Diagnostic device for permanent magnet synchronous motor and inverter having the same

Abstract

A permanent magnet synchronous motor diagnostic device (7) comprises: a reverse phase current calculator (4) for calculating a reverse phase current based on the magnitude of a plurality of phase currents flowing in a permanent magnet synchronous motor (2) for rotating a load; and a degradation diagnostic device (5) for diagnosing degradation of a sliding bearing (9) supporting the permanent magnet synchronous motor (2) based on the reverse phase current.

Description

Technical Field

[0001] The present disclosure relates to a diagnostic device for a permanent magnet synchronous motor and an inverter including the diagnostic device. Background Art

[0002] There is a known device for diagnosing deterioration of a sliding bearing supporting a permanent magnet synchronous motor. For example, a bearing abnormality detection device disclosed in Patent Document 1 compares the stop time from a specific rotation speed to a stop of the motor with a predetermined reference stop time to determine whether there is an abnormality in the bearing.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2008-175821

[0004] However, the bearing abnormality detection device described in Patent Document 1 does not necessarily have high detection accuracy for bearing abnormalities. This is because when the load torque driven by the motor changes due to environmental factors, the stop time of the motor from a specific rotation speed to the stop of rotation also changes. The bearing abnormality detection device described in Patent Document 1 cannot distinguish between changes in load torque and bearing abnormalities. Summary of the invention

[0005] Therefore, an object of the present disclosure is to provide a diagnosis device for a permanent magnet synchronous motor capable of detecting deterioration of a sliding bearing supporting the permanent magnet synchronous motor with high accuracy, and an inverter including the diagnosis device.

[0006] The permanent magnet synchronous motor diagnostic device disclosed in the present invention includes: a reverse phase current calculator that calculates a reverse phase current based on the magnitude of a plurality of phase currents flowing through the permanent magnet synchronous motor that rotates a load; and a degradation diagnostic device that diagnoses degradation of a sliding bearing that supports the permanent magnet synchronous motor based on the reverse phase current.

[0007] Preferably, the permanent magnet synchronous motor diagnostic device of the present disclosure detects the expansion of the gap between the sliding bearing and the main shaft based on the reverse phase current.

[0008] According to the present disclosure, a diagnostic device for a permanent magnet synchronous motor calculates a reverse current based on the magnitude of currents of multiple phases, and diagnoses the deterioration of a sliding bearing supporting the permanent magnet synchronous motor based on the reverse current. The diagnostic device for a permanent magnet synchronous motor detects the expansion of a gap between the sliding bearing and the main shaft based on the reverse current. Thus, the deterioration of the sliding bearing supporting the permanent magnet synchronous motor can be diagnosed with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a diagram showing a configuration of a system including a motor diagnostic device 7 , a compressor 6 , and an inverter 1 according to the first embodiment.

[0010] Figure 2It is a diagram showing the structure of the compressor 6.

[0011] Figure 3 It is a diagram showing a cross section of the permanent magnet synchronous motor 2 and the main shaft 10 when the sliding bearing 9 is normal.

[0012] Figure 4 It is a diagram showing a cross section of the sliding bearing 9 and the main shaft 10 when the sliding bearing 9 is normal.

[0013] Figure 5 This is a diagram showing the waveform of the motor current when the sliding bearing 9 is normal.

[0014] Figure 6 It is a diagram showing a cross section of the permanent magnet synchronous motor 2 and the main shaft 10 when the sliding bearing 9 is worn.

[0015] Figure 7 It is a diagram showing a cross section of the sliding bearing 9 and the main shaft 10 when the sliding bearing 9 is worn.

[0016] Figure 8 This is a diagram showing the waveform of the motor current when the sliding bearing 9 is worn.

[0017] Fig. 9 This is a diagram for explaining a method of detecting the frequency f of the three-phase currents Iu, Iv, and Iw by the phase generator 100.

[0018] Fig.10 This is a diagram for explaining a method of generating a voltage phase θe from a frequency f.

[0019] Fig.11 1 is a diagram showing a configuration of the reverse phase current detector 4 according to the first embodiment.

[0020] Fig.12 A diagram showing a schematic cross-sectional view of a 9-slot motor.

[0021] Fig.13 This is a diagram showing a configuration of a system including an inverter 1A and a compressor 6 according to a second embodiment.

[0022] Fig.14 This is a diagram showing a configuration of a system including an inverter 1B, a compressor 6 , and an earth leakage breaker 29 according to the third embodiment.

[0023] Fig.15 1 is a diagram showing a configuration of a reverse phase current detector 4A according to a third embodiment. DETAILED DESCRIPTION

[0024] Hereinafter, the embodiments will be described with reference to the drawings. In the multiple drawings, the same reference numerals are given to the same components.

[0025] Implementation method 1.

[0026] The motor diagnosis device 7 according to the first embodiment detects the motor current of the compressor 6 to diagnose the deterioration state of the sliding bearing in the permanent magnet synchronous motor.

[0027] Figure 1 This is a diagram showing a configuration of a system including a motor diagnostic device 7 , a compressor 6 , and an inverter 1 according to the first embodiment.

[0028] The motor diagnostic device 7 includes current detectors 3 u , 3 v , and 3 w , a phase generator 100 , a reverse-phase current detector 4 , and a degradation diagnostic device 5 .

[0029] The current detector 3u is provided in the U-phase line between the inverter 1 and the permanent magnet synchronous motor 2. The current detector 3v is provided in the V-phase line between the inverter 1 and the permanent magnet synchronous motor 2. The current detector 3w is provided in the W-phase line between the inverter 1 and the permanent magnet synchronous motor 2. The current detectors 3u, 3v, and 3w detect the currents of the U-phase, V-phase, and W-phase lines, respectively.

[0030] The phase generator 100 outputs −θe, which is an opposite phase (inverse phase information) of the voltage phase θe of the three-phase AC voltage.

[0031] The reverse current detector 4 receives the currents Iu, Iv, Iw outputted from the current detectors 3u, 3v, 3w and the reverse phase information -θe outputted from the phase generator 100. The reverse current detector 4 calculates the reverse current I2 based on the reverse phase information -θe and the three-phase currents Iu, Iv, Iw.

[0032] The degradation diagnostic device 5 diagnoses degradation of the sliding bearing 9 supporting the permanent magnet synchronous motor 2 based on the reverse phase current I2 .

[0033] Figure 2 It is a diagram showing the structure of the compressor 6. Figure 3 It is a diagram showing a cross section of the permanent magnet synchronous motor 2 and the main shaft 10 when the sliding bearing 9 is normal. Figure 4 It is a diagram showing a cross section of the sliding bearing 9 and the main shaft 10 when the sliding bearing 9 is normal.

[0034] The compressor 6 includes a compression element 8, a permanent magnet synchronous motor 2, a main shaft 10, a sliding bearing 9, and a ball bearing 11. The permanent magnet synchronous motor 2 includes a stator 2a and a rotor 2b.

[0035] The compression member 8 compresses the gas load.

[0036] The permanent magnet synchronous motor 2 rotates a compression element 8 as a load.

[0037] The main shaft 10 connects the rotor 2 b and the compression element 8 .

[0038] The ball bearing 11 and the sliding bearing 9 maintain the centrifugal force and the gravity for the main shaft 10 to perform the rotational motion. The sliding bearing 9 supports the permanent magnet synchronous motor 2 .

[0039] In order to allow the rotational movement of the main shaft 10, a gap AG having a predetermined width is provided in the radial direction between the sliding bearing 9 and the main shaft 10. The gap AG is usually lubricated with lubricating oil.

[0040] The stator 2a is composed of a winding and a stator core.

[0041] The rotor 2 b is composed of permanent magnets 13 and a rotor core 14 .

[0042] like Figure 4 As shown, when the sliding bearing 9 is normal, the rotor 2b and the stator 2a are arranged coaxially with a gap 12 therebetween. The width of the gap 12 is substantially uniform.

[0043] Figure 5 This is a diagram showing the waveform of the motor current when the sliding bearing 9 is normal.

[0044] In the permanent magnet synchronous motor 2 , since the impedance of the windings is designed to be balanced in three phases, when a balanced voltage is applied to the three phases, balanced currents Iu, Iv, and Iw of the three phases can be obtained.

[0045] Figure 6 It is a diagram showing a cross section of the permanent magnet synchronous motor 2 and the main shaft 10 when the sliding bearing 9 is worn. Figure 7 It is a diagram showing a cross section of the sliding bearing 9 and the main shaft 10 when the sliding bearing 9 is worn. Figure 8 This is a diagram showing the waveform of the motor current when the sliding bearing 9 is worn.

[0046] In the compressor 6, the sliding bearing 9 is worn due to various factors such as poor lubrication or foreign matter mixing. Figure 7 As shown in FIG. 1 , the gap AG is wider than the initial design. In the compressor 6, the gap AG also serves as a passage for the refrigerant. Under unfavorable conditions such as a wide gap AG, the lubricating oil is sometimes drawn into the refrigerant flow and flows out of the compressor 6. As a result, the compressor 6 becomes poorly lubricated. If the poorly lubricated state of the compressor 6 continues, the wear of the sliding bearing 9 increases.

[0047] Since the sliding bearing 9 maintains the radial movement of the main shaft 10, if the gap AG is wide, the main shaft 10 will be displaced. Figure 6 As shown in FIG. 1 , the width of the gap 12 of the permanent magnet synchronous motor 2 in the radial direction becomes uneven, and the permanent magnet synchronous motor 2 becomes eccentric. The impedance balance of the permanent magnet synchronous motor 2 is destroyed due to the unevenness of the gap 12, and the impedances of the three phases are different. As a result, Figure 8As shown, the three-phase currents Iu, Iv, and Iw include unbalanced components. This unbalanced current component is generally called a reverse current. The reverse current is theoretically derived as a component rotating in the direction opposite to the phase rotation direction of the three-phase alternating current.

[0048] When the current detectors 3u, 3v, 3w detect the currents Iu, Iv, Iw, the phase generator 100 and the reverse-phase current detector 4 perform the following processing to extract the unbalanced components of the currents.

[0049] It is known that the unbalanced component of the current is a component having a frequency equal to the frequency of the three-phase alternating current and having a phase rotation direction opposite to that of the three-phase alternating current.

[0050] The phase generator 100 detects the frequency f of the detected three-phase currents Iu, Iv, and Iw. The phase generator 100 uses the detected frequency f to generate a reverse rotation voltage phase -θe that rotates in the opposite direction to the phase rotation direction of the three-phase AC.

[0051] Fig. 9 This is a diagram for explaining a method of detecting the frequency f of the three-phase currents Iu, Iv, and Iw by the phase generator 100.

[0052] The phase generator 100 measures a predetermined time ΔT for the number of times N that the polarity of the current Iu is reversed when it rises. The phase generator 100 uses ΔT and N to calculate the frequency f.

[0053] f=N / ΔT···(1)

[0054] Fig.10 This is a diagram for explaining a method of generating a voltage phase θe from a frequency f.

[0055] The phase generator 100 generates a voltage phase θe by time-integrating the frequency f. The voltage phase θe is multiplied by -1 (sign inversion) to generate a reverse-rotating voltage phase -θe that rotates in the opposite direction to the phase rotation direction of the multiple-phase alternating current.

[0056] Fig.11 1 is a diagram showing a configuration of the reverse phase current detector 4 according to the first embodiment.

[0057] The reverse-phase current detector 4 includes a first phase converter 31 , a rotation coordinate converter 32 , a first low-pass filter 33 a , a second low-pass filter 33 b , and an absolute value calculator 34 .

[0058] The first phase converter 31 converts the three-phase currents Iu, Iv, and Iw at a predetermined timing into the two-phase currents Iα and Iβ based on the equation (2).

[0059] [Formula 1]

[0060]

[0061] The rotating coordinate converter 32 converts the two-phase currents Iα and Iβ into a first-axis direct current component Id and a second-axis direct current component Iq that are orthogonal to each other based on the equation (3).

[0062] [Formula 2]

[0063]

[0064] The first low-pass filter 33a receives the DC component Id of the first axis and removes the AC component included in the DC component Id of the first axis. The second low-pass filter 33b receives the DC component Iq of the second axis and removes the AC component included in the DC component Iq of the second axis.

[0065] The absolute value calculator 34 calculates the square root of the sum of the squares of the output of the first low-pass filter 33 a and the output of the second low-pass filter 33 b as the reverse phase current I2 .

[0066] The rotating coordinate converter 32, the first low-pass filter 33a and the second low-pass filter 33b form a bandpass filter that specifies the current component rotating in the opposite direction. The reverse phase component, which is AC, is converted into DC by the coordinate conversion into the coordinate system inverted by the rotating coordinate converter 32.

[0067] The degradation diagnostic device 5 detects the expansion of the gap AG between the sliding bearing 9 and the main shaft 10 supporting the permanent magnet synchronous motor 2 based on the reverse current I2. More specifically, the degradation diagnostic device 5 estimates the wear amount AT of the sliding bearing 9 based on the relationship between the reverse current I2 and the wear amount AT of the sliding bearing obtained in advance. The wear amount AT represents the expansion of the gap AG.

[0068] The relational expression may be, for example, a linear expression as shown below: a1 and b1 are coefficients.

[0069] AT=a1×I2+b1···(4)

[0070] Alternatively, the degradation diagnostic device 5 can estimate the eccentricity EC of the permanent magnet synchronous motor 2 based on the relationship between the reverse current I2 and the eccentricity EC of the permanent magnet synchronous motor obtained in advance. The eccentricity EC of the permanent magnet synchronous motor 2 represents the expansion of the gap AG. The wear amount AT of the sliding bearing 9 can be estimated based on the eccentricity EC of the permanent magnet synchronous motor 2. The relationship can be a linear equation as shown below. a2 and b2 are coefficients.

[0071] EC=a2×I2+b2···(5)

[0072] When the estimated value AT of the wear amount of the sliding bearing 9 reaches a value that cannot be ignored relative to the size of the gap 12 (generally in the range of 0.1 to 1 mm), it can be diagnosed that the sliding bearing 9 is abnormal.

[0073] In the present embodiment, since the permanent magnet synchronous motor 2 is a three-phase motor, the number of slots of the stator 2a is an integer multiple of 3. When the number of slots of the stator 2a is an odd number, since the phase whose gap is reduced and the phase whose gap is expanded due to eccentricity are necessarily different, the change of the reverse current I2 becomes relatively large, and diagnosis can be performed with higher accuracy.

[0074] Fig.12 The figure shows a schematic cross-sectional view of a 9-slot motor.

[0075] exist Fig.12 Only 3 slots are shown in the figure.

[0076] The slots 20, the stator core 21, and the teeth 21a of the stator core are shown. There are nine teeth 21a, and any one of the U, V, and W windings is wound around each of them.

[0077] When the rotor 2b is eccentric toward the upper V phase (V1 tooth), the gap between the V1 tooth and the rotor 2b is reduced, and the gaps between the U3 tooth and the W2 tooth and the rotor 2b are increased. This eccentric state causes an imbalance in the impedance of each phase.

[0078] As described above, the motor diagnostic device of the present embodiment extracts the unbalanced component of the motor current to estimate the eccentricity of the permanent magnet synchronous motor 2 or the wear of the sliding bearing 9. As a result, the wear of the sliding bearing can be detected without disassembling the sliding bearing 9 and without newly installing a vibration sensor or the like. If a clamp-type sensor is used as the current detector 3u, 3v, 3w, it is not necessary to remove the wiring of the device to be measured, so the inspection can be made simpler. The diagnosis of the wear of the sliding bearing is highly required in compressors that are difficult to oil and maintain, and as an application, it can be said that the utilization rate is particularly high.

[0079] Implementation method 2.

[0080] Fig.13 This is a diagram showing a configuration of a system including an inverter 1A and a compressor 6 according to a second embodiment.

[0081] Inverter 1A incorporates motor diagnostic device 7A and current detectors 3u, 3v, and 3w.

[0082] Phase generator 100A in motor diagnosis device 7A inverts and outputs voltage phase θe, which is an internal signal of inverter 1A. Voltage phase θe is used for inverter 1A to generate three-phase AC voltages Vu, Vv, and Vw.

[0083] That is, the three-phase AC voltage command generator 110 generates three-phase AC voltage command values ​​Vu*, Vv*, and Vw* according to the following equation: V is the amplitude of the output voltage command.

[0084] Vu*=Vsinθe···(6u)

[0085] Vv*=Vsin(θe-π / 3)···(6v)

[0086] Vw*=Vsin(θe+2π / 3)···(6w)

[0087] In the inverter 1A configured as described above, it is not necessary to detect the frequency f of the three-phase current as described in Embodiment 1. As a result, the processing of the phase generator 100A becomes simple, and the followability when the frequency changes is excellent.

[0088] Furthermore, since the inverter 1 includes the current detectors 3u, 3v, and 3w, there is no need to separately add the current detectors 3u, 3v, and 3w, and thus the motor diagnosis can be performed at a low cost.

[0089] Since the inverter 1A is independent of the compressor 6 and can recognize wear of the sliding bearing 9 of the compressor 6, the inverter 1A can always monitor the compressor 6. This allows measures to extend the life of the sliding bearing 9 such as reducing the frequency f of the three-phase current to be taken in real time.

[0090] Implementation method 3.

[0091] Fig.14 This is a diagram showing a configuration of a system including an inverter 1B, a compressor 6 , and an earth leakage breaker 29 according to the third embodiment.

[0092] The system of the third embodiment is different from the system of the second embodiment in the following points: The inverter 1B of the third embodiment does not include the current detector 3v of the V phase. The earth leakage breaker 29 is arranged between the inverter 1B and the system power supply 22.

[0093] When a leakage current, ie, a zero-phase current, of a predetermined value TH or more flows between the system power supply 22 and the inverter 1B, the leakage breaker 29 performs a circuit break.

[0094] In this way, it is ensured that the zero-phase current is less than the predetermined value TH when the circuit is not disconnected. When the circuit is not disconnected, if the reverse current I2 to be detected is sufficiently greater than the trip level of the leakage circuit breaker 29, that is, the predetermined value TH, a reverse current detector that ignores the zero-phase current can be constructed.

[0095] The current detectors 3u and 3w detect the two-phase currents Iu and Iw and output the detected currents to the reverse-phase current detector 4A.

[0096] Fig.15 1 is a diagram showing a configuration of a reverse phase current detector 4A according to a third embodiment.

[0097] The reverse current detector 4A of the third embodiment and Figure 2 The reverse phase current detector 4 of the first embodiment is different in that the reverse phase current detector 4A further includes a phase converter 35 .

[0098] Since the leakage current is negligibly small, the phase converter 35 calculates the undetected Iv based on the following equation. That is, the phase converter 35 calculates Iv by adding Iu to Iv and inverting the sign of the addition result. The phase converter 35 outputs the three-phase currents Iu, Iv, and Iw to the phase converter 31.

[0099] Iv=-(Iu+Iw)···(7)

[0100] As described above, in the present embodiment, since the number of current detectors is reduced from three to two on the premise of a system in which the leakage current can be ignored, the motor diagnosis can be performed at low cost.

[0101] In this embodiment, the upper limit value of the zero-phase current is ensured to be negligible by the leakage circuit breaker. However, if it is known in advance that the leakage current is negligibly small, it is of course possible to reduce the number of current detectors without using the leakage circuit breaker.

[0102] Furthermore, in the above-described embodiment, the motor diagnosis device is described as a device for detecting wear of a bearing, but it can of course also be used for a motor such as a magnetic bearing that may have a total bearing eccentricity.

[0103] The embodiments disclosed herein are to be considered in all respects as illustrative rather than restrictive. The scope of the present disclosure is indicated by the technical solutions rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the technical solutions.

[0104] Description of reference numerals:

[0105] 1, 1A, 1B…inverter; 2…permanent magnet synchronous motor; 2a…stator; 2b…rotor; 3u, 3v, 3w…current detector; 4, 4A…reverse current detector; 5…deterioration diagnostic device; 6…compressor; 7, 7A…motor diagnostic device; 8…compression member; 9…sliding bearing; 10…main shaft; 11…ball bearing; 12…gap; 13…permanent magnet; 14…rotor core; 20…slot; 21…stator core; 21a…tooth; 22…system power supply; 29…leakage circuit breaker; 31, 35…phase converter; 32…rotating coordinate converter; 33a…first low-pass filter; 33b…second low-pass filter; 34…absolute value operator; 100, 100A…phase generator; 110…AC voltage command generator.

Claims

1. A diagnostic device for a permanent magnet synchronous motor, characterized in that: have: a reverse-phase current calculator that calculates a reverse-phase current based on the magnitudes of currents of a plurality of phases flowing in the permanent magnet synchronous motor that rotates a load; and a degradation diagnostic device for diagnosing degradation of a sliding bearing supporting a main shaft connected to the permanent magnet synchronous motor based on the reverse current, A phase generator is further provided, the phase generator detecting the frequency of the current of the plurality of phases and using the frequency to generate a reverse rotating voltage phase, the reverse rotating voltage phase being a voltage phase rotating in a direction opposite to the phase rotation direction of the alternating current of the plurality of phases, The reverse phase current calculator calculates the reverse phase current based on the reverse rotation voltage phase and the currents of the plurality of phases.

2. The permanent magnet synchronous motor diagnostic device according to claim 1, characterized in that: The degradation diagnostic device detects an increase in a gap between the sliding bearing and the main shaft based on the reverse phase current.

3. The diagnostic device for a permanent magnet synchronous motor according to claim 2, characterized in that: The degradation diagnostic device estimates the wear amount of the sliding bearing based on the reverse phase current.

4. The permanent magnet synchronous motor diagnostic device according to claim 2, characterized in that: The degradation diagnostic device estimates an eccentricity amount of the permanent magnet synchronous motor based on the reverse phase current.

5. The permanent magnet synchronous motor diagnostic device according to claim 1, characterized in that: The currents of the plurality of phases are three-phase currents, The reverse current calculator comprises: A phase converter, which converts the magnitude of the three-phase current into the magnitude of the two-phase current; A rotating coordinate converter converts the magnitude of the two-phase current into a DC component of a first axis and a DC component of a second axis that are orthogonal to each other; a first low-pass filter receiving a DC component of the first axis; a second low-pass filter receiving a DC component of the second axis; and The computing unit calculates a square root of the sum of squares of an output of the first low-pass filter and an output of the second low-pass filter as the reverse phase current.

6. The permanent magnet synchronous motor diagnostic device according to claim 5, characterized in that: Three current detectors are provided for respectively detecting magnitudes of currents of corresponding phases among the three-phase currents.

7. The permanent magnet synchronous motor diagnostic device according to claim 1, characterized in that: A leakage circuit breaker is arranged between an inverter driving the permanent magnet synchronous motor and a system power supply, and the leakage circuit breaker is disconnected when a zero-phase current exceeding a predetermined value flows between the system power supply and the inverter. The currents of the plurality of phases are three-phase currents, The diagnostic device for the permanent magnet synchronous motor comprises: a first current detector for detecting a magnitude of a current of a first phase among the three-phase currents; and a second current detector for detecting the magnitude of the current of the second phase among the three phase currents; The reverse current calculator comprises: a first phase converter, which adds the magnitude of the current of the first phase and the magnitude of the current of the second phase, calculates a value with the sign of the addition result inverted as the magnitude of the current of the third phase among the three-phase currents, and outputs the magnitudes of the three-phase currents consisting of the first phase, the second phase, and the third phase; A second phase converter converts the magnitude of the three-phase current into the magnitude of a two-phase current; A rotating coordinate converter converts the magnitude of the two-phase current into a DC component of a first axis and a DC component of a second axis that are orthogonal to each other; a first low-pass filter receiving a DC component of the first axis; a second low-pass filter receiving a DC component of the second axis; as well as The computing unit calculates a square root of the sum of squares of an output of the first low-pass filter and an output of the second low-pass filter as the reverse phase current.

8. An inverter, characterized in that: have: The permanent magnet synchronous motor diagnostic device according to claim 1; and a voltage command generator that generates voltage command values ​​for driving a plurality of phases of the permanent magnet synchronous motor based on the voltage phase, The permanent magnet synchronous motor diagnostic device further includes a phase generator for generating a reverse rotating voltage phase by inverting the sign of the voltage phase, the reverse rotating voltage phase being a voltage phase rotating in a direction opposite to a phase rotation direction of the alternating current of the plurality of phases. The reverse phase current calculator calculates the reverse phase current based on the reverse rotation voltage phase and magnitudes of the currents of the plurality of phases.

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