Fault detection device and power converter equipped therewith

Abstract

The present invention provides a fault detection device capable of easily detecting failures in capacitor units that include multiple capacitors connected in parallel. [Solution] This fault detection device detects the effective values ​​I1e to Ine of the currents I1 to In flowing through multiple capacitors C1 to Cn when an AC voltage is applied to the capacitor unit, calculates the average value Iav of the detected effective values, and determines that the capacitor unit has failed if the magnitude of the deviation between any of the effective values ​​and the average value exceeds a reference value Is1. Therefore, a fault in the capacitor unit can be easily detected.

Description

Technical Field

[0001] The present disclosure relates to a fault detection device and a power conversion device including the same, and particularly to a fault detection device for detecting a fault in a capacitor unit including a plurality of capacitors connected in parallel, and a power conversion device including the same.

Background Art

[0002] For example, Japanese Patent Laid-Open No. 8-62270 (Patent Document 1) discloses a fault detection device for detecting a fault in a capacitor unit including a plurality of capacitor series bodies connected in parallel. Each capacitor series body includes two capacitors connected in series.

[0003] The fault detection device includes a plurality of diode series bodies connected in parallel between DC terminal pairs, and a voltage detector for detecting a DC voltage between the DC terminal pairs. The plurality of diode series bodies are provided corresponding to the plurality of capacitor series bodies, respectively. Each diode series body includes two diodes connected in series. The intermediate node of each diode series body is connected to the intermediate node of the corresponding capacitor series body.

[0004] When all the capacitors of the capacitor unit are normal, no DC voltage is generated between the DC terminal pairs. When any one of the plurality of capacitors of the capacitor unit fails, a DC voltage is generated between the DC terminal pairs. Therefore, when a DC voltage is detected by the voltage detector, it can be determined that the capacitor unit has failed.

[0005] Also, for example, Japanese Patent Laid-Open No. 2019-158456 (Patent Document 2) discloses a fault detection device for detecting a fault in a capacitor included in an AC filter provided between a power converter and a load. This fault detection device obtains a reference value of the current flowing through the capacitor based on the AC output voltage of the power converter and its frequency, and the initial capacitance value of the capacitor. Then, the current value of the capacitor is detected, and when the current value is lower than the reference value, it is determined that the capacitor has failed. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-62270 [Patent Document 2] Japanese Patent Publication No. 2019-158456 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, while the fault detection device described in Patent Document 1 could detect a fault in a capacitor unit containing multiple capacitors connected in parallel in a series, it could not detect a fault in a capacitor unit containing multiple capacitors connected in parallel.

[0008] Furthermore, while the fault detection device described in Patent Document 2 could detect a fault in a single capacitor, it could not detect a fault in a capacitor unit that included multiple capacitors connected in parallel.

[0009] Furthermore, the fault detection device described in Patent Document 2 required pre-measuring the initial capacitance value of the capacitor and inputting it into the device, which presented a problem due to the considerable effort involved.

[0010] Therefore, the primary object of this disclosure is to provide a fault detection device capable of easily detecting a fault in a capacitor unit including a plurality of capacitors connected in parallel, and a power conversion device equipped with the same. [Means for solving the problem]

[0011] The fault detection device according to this disclosure is a fault detection device for detecting a fault in a capacitor unit including a plurality of capacitors connected in parallel, and comprises a plurality of current detection units that detect the current values ​​of each of the plurality of capacitors when an AC voltage is applied to the capacitor unit, and a fault detection circuit that calculates the average value of the plurality of current values ​​detected by the plurality of current detection units, and determines that the capacitor unit has failed if the magnitude of the deviation between any of the plurality of current values ​​and the average value exceeds a predetermined value.

[0012] Furthermore, another fault detection device relating to this disclosure is a fault detection device for detecting faults in a capacitor unit that includes a plurality of capacitors connected in parallel. The plurality of capacitors are pre-divided into first and second capacitor groups, each containing the same number of capacitors. The capacitor unit includes first and second wires that carry current to the first and second capacitor groups, respectively.

[0013] The first portion of the first wire is positioned in a first direction, and the second portion of the second wire is positioned in a second direction opposite to the first direction, with the first and second wire portions positioned adjacent to each other to form a wire pair. This fault detection device includes a current detection unit that detects the current value of the wire pair when an AC voltage is applied to the capacitor unit, and a fault detection circuit that determines that the capacitor unit has failed when the current value detected by the current detection unit exceeds a predetermined value. [Effects of the Invention]

[0014] The fault detection device according to this disclosure detects the current values ​​of multiple capacitors, calculates the average value of the detected current values, and determines that a capacitor unit has failed if the magnitude of the deviation between any of the current values ​​and the average value exceeds a predetermined value. Therefore, it is possible to easily detect failures in capacitor units that include multiple capacitors connected in parallel.

[0015] In addition, in another failure detection device according to the present disclosure, a plurality of capacitors are previously divided into first and second capacitor groups each including the same number of capacitors, and first and second electric wires for flowing current through the first and second capacitor groups are provided, respectively. A first electric wire portion of the first electric wire is arranged in a first direction, a second electric wire portion of the second electric wire is arranged in a second direction opposite to the first direction, and the first and second electric wire portions are arranged adjacent to each other to form an electric wire pair. Then, the current value of the electric wire pair is detected, and when the current value exceeds a predetermined value, it is determined that the capacitor unit has failed. Therefore, it is possible to easily detect the failure of a capacitor unit including a plurality of capacitors connected in parallel.

Brief Description of Drawings

[0016] [Figure 1] It is a circuit block diagram showing the configuration of a power conversion device according to Embodiment 1 of the present disclosure. [Figure 2] It is a block diagram showing the configuration of the failure detection circuit shown in FIG. 1. [Figure 3] It is a time chart for explaining the principle of the failure detection method shown in FIGS. 1 and 2. [Figure 4] It is another time chart for explaining the principle of the failure detection method shown in FIGS. 1 and 2. [Figure 5] It is a circuit block diagram showing the configuration of a power conversion device according to Embodiment 2 of the present disclosure. [Figure 6] It is a block diagram showing the configuration of the failure detection circuit shown in FIG. 5. [Figure 7] It is a time chart for explaining the principle of the failure detection method shown in FIGS. 5 and 6. [Figure 8] It is another time chart for explaining the principle of the failure detection method shown in FIGS. 5 and 6.

Embodiments for Carrying Out the Invention

[0017] [Embodiment 1] FIG. 1 is a circuit block diagram showing the configuration of a power conversion device according to Embodiment 1 of the present disclosure. In FIG. 1, this power conversion device includes input terminals T1 and T2, an inverter 1, a reactor 2, capacitors C1 to Cn, current detectors 3, CD1 to CDn, a fault detection circuit 4, a notification unit 5, a control device 6, and output terminals T3 and T4. Here, n is an integer of 2 or more.

[0018] The input terminals T1 and T2 receive a DC voltage VI from a DC power source 7. The DC power source 7 may be a battery or a converter that converts an AC voltage into a DC voltage. The output terminals T3 and T4 are connected to a load 8. The load 8 is driven by an AC voltage VO having a predetermined frequency (for example, a commercial frequency) supplied from the power conversion device. The DC voltage VI and the AC voltage VO are detected by the control device 6.

[0019] The inverter 1 is PWM (Pulse Width Modulation) controlled by the control device 6, and converts the DC voltage VI received from the input terminals T1 and T2 into an AC voltage VP having a predetermined frequency (for example, a commercial frequency) and outputs it between the AC nodes 1a and 1b.

[0020] The inverter 1 is a well-known one including a plurality of IGBTs (Insulated Gate Bipolar Transistors) and a plurality of diodes. Each IGBT is turned on and off at a switching frequency sufficiently higher than the predetermined frequency. The inverter 1 outputs a positive pulse voltage train and a negative pulse voltage train alternately by half a cycle as the AC voltage VP. Therefore, the AC voltage VP includes a predetermined frequency component and a high frequency component.

[0021] One terminal of the reactor 2 is connected to the output node 1a of the inverter 1, and the other terminal of the reactor 2 is connected to the output terminal T3. The current detector 3 detects the AC current flowing through the reactor 2, that is, the output current IO of the inverter 1, and outputs a signal IOf indicating the detected value to the control device 6.

[0022] [ Capacitors C1 to Cn are connected in parallel between nodes N1 and N2 to form a capacitor unit. Nodes N1 and N2 are connected to output terminals T3 and T4, respectively. Capacitors C1 to Cn are the same product and have the same initial capacitance value. By connecting capacitors C1 to Cn in parallel, a capacitor unit with the desired capacitance value is formed.

[0023] Reactor 2 and capacitors C1 to Cn constitute an AC filter (low-pass filter) that removes high-frequency components from the AC output voltage VP of inverter 1 and allows the AC voltage VO with predetermined frequency components to pass to output terminals T3 and T4. In other words, the AC filter converts the output voltage VP of inverter 1 into a sinusoidal AC voltage VO.

[0024] When such a capacitor unit fails, the performance of the AC filter deteriorates. Furthermore, continued use of a faulty capacitor unit may lead to smoke emission accidents or ground fault accidents. Therefore, in this embodiment 1, current detectors CD1 to CDn and fault detection circuit 4 are used to detect capacitor unit failures and prevent smoke emission accidents and ground fault accidents from occurring.

[0025] Current detectors CD1 to CDn detect the instantaneous values ​​of the alternating currents I1 to In flowing through capacitors C1 to Cn, respectively, and provide signals I1f to Inf indicating the detected values ​​to the fault detection circuit 4. Based on the output signals I1f to Inf from current detectors CD1 to CDn, the fault detection circuit 4 generates signals F1 to Fn indicating whether or not capacitors C1 to Cn are faulty.

[0026] If capacitors C1 to Cn are not faulty, signals F1 to Fn will both be set to the deactivating level "L". In other words, if signals F1 to Fn are both at the "L" level, it is determined that the capacitor unit (capacitors C1 to Cn) is not faulty.

[0027] If capacitors C1 to Cn are faulty, signals F1 to Fn will be set to the activation level "H" (high). In other words, if at least one of signals F1 to Fn, signal B, is set to the "H" level, it is determined that the capacitor unit is faulty.

[0028] Figure 2 is a block diagram showing the configuration of the fault detection circuit 4. In Figure 2, the fault detection circuit 4 includes low-pass filters (LPFs) A1 to An, RMS calculation units B1 to Bn, average value calculation unit 10, deviation calculation units D1 to Dn, reference value generation unit 11, and comparison units E1 to En.

[0029] Low-pass filters A1 to An receive the output signals I1f to Inf from current detectors CD1 to CDn, respectively. Each of the signals I1f to Inf contains a predetermined frequency component and a high-frequency component. Only the predetermined frequency component from the predetermined frequency component and high-frequency component of the signals I1f to Inf pass through the low-pass filters A1 to An, respectively, to become signals I1fa to Infa, respectively.

[0030] The RMS calculation units B1 to Bn each determine the RMS values ​​I1e to Ine of predetermined frequency components of the capacitor currents I1 to In based on the signals I1fa to Infa. The current detectors CD1 to CDn, the low-pass filters A1 to An, and the RMS calculation units B1 to Bn constitute multiple current detection units that detect the current values ​​of multiple capacitors C1 to Cn. The average value calculation unit 10 determines the average value Iav of the RMS values ​​I1e to Ine.

[0031] The deviation calculation units D1 to Dn calculate the magnitude of the deviation between the effective values ​​I1e to Ine and the mean value Iav, respectively, |I1e-Iav| to |Ine-Iav|. The reference value generation unit 11 generates a reference value Is1 of a predetermined magnitude. The reference value Is1 is set to a predetermined positive value based on the tolerance range of the capacitance values ​​of capacitors C1 to Cn. The comparison units E1 to En compare the magnitude of the deviation |I1e-Iav| to |Ine-Iav| with the reference value Is1, respectively, and output signals F1 to Fn indicating the comparison result.

[0032] If |I1e-Iav|~|Ine-Iav| is less than the reference value Is1, signals F1~Fn are set to the deactivation level "L". If |I1e-Iav|~|Ine-Iav| is greater than the reference value Is1, signals F1~Fn are set to the activation level "H".

[0033] For example, if capacitors C1 to Cn are both undegraded and functioning normally, the variation in the effective values ​​I1e to Ine of the currents I1 to In flowing through capacitors C1 to Cn is small. Therefore, the magnitude of the deviation |I1e-Iav| to |Ine-Iav| will be smaller than the reference value Is1, and signals F1 to Fn will both be at the "L" level.

[0034] Furthermore, if, for example, capacitor C1 among capacitors C1 to Cn deteriorates and its capacitance decreases, the effective value I1e of the current I1 flowing through capacitor C1 becomes smaller than the effective values ​​I2e to Ine of the currents I2 to In flowing through the other capacitors C2 to Cn. As a result, the magnitude of the deviation |I1e-Iav| becomes larger than the reference value Is1, and signal F1 is set to the activation level "H". The other signals F2 to Fn are both maintained at the "L" level.

[0035] Referring again to Figure 1, the output signals F1 to Fn of the fault detection circuit 4 are supplied to the notification unit 5. When at least one of the output signals F1 to Fn of the fault detection circuit 4 reaches the activation level "H", the notification unit 5 notifies the user of the power converter that the capacitor unit has failed using sound, light, images, etc.

[0036] If the notification unit 5 notifies that the capacitor unit has failed, the user of the power converter shall, for example, stop the operation of the inverter 1 and replace the capacitor unit with a new one.

[0037] The control device 6 controls the inverter 1 according to the DC input voltage VI, the AC output voltage VO, the AC output current IO of the inverter 1, and the reference AC voltage VR. The control device 6 performs PWM control of the inverter 1 so that the waveform of the AC output voltage VO matches the waveform of the reference AC voltage VR.

[0038] Next, the operation of this power converter will be described. When a DC voltage VI is supplied from the DC power supply 7 and the power switch (not shown) of the power converter is turned on, the operation of the power converter begins. The control device 6 controls the inverter 1, and the DC voltage VI supplied from the DC power supply 7 is converted into an AC voltage VP by the inverter 1.

[0039] This AC voltage VP contains predetermined frequency components and high-frequency components. Reactor 2 and capacitor units (capacitors C1 to Cn) constitute an AC filter. The high-frequency components of the AC voltage VP generated by inverter 1 are blocked by the AC filter, and the predetermined frequency components of the AC voltage VP pass through the AC filter and are supplied to load 8 as AC voltage VO. Load 8 is driven by AC voltage VO.

[0040] Furthermore, the instantaneous values ​​of the alternating currents I1 to In flowing through capacitors C1 to Cn are detected by current detectors CD1 to CDn, and signals I1f to Inf indicating the detected values ​​of the alternating currents I1 to In are supplied to the fault detection circuit 4.

[0041] In the fault detection circuit 4 (Figure 2), predetermined frequency components of the signals I1f to Inf pass through the low-pass filters A1 to An to become the signals I1fa to Infa, which are then supplied to the RMS calculation units B1 to Bn. Based on the signals I1fa to Infa, the RMS calculation units B1 to Bn determine the RMS values ​​I1e to Ine of the predetermined frequency components of the capacitor currents I1 to In. The RMS values ​​I1e to Ine are supplied to the average value calculation unit 10 and the deviation calculation units D1 to Dn.

[0042] The average calculation unit 10 calculates the average value Iav of the effective values ​​I1e to Ine. This average value Iav is provided to each of the deviation calculation units D1 to Dn. The deviation calculation units D1 to Dn each calculate the magnitude of the deviation |I1e-Iav| to |Ine-Iav| between the effective values ​​I1e to Ine and the average value Iav. The magnitude of the deviation |I1e-Iav| to |Ine-Iav| is provided to each of the comparison units E1 to En. In addition, the reference value generation unit 11 generates a reference value Is1 of a predetermined magnitude and provides it to each of the comparison units E1 to En.

[0043] In the comparison units E1 to En, the magnitude of the deviation |I1e-Iav| to |Ine-Iav| is compared with the reference value Is1, and signals F1 to Fn indicating the comparison result are output. If capacitors C1 to Cn are normal, signals F1 to Fn are set to the deactivation level "L". If capacitors C1 to Cn are degraded, signals F1 to Fn are set to the activation level "H". Signals F1 to Fn are supplied to the notification unit 5 (Figure 1).

[0044] If at least one of signals F1 to Fn reaches the activation level "H", the notification unit 5 notifies the user of the power converter that the capacitor unit has failed. The user of the power converter then, for example, stops the operation of the inverter 1 and replaces the capacitor unit with a new one.

[0045] Figure 3 is a time chart illustrating the principle of this embodiment 1. Figure 3 shows the simulation results when the number of capacitors C n is 5, the capacitance values ​​of capacitors C1 to C5 are the same, and the capacitor unit (capacitors C1 to C5) is functioning normally.

[0046] In Figure 3, (A) shows the waveform of the AC output voltage VO of the power converter, (B) shows the waveform of the AC current IC flowing through the capacitor unit, (C) shows the waveform of the AC current I1 flowing through capacitor C1, (D) shows the waveform of the average current IAV = IC / 5 of the AC currents I1 to I5 flowing through capacitors C1 to C5, and (E) shows the waveform of the deviation ΔI1 = IAV - I1 between the average current IAV and the AC current I1.

[0047] In Figure 3(A), the AC output voltage VO changes sinusoidally at a predetermined frequency (50 Hz). In Figures 3(B) to (D), the AC current IC, AC current I1, and average current IAV each contain a predetermined frequency component and a high-frequency component.

[0048] In Figure 3, since the capacitance values ​​of capacitors C1 to C5 are the same, the magnitudes of the AC currents I1 and IAV are both 1 / 5 of the AC current IC. Therefore, the deviation ΔI1 = IAV - I1 is 0A.

[0049] Figure 4 is another time chart illustrating the principle of this embodiment 1, and is shown in comparison to Figure 3. Figure 4 shows the simulation results when capacitor C1 among capacitors C1 to C5 deteriorates, its capacitance value decreases to 50% of its initial value, and the capacitor unit fails.

[0050] Figures 4(A) to 4(E), similar to Figures 3(A) to 4(E), show the waveforms of the AC output voltage VO, AC current IC, AC current I1, average current IAV, and deviation ΔI1 = IAV - I1, respectively.

[0051] Here, the capacitance value of capacitor C1 has decreased to 50% of its initial value, so as shown in Figure 4(C), the magnitude of the AC current I1 decreases to 50% of its initial value (Figure 3(C)). Therefore, as shown in Figure 4(E), the deviation ΔI1 = IAV - I1 changes sinusoidally. Thus, as can be seen from Figures 3(E) and 4(E), by monitoring the magnitude of the deviation ΔI1, it is possible to determine whether capacitor C1 is functioning normally or not.

[0052] Therefore, in this embodiment 1, as shown in Figures 1 and 2, the instantaneous values ​​of the currents I1 to In flowing through capacitors C1 to Cn are detected, the effective values ​​I1e to Ine, which are the magnitudes of the currents I1 to In, are determined, their average value Iav is determined, the magnitude of the deviation between the effective values ​​I1e to Ine and the average value Iav, |I1e-Iav| to |Ine-Iav|, and if either of the magnitudes of the deviation |I1e-Iav| to |Ine-Iav| exceeds the reference value Is1, it is determined that the capacitor unit has failed.

[0053] As described above, in this embodiment 1, a failure in a capacitor unit including multiple capacitors C1 to Cn connected in parallel can be easily detected. Therefore, it is possible to prevent smoke emission accidents or ground fault accidents from occurring due to the continued use of a failed capacitor unit.

[0054] Furthermore, since the average value Iav of the effective values ​​I1e to Ine of multiple currents I1 to In flowing through multiple capacitors C1 to Cn is used as the reference value Is1, capacitor unit failures can be detected regardless of the operating status of the power converter. Also, unlike the fault detection device described in Patent Document 2, there is no need to measure and input the initial capacitance values ​​of capacitors C1 to Cn into the device, so the reference value Is1 can be easily generated.

[0055] In this embodiment 1, the notification unit 5 notified that the capacitor unit had failed when, for example, the output signal F1 of the fault detection circuit 4 reached the "H" level. However, instead of this, or in addition to this, it may also notify that the capacitor C1 corresponding to signal F1 has failed. In this case, the user of the power converter may stop the operation of the inverter 1 and replace only the faulty capacitor C1 of the capacitor unit with a new one.

[0056] [Embodiment 2] Figure 5 is a circuit block diagram showing the configuration of a power converter according to Embodiment 2 of the present disclosure, and is shown in comparison with Figure 1. Referring to Figure 5, the differences between this power converter and the power converter of Figure 1 are that capacitors C1 to Cn are replaced by multiple capacitors 21, multiple capacitors 22, and electric wires 23 and 24, current detectors C1 to Cn are replaced by current detectors 26, and fault detection circuit 4 and notification unit 5 are replaced by fault detection circuit 27 and notification unit 28, respectively.

[0057] Multiple capacitors 21, multiple capacitors 22, and wires 23 and 24 constitute a capacitor unit. Multiple capacitors 21 constitute a first capacitor group, and multiple capacitors 22 constitute a second capacitor group. The number of capacitors 21 in the first capacitor group is the same as the number of capacitors 22 in the second capacitor group. Capacitors 21 and 22 are the same product and have the same initial capacitance value.

[0058] One electrode of each of the multiple capacitors 21 is connected to node N21, and their other electrodes are both connected to node N23. One electrode of each of the multiple capacitors 22 is connected to node N22, and their other electrodes are both connected to node N23. Node N23 is connected to output terminal T4.

[0059] One end of wire 23 (the first wire) is connected to node N24, and the other end is connected to node N21. One end of wire 24 is connected to node N24, and the other end is connected to node N22. Node N24 is connected to output terminal T3.

[0060] At least a portion of the electric wire 23, wire portion 23a (first wire portion), is oriented in a first direction (from top to bottom in Figure 5), and at least a portion of the electric wire 24, wire portion 24a (second wire portion), is oriented in a second direction opposite to the first direction (from bottom to top in Figure 5). The wire portions 23a and 24a are arranged adjacent to each other to form a wire pair 25.

[0061] In the second embodiment, the electric wire 24 is wound in a square shape so that the wire portions 23a and 24a face in opposite directions and are arranged adjacent to each other, constituting the wire pair 25.

[0062] The current detector 26 detects the instantaneous value of the alternating current I25 flowing through the wire pair 25 and outputs a signal I25f indicating the detected value to the fault detection circuit 27. The alternating current I25 is the deviation I25 = I23 - I24 between the alternating current I23 flowing through the electric wire 23 and the current I24 flowing through the electric wire 24.

[0063] The fault detection circuit 27 compares the effective value I25e of the alternating current I25 indicated by the output signal I25f of the current detector 26 with a predetermined reference value Is2 and outputs a signal φ27 indicating the comparison result to the notification unit 28. When I25e < Is2, the signal φ27 becomes the "L" level of the non-activated level, and when I25e > Is2, the signal φ27 becomes the "H" level of the activated level.

[0064] Fig. 6 is a block diagram showing the configuration of the fault detection circuit 27. In Fig. 6, the fault detection circuit 27 includes a low-pass filter (LPF) 31, an effective value calculation unit 32, a reference value generation unit 33, and a comparison unit 34.

[0065] The low-pass filter (LPF) 31 receives the output signal I25f of the current detector 26. The signal I25f includes a predetermined frequency component and a high-frequency component. Only the predetermined frequency component among the predetermined frequency component and the high-frequency component of the signal I25f passes through the low-pass filter 31 and becomes the signal I25fa.

[0066] The effective value calculation unit 32 obtains the effective value I25e of the predetermined frequency component of the alternating current I25 based on the signal I25fa. The current detector 26, the low-pass filter 31, and the effective value calculation unit 32 constitute a current detection unit that detects the current value of the wire pair 25. The reference value generation unit 33 generates a reference value Is2 of a predetermined magnitude. The reference value Is2 is set to a predetermined positive value based on the allowable range of the capacitance values of the capacitors 21 and 22.

[0067] The comparison unit 34 compares the magnitudes of the effective value I25e and the reference value Is2, and outputs a signal φ27 indicating the comparison result. When the effective value I25 is smaller than the reference value Is2, the signal φ27 is set to the "L" level of the non-activated level. When the effective value I25e is larger than the reference value Is2, the signal φ27 is set to the "H" level of the activated level.

[0068] When the plurality of capacitors 21 and the plurality of capacitors 22 are new and their capacitance values are within the normal range, the variation in the values of the currents flowing through the plurality of capacitors 21 and the plurality of capacitors 22 is sufficiently small. Therefore, the effective value I25e of the alternating current I25 becomes sufficiently small, I25e < Is2, and the signal φ27 becomes the "L" level of the non-activated level.

[0069] When the usage time of the plurality of capacitors 21 and the plurality of capacitors 22 becomes long, for example, when any one of the plurality of capacitors 21 deteriorates and the capacitance value of that capacitor 21 decreases, the current I23 becomes smaller than the current I24, and the effective value I25e of the alternating current I25 increases. When I25e > Is2, the signal φ27 becomes the "H" level of the activated level.

[0070] Referring to FIG. 5 again, when the output signal φ27 of the failure detection circuit 27 becomes the "H" level of the activated level, the notification unit 28 notifies the user of the power conversion device that the capacitor unit has failed using sound, light, an image, or the like.

[0071] If the notification unit 28 notifies that the capacitor unit has failed, the user of the power converter shall, for example, stop the operation of the inverter 1 and replace the capacitor unit with a new one.

[0072] Figure 7 is a time chart illustrating the principle of this second embodiment. Figure 7 shows the simulation results when there are two capacitors 21 and two capacitors 22, the capacitance values ​​of capacitors 21 and 22 are the same, and the capacitor unit is functioning normally.

[0073] In Figure 7, (A) shows the waveform of the AC output voltage VO of the power converter, (B) shows the waveform of the AC current IC flowing through the capacitor unit, (C) shows the waveform of the AC current I23 flowing through wire section 23a, (D) shows the waveform of the AC current (-I24) flowing through wire section 24a, and (E) shows the waveform of the AC current I25 = I23 - I24 flowing through wire pair 25.

[0074] In Figure 7(A), the AC output voltage VO changes sinusoidally at a predetermined frequency (50 Hz). In Figures 7(B) to (D), each of the AC current IC, AC current I23, and AC current (-I24) includes a predetermined frequency component and a high-frequency component.

[0075] In Figure 7, since the capacitance values ​​of the two capacitors 21 and the two capacitors 22 are the same, the magnitudes of the AC currents I23 and I24 are both half of the AC current IC. Therefore, the AC current I25 = I23 - I24 is 0A.

[0076] Figure 8 is another time chart illustrating the principle of this second embodiment, and is shown in comparison to Figure 7. Figure 8 shows the simulation results when one of the two capacitors 21 deteriorates and its capacitance value decreases to 50% of its initial value, causing the capacitor unit to fail.

[0077] Figures 8(A) to 8(E), similar to Figures 7(A) to 8(E), show the waveforms of the AC output voltage VO, AC current IC, AC current I23, AC current (-I24), and AC current I25, respectively.

[0078] Here, the capacitance value of one capacitor 21 has decreased to 50% of its initial value, so as shown in Figure 8(C), the magnitude of the AC current I23 decreases to 75% of its initial value (Figure 7(C)). Consequently, as shown in Figure 6(E), the amplitude of the AC current I25 increases. Therefore, as can be seen from Figures 7(E) and 8(E), by monitoring the magnitude of the AC current I25, it is possible to determine whether the capacitor unit is functioning correctly or not.

[0079] Therefore, in this second embodiment, as shown in Figures 5 and 6, the current I25 flowing through the wire pair 25 is detected, the effective value I25e, which is the magnitude of the current I25, is determined, and if the effective value I25e exceeds the reference value Is2, it is determined that the capacitor unit has failed.

[0080] Other configurations and operations are the same as in Embodiment 1, so their description will not be repeated. In this Embodiment 2, the same effects as in Embodiment 1 can be obtained. In addition, the number of current detectors can be reduced compared to Embodiment 1.

[0081] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The technical scope provided herein is defined by the claims rather than by the embodiments described above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0082] T1, T2 Input terminals, 1 Inverter, 2 Reactor, C1~Cn, 21, 22 Capacitors, 3, CD1~CDn, 26 Current detector, 4, 27 Fault detection circuit, 5, 28 Notification unit, 6 Control device, T3, T4 Output terminals, 7 DC power supply, 8 Load, A1~An, 31 Low-pass filter, B1~Bn, 32 RMS calculation unit, 10 Average value calculation unit, D1~Dn Deviation calculation unit, 11, 33 Reference value generation unit, E1~En, 34 Comparison unit, 23, 24 Wire, 25 Wire pair.

Claims

1. A fault detection device for detecting a fault in a capacitor unit that includes multiple capacitors connected in parallel, When an AC voltage is applied to the capacitor unit, a plurality of current detection units detect the current value of each of the plurality of capacitors, A fault detection device comprising: a fault detection circuit that calculates the average value of a plurality of current values ​​detected by the plurality of current detection units, and determines that the capacitor unit has failed if the magnitude of the deviation between any of the plurality of current values ​​and the average value exceeds a predetermined value.

2. The fault detection device according to claim 1, further comprising a notification unit that notifies the user if the fault detection circuit determines that the capacitor unit has failed.

3. The fault detection device according to claim 1, A power converter that converts DC voltage to AC voltage, The system includes an AC filter that removes high-frequency components from the AC voltage, The AC filter is a power conversion device that includes a reactor and the capacitor unit.

4. A fault detection device for detecting a fault in a capacitor unit that includes multiple capacitors connected in parallel, The plurality of capacitors are pre-divided into first and second capacitor groups, each containing the same number of capacitors. The capacitor unit includes first and second wires that carry current to the first and second capacitor groups, respectively. The first portion of the first wire is positioned in a first direction, the second portion of the second wire is positioned in a second direction opposite to the first direction, and the first and second portions of the wire are positioned adjacent to each other to form a wire pair. The fault detection device, A current detection unit detects the current value of the wire pair when an AC voltage is applied to the capacitor unit, A fault detection device comprising: a fault detection circuit that determines that the capacitor unit has failed when the current value detected by the current detection unit exceeds a predetermined value.

5. The fault detection device according to claim 4, further comprising a notification unit that notifies the user if the fault detection circuit determines that the capacitor unit has failed.

6. The fault detection device according to claim 4, A power converter that converts DC voltage to AC voltage, The system includes an AC filter that removes high-frequency components from the AC voltage, The AC filter is a power conversion device that includes a reactor and the capacitor unit.

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