Power conversion device and control device

Abstract

A power conversion device according to the present invention comprises: an inverter device including a DC input unit having a positive electrode terminal and a negative electrode terminal, an inverter circuit for converting power on the basis of a switching operation of a switching element, a DC capacitor for absorbing and smoothing a ripple current, generated by the switching operation of the inverter circuit, between the positive electrode terminal and the negative electrode terminal, a discharge resistor for discharging the DC capacitor, and a DC voltage sensor for detecting the DC voltage value of the DC capacitor; and a control device including a monitoring unit for monitoring the DC voltage value detected by the DC voltage sensor, a timing unit for measuring the time elapsed since the inverter device stopped, a determination unit that determines that the DC capacitor is abnormal when the DC voltage value monitored by the monitoring unit falls at least a predetermined range below a predetermined threshold smaller than the normal value, and a reporting unit for reporting that the DC capacitor is abnormal when the DC capacitor is determined to be abnormal by the determination unit.

Description

Power conversion device and control device

[0001] The present invention relates to a power conversion device and a control device.

[0002] For example, in a power conversion device that converts power between DC power and AC power, a DC input section is provided with a DC capacitor for absorbing (smoothing) ripple current. The DC capacitor may develop an abnormality, such as a decrease in capacity, due to, for example, aging or a malfunction. However, it has been difficult to appropriately detect an abnormality in the DC capacitor.

[0003] For this reason, a method has been proposed in the past to detect abnormalities such as a decrease in the capacitance of a DC capacitor in an inverter based on the magnitude of the resistor current and the magnitude of the voltage between the capacitor terminals when a predetermined reference time has elapsed since the start of current flow (see, for example, Patent Document 1).

[0004] Japanese Patent Application Publication No. 2008-228370

[0005] Generally, when the capacity of a DC capacitor decreases, the voltage of the DC capacitor will be different from that in normal conditions when the DC capacitor is charged at the time of device startup and when the DC capacitor is discharged at the time of device shutdown.

[0006] However, with conventional methods, it was possible to detect an abnormality in a DC capacitor based on the charging voltage of the DC capacitor when the device was started up, but it was not possible to detect an abnormality in a DC capacitor based on the discharge voltage of the DC capacitor when the device was stopped.

[0007] Therefore, the present disclosure aims to provide a means for detecting an abnormality in a DC capacitor connected to the DC input side of a power conversion device based on the discharge voltage of the DC voltage when the device is stopped by monitoring the discharge rate of the DC voltage when the device is stopped.

[0008] a DC capacitor that absorbs and smoothes ripple current generated by the switching operation of the inverter circuit between the positive and negative terminals; a discharge resistor through which the charge of the DC capacitor is discharged; and a DC voltage sensor that detects the DC voltage value of the DC capacitor; and a control device that includes: a monitoring unit that monitors the DC voltage value detected by the DC voltage sensor; a timing unit that measures the elapsed time since the inverter device was stopped; a determination unit that determines that an abnormality has occurred in the DC capacitor when the DC voltage value monitored by the monitoring unit falls below a predetermined threshold value that is lower than a normal value by a predetermined range or more when the timing unit measures that a predetermined time has elapsed since the inverter device was stopped; and a warning unit that issues a warning about an abnormality in the DC capacitor when the determination unit determines that an abnormality has occurred in the DC capacitor.

[0009] According to another aspect, a power conversion device includes an inverter device having a DC input unit having a positive terminal and a negative terminal, an inverter circuit that converts power based on the switching operation of a switching element, a plurality of DC capacitors that are connected in series between the positive terminal and the negative terminal via a DC neutral point and absorb and smooth ripple current generated by the switching operation of the inverter circuit, discharge resistors through which the charges of the plurality of DC capacitors are respectively discharged, and DC voltage sensors that detect DC voltage values ​​of the plurality of DC capacitors, and a monitoring unit that monitors the DC voltage values ​​of the plurality of DC capacitors detected by the DC voltage sensors, and a monitoring unit that monitors the DC voltage values ​​of the plurality of DC capacitors when the inverter device is stopped. a determination unit that, when the timing unit determines that a predetermined time has elapsed since the inverter device was stopped, compares the DC voltage values ​​of the plurality of DC capacitors monitored by the monitoring unit, and determines that one of the plurality of compared DC capacitors is abnormal if the DC voltage values ​​of the plurality of DC capacitors differ by a predetermined threshold or more; and a warning unit that, when the determination unit determines that one of the plurality of DC capacitors is abnormal, issues a warning that one of the plurality of DC capacitors is abnormal.

[0010] A control device according to one embodiment is a control device for a power conversion device including an inverter device having a DC input unit having a positive terminal and a negative terminal, an inverter circuit that converts power based on the switching operation of a switching element, a DC capacitor that absorbs and smooths ripple current generated by the switching operation of the inverter circuit between the positive terminal and the negative terminal, a discharge resistor through which the charge of the DC capacitor is discharged, and a DC voltage sensor that detects the DC voltage value of the DC capacitor, and is characterized by comprising: a monitoring unit that monitors the DC voltage value detected by the DC voltage sensor; a timing unit that measures the elapsed time since the inverter device was stopped; a determination unit that determines that there is an abnormality in the DC capacitor when the timing unit measures that a predetermined time has elapsed since the inverter device was stopped and the DC voltage value monitored by the monitoring unit falls below a predetermined threshold value that is lower than the normal value by more than a predetermined range; and a warning unit that issues a warning about an abnormality in the DC capacitor when the determination unit determines that there is an abnormality in the DC capacitor.

[0011] According to the present disclosure, by monitoring the discharge rate of the DC voltage when the device is stopped, it is possible to provide a means for detecting an abnormality in a DC capacitor connected to the DC input side of a power conversion device based on the discharge voltage of the DC voltage when the device is stopped.

[0012] 9 is a diagram showing an example of the configuration of a power conversion device according to a first embodiment. FIG. 1 is a diagram showing an example of the configuration of a control device in the power conversion device shown in FIG. 1. FIG. 2 is a flowchart showing an example of the operation of the control device in the power conversion device shown in FIGS. 1 and 2. FIG. 3 is a diagram showing an example of a discharge curve when a DC capacitor discharges after an inverter device is stopped. FIG. 4 is a diagram showing an example of the discharge curve of a normal DC capacitor shown in FIG. 4 and a discharge curve as a predetermined threshold. FIG. 5 is a diagram showing an example of the discharge curve of a normal DC capacitor according to a modified example of the first embodiment, a discharge curve as a predetermined threshold, and a discharge curve as a second predetermined threshold. FIG. 6 is a diagram showing an example of the configuration of a power conversion device according to a second embodiment. FIG. 7 is a diagram showing an example of the configuration of a control device in the power conversion device shown in FIG. 7. A flowchart showing an example of the operation of the control device in the power conversion device shown in FIGS. 7 and 8. FIG. 9 is a conceptual diagram showing an example of the hardware configuration of a processing circuit included in the control device in the embodiments shown in FIGS. 1 to 9.

[0013] Hereinafter, embodiments of a power conversion device and a control device according to the present disclosure will be described with reference to the drawings.

[0014] <Configuration of First Embodiment> FIG. 1 is a diagram showing an example of the configuration of a power conversion device 1 according to a first embodiment.

[0015] As shown in FIG. 1 , the power conversion device 1 includes an inverter device 10 and a control device 30 .

[0016] The inverter device 10 includes a DC input unit 11, a DC capacitor 12, a discharge resistor 13, an inverter circuit 14, and an AC output unit 15. The inverter device 10 converts, for example, DC power supplied from the DC input unit 11 side into AC power via the inverter circuit 14, and outputs the converted AC power to the AC output unit 15 side.

[0017] The inverter device 10 is, for example, a DC-AC inverter that converts DC power to AC power, and the DC input unit 11 is connected to DC power from a solar panel (solar cell), a storage battery, or the like, and the AC output unit 15 is connected to a load such as an AC power system or a motor. In the following embodiment, the inverter device 10 will be described using a DC-AC inverter that converts DC power to AC power as an example. However, the inverter device 10 is not limited to this, and the inverter device 10 disclosed herein can be any device that includes a DC capacitor 12, a discharge resistor 13, and a means for detecting a DC voltage Vdc of the DC capacitor 12, which will be described later.

[0018] That is, the inverter device 10 may be, for example, a converter that converts AC to DC, as long as it has the DC capacitor 12, the discharge resistor 13, and a means for detecting the DC voltage Vdc of the DC capacitor 12 (described later). Alternatively, the inverter device 10 may be, for example, a reactive power compensator that generates a DC voltage by the operation of the inverter circuit 14, controls the DC voltage to a constant level, and exchanges reactive power between the DC capacitor and the grid to stabilize the voltage. Alternatively, the inverter device 10 may be a DC-DC converter such as a DC chopper. Note that, hereinafter, in this specification, the inverter device 10 may also be simply referred to as "device" or "device 10."

[0019] The DC input unit 11 has a positive terminal 11P and a negative terminal 11N. The positive terminal 11P and the negative terminal 11N of the DC input unit 11 are connected to a DC power source (not shown), such as a solar cell, at one end on the left side in Fig. 1, and are connected to the inverter device 10 at the other end on the right side in Fig. 1. Note that if the inverter device 10 is, for example, a reactive power compensation device, nothing may be connected to one end of the positive terminal 11P and the negative terminal 11N of the DC input unit 11.

[0020] The DC capacitor 12 is disposed, for example, between the positive terminal 11P and the negative terminal 11N, and absorbs and smoothes ripple current generated by the switching operation of the switching elements of the inverter circuit 14. The DC capacitor 12 is almost always provided in a voltage-type inverter, and is charged when the inverter device 10 starts up (when current begins to flow) and discharged when the inverter device 10 stops.

[0021] When the capacity of the DC capacitor 12 decreases due to aging or the occurrence of an abnormality (failure), the voltage magnitude differs from that in normal conditions when charging at the start of the inverter device 10 and when discharging at the stop of the inverter device 10. In this case, the slope and magnitude of the charge curve indicating the charge rate during charging and the discharge curve indicating the discharge rate during discharging of the DC capacitor 12 differ from those in normal conditions.

[0022] The discharge resistor 13 is disposed, for example, between the positive terminal 11P and the negative terminal 11N, and serves to discharge the charge of the DC capacitor 12 after the inverter device 10 is stopped. The discharge resistor 13 may be permanently connected, or may be turned on and connected after the inverter device 10 is stopped. For example, the discharge resistor 13 is permanently connected in an inverter device 10 having a small- to medium-capacity DC capacitor 12, and may be turned on and connected by a switch (not shown) or the like in an inverter device 10 having a large-capacity DC capacitor 12 after the inverter device 10 is stopped.

[0023] The inverter circuit 14 is configured with a plurality of semiconductor switching elements Q, such as insulated gate bipolar transistors (IGBTs), and a plurality of freewheeling diodes D. Note that the semiconductor switching elements Q are not limited to IGBTs and may be metal-oxide-semiconductor field-effect transistors (MOSFETs) or the like. For example, one end of the inverter circuit 14, which is the input side, is connected to a DC power source (not shown) via a DC input unit 11, and the other end of the inverter circuit 14, which is the output side, is connected to an AC power system (not shown) via an AC output unit.

[0024] The operation of the inverter circuit 14 is controlled by a pulse width modulation (PWM) signal, which is a gate drive signal (gate signal) for the semiconductor switching element Q, generated by the control device 30. The inverter circuit 14, for example, acquires DC power supplied from the DC input unit 11, converts the acquired DC power into AC power under control of the PWM signal (gate signal), and outputs the converted AC power from the AC output unit 15.

[0025] The inverter circuit 14 has, for example, three legs (a U-phase leg, a V-phase leg, and a W-phase leg) connected in parallel. Each leg is configured, for example, by connecting two arms in series, each arm having a semiconductor switching element Q and a freewheeling diode D connected in anti-parallel. The legs are connected in parallel, for example, between the positive terminal 11P and the negative terminal 11N, and the midpoints of the legs are connected to a U-phase terminal 15U, a V-phase terminal 15V, and a W-phase terminal 15W, respectively, of the AC output unit 15, which will be described later. Note that the inverter circuit 14 is not limited to a three-phase inverter, and may be a single-phase inverter or another type of inverter.

[0026] The AC output unit 15 has a U-phase terminal 15U, a V-phase terminal 15V, and a W-phase terminal 15W. One end of the AC output unit 15, shown on the left in FIG. 1 , is connected to the inverter device 10, and the other end, shown on the right in FIG. 1 , is connected to a power system, a load, or the like (not shown). The AC output unit 15 is, for example, a three-phase, three-wire three-phase AC circuit that supplies three-phase AC power by combining three systems of single-phase AC, with the current or voltage phases shifted from one another, using three electric wires, cables, or conductors. The AC output unit 15 is not limited to a three-phase AC circuit, and may be a single-phase AC circuit or another type of AC circuit. The AC output unit 15 outputs the AC power converted by the inverter circuit 14 to a power system, a load, or the like (not shown).

[0027] The inverter device 10 also includes a DC current sensor 21 , a DC voltage sensor 22 , an AC current sensor 23 , and an AC voltage sensor 24 .

[0028] The DC current sensor 21 is, for example, a known DC ammeter or DC current sensor, and detects the value of the DC current Idc flowing between the positive terminal 11P and the negative terminal 11N of the DC input unit 11. The position at which the DC current sensor 21 is disposed is not limited to the position shown in FIG. 1 , and may be any position at which the value of the DC current Idc can be detected. Hereinafter, in this specification, the value of the DC current Idc will also be simply referred to as the "DC current Idc." The DC current Idc detected by the DC current sensor 21 is monitored by the control device 30.

[0029] The DC voltage sensor 22 is, for example, a known DC voltmeter or DC voltage sensor, and detects the value of the DC voltage Vdc of the DC capacitor 12 of the DC input unit 11. The position at which the DC voltage sensor 22 is disposed is not limited to the position shown in FIG. 1 , and may be any position where the value of the DC voltage Vdc of the DC capacitor 12 can be detected. Hereinafter, in this specification, the value of the DC voltage Vdc may also be simply referred to as the "DC voltage Vdc." The DC voltage Vdc detected by the DC voltage sensor 22 is monitored by the control device 30.

[0030] The AC current sensor 23 is, for example, a known AC ammeter or AC current sensor, and detects the value of the AC current Iac of the AC output unit 15, which is the output current of the inverter circuit 14. The location of the AC current sensor 23 is not limited to the location shown in FIG. 1 , and may be any location where the value of the AC current Iac can be detected. Hereinafter, in this specification, the value of the AC current Iac will also be simply referred to as "AC current Iac." The AC current Iac detected by the AC current sensor 23 is monitored and controlled by the control device 30.

[0031] The AC voltage sensor 24 is, for example, a known AC voltmeter or AC voltage sensor, and detects the value of the AC voltage Vac of the AC output unit 15, which is the output voltage of the inverter circuit 14. The location of the AC voltage sensor 24 is not limited to the location shown in FIG. 1 , and may be any location where the value of the AC voltage Vac of the AC voltage sensor 24 can be detected. Hereinafter, in this specification, the value of the AC voltage Vac will also be simply referred to as the "AC voltage Vac." The AC voltage Vac detected by the AC voltage sensor 24 is monitored and controlled by the control device 30.

[0032] The control device 30 is provided, for example, inside or outside the power conversion device 1, and although wiring and the like are omitted in the figure, it is electrically connected by wire or wirelessly to each component of the inverter device 10, including the inverter circuit 14. Note that the control device 30 may be realized as a function of an inverter control circuit (not shown).

[0033] The control device 30 has a processor 91 (see FIG. 10 ), which will be described later, such as a CPU (Central Processing Unit) that operates by executing a program. The control device 30 has a storage unit 40 (see FIG. 2 ), a memory 92 (see FIG. 10 ), and the like, which will be described later, and for example, operates the processor 91 by executing a predetermined program stored in the storage unit 40 or the memory 92, thereby comprehensively controlling the operation of the inverter device 10. Note that the control device 30 may control the operation of the inverter device 10 in accordance with instructions received from a higher-level device (not shown) or instructions received from an operator (not shown) via an operation unit (not shown).

[0034] The control device 30 detects a failure, an abnormality, a decrease in capacity, etc. of the DC capacitor 12 based on the DC voltage Vdc detected by the DC voltage sensor 22. When the control device 30 detects an abnormality, etc. of the DC capacitor 12, it issues a report that an abnormality, etc. of the DC capacitor 12 has been detected.

[0035] FIG. 2 is a diagram showing an example of the configuration of the control device 30 in the power conversion device 1 shown in FIG.

[0036] The control device 30 has a storage unit 40, and functions as each of the following units by executing a predetermined program stored in the storage unit 40 or a memory 92 (see FIG. 10 ), which will be described later. That is, by executing the predetermined program, the control device 30 functions as a monitoring unit 31, a timing unit 32, a determination unit 33, an alarm issuing unit 34, and a PWM control unit 35. Note that each of the above functions may be realized by a program executed by a processor 91 (see FIG. 10 ) included in the control device 30, or may be realized by hardware 93 (see FIG. 10 ). Each of the above units executes the predetermined program to perform the following processes.

[0037] The monitoring unit 31 is connected to the DC voltage sensor 22 and constantly acquires and monitors information on the DC voltage Vdc of the DC capacitor 12 detected by the DC voltage sensor 22. The monitoring unit 31 may acquire and monitor the information on the DC voltage Vdc of the DC capacitor 12, for example, at predetermined time intervals, or may acquire and monitor the information in accordance with instructions received from an operator or the like via a higher-level device (not shown) or an operation unit (not shown). The monitoring unit 31 may also acquire and monitor information on the DC voltage Vdc of the DC capacitor 12 when the inverter device 10 is stopped. The monitoring unit 31 may also be connected to the DC current sensor 21, the AC current sensor 23, and the AC voltage sensor 24 and acquire and monitor information on the DC current Idc, the AC current Iac, and the AC voltage Vac detected by these sensors.

[0038] When the inverter device 10 is stopped, the timer 32 measures the elapsed time from the time the inverter device 10 is stopped. The elapsed time measured by the timer 32 is acquired by the determination unit 33. The timer 32 measures the elapsed time from the time the inverter device 10 is stopped, i.e., the time t １ In this case, the timer 32 may measure whether a predetermined time t has elapsed since the inverter device 10 was stopped. １ When the predetermined time t has elapsed since the inverter device 10 was stopped, １ Information indicating that the time has elapsed is output to the determination unit 33 .

[0039] The determination unit 33 determines whether the predetermined time t has elapsed since the inverter device 10 was stopped by the timer unit 32. １ The determination unit 33 acquires information on the DC voltage Vdc monitored by the monitoring unit 31 when the timer 32 determines that a predetermined time t has elapsed since the inverter device 10 was stopped. １ When the time has elapsed, the DC voltage Vdc monitored by the monitoring unit 31 and the predetermined threshold V ｔｈ Compare with.

[0040] The determination unit 33 may constantly acquire information on the DC voltage Vdc monitored by the monitoring unit 31. The determination unit 33 then compares the DC voltage Vdc monitored by the monitoring unit 31 with a predetermined threshold value V ｔｈ The comparison may be continued at all times.

[0041] The determination unit 33 determines whether the DC voltage Vdc monitored by the monitoring unit 31 is equal to or exceeds a predetermined threshold value V ｔｈ If the difference is less than 0.05, it is determined that an abnormality has occurred in the DC capacitor 12. This is because when an abnormality occurs in the DC capacitor 12, the capacitance of the DC capacitor 12 decreases. When the determination unit 33 determines that an abnormality has occurred in the DC capacitor 12, it outputs information indicating that an abnormality has occurred in the DC capacitor 12 to the alarm unit 34. When the determination unit 33 determines that an abnormality has occurred in the DC capacitor 12, it may output information indicating that an abnormality has occurred in the DC capacitor 12 to an external device such as a higher-level device (not shown).

[0042] Note that the predetermined threshold V ｔｈmay vary depending on the operating conditions of the inverter device 10, or may be determined in advance by experiment, simulation, or the like, and stored in the storage unit 40. ｔｈ may be determined, for example, according to an instruction received from a higher-level device (not shown) or an instruction received from an operator (not shown) via an operation unit (not shown).

[0043] Here, the predetermined threshold V ｔｈ is a predetermined time t １ The predetermined threshold value V is a value (voltage value) smaller than the normal DC voltage Vdc (normal value) detected in the normal DC capacitor 12 when the predetermined threshold value V ｔｈ may have a bandwidth or margin of a predetermined range (predetermined voltage value) (upper or lower). ｔｈ When the voltage V falls below a predetermined threshold value V, it is not immediately determined that the DC capacitor 12 is abnormal. ｔｈ If the difference falls below the predetermined range or more, it may be determined that there is an abnormality in the DC capacitor 12. The bandwidth and margin of the predetermined range may be varied depending on the expected life of the DC capacitor 12, etc.

[0044] As a result, for example, the determination unit 33 will not detect an abnormality in the DC capacitor 12 due to a temporary or accidental fluctuation in the DC voltage Vdc. ｔｈ In this case, the judgment unit 33 is less likely to erroneously detect an abnormality than when the bandwidth or margin does not fall within the predetermined range, and the judgment unit 33 can more accurately detect an abnormality in the DC capacitor 12.

[0045] As described above, the determination unit 33 determines whether the DC voltage Vdc is equal to or lower than the predetermined threshold value V ｔｈ However, the present invention is not limited to this. The determination unit 33 may determine that the DC capacitor 12 is abnormal when the DC voltage Vdc falls below a predetermined threshold V for a predetermined period of time or more. ｔｈ Alternatively, the determination unit 33 may determine that the DC capacitor 12 is abnormal when the DC voltage Vdc falls below a predetermined threshold V ｔｈIf the voltage drops below 10 V, it may be determined that the DC capacitor 12 is abnormal.

[0046] Furthermore, the determination unit 33 determines whether a predetermined threshold value V ｔｈ For example, the determination unit 33 may determine whether the DC capacitor 12 is abnormal by combining any one or all of the following: a bandwidth or margin within a predetermined range set in the above table, the time, and the number of times. ｔｈ If the voltage drops below 10 V, it may be determined that the DC capacitor 12 is abnormal.

[0047] Furthermore, for example, the determination unit 33 determines whether the DC voltage Vdc is equal to or exceeds a predetermined threshold V ｔｈ Alternatively, the determination unit 33 may determine that the DC capacitor 12 is abnormal when the DC voltage Vdc falls below a predetermined threshold V for a predetermined number of times or more. ｔｈ Alternatively, for example, the determination unit 33 may determine that the DC capacitor 12 is abnormal when the DC voltage Vdc falls below a predetermined threshold V for a predetermined period of time or more and a predetermined number of times or more. ｔｈ If the voltage falls below a predetermined range (predetermined voltage value) or more, it may be determined that the DC capacitor 12 is abnormal.

[0048] This allows the predetermined threshold V ｔｈ This reduces the likelihood of false detection of an abnormality by the judgment unit 33 compared to when the predetermined range of bandwidth and margin set in the above is not combined with the time and the number of times, and the judgment unit 33 can more accurately detect an abnormality in the DC capacitor 12.

[0049] When the reporting unit 34 receives information from the determination unit 33 indicating that the DC capacitor 12 has been determined to be abnormal, the reporting unit 34 reports the abnormality of the DC capacitor 12. The reporting unit 34 reports the abnormality of the DC capacitor 12, for example, by outputting fault information to a higher-level device (not shown) or by outputting a display or sound such as an alert or alarm on a display unit or operation unit (not shown) of the power conversion device 1. The reporting unit 34 may stop the discharge of the DC capacitor 12. The function of the reporting unit 34 may be provided by an external device such as a higher-level device (not shown).

[0050] The PWM control unit 35 performs PWM control based on, for example, a predetermined output voltage command signal and a predetermined triangular-wave carrier signal, and generates a gate signal that turns on and off the semiconductor switching element Q of the inverter circuit 14. The PWM control unit 35 outputs the generated gate signal to the inverter circuit 14 of the inverter device 10, and controls the operation of the inverter circuit 14. When the inverter device 10 stops and stops outputting the gate signal, the PWM control unit 35 may output information to the timer unit that the inverter device 10 has stopped.

[0051] The storage unit 40 is, for example, a volatile or non-volatile storage medium such as a hard disk drive (HDD), a solid state drive (SSD), a dynamic random access memory (DRAM), or other semiconductor memory. The storage unit 40 stores, for example, programs required for the operation of each unit of the control device 30, and various pieces of information are written to and read from the storage unit 40 by each unit of the control device 30. The storage unit 40 stores, for example, information on values ​​of a direct current Idc, a direct current voltage Vdc, an alternating current Iac, an alternating current voltage Vac, etc., which are monitored by the monitoring unit 31. The storage unit 40 also stores, for example, a predetermined time t １ or a predetermined threshold V ｔｈ The memory 31 stores information such as the above, various calculation formulas and various thresholds used for the judgment of the judgment unit 33, etc.

[0052] The storage unit 40 is connected to each part of the control device 30 via, for example, a bus (not shown) or the like so that each part of the control device 30 can input and output various information. The storage unit 40 may be provided outside the control device 30 and connected to the control device 30 by wire or wirelessly, and may be an external storage medium such as a memory card or a DVD (Digital Versatile Disc), or may be online storage. The storage unit 40 may also be used in common with a memory 92 (see FIG. 10 ) described below.

[0053] <Operation of First Embodiment> Fig. 3 is a flowchart showing an example of the operation of the control device 30 in the power conversion device 1 shown in Fig. 1 and Fig. 2. The flowchart shown in Fig. 3 starts when the inverter device 10 stops.

[0054] In step S1, the timer 32 of the control device 30 receives information that the inverter device 10 has stopped, and starts measuring the time that has elapsed since the inverter device 10 stopped.

[0055] In step S2, the determination unit 33 of the control device 30 acquires the time measured by the timer unit 32 from the timer unit 32, and determines whether the timer unit 32 has detected a predetermined time t since the inverter device 10 was stopped. １ The determination unit 33 determines whether or not the timer unit 32 has counted the time t since the inverter device 10 was stopped. １ On the other hand, when it is determined that the predetermined time t has elapsed since the inverter device 10 was stopped by the timer 32, the determination unit 33 proceeds to step S3. １ When it is determined that the predetermined time t １ The process of step S2 is repeated until it is determined that the time has elapsed.

[0056] In step S3, the determination unit 33 determines whether or not the predetermined time t １ The determination unit 33 obtains information on the DC voltage Vdc of the DC capacitor 12 at the time when the predetermined time t １ A predetermined threshold value V ｔｈ The information is acquired from the storage unit 40.

[0057] In step S4, the determination unit 33 determines whether or not the predetermined time t １ When the DC voltage Vdc reaches a predetermined threshold V ｔｈ It is determined whether the value falls within a predetermined range.

[0058] Then, the determination unit 33 determines whether the predetermined time t １ When the DC voltage Vdc reaches a predetermined threshold V ｔｈIf it is determined that the difference is within the predetermined range (Yes side), the process proceeds to step S5.

[0059] On the other hand, the determination unit 33 determines whether or not the predetermined time t １ When the DC voltage Vdc reaches a predetermined threshold V ｔｈ When it is determined that the value of the power consumption is not within the predetermined range (No), the determination unit 33 proceeds to step S6. １ When the time has elapsed, the DC voltage Vdc reaches a predetermined threshold V ｔｈ When it is determined that the predetermined threshold value V is smaller than the predetermined range (No), the process proceeds to step S6. ｔｈ may be determined based on a discharge curve.

[0060] Fig. 4 is a diagram showing an example of a discharge curve when the DC capacitor 12 discharges after the inverter device 10 is stopped. That is, Fig. 4 is a diagram showing a discharge curve indicating the transition of the DC voltage value when the DC capacitor 12 discharges after the inverter device 10 is stopped.

[0061] In Fig. 4, the vertical axis represents voltage value (V) and the horizontal axis represents time (t). In Fig. 4, the DC voltage Vdc represents the value of the DC voltage when the inverter device 10 is operating (when it is stopped). That is, in Fig. 4, the DC voltage Vdc represents the value of the DC voltage when the inverter device 10 is operating (when it is stopped). ０ ) is maintained at the DC voltage Vdc. ０ When the inverter device 10 is stopped at time t ０ 1 shows a discharge curve (v(t)) that indicates the transition of the DC voltage value when the DC capacitor 12 discharges after the inverter device 10 has stopped. The discharge curve (v(t)) can be calculated by the following equation (1).

[0062]

[0063] In equation (1), C is the design value of the capacitance of the DC capacitor 12, R is the design value of the resistance of the discharge resistor 13, Vdc is the DC voltage value of the DC capacitor 12 when the inverter device 10 is stopped, and t is the elapsed time since the inverter device 10 was stopped.

[0064] Equation (1) represents a discharge curve (v(t)) that indicates the natural attenuation of the DC voltage value when the DC capacitor 12 discharges after the inverter device 10 has stopped. ０ is set to 0 when the inverter device 10 is stopped, and t １ When a predetermined time has elapsed since the inverter device 10 was stopped, the time when the inverter device 10 was stopped (t ０ ) after a predetermined time (t １ The DC voltage value of the DC capacitor 12 at １ )

[0065] The design value (C) of the capacitance of the DC capacitor 12 is often a value on the order of, for example, uF or mF. The design value (R) of the resistance value of the discharge resistor 13 is often a value on the order of, for example, kΩ. Note that since a large-capacity inverter device 10 rarely has only one DC capacitor 12, the design value (C) of the capacitance of the DC capacitor 12 is the combined value (combined capacitance) of the DC capacitors 12 connected in parallel.

[0066] FIG. 5 shows the discharge curve of the normal DC capacitor 12 shown in FIG. 4 and the predetermined threshold V ｔｈ 10A and 10B are diagrams showing examples of discharge curves as a function of the current.

[0067] In Fig. 5, the vertical axis, horizontal axis, and symbols are the same as those in Fig. 4. That is, in Fig. 5 as well, the DC voltage Vdc indicates the value of the DC voltage when the inverter device 10 is operating (stopped). １ is the same as the discharge curve shown in FIG. 4 and indicates the discharge curve of a normal DC capacitor 12. On the other hand, the dashed line L ２ is a predetermined threshold V ｔｈ The discharge curve is shown as follows.

[0068] 5, when the capacitance of the DC capacitor 12 decreases due to an abnormality, deterioration, or the like, the charge is small and therefore discharged quickly through the same discharge resistor 13, causing the voltage to drop quickly. For example, when an abnormality such as a break occurs in one of the combined capacitances of multiple DC capacitors 12 connected in parallel, the charge is small by one capacitor, so discharged quickly through the same discharge resistor 13, causing the voltage to drop quickly.

[0069] Therefore, the discharge curve of the DC capacitor 12 with a reduced capacitance has a lower voltage value than the discharge curve of the normal DC capacitor 12, and is therefore a lower line. １ than the predetermined threshold V ｔｈ The dashed line L shows the discharge curve as ２ The lower line is the one shown.

[0070] Note that the predetermined threshold V ｔｈ The dashed line L shows the discharge curve as ２ As described above, the voltage may have a bandwidth or margin within a predetermined range (predetermined voltage value). １ When the time has elapsed, the value of the DC voltage monitored by the monitoring unit 31 reaches a predetermined threshold value V ｔｈ It may be determined that the DC capacitor 12 is abnormal when the voltage Vcc falls below the predetermined range or more.

[0071] In addition, the predetermined time t １ is not limited to one time, but may be measured multiple times and may have a predetermined time length. ｔｈ Whether or not the discharge current is below the threshold may be determined not only at a single sample point but also at multiple sample points, or may be determined for the entire discharge curve or a predetermined portion of the discharge curve.

[0072] Here, the predetermined threshold V ｔｈmay be calculated (or determined) based on a discharge curve based on actual measurements of the DC voltage value after the inverter device 10 is stopped during a factory shipping test of the power conversion device 1. For example, ｔｈ The dashed line L indicates ２ may be a value (discharge curve) calculated based on an experiment or simulation from a discharge curve based on actual measurements at the time of a factory shipping test of the power conversion device 1 and stored in the storage unit 40. ｔｈ =L ２ ) may be calculated based on a time constant (τ) based on actual measurements of the capacitance (C) of the DC capacitor 12 and the resistance value (R) of the discharge resistor at the time of factory shipping test. Note that the predetermined threshold value (V) calculated based on the discharge curve or the time constant (τ) based on the actual measurements at the time of factory shipping test may be calculated based on the time constant (τ) ｔｈ =L ２ ) may be calculated in advance and stored in the storage unit 40 in advance.

[0073] In this case, the determination unit 33 determines the time when the inverter device 10 is stopped (t ０ ) to a predetermined time (t １ When it is determined that the predetermined threshold value (V ｔｈ =L ２ ) and compare.

[0074] The determination unit 33 determines whether the actual measured value of the DC voltage monitored by the monitoring unit is equal to or exceeds a predetermined threshold value (V ｔｈ =L ２ ) by a predetermined range or more, it is determined that the DC capacitor 12 is abnormal.

[0075] In this way, the predetermined threshold V ｔｈ is calculated based on the actual measurement value at the time of the factory shipping test of the power conversion device 1, and thus a predetermined threshold value V ｔｈ It is possible to determine the abnormality of the DC capacitor 12 more accurately than in the case where the actual device is not used.

[0076] In addition, a predetermined threshold Vｔｈ may be calculated (determined) based on the design value (C) of the capacitance of the DC capacitor and the design value (R) of the resistance of the discharge resistor, using the value calculated by the above formula (1). For example, the predetermined threshold value V ｔｈ The dashed line L indicates ２ may be a value calculated based on an experiment or simulation from the discharge curve (v(t)) calculated by the above formula (1). ｔｈ is the timing at which a predetermined diagnosis is performed (a predetermined time (t １ )) into the above equation (1), the value may be determined based on an experiment, a simulation, or the like.

[0077] In this case, the determination unit 33 determines the time when the inverter device 10 is stopped (t ０ ) to a predetermined time (t １ When it is determined that the predetermined time (t １ ) is substituted, the voltage value (v(t １ )) is calculated by adding a predetermined time (t １ ) is substituted, the voltage value (v(t １ )) may be calculated in advance and stored in the storage unit 40 in advance.

[0078] The determination unit 33 determines the time when the inverter device 10 is stopped (t ０ ) to a predetermined time (t １ When it is determined that the time has elapsed, the actual measured value of the DC voltage monitored by the monitoring unit 31 and the calculated voltage value (v(t １ Then, the determination unit 33 compares the actual measured value of the DC voltage monitored by the monitoring unit 31 with the obtained voltage value (v(t １ )) by a predetermined range or more, it is determined that the DC capacitor 12 is abnormal.

[0079] In this way, the predetermined threshold V ｔｈHowever, by determining this based on the design value (C) of the capacitance of the DC capacitor and the design value (R) of the resistance of the discharge resistor, an abnormality in the DC capacitor 12 can be accurately detected based on the design values.

[0080] Returning to Figure 3, in step S5, the alarm unit 34 has not received information from the judgment unit 33 that the DC capacitor 12 has been judged to be abnormal, so the control device 30 continues discharging the DC capacitor 12 and terminates the processing of the flowchart in Figure 3.

[0081] In step S6, the alarm issuing unit 34 receives information from the determining unit 33 indicating that an abnormality has been determined in the DC capacitor 12, and issues an alarm about the abnormality in the DC capacitor 12. Then, the control device 30 ends the processing of the flowchart in FIG.

[0082] <Operation and Effect of First Embodiment> As described above, in the first embodiment shown in FIGS. 1 to 5, the inverter device 10 is turned on after a predetermined time t １ When time has passed, the DC voltage value Vdc reaches a predetermined threshold value V ｔｈ falls below a predetermined range or more, it is determined that there is an abnormality in the DC capacitor 12. Thus, according to this embodiment, by monitoring the discharge rate of the DC voltage Vdc when the inverter device 10 is stopped, it is possible to discover an abnormality in the DC capacitor 12 based on the discharge voltage of the DC voltage Vdc when the inverter device 10 is stopped.

[0083] According to the first embodiment shown in FIGS. 1 to 5, the predetermined threshold value V ｔｈ may have a bandwidth or margin within a predetermined range (predetermined voltage value). ｔｈ In this case, the judgment unit 33 is less likely to erroneously detect an abnormality than when the bandwidth or margin does not fall within the predetermined range, and the judgment unit 33 can more accurately detect an abnormality in the DC capacitor 12.

[0084] According to the first embodiment shown in FIGS. 1 to 5, the predetermined threshold value V ｔｈmay be calculated based on a discharge curve based on actual measurements of the transition of the DC voltage value after the inverter device 10 is stopped during a factory shipping test of the power conversion device 1. As a result, according to this embodiment, a predetermined threshold value V ｔｈ It is possible to determine the abnormality of the DC capacitor 12 more accurately than in the case where the actual device is not used.

[0085] According to the first embodiment shown in FIGS. 1 to 5, the predetermined threshold value V ｔｈ may be calculated based on the design value (C) of the capacitance of the DC capacitor and the design value (R) of the resistance of the discharge resistor, using the value calculated by the above formula (1). As a result, according to this embodiment, an abnormality in the DC capacitor 12 can be accurately detected based on the design values.

[0086] <Modification of First Embodiment> FIG. 6 shows a diagram illustrating a discharge curve of a normal DC capacitor 12 and a predetermined threshold V ｔｈ and the second predetermined threshold V ｔｈ２ 10A and 10B are diagrams showing examples of discharge curves as a function of the current.

[0087] In the modification of the first embodiment, the same or similar components as those in the first embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals, and detailed descriptions thereof will be omitted or simplified. In the modification of the first embodiment, the configuration and operation of the power conversion device 1 are the same as or similar to those in the first embodiment shown in FIGS. 1 to 5, and therefore will not be illustrated. In the modification of the first embodiment, the predetermined threshold V ｔｈ In addition to the second predetermined threshold V ｔｈ２ is used.

[0088] In Fig. 6, the vertical axis, horizontal axis, and symbols are the same as those in Fig. 4 and Fig. 5. That is, in Fig. 6, the solid line L １ is the solid line L of the discharge curve shown in FIG. １ , and shows an example of a discharge curve of a normal DC capacitor 12. For example, the solid line L １shows an example of a discharge curve as a reference value based on the actual measured value at the time of factory shipping test of the power conversion device 1, or a reference value based on the design value of the capacitance of the DC capacitor and the design value of the resistance of the discharge resistor.

[0089] In addition, in FIG. ２ is the dashed line L of the discharge curve shown in FIG. ２ and a predetermined threshold value V for detecting (determining) an abnormality in the DC capacitor 12 is set to ｔｈ 1 shows an example of a discharge curve as follows.

[0090] Furthermore, in FIG. 6, the dashed line L ３ The dashed line L ３ is a second predetermined threshold value V for detecting the replacement time of the DC capacitor 12 (determining the replacement time). ｔｈ２ 1 shows an example of a discharge curve of the second predetermined threshold V ｔｈ２ The dashed line L indicates ３ is the solid line L indicating the reference value. １ is smaller than the predetermined threshold V ｔｈ The dashed line L indicates ２ is greater than.

[0091] When an abnormality occurs in the DC capacitor 12, such as when the DC capacitor 12 breaks down or when one of the DC capacitors 12 is disconnected, the capacitance of the DC capacitor 12 drops significantly more than when it is caused by aging or other factors. On the other hand, when the DC capacitor 12 is used for capacity reduction due to aging or end of life, the capacitance of the DC capacitor 12 drops more slowly (the capacitance does not decrease as much) than when it is caused by a loss of capacitance or an abnormality in the DC capacitor 12. For this reason, the second predetermined threshold V ｔｈ２ The dashed line L indicates ３ is a predetermined threshold value V for detecting an abnormality in the DC capacitor 12. ｔｈ The dashed line L indicates ２ is considered to be greater than

[0092] In the modification of the first embodiment, the determination unit 33 determines whether the DC voltage Vdc monitored by the monitoring unit 31 is equal to or lower than a second predetermined threshold V ｔｈ２ and is below a predetermined threshold V ｔｈIf the difference is greater than , it is determined that it is time to replace the DC capacitor 12. When the determination unit 33 determines that it is time to replace the DC capacitor 12, the alarm unit 34 issues an alarm indicating that it is time to replace the DC capacitor 12.

[0093] In the modification of the first embodiment, similarly to the first embodiment shown in FIGS. 1 to 5, the determination unit 33 determines whether the DC voltage Vdc monitored by the monitoring unit 31 is equal to or lower than the predetermined threshold value V ｔｈ If the voltage Vcc is lower than the reference voltage Vcc, it is determined that there is an abnormality in the DC capacitor 12. When the determination unit 33 determines that there is an abnormality in the DC capacitor 12, the alarm unit 34 issues an alarm that there is an abnormality in the DC capacitor 12.

[0094] In the modified example of the first embodiment, the second predetermined threshold V ｔｈ２ is a predetermined threshold V ｔｈ Similarly, the DC voltage Vdc may have a bandwidth or margin of a predetermined range (predetermined voltage value) (upper or lower). ｔｈ２ When the voltage V falls below a second predetermined threshold V, it is not immediately determined that it is time to replace the DC capacitor 12. ｔｈ２ It may be determined that it is time to replace the DC capacitor 12 when the voltage Vcc falls below the predetermined range or more.

[0095] The second predetermined threshold V ｔｈ２ Even in this case, a predetermined threshold V ｔｈ Similarly, the bandwidth and margin of the predetermined range may be varied depending on the expected life of the DC capacitor 12. ｔｈ The dashed line L indicates ２ and a second predetermined threshold V ｔｈ２ The dashed line L indicates ３ may be determined by experiment, calculation, simulation, etc., and stored in the storage unit 40.

[0096] In addition, a predetermined threshold V ｔｈ The dashed line L indicates ２ and a second predetermined threshold V ｔｈ２ The dashed line L indicates ３This may be expressed by varying the bandwidth, margin, etc. from one threshold (discharge curve). That is, in one threshold (discharge curve), the first bandwidth is set to a predetermined threshold V ｔｈ and a second bandwidth smaller than the first bandwidth is set to a second predetermined threshold V ｔｈ２ It may also be possible to use the following.

[0097] In addition, a predetermined threshold V ｔｈ The dashed line L indicates ２ and a second predetermined threshold V ｔｈ２ The dashed line L indicates ３ The above may be expressed by changing the slope of the discharge curve. That is, the discharge curve with the first slope may be expressed by changing the slope of the discharge curve with the first slope. ｔｈ and the discharge curve having a second slope that is gentler than the first slope is set to a second predetermined threshold value V ｔｈ２ It may also be possible to use the following.

[0098] In addition, other second predetermined threshold values ​​V ｔｈ２ Regarding the handling of the threshold value V and the determination operation by the determination unit 33, the predetermined threshold value V in the first embodiment shown in FIGS. ｔｈ The handling of the image forming apparatus 10 and the determination operation by the determination unit 33 are the same as or similar to those of the image forming apparatus 10 and the determination operation by the determination unit 33. Therefore, detailed explanation and illustrations thereof will be omitted.

[0099] <Operations and Effects of Modification of First Embodiment> As described above, the modification of the first embodiment shown in FIG. 6 provides the same operations and effects as the first embodiment shown in FIGS.

[0100] Furthermore, in the modification of the first embodiment shown in FIG. 6, a second predetermined threshold value (V ｔｈ２ =L ３ ) is used. Thus, according to this embodiment, not only an abnormality in the DC capacitor 12 but also the time to replace the DC capacitor 12 can be detected based on the discharge voltage of the DC voltage Vdc when the inverter device 10 is stopped.

[0101] Second Embodiment FIG. 7 is a diagram showing an example of the configuration of a power conversion device 1A according to a second embodiment.

[0102] In the second embodiment, the same or similar components as those in the first embodiment and its modified examples shown in FIGS. 1 to 6 are denoted by the same reference numerals, and detailed descriptions thereof will be omitted or simplified.

[0103] In the second embodiment, the inverter device 10A of the power conversion device 1A is a multilevel power converter in which two DC capacitors 12P, 12N are connected in series via a DC neutral point C. Note that, in Fig. 7, as an example of the inverter device 10A, a three-level multilevel power converter in which two DC capacitors 12P, 12N are connected in series via a DC neutral point C is described, but the number of DC capacitors 12P, 12N may be two or more. Note that the number of discharge resistors 13 may also be multiple, corresponding to the number of DC capacitors 12P, 12N.

[0104] 7, in the inverter device 10A, two (plural) DC capacitors 12P, 12N are connected in series via a DC neutral point C, and two semiconductor switching elements (neutral point elements) Q are connected in anti-series for each of the three phases to the DC neutral point C. In the example shown in FIG. 7, the semiconductor switching elements (neutral point elements) Q are connected in anti-series with the collector sides of the IGBTs in common, but they may also be connected in anti-series with the emitter sides in common.

[0105] Fig. 8 is a diagram showing a configuration example of a control device 30A in the power conversion device 1A shown in Fig. 7. As shown in Fig. 8, the control device 30A in the second embodiment has a monitoring unit 31A instead of the monitoring unit 31 in the first embodiment and its modified examples shown in Figs. 1 to 6, and has a determining unit 33A instead of the determining unit 33.

[0106] The monitoring unit 31A constantly acquires and monitors information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N detected by the DC voltage sensor 22. The monitoring unit 31A may acquire and monitor the information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N, for example, at predetermined time intervals. The monitoring unit 31A may also acquire and monitor the information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N, for example, in accordance with instructions received from an operator via a higher-level device (not shown) or an operation unit (not shown). The monitoring unit 31A may also acquire and monitor the information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N when the inverter device 10A is stopped.

[0107] The determination unit 33A determines whether the predetermined time t has elapsed since the inverter device 10A was stopped by the timer unit 32. １ The determination unit 33A acquires information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N monitored by the monitoring unit 31A when the timer 32 determines that a predetermined time t has elapsed since the inverter device 10 was stopped. １ When the time measurement indicates that the DC voltage Vdcp of the DC capacitor 12P has elapsed, the determination unit 33A compares the DC voltage Vdcp of the DC capacitor 12P with the DC voltage Vdcn of the DC capacitor 12N. In other words, the determination unit 33A compares the DC voltage values ​​of the multiple DC capacitors 12P and 12N.

[0108] The determination unit 33A may constantly acquire information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N monitored by the monitoring unit 31A. The determination unit 33A may constantly compare the DC voltage Vdcp of the DC capacitor 12P with the DC voltage Vdcn of the DC capacitor 12N.

[0109] The determination unit 33A determines whether the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N are equal to or lower than a predetermined threshold value V ｔｈ３If there is a difference between the above, it is determined that either the DC capacitor 12P or 12N is abnormal. When the determination unit 33A determines that either the DC capacitor 12P or 12N is abnormal, it outputs information indicating that either the DC capacitor 12P or 12N is abnormal to the alarm unit 34. Note that when the determination unit 33A determines that the DC capacitor 12 is abnormal, it may output information indicating that either the DC capacitor 12P or 12N is abnormal to an external device such as a higher-level device (not shown).

[0110] That is, when an abnormality occurs in either the DC capacitor 12P or 12N, the capacitance of either one of them decreases. Therefore, when an abnormality occurs in either the DC capacitor 12P or 12N, when the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N are compared, the voltage values ​​of both are equal to or lower than a predetermined threshold value V ｔｈ３ On the other hand, when both the DC capacitors 12P and 12N are normal, when the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N are compared, the voltage values ​​of both are equal to or greater than a predetermined threshold value V ｔｈ３ In the second embodiment, an abnormality in either the DC capacitor 12P or 12N is detected based on the above-described principle.

[0111] Note that the predetermined threshold V ｔｈ３ may vary depending on the operating conditions of the inverter device 10A, or may be determined in advance by experiment, simulation, or the like, and stored in the storage unit 40. ｔｈ３ may be determined, for example, according to an instruction received from a higher-level device (not shown) or an instruction received from an operator (not shown) via an operation unit (not shown).

[0112] In the second embodiment, the predetermined threshold V ｔｈ３ is a predetermined threshold V ｔｈ Similarly, the DC voltage Vdc may have a bandwidth or margin of a predetermined range (predetermined voltage value) (upper or lower). ｔｈ３If there is a difference of more than this, it is not immediately determined that there is an abnormality in either the DC capacitor 12P or 12N, but rather the predetermined threshold value V ｔｈ３ It may be determined that there is an abnormality when the difference is greater than or equal to the predetermined range. ｔｈ３ Even in this case, a predetermined threshold V ｔｈ Similarly, the bandwidth and margin of the predetermined range may be varied depending on the expected lifespan of the DC capacitor 12P or 12N.

[0113] Also in the second embodiment, similarly to the modification of the first embodiment shown in FIG. 6, a second predetermined threshold value V ｔｈ４ In this case, the determination unit 33A compares the DC voltage Vdcp of the DC capacitor 12P with the DC voltage Vdcn of the DC capacitor 12N, and determines whether or not they are equal to or lower than a second predetermined threshold value V ｔｈ４ If the difference is more than the second predetermined threshold value V ｔｈ４ is larger than the predetermined threshold V ｔｈ３ It will be a smaller value than

[0114] The second predetermined threshold V ｔｈ４ Even in this case, a predetermined threshold V ｔｈ３ Similarly, the second predetermined threshold V may have a bandwidth or margin of a predetermined range (predetermined voltage value) (upper or lower). ｔｈ４ Even in this case, a predetermined threshold V ｔｈ Similarly, the bandwidth and margin of the predetermined range may be varied depending on the expected life of the DC capacitor 12, etc.

[0115] Fig. 9 is a flowchart showing an example of the operation of the control device 30A in the power conversion device 1A shown in Fig. 7 and Fig. 8. The flowchart shown in Fig. 9 has steps S3A and S4A instead of steps S3 and S4 of the flowchart shown in Fig. 3.

[0116] In step S3A, the determination unit 33A determines whether the predetermined time t １The information on the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N at the time point when the time has elapsed is obtained from the monitoring unit 31A.

[0117] In step S4A, the determination unit 33A determines whether the predetermined time t １ After the time has elapsed, the DC voltage Vdcp of the DC capacitor 12P is compared with the DC voltage Vdcn of the DC capacitor 12N. Then, the determination unit 33A determines whether the difference between the compared DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N is equal to or greater than a predetermined threshold value V ｔｈ３ within the range of the predetermined threshold V ｔｈ３ It is determined whether the value is within a predetermined range.

[0118] The determination unit 33A then determines whether the difference between the compared DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N is greater than or equal to a predetermined threshold value V ｔｈ３ If it is determined that the difference is within the range (Yes side), the process proceeds to step S5.

[0119] On the other hand, the determination unit 33A determines whether the difference between the compared DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N is greater than or equal to a predetermined threshold value V ｔｈ３ If it is determined that the value is not within the range (No), the process proceeds to step S6.

[0120] Other configurations or operations of the second embodiment are the same as or similar to those of the first embodiment and its modified examples shown in Figures 1 to 6. Therefore, detailed explanations and illustrations will be omitted.

[0121] <Operations and Effects of Second Embodiment> As described above, the second embodiment shown in FIGS. 7 to 9 has the same operations and effects as the first embodiment shown in FIGS. 1 to 6 and its modified example.

[0122] 7 to 9, by comparing the DC voltage Vdcp of the DC capacitor 12P with the DC voltage Vdcn of the DC capacitor 12N, it is possible to know whether either the DC capacitor 12P or the DC capacitor 12N is abnormal or when it is time to replace it. ｔｈ and a second predetermined threshold V ｔｈ２ Therefore, according to this embodiment, it is possible to know whether either the DC capacitor 12P or 12N is abnormal or when it needs to be replaced, without using a measurement device.

[0123] <Hardware Configuration Example> Fig. 10 is a conceptual diagram showing an example of the hardware configuration of the processing circuitry 90 included in the control device 30 or 30A in the embodiment shown in Figs. 1 to 9. The functions described above are realized by the processing circuitry 90. In one aspect, the processing circuitry 90 includes at least one processor 91 and at least one memory 92. In another aspect, the processing circuitry 90 includes at least one dedicated hardware 93.

[0124] When the processing circuit 90 includes a processor 91 and a memory 92, each function is realized by software, firmware, or a combination of software and firmware. At least one of the software and firmware is written as a program. At least one of the software and firmware is stored in the memory 92. The processor 91 realizes each function by reading and executing the program stored in the memory 92.

[0125] When the processing circuitry 90 includes dedicated hardware 93, the processing circuitry 90 may be, for example, a single circuit, multiple circuits, a programmed processor, or a combination thereof. Each function is implemented by the processing circuitry 90.

[0126] Each function of the control device 30 or 30A may be partially or entirely configured by hardware, or may be configured as a program executed by a processor. That is, the control device 30 or 30A can be realized by a computer and a program, and the program can be stored in a storage medium or provided via a network.

[0127] <Supplementary Notes on the Embodiments> As described above, the embodiments shown in Figures 1 to 10 are divided into the first embodiment and its modified example shown in Figures 1 to 6, and the second embodiment shown in Figures 7 to 9. However, any two or more of these embodiments may be combined in series or in parallel. The combined embodiments can also achieve the same effects as the respective effects achieved by the respective embodiments before being combined.

[0128] 1 to 10, the power conversion devices 1 and 1A and the control devices 30 and 30A included therein have been described as examples of one aspect of the present disclosure, but the present disclosure is not limited to this. The present disclosure can also be realized as a control method in which processing steps are performed in each part of the control device 30 or 30A.

[0129] The present disclosure can also be realized as a control program that causes a computer to execute the processing steps in each part of the control device 30 or 30A.

[0130] The present disclosure can also be realized as a storage medium (non-transitory computer-readable storage medium) on which a control program is stored. The control program can be stored and distributed on removable media such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a USB (Universal Serial Bus) memory. The control program may be uploaded to a network via a network interface (not shown) of the control device 30 or 30A, or may be downloaded from the network and stored in the storage unit 40, memory 92, or the like.

[0131] The features and advantages of the embodiments will be apparent from the above detailed description. It is intended that the claims encompass the features and advantages of the above-described embodiments without departing from the spirit and scope of the claims. Furthermore, any improvements and modifications will be readily apparent to those skilled in the art. Therefore, it is not intended that the scope of the inventive embodiments be limited to the above-described embodiments, and appropriate improvements and equivalents within the scope of the disclosed embodiments may be utilized.

[0132] 1, 1A...power conversion device; 10, 10A...inverter device (device); 11...DC input unit; 11N...negative terminal; 11P...positive terminal; 12, 12P, 12N...DC capacitor; 13...discharge resistor; 14...inverter circuit; 15...AC output unit; 15U...U-phase terminal; 15V...V-phase terminal; 15W...W-phase terminal; 21...DC current sensor; 22...DC voltage sensor; 23...AC current sensor; 24...AC voltage sensor; 30, 30A...control device; 31, 31A...monitoring unit; 32...timekeeping unit; 33, 33A...determination unit; 34...alarm unit; 35...PWM control unit; 40...storage unit; 90...processing circuit; 91...processor; 92...memory; 93...hardware; C...DC neutral point; D...freewheel diode; Iac...AC current; Idc...DC current; L １ ...solid line; L ２ ...Dotted line; L ３ ... dashed line; Q... semiconductor switching element; t ０ , t １ ...time; Vac...AC voltage (AC voltage value); Vdc, Vdcn, Vdcp...DC voltage (DC voltage value); V ｔｈ ...predetermined threshold value; V ｔｈ２ ...second predetermined threshold; V ｔｈ３ ...predetermined threshold value; V ｔｈ４ ...second predetermined threshold

Claims

a DC input unit having a positive terminal and a negative terminal; an inverter circuit which converts power based on the switching operation of a switching element; a DC capacitor which absorbs and smoothes a ripple current generated by the switching operation of the inverter circuit between the positive terminal and the negative terminal, a discharge resistor through which the charge of the DC capacitor is discharged; and a DC voltage sensor which detects a DC voltage value of the DC capacitor; and a control device having: a monitoring unit which monitors the DC voltage value detected by the DC voltage sensor; a timing unit which measures the elapsed time since the inverter device was stopped; a determination unit which determines that an abnormality has occurred in the DC capacitor when the DC voltage value monitored by the monitoring unit falls below a predetermined threshold value, which is a value smaller than a normal value, by a predetermined range or more when the timing unit has measured that a predetermined time has passed since the inverter device was stopped; and 2. A power conversion device as claimed in claim 1, wherein the predetermined threshold is determined based on a discharge curve which shows the change in the DC voltage value when the DC capacitor discharges after the inverter device is stopped, the discharge curve being calculated based on an actual measurement of the change in the DC voltage value after the inverter device is stopped during a factory shipping test of the power conversion device, and the determination unit determines that there is an abnormality in the DC capacitor when the DC voltage value monitored by the monitoring unit falls below the predetermined threshold value determined based on the discharge curve by a predetermined range or more when the timing unit has timed the passage of the predetermined time since the inverter device was stopped.

3. In the power conversion device according to claim 1, the predetermined threshold value is determined based on a discharge curve (v(t)) which indicates a transition of the DC voltage value when the DC capacitor discharges after the inverter device is stopped, and the discharge curve (v(t)) is found by substituting a design value (C) of the capacitance of the DC capacitor, a design value (R) of the resistance of the discharge resistor, a DC voltage value (Vdc) when the inverter device is stopped, and a time (t) which has elapsed since the inverter device was stopped into the following formula (1): The determination unit determines the predetermined time (t １ When it is determined that the predetermined time (t １ ) is substituted into the DC voltage value (v(t １ ) is calculated by the timer unit, and the predetermined time (t １ When the DC voltage value monitored by the monitoring unit is equal to or greater than the determined DC voltage value (v(t １ and determining that an abnormality has occurred in the DC capacitor when the DC capacitor falls below the predetermined threshold value determined based on the predetermined range or more based on the predetermined threshold value determined based on the predetermined range or more.

4. A power conversion device as described in claim 1, wherein the judgment unit judges that it is time to replace the DC capacitor when, when the timing unit has timed a predetermined time since the inverter device was stopped, the DC voltage value monitored by the monitoring unit is below a predetermined range or more of a second predetermined threshold value that is smaller than the normal value and larger than the predetermined threshold value, and is above the predetermined threshold value, and when the judgment unit judges that it is time to replace the DC capacitor, the judgment unit issues a report indicating that it is an indication of when to replace the DC capacitor.

5. An inverter device having: a DC input unit having a positive terminal and a negative terminal; an inverter circuit for converting power based on the switching operation of a switching element; a plurality of DC capacitors connected in series between the positive terminal and the negative terminal via a DC neutral point, absorbing and smoothing a ripple current generated by the switching operation of the inverter circuit; discharge resistors through which the charges of the plurality of DC capacitors are respectively discharged; and a DC voltage sensor for detecting DC voltage values ​​of the plurality of DC capacitors respectively; a monitoring unit for monitoring the DC voltage values ​​of the plurality of DC capacitors detected by the DC voltage sensors; a timing unit for timing an elapsed time from the stop of the inverter device; and a determination unit for comparing the DC voltage values ​​of the plurality of DC capacitors monitored by the monitoring unit when the timing unit has timed that a predetermined time has elapsed since the stop of the inverter device, and determining that an abnormality has occurred in any of the plurality of DC capacitors compared when the difference between the DC voltage values ​​of the plurality of DC capacitors is equal to or greater than a predetermined threshold value. a control device having a warning unit that, when the determination unit determines that any one of the plurality of DC capacitors is abnormal, issues a warning that any one of the plurality of DC capacitors is abnormal.

6. A control device for a power conversion device including an inverter device having a DC input unit having a positive terminal and a negative terminal; an inverter circuit that converts power based on the switching operation of a switching element; a DC capacitor that absorbs and smoothes a ripple current generated by the switching operation of the inverter circuit between the positive terminal and the negative terminal, a discharge resistor through which the charge of the DC capacitor is discharged; and a DC voltage sensor that detects a DC voltage value of the DC capacitor, comprising: a monitoring unit that monitors the DC voltage value detected by the DC voltage sensor; a timing unit that measures the elapsed time since the inverter device was stopped; a determination unit that determines that an abnormality has occurred in the DC capacitor when the DC voltage value monitored by the monitoring unit falls below a predetermined threshold value, which is a value smaller than a normal value, by a predetermined range or more when the timing unit has measured that a predetermined time has passed since the inverter device was stopped; and a reporting unit that issues a report of an abnormality in the DC capacitor when the determination unit determines that an abnormality has occurred in the DC capacitor.

Images