Power conversion device, equipment system, and

Abstract

This power conversion device is provided with: a diagnosis condition determination unit that determines a prescribed diagnosis condition on the basis of a diagnosis frequency for performing abnormality diagnosis, a motor speed, and a modulation rate of an output voltage; a control changing unit that reduces the modulation rate on the basis of the determination result of the diagnosis condition determination unit; and an abnormality diagnosis unit that performs an abnormality diagnosis of the device on the basis of the motor current on the basis of the determination result of the diagnosis condition determination unit.

Description

Technical Field

[0001] The present invention relates to a power conversion device, an equipment system, and an abnormality diagnosis method. Background Art

[0002] In recent years, the popularization of IoT (Internet of Things), the progress of AI (Artificial Intelligence), and the decrease in the working population have coexisted. For the purpose of improving the efficiency of maintenance work and saving labor, a technology for performing abnormality diagnosis of mechanical devices based on information obtained by sensors and the like has been developed.

[0003] Among them, an abnormality diagnosis technology using a motor current that is easy to set and can monitor both the motor itself and mechanical components connected to the motor with a single sensor has attracted attention.

[0004] For example, in Patent Document 1, a technology is disclosed in which a motor current obtained as time-series data is transformed into a frequency spectrum, and the presence or absence of an abnormality is diagnosed by comparing a specific frequency component (amplitude value) caused by a mechanical component to be detected for an abnormality with a frequency component obtained during normal operation.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-34037 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, when the method of Patent Document 1 is applied to a motor system using a power conversion device (inverter) that performs asynchronous PWM (Pulse Width Modulation) control, there is a possibility of the following problems occurring.

[0010] In a power conversion device, a sinusoidal voltage after pulse width modulation is supplied to a motor. However, when the load size increases or the input voltage to the power conversion device decreases, there is a case where the supply voltage to the motor becomes an overmodulation state (a state where the output voltage command value calculated inside the power conversion device exceeds the input voltage level of the power conversion device).

[0011] When it becomes such a state, the voltage waveform is not close to a sine wave but close to a square wave, and the harmonic components (harmonic noise) of the fundamental frequency of the output voltage increase. At this time, when the specific frequency caused by the mechanical component shown in Patent Document 1 is near the above-mentioned harmonics, there is a possibility of misdiagnosis due to the increase in the frequency components even in the case where no abnormality occurs.

[0012] An object of the present invention is to prevent misdiagnosis when performing an abnormality diagnosis of a device driven by a motor in a power conversion device.

[0013] Technical means for solving the problem

[0014] A power conversion device according to one aspect of the present invention is a power conversion device capable of performing an abnormality diagnosis of a device driven by a motor, and is characterized in that it includes: a motor control unit that controls the motor current of the motor, the motor speed of the motor, and the output voltage of the power conversion device; a diagnosis condition determination unit that determines a specified diagnosis condition based on a diagnosis frequency for performing the abnormality diagnosis, the motor speed, and the modulation rate of the output voltage; a control change unit that reduces the modulation rate based on the determination result of the diagnosis condition determination unit; and an abnormality diagnosis unit that performs the abnormality diagnosis of the device based on the motor current according to the determination result of the diagnosis condition determination unit.

[0015] Effects of the invention

[0016] According to one aspect of the present invention, it is possible to prevent misdiagnosis when performing an abnormality diagnosis of a device driven by a motor in a power conversion device. Description of the drawings

[0017] Figure 1 It is a system configuration diagram of Embodiment 1 of the present invention.

[0018] Figure 2 It is a diagram showing the processing content of the diagnosis frequency setting unit 7.

[0019] Figure 3 It is a diagram showing the processing content of the diagnosis condition determination unit 8.

[0020] Figure 4 It is a diagram showing the mode when determining the state transition signal.

[0021] Figure 5 It is a diagram showing the processing content of the control change unit 9.

[0022] Figure 6 It is a diagram showing other processing content of the control change unit 9.

[0023] Figure 7It is a diagram showing other processing contents of the control change unit 9.

[0024] Figure 8 It is a diagram showing other processing contents of the control change unit 9.

[0025] Figure 9 It is a diagram showing an example of current waveforms before and after modulation rate reduction.

[0026] Figure 10 It is a diagram showing the processing contents of the abnormality diagnosis unit 10.

[0027] Figure 11 It is a basic timing diagram of the processing.

[0028] Figure 12 It is a system configuration diagram of Embodiment 2 of the present invention.

[0029] Figure 13 It is a system configuration diagram of Embodiment 3 of the present invention.

[0030] Figure 14 It is a system configuration diagram of Embodiment 4 of the present invention. Detailed implementation manners

[0031] Hereinafter, embodiments will be described with reference to the drawings.

[0032] Embodiment 1

[0033] In Embodiment 1 of the present invention, a power conversion device having an abnormality diagnosis function of reducing high - order harmonic noise generated by the power conversion device and reducing the occurrence frequency of misdiagnosis will be described.

[0034] In Figure 1 the system configuration diagram of this Embodiment 1 is shown. In this example, a system for driving a fan (air blower) is taken as an example for description, but the present invention can be applied to any device driven by a motor.

[0035] The fan system 1 is composed of an AC or DC power supply 2 (described with DC in this example), a power conversion device 3 driven by the power supply 2, a motor 4 driven by a three - phase AC voltage / current supplied from the power conversion device 3, and a fan 5.

[0036] Here, the inside of the power conversion device 3 in this Embodiment 1 is divided into a motor control unit 13 and an abnormality diagnosis system 6. The motor control unit 13 calculates various command values in order to control the motor current, output voltage, motor speed, and motor torque. In this example, it is assumed that the output voltage of the power conversion device 3 is under asynchronous PWM control.

[0037] On the other hand, the abnormality detection system 6 includes a diagnostic frequency setting unit 7 that sets the motor speed (diagnostic frequency) for performing abnormality diagnosis, a diagnostic condition determination unit 8 that uses the diagnostic frequency, the motor speed obtained from the motor control unit 13, and the modulation rate of the output voltage of the power conversion device 3 as inputs to determine whether abnormality diagnosis can be performed or whether the modulation rate of the output voltage of the power conversion device 3 needs to be reduced, a control change unit 9 that reduces the modulation rate of the output voltage of the power conversion device 3 according to the result of the diagnostic condition determination unit 8, and an abnormality diagnosis unit 10.

[0038] Moreover, a structure is adopted in which the diagnostic result of the abnormality diagnosis unit 10 is input to a display device 11 such as a display, a notification device 12 such as a speaker or an indicator light, and the motor control unit 13 using a communication unit such as wired or wireless. Details of each processing module are described below.

[0039] First, the diagnostic frequency setting unit 7 sets the motor speed (diagnostic frequency) for performing diagnosis based on information input from the outside. For example, the name of the target component and the abnormal state can be input as external input information, and the diagnostic frequency is retrieved and determined from the database 21 stored in the diagnostic frequency retrieval unit 20 as shown. In addition, multiple diagnostic frequencies can be output for each mechanical component to be diagnosed. Hereafter, it is assumed that one diagnostic frequency is set for explanation. Figure 2 Shown in the diagnostic frequency retrieval unit 20 stored in the database 21 retrieved to determine the diagnostic frequency. In addition, multiple diagnostic frequencies can be output for each mechanical component to be diagnosed. Hereafter, it is assumed that one diagnostic frequency is set for explanation.

[0040] Next, in the diagnostic condition determination unit 8, the processing as shown is performed. Figure 3 Shown in the processing.

[0041] First, the diagnostic frequency fd, the motor speed fm, and the modulation rate M of the output voltage of the power conversion device are input (S1). At this time, for fm, for example, the sensor value of the measured motor speed or the estimated value of the motor speed can be used, or the fundamental frequency of the motor current can be used as fm.

[0042] In addition, the modulation rate M is typically a value defined by "amplitude (peak-to-peak) of the output voltage command value / input DC voltage value of the power conversion device" or "amplitude (peak-to-peak) of the output voltage command value / amplitude (peak-to-peak) of the PWM carrier (carrier)", etc. After inputting the above information, conditional judgments are made for the motor speed and the modulation rate respectively.

[0043] In the judgment of the motor speed, it is judged whether |fd - fm| is less than the threshold value Δfth (for example, within 5% of fd) (S2). If it is "yes", the speed state flag is set to 1 (S3), and if it is "no", it is set to 0 (S4).

[0044] On the other hand, in the determination of the modulation rate, it is determined whether the modulation rate M is below the threshold Mth (generally set to 1) (S5). If it is "yes", the voltage state flag is set to 1 (S6), and if it is "no", the voltage state flag is set to 0 (S7). At this time, the modulation rate M can be an instantaneous value or an average value in a certain past time range.

[0045] After that, in the state transition signal determination step (S8), for example, the state transition signal is determined according to Figure 4 the rules. In addition, when performing subsequent processing, even if the motor speed or the modulation rate changes, the value of the flag determined above is maintained until the next condition judgment is implemented. This is to suppress the instantaneous change of the flag and the frequent switching of the state transition in the case where the motor speed or the modulation rate changes near the threshold. Then, based on the state transition signal, the control change unit 9 and the abnormality diagnosis unit 10 are executed.

[0046] As Figure 4 shown, when the speed state flag is 0 and the voltage state flag is 0, the state transition signal (SS) is 0, and neither the modulation rate reduction control nor the abnormality diagnosis is implemented. Here, the case where the speed state flag is 0 indicates, for example, the state where the motor 4 stops.

[0047] In addition, when the speed state flag is 0 and the voltage state flag is 1, the state transition signal (SS) is 0, and neither the modulation rate reduction control nor the abnormality diagnosis is implemented.

[0048] In addition, when the speed state flag is 1 and the voltage state flag is 0, the state transition signal (SS) is 1, and the modulation rate reduction control is implemented.

[0049] In addition, when the speed state flag is 1 and the voltage state flag is 1, the state transition signal (SS) is 2, and the abnormality diagnosis is implemented.

[0050] When the state transition signal SS is 1, the modulation rate of the output voltage of the power conversion device 3 is greater than the threshold, that is, in an overmodulation state where high-order harmonic noise affecting the diagnosis is generated. Therefore, it is necessary to reduce the modulation rate to reduce the noise. Therefore, the control change unit 9 executes the modulation rate reduction control as Figure 5 , Figure 6 , Figure 7 , Figure 8 shown.

[0051] Figure 5In the case where the motor 4 is assumed to be a magnet motor, the current component that controls the motor magnetic flux, called the d-axis current command value, is increased toward the negative side (S13). When performing such control, since the magnetic flux generated by the motor itself is reduced to lower the induced voltage of the motor, the necessary voltage output from the power conversion device 3 is reduced, so the modulation rate can be lowered.

[0052] In addition, Figure 6 in the case of an induction motor, at least one of the d-axis current command value and the current component that controls the motor torque, i.e., the q-axis current command value, is increased or decreased within the range of zero or more. In an induction motor, the output voltage of the power conversion device 3 varies due to the relationship among the d-axis current, the q-axis current, and the motor speed. Therefore, not only are the q-axis current command value and the d-axis current command value reduced, but they are also increased to adjust in the direction of reducing the output voltage.

[0053] In addition to this, Figure 7 , Figure 8 a method of reducing the modulation rate by reducing the amplitude of the output voltage command value of the power conversion device 3 and the motor speed command value without changing the current command value is shown (refer to (S53) of Figure 7 and (S43) of Figure 8 ).

[0054] As previously described, the amplitude of the output voltage command value is a direct value that determines the modulation rate. If the amplitude value is reduced, the modulation rate is also reduced. In addition, the motor speed command value also has the effect of reducing the modulation rate in the case of applications such as a fan where the load increases or decreases significantly according to the speed.

[0055] That is, by reducing the speed to reduce the load, the necessary voltage is reduced as a result, and the modulation rate is reduced. In addition, when performing the control shown in Figure 6 , Figure 7 , Figure 8 , a speed reduction of several percent is allowed. In addition, such control changes can be made step by step or at a set time rate.

[0056] By implementing such control, as shown in Figure 9 , the voltage waveform changes from a state close to a square wave (a waveform with the upper and lower limits of a sine wave restricted) to a sine wave waveform, and the high-order harmonic noise superimposed on the current is reduced, and a motor current suitable for diagnosis can be obtained ( Figure 9 shows an ideal waveform without abnormal vibrations or the like).

[0057] Then, after performing the control to reduce the modulation rate, or when the state transition signal SS indicating that the original modulation rate is less than the threshold value is 2, the abnormal diagnosis process shown in Figure 10 is executed.

[0058] In abnormal diagnosis, first, after reducing the modulation rate, standby is performed for a necessary time (S33). This is implemented to wait for the transient effects of the reduced modulation rate to become stable, and it varies depending on the set state of the motor control and the magnitude of the motor inertia, etc., so it can be preset accordingly for the target device.

[0059] Next, after obtaining the motor current (S34), a feature quantity for diagnosis is extracted from the motor current (S35). Here, the motor current can be the phase current or the torque current itself, or a time-series signal calculated based on them. The feature quantity needs to be changed according to the target device and the type of abnormality. For example, statistical indicators representing the average value or error of the time-series signal, and specific frequency components obtained by performing frequency transformation on the time-series signal, etc. can be cited as candidates.

[0060] After extracting the feature quantity, binary information such as normal / abnormal can be calculated by performing threshold judgment on the feature quantity, or the degree of abnormality can be numerically calculated using the MT method or 1class-SVM, etc. which is a type of machine learning. Additionally, a model for classifying the type of abnormality can be prepared based on a decision tree, etc., and the state and type of the abnormality can be output (S36). In any case, in this example, it is called calculating the degree of abnormality.

[0061] Then, in the case where the control of reducing the modulation rate is executed before performing the abnormal diagnosis, a process of restoring the modulation rate is executed (S37, S38). When restoring the modulation rate, it can be executed step by step, or changed at a set time rate.

[0062] Finally, the calculated degree of abnormality is input to the display device 11, the notification device 12, or the motor control device 13 using a communication unit such as wired or wireless, etc., to notify the operator or the machine. For example, the binary state of normal / abnormal can be input to an indicator light or a speaker which is an example of the notification device 12, and the state can be notified to the operator by light or sound. Furthermore, the numerical degree of abnormality can also be displayed on the display of the display device 11. Furthermore, when the abnormal diagnosis result is input to the motor control device 13, it can be used to automatically stop or change the operation of the target device according to the degree of abnormality.

[0063] Regarding the processing flow shown above, it is Figure 11 re - summarized as a timing diagram in

[0064] There are roughly three modes in the basic processing flow. The first is mode 1 where SS = 0 (diagnosis not performed) in the condition judgment, the second is mode 2 from SS = 1 (executing the modulation rate reduction control) to SS = 2, and the third is mode 3 where SS = 2 (executing the diagnosis).

[0065] In addition, regarding the timing of the condition judgment, it can beFigure 11 It can be implemented immediately after the end of each processing mode, or can be implemented at specific time intervals, or can be implemented irregularly.

[0066] Thus, according to Embodiment 1, it is possible to reduce the high-order harmonic noise generated by the power conversion device and reduce the number of occurrences of misdiagnosis.

[0067] Embodiment 2

[0068] In Embodiment 2 of the present invention, a power conversion device having another abnormality diagnosis function of reducing the high-order harmonic noise generated by the power conversion device and reducing the number of occurrences of misdiagnosis will be described.

[0069] In addition, the description of the same processing as in Embodiment 1 is omitted, and the description will focus on the differences from Embodiment 1.

[0070] In Figure 12 shows the system diagram of Embodiment 2. The difference between Embodiment 2 and Embodiment 1 is that the output of the abnormality diagnosis unit 110 is input to the control device 111, the display device 112, the notification device 113, and the monitoring device 114 located outside the power conversion device 103. The display device 112 and the notification device 113 are the same as those described in Embodiment 1.

[0071] On the other hand, the control device 111 is a control device (such as a PLC, etc.) superior to the motor control unit 115 or a superior control device that controls the entire factory. In addition, the monitoring device 114 is a monitoring device for other devices or the entire factory.

[0072] Thus, according to Embodiment 2, compared with Embodiment 1, the notification function that should be provided in the power conversion device can be simplified, so the power conversion device can be configured at low cost.

[0073] Embodiment 3

[0074] In Embodiment 3 of the present invention, a power conversion device having another abnormality diagnosis function of reducing the high-order harmonic noise generated by the power conversion device and reducing the number of occurrences of misdiagnosis will be described.

[0075] In addition, the description of the same processing as in Embodiment 1 is omitted, and the description will focus on the differences from Embodiment 1.

[0076] In Figure 13 shows the system diagram of Embodiment 3. The difference between Embodiment 3 and Embodiment 1 is that the diagnosis frequency setting unit 7 shown in Embodiment 1 does not exist. In Embodiment 2, the structure is such that the diagnosis frequency is directly input to the diagnosis condition determination unit 208. In this case, the diagnosis frequency can be determined according to an external database or the like.

[0077] Thus, according to Embodiment 3, the processing can be reduced compared to Embodiment 1 by deleting a part of the functions implemented in the power conversion device 203, and the storage burden can be reduced by reducing the amount of information to be stored.

[0078] Embodiment 4

[0079] In Embodiment 4 of the present invention, a power conversion device having another abnormality diagnosis function for reducing high-order harmonic noise generated by the power conversion device and reducing the occurrence frequency of misdiagnosis will be described.

[0080] In addition, the description of the same processing as in Embodiments 1, 2, and 3 will be omitted, and the description will focus on the differences from Embodiment 3.

[0081] In Figure 14 shows the system diagram of Embodiment 4. The difference between Embodiment 4 and Embodiment 3 is that the output of the abnormality diagnosis unit 310 is input to a control device 311, a display device 312, a notification device 313, and a monitoring device 314 located outside the power conversion device 303. The display device 312 and the notification device 313 are the same as those described in Embodiment 1. In addition, the control device 311 and the monitoring device 314 are the same as those described in Embodiment 2.

[0082] Thus, according to Embodiment 4, the processing can be reduced compared to Embodiments 1 and 2 by deleting a part of the functions, and the storage burden can be reduced by reducing the amount of information to be stored. In addition, compared to Embodiment 3, the notification function that should be provided in the power conversion device can be simplified, so the power conversion device can be configured at low cost.

[0083] Here, for example Figure 1 the power conversion device 3 shown is composed of a computer having a memory and a processor (such as a CPU).

[0084] Figure 1 The functions “~ unit” shown are realized by the processor executing a program to achieve their “functions”.

[0085] For example, Figure 1 the motor control unit 13 shown realizes the motor control function by the processor executing a program. Figure 1 the diagnosis frequency setting unit 7 shown realizes the diagnosis frequency setting function by the processor executing a program.

[0086] Figure 1 the diagnosis condition determination unit 8 shown realizes the diagnosis condition determination function by the processor executing a program. Figure 1 the control change unit 9 shown realizes the control change function by the processor executing a program. Figure 1The abnormal diagnosis unit 10 shown realizes the abnormal diagnosis function by executing a program by a processor.

[0087] According to the above embodiment, it is possible to reduce the high-order harmonic noise generated by the power conversion device and reduce the occurrence frequency of misdiagnosis.

[0088] Explanation of reference numerals

[0089] 1... Fan system, 2... Power supply, 3... Power conversion device, 4... Motor, 5... Fan, 6... Abnormal diagnosis system, 7... Diagnosis frequency setting unit, 8... Diagnosis condition determination unit, 9... Control change unit, 10... Abnormal diagnosis unit, 11... Display device, 12... Notification device, 13... Motor control unit.

Claims

1. A power conversion device capable of performing abnormal diagnosis of a device driven by an electric motor, characterized in that, Comprising: A motor control unit that controls the motor current of the motor, the motor speed of the motor, and the output voltage of the power conversion device; A diagnostic condition determination unit that determines a specified diagnostic condition based on the diagnostic frequency for performing the abnormality diagnosis, the motor speed, and the modulation rate of the output voltage; A control change unit that reduces the modulation rate based on the determination result of the diagnostic condition determination unit; And An abnormality diagnosis unit that performs the abnormality diagnosis of the device based on the motor current according to the determination result of the diagnostic condition determination unit.

2. The power conversion device according to claim 1, wherein: It further has a diagnostic frequency setting unit that sets the diagnostic frequency for performing the abnormality diagnosis, and the diagnostic frequency is the motor speed.

3. The power conversion device according to claim 1, wherein: It further has a display device or a notification device that notifies the result of the abnormality diagnosis of the device performed by the abnormality diagnosis unit.

4. The power conversion device according to claim 1, wherein: The result of the abnormality diagnosis of the device performed by the abnormality diagnosis unit is input to the motor control unit.

5. The power conversion device according to claim 1, wherein: The power conversion device supplies a voltage of a sine wave after pulse width modulation to the motor, The waveform of the output voltage before performing the abnormality diagnosis is a square wave with the top and bottom of the sine wave limited, The waveform of the output voltage when performing the abnormality diagnosis is the sine wave, The waveform of the output voltage after performing the abnormality diagnosis returns to the square wave.

6. The power conversion device according to claim 1, wherein: The diagnostic condition determination unit, When the motor speed and the diagnostic frequency are within a certain value and are the same, and the modulation rate is below the threshold value, it outputs an abnormality diagnosis execution determination flag indicating that the abnormality diagnosis is to be performed, When the motor speed and the diagnostic frequency are within the certain value and are the same, and the modulation rate is greater than the threshold value, it outputs a modulation rate reduction control execution determination flag indicating that the control of reducing the modulation rate is to be performed, When the motor speed and the diagnostic frequency differ by more than the certain value, it outputs a non-execution determination flag indicating that neither the abnormality diagnosis nor the control of reducing the modulation rate is to be performed, Determines the specified diagnostic condition with reference to the abnormality diagnosis execution determination flag, the modulation rate reduction control execution determination flag, and the non-execution determination flag, The control change unit reduces the modulation rate with reference to the modulation rate reduction control execution determination flag, The abnormality diagnosis unit performs the abnormality diagnosis of the device with reference to the abnormality diagnosis execution determination flag.

7. The power conversion device according to claim 1, wherein: The control change unit reduces the modulation rate by increasing the d-axis current command value calculated by the motor control unit to the negative side.

8. The power conversion device according to claim 1, wherein: The control change unit reduces the modulation rate by increasing or decreasing at least one of the d-axis current command value and the q-axis current command value calculated by the motor control unit within a range of zero or more.

9. The power conversion device according to claim 1, wherein: The control change unit reduces the modulation rate by reducing the voltage command value calculated by the motor control unit.

10. The power conversion device according to claim 1, wherein: The control change unit reduces the modulation rate by reducing the speed command value calculated by the motor control unit.

11. The power conversion device according to claim 1, wherein: The abnormality diagnosis unit calculates the degree of abnormality using the feature amount extracted from the motor current, thereby performing the abnormality diagnosis, and when the control change unit executes the control for reducing the modulation rate, restores the modulation rate to the state before the abnormality diagnosis is performed.

12. An equipment system having equipment driven by a motor and a power conversion device for controlling the motor, wherein: The power conversion device includes: a motor control unit that controls the motor current of the motor, the motor speed of the motor, and the output voltage of the power conversion device; a diagnosis condition determination unit that determines a prescribed diagnosis condition based on the diagnosis frequency for performing the abnormality diagnosis, the motor speed, and the modulation rate of the output voltage; a control change unit that reduces the modulation rate based on the determination result of the diagnosis condition determination unit; and an abnormality diagnosis unit that performs the abnormality diagnosis of the equipment based on the motor current according to the result of the diagnosis condition determination unit.

13. The equipment system according to claim 12, wherein: The equipment is a fan or a pump.

14. The equipment system according to claim 12, wherein: It further has a display device or a notification device that notifies the result of the abnormality diagnosis of the equipment performed by the abnormality diagnosis unit.

15. An abnormality diagnosis method using a power conversion device capable of performing an abnormality diagnosis of a device driven by an electric motor, characterized in that, including: a motor control step of controlling the motor current of the motor, the motor speed of the motor, and the output voltage of the power conversion device; a diagnosis condition determination step of determining a prescribed diagnosis condition based on the diagnosis frequency for performing the abnormality diagnosis, the motor speed, and the modulation rate of the output voltage; a control change step of reducing the modulation rate based on the determination result of the diagnosis condition determination unit; and an abnormality diagnosis step of performing the abnormality diagnosis of the equipment based on the motor current according to the result of the diagnosis condition determination unit.

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