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

[Technical Field]

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

[0002] For example, in a power converter that converts power between DC and AC, the DC input section is equipped with a DC capacitor to absorb (smooth) ripple current. DC capacitors can experience abnormalities such as reduced capacitance due to aging or malfunction. However, properly detecting these abnormalities in DC capacitors has been difficult.

[0003] Therefore, conventional methods have been proposed to detect abnormalities such as a decrease in the capacitance of a DC capacitor in an inverter based on the magnitude of the resistive current and the magnitude of the voltage across the capacitor terminals after a predetermined reference time has elapsed since the start of power supply (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-228370 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, when the capacitance of a DC capacitor decreases, the voltage across the DC capacitor will be different from that under normal conditions during charging when the device is started and during discharge when the device is stopped.

[0006] However, while conventional methods could detect abnormalities in DC capacitors based on their charging voltage during device startup, they could not detect abnormalities in DC capacitors based on their discharge voltage during device shutdown.

[0007] Therefore, the present disclosure aims to provide a means for detecting abnormalities in a DC capacitor connected to the DC input side of a power converter 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. [Means for solving the problem]

[0008] A power conversion device according to one embodiment is characterized by comprising: 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 between the positive terminal and the negative terminal that absorbs and smooths the ripple current generated by the switching operation of the inverter circuit; a discharge resistor from which the charge of the DC capacitor is discharged; and a DC voltage sensor that detects the DC voltage value of the DC capacitor; 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 has measured 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 which is smaller than a normal value by a predetermined range; and an alarm unit that issues an alarm about the abnormality in the DC capacitor when the determination unit has determined that there is an abnormality in the DC capacitor.

[0009] Another embodiment of the power conversion device includes an inverter device having a DC input section 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 connected in series between the positive terminal and the negative terminal via a DC neutral point to absorb and smooth the ripple current generated by the switching operation of the inverter circuit, a discharge resistor through which the charge of the plurality of DC capacitors is discharged, and a DC voltage sensor that detects the 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 sensor, and when the inverter device is stopped The control device is characterized by comprising: a timing unit that measures the elapsed time; a determination unit that, when the timing unit measures that a predetermined time has elapsed since the inverter device was stopped, compares the DC voltage values ​​of a plurality of DC capacitors monitored by a monitoring unit, and determines that one of the DC capacitors among the plurality of DC capacitors is abnormal if the DC voltage values ​​of the plurality of DC capacitors differ by a predetermined threshold or more; and an alarm unit that, when the determination unit determines that one of the DC capacitors among the plurality of DC capacitors is abnormal, issues an alarm indicating that one of the DC capacitors among the plurality of DC capacitors is abnormal.

[0010] A control device according to one embodiment is a control device for a power converter comprising 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 between the positive terminal and the negative terminal that absorbs and smooths the ripple current generated by the switching operation of the inverter circuit, a discharge resistor on 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 has measured 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 which is smaller than a normal value by a predetermined range, and an alarm unit that issues an alarm about the abnormality of the DC capacitor when the determination unit has determined that there is an abnormality in the DC capacitor. [Effects of the Invention]

[0011] According to this disclosure, by monitoring the discharge rate of the DC voltage when the device is stopped, it is possible to provide a means for detecting abnormalities in a DC capacitor connected to the DC input side of a power converter based on the discharge voltage of the DC voltage when the device is stopped. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example configuration of a power conversion device according to the first embodiment. [Figure 2] This figure shows an example of the configuration of a control device in the power conversion device shown in Figure 1. [Figure 3] Figures 1 and 2 are flowcharts illustrating an example of the operation of the control device in the power converter. [Figure 4] This figure shows an example of a discharge curve when a DC capacitor discharges after an inverter device is shut down. [Figure 5]Figure 4 shows an example of a discharge curve for a normal DC capacitor and a discharge curve representing a predetermined threshold. [Figure 6] This figure shows an example of a discharge curve for a normal DC capacitor, a discharge curve as a predetermined threshold, and a discharge curve as a second predetermined threshold, according to a modification of the first embodiment. [Figure 7] This figure shows an example configuration of a power conversion device according to the second embodiment. [Figure 8] This figure shows an example of the configuration of a control device in the power conversion device shown in Figure 7. [Figure 9] Figures 7 and 8 are flowcharts illustrating an example of the operation of the control device in the power converter shown in Figures 7 and 8. [Figure 10] Figures 1 to 9 are conceptual diagrams showing examples of the hardware configuration of the processing circuit of the control device in the embodiment shown. [Modes for carrying out the invention]

[0013] The embodiments of the power conversion device and control device related to this disclosure will be described below with reference to the drawings.

[0014] <Configuration of the first embodiment> Figure 1 shows an example of the configuration of the power converter 1 according to the first embodiment.

[0015] As shown in Figure 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 section 11, a DC capacitor 12, a discharge resistor 13, an inverter circuit 14, and an AC output section 15. For example, the inverter device 10 converts DC power supplied from the DC input section 11 into AC power via the inverter circuit 14, and outputs the converted AC power to the AC output section 15.

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

[0018] In other words, the inverter device 10 may be, for example, a converter that converts AC to DC, as long as it has a DC capacitor 12, a discharge resistor 13, and 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 compensation device that generates a DC voltage by the operation of an inverter circuit 14, controls the DC voltage to be constant, and stabilizes the voltage by exchanging reactive power between the DC capacitor and the grid. Alternatively, the inverter device 10 may be a DC to DC converter such as a DC chopper. In this specification and elsewhere, the inverter device 10 will also be simply referred to as "device" or "device 10".

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

[0020] The DC capacitor 12 is placed, for example, between the positive terminal 11P and the negative terminal 11N, and absorbs and smooths the ripple current generated by the switching operation of the switching elements of the inverter circuit 14. The DC capacitor 12 is almost always included in voltage-type inverters, and is charged when the inverter device 10 starts up (when power is turned on) and discharged when the inverter device 10 stops.

[0021] When the capacitance of the DC capacitor 12 decreases due to aging or malfunction, the voltage will be different from that under normal conditions during charging when the inverter device 10 is started and during discharging when the inverter device 10 is stopped. In this case, the slope and magnitude of the charging curve, which indicates the charging speed during charging, and the discharge curve, which indicates the discharge speed during discharging, will also be different from those under normal conditions.

[0022] The discharge resistor 13 is, for example, placed between the positive terminal 11P and the negative terminal 11N, and is a resistor that discharges the charge of the DC capacitor 12 after the inverter device 10 has stopped. The discharge resistor 13 may be connected at all times, or it may be switched on and connected after the inverter device 10 has stopped. For example, in an inverter device 10 having a small to medium-capacity DC capacitor 12, the discharge resistor 13 may be connected at all times, and in an inverter device 10 having a large-capacity DC capacitor 12, it may be switched on and connected by a switch (not shown) after the inverter device 10 has stopped.

[0023] The inverter circuit 14 is constructed of multiple semiconductor switching elements Q, such as IGBTs (Insulated Gate Bipolar Transistors), and multiple freewheeling diodes D. Note that the semiconductor switching elements Q are not limited to IGBTs, but may also be MOSFETs (metal-oxide-semiconductor field-effect transistors), etc. The inverter circuit 14 is connected, for example, at one end (the input side) via a DC input section 11 to a DC power source (not shown), and at the other end (the output side) via an AC output section to an AC power system (not shown).

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

[0025] The inverter circuit 14 has, for example, a circuit in which three legs (U-phase leg, V-phase leg, and W-phase leg) are connected in parallel. Each leg is constructed by connecting two arms in series, each arm consisting of a semiconductor switching element Q and a freewheeling diode D connected in antiparallel. Each leg is connected in parallel between, for example, the positive terminal 11P and the negative terminal 11N, and the midpoint of each leg is connected to the U-phase terminal 15U, V-phase terminal 15V, and W-phase terminal 15W of the AC output section 15, respectively. Note that the inverter circuit 14 is not limited to a three-phase inverter, but may be a single-phase or other 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. The AC output unit 15 is connected to the inverter device 10 at one end on the left side in Figure 1, and to a power system or load (not shown) at the other end on the right side in Figure 1. 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 single-phase AC circuits with phases shifted relative to each other using three wires / cables / conductors. Note that the AC output unit 15 is not limited to a three-phase AC circuit, but may be a single-phase AC circuit or any other type of AC circuit. The AC output unit 15 outputs the AC power converted by the inverter circuit 14 to a power system or load (not shown).

[0027] Furthermore, the inverter device 10 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 in which the DC current sensor 21 is placed is not limited to the position shown in Figure 1, but can be anywhere as long as 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 "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 in which the DC voltage sensor 22 is placed is not limited to the position shown in Figure 1, but can be anywhere as long as 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 will also be simply referred to as "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 position in which the AC current sensor 23 is placed is not limited to the position shown in Figure 1, but can be anywhere as long as 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 position in which the AC voltage sensor 24 is placed is not limited to the position shown in Figure 1, but can be anywhere as long as 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 "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 converter 1. Although wiring and other details are omitted in the figure, it is electrically connected by wire or wireless means to the inverter circuit 14 and other components of the inverter device 10. The control device 30 may also be implemented as a function of an inverter control circuit, which is not shown.

[0033] The control device 30 has a processor 91 (see Figure 10), such as a CPU (Central Processing Unit), which operates by executing a program. The control device 30 also has a storage unit 40 (see Figure 2) and a memory 92 (see Figure 10), and for example, it operates the processor 91 by executing a predetermined program stored in the storage unit 40 or the memory 92 to comprehensively control the operation of the inverter device 10. The control device 30 may also control the operation of the inverter device 10 according to 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 fault, abnormality, or capacitance reduction in 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 in the DC capacitor 12, it issues an alert indicating that an abnormality has been detected in the DC capacitor 12.

[0035] Figure 2 shows an example of the configuration of the control device 30 in the power conversion device 1 shown in Figure 1.

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

[0037] The monitoring unit 31 is connected to the DC voltage sensor 22 and continuously 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 it may acquire and monitor the information according to 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 the information on the DC voltage Vdc of the DC capacitor 12 when the inverter device 10 stops. 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 may acquire and monitor information on the DC current Idc, AC current Iac, and AC voltage Vac detected by these sensors.

[0038] When the inverter device 10 stops, the timing unit 32 measures the elapsed time since the inverter device 10 stopped. The elapsed time measured by the timing unit 32 is acquired by the determination unit 33. The timing unit 32 may also measure whether a predetermined time t1 has elapsed since the inverter device 10 stopped. In this case, when the predetermined time t1 has elapsed since the inverter device 10 stopped, the timing unit 32 outputs information to the determination unit 33 indicating that a predetermined time t1 has elapsed since the inverter device 10 stopped.

[0039] The determination unit 33 acquires information on the DC voltage Vdc monitored by the monitoring unit 31 when the timing unit 32 has determined that a predetermined time t1 has elapsed since the inverter device 10 stopped. When the timing unit 32 has determined that a predetermined time t1 has elapsed since the inverter device 10 stopped, the determination unit 33 acquires information on the DC voltage Vdc monitored by the monitoring unit 31 and a predetermined threshold V th Compare them.

[0040] The determination unit 33 may also continuously acquire information on the DC voltage Vdc monitored by the monitoring unit 31. The determination unit 33 then uses the DC voltage Vdc monitored by the monitoring unit 31 and a predetermined threshold V th It's fine to keep comparing them constantly.

[0041] The determination unit 33 determines that the DC voltage Vdc monitored by the monitoring unit 31 is at a predetermined threshold V th When the DC voltage Vdc is below the threshold, it is determined that the DC capacitor 12 is abnormal. 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 the DC capacitor 12 is abnormal, it outputs information indicating that the DC capacitor 12 is abnormal to the notification unit 34. Note that when the determination unit 33 determines that the DC capacitor 12 is abnormal, it may output information indicating that the DC capacitor 12 is abnormal to an external device such as a host device (not shown).

[0042] Note that the predetermined threshold V th may, for example, vary according to the operating status of the inverter device 10, may be predetermined through experiments, simulations, or the like, and may be stored in the storage unit 40. Further, the predetermined threshold V th may be determined in accordance with, for example, an instruction received from a host 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 value (voltage value) smaller than the normal DC voltage Vdc (normal value) detected in a normal DC capacitor 12 when a predetermined time t1 elapses after the inverter device 10 stops. The predetermined threshold V th may have a bandwidth or margin of a predetermined range (predetermined voltage value) (vertically or downwardly). That is, the determination unit 33 does not immediately determine that the DC capacitor 12 is abnormal as soon as the DC voltage Vdc falls below the predetermined threshold V th Instead, the determination unit 33 may determine that the DC capacitor 12 is abnormal when the DC voltage Vdc falls below the predetermined threshold V th by more than the predetermined range. Note that the bandwidth and margin of the predetermined range may be varied according to the expected lifespan of the DC capacitor 12 and the like.

[0044] As a result, for example, in the event of a temporary or accidental fluctuation in the DC voltage Vdc, the determination unit 33 will not detect an abnormality in the DC capacitor 12. Therefore, a predetermined threshold V th Compared to the case where the bandwidth or margin does not fall within a predetermined range, the determination unit 33 is less likely to falsely detect abnormalities, and the determination unit 33 can more accurately detect abnormalities in the DC capacitor 12.

[0045] As described above, the determination unit 33 determines if the DC voltage Vdc is a predetermined threshold V th The DC capacitor 12 may be deemed abnormal if the voltage falls below a predetermined range (a predetermined voltage value) or more. However, the determination unit 33 may determine that the DC voltage Vdc has exceeded a predetermined threshold V for a predetermined period of time or longer. th When the DC voltage Vdc falls below a predetermined threshold V, the DC capacitor 12 may be deemed to be abnormal. Alternatively, the determination unit 33 may determine that the DC voltage Vdc has exceeded a predetermined threshold V for a predetermined number of times. th If the value falls below a certain level, it may be determined that there is an abnormality in the DC capacitor 12.

[0046] Furthermore, the determination unit 33 determines a predetermined threshold V th An abnormality in the DC capacitor 12 may be determined by a combination of several or all of the following: a predetermined bandwidth or margin, time, and the number of cycles. For example, the determination unit 33 may determine if the DC voltage Vdc exceeds a predetermined threshold V if the DC voltage Vdc exceeds a predetermined threshold th If the value falls below a certain level, it may be determined that there is an abnormality in the DC capacitor 12.

[0047] Furthermore, for example, the determination unit 33 determines if the DC voltage Vdc has been at a predetermined threshold V for a predetermined time or longer. th When the voltage falls below a predetermined range (a predetermined voltage value) or more, the DC capacitor 12 may be deemed to be abnormal. Also, for example, the determination unit 33 may determine that the DC voltage Vdc falls below a predetermined threshold V if the DC voltage Vdc has been exceeded for a predetermined number of times or more. th When the voltage falls below a predetermined range (a predetermined voltage value) or more, the DC capacitor 12 may be deemed to be abnormal. Alternatively, for example, the determination unit 33 may determine that the DC voltage Vdc falls below a predetermined threshold V for a predetermined period of time and a predetermined number of times or more. thIf the voltage falls below a predetermined range (a predetermined voltage value), it may be determined that there is an abnormality in the DC capacitor 12.

[0048] This results in a predetermined threshold V th By combining the predetermined bandwidth and margin range, time, and number of cycles, the determination unit 33 can suppress false detections of abnormalities, and the determination unit 33 can more accurately detect abnormalities in the DC capacitor 12.

[0049] When the alarm unit 34 receives information from the determination unit 33 indicating that it has determined that the DC capacitor 12 is abnormal, it issues an alarm about the abnormality of the DC capacitor 12. The alarm unit 34 issues an alarm about the abnormality of the DC capacitor 12 by, for example, outputting fault information to a higher-level device (not shown) or by outputting a warning, alarm, or other display or sound to a display unit or operation unit (not shown) of the power converter 1. The alarm unit 34 may also stop the discharge of the DC capacitor 12. The function of the alarm 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 to generate a gate signal that turns the semiconductor switching element Q of the inverter circuit 14 on and off. The PWM control unit 35 outputs the generated gate signal to the inverter circuit 14 of the inverter device 10 to control the operation of the inverter circuit 14. When the inverter device 10 stops and the output of the gate signal stops, the PWM control unit 35 may output information to the timing unit indicating that the inverter device 10 has stopped.

[0051] The storage unit 40 is a volatile or non-volatile storage medium such as an HDD (Hard Disk Drive), SSD (Solid State Drive), DRAM (Dynamic Random Access Memory), or other semiconductor memory. The storage unit 40 stores programs necessary for the operation of each part of the control device 30, and various types of information are written to and read from the storage unit 40 by each part of the control device 30. The storage unit 40 stores information such as DC current Idc, DC voltage Vdc, AC current Iac, and AC voltage Vac, which are monitored by the monitoring unit 31. The storage unit 40 also stores, for example, a predetermined time t1 and a predetermined threshold V th It stores information such as various calculation formulas and threshold values ​​used for the determination of the determination unit 33.

[0052] The storage unit 40 is connected to various parts of the control device 30, for example, by a bus (not shown), so that various types of information can be input and output by each part of the control device 30. The storage unit 40 may be located outside the control device 30 and connected to the control device 30 by wire or wireless connection, and may be an external storage medium such as a memory card or DVD (Digital Versatile Disc), or online storage. Furthermore, the storage unit 40 may be the same as the memory 92 (see Figure 10) described later.

[0053] <Operation of the first embodiment> Figure 3 is a flowchart showing an example of the operation of the control device 30 in the power converter 1 shown in Figures 1 and 2. The flowchart shown in Figure 3 starts when the inverter device 10 stops.

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

[0055] In step S2, the determination unit 33 of the control device 30 obtains the time measured by the timing unit 32 from the timing unit 32 and determines whether the timing unit 32 has measured a predetermined time t1 elapsed since the inverter device 10 stopped. If the determination unit 33 determines that the timing unit 32 has measured a predetermined time t1 elapsed since the inverter device 10 stopped (Yes side), it proceeds to step S3. On the other hand, if the determination unit 33 determines that the timing unit 32 has not measured a predetermined time t1 elapsed since the inverter device 10 stopped (No side), it repeats the process in step S2 until it determines that the predetermined time t1 elapsed.

[0056] In step S3, the determination unit 33 obtains information on the DC voltage Vdc of the DC capacitor 12 at the time a predetermined time t1 has elapsed from the monitoring unit 31. The determination unit 33 also obtains information on a predetermined threshold V at the time a predetermined time t1 has elapsed. th The information is obtained from the storage unit 40.

[0057] In step S4, the determination unit 33 determines that, at a predetermined time t1, the DC voltage Vdc is equal to a predetermined threshold V th It is determined whether or not it falls within a predetermined range.

[0058] Then, the determination unit 33 determines that, at a predetermined time t1, the DC voltage Vdc is equal to a predetermined threshold V th If it is determined that the value falls within the specified range (Yes), the process proceeds to step S5.

[0059] On the other hand, the determination unit 33 determines that when a predetermined time t1 has elapsed, the DC voltage Vdc is below a predetermined threshold V th If it is determined that the value is not within the predetermined range (No side), the process proceeds to step S6. That is, when the timing unit 32 has timed that a predetermined time t1 has elapsed since the inverter device 10 stopped, the determination unit 33 determines that the DC voltage Vdc is within a predetermined threshold V thIf it is determined that the value falls below a predetermined range (No side), the process proceeds to step S6. Here, the predetermined threshold V th This may be determined based on the discharge curve.

[0060] Figure 4 shows an example of a discharge curve when the DC capacitor 12 discharges after the inverter device 10 stops. In other words, Figure 4 shows a discharge curve that shows the change in DC voltage value when the DC capacitor 12 discharges after the inverter device 10 stops.

[0061] In Figure 4, the vertical axis represents voltage (V), and the horizontal axis represents time (t). In Figure 4, the DC voltage Vdc represents the DC voltage value when the inverter device 10 is in operation (or stopped). That is, in Figure 4, it is assumed that the DC voltage value is maintained at DC voltage Vdc from the time the inverter device 10 is in operation until it is stopped (time t0). When the inverter device 10 is stopped at time t0, the charge of the DC capacitor 12 is discharged into the discharge resistor 13. Figure 4 shows the discharge curve (v(t)) which shows the change in the DC voltage value when the DC capacitor 12 discharges after the inverter device 10 has stopped at time t0. The discharge curve (v(t)) is obtained by the following equation (1).

[0062]

number

[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) shows a discharge curve (v(t)) that illustrates how the DC voltage value of the DC capacitor 12 naturally decays when it discharges after the inverter device 10 has stopped. If t0 is the time when the inverter device 10 stops (=0) and t1 is the time after a predetermined period of time has elapsed since the inverter device 10 stopped, then the DC voltage value of the DC capacitor 12 at the time after the predetermined period of time (t1) from the time the inverter device 10 stops (t0) is v(t1).

[0065] The design value (C) of the DC capacitor 12 is often on the order of uF or mF. Similarly, the design value (R) of the discharge resistor 13 is often on the order of kΩ. In the case of a large-capacity inverter device 10, there is almost never only one DC capacitor 12; therefore, the design value (C) of the DC capacitor 12 is the combined value (combined capacitance) if the DC capacitors 12 are connected in parallel.

[0066] Figure 5 shows the discharge curve of a normal DC capacitor 12 as shown in Figure 4 and a predetermined threshold V. th This figure shows an example of a discharge curve.

[0067] In Figure 5, the vertical axis, horizontal axis, and each symbol represent the same as in Figure 4. That is, in Figure 5 as well, the DC voltage Vdc represents the DC voltage value when the inverter device 10 is operating (or stopped). In Figure 5, the solid line L1 is the same as the discharge curve shown in Figure 4 and represents the discharge curve of a normal DC capacitor 12. On the other hand, the dashed line L2 represents a predetermined threshold V th The discharge curve is shown.

[0068] As shown in Figure 5, when the capacitance of a DC capacitor 12 decreases due to an abnormality or deterioration, the reduced charge causes it to discharge faster against the same discharge resistance 13, resulting in a faster voltage drop. For example, if an abnormality such as a break occurs in one of the combined capacitances of multiple DC capacitors 12 connected in parallel, the reduced charge (equivalent to one capacitor) causes it to discharge faster against the same discharge resistance 13, resulting in a faster voltage drop.

[0069] Therefore, the discharge curve of the DC capacitor 12 with reduced capacitance will have a lower voltage value than the discharge curve of a normal DC capacitor 12, and will be the lower line. Therefore, as shown in Figure 5, the discharge curve of the DC capacitor 12 will be lower than the solid line L1 which shows the discharge curve of a normal DC capacitor 12, and will be below the predetermined threshold V. th The dashed line L2, which shows the discharge curve, is the lower line.

[0070] Note that a predetermined threshold V th The dashed line L2, which shows the discharge curve, may have a bandwidth or margin (width) within a predetermined range (predetermined voltage value), as described above. Therefore, when a predetermined time t1 has elapsed, the determination unit 33 determines that the value of the DC voltage monitored by the monitoring unit 31 is within a predetermined threshold V th An abnormality in the DC capacitor 12 may be determined when the value falls below the predetermined range.

[0071] Furthermore, the predetermined time t1 is not limited to one time, but may be measured multiple times, and may have a predetermined duration. Also, a predetermined threshold V th Whether or not it is below a certain level may be determined not by a single sample point, but by multiple sample points, or by the discharge curve as a whole or by a predetermined portion of the discharge curve.

[0072] Here, a predetermined threshold V th This may be determined (or defined) based on a discharge curve based on the measured values ​​of the DC voltage change after the inverter device 10 stops during the factory shipment test of the power converter 1. For example, a predetermined threshold V th The dashed line L2 shown may be a value (discharge curve) that is determined from the discharge curve based on actual measured values ​​during factory shipment testing of the power converter 1, based on experiments or simulations, and stored in the memory unit 40. th=L2) may be determined based on the time constant (τ) derived from the measured values ​​of the capacitance (C) of the DC capacitor 12 and the resistance (R) of the discharge resistor during factory shipment testing. Furthermore, a predetermined threshold (V) can be determined based on the discharge curve or time constant (τ) derived from the measured values ​​during the factory shipment testing described above. th =L2) may be determined in advance and stored in the memory unit 40 beforehand.

[0073] In this case, when the timing unit 32 has timed that a predetermined time (t1) has elapsed since the inverter device 10 stopped (t0), the determination unit 33 determines the actual value of the DC voltage monitored by the monitoring unit and the predetermined threshold value (V) obtained above. th Compare this with (=L2).

[0074] Then, the determination unit 33 determines that the measured value of the DC voltage monitored by the monitoring unit is determined to be a predetermined threshold (V) based on the measured value during the factory shipment test of the power converter 1. th If the value falls below L2 by a predetermined range or more, it is determined that there is an abnormality in the DC capacitor 12.

[0075] Thus, a predetermined threshold V th However, since it is determined based on the actual measured values ​​during the factory shipment test of the power converter 1, a predetermined threshold V that is appropriate for the actual device is obtained. th This allows for the determination of the parameters, enabling more accurate detection of abnormalities in the DC capacitor 12 than in cases that do not conform to the actual equipment.

[0076] Furthermore, a predetermined threshold V th This may be determined (or defined) based on a value calculated by equation (1) above, based on the design value of the capacitance (C) of the DC capacitor and the design value of the resistance (R) of the discharge resistor. For example, a predetermined threshold V th The dashed line L2 shown may be a value obtained from the discharge curve (v(t)) based on the value calculated by equation (1) above, or from experiments or simulations. For example, a predetermined threshold V thThis value may be obtained by substituting a predetermined timing for the diagnosis (a specified time (t1)) into equation (1) above, or it may be a value determined based on experiments, simulations, etc.

[0077] In this case, the determination unit 33 calculates the voltage value (v(t1)) when it substitutes the predetermined time (t1) into equation (1) above, when the timing unit 32 has measured that a predetermined time (t1) has elapsed since the inverter device 10 stopped (t0). Note that the voltage value (v(t1)) when the predetermined time (t1) is substituted into equation (1) above may be determined in advance and stored in the storage unit 40 beforehand.

[0078] Then, when the timing unit 32 has timed a predetermined period of time (t1) since the inverter device 10 stopped (t0), the determination unit 33 compares the measured value of the DC voltage monitored by the monitoring unit 31 with the determined voltage value (v(t1)). If the measured value of the DC voltage monitored by the monitoring unit 31 is lower than the determined voltage value (v(t1)) by a predetermined range or more, the determination unit 33 determines that there is an abnormality in the DC capacitor 12.

[0079] Thus, a predetermined threshold V th However, since it is determined based on the design value of the capacitance (C) of the DC capacitor and the design value of the discharge resistance (R), it is possible to accurately detect abnormalities in the DC capacitor 12 based on the design values.

[0080] Returning to Figure 3, in step S5, the alarm unit 34 has not received any information from the determination unit 33 indicating that an abnormality has been determined in the DC capacitor 12. Therefore, the control device 30 continues to discharge the DC capacitor 12 and terminates the process of the flowchart in Figure 3.

[0081] In step S6, the alarm unit 34 receives information from the determination unit 33 indicating that it has determined that the DC capacitor 12 is abnormal, and issues an alarm about the abnormality of the DC capacitor 12. The control device 30 then completes the processing shown in the flowchart of Figure 3.

[0082] <Effects of the First Embodiment> In the first embodiment shown in Figures 1 to 5 above, when a predetermined time t1 has elapsed since the inverter device 10 stopped, the DC voltage value Vdc reaches a predetermined threshold V th When the value falls below a predetermined range, 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 detect 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] Furthermore, according to the first embodiment shown in Figures 1 to 5, a predetermined threshold V th It may have a bandwidth or margin within a predetermined range (a predetermined voltage value). Thus, according to this embodiment, a predetermined threshold V th Compared to the case where the bandwidth or margin does not fall within a predetermined range, the determination unit 33 is less likely to falsely detect abnormalities, and the determination unit 33 can more accurately detect abnormalities in the DC capacitor 12.

[0084] Furthermore, according to the first embodiment shown in Figures 1 to 5, a predetermined threshold V th This may be determined based on a discharge curve based on the measured value of the DC voltage change after the inverter device 10 stops during the factory shipment test of the power converter 1. Thus, according to this embodiment, a predetermined threshold V that is appropriate for the actual machine can be determined. th This allows for the determination of the parameters, enabling more accurate detection of abnormalities in the DC capacitor 12 than in cases that do not conform to the actual equipment.

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

[0086] <Modified form of the first embodiment> Figure 6 shows the discharge curve of a normal DC capacitor 12 and a predetermined threshold V according to a modified example of the first embodiment. th The discharge curve as and a second predetermined threshold V th2 This figure shows an example of a discharge curve.

[0087] In the modified version of the first embodiment, components identical or similar to those in the first embodiment shown in Figures 1 to 5 are denoted by the same reference numerals, and detailed descriptions are omitted or simplified. In the modified version of the first embodiment, the configuration and operation of the power converter 1 are identical or similar to those in the first embodiment shown in Figures 1 to 5, and therefore are not shown. In the modified version of the first embodiment, the predetermined threshold V of the first embodiment shown in Figures 1 to 5 is... th In addition, a second predetermined threshold V th2 This is used.

[0088] In Figure 6, the vertical axis, horizontal axis, and each symbol are the same as in Figures 4 and 5. That is, in Figure 6, the solid line L1 is the same as the solid line L1 of the discharge curve shown in Figure 5, and shows an example of a discharge curve of a normal DC capacitor 12. For example, the solid line L1 shows an example of a discharge curve as a reference value based on the measured value during factory shipment testing of the power converter 1, or as 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] Furthermore, in Figure 6, the dashed line L2 is the same as the dashed line L2 of the discharge curve shown in Figure 5, and a predetermined threshold V is used to detect (determine) an abnormality in the DC capacitor 12. th An example of a discharge curve is shown.

[0090] Furthermore, Figure 6 shows a dashed line L3. The dashed line L3 represents a second predetermined threshold V for detecting an indication that the DC capacitor 12 should be replaced (determining the replacement timing). th2 An example of the discharge curve is shown. The second predetermined threshold V th2 The dashed line L3, which indicates the value, is smaller than the solid line L1, which indicates the reference value, and is a predetermined threshold V for detecting an abnormality in the DC capacitor 12. thIt is greater than the dashed line L2 that indicates this.

[0091] When a DC capacitor 12 malfunctions, for example, or when one of its capacitances is lost, the capacitance of the DC capacitor 12 decreases significantly more than in cases of aging or other abnormalities. On the other hand, the capacitance of the DC capacitor 12 decreases more gradually due to aging or lifespan than due to capacitance loss or other abnormalities (the capacitance does not decrease as much). For this reason, the second predetermined threshold V th2 The dashed line L3 indicates a predetermined threshold V for detecting an abnormality in the DC capacitor 12. th It is considered to be greater than the dashed line L2 that indicates this.

[0092] Furthermore, in a modified version of the first embodiment, the determination unit 33 determines that the DC voltage Vdc monitored by the monitoring unit 31 is equal to a second predetermined threshold V th2 It falls below a predetermined threshold V. th If the value exceeds a certain level, 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 addition, in the modified version of the first embodiment, similar to the first embodiment shown in Figures 1 to 5, the determination unit 33 determines if the DC voltage Vdc monitored by the monitoring unit 31 is a predetermined threshold V th If the value falls below a certain level, it is determined that there is an abnormality in the DC capacitor 12. Then, if the determination unit 33 determines that there is an abnormality in the DC capacitor 12, the alarm unit 34 will issue an alarm indicating the abnormality of the DC capacitor 12.

[0094] In addition, in the modified example of the first embodiment, the second predetermined threshold V th2 The predetermined threshold V th Similarly, it may have a bandwidth or margin (a predetermined range of voltage values) (up or down). Then, the determination unit 33 determines if the DC voltage Vdc is a second predetermined threshold V th2Instead of immediately determining that it is time to replace the DC capacitor 12 when it falls below a second predetermined threshold V th2 The replacement time for the DC capacitor 12 may be determined when the value falls below the predetermined range.

[0095] Furthermore, the second predetermined threshold V th2 Even in a predetermined threshold V th Similarly, the bandwidth and margin within a predetermined range may be varied according to the expected lifespan of the DC capacitor 12, etc. Also, a predetermined threshold V th The dashed line L2 indicates the second predetermined threshold V th2 The dashed line L3 indicating this may be determined by experiments, calculations, simulations, etc., and stored in the memory unit 40.

[0096] Furthermore, a predetermined threshold V th The dashed line L2 indicates the second predetermined threshold V th2 The dashed line L3, which indicates this, may be represented by varying the bandwidth, margin, etc., from a single threshold (discharge curve). That is, in a single threshold (discharge curve), the first bandwidth is set to a predetermined threshold V th A second bandwidth smaller than the first bandwidth is set to a second predetermined threshold V. th2 That is also acceptable.

[0097] Furthermore, a predetermined threshold V th The dashed line L2 indicates the second predetermined threshold V th2 The dashed line L3, which indicates this, may be represented by varying the slope of the discharge curve. That is, the discharge curve with the first slope is defined by a predetermined threshold V th The discharge curve with a second slope, which is gentler than the first slope, is set to a second predetermined threshold V. th2 That is also acceptable.

[0098] Furthermore, there is another second predetermined threshold V th2 Regarding the handling of and the determination operation by the determination unit 33, a predetermined threshold V in the first embodiment shown in Figures 1 to 5 will be used. thThe handling and determination operations by the determination unit 33 are the same as or identical to those described above. Therefore, detailed explanations and illustrations are omitted.

[0099] <Effects and Effects of Modified Examples of the First Embodiment> As described above, the modified version of the first embodiment shown in Figure 6 provides the same effects and advantages as the first embodiment shown in Figures 1 to 5.

[0100] Furthermore, in the modified version of the first embodiment shown in Figure 6, a second predetermined threshold (V) is used to determine when to replace the DC capacitor 12. th2 =L3) is used. As a result, according to this embodiment, based on the discharge voltage of the DC voltage Vdc when the inverter device 10 is stopped, it is possible to know not only the abnormality of the DC capacitor 12 but also when it is time to replace the DC capacitor 12.

[0101] <Second Embodiment> Figure 7 shows an example of the configuration of the power converter 1A according to the second embodiment.

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

[0103] In the second embodiment, the inverter device 10A of the power converter 1A is a multilevel power converter in which two DC capacitors 12P and 12N are connected in series via a DC neutral point C. In Figure 7, as an example of the inverter device 10A, a three-level multilevel power converter in which two DC capacitors 12P and 12N are connected in series via a DC neutral point C is described, but there may be more than two DC capacitors 12P and 12N. The discharge resistors 13 may also be multiple in number depending on the DC capacitors 12P and 12N.

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

[0105] Figure 8 shows an example of the configuration of the control device 30A in the power converter 1A shown in Figure 7. As shown in Figure 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 Figures 1 to 6, and a determination unit 33A instead of the determination unit 33.

[0106] The monitoring unit 31A continuously acquires and monitors information on the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N, which are detected by the DC voltage sensor 22. The monitoring unit 31A may also acquire and monitor the information on the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N, for example, at predetermined time intervals. Alternatively, the monitoring unit 31A may acquire and monitor the information on the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N, for example, according to instructions received from an operator or the like via a higher-level device (not shown) or an operation unit (not shown). Furthermore, the monitoring unit 31A may acquire and monitor the information on the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N when the inverter device 10A stops.

[0107] The determination unit 33A acquires information on the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N, which are monitored by the monitoring unit 31A, when the timing unit 32 has measured that a predetermined time t1 has elapsed since the inverter device 10A stopped. Then, when the timing unit 32 has measured that a predetermined time t1 has elapsed since the inverter device 10 stopped, the determination unit 33A compares the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N. In other words, the determination unit 33A compares the DC voltage values ​​of multiple DC capacitors 12P and 12N.

[0108] Furthermore, the determination unit 33A may continuously acquire information on the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N, which are monitored by the monitoring unit 31A. The determination unit 33A may also continuously compare the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N.

[0109] The determination unit 33A determines if the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N are equal to a predetermined threshold V th3 If the above discrepancies are found, it is determined that there is an abnormality in either the DC capacitor 12P or 12N. When the determination unit 33A determines that there is an abnormality in either the DC capacitor 12P or 12N, it outputs information to the alarm unit 34 indicating that it has determined there is an abnormality in either the DC capacitor 12P or 12N. If the determination unit 33A determines that there is an abnormality in the DC capacitor 12, it may output information to an external device such as a host device (not shown) indicating that it has determined there is an abnormality in either the DC capacitor 12P or 12N.

[0110] In other words, if an abnormality occurs in either DC capacitor 12P or 12N, the capacitance of the other capacitor will decrease. Therefore, when an abnormality occurs in either DC capacitor 12P or 12N, the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N are compared, and the voltage values ​​of both are set to a predetermined threshold Vth3 or more differ from each other. On the other hand, when both the DC capacitors 12P and 12N are normal, when the DC voltage Vdcp of the DC capacitor 12P is compared with the DC voltage Vdcn of the DC capacitor 12N, the voltage values of the two do not differ by the predetermined threshold value V th3 or more. In the second embodiment, an abnormality in either the DC capacitor 12P or 12N is detected based on this principle.

[0111] Note that the predetermined threshold value V th3 may, for example, vary according to the operating conditions of the inverter device 10A, may be determined in advance through experiments, simulations, or the like, and may be stored in the storage unit 40. Further, the predetermined threshold value V th3 may be determined in accordance with, for example, an instruction received from a host device (not shown), an instruction received from an operator (not shown) via an operation unit (not shown), or the like.

[0112] Further, in the second embodiment, the predetermined threshold value V th3 , similarly to the predetermined threshold value V th , may have a bandwidth or margin of a predetermined range (predetermined voltage value) (vertically or downward). Then, the determination unit 33A does not immediately determine that either the DC capacitor 12P or 12N is abnormal as soon as the DC voltage Vdc differs by the predetermined threshold value V th3 or more, and may determine that there is an abnormality when the difference exceeds the predetermined threshold value V th3 by more than the predetermined range. Note that, also for the predetermined threshold value V th3 , similarly to the predetermined threshold value V th , the bandwidth and margin of the predetermined range may be varied according to the expected service life of the DC capacitor 12P or 12N, or the like.

[0113] Also in the second embodiment, similarly to the modification of the first embodiment shown in FIG. 6, a second predetermined threshold value V for detecting an indicator of replacement timing (determining replacement timing) of either the DC capacitor 12P or 12N th4may be used. In this case, the determination unit 33A compares the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N, and determines that when a difference between these voltages is equal to or greater than a second predetermined threshold V th4 , it is time to replace either the DC capacitor 12P or the DC capacitor 12N. The second predetermined threshold V th4 is a smaller value than the predetermined threshold V th3 .

[0114] Furthermore, similarly to the predetermined threshold V th4 , the second predetermined threshold V th3 may also have a bandwidth or margin of a predetermined range (a predetermined voltage value) (vertically or downward). Furthermore, similarly to the predetermined threshold V th4 , for the second predetermined threshold V th , the bandwidth or margin of the predetermined range may also be varied according to the expected service life of the DC capacitor 12 or the like.

[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 includes 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 acquires, from the monitoring unit 31A, 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 a predetermined time t1 has elapsed.

[0117] In step S4A, the determination unit 33A compares 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 predetermined time t1 has elapsed. Then, the determination unit 33A determines whether a difference between the compared DC voltage Vdcp of the DC capacitor 12P and DC voltage Vdcn of the DC capacitor 12N falls within the range of the predetermined threshold V th3 (within the predetermined range from the predetermined threshold V th3 ).

[0118] Then, the determination unit 33A determines that the difference between the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N is a predetermined threshold V th3 If it is determined that the value falls within the specified range (Yes), the process proceeds to step S5.

[0119] On the other hand, the determination unit 33A determines that the difference between the DC voltage Vdcp of the DC capacitor 12P and the DC voltage Vdcn of the DC capacitor 12N is a predetermined threshold V th3 If it is determined that the result does not fall within the specified range (No side), the process proceeds to step S6.

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

[0121] <Effects of the second embodiment> As described above, the second embodiment shown in Figures 7 to 9 provides the same effects and advantages as the first embodiment and its modified form shown in Figures 1 to 6.

[0122] Furthermore, in the second embodiment shown in Figures 7 to 9, by comparing the DC voltage Vdcp of DC capacitor 12P and the DC voltage Vdcn of DC capacitor 12N, it is possible to determine if there is an abnormality or replacement time for either DC capacitor 12P or 12N. This allows a predetermined threshold V in a multilevel power converter to be determined based on the discharge curve based on factory test conditions or design values. th or a second predetermined threshold V th2 Without using [a specific method], it is possible to determine if there is a problem with either the DC capacitor 12P or 12N, or if it is time to replace it. Thus, according to this embodiment, it is possible to determine if there is a problem with either the DC capacitor 12P or 12N, or if it is time to replace it, using a simple method.

[0123] <Example Hardware Configuration> Figure 10 is a conceptual diagram showing an example of the hardware configuration of the processing circuit 90 in the control device 30 or 30A in the embodiments shown in Figures 1 to 9. Each of the functions described above is realized by the processing circuit 90. In one embodiment, the processing circuit 90 comprises at least one processor 91 and at least one memory 92. In another embodiment, the processing circuit 90 comprises at least one dedicated hardware 93.

[0124] When the processing circuit 90 includes a processor 91 and 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 memory 92. The processor 91 realizes each function by reading and executing the program stored in memory 92.

[0125] If the processing circuit 90 includes dedicated hardware 93, the processing circuit 90 may be, for example, a single circuit, a composite circuit, a programmed processor, or a combination thereof. Each function is realized by the processing circuit 90.

[0126] Each function of the control device 30 or 30A may be partially or entirely comprised of hardware, or it may be comprised of a program executed by a processor. In other words, the control device 30 or 30A can also be implemented by a computer and a program, and the program may be stored on a storage medium or provided over a network.

[0127] <Supplementary information on the embodiment> As described above, the embodiments shown in Figures 1 to 10 are divided into the first embodiment and its modifications shown in Figures 1 to 6, and the second embodiment shown in Figures 7 to 9. However, any or all of these embodiments may be combined in series or in parallel. The combined embodiments can also produce the same effects and benefits as the individual embodiments before they were combined.

[0128] Furthermore, while the embodiments shown in Figures 1 to 10 describe power converters 1 and 1A and control devices 30 and 30A having them as an example, the disclosure is not limited to this. The disclosure can also be implemented as a control method in which processing steps are performed in each part of the control device 30 or 30A.

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

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

[0131] The features and advantages of the embodiments will become clear from the detailed description above. This is intended to be so as not to deviate from the spirit and scope of the claims, that the features and advantages of the embodiments described above are included. Furthermore, any improvement and modification should be readily conceivable to a person with ordinary skill in the art. Therefore, there is no intention to limit the scope of inventive embodiments to those described above, and it is also possible to rely on appropriate improvements and equivalents that fall within the scope disclosed in the embodiments. [Explanation of Symbols]

[0132] 1, 1A…Power converter; 10, 10A…Inverter device; 11…DC input; 11N…Negative terminal; 11P…Positive terminal; 12, 12P, 12N…DC capacitor; 13…Discharge resistor; 14…Inverter circuit; 15…AC output; 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…Alert unit;35…PWM control unit;40…Storage unit;90…Processing circuit;91…Processor;92…Memory;93…Hardware;C…DC neutral point;D…Freewheeling diode;Iac…AC current;Idc…DC current;L1…Solid line;L2…Dashed line;L3…Dotted line;Q…Semiconductor switching element;t0,t1…Time;Vac…AC voltage (AC voltage value);Vdc,Vdcn,Vdcp…DC voltage (DC voltage value);V th ... predetermined threshold; V th2 ...a second predetermined threshold; V th3 ... predetermined threshold; V th4 ...a second predetermined threshold

Claims

1. A DC input section 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 are connected in series between the positive terminal and the negative terminal via a DC neutral point, and absorb and smooth the ripple current generated by the switching operation of the inverter circuit. A discharge resistor through which the charge of each of the aforementioned multiple DC capacitors is discharged, A DC voltage sensor that detects the DC voltage values ​​of each of the aforementioned plurality of DC capacitors, An inverter device having, A monitoring unit that monitors the DC voltage values ​​of each of the plurality of DC capacitors detected by the DC voltage sensor, A timing unit that measures the elapsed time since the inverter device stopped, When the timing unit has timed a predetermined period of time since the inverter device stopped, the monitoring unit compares the DC voltage values ​​of the plurality of DC capacitors being monitored, and if the DC voltage values ​​of the plurality of DC capacitors being compared differ by a predetermined threshold or more, the determination unit determines that there is an abnormality in one of the plurality of DC capacitors being compared. When the determination unit determines that any of the DC capacitors among the plurality of DC capacitors is abnormal, the alarm unit issues an alarm indicating that any of the DC capacitors among the plurality of DC capacitors is abnormal. A control device having, A power conversion device characterized by comprising the following features.

2. A DC input section 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 are connected in series between the positive terminal and the negative terminal via a DC neutral point, and absorb and smooth the ripple current generated by the switching operation of the inverter circuit. A discharge resistor through which the charge of each of the aforementioned multiple DC capacitors is discharged, A DC voltage sensor that detects the DC voltage values ​​of each of the aforementioned plurality of DC capacitors, A control device for a power conversion device equipped with an inverter device having, A monitoring unit that monitors the DC voltage values ​​of each of the plurality of DC capacitors detected by the DC voltage sensor, A timing unit that measures the elapsed time since the inverter device stopped, When the timing unit has timed a predetermined period of time since the inverter device stopped, the monitoring unit compares the DC voltage values ​​of the plurality of DC capacitors being monitored, and if the DC voltage values ​​of the plurality of DC capacitors being compared differ by a predetermined threshold or more, the determination unit determines that there is an abnormality in one of the plurality of DC capacitors being compared. When the determination unit determines that any of the DC capacitors among the plurality of DC capacitors is abnormal, the alarm unit issues an alarm indicating that any of the DC capacitors among the plurality of DC capacitors is abnormal. A control device characterized by comprising:

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