the same as that of the first embodiment, the description thereof will be omitted. The initial setting flow of this embodiment sets the reference vector μ in the same manner as the initial setting flow of the first embodiment, and further, the sum of squares ΣIsn of the reverse-phase current vectors in the first period 2 is obtained, and the threshold value α is set based on this.

[0050] Specifically, the initial setting flow of this embodiment is the processing with the content as shown in FIG. 13. The initial setting flow of this embodiment shown in FIG. 13 is different from the initial setting flow of the first embodiment shown in FIG. 2 in that step S131 is added, etc. In this case, after the execution of step S106, step S131 is executed.

[0051] In step S131, the sum of squares ΣIsn of the reverse-phase current vector Isn 2 is calculated. Also, in step S131, the standard deviation σ is obtained by the following equation (5) using the sum of squares ΣIsn 2 . However, N is the number of times the reverse-phase current vector Isn is obtained, that is, the number of measurement points.

[0052] [Equation] Furthermore, in step S131, a multiple of the standard deviation σ obtained by the above equation (5), for example, 3σ, 5σ, etc., is set as the threshold value α.

[0053] According to the present embodiment described above, the value of the standard deviation of the reverse-phase current is statistically obtained based on the variation of the reverse-phase current vector in the first period, and the diagnostic process is executed using, as a threshold value, a value obtained by multiplying the value of the standard deviation by a predetermined value. Thus, according to the present embodiment, the effect of being able to realize a diagnosis reflecting the variation in voltage balance can be obtained by statistically obtaining the threshold value. That is, since the standard deviation σ becomes small if the power supply is stable, if the threshold value α is set based on the value of the standard deviation σ, it becomes possible to detect even a small rare short circuit, and a situation where only a severe rare short circuit can be detected can be avoided.

[0054] (Fourth Embodiment) Hereinafter, the fourth embodiment will be described with reference to FIG. 14. As shown in FIG. 14, the diagnostic device 41 of the present embodiment is different from the diagnostic device 21 of the second embodiment in that it includes a processing unit 42 instead of the processing unit 22. The processing unit 42 is different from the processing unit 22 of the second embodiment in that a functional block called a statistical processing unit 33 is added, and a diagnostic processing unit 34 is provided instead of the diagnostic processing unit 14.

[0055] Regarding the method for diagnosing a rare short circuit of the electric motor 2 by the diagnostic device 41 of the present embodiment, the initial setting flow has the same content as that of the third embodiment, and the diagnostic flow has the same content as that of the second embodiment. According to such a present embodiment, a diagnosis having the features of both the second embodiment and the third embodiment can be realized.

[0056] (Other Embodiments) Note that the present invention is not limited to the embodiments described above and illustrated in the drawings, and can be arbitrarily modified, combined, or extended without departing from the gist thereof. The numerical values and the like shown in the above embodiments are examples and are not limited thereto.

[0057] As described above, several embodiments of the present invention have been explained. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0058] 1, 21, 31, 41... diagnostic device, 2... electric motor, 5... current detection circuit, 6... voltage detection circuit, 7, 22, 32, 42... processing unit, 11... acquisition processing unit, 12... setting processing unit, 13... calculation processing unit, 14, 34... diagnostic processing unit, 23... update processing unit, 33... statistical processing unit.

Claims

1. A current detection circuit for detecting the current of the motor, A voltage detection circuit for detecting the voltage of the motor, A processing unit that executes various processes for diagnosing a rare short circuit of the motor based on the current and voltage of the motor detected by the current detection circuit and the voltage detection circuit, Comprising, The processing unit, An acquisition process of calculating and acquiring an inverse-phase current vector based on the voltage phase using the current of the motor and the voltage of the motor, A setting process of setting a reference value based on the inverse-phase current vector acquired during a predetermined first period in a normal state, A calculation process of calculating a difference vector that is the difference between the inverse-phase current vector acquired during operation and the reference value, A diagnosis process of diagnosing that a rare short circuit has occurred in the motor when the difference vector is equal to or greater than a predetermined threshold value, A diagnostic device for a motor that executes the above.

2. The processing unit, Furthermore, the diagnostic device for a motor according to claim 1, which executes an update process of updating the reference value based on a value obtained by averaging the inverse-phase current vector acquired during operation for each predetermined second period.

3. The processing unit, Furthermore, it executes a statistical process of statistically obtaining a value of the standard deviation of the inverse-phase current based on the variation of the inverse-phase current vector in the first period, In the diagnosis process, the diagnostic device for a motor according to claim 1 or 2 uses a value obtained by multiplying the value of the standard deviation by a predetermined value as the threshold value.

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