Power conversion system

Abstract

To provide a power conversion system capable of suppressing occurrence of a chain failure of a healthy switching element without requiring periodic replacement of parts.SOLUTION: A power conversion system includes: a main circuit unit that performs power conversion by switching of a plurality of switching elements connected in series; and a control circuit that controls operation of power conversion by the main circuit unit by controlling switching of the plurality of switching elements. The plurality of switching elements include a pair of main terminals and a control terminal. The switching elements are connected in series via a pair of main terminals, the main circuit unit includes a plurality of monitoring circuits that detect a failure of a plurality of switching elements by monitoring whether or not there is a periodic change in a voltage application state between the pair of main terminals of the plurality of switching elements. The control circuit stops an operation of the power conversion by the main circuit unit when a failure of any of the plurality of switching elements is detected by the plurality of monitoring circuits.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] There is a power conversion device that has a plurality of switching elements and converts power by switching the plurality of switching elements. In such a power conversion device, the plurality of switching elements are connected in series to achieve a higher voltage. A switched capacitor circuit, for example, is known as an example of a power conversion device that has a plurality of switching elements connected in series.

[0003] In a power conversion device having multiple switching elements connected in series, if one of the multiple switching elements connected in series fails, the load of the other healthy switching elements increases, and there is a possibility that the other healthy switching elements will also fail in a chain reaction. Furthermore, if a chain reaction occurs, for example, a short circuit may occur between the input and output of the device, causing an excessive current to flow and damaging other elements, which may cause a more serious failure in the device.

[0004] For example, it has been proposed to provide a fuse in a current path, such as an input section, in the event of a cascading failure, and to melt the fuse when the cascading failure occurs, thereby preventing serious failures due to excessive current. However, fuses are limited-life components and must be replaced periodically. This requires time and effort for fuse maintenance, and there are concerns about the associated increase in costs and work time. Furthermore, while providing a fuse can prevent serious failures due to excessive current, it cannot prevent cascading failures of other healthy switching elements caused by a failure of one of the multiple switching elements.

[0005] Therefore, in a power conversion device having multiple switching elements connected in series, it is desirable to be able to suppress the occurrence of chain failures of healthy switching elements without requiring periodic replacement of components. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-74472 Summary of the Invention [Problem to be solved by the invention]

[0007] An embodiment of the present invention provides a power conversion device that has multiple switching elements connected in series and can suppress the occurrence of cascading failures of healthy switching elements without requiring periodic replacement of components. [Means for solving the problem]

[0008] According to an embodiment of the present invention, there is provided a power conversion device comprising: a main circuit unit having a plurality of switching elements connected in series and converting power by switching the plurality of switching elements; and a control circuit that controls the power conversion operation by the main circuit unit by controlling the switching of the plurality of switching elements, wherein the plurality of switching elements have a pair of main terminals and a control terminal and are connected in series via the pair of main terminals, the main circuit unit has a plurality of monitoring circuits that detect failures of the plurality of switching elements by monitoring whether or not there is a periodic change in the state of application of voltage between the pair of main terminals of the plurality of switching elements, and the control circuit stops the power conversion operation by the main circuit unit when a failure of any of the plurality of switching elements is detected by the plurality of monitoring circuits. [Effects of the Invention]

[0009] A power conversion device is provided that has a plurality of switching elements connected in series, does not require periodic replacement of components, and can suppress the occurrence of chain failures of healthy switching elements. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram schematically illustrating a power conversion device according to an embodiment. [Figure 2] 2(a) and 2(b) are explanatory diagrams that schematically show the operation of the switching circuit. [Figure 3] FIG. 2 is a block diagram schematically illustrating a part of a switching circuit. [Figure 4] FIG. 2 is a block diagram schematically illustrating a monitoring circuit. [Figure 5] 5(a) to 5(f) are graphs that schematically show an example of the operation of the monitoring circuit. [Figure 6] FIG. 10 is a block diagram schematically illustrating a modified example of the monitoring circuit. [Figure 7] 7(a) and 7(b) are graphs that schematically show an example of the operation of the monitoring circuit of the modified example. [Figure 8] FIG. 10 is a block diagram schematically illustrating a modification of the switching circuit. [Figure 9] FIG. 10 is a block diagram schematically illustrating a modified example of the power conversion device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Each embodiment will be described below with reference to the drawings. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0012] FIG. 1 is a block diagram schematically illustrating a power conversion device according to an embodiment. 1, the power conversion device 10 includes a main circuit unit 12 and a control circuit 14. The main circuit unit 12 converts power. The control circuit 14 controls the power conversion operation performed by the main circuit unit 12.

[0013] The main circuit unit 12 is connected to, for example, a DC power supply 2. The main circuit unit 12 performs an operation of, for example, stepping down a DC input voltage supplied from the DC power supply 2 and outputting the stepped down voltage. In this example, the main circuit unit 12 is a step-down power converter (DC-DC converter). The main circuit unit 12 is, for example, a switched capacitor circuit.

[0014] However, the main circuit unit 12 is not limited to a step-down power converter, but may be a step-up power converter. Furthermore, the power conversion by the main circuit unit 12 is not limited to conversion from DC power to another DC power, but may be conversion from DC power to AC power or conversion from AC power to DC power. The power conversion by the main circuit unit 12 may be any conversion that converts input power into another power. The following description will be given taking as an example a case where the main circuit unit 12 is a switched capacitor circuit.

[0015] The main circuit unit 12 has a switching circuit 20 and a connection circuit 22. The switching circuit 20 has a pair of input terminals 20a, 20b, a pair of output terminals 20c, 20d, a plurality of power storage elements 30a to 30e, and a plurality of first switching elements 31a to 31d. The pair of input terminals 20a, 20b are connected to a DC power source 2 via the connection circuit 22. The pair of output terminals 20c, 20d are connected to a load (not shown). The load connected to the pair of output terminals 20c, 20d may be any load that requires a supply of DC power.

[0016] 2(a) and 2(b) are explanatory diagrams that schematically show the operation of the switching circuit. As shown in FIGS. 2(a) and 2(b), the switching circuit 20 has a first state and a second state. In the first state, as shown in FIG. 2(a), the plurality of energy storage elements 30a-30e are connected in series between a pair of input terminals 20a, 20b. In the second state, as shown in FIG. 2(b), the plurality of energy storage elements 30a-30e are connected in parallel to a pair of output terminals 20c, 20d. In other words, in the second state, one end of each of the plurality of energy storage elements 30a-30e is connected to one output terminal 20c, and the other end of each of the plurality of energy storage elements 30a-30e is connected to the other output terminal 20d.

[0017] The switching circuit 20 switches between a first state and a second state by switching a plurality of first switching elements 31a to 31d. Each of the first switching elements 31a to 31d has, for example, a pair of main terminals and a control terminal. Each of the first switching elements 31a to 31d has an ON state in which a current flows between the pair of main terminals, and an OFF state in which the current flow between the pair of main terminals is blocked. Each of the first switching elements 31a to 31d switches between the ON state and the OFF state depending on the magnitude of the voltage applied to the control terminal.

[0018] Each of the first switching elements 31a to 31d is, for example, a self-excited switching element such as a MOSFET or an IGBT. Note that each of the first switching elements 31a to 31d is not limited to the above and may be any element that can appropriately switch between an on state and an off state. Furthermore, the off state is not limited to a state in which no current flows between the pair of main terminals, but may be a state in which a weak current flows between the pair of main terminals within a range that does not affect the operation of the switching circuit 20.

[0019] As shown in FIG. 1, the energy storage elements 30a to 30d are connected in series between one input terminal 20a and one output terminal 20c. In other words, the one output terminal 20c is electrically connected to one input terminal 20a via the energy storage elements 30a to 30d connected in series. The other output terminal 20d is electrically connected to the other input terminal 20b. One end of the energy storage element 30e is connected to the connection point between the energy storage element 30d and the output terminal 20c. The other end of the energy storage element 30e is connected to the input terminal 20b and the output terminal 20d. In other words, the energy storage element 30e is provided between the pair of output terminals 20c, 20d, at a position closer to the output terminal 20c than the energy storage elements 30a to 30d.

[0020] The first switching element 31a is provided in parallel to the power storage element 30a. The first switching element 31b is provided in parallel to the power storage element 30b. The first switching element 31c is provided in parallel to the power storage element 30c. The first switching element 31d is provided in parallel to the power storage element 30d.

[0021] In other words, the first switching elements 31a to 31d are connected in parallel to the power storage elements 30a to 30d connected in series between the input terminal 20a and the output terminal 20c, and are thereby connected in series between the input terminal 20a and the output terminal 20c. The first switching elements 31a to 31d are connected in series via a pair of main terminals.

[0022] The switching circuit 20 further includes, for example, rectifying elements 32a to 32d, rectifying elements 33a to 33d, and rectifying elements 34a to 34d. The rectifying elements 32a to 32d are connected in anti-parallel to the first switching elements 31a to 31d.

[0023] Rectifying element 33a is provided between power storage element 30a and power storage element 30b. Rectifying element 33b is provided between power storage element 30b and power storage element 30c. Rectifying element 33c is provided between power storage element 30c and power storage element 30d. Rectifying element 33d is provided between power storage element 30d and power storage element 30e. In the first state, rectifying elements 33a to 33d rectify current in the direction of flow from input terminal 20a to input terminal 20b via power storage elements 30a to 30e.

[0024] One main terminal of the first switching element 31a is connected between the input terminal 20a and the energy storage element 30a. The other main terminal of the first switching element 31a is connected between the rectifying element 33a and the energy storage element 30b. One main terminal of the first switching element 31b is connected between the rectifying element 33a and the energy storage element 30b. The other main terminal of the first switching element 31b is connected between the rectifying element 33b and the energy storage element 30c. One main terminal of the first switching element 31c is connected between the rectifying element 33b and the energy storage element 30c. The other main terminal of the first switching element 31c is connected between the rectifying element 33c and the energy storage element 30d. One main terminal of the first switching element 31d is connected between the rectifying element 33c and the energy storage element 30d. The other main terminal of the first switching element 31d is connected between the rectifying element 33d and the power storage element 30e.

[0025] One end of rectifying element 34a is connected between the power storage element 30a and rectifying element 33a. The other end of rectifying element 34a is connected between the power storage element 30b and rectifying element 33b. One end of rectifying element 34b is connected between the power storage element 30b and rectifying element 33b. The other end of rectifying element 34b is connected between the power storage element 30c and rectifying element 33c. One end of rectifying element 34c is connected between the power storage element 30c and rectifying element 33c. The other end of rectifying element 34c is connected between the power storage element 30d and rectifying element 33d. One end of rectifying element 34d is connected between the power storage element 30d and rectifying element 33d. The other end of rectifying element 34d is connected between the power storage element 30e and output terminal 20d. In the second state, rectifying elements 34a to 34d rectify the current in the direction that the current flows from power storage elements 30a to 30e to output terminal 20c.

[0026] In the switching circuit 20 configured as described above, the first state is achieved by turning off the first switching elements 31a to 31d, and the second state is achieved by turning on the first switching elements 31a to 31d. However, the configuration of the switching circuit 20 is not limited to the above, and any configuration may be used that can appropriately switch between the first state and the second state by switching the multiple first switching elements 31a to 31d.

[0027] The connection circuit 22 connects the switching circuit 20 to the DC power supply 2 and switches between a supply state in which DC power from the DC power supply 2 is supplied between a pair of input terminals 20a, 20b of the switching circuit 20 and a stop state in which supply of DC power from the DC power supply 2 to the pair of input terminals 20a, 20b is stopped. The connection circuit 22 has a second switching element 22a, and switches between the supply state and the stop state by switching the second switching element 22a.

[0028] The second switching element 22a is provided, for example, between the positive electrode of the DC power supply 2 and the input terminal 20a. The input terminal 20b is connected to the negative electrode of the DC power supply 2. The supply state of the connection circuit 22 is, for example, a state in which the second switching element 22a is in an ON state. This causes DC power from the DC power supply 2 to be supplied between the pair of input terminals 20a, 20b. The stopped state of the connection circuit 22 is, for example, a state in which the second switching element 22a is in an OFF state. This causes the supply of DC power from the DC power supply 2 to be stopped between the pair of input terminals 20a, 20b.

[0029] However, the configuration of the connection circuit 22 is not limited to the above, and may be any configuration that allows appropriate switching between a supply state and a stop state by at least one second switching element 22a.

[0030] The control circuit 14 controls the switching between the first state and the second state of the switching circuit 20, and also controls the switching between the supply state and the stop state of the connection circuit 22. The control circuit 14 controls the switching between the first state and the second state of the switching circuit 20 by controlling the switching of each of the first switching elements 31a to 31d. The control circuit 14 also controls the switching between the supply state and the stop state of the connection circuit 22 by controlling the switching of the second switching element 22a.

[0031] When the switching circuit 20 is in the first state, the control circuit 14 puts the connection circuit 22 in the supply state. In other words, when the control circuit 14 puts each of the first switching elements 31a to 31d in the off state, the control circuit 14 puts the second switching element 22a in the on state. As a result, each of the storage elements 30a to 30e is charged by the DC power supplied from the DC power source 2.

[0032] When the switching circuit 20 is in the second state, the control circuit 14 stops the connection circuit 22. In other words, when the control circuit 14 turns on each of the first switching elements 31a to 31d, the control circuit 14 turns off the second switching element 22a. As a result, the charges stored in each of the storage elements 30a to 30e are output between the pair of output terminals 20c, 20d.

[0033] The control circuit 14 alternately switches, at a predetermined period, between a state in which the switching circuit 20 is in a first state and the connection circuit 22 is in a supply state, and a state in which the switching circuit 20 is in a second state and the connection circuit 22 is in a stopped state. As a result, the main circuit unit 12 (switched capacitor circuit) can output, between a pair of output terminals 20c, 20d, a DC voltage whose magnitude is calculated by dividing the DC input voltage supplied from the DC power source 2 by the number of the plurality of storage elements 30a-30e. When the output voltage of the main circuit unit 12 (switching circuit 20) is Vout, the input voltage supplied from the DC power source 2 is Vin, and the number of the plurality of storage elements 30a-30e is n, the output voltage Vout can be expressed by the following equation: Vout=Vin / n

[0034] In this way, the main circuit unit 12 alternately switches between a state in which the switching circuit 20 is in a first state and the connection circuit 22 is in a supply state, and a state in which the switching circuit 20 is in a second state and the connection circuit 22 is in a stopped state at a predetermined period, thereby reducing the DC input voltage supplied from the DC power source 2 to a voltage of a magnitude corresponding to the number of the multiple storage elements 30a to 30e and outputting it.

[0035] The main circuit unit 12 has a plurality of first switching elements 31a-31d connected in series, as well as a second switching element 22a, and performs power conversion by switching the plurality of first switching elements 31a-31d and the second switching element 22a. In this example, the main circuit unit 12 has five power storage elements 30a-30e and four first switching elements 31a-31d. The number of these elements is not limited to this and may be set appropriately depending on the magnitude of the required output voltage Vout.

[0036] The control circuit 14 generates first control signals corresponding to the first switching elements 31a to 31d and controls the switching of the first switching elements 31a to 31d by inputting the generated first control signals to the switching circuit 20. The control circuit 14 also generates second control signals corresponding to the second switching element 22a and inputs the generated second control signals to the connection circuit 22 to control the switching of the second switching element 22a.

[0037] In this way, the control circuit 14 controls the switching of each of the first switching elements 31a to 31d based on the first control signal, and controls the switching of the second switching element 22a based on the second control signal, thereby alternately switching between a state in which the switching circuit 20 is in the first state and the connection circuit 22 is in the supply state, and a state in which the switching circuit 20 is in the second state and the connection circuit 22 is in the stopped state, at a predetermined period.

[0038] In addition, the control circuit 14 controls the switching of each of the first switching elements 31a to 31d and the second switching element 22a at a predetermined switching frequency and a predetermined duty ratio, thereby alternately switching between a state in which the switching circuit 20 is in a first state and the connection circuit 22 is in a supply state, and a state in which the switching circuit 20 is in a second state and the connection circuit 22 is in a stopped state, at a predetermined period.

[0039] The first control signal is, for example, a pulse signal that alternates between a state corresponding to the ON state of each of the first switching elements 31a-31d and a state corresponding to the OFF state of each of the first switching elements 31a-31d at a predetermined period. Similarly, the second control signal is, for example, a pulse signal that alternates between a state corresponding to the ON state of the second switching element 22a and a state corresponding to the OFF state of the second switching element 22a at a predetermined period. The state corresponding to the ON state is, for example, a high state of the pulse signal. The state corresponding to the OFF state is, for example, a low state of the pulse signal.

[0040] This makes it possible to control the switching of the first switching elements 31a to 31d and the second switching element 22a at a predetermined switching frequency and a predetermined duty ratio based on the first control signal and the second control signal.

[0041] More specifically, the first control signal and the second control signal are PWM (Pulse Width Modulation) signals. In other words, the control circuit 14 controls the switching of the first switching elements 31a to 31d and the second switching element 22a at a predetermined switching frequency and a predetermined duty ratio by PWM control.

[0042] The control circuit 14 controls the switching of each of the first switching elements 31a to 31d and the second switching element 22a at a predetermined switching frequency and a predetermined duty ratio, for example, by controlling the switching period between the states corresponding to the on state and the states corresponding to the off state of the first control signal and the second control signal, and the duty ratio between the states corresponding to the on state and the states corresponding to the off state.

[0043] FIG. 3 is a block diagram schematically illustrating a part of the switching circuit. 3, the switching circuit 20 further includes a plurality of drive circuits 35a-35d and a plurality of monitoring circuits 36a-36d. For convenience, only the plurality of first switching elements 31a-31d, the plurality of drive circuits 35a-35d, and the plurality of monitoring circuits 36a-36d are extracted from the switching circuit 20 and illustrated in FIG.

[0044] The plurality of drive circuits 35a-35d are provided corresponding to the plurality of first switching elements 31a-31d, respectively. The plurality of drive circuits 35a-35d are connected to the control terminals of the plurality of first switching elements 31a-31d. The plurality of drive circuits 35a-35d receive a first control signal input from the control circuit 14, and change the magnitude of the voltage applied to the control terminals of the plurality of first switching elements 31a-31d based on the first control signal, thereby switching the plurality of first switching elements 31a-31d between an ON state and an OFF state in accordance with the first control signal.

[0045] The drive circuits 35a-35d may be omitted if the first switching elements 31a-31d can be directly driven by the first control signal input from the control circuit 14. For example, the first switching elements 31a-31d may be switched between an ON state and an OFF state by directly inputting the first control signal to the control terminals of the first switching elements 31a-31d. The drive circuits 35a-35d are provided as needed and may be omitted.

[0046] The plurality of monitoring circuits 36a to 36d are provided corresponding to the plurality of first switching elements 31a to 31d, respectively. The plurality of monitoring circuits 36a to 36d are connected to pairs of main terminals of the plurality of first switching elements 31a to 31d. More specifically, the monitoring circuit 36a is connected to the pair of main terminals of the first switching element 31a, the monitoring circuit 36b is connected to the pair of main terminals of the first switching element 31b, the monitoring circuit 36c is connected to the pair of main terminals of the first switching element 31c, and the monitoring circuit 36d is connected to the pair of main terminals of the first switching element 31d.

[0047] The plurality of monitoring circuits 36a to 36d detects failures in the plurality of first switching elements 31a to 31d by monitoring whether or not there is a periodic change in the state of voltage application between pairs of main terminals of the plurality of first switching elements 31a to 31d.

[0048] When the first switching elements 31a to 31d are healthy, the voltage between the pair of main terminals of the first switching elements 31a to 31d changes periodically in response to the first control signal. As described above, the on and off states of the first switching elements 31a to 31d are switched at predetermined intervals in response to the first control signal. When the first switching elements 31a to 31d are on, the voltage between the pair of main terminals is substantially 0 V. On the other hand, when the first switching elements 31a to 31d are off, the voltage between the pair of main terminals corresponds to the inter-terminal voltage of the energy storage elements 30a to 30d. Therefore, when the first switching elements 31a to 31d are healthy, the voltage between the pair of main terminals of the first switching elements 31a to 31d changes periodically between a low-voltage state and a high-voltage state.

[0049] On the other hand, if any of the first switching elements 31a-31d fails, the voltage between the pair of main terminals of the first switching elements 31a-31d will no longer change periodically. For example, if any of the first switching elements 31a-31d fails due to a short circuit, the voltage between the pair of main terminals will remain substantially at 0V (low voltage state). Also, if any of the first switching elements 31a-31d fails due to an open circuit, the voltage between the pair of main terminals will remain at a value corresponding to the inter-terminal voltage of the energy storage elements 30a-30d (high voltage state).

[0050] Therefore, the plurality of monitoring circuits 36a to 36d detect a failure in the first switching elements 31a to 31d when the voltage between a pair of main terminals does not change for a predetermined time or longer according to the switching cycle of the first control signal.

[0051] The plurality of monitoring circuits 36a-36d detects failures in the plurality of first switching elements 31a-31d and outputs failure detection signals according to the detection results. The failure detection signal is, for example, a signal that is high (high voltage state) when no failure is detected and is low (low voltage state) when a failure is detected. In other words, the failure detection signal is, for example, a digital signal that is in a state corresponding to a logic "1" when no failure is detected and is in a state corresponding to a logic "0" when a failure is detected.

[0052] The plurality of monitoring circuits 36a to 36d are connected to, for example, the control circuit 14 and output failure detection signals to the control circuit 14. As a result, the failure detection signals of the plurality of first switching elements 31a to 31d are input to the control circuit 14.

[0053] However, the method of inputting the fault detection signals from the plurality of monitoring circuits 36a-36d to the control circuit 14 is not limited to the above. The fault detection signals may be input to the control circuit 14 via other devices such as a communication device. In this case, communication between the control circuit 14 and the switching circuit 20 may be wired communication or wireless communication. The method of inputting the fault detection signals to the control circuit 14 may be any method that can appropriately input the plurality of fault detection signals corresponding to the plurality of first switching elements 31a-31d to the control circuit 14.

[0054] The control circuit 14 stops the power conversion operation of the main circuit unit 12 when the plurality of monitoring circuits 36a-36d detect a failure in any of the plurality of first switching elements 31a-31d based on the plurality of input failure detection signals. For example, when the plurality of monitoring circuits 36a-36d detect a failure in any of the plurality of first switching elements 31a-31d, the control circuit 14 stops the switching operation of the plurality of first switching elements 31a-31d and turns the plurality of first switching elements 31a-31d off. This makes it possible to prevent a chain reaction of failures in the other healthy first switching elements 31a-31d when a failure occurs in any of the plurality of first switching elements 31a-31d.

[0055] The control circuit 14 includes, for example, AND circuits 40 and 42. A plurality of fault detection signals are input to the AND circuit 40. The AND circuit 40 calculates the logical product of the plurality of fault detection signals and inputs an output signal representing the calculation result to the AND circuit 42.

[0056] As described above, the plurality of fault detection signals are high when no fault is detected, and low when a fault is detected. In this case, the output signal of the AND circuit 40 is high when no fault is detected in any of the plurality of first switching elements 31a to 31d, and is low when a fault is detected in any of the plurality of first switching elements 31a to 31d.

[0057] The AND circuit 42 receives the output signal of the AND circuit 40 and the first control signal generated in the control circuit 14. The AND circuit 42 calculates the logical product of the output signal of the AND circuit 40 and the first control signal, and inputs the output signal after the calculation to the switching circuit 20 as the first control signal.

[0058] As a result, when a failure is not detected in any of the plurality of first switching elements 31a-31d, the first control signal input to the AND circuit 42 is input as is to the switching circuit 20. When a failure is detected in any of the plurality of first switching elements 31a-31d, the first control signal input to the switching circuit 20 remains in a low state that sets each of the first switching elements 31a-31d to an off state, regardless of the high / low switching state of the first control signal input to the AND circuit 42. Therefore, as described above, when a failure is detected in any of the plurality of first switching elements 31a-31d, the switching operation of the plurality of first switching elements 31a-31d can be stopped and the plurality of first switching elements 31a-31d can be set to an off state.

[0059] However, the configuration of the control circuit 14 that stops the switching operation of the multiple first switching elements 31a to 31d when a failure is detected in any of the multiple first switching elements 31a to 31d is not limited to the above, and may be any configuration that can appropriately stop the switching operation of the multiple first switching elements 31a to 31d when a failure is detected in any of the multiple first switching elements 31a to 31d.

[0060] FIG. 4 is a block diagram schematically illustrating the monitoring circuit. 4, the monitoring circuit 36a includes resistive elements 50 and 51, a capacitor 52, diodes 53 and 54, a Zener diode 55, a capacitor 56, a resistive element 57, a comparator 58, a first power supply circuit 61, and a second power supply circuit 62. The configurations of the other monitoring circuits 36b to 36d can be substantially the same as the configuration of the monitoring circuit 36a, and therefore detailed description thereof will be omitted.

[0061] The first power supply circuit 61 is a circuit that outputs DC power of a first voltage V1. The second power supply circuit 62 is a circuit that outputs DC power of a second voltage V2. In other words, the first power supply circuit 61 and the second power supply circuit 62 are DC power supplies. For example, a regulator or a voltage divider circuit is used for the first power supply circuit 61 and the second power supply circuit 62. However, the first power supply circuit 61 and the second power supply circuit 62 are not limited to these and may be any circuit that can output DC power of a predetermined voltage (first voltage V1 and second voltage V2).

[0062] One end of the resistor element 50 is connected to the high-potential side main terminal of the first switching element 31a. The other end of the resistor element 50 is connected to one end of the resistor element 51. The other end of the resistor element 51 is connected to the cathode of the diode 53. The capacitor 52 is connected in parallel to the resistor element 51.

[0063] The anode of the diode 53 is connected to one end of the capacitor 56. In other words, one end of the capacitor 56 is connected to the high-potential side main terminal of the first switching element 31a via the diode 53 and the resistor elements 50 and 51. The other end of the capacitor 56 is connected to the low-potential side main terminal of the first switching element 31a. In other words, the capacitor 56 is provided in parallel with the first switching element 31a.

[0064] The anode of the diode 54 is connected to the connection point between the other end of the resistor element 51 and the cathode of the diode 53. The cathode of the diode 54 is connected to the cathode of the Zener diode 55. The anode of the Zener diode 55 is connected to the main terminal on the low potential side of the first switching element 31a.

[0065] One end of the resistor element 57 is connected to the connection point between the anode of the diode 53 and one end of the capacitor 56. The other end of the resistor element 57 is connected to the high potential terminal of the first power supply circuit 61. The low potential terminal of the first power supply circuit 61 is connected to the low potential side main terminal of the first switching element 31a.

[0066] The comparator 58 has a pair of input terminals and an output terminal. One input terminal of the comparator 58 is connected to one end of the capacitor 56. As a result, the voltage across the terminals of the capacitor 56 is input to one input terminal of the comparator 58. The other input terminal of the comparator 58 is connected to the high potential terminal of the second power supply circuit 62. The low potential terminal of the second power supply circuit 62 is connected to the low potential side main terminal of the first switching element 31a. As a result, the second voltage V2 output from the second power supply circuit 62 is input to the other input terminal of the comparator 58.

[0067] The output terminal of the comparator 58 is connected to, for example, the control circuit 14. The monitoring circuit 36a outputs the output signal of the comparator 58 as a fault detection signal.

[0068] 5(a) to 5(f) are graphs that schematically show an example of the operation of the monitoring circuit. FIG. 5(a) schematically shows an example of the change over time in the voltage between the pair of main terminals of the first switching element 31a when the first switching element 31a is healthy. FIG. 5(b) shows a schematic example of the change over time in the voltage of the capacitor 56 when the first switching element 31a is healthy. FIG. 5(c) shows a schematic example of a change over time in the voltage between the pair of main terminals of the first switching element 31a when a short-circuit fault occurs in the first switching element 31a. FIG. 5(d) shows a schematic example of the change over time in the voltage of the capacitor 56 when a short-circuit fault occurs in the first switching element 31a. FIG. 5(e) schematically shows an example of the change over time in the voltage between the pair of main terminals of the first switching element 31a when an open circuit fault occurs in the first switching element 31a. FIG. 5(f) shows a schematic example of the change over time in the voltage of the capacitor 56 when an open circuit failure occurs in the first switching element 31a. 5(b), 5(d), and 5(f) schematically show an example of the change over time in the voltage input to one input terminal of the comparator 58. In other words, FIG.

[0069] 5(a), when the first switching element 31a is healthy, the first switching element 31a switches between an ON state and an OFF state at a predetermined cycle in response to the first control signal. The voltage across the pair of main terminals of the first switching element 31a is in a high voltage state when the first switching element 31a is in an OFF state, and is in a low voltage state (substantially 0 V) ​​when the first switching element 31a is in an ON state.

[0070] 4, in the monitoring circuit 36a, the first power supply circuit 61 charges the capacitor 56 via the resistance element 57 when the first switching element 31a is in the OFF state. Therefore, when the first switching element 31a is in the OFF state, the voltage of the capacitor 56 increases over time.

[0071] Furthermore, when the first switching element 31a is in the off state, as shown by the arrow A2 in FIG. 4, the capacitor 52 is charged via the resistance element 50 based on the voltage at the main terminal on the high potential side of the first switching element 31a.

[0072] When the first switching element 31a remains in the off state for a long period of time, the resistance element 51 limits the current flowing through the Zener diode 55. The resistance value of the resistance element 51 is preferably larger than the resistance value of the resistance element 50.

[0073] When the first switching element 31a switches from the OFF state to the ON state, the charge stored in the capacitor 56 is discharged via the ON-state first switching element 31a, as indicated by the arrow A3 in Fig. 4. Therefore, when the first switching element 31a is in the ON state, the voltage of the capacitor 56 decreases over time.

[0074] Capacitor 52 is charged with the reverse polarity while first switching element 31a is in the OFF state. Therefore, capacitor 52 promotes the discharge of capacitor 56 while first switching element 31a is in the ON state. In other words, capacitor 52 functions as a speed-up capacitor.

[0075] The diode 54 prevents the capacitor 52 from discharging through a path that does not pass through the capacitor 56 while the first switching element 31a is in the on state. On the other hand, the Zener diode 55 prevents the capacitor 56 from discharging through a path that does not pass through the capacitor 52 while the first switching element 31a is in the on state. Therefore, the breakdown voltage of the Zener diode 55 is set to be equal to or higher than the first voltage V1 of the first power supply circuit 61 and lower than the voltage at the high-potential side main terminal of the first switching element 31a when the first switching element 31a is in the off state. As a result, when the first switching element 31a is in the off state, the Zener diode 55 is made conductive based on the voltage at the high-potential side main terminal of the first switching element 31a, and when the first switching element 31a is in the on state, the Zener diode 55 is made non-conductive based on the voltage of the capacitor 56.

[0076] Through the above operation, when the first switching element 31a is healthy, the capacitor 56 repeatedly charges and discharges in response to the switching of the first switching element 31a, as shown in Fig. 5(b). The second voltage V2 of the second power supply circuit 62 is set to be higher than the voltage of the capacitor 56, which repeatedly charges and discharges when the first switching element 31a is healthy. As a result, when the first switching element 31a is healthy, the output signal of the comparator 58 becomes high, and a fault detection signal that becomes high when no fault is detected can be generated.

[0077] 5(c) and 5(d), when a short-circuit fault occurs in the first switching element 31a, the voltage of the capacitor 56 is charged to a voltage obtained by dividing the first voltage V1 of the first power supply circuit 61 by the resistor element 57, and the resistor elements 50 and 51, and then adding the forward voltage of the diode 53. More specifically, after a short-circuit fault occurs in the first switching element 31a and the capacitor 52 is charged by the first power supply circuit 61, the voltage of the capacitor 56 is charged as described above.

[0078] If the voltage of capacitor 56 is C1, the resistance value of resistor element 57 is R1, the resistance value of resistor element 50 is R2, the resistance value of resistor element 51 is R3, and the forward voltage of diode 53 is Vf, the voltage of capacitor 56 when a short-circuit fault occurs in first switching element 31a can be expressed by the following equation. C1=V1×(R2+R3) / (R1+R2+R3)+Vf

[0079] The second voltage V2 of the second power supply circuit 62 is set lower than the voltage of the capacitor 56 when a short-circuit fault occurs in the first switching element 31a. As a result, as shown in Fig. 5(d), when a short-circuit fault occurs in the first switching element 31a, the voltage of the capacitor 56 becomes higher than the second voltage V2. Therefore, when a short-circuit fault occurs in the first switching element 31a, the output signal of the comparator 58 becomes low, and a fault detection signal that becomes low when a fault is detected can be generated.

[0080] As shown in FIGS. 5(e) and 5(f), when an open circuit fault occurs in the first switching element 31a, the voltage of the capacitor 56 is charged up to the first voltage V1 of the first power supply circuit 61.

[0081] The second voltage V2 of the second power supply circuit 62 is set lower than the voltage of the capacitor 56 when an open circuit fault occurs in the first switching element 31a. That is, the second voltage V2 of the second power supply circuit 62 is set lower than the first voltage V1 of the first power supply circuit 61. As a result, as shown in FIG. 5(f), when an open circuit fault occurs in the first switching element 31a, the voltage of the capacitor 56 becomes higher than the second voltage V2. Therefore, when an open circuit fault occurs in the first switching element 31a, the output signal of the comparator 58 becomes low, and a fault detection signal that becomes low when a fault is detected can be generated.

[0082] In this way, the monitoring circuit 36a can generate a fault detection signal that is high when no fault in the first switching element 31a is detected and that is low when a short-circuit fault or open-circuit fault in the first switching element 31a is detected. When the first switching element 31a is healthy, the capacitor 56 repeatedly charges and discharges in response to the switching of the first switching element 31a, thereby keeping the voltage below a predetermined voltage (second voltage V2). When the first switching element 31a is faulty, the capacitor 56 is charged by the first power supply circuit 61 in response to the cessation of switching of the first switching element 31a, thereby keeping the voltage above the predetermined voltage. The monitoring circuit 36a (plurality of monitoring circuits 36a-36d) detects a fault in the first switching element 31a (first switching elements 31a-31d) when the voltage of the capacitor 56 is above the predetermined voltage.

[0083] The monitoring circuit 36a can detect a fault in the first switching element 31a by monitoring whether or not there is a periodic change in the voltage application state between a pair of main terminals of the first switching element 31a, and output a fault detection signal according to the detection result.

[0084] As described above, in the power conversion device 10 according to this embodiment, when the monitoring circuits 36a to 36d detect a failure in any of the first switching elements 31a to 31d, the control circuit 14 stops the power conversion operation by the main circuit unit 12. This makes it possible to prevent a failure in any of the first switching elements 31a to 31d from causing a chain reaction of failures in the other healthy first switching elements 31a to 31d.

[0085] This also makes it possible to prevent a more serious failure in the device, such as a short circuit occurring between the input terminal 20a and the output terminal 20c of the switching circuit 20, causing an excessive current to flow and damaging other elements. For example, it is possible to prevent a chain reaction of failures of the first switching elements 31a to 31d of the switching circuit 20 from causing an expanded failure of the second switching element 22a of the connection circuit 22.

[0086] Furthermore, unlike when fuses or other components with limited life spans are provided, the monitoring circuits 36a to 36d do not require periodic replacement of components, and therefore, for example, it is possible to suppress increases in costs and work time associated with maintenance.

[0087] In this way, the power conversion device 10 according to this embodiment can prevent the occurrence of chain failures among healthy first switching elements 31a to 31d without requiring periodic replacement of components.

[0088] FIG. 6 is a block diagram schematically illustrating a modified example of the monitoring circuit. 6, in this example, the monitoring circuit 36a includes resistive elements 70 and 71, a capacitor 72, comparators 73 and 74, an AND circuit 75, a first power supply circuit 81, and a second power supply circuit 82. Components that are substantially the same in function and configuration as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0089] One end of the resistor element 70 is connected to the high-potential side main terminal of the first switching element 31a. The other end of the resistor element 70 is connected to one end of a capacitor 72. The other end of the capacitor 72 is connected to the low-potential side main terminal of the first switching element 31a. In other words, the capacitor 72 is provided in parallel with the first switching element 31a.

[0090] One end of the resistor element 71 is connected to the connection point between the other end of the resistor element 70 and one end of the capacitor 72. The other end of the resistor element 71 is connected to the low-potential side main terminal of the first switching element 31a. In other words, the resistor element 71 is provided in parallel with the capacitor 72.

[0091] The comparator 73 has a pair of input terminals and an output terminal. One input terminal of the comparator 73 is connected to one end of the capacitor 72. As a result, the voltage across the terminals of the capacitor 72 is input to one input terminal of the comparator 73. The other input terminal of the comparator 73 is connected to a high potential terminal of the first power supply circuit 81. A low potential terminal of the first power supply circuit 81 is connected to a low potential side main terminal of the first switching element 31a. As a result, the first voltage V1 output from the first power supply circuit 81 is input to the other input terminal of the comparator 73. The output terminal of the comparator 73 is connected to one input terminal of the AND circuit 75.

[0092] The comparator 74 has a pair of input terminals and an output terminal. One input terminal of the comparator 74 is connected to one end of the capacitor 72. As a result, the voltage across the terminals of the capacitor 72 is input to one input terminal of the comparator 74. The other input terminal of the comparator 74 is connected to the high potential terminal of the second power supply circuit 82. The low potential terminal of the second power supply circuit 82 is connected to the low potential side main terminal of the first switching element 31a. As a result, the second voltage V2 output from the second power supply circuit 82 is input to the other input terminal of the comparator 74. The output terminal of the comparator 74 is connected to the other input terminal of the AND circuit 75.

[0093] The AND circuit 75 calculates the logical sum of the output signal of the comparator 73 and the output signal of the comparator 74, and outputs the calculation result. The output terminal of the AND circuit 75 is connected to, for example, the control circuit 14. In this example, the monitoring circuit 36a outputs the output signal of the AND circuit 75 as a fault detection signal.

[0094] 7(a) and 7(b) are graphs that schematically show an example of the operation of the monitoring circuit of the modified example. FIG. 7(a) schematically shows an example of the change over time in the voltage between the pair of main terminals of the first switching element 31a. FIG. 7(b) shows a schematic example of the change in the voltage of the capacitor 72 over time.

[0095] As in the above embodiment, when the first switching element 31a is healthy, the first switching element 31a switches between an ON state and an OFF state at a predetermined cycle in response to the first control signal. The voltage across the pair of main terminals of the first switching element 31a is in a high voltage state when the first switching element 31a is in an OFF state, and is in a low voltage state (substantially 0 V) ​​when the first switching element 31a is in an ON state.

[0096] In the monitoring circuit 36a of this example, when the first switching element 31a is in the OFF state, the capacitor 72 is charged based on the voltage at the main terminal on the high potential side of the first switching element 31a. When the first switching element 31a is in the OFF state, the voltage of the capacitor 72 increases over time.

[0097] When the first switching element 31a switches from the OFF state to the ON state, the charge stored in the capacitor 72 is discharged via the ON-state first switching element 31a. Therefore, when the first switching element 31a is in the ON state, the voltage of the capacitor 72 decreases over time. Therefore, in this example as well, when the first switching element 31a is healthy, the capacitor 72 repeatedly charges and discharges in response to the switching of the first switching element 31a.

[0098] On the other hand, if the first switching element 31a has an open circuit failure, where the voltage at the main terminal on the high potential side of the first switching element 31a is Vds, the resistance value of the resistor element 70 is R1, the resistance value of the resistor element 71 is R2, and the resistance value of the capacitor 72 is Vc, the capacitor 72 is charged to the voltage Vc expressed by the following equation. Vc=Vds×R2 / (R1+R2) When the first switching element 31a is short-circuited, the capacitor 72 is discharged to substantially 0V.

[0099] As shown in Figure 7(b), the first voltage V1 of the first power supply circuit 81 is set to be higher than the maximum voltage of the capacitor 56, which repeatedly charges and discharges when the first switching element 31a is healthy, and lower than the voltage Vc of the capacitor 72, which is charged when the first switching element 31a has an open circuit fault.

[0100] In addition, the second voltage V2 of the second power supply circuit 82 is set to be lower than the minimum value of the voltage of the capacitor 56, which repeatedly charges and discharges when the first switching element 31a is healthy, and higher than the minimum voltage (e.g., 0 V) ​​of the capacitor 72 when the first switching element 31a is short-circuited.

[0101] The comparator 73 outputs a high signal when the voltage of the capacitor 56 is less than the first voltage V1, and outputs a low signal when the voltage of the capacitor 56 is equal to or greater than the first voltage V1. That is, the comparator 73 is configured to detect a rise in the voltage of the capacitor 56 that occurs due to an open circuit failure of the first switching element 31a. In other words, the comparator 73 outputs a high signal when the first switching element 31a is functioning properly, and outputs a low signal when the first switching element 31a has an open circuit failure.

[0102] The comparator 74 outputs a high signal when the voltage of the capacitor 56 is equal to or greater than the second voltage V2, and outputs a low signal when the voltage of the capacitor 56 is less than the second voltage V2. That is, the comparator 74 is capable of detecting a drop in the voltage of the capacitor 56 due to a short-circuit fault in the first switching element 31a. In other words, the comparator 74 outputs a high signal when the first switching element 31a is healthy, and outputs a low signal when the first switching element 31a is short-circuit faulty.

[0103] The AND circuit 75 outputs a high signal when the output signals of the comparators 73 and 74 are both high. As a result, when the first switching element 31a is operating normally, the output signal of the AND circuit 75 becomes high, and a fault detection signal that becomes high when no fault is detected can be generated.

[0104] The AND circuit 75 outputs a low signal when at least one of the output signals from the comparators 73 and 74 is low. As a result, when a short-circuit fault or an open-circuit fault occurs in the first switching element 31a, the output signal from the AND circuit 75 becomes low, and a fault detection signal that becomes low when a fault is detected can be generated.

[0105] The first voltage V1 is, in other words, the upper limit of the voltage of the capacitor 56. The second voltage V2 is, in other words, the lower limit of the voltage of the capacitor 56. The monitoring circuit 36a (the plurality of monitoring circuits 36a to 36d) has a capacitor 56 that is provided in parallel with the first switching element 31a so that when the first switching element 31a is in the OFF state, it is charged based on the voltage at the main terminal on the high potential side of the first switching element 31a, and when the first switching element 31a is in the ON state, it is discharged via the first switching element 31a in the ON state. The monitoring circuit 36a detects a fault in the first switching element 31a when the voltage of the capacitor 56 is equal to or higher than the upper limit or when the voltage of the capacitor 56 is lower than the lower limit.

[0106] In this way, in the monitoring circuit 36a of this example, as in the above embodiment, a fault detection signal can be generated that is high when no fault is detected in the first switching element 31a and is low when a short-circuit fault or open-circuit fault in the first switching element 31a is detected.

[0107] The configuration of the monitoring circuit 36a is not limited to the above, and may be any configuration that can appropriately detect a failure of the first switching elements 31a by monitoring whether or not there is a periodic change in the state of voltage application between a pair of main terminals of the multiple first switching elements 31a.

[0108] FIG. 8 is a block diagram schematically showing a modified example of the switching circuit. 8, in this example, the switching circuit 20 (main circuit unit 12) further includes a plurality of diodes 38. The plurality of diodes 38 connect the output terminals of the plurality of monitoring circuits 36a to 36d in a diode chain.

[0109] In this example, the configurations of the multiple monitoring circuits 36a to 36d are substantially the same as the configuration of the monitoring circuit 36a shown in Fig. 4, so detailed description will be omitted. However, in the monitoring circuits 36a to 36d of this example, an open-collector or open-drain comparator is used as the comparator 58.

[0110] The open-collector or open-drain comparator 58 includes, for example, a resistive element and a switching element (both not shown). The resistive element is connected to the output terminal of the comparator 58 and sets a high voltage at the output terminal. The resistive element may also be called, for example, a pull-up resistor. The switching element is connected to the output terminal of the comparator 58. The switching element is, for example, a transistor or an FET.

[0111] The open-collector or open-drain comparator 58 outputs a low signal by turning on the switching element and electrically connecting the output terminal of the comparator 58 to the low-potential-side main terminals of the first switching elements 31a to 31d. The open-collector or open-drain comparator 58 outputs a high signal by turning off the switching element and outputting a voltage set via a resistive element to the output terminal of the comparator 58.

[0112] As described above, in the multiple monitoring circuits 36a to 36d connected in a diode chain via multiple diodes 38, when each of the multiple first switching elements 31a to 31d is healthy, the voltage at the output terminal (output terminal of the comparator 58) of the lowest monitoring circuit 36d becomes high, and when a failure is detected in any of the multiple first switching elements 31a to 31d, the voltage at the output terminal of the lowest monitoring circuit 36d becomes low.

[0113] As a result, the multiple monitoring circuits 36a-36d connected in a diode chain via the multiple diodes 38 output to the control circuit 14 one fault detection signal that is high when each of the multiple first switching elements 31a-31d is healthy and that is low when a fault is detected in any of the multiple first switching elements 31a-31d. In other words, the multiple monitoring circuits 36a-36d output to the control circuit 14 one fault detection signal that has two states: one indicating that each of the multiple first switching elements 31a-31d is healthy and one indicating that a fault has been detected in any of the multiple first switching elements 31a-31d.

[0114] The control circuit 14 is connected to, for example, the lowest-stage monitoring circuit 36d among the plurality of first switching elements 31a to 31d. As a result, one fault detection signal output from the plurality of monitoring circuits 36a to 36d is input to the control circuit 14. However, the method of inputting the fault detection signal to the control circuit 14 is not limited to the above, and any method that can appropriately input the fault detection signal to the control circuit 14 may be used.

[0115] In this example, the control circuit 14, for example, omits the AND circuit 40, and inputs one fault detection signal input from the plurality of first switching elements 31a to 31d to one input terminal of the AND circuit 42. The AND circuit 42 calculates the logical AND of the fault detection signal and the first control signal, and inputs the output signal after the calculation to the switching circuit 20 as the first control signal.

[0116] As a result, similar to the above embodiment, when a failure is not detected in any of the plurality of first switching elements 31a-31d, the first control signal input to the AND circuit 42 is input as is to the switching circuit 20. Then, when a failure is detected in any of the plurality of first switching elements 31a-31d, the first control signal input to the switching circuit 20 remains in a low state that sets each of the first switching elements 31a-31d to an off state, regardless of the high / low switching state of the first control signal input to the AND circuit 42. Therefore, in this example as well, when a failure is detected in any of the plurality of first switching elements 31a-31d, the switching operation of the plurality of first switching elements 31a-31d can be stopped and the plurality of first switching elements 31a-31d can be set to an off state.

[0117] In this way, the switching circuit 20 may be configured such that the output terminals of the plurality of monitoring circuits 36a to 36d are connected in a diode chain. In this case, the form of communication between the switching circuit 20 and the control circuit 14 can be simplified compared to, for example, a case in which a plurality of fault detection signals corresponding to the plurality of monitoring circuits 36a to 36d are input to the control circuit 14. For example, the configuration of the power conversion device 10 can be simplified.

[0118] Furthermore, when the plurality of monitoring circuits 36a-36d are connected in multiple stages using a diode chain connection, insulating components such as photocouplers are not required, and the plurality of monitoring circuits 36a-36d can be connected in multiple stages with a simpler configuration. For example, even when the plurality of monitoring circuits 36a-36d are connected in multiple stages, it is possible to prevent the configuration of the switching circuit 20 from becoming complicated and the manufacturing costs from increasing.

[0119] Furthermore, if a single fault detection signal is output to the control circuit 14, for example, the AND circuit 40 can be omitted from the control circuit 14, and the configuration of the control circuit 14 can be simplified.

[0120] FIG. 9 is a block diagram schematically illustrating a modified example of the power conversion device according to the embodiment. As shown in FIG. 9, in a power conversion device 10a, a main circuit unit 12a has a plurality of switching elements 90 and a plurality of rectifying elements 92.

[0121] The multiple switching elements 90 are connected in a three-phase full bridge configuration, with multiple rectifier elements 92 connected in anti-parallel to each of the multiple switching elements 90.

[0122] The main circuit unit 12a performs at least one of conversion from DC power to AC power and conversion from AC power to DC power by switching on a plurality of switching elements 90 connected in series to each arm. The control circuit 14a controls the switching of the plurality of switching elements 90 to control at least one of power conversion from DC power to AC power and conversion from AC power to DC power by the main circuit unit 12a.

[0123] The main circuit section 12a also has a plurality of monitoring circuits that detect faults in the plurality of switching elements 90 by monitoring whether or not there is a periodic change in the state of voltage application between pairs of main terminals of the plurality of switching elements 90.

[0124] The control circuit 14a stops the power conversion operation by the main circuit unit 12a when the plurality of monitoring circuits detect a failure in any of the plurality of switching elements 90. As a result, in the power conversion device 10a, as in the above embodiment, when any of the plurality of switching elements 90 fails, it is possible to prevent other healthy switching elements 90 from failing in a chain reaction.

[0125] In this way, the configuration of the main circuit unit is not limited to a switched capacitor circuit, and may be any configuration that has multiple switching elements connected in series and performs power conversion by switching the multiple switching elements. The power conversion by the main circuit unit may be any conversion that converts input power into another power.

[0126] The present embodiment includes the following aspects. (Appendix 1) a main circuit section having a plurality of switching elements connected in series and converting power by switching the plurality of switching elements; a control circuit that controls the switching of the plurality of switching elements to control the power conversion operation of the main circuit unit; Equipped with The plurality of switching elements each have a pair of main terminals and a control terminal, and are connected in series via the pair of main terminals, the main circuit unit includes a plurality of monitoring circuits that detect failures of the plurality of switching elements by monitoring whether or not there is a periodic change in the state of application of voltage between the pair of main terminals of the plurality of switching elements; The control circuit is a power conversion device that stops the power conversion operation of the main circuit unit when a failure in any of the plurality of switching elements is detected by the plurality of monitoring circuits.

[0127] (Appendix 2) The plurality of monitoring circuits include: a capacitor provided in parallel with the switching element; a power supply circuit that charges the capacitor; and When the switching element is in a normal state, the capacitor repeatedly charges and discharges in response to switching of the switching element, thereby keeping the voltage below a predetermined voltage, and when the switching element is faulty, the capacitor is charged by the power supply circuit in response to stopping of switching of the switching element, thereby keeping the voltage above the predetermined voltage; 2. The power conversion device according to claim 1, wherein the plurality of monitoring circuits detect a failure of the switching element when the voltage of the capacitor is equal to or higher than the predetermined voltage.

[0128] (Appendix 3) The power conversion device according to claim 1, wherein the plurality of monitoring circuits have capacitors arranged in parallel with the switching elements so as to be charged based on the voltage of the main terminal on the high potential side of the switching elements when the switching elements are in an off state, and to be discharged via the switching elements in an on state when the switching elements are in an on state, and detect a failure of the switching elements when the voltage of the capacitor is equal to or higher than an upper limit value and when the voltage of the capacitor is lower than a lower limit value.

[0129] (Appendix 4) the main circuit unit further includes a plurality of diodes that connect the output terminals of the plurality of monitoring circuits in a diode chain; The power conversion device according to any one of appendices 1 to 3, wherein the plurality of monitoring circuits output to the control circuit one fault detection signal having a state indicating that each of the plurality of switching elements is healthy and a state indicating that a fault has been detected in any of the plurality of switching elements.

[0130] (Appendix 5) The main circuit section includes: a switching circuit having a pair of input terminals, a pair of output terminals, and a plurality of storage elements, and switching between a first state in which the plurality of storage elements are connected in series between the pair of input terminals and a second state in which each of the plurality of storage elements is connected in parallel to the pair of output terminals; a connection circuit that connects the switching circuit to a DC power source and switches between a supply state in which DC power from the DC power source is supplied between the pair of input terminals of the switching circuit and a stop state in which supply of DC power from the DC power source to the pair of input terminals is stopped; and the plurality of storage elements are connected in series between one of the pair of input terminals and one of the pair of output terminals; the plurality of switching elements are provided in the switching circuit and connected in parallel to the plurality of storage elements, thereby being connected in series between the one of the pair of input terminals and the one of the pair of output terminals; the switching circuit switches between the first state and the second state by switching the plurality of switching elements; The power conversion device according to any one of appendices 1 to 4, wherein the control circuit controls the switching of the plurality of switching elements to control the switching of the switching circuit between the first state and the second state, and controls the switching of the connection circuit between the supply state and the stop state.

[0131] 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. [Explanation of symbols]

[0132] DESCRIPTION OF SYMBOLS 2...DC power supply, 10, 10a...power conversion device, 12, 12a...main circuit section, 14, 14a...control circuit, 20...switching circuit, 20a, 20b...input terminal, 20c, 20d...output terminal, 22...connection circuit, 22a...second switching element, 30a to 30e...storage element, 31a to 31d...first switching element, 32a to 32d...rectifier element, 33a to 33d...rectifier element, 34a to 34d...rectifier element, 35a to 35d...drive circuit, 36a to 36d...monitoring circuit, 38...diode, 40, 42...AND circuit, 50, 51...resistor element, 52...capacitor, 53, 54...diode, 55...zener diode, 56...capacitor, 57...resistor element 58...Comparator, 61...First power supply circuit, 62...Second power supply circuit, 70, 71...Resistance element, 72...Capacitor, 73, 74...Comparator, 75...AND circuit, 81...First power supply circuit, 82...Second power supply circuit, 90...Switching element, 92...Rectifier element

Claims

1. a main circuit section having a plurality of switching elements connected in series and converting power by switching the plurality of switching elements; a control circuit that controls the switching of the plurality of switching elements to control the power conversion operation of the main circuit unit; Equipped with The plurality of switching elements each have a pair of main terminals and a control terminal, and are connected in series via the pair of main terminals, the main circuit unit includes a plurality of monitoring circuits that detect failures of the plurality of switching elements by monitoring whether or not there is a periodic change in the state of application of voltage between the pair of main terminals of the plurality of switching elements; The control circuit is a power conversion device that stops the power conversion operation of the main circuit unit when a failure in any of the plurality of switching elements is detected by the plurality of monitoring circuits.

2. The plurality of monitoring circuits include: a capacitor provided in parallel with the switching element; a power supply circuit that charges the capacitor; and When the switching element is in a normal state, the capacitor repeatedly charges and discharges in response to switching of the switching element, thereby keeping the voltage below a predetermined voltage, and when the switching element is faulty, the capacitor is charged by the power supply circuit in response to stopping of switching of the switching element, thereby keeping the voltage above the predetermined voltage; 2. The power conversion device according to claim 1, wherein the plurality of monitoring circuits detect a failure of the switching element when the voltage of the capacitor is equal to or higher than the predetermined voltage.

3. 2. The power conversion device according to claim 1, wherein the plurality of monitoring circuits have capacitors arranged in parallel with the switching elements so as to be charged based on the voltage of the main terminals on the high potential side of the switching elements when the switching elements are in an off state, and to be discharged via the switching elements in an on state when the switching elements are in an on state, and detect a failure of the switching elements when the voltage of the capacitor is equal to or higher than an upper limit value and when the voltage of the capacitor is lower than a lower limit value.

4. the main circuit unit further includes a plurality of diodes that connect the output terminals of the plurality of monitoring circuits in a diode chain; 2. The power conversion device according to claim 1, wherein the plurality of monitoring circuits output to the control circuit a single fault detection signal having a state indicating that each of the plurality of switching elements is healthy and a state indicating that a fault has been detected in any of the plurality of switching elements.

5. The main circuit section includes: a switching circuit having a pair of input terminals, a pair of output terminals, and a plurality of storage elements, and switching between a first state in which the plurality of storage elements are connected in series between the pair of input terminals and a second state in which each of the plurality of storage elements is connected in parallel to the pair of output terminals; a connection circuit that connects the switching circuit to a DC power source and switches between a supply state in which DC power from the DC power source is supplied between the pair of input terminals of the switching circuit and a stop state in which supply of DC power from the DC power source to the pair of input terminals is stopped; and the plurality of storage elements are connected in series between one of the pair of input terminals and one of the pair of output terminals; the plurality of switching elements are provided in the switching circuit and connected in parallel to the plurality of storage elements, thereby being connected in series between the one of the pair of input terminals and the one of the pair of output terminals; the switching circuit switches between the first state and the second state by switching the plurality of switching elements; 2. The power conversion device according to claim 1, wherein the control circuit controls switching of the plurality of switching elements to control switching of the switching circuit between the first state and the second state and to control switching of the connection circuit between the supply state and the stop state.

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