Power conversion device

Abstract

To provide a power conversion device that can more reliably protect a load circuit from the application of overvoltage.SOLUTION: A power conversion device of an embodiment includes: a first input terminal; a second input terminal; a first output terminal; a second output terminal; a power conversion unit that steps down an input DC voltage, converts it into another DC voltage, and outputs the converted DC voltage to a load circuit; a control device that transmits a gate signal to the power conversion unit so as to control the voltage and current supplied to the load circuit; unit element failure determination means for determining a sign of abnormality in the power conversion unit based on an output current of the power conversion unit and outputting an active determination signal; and overvoltage protection means for preventing overvoltage from being applied to the load circuit based on the determination signal output by the unit element failure determination circuit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device.

Background Art

[0002] There is a power conversion device that supplies power to a load circuit sensitive to the application of overvoltage. In order to protect such a load circuit, it is usually performed to add an overvoltage protection circuit such as a clover circuit to the power conversion device.

[0003] In such an overvoltage protection circuit, due to variations in set values, etc., it may not be sufficient to protect a load circuit sensitive to the application of overvoltage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Embodiments of the present invention provide a power conversion device that can more reliably protect a load circuit from the application of overvoltage.

Means for Solving the Problems

[0006] Embodiments of the present invention include a first input terminal, a second input terminal to which a potential lower than the potential applied to the first input terminal is applied, a first output terminal, a second output terminal having a potential lower than that of the first output terminal, a unit for power conversion that steps down a DC voltage applied between the first input terminal and the second input terminal, converts it into another DC voltage, and outputs it to a load circuit connected between the first output terminal and the second output terminal, a control device that transmits a gate signal to the unit so as to control the voltage applied to the load circuit and the current flowing through the load circuit, unit element failure determination means for determining signs of an abnormality of the unit based on the output current of the unit and outputting an active determination signal, and means overvoltage protection means for preventing an overvoltage from being applied to the load circuit based on the determination signal output by the unit element failure determination. The unit includes a first switching element connected between the first input terminal and the second input terminal, a second switching element connected in series to the low potential side of the first switching element, a first fuse provided to be opened when a short-circuit failure occurs in the first switching element, a second fuse provided to be opened when a short-circuit failure occurs in the second switching element, a choke coil connected between a connection node of the first switching element and the second switching element and the first output terminal. The unit element failure determination means determines signs of a short-circuit failure of the first switching element based on the output current of the unit and outputs the determination signal. The overvoltage protection means forms a current path including the first switching element and blows the first fuse.

Advantages of the Invention

[0007] According to the embodiment, a power conversion device is provided that can more reliably protect the load circuit from the application of overvoltage.

Brief Description of the Drawings

[0008]

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Embodiments for Carrying Out the Invention

[0009] Hereinafter, each embodiment will be described with reference to the drawings. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between parts, etc. are not necessarily the same as those in reality. Also, even when representing the same part, the dimensions and ratios may be represented differently in the drawings. In the present specification and each figure, the same reference numerals are given to the same elements as those described above with respect to the previously presented figures, and detailed descriptions thereof are appropriately omitted.

[0010] (First Embodiment) FIG. 1 is a schematic block diagram illustrating the power conversion device according to the first embodiment. As shown in FIG. 1, the power conversion device 10 according to the present embodiment includes units 20-1 to 20-n, a control device 40, an OVP gate circuit 42, and an overvoltage protection circuit 50.

[0011] Units 20-1 to 20-n are power converters that input a DC voltage and convert and output it to other DC voltages or DC currents. Units 20-1 to 20-n are connected in parallel between input terminals 12a and 12b and output terminals 14a and 14b. In this example, n units of 20-1 to 20-n are connected in parallel. A DC voltage is applied to input terminals 12a and 12b. A DC voltage converted by a rectifying and smoothing circuit or the like may be supplied to units 20-1 to 20-n via input terminals 12a and 12b, or a DC voltage generated by a solar power generation device, a fuel cell, or the like may be supplied.

[0012] The units 20-1 to 20-n connected in parallel are connected to the load circuit 1 via output terminals 14a and 14b. The load circuit 1 includes, for example, an electrolytic cell, and output terminal 14a is connected to the positive electrode of the electrolytic cell, and output terminal 14b is connected to the negative electrode of the electrolytic cell.

[0013] In this embodiment, units 20-1 to 20-n have the same input / output voltage rating and output power rating. The number of units that can supply the DC power required to supply the load circuit 1 is connected in parallel. In this embodiment, the number of units is not limited to a plurality, and may be one unit.

[0014] The configuration of units 20-1 to 20-n will be described. FIG. 2 is a schematic block diagram illustrating the configuration of a unit that is a part of the power conversion device according to the first embodiment. In this embodiment and other embodiments described later, units 20-1 to 20-n have the same input / output voltage rating and output power rating, and when not distinguishing between a plurality of units, they shall be denoted as unit 20. In FIG. 2, the unit is denoted by the symbol "20", and the symbols of the distinguished units "20-1 to 20-n" are denoted in parentheses.

[0015] As shown in FIG. 2, the unit 20 has input terminals 21a and 21b and output terminals 22a and 22b. The output terminal 22b is connected to the input terminal 21b at the same potential. The unit 20 includes a capacitor 23, an upper arm switching element 24U, a lower arm switching element 24L, an upper arm fuse 25U, a lower arm fuse 25L, and a choke coil 26.

[0016] In the unit 20, the capacitor 23 is connected between the input terminals 21a and 21b. A potential higher than the potential of the input terminal 21b is applied to the input terminal 21a. The capacitor 23 is, for example, a film capacitor, and reduces the ripple voltage generated between the input terminals 21a and 21b by passing the ripple current input from the input terminals 21a and 21b.

[0017] The upper arm switching element (first switching element) 24U and the lower arm switching element (second switching element) 24L are connected in series between the input terminals 21a and 21b. The upper arm switching element 24U and the lower arm switching element 24L may be connected in parallel in plural numbers as in this example. The number of parallel elements of the upper arm switching element 24U and the lower arm switching element 24L is determined according to the power capacity output by the unit 20.

[0018] The upper arm switching element 24U and the lower arm switching element 24L are self - extinguishing semiconductor switching elements, for example, IGBT (Insulated Gate Bipolar Transistor). In the upper arm switching element 24U and the lower arm switching element 24L, diodes are connected in anti - parallel to the IGBTs.

[0019] In this example, the upper arm fuse (first fuse) 25U is connected between the input terminal 21a and the upper arm switching element 24U. The lower arm fuse (second fuse) 25L is connected between the lower arm switching element 24L and the input terminal 21b. The upper arm fuse 25U is provided to open the upper arm when a short circuit fault occurs in the upper arm switching element 24U. The lower arm fuse 25L is provided to open the lower arm when a short circuit fault occurs in the lower arm switching element 24L.

[0020] The choke coil 26 is connected between the connection node of the upper arm and the lower arm and the output terminal 22a. The choke coil 26 operates to accumulate energy by passing current during the period when the upper arm switching element 24U is on, and to release the accumulated energy to the output terminal 22a side during the period when the lower arm switching element 24L is on.

[0021] In this way, the unit 20 is constituted by a step-down type power conversion circuit. The unit 20 converts the DC voltage input between the input terminals 21a and 21b into a DC voltage corresponding to the on-duty of the upper arm switching element 24U and the output current, and outputs it.

[0022] Returning to FIG. 1, the description will be continued. The current detectors 30-1 to 30-n are respectively connected to the outputs of the units 20-1 to 20-n. The current detectors 30-1 to 30-n detect the respective output currents IO1 to IOn of the units 20-1 to 20-n. The installation location of the current detectors 30-1 to 30-n is not limited to being provided outside the units 20-1 to 20-n as long as the respective output currents IO1 to IOn of the units 20-1 to 20-n can be detected with a desired accuracy. For example, the current detectors 30-1 to 30-n may be provided inside the units 20-1 to 20-n.

[0023] The control device 40 is connected to the units 20-1 to 20-n. The control device 40 generates gate signals vG1 to vGn according to the voltage applied to the load circuit 1, the current flowing through the load circuit 1, and the conditions preset in the control device 40, etc., and controls the units 20-1 to 20-n.

[0024] The OVP gate circuit (unit element failure determination means) 42 is connected to the control device 40, the current detectors 30-1 to 30-n, and the overvoltage protection circuit 50. When the voltage applied to the load circuit 1 becomes equal to or higher than the OVP threshold value, or when the current output from the units 20-1 to 20-n satisfies a predetermined condition, the OVP gate circuit 42 outputs a trigger signal to the overvoltage protection circuit 50.

[0025] The OVP threshold voltage is preset to a value higher than the maximum value of the rated output voltage output from the units 20-1 to 20-n. The OVP threshold voltage is set to a voltage, for example, 5% to 15% higher than the maximum value of the rated output voltage.

[0026] The predetermined conditions regarding the output current of the units 20-1 to 20-n are conditions indicating failures or signs of failures of the units 20-1 to 20-n, and multiple types of conditions are set. In this example, three types of conditions are set. Note that the failures or signs of failures of the units 20-1 to 20-n are short-circuit failures or signs of short-circuit failures of the upper arm switching elements 24U.

[0027] The first condition regarding the output current is the overcurrent condition. A value that is α (α > 1) times or more the current command value set in each of units 20-1 to 20-n is set as the abnormal current threshold. When any of the output currents IO1 to IOn from units 20-1 to 20-n becomes equal to or greater than the abnormal current threshold, the OVP gate circuit 42 outputs a trigger signal. The coefficient α is set based on the setting accuracy of the output current. For example, the coefficient α is set such that the abnormal current threshold is +10% higher than the upper limit value of the setting accuracy of the output current. When the current command value is not set according to the type and state of the load circuit 1, the abnormal current threshold is set with respect to the maximum value of the rated output current of units 20-1 to 20-n.

[0028] The second condition regarding the output current is the condition regarding waveform abnormality of the output currents IO1 to IOn. In a step-down type converter circuit, the output current is output via the choke coil 26 during the period when the lower arm switching element 24L is on, and shows a decreasing trend over time. If the current value of the output current increases over time during this period, it is considered that an abnormality has occurred in the upper arm switching element 24U of that unit.

[0029] The OVP gate circuit 42 monitors the gate signals vG1 to vGn supplied from the control device 40 to each of the units 20-1 to 20-n. When the OVP gate circuit 42 detects that the current value of the output current increases over the period during which the gate signal for the lower arm switching element 24L among the gate signals vG1 to vGn of any of the units 20-1 to 20-n is active, it outputs a trigger signal. In the second condition, the OVP gate circuit 42 may use, as the determination condition, not only the change in the output current for one cycle of the switching period but also the change in the output current for several cycles, and determine that the output current continuously increases. By doing so, false detection due to noise or the like can be prevented.

[0030] The third condition regarding the output current is a condition for detecting that one output current value deviates from the variation range of each of the n - 1 output current values. For example, the OVP gate circuit 42 stores the i-th current value IOi among the n current values, calculates the average value IO(k≠i) of the remaining n - 1 current values, and stores the average value IO(k≠i). The OVP gate circuit 42 calculates these ratios IOi / IO(k≠i), and outputs a trigger signal when the calculation result is equal to or greater than a preset threshold β (>1). The OVP gate circuit 42 sequentially changes i from 1 to n to identify the unit that outputs an output current exceeding the threshold β among the n current values.

[0031] In setting the variation range of the n - 1 output currents, in addition to using the average value, other statistical quantities can of course be used. Another statistical quantity is, for example, the median of the n - 1 output currents. Since it is rare for a plurality of units 20-1 to 20-n to fail simultaneously, when n is sufficiently large, the variation range may be calculated using the values of the n output currents.

[0032] At least one of the first to third conditions regarding the output current is a determination condition for outputting a trigger signal. In the present embodiment, the OVP gate circuit 42 outputs a trigger signal to the overvoltage protection circuit 50 when the voltage output by the units 20-1 to 20-n is equal to or higher than the OVP threshold, when the first condition is satisfied, when the second condition is satisfied, or when the third condition is satisfied.

[0033] The overvoltage protection circuit (overvoltage protection means) 50 is connected between the output terminals 14a and 14b. A thyristor 52 is connected between the output terminals 14a and 14b of the overvoltage protection circuit 50. The overvoltage protection circuit 50 detects the voltage at a position close to the power supply end of the load circuit 1 and outputs the voltage value to the OVP gate circuit 42. In the overvoltage protection circuit 50, the gate terminal of the thyristor 52 is connected to the output of the OVP gate circuit 42.

[0034] When the OVP gate circuit 42 outputs a trigger signal to the overvoltage protection circuit 50, the thyristor 52 turns on. When the thyristor 52 turns on, the output terminals 14a and 14b are short-circuited. The overvoltage protection circuit 50 short-circuits the power supply terminal of the load circuit 1 by the trigger signal output by the OVP gate circuit 42, preventing an overvoltage from being applied to the power supply terminal of the load circuit 1.

[0035] Instead of the thyristor 52, the overvoltage protection circuit 50 may be a self-extinguishing switching element such as an IGBT.

[0036] FIG. 3 is a schematic block diagram for explaining the operation of the power conversion device according to the first embodiment. The operation of the power conversion device 10 according to the present embodiment will be described. As shown in FIG. 3, when the OVP gate circuit 42 shown in FIG. 1 satisfies any of the first to third conditions regarding the overvoltage of the output voltage VO and the output current, the OVP gate circuit 42 outputs a trigger signal to the overvoltage protection circuit 50. In the overvoltage protection circuit 50, the thyristor 52 turns on.

[0037] When the thyristor 52 turns on, current flows into the unit 20 through the input terminal 21a, and flows out from the output terminal 22a through the upper arm fuse 25U, the short-circuited upper arm switching element 24U, and the choke coil 26. The current flowing out from the unit 20 flows into the overvoltage protection circuit 50. When this current reaches the fusing condition of the upper arm fuse 25U, the upper arm fuse 25U fuses, and the above-described current path is interrupted.

[0038] The effects of the power conversion device 10 according to the present embodiment will be described. The power conversion device 10 according to the present embodiment includes an OVP gate circuit 42. The OVP gate circuit 42 monitors not only the voltage value at the power supply terminal of the load circuit 1 but also whether or not the conditions regarding the output current are satisfied for each of the units 20-1 to 20-n.

[0039] There are multiple causes for the output voltage of the power conversion device 10 to become overvoltage. One of them is a short-circuit fault in the upper-arm switching element 24U. The course of the short-circuit fault in the upper-arm switching element 24U may vary depending on variations in the short-circuit withstand capacity of the switching element, the input / output conditions of the unit, the environmental conditions where the power conversion device is installed, and the like. For example, the upper-arm switching element 24U may short-circuit all at once, causing the output voltage to rise to the magnitude of the input voltage. There are various cases such as when the cutoff ability deteriorates due to an excessive current flowing through the upper-arm switching element 24U or an excessive surge voltage applied thereto, and gradually leads to a short circuit.

[0040] The load circuit 1 may include, for example, an electrolytic cell for hydrogen production. Each of the numerous cells constituting the electrolytic cell is provided with a positive electrode, a negative electrode, and an electrolytic membrane between the positive electrode and the negative electrode. The electrolytic membrane is formed of, for example, a solid polymer material or the like. When an excessive voltage is applied to the electrolytic membrane formed of a solid polymer material, it suffers irreversible damage. If some of the cells in the series cells are damaged by an excessive voltage, it may affect the function of the entire electrolytic cell, and there is a risk of operation interruption or stop. On the other hand, since the voltage applied to the cell affects the efficiency of electrolysis, it is necessary to set a sufficiently high voltage.

[0041] The power conversion device 10 that supplies power to such a load circuit 1 is required to provide sufficient protection against the application of overvoltage while supplying a sufficiently high DC voltage to the load circuit 1.

[0042] When configuring the overvoltage protection circuit 50 by monitoring the voltage at the power supply terminal of the load circuit 1, the accuracy of the detected voltage may be a problem. If the overvoltage detection value is set to just below the upper limit of the rated voltage that the power conversion device 10 can output, and the set value varies low due to the setting accuracy of the detection value, there is a risk that a sufficiently high output voltage cannot be obtained during normal operation. If the overvoltage detection value is set to a sufficiently high value with a margin from the upper limit of the rated voltage that the power conversion device 10 can output, there is a risk that the protection of the electrolytic membrane from overvoltage becomes insufficient.

[0043] In the power conversion device 10 according to this embodiment, in the process leading to a short-circuit fault of the upper-arm switching element 24U, the fact that an abnormality occurs in the current flowing through the upper-arm switching element 24U is utilized. As a sign that the upper-arm switching element 24U is about to have a short-circuit fault, a current larger than the current command value may flow. By monitoring such a current, it becomes possible to detect the sign of a short-circuit fault of the upper-arm switching element 24U. In the power conversion device 10 according to this embodiment, by monitoring the output currents IO1 to IOn, the sign of a short-circuit fault of the upper-arm switching element 24U is detected, and the overvoltage protection circuit 50 is made to function before an overvoltage is applied to the load circuit 1.

[0044] The first condition is to set the abnormal current threshold value to α times the current command value for the output current of each unit. Thereby, it is possible to simply monitor the sign of a short-circuit fault of the upper-arm switching element 24U of each unit.

[0045] The second condition is to monitor whether the output current value increases over the off period of the upper-arm switching element 24U. Even for current fluctuations within the detection accuracy of the output current of each unit, by measuring the ratio of the change within the same period, it is possible to detect the presence or absence of an abnormality in the output current value with higher accuracy.

[0046] The third condition is applied when n units are operated in parallel. By statistically processing the data of n or n - 1 output currents, the sign of a short-circuit fault of the upper-arm switching element 24U of any one of the units is detected.

[0047] To execute this condition, as in the above specific example, as the statistical value of the output current data, the average value of n or n - 1 output currents may be used, or the median value may be used. When the number of parallel units is sufficiently large, the standard deviation of the output currents of n units may be sequentially obtained, and a threshold value may be set based on the obtained standard deviation. Under this condition, by statistically processing the values of the output currents of n units, abnormal values can be accurately detected, and it becomes possible to detect signs of a short - circuit failure of the upper - arm switching element 24U.

[0048] In the power conversion device 10 according to this embodiment, in the OVP gate circuit 42, by applying at least one, preferably a plurality of the first to third conditions for detecting an abnormality in the output current value, it is possible to more reliably prevent overvoltage application to the load circuit due to a short - circuit accident of the upper - arm switching element 24U.

[0049] (Second Embodiment) FIG. 4 is a schematic block diagram illustrating a power conversion device according to the second embodiment. In the power conversion device 210 according to this embodiment, instead of the over - voltage protection circuit 50 in the case of the first embodiment, the lower - arm switching element 24L of the unit 20 is used. Of course, for the purpose of multiplexing and redundancy of over - voltage protection, a voltage near the power supply terminal of the load circuit 1 may be detected, and an over - voltage protection circuit 50 that operates based on the detected voltage may be provided. The power conversion device 210 according to this embodiment is different from the case of the first embodiment in that it includes a control device 240 instead of the control device 40 in the case of the first embodiment. The power conversion device 210 according to this embodiment is different from the case of the first embodiment in that it includes a unit element failure determination circuit 242 instead of the OVP gate circuit 42 in the case of the first embodiment. In other respects, the power conversion device 210 according to this embodiment is the same as the case of the first embodiment, and the same reference numerals are assigned to the same components, and detailed descriptions are appropriately omitted.

[0050] As shown in FIG. 4, the power conversion device 210 according to the present embodiment includes units 20-1 to 20-n, a control device 240, and a unit element failure determination circuit 242. The units 20-1 to 20-n are connected in parallel in such a number that can supply the DC power necessary for supplying to the load circuit 1. In the present embodiment, the number of units is not limited to a plurality, and may be one unit. The control device 240 generates gate signals vG1 to vGn according to the voltage applied to the load circuit 1, the current flowing through the load circuit 1, and conditions set in advance in the control device 240, etc., and controls the units 20-1 to 20-n.

[0051] The unit element failure determination circuit (unit element failure determination means) 242 is connected to the control device 240 and current detectors 30-1 to 30-n. The unit element failure determination circuit 242 inputs the data of the output currents IO1 to IOn output from the current detectors 30-1 to 30-n. The unit element failure determination circuit 242 inputs the gate signals vG1 to vGn for each of the units 20-1 to 20-n from the control device 240.

[0052] Similar to the case of the first embodiment, the unit element failure determination circuit 242 detects signs of a short-circuit failure of the upper arm switching element 24U for each of the units 20-1 to 20-n based on the output currents IO1 to IOn. When detecting signs of a short-circuit failure of the upper arm switching element 24U, the unit element failure determination circuit 242 uses at least one of the first to third conditions. The first to third conditions are the same as those in the case of the first embodiment, and detailed description thereof is omitted.

[0053] When the unit element failure determination circuit 242 detects signs of a short-circuit failure of the upper arm switching element 24U, it outputs a fuse forced cut-off command for the unit having the upper arm switching element 24U to the control device 240.

[0054] Based on the fuse forced cut-off command, the control device 240 sends a gate signal that keeps the lower arm switching element 24L constantly on to the unit that has detected signs of a short-circuit fault. The control device 240 sends a command for gate block (GB) to units other than the unit that has detected signs of a short-circuit fault. As a result, in the unit that has detected signs of a short-circuit fault, the upper arm fuse 25U is blown to perform fault processing, and the other units stop.

[0055] FIG. 5 is a schematic block diagram for explaining the operation of the power conversion device according to the second embodiment. The operation of the power conversion device 210 according to this embodiment will be described. As shown in FIG. 5, the unit 20 that has received the gate signal from the control device 240 that has received the fuse forced cut-off command turns on the lower arm switching element 24L and keeps it constantly on. The current flows into the unit 20 through the input terminal 21a, and flows through the current path of the upper arm fuse 25U, the short-circuited upper arm switching element 24U, the lower arm switching element 24L, and the lower arm fuse 25L, and flows out from the input terminal 21b. The output terminals 14a and 14b of the power conversion device 10 are short-circuited by the choke coil 26, the lower arm switching element 24L, and the lower arm fuse 25L.

[0056] When the current flowing through the upper arm fuse 25U reaches the fusing condition of the upper arm fuse 25U, the upper arm fuse 25U blows, and the unit 20 is disconnected from the load circuit 1. Therefore, an overvoltage is not applied to the load circuit 1, and the load circuit 1 is protected.

[0057] The effects of the power conversion device 210 according to this embodiment will be described. The power conversion device 210 according to this embodiment includes a unit element failure determination circuit 242. The unit element failure determination circuit 242 monitors the output currents IO1 to IOn for each of the units 20-1 to 20-n. In the unit element failure determination circuit 242, similar to the case of the first embodiment, among the first to third conditions regarding the output current, at least one condition is used to detect signs of a short-circuit failure of the upper arm switching element 24U for each of the units 20-1 to 20-n. Therefore, overvoltage protection of the load circuit 1 can be surely performed without considering variations in the voltage detection values for overvoltage protection.

[0058] In the power conversion device 210 according to this embodiment, since the lower arm switching element 24L constituting the unit is used for a short circuit at the power supply end of the load circuit 1, the number of components for the protection circuit can be reduced.

[0059] (Third Embodiment) FIG. 6 is a schematic block diagram illustrating a power conversion device according to the third embodiment. In the power conversion device 310 according to this embodiment, the lower arm switching element 24L of the unit in which signs of a short-circuit failure of the upper arm switching element 24U are detected is always turned on, and the lower arm switching elements 24L of the other units are always turned on. Thereby, the upper arm fuse 25U of the unit in which signs of a short-circuit failure of the upper arm switching element 24U are detected can be surely blown. The power conversion device 310 according to this embodiment is different from the case of the second embodiment in that it includes a control device 340 instead of the control device 240 in the case of the second embodiment. The power conversion device 310 according to this embodiment is different from the case of the second embodiment in that it includes a unit element failure determination circuit 342 instead of the unit element failure determination circuit 242 in the case of the second embodiment. The power conversion device 310 according to this embodiment is the same as the cases of the other above-described embodiments in other respects, and the same reference numerals are given to the same components and detailed descriptions are appropriately omitted.

[0060] As shown in FIG. 6, the power conversion device 310 according to the present embodiment includes units 20-1 to 20-n, a control device 340, and a unit element failure determination circuit 342. The control device 340 is connected to the units 20-1 to 20-n. The control device 340 generates gate signals vG1 to vGn according to the state of the load circuit 1 and the states of the units 20-1 to 20-n, and controls the units 20-1 to 20-n. In the present embodiment, a plurality of units 20-1 to 20-n are provided.

[0061] The unit element failure determination circuit (unit element failure determination means) 342 monitors the output currents IO1 to IOn for each of the units 20-1 to 20-n, detects signs of a short-circuit failure of the upper arm switching element 24U, and transmits a fuse forced break command to the control device 340.

[0062] The control device 340 transmits a gate signal that keeps the upper arm switching element 24U always off and the lower arm switching element 24L always on to all the units. Thereby, the power conversion device 10 is disconnected from the power supply end of the load circuit 1. Also, a large current flows through the upper arm fuse 25U of the unit in which signs of a short-circuit failure of the upper arm switching element 24U are detected, and when the fusing condition of the upper arm fuse 25U is reached, that unit is disconnected from the power conversion device 310.

[0063] Note that in the above description, the lower arm switching elements 24L of all the units other than the faulty unit are set to be always on, but the present invention is not limited to this, and it may be a plurality of units among all the units. The plurality of units in which the lower arm switching element 24L is always on may or may not include the unit having signs of a failure.

[0064] Also, when minor current control is being performed for each of the units 20-1 to 20-n when a sign of a failure is detected, the control device 340 sets a negative current command value for the units 20-1 to 20-n so as to suck in current. Thereby, the on-period of the lower-arm switching element 24L may be set longer.

[0065] FIG. 7 is a schematic block diagram for explaining the operation of the power conversion device according to the present embodiment. As shown in FIG. 7, the current flowing through the upper-arm switching element 24U of the unit 20-1 having a sign of a short-circuit failure flows not only through the lower-arm switching element 24L of that unit 20-1 but also through the lower-arm switching elements 24L of the other units 20-2 to 20-n. As a result, a sufficiently large current can flow through the upper-arm fuse 25U of the unit 20-1, and the current can easily reach the fusing condition of the upper-arm fuse 25U and fuse the upper-arm fuse 25U.

[0066] In the present embodiment, after fusing the upper-arm fuse 25U, the other units 20-2 to 20-n can be restarted to supply power to the load circuit 1 again. The unit element failure determination circuit 342 monitors the output currents IO1 to IOn even after outputting a fuse forced break command. FIG. 8 is an example of a flowchart for explaining the operation of the power conversion device 310 according to the present embodiment.

[0067] As shown in FIG. 8, in step S1, the unit element failure determination circuit 242 determines whether or not the first to third conditions (denoted as conditions 1 to 3 in FIG. 8) are detected. When the unit element failure determination circuit 342 detects any one of the first to third conditions, the process proceeds to step S2. When the unit element failure determination circuit 342 does not detect any of the first to third conditions, it waits.

[0068] In step S2, the unit element failure determination circuit 342 that has detected any of the first to third conditions outputs a fuse forced cut-off command to the control device 340. Based on the fuse forced cut-off command, the control device 340 transmits gate signals that keep the upper arm switching element 24U constantly off and the lower arm switching element 24L constantly on to each unit 20-1 to 20-n.

[0069] In step S3, when at least any one of the output currents IO1 to IOn of each unit 20-1 to 20-n becomes a value smaller than a predetermined threshold value, the unit element failure determination circuit 342 determines that the upper arm fuse 25U of unit 20-1 has blown and transfers the process to step S4. When the output currents IO1 to IOn are equal to or greater than the predetermined threshold value, the unit element failure determination circuit 242 continues to monitor the current value and waits.

[0070] In step S4, the unit element failure determination circuit 342 outputs a fuse cut-off signal to the control device 340.

[0071] In step S5, based on the fuse cut-off signal, the control device 340 transmits gate signals vG2 to vGn to n-1 normal units 20-2 to 20-n respectively. The normal units that have received the gate signals vG2 to vGn start normal operation again and resume power supply to the load circuit 1.

[0072] In the above description, the blown state of the upper arm fuse 25U is monitored by monitoring the output current of each unit. However, if the upper arm fuse 25U blows, all output currents are cut off, so it is of course possible to monitor at least one output current. Also, when directly monitoring the presence or absence of the upper arm fuse 25U blowing with a microswitch or the like, it is possible to monitor the microswitch or the like instead of monitoring the output current.

[0073] The effects of the power conversion device 310 according to this embodiment will be described. The power conversion device 310 according to this embodiment has the same effects as those in the case of the above-described other embodiments. That is, the power conversion device 310 includes a unit element failure determination circuit 342, and the unit element failure determination circuit 342 monitors the output currents IO1 to IOn of the units 20-1 to 20-n, and based on the output currents IO1 to IOn, it can detect signs of a short-circuit failure of the upper arm switching element 24U of any unit. Therefore, overvoltage at the power supply end of the load circuit 1 can be prevented regardless of the accuracy of the voltage detection value for overvoltage detection.

[0074] In addition, in the power conversion device 310 of this embodiment, by keeping the lower arm switching elements 24L of a plurality of units always on, it is possible to allow a large current to flow through the upper arm fuse 25U of the unit having signs of failure. Therefore, the upper arm fuse 25U of the unit having signs of failure can be quickly and surely blown.

[0075] In each of the units 20-1 to 20-n, an upper arm fuse 25U and a lower arm fuse 25L are provided so that short-circuit failures of the upper arm switching element 24U and the lower arm switching element 24L respectively do not affect other units or components. In this embodiment, since the lower arm switching elements 24L of a plurality of units are always on, it is possible to quickly and surely blow the upper arm fuse 25U of the unit having signs of failure and disconnect the failed unit from the load circuit 1.

[0076] Also, in the power conversion device 310 according to the present embodiment, the unit element failure determination circuit 342 can detect the fuse blowing of the upper arm fuse 25U by continuously monitoring the output currents IO1 to IOn. The unit element failure determination circuit 342 outputs a fuse blown completion signal to the control device 340, and the control device 340 can send a gate signal to a normal unit to resume normal operation. Therefore, it is possible to shorten the operation interruption period of the manufacturing plant including the load circuit 1 composed of an electrolytic cell or the like, and substantially improve the productivity of the manufacturing plant. In the second embodiment, the unit element failure determination circuit 342 can be applied when a plurality of units are connected in parallel. In that case, also in the case of the second embodiment, after disconnecting the unit having a sign of failure from the load circuit 1, the remaining normal units can be restarted to resume power supply to the load circuit 1.

[0077] In this way, a power conversion device that can more reliably protect the load circuit from the application of overvoltage can be realized.

[0078] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0079] 1... Load circuit, 10... Power conversion device, 20... Unit, 20-1 to 20-n... Units, 24L... Lower arm switching element, 24U... Upper arm switching element, 25L... Lower arm fuse, 25U... Upper arm fuse, 30-1 to 30-n... Current detectors, 40... Control device, 42... OVP gate circuit, 50... Overvoltage protection circuit, 210... Power conversion device, 240... Control device, 242... Unit element failure determination circuit, 310... Power conversion device, 340... Control device, 342... Unit element failure determination circuit

Claims

1. a first input terminal; a second input terminal to which a potential lower than the potential applied to the first input terminal is applied; a first output terminal; a second output terminal having a potential lower than that of the first output terminal; a unit for power conversion that steps down a DC voltage applied between the first input terminal and the second input terminal, converts it into another DC voltage, and outputs it to a load circuit connected between the first output terminal and the second output terminal; a control device that transmits a gate signal to the unit so as to control the voltage applied to the load circuit and the current flowing through the load circuit; unit element failure determination means for determining signs of an abnormality of the unit based on the output current of the unit and outputting an active determination signal; overvoltage protection means for preventing an overvoltage from being applied to the load circuit based on the determination signal output by the unit element failure determination means; comprising the unit is a first switching element connected between the first input terminal and the second input terminal; a second switching element connected in series to the low potential side of the first switching element; a first fuse provided to be opened in the event of a short circuit failure of the first switching element; a second fuse provided to be opened in the event of a short circuit failure of the second switching element; an inductor connected between a connection node of the first switching element and the second switching element and the first output terminal; including the unit element failure determination means determines signs of a short circuit failure of the first switching element based on the output current of the unit and outputs the determination signal; the overvoltage protection means is a power conversion device that forms a current path including the first switching element and blows the first fuse.

2. The power conversion device according to claim 1, wherein the overvoltage protection means forms the current path by short-circuiting between the first output terminal and the second output terminal based on the determination signal.

3. The power conversion device according to claim 1, wherein the overvoltage protection means forms the current path by keeping the second switching element always on based on the determination signal.

4. a plurality of the units are provided and connected in parallel, the unit element failure determination means is Based on the output currents of the plurality of units, determine a faulty unit, which is a unit with signs of abnormality among the plurality of units, and output the determination signal. The overvoltage protection means forms the current path by always turning off the first switching elements of two or more of the plurality of units and always turning on the second switching elements based on the determination signal. The power conversion device according to claim 1.

5. The unit element failure determination means: After outputting the determination signal, monitor the values of the output currents of the plurality of units. Based on the output currents of the plurality of units, determine the fusing of the first fuse and output a fusing completion signal to the control device. The control device resumes the operation of the normal units among the plurality of units based on the fusing completion signal. The power conversion device according to claim 4.

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