Auxiliary power supply device

Abstract

To provide a highly reliable auxiliary power unit.SOLUTION: An auxiliary power unit comprises: a high frequency transformer 22; a chopper circuit 31 for converting DC power supplied from a DC power source; inverters S1 and S2 by which output power of the chopper circuit 31 is converted into AC power and supplied to the high frequency transformer 22; a DC capacitor FC1 connected to DC terminals of the inverters; resonant capacitors C1 and C2 which generate resonating operations with switching of the inverters; a rectifier 23 by which AC power supplied from the inverters S1 and S2 via the high frequency transformer 22 is converted into DC power; detection units 32 and 33 by which values of DC input currents of the inverters S1 and S2 or values for calculating the values of the DC input currents are detected; and a control circuit 41 which calculates a resonant frequency of a resonance circuit, using the values supplied from the detection units 32 and 33, and detects capacity reduction of the resonant capacitors C1 and C2, using the resonant frequency and the values of the DC input currents.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to an auxiliary power supply. [Background technology]

[0002] For example, an electric vehicle (mobile object) is equipped with a power conversion device as a power supply device that converts DC voltage supplied from a high-voltage train line (for example, an overhead train line or a third rail) into a voltage appropriate for the load and outputs the DC voltage to the load. An electric vehicle is equipped with, as an electric vehicle power supply device, for example, a power supply device for driving the traction motor and an auxiliary power supply device for supplying power to other devices such as lighting and air conditioning.

[0003] Auxiliary power conversion equipment typically consists of an inverter and a commercial frequency transformer (isolation transformer), but the use of high-frequency transformers (isolation transformers) is becoming more common in order to miniaturize the system. One example of an auxiliary power supply configuration includes a high-frequency transformer (isolation transformer) that is excited by high-frequency AC current, a chopper circuit that adjusts the DC voltage from the electric power line, an inverter that converts the output of the chopper circuit into high-frequency AC and supplies it to the high-frequency transformer, and a rectifier that converts the high-frequency AC to DC. Hereinafter, the configuration including the inverter, high-frequency transformer, and rectifier will be referred to as a high-frequency isolation circuit. Furthermore, by applying a resonant circuit to the inverter, the loss during switching can be significantly reduced, and high frequency switching of the inverter becomes possible. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2015 / 079528 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the capacity of the resonant capacitor that makes up the resonant circuit decreases due to deterioration over time, the resonant frequency of the resonant circuit will rise, causing the peak value and effective value of the AC current output by the inverter to increase, which will lead to increased losses in the inverter, high-frequency transformer, and rectifier, and may cause the temperature to rise beyond the allowable value.If the resonant capacitor deteriorates further, this may cause the device to stop due to an abnormal temperature.

[0006] If the AC current output by the resonant inverter is monitored, it is possible to detect changes in the current, but this requires an additional current detector. Also, in a resonant inverter using a half-bridge circuit, one end of the AC output is connected to the midpoint of two series-connected resonant capacitors, so it is difficult to detect which resonant capacitor has reduced in capacitance using the AC current.

[0007] The embodiments of the present invention have been made in consideration of the above circumstances, and an object of the present invention is to provide a highly reliable auxiliary power supply device. [Means for solving the problem]

[0008] The auxiliary power supply device according to the embodiment includes a high-frequency transformer, a chopper circuit that converts DC power supplied from a DC power supply, and an upper arm switch for switching an electrical connection between a high potential side DC end and an AC end; a lower arm switch for switching an electrical connection between a low potential side DC end and an AC end; a DC capacitor connected between the high potential side DC end and the low potential side DC end; and a resonant capacitor for generating a resonant operation in association with switching of the switch; an inverter that converts the output power of the chopper circuit into AC power and supplies the AC power to the high-frequency transformer; 、 The power supply comprises a rectifier that converts AC power supplied from the inverter via the high-frequency transformer into DC power, a detection unit that detects the value of the DC input current of the inverter or a value for calculating the value of the DC input current, and a control circuit that calculates the resonant frequency of a resonant circuit including the resonant capacitor based on the value supplied from the detection unit and detects a reduction in capacitance of the resonant capacitor using the resonant frequency and the value of the DC input current. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration example of a power conversion device according to a first embodiment. [Figure 2] FIG. 2 is a diagram for explaining a current path when the upper arm of the resonant inverter shown in FIG. 1 is on. [Figure 3] FIG. 3 is a diagram for explaining a current path when the lower arm of the resonant inverter shown in FIG. 1 is on. [Figure 4] FIG. 4 is a diagram for explaining an example of each current in the power conversion device shown in FIG. 1 when there is no reduction in the capacitance of the resonant capacitor. [Figure 5] FIG. 5 is a diagram for explaining an example of each current when there is a capacitance reduction in the resonant capacitor in the power conversion device shown in FIG. [Figure 6] FIG. 6 is a flowchart for explaining an example of an operation for detecting an abnormality in the resonant capacitor in the power conversion device of the first embodiment. [Figure 7] FIG. 7 is a diagram schematically illustrating a configuration example of a power conversion device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a power conversion device according to an embodiment will be described in detail with reference to the drawings. (First embodiment) FIG. 1 is a diagram schematically illustrating a configuration example of a power conversion device according to a first embodiment. Here, as an example, a power conversion device 1 mounted on a moving body such as an electric vehicle will be described. The power conversion device 1 for an electric vehicle is an auxiliary power supply device for an electric vehicle that receives DC power from a contact line 2 such as an overhead contact line or a third rail via a current collector 3, and outputs the received DC power from output terminals 4P and 4N.

[0011] In this embodiment, the power conversion device 1 for an electric vehicle will be described as an auxiliary power supply device that supplies power to loads such as lighting and air conditioning of the electric vehicle. The electric vehicle is equipped with a main power supply device (not shown) for driving the traction motor. The main power supply device drives the traction motor with DC power received from the electric rail 2 via a current collector 3, thereby causing the electric vehicle to run on tracks 5.

[0012] The power conversion device 1, which serves as an auxiliary power supply device for an electric vehicle, is connected to devices that operate at lower voltages than the traction motor. For this reason, the power conversion device 1 for an electric vehicle must be insulated between the primary side, where power is input, and the secondary side, where power is output.

[0013] As an example of a configuration for ensuring insulation between the primary side and the secondary side, there is a transformer that uses a transformer including a pair of electromagnetically coupled windings (coils) to insulate the primary side from the secondary side. The lower the excitation frequency of a transformer, the larger the transformer becomes. For example, a transformer set with an excitation frequency corresponding to the frequency of a commercial power supply becomes large. Therefore, the power conversion device 1 of this embodiment uses a high-frequency transformer to insulate the primary side from the secondary side and achieve a compact size.

[0014] The power conversion device 1 includes a chopper circuit 31, a power conversion circuit (high frequency insulating circuit) 11, a current detector 32, a voltage detector 33, and a control circuit 41. The chopper circuit 31 converts DC power input from the electric train line 2 via the current collector 3 into desired DC power. In this embodiment, for example, the electric train line 2 is the DC power source.

[0015] The current detector 32 detects the output current of the chopper circuit 31. The detection result of the current detector 32 is supplied to the control circuit 41. The voltage detector 33 detects the output voltage of the chopper circuit 31 (the voltage of the first DC capacitor FC1). The detection result of the voltage detector 33 is supplied to the control circuit 41.

[0016] The power conversion circuit 11 insulates the DC power output from the chopper circuit 31 via a high-frequency transformer 22 and converts it into power for a DC load. The power conversion circuit 11 includes, for example, a resonant inverter 21, a high-frequency transformer 22, a rectifier 23, and a second DC capacitor FC2.

[0017] The resonant inverter 21 is an inverter circuit that supplies AC power to the high-frequency transformer 22 using DC power supplied from the chopper circuit 31. The resonant inverter 21 is configured as a resonant single-phase half-bridge inverter, for example, having a DC end electrically connected to the chopper circuit 31 and an AC end electrically connected to the primary side of the high-frequency transformer 22. The resonant inverter 21 includes a first switch S1, a second switch S2, a first DC capacitor FC1, a first resonant capacitor C1, and a second resonant capacitor C2. One AC end of the resonant inverter 21 is electrically connected to the primary side of the high-frequency transformer 22 via an inductance. The first DC capacitor FC1 is connected between the high-potential side DC end and the low-potential side DC end of the resonant inverter 21, and smoothes the DC power supplied from the chopper circuit 31.

[0018] The first switch S1 switches the electrical connection between the high-potential DC terminal and one of the AC terminals. The first switch S1 is, for example, a MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), and is electrically connected at its drain to the high-potential DC terminal and at its source to one of the AC terminals.

[0019] The second switch S2 switches the electrical connection between the DC end on the low potential side and one of the AC ends. The second switch S2 is, for example, a MOSFET, and is electrically connected to one of the AC ends at its drain and to the DC end on the low potential side at its source. The first switch S1 and the second switch S2 are not limited to MOSFETs, and other power semiconductor elements such as bipolar transistors and IGBTs (Insulated Gate Bipolar Transistors) may also be used.

[0020] The first resonant capacitor C1 is electrically connected between the DC end on the high potential side and the other AC end, and the second resonant capacitor C2 is electrically connected between the DC end on the low potential side and the other AC end.

[0021] That is, the primary winding of the high-frequency transformer 22 is connected to the connection point (one AC end) between the first switch S1 and the second switch S2, and to the connection point (the other AC end) between the first resonant capacitor C1 and the second resonant capacitor C2. The resonant inverter 21 supplies AC power to the primary winding of the high-frequency transformer 22 by controlling the on / off operations of the first switch S1 and the second switch S2 by the control circuit 41. In the following description, the first switch S1 side of the resonant inverter 21 will be referred to as the upper arm of the resonant inverter 21, and the second switch S2 side of the resonant inverter 21 will be referred to as the lower arm of the resonant inverter 21.

[0022] High-frequency transformer 22 is an isolation transformer having a primary winding (primary winding) that generates magnetic flux and a secondary winding (secondary winding) that is insulated from the primary winding and is excited by the magnetic flux generated in the primary winding. When AC current is supplied from resonant inverter 21 to the primary winding of high-frequency transformer 22, magnetic flux is generated in the primary winding. The magnetic flux generated in the primary winding generates an induced current in the secondary winding. As a result, high-frequency transformer 22 supplies power to the secondary side according to the AC current input from the primary side.

[0023] The rectifier 23 is a circuit that rectifies the power generated in the secondary winding of the high-frequency transformer 22, and is configured as, for example, a rectifier bridge circuit in which a plurality of diodes are combined. The second DC capacitor FC2 smoothes the DC voltage supplied from the rectifier 23. The third DC capacitor FC2 outputs DC power from output terminals 4P and 4N connected in parallel. The DC power output from the output terminals 4P and 4N is converted into AC power of, for example, 50 Hz or 60 Hz by a circuit such as an inverter (not shown).

[0024] The control circuit 41 acquires the detection values ​​of the current detector 32 and the voltage detector 33 and controls the operations of the chopper circuit 31 and the power conversion circuit 11. The control circuit 41 is, for example, an arithmetic device including at least one processor and a memory that stores programs executed by the processor and data used by the programs. The control circuit 41 can realize various functions for controlling the chopper circuit 31 and the power conversion circuit 11 by software or a combination of software and hardware.

[0025] The control circuit 41 may be configured as, for example, a logic circuit that generates a pulse signal, and may be configured to generate the pulse signal by having a processor in the control circuit 41 execute a program. The control circuit 41 controls the operations of the semiconductor elements in the chopper circuit 31 and the power conversion circuit 11 by inputting the pulse signal to the chopper circuit 31 and the power conversion circuit 11, respectively. For example, the control circuit 41 performs PWM control to adjust the on / off duty ratio of the pulse signal. In this way, the control circuit 41 adjusts the output of the chopper circuit 31 and the output of the power conversion circuit 11, respectively.

[0026] Next, an example of the operation of the control circuit 41 in the power conversion device of this embodiment to detect a decrease in the capacitance of the first resonant capacitor C1 and the second resonant capacitor C2 will be described. FIG. 2 is a diagram for explaining a current path when the upper arm of the resonant inverter shown in FIG. 1 is on.

[0027] The AC current supplied to the high-frequency transformer 22 is output from the first switch S1 of the upper arm, passes through the rectifier 23 and the second DC capacitor FC2, returns to the junction between the first resonant capacitor C1 and the second resonant capacitor C2, and is then branched to the first resonant capacitor C1 and the second resonant capacitor C2. A current equal to that of the second resonant capacitor C2 flows in the DC input part A of the resonant inverter 21.

[0028] FIG. 3 is a diagram for explaining a current path when the lower arm of the resonant inverter shown in FIG. 1 is on. An AC current joined at the connection point between the first resonant capacitor C1 and the second resonant capacitor C2 is output to the high-frequency transformer 22. The AC current supplied to the high-frequency transformer 22 returns to the second switch S2 of the lower arm via the rectifier 23 and the second DC capacitor FC2, and then branches off and flows to the second resonant capacitor C2 and the first DC capacitor FC1. A current equal to that of the first resonant capacitor C1 flows in the DC input section A of the resonant inverter 21.

[0029] FIG. 4 is a diagram for explaining an example of each current in the power conversion device shown in FIG. 1 when there is no reduction in the capacitance of the resonant capacitor. The resonant current on the AC side of the resonant inverter 21 occurs after the first switch S1 or the second switch S2 is turned on due to a resonance phenomenon at a resonant frequency determined by the parallel capacitance of the first resonant capacitor C1 and the second resonant capacitor C2 and the total inductance of the main circuit. The diode of the rectifier 23 cuts off the current in a resonant half cycle, and the current value remains near zero (below a predetermined value) until the next opposing arm is turned on. Therefore, by detecting the cycle at which the value of the AC current becomes near zero (below a predetermined value), the resonant half cycle can be estimated, making it possible to estimate the resonant frequency of the resonant circuit including the first resonant capacitor C1 and the second resonant capacitor C2.

[0030] In addition, if there is no reduction in capacitance, the current flowing through the resonant capacitors C1 and C2 is divided equally between the first resonant capacitor C1 and the second resonant capacitor C2. Furthermore, as shown in FIGS. 2 and 3, the same current flows through the DC input section A of the resonant inverter 21 as through either the first resonant capacitor C1 or the second resonant capacitor C2. Therefore, like the AC current, the current flowing through the DC input section A (the DC input current) also experiences periods when its current value is near zero (below a predetermined value). Therefore, if the value of the DC input current of the resonant inverter 21 can be detected, or if a value equivalent to the DC input current (e.g., a calculated DC input current value) can be obtained, it is possible to estimate the resonant frequency of the resonant circuit including the first resonant capacitor C1 and the second resonant capacitor C2.

[0031] FIG. 5 is a diagram for explaining an example of each current when there is a capacitance reduction in the resonant capacitor in the power conversion device shown in FIG. As described above, the resonant frequency is determined by the parallel capacitance of the resonant capacitors C1 and C2, so when a reduction in capacitance occurs, the resonant frequency becomes higher.

[0032] Furthermore, since the current flowing through the first resonant capacitor C1 and the current flowing through the second resonant capacitor C2 are divided in proportion to the capacitance ratio, for example, if the second resonant capacitor C2 deteriorates and its capacitance decreases, the current through the first resonant capacitor C1 decreases and the current through the second resonant capacitor C2 increases. However, because the AC current is the sum of the currents through the first resonant capacitor C1 and the second resonant capacitor C2, the current imbalance between the first resonant capacitor C1 and the second resonant capacitor C2 does not appear in the AC current, and it is difficult to estimate which resonant capacitor has reduced in capacitance even if the AC current is detected.

[0033] On the other hand, as shown in Figures 2 and 3, the same current flows through the DC input section A of the resonant inverter 21 as through either the first resonant capacitor C1 or the second resonant capacitor C2. Therefore, if the DC input current of the resonant inverter 21 can be detected or estimated, it becomes possible to estimate the individual capacitance reduction of the first resonant capacitor C1 and the second resonant capacitor C2 due to the increase in the resonant frequency of the resonant circuit including the first resonant capacitor C1 and the second resonant capacitor C2 and the imbalance in the current peak values.

[0034] FIG. 6 is a flowchart for explaining an example of an operation for detecting an abnormality in the resonant capacitor in the power conversion device of the first embodiment. In the power conversion device of this embodiment, the control circuit 41 calculates the DC input current of the resonant inverter 21 using the detected values ​​of the current detector 32 and the voltage detector 33. That is, in this embodiment, the current detector 32 and the voltage detector 33 are detection units that detect values ​​for calculating the DC input current. The chopper output current detected by the current detector 32 is i CH (t), the chopper output voltage detected by the voltage detector 33 is v DC (t), the capacitance of the first DC capacitor FC1 is C FC Then, the DC input current i of the resonant inverter 21 in (t) can be calculated using the following formula:

number

[0035] The control circuit 41 calculates the resonant frequency of the resonant circuit including the resonant capacitors C1 and C2 based on the cycle of timing at which the value of the DC input current of the resonant inverter 21 calculated by the above formula becomes equal to or less than a predetermined value (step S1). The control circuit 41 acquires the peak value of the DC input current when the resonant frequency of the resonant circuit is equal to or higher than a predetermined threshold (step S2). The control circuit 41 can detect the capacitance reduction of each of the first resonant capacitor C1 and the second resonant capacitor C2 based on the peak value of the DC input current per half cycle and the switching states of the first switch S1 and the second switch S2 (step S3).

[0036] For example, when the upper arm of inverter 21 is on, a current of the same value as that of second resonant capacitor C2 flows through DC input unit A, and when the lower arm is on, a current of the same value as that of first resonant capacitor C1 flows through DC input unit A. Based on this, control circuit 41 compares the peak values ​​of the DC input current in each switching state of first switch S1 and second switch S2, and can detect a reduction in the capacitance of each of first resonant capacitor C1 and second resonant capacitor C2 when, for example, the difference in peak values ​​is equal to or greater than a predetermined threshold.

[0037] For example, when there is no need to identify whether the capacitance of the first resonant capacitor C1 or the second resonant capacitor C2 has decreased, the control circuit 41 can compare the peak values ​​of the DC input current for each half cycle regardless of the switching state of the first switch S1 and the second switch S2, and detect that the capacitance of either the first resonant capacitor C1 or the second resonant capacitor C2 has decreased when, for example, the difference in the peak values ​​is greater than or equal to a predetermined threshold value.

[0038] When the control circuit 41 detects a decrease in the capacitance of each of the first resonant capacitor C1 and the second resonant capacitor C2, or when it detects a decrease in the capacitance of either the first resonant capacitor C1 or the second resonant capacitor C2, it determines that an abnormality has occurred (step S4), and can notify, for example, a higher-level control device (not shown) of the abnormality (step S5).

[0039] For example, if the capacitance of the first resonant capacitor C1 and the second capacitor C2 decreases due to aging, the resonant frequency will rise, increasing the peak value and effective value of the AC current output by the resonant inverter 21, which may cause increased losses in the resonant inverter 21, the high-frequency transformer 22, and the rectifier 23, resulting in a risk of temperature rise exceeding the allowable value. In other words, if the degradation of the first resonant capacitor C1 and the second resonant capacitor C2 progresses, this may cause the device to stop or break down due to abnormal temperatures.

[0040] As described above, in the power conversion device 1 of this embodiment, by detecting the resonant frequency of the resonant inverter 21 and the reduction in capacitance of each (or either) of the first resonant capacitor C1 and the second resonant capacitor C2, it is possible to detect signs of an abnormality while the temperature of the power conversion device 1 is within an allowable range, and to avoid an abnormal shutdown or failure of the power conversion device 1. In other words, according to this embodiment, it is possible to provide a highly reliable auxiliary power supply device.

[0041] (Second embodiment) Next, a power conversion device according to a second embodiment will be described in detail with reference to the drawings. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted.

[0042] FIG. 7 is a diagram schematically illustrating a configuration example of a power conversion device according to the second embodiment. The power conversion device 1 of this embodiment differs from the first embodiment described above in that it includes a current detector 34 instead of the current detector 32 and the voltage detector 33.

[0043] The current detector 34 detects the current flowing through the DC input section A of the resonant inverter 21, and supplies the detection result to the control circuit 41. That is, in this embodiment, the current detector 34 is a detection section that acquires the DC input current value.

[0044] That is, in the power conversion device 1 of this embodiment, the current value of the DC input section A, which was calculated by a formula in the first embodiment, can be directly acquired from the current detector 34. The control circuit 41 can detect the reduction in capacitance of each of the first resonant capacitor C1 and the second resonant capacitor C2 based on the current value acquired from the current detector 34 and the switching states of the first switch S1 and the second switch S2.

[0045] Therefore, according to this embodiment, it is possible to obtain the same effects as in the first embodiment, and to provide a highly reliable auxiliary power supply device.

[0046] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. (Appendix 1) a high frequency transformer; a chopper circuit that converts DC power supplied from a DC power supply; an inverter that converts the output power of the chopper circuit into AC power and supplies the AC power to the high-frequency transformer; a DC capacitor connected to the DC end of the inverter; a resonant capacitor that generates a resonant operation in response to switching of the inverter; a rectifier that converts AC power supplied from the inverter via the high-frequency transformer into DC power; a detection unit that detects a value of a DC input current of the inverter or a value for calculating the value of the DC input current; a control circuit that calculates a resonant frequency of a resonant circuit including the resonant capacitor based on the value supplied from the detection unit, and detects a reduction in capacitance of the resonant capacitor using the resonant frequency and the value of the DC input current. (Appendix 2) the detection unit includes a voltage detector that detects a voltage of the DC capacitor and a current detector that detects an output current of the chopper circuit, 2. The auxiliary power supply device according to claim 1, wherein the control circuit determines the value of the DC input current to be a difference between the current value detected by the current detector and a value obtained by multiplying the differential value of the voltage value detected by the voltage detector by the capacitance of the DC capacitor. (Appendix 3) 2. The auxiliary power supply according to claim 1, wherein the detection unit includes a current detector that detects a value of the DC input current of the inverter. (Appendix 4) 4. The auxiliary power supply device according to claim 2, wherein the control circuit detects a timing at which the value of the DC input current becomes equal to or less than a predetermined value, and calculates the resonant frequency based on a cycle of the timing. (Appendix 5) 2. The auxiliary power supply device according to claim 1, wherein the control circuit notifies an external device of an abnormality when the resonant frequency is equal to or greater than a predetermined threshold value and a difference in current peak values ​​per half cycle of the DC input current is equal to or greater than a predetermined value. (Appendix 6) the inverter includes an upper arm switch and a lower arm switch, 2. The auxiliary power supply device according to claim 1, wherein the control circuit notifies an external device of an abnormality when the resonant frequency is equal to or higher than a predetermined threshold and when a difference between a current peak value of the DC input current when the upper arm switch is on and the lower arm switch is off and the current peak value when the upper arm switch is off and the lower arm switch is on is equal to or higher than a predetermined value. [Explanation of symbols]

[0047] 1...power conversion device (auxiliary power supply device), 2...electrical line, 3...current collector, 4P, 4N...output terminal, 5...line, 11...power conversion circuit (high frequency isolation circuit), 21...resonant inverter, 22...high frequency transformer, 23...rectifier, 31...chopper circuit, 32...current detector, 33...voltage detector, 34...current detector, 41...control circuit, C1...first resonant capacitor, C2...second resonant capacitor, FC1...first DC capacitor, FC2...second DC capacitor, S1...first switch, S2...second switch

Claims

1. a high frequency transformer; a chopper circuit that converts DC power supplied from a DC power supply; an inverter including an upper arm switch that switches the electrical connection between a high potential side DC end and an AC end, a lower arm switch that switches the electrical connection between a low potential side DC end and an AC end, a DC capacitor connected between the high potential side DC end and the low potential side DC end, and a resonant capacitor that generates a resonant operation in response to switching of the switch, and that converts the output power of the chopper circuit into AC power and supplies it to the high frequency transformer; a rectifier that converts AC power supplied from the inverter via the high-frequency transformer into DC power; a detection unit that detects a value of a DC input current of the inverter or a value for calculating the value of the DC input current; a control circuit that calculates a resonant frequency of a resonant circuit including the resonant capacitor based on the value supplied from the detection unit, and detects a reduction in capacitance of the resonant capacitor using the resonant frequency and the value of the DC input current.

2. the detection unit includes a voltage detector that detects a voltage of the DC capacitor and a current detector that detects an output current of the chopper circuit, 2. The auxiliary power supply device according to claim 1, wherein the control circuit determines the value of the DC input current to be a difference obtained by subtracting a value obtained by multiplying a differential value of a voltage value detected by the voltage detector by a capacitance of the DC capacitor from a current value detected by the current detector.

3. 2. The auxiliary power supply according to claim 1, wherein the detection unit includes a current detector that detects the value of the DC input current of the inverter.

4. 4. The auxiliary power supply according to claim 2, wherein the control circuit detects a timing at which the value of the DC input current becomes equal to or less than a predetermined value, and calculates the resonant frequency based on a cycle of the timing.

5. 2. The auxiliary power supply device according to claim 1, wherein the control circuit notifies an external device of an abnormality when the resonant frequency is equal to or higher than a predetermined threshold value and a difference between current peak values ​​for each half cycle of the DC input current is equal to or higher than a predetermined value.

6. An auxiliary power supply device as described in claim 1, wherein the control circuit notifies an external device of an abnormality when the resonant frequency is equal to or higher than a predetermined threshold value and when the difference between the current peak value of the DC input current when the switch of the upper arm is on and the switch of the lower arm is off and the current peak value when the switch of the upper arm is off and the switch of the lower arm is on is equal to or higher than a predetermined value.

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