CN106469980B - DC-DC converter - Google Patents

Abstract

The invention provides a DC-DC conversion device, which can restrain the continuous rise of the capacitor voltage when the short-circuit fault occurs in the switching element, and can safely use the switching element or the capacitor with low voltage resistance. The method comprises the following steps: a series circuit of switching elements (5, 6); a series circuit of capacitors (8, 10); diodes (7, 9) connected between respective ends of the two series circuits; a series circuit composed of a DC power supply (1), a circuit breaker (2) and reactors (3, 4); and a control circuit (20) that boosts the voltage of the DC power supply (1) by a chopping operation and outputs the boosted voltage from both ends of the capacitor series circuit, wherein the control circuit (20) turns on the switching element (5) before the circuit breaker (2) is turned off when it is estimated that the switching element (6) has a short-circuit fault, and turns on the switching element (6) before the circuit breaker (2) is turned off when it is estimated that the switching element (5) has a short-circuit fault, thereby suppressing an overvoltage due to the short-circuit fault.

Description

DC-DC converter

technical field

The present invention relates to a DC-DC converter with a boost chopper circuit, and in particular, to a DC-DC converter with a protection function when a semiconductor switching element has a short-circuit fault.

Background technique

FIG. 17 shows the boost chopper circuit described in Patent Document 1. As shown in FIG.

In Fig. 17, IN1 and IN2 are positive and negative input terminals to which a DC power supply (not shown) is connected, OUT1 and OUT2 are positive and negative output terminals, L1 is a reactor, Q1 and Q2 are transistors, D1 and D2 are diodes, and C1 , C2 is a capacitor. In addition to the reactor L1, other reactors may be inserted between the negative side input terminal IN2 and the emitter of the transistor Q2.

Next, an outline of the operation of the conventional technique will be described.

By turning on both the transistors Q1 and Q2, a current flows from the DC power source along a path from the input terminal IN1→reactor L1→transistors Q1, Q2→input terminal IN2, and energy is stored in the reactor L1. Next, by turning off the transistor Q2 while turning on the transistor Q1, the stored energy of the DC power supply and the reactor L1 is supplied along the path of the transistor Q1→capacitor C2→diode D2→input terminal IN2 to charge the capacitor C2.

Next, by turning off the transistor Q1 and turning on the transistor Q2, a current flows along the path of the input terminal IN1→reactor L1→diode D1→capacitor C1→transistor Q2→input terminal IN2, and the capacitor C1 is charged. When the transistor Q2 is turned off in this state, the stored energy of the DC power supply and the reactor L1 is supplied along the path of the diode D1→capacitor C1→capacitor C2→diode D2 to charge the capacitors C1 and C2.

By repeating the above operation, the voltage between the output terminals OUT1 and OUT2 is boosted to a voltage higher than the DC power supply voltage. The output voltage of the boost chopper circuit can obtain three levels, which are the voltage of the capacitor C1, the voltage of the capacitor C2, and the voltage sum of the capacitors C1 and C2, so it is also called a three-level boost chopper circuit.

When a DC-DC converter is constructed using this boost chopper circuit, although not shown in the figure, a circuit breaker for disconnecting the DC power supply in the event of a circuit failure, and a circuit breaker for controlling the transistors Q1 and Q2 and the circuit breaker are usually provided separately. control circuit of the device, etc.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2013-38921 (paragraphs [0021] to [0028], FIG. 1 , FIG. 3 , etc.)

SUMMARY OF THE INVENTION

technical problem to be solved

In the three-level boost chopper circuit shown in Figure 17, when one of the transistors Q1 and Q2 is short-circuited, the circuit structure that should have alternately boosted the capacitors C1 and C2 will be changed to only one capacitor. Boost circuit structure. As a result, it sometimes results in an excess boost of a capacitor whose voltage exceeds its rated value.

In a power conversion device such as a DC-DC converter, when an abnormal voltage is detected, all semiconductor switching elements (hereinafter also simply referred to as switching elements) are turned off to stop the power conversion operation. At the same time, circuit breakers are often used to isolate incoming power from the device for protection.

However, in the failure mode in which one of the transistors Q1 and Q2 is short-circuited in FIG. 17, even if one transistor is turned off, the other transistor is still in a short-circuited state. Therefore, in the period before the device is actually disconnected from the DC power supply by the circuit breaker, a path for charging any one of the capacitors with the energy stored in the reactor L1 remains. In this way, the capacitor voltage will further rise.

The three-level boost chopper circuit has the advantage that the output voltage is shared by the two capacitors C1 and C2 connected in series, and only about half of the output voltage is applied to one capacitor. Therefore, switching elements such as transistors Q1 and Q2 are generally used with low withstand voltage. In addition, capacitors C1 and C2 are generally also used with low withstand voltage.

However, when the above-mentioned short-circuit failure mode occurs, the rise of the capacitor voltage may cause the low withstand voltage switching element or the low withstand voltage capacitor to be damaged.

Therefore, the problem to be solved by the present invention is to provide a DC-DC power conversion device which suppresses the increase in capacitor voltage when a switching element has a short-circuit fault, and which can safely use a switching element with a low withstand voltage or a capacitor with a low withstand voltage.

Technical solutions for solving technical problems

In order to solve the above-mentioned problems, the invention described in claim 1 includes: a switching element series circuit in which the first and second switching elements are connected in series and connected to both ends of the DC power supply; a reactor connected to the reactor Between the DC power supply and the switching element series circuit; a capacitor series circuit, which is connected in series with first and second capacitors; first and second diodes, the first and second diodes tubes are respectively connected between two ends of the switching element series circuit and both ends of the capacitor series circuit; and

a control circuit, the control circuit performs on/off control of the first and second switching elements,

The connection points of the first and second switching elements are connected to the connection points of the first and second capacitors,

The DC-DC converter device boosts the voltage of the DC power supply and outputs it from both ends of the capacitor series circuit by performing a chopping operation of turning on/off the first and second switching elements. is characterized by,

When it is concluded that at least one of the first and second switching elements has a short-circuit fault, the control circuit sends a turn-on instruction to the other switching element or both switching elements.

The invention according to claim 2 is the DC-DC converter device according to claim 1, wherein:

A circuit breaker is further included between the DC power supply and the series circuit of the switching element,

The control circuit sends a conduction command to the switching element and an opening command to the circuit breaker, and the circuit breaker opens after the switching element is turned on.

The invention according to claim 3 is the DC-DC converter device according to claim 1, wherein:

comprising first and second voltage detectors, the first and second voltage detectors respectively detect the voltages of the first and second capacitors,

The control circuit infers that the second switching element has a short-circuit failure when determining that an overvoltage is applied to the first capacitor, and infers that the second switching element has an overvoltage applied to the second capacitor. A switching element has a short circuit failure.

The invention according to claim 4 is the DC-DC converter according to claim 1, wherein:

comprising first and second voltage detectors, the first and second voltage detectors respectively detect the voltages of the first and second capacitors,

When the control circuit determines that the voltage of the first capacitor is higher than the voltage of the second capacitor and the voltage values of the two capacitors deviate by a predetermined value or more, infer that the second switching element has a short-circuit failure, and When it is determined that the voltage of the second capacitor is higher than the voltage of the first capacitor and the voltage values of the two capacitors vary by a predetermined value or more, it is estimated that the first switching element has a short-circuit failure.

The invention according to claim 5 is the DC-DC converter according to claim 1, wherein:

comprising first and second current detectors, the first and second current detectors respectively detect the currents of the first and second switching elements,

The control circuit infers that a short-circuit failure has occurred in the first switching element when determining that an overcurrent is flowing in the first switching element, and infers that an overcurrent is flowing in the second switching element. The second switching element has a short-circuit fault.

The invention according to claim 6 is the DC-DC converter device according to claim 1, wherein:

comprising first and second voltage detectors, the first and second voltage detectors respectively detect the voltages of the first and second switching elements,

The control circuit infers that a short-circuit failure has occurred in the first switching element when it is determined that the voltage across the first switching element is greater than or equal to a predetermined value or less than a predetermined value during a period in which an on command is issued to the first switching element and when it is determined that the voltage across the second switching element is greater than or equal to a predetermined value or less than a predetermined value during a period in which an on command is issued to the second switching element, it is estimated that the second switching element has a short-circuit failure.

The invention according to claim 7 is the DC-DC converter according to claim 1, wherein:

comprising first and second voltage detectors, the first and second voltage detectors respectively detect the voltages of the first and second switching elements,

When the control circuit determines that the voltage across the first switching element is equal to or less than a predetermined value during a period in which an off command is issued to the first switching element, it is estimated that a short-circuit failure has occurred in the first switching element, and the control circuit determines that the first switching element has a short-circuit failure. When the voltage across both ends of the second switching element is equal to or less than a predetermined value during a period in which an off command is issued to the second switching element, it is estimated that a short-circuit failure has occurred in the second switching element.

The invention according to claim 8 is the DC-DC converter according to claim 1, wherein:

comprising first and second current detectors, the first and second current detectors respectively detect the currents of the first and second diodes,

When the control circuit determines that an overcurrent flows in the first diode, it infers that the second switching element has a short-circuit failure, and when it determines that an overcurrent flows in the second diode, It is inferred that the first switching element has a short-circuit failure.

The invention according to claim 9 is the DC-DC converter device according to claim 1, wherein:

comprising first and second voltage detectors, the first and second voltage detectors respectively detect the voltages of the first and second diodes,

When the control circuit determines that the voltage across the first diode is equal to or greater than a predetermined value during a period in which an off command is issued to the first switching element, it is estimated that a short-circuit failure has occurred in the second switching element, and When it is determined that the voltage across the second diode is equal to or greater than a predetermined value during the period in which the off command is issued to the second switching element, it is estimated that a short-circuit failure has occurred in the first switching element.

The invention according to claim 10 is the DC-DC converter according to claim 1, wherein:

including a current detector that detects the current of the reactor,

The control circuit infers that at least one of the first and second switching elements has a short-circuit failure when it is determined that an overcurrent flows in the reactor.

The invention according to claim 11 is the DC-DC converter according to claim 1, wherein:

including a voltage detector that detects the voltage of the reactor,

When the control circuit determines that the voltage across the reactor is equal to or greater than a predetermined value, it is estimated that at least one of the first and second switching elements has a short-circuit failure.

The invention according to claim 12 is the DC-DC converter according to claim 1, wherein:

including a current detector that detects a current in a wiring that connects a connection point between the first and second switching elements and a connection point between the first and second capacitors,

The control circuit infers that at least one of the first and second switching elements has a short-circuit failure when it is determined that an overcurrent flows in the wiring.

The invention according to claim 13 is the DC-DC converter according to claim 1, wherein:

When determining that the control electrode of the first switching element is always short-circuited or the potential of the control electrode is always high, the control circuit infers that the first switching element has a short-circuit failure, and determines that the second switch is short-circuited. When the control electrode of the element is always short-circuited or the potential of the control electrode is always at a high level, it is inferred that the second switching element has a short-circuit fault.

The invention according to claim 14 is the DC-DC converter according to claim 1, wherein:

When determining that the current flowing in the control electrode of the first switching element is an overcurrent or always flowing, the control circuit infers that a short-circuit failure has occurred in the first switching element, and determines that the second switching element has a short-circuit fault. When the current flowing in the control electrode is an overcurrent or always flows, it is presumed that the second switching element has a short-circuit failure.

The invention according to claim 15 is the DC-DC converter according to claim 1, wherein:

comprising first and second current detectors, the first and second current detectors respectively detect the currents of the first and second capacitors,

The control circuit infers that the second switching element has a short-circuit failure when determining that an overcurrent flows in the first capacitor, and infers that the second switching element has an overcurrent flowing in the second capacitor. A switching element has a short circuit failure.

The invention according to claim 16 is the DC-DC converter according to claim 1, wherein:

The control circuit generates an alarm upon inferring a short circuit failure of the first or second switching element.

Invention effect

In the present invention, when a short-circuit fault occurs in one switching element, the other intact switching element can be fixed in a conducting state before the circuit breaker is opened, and the current path flowing in the capacitor can be eliminated. In this way, it is possible to suppress a continuous rise of the capacitor voltage, and even when a low withstand voltage switching element or a low withstand voltage capacitor is used, damage to the switching element or the capacitor can be prevented beforehand.

Description of drawings

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the first mode of the first embodiment of the present invention.

3 is an explanatory diagram of the operation of the second mode of the first embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the third mode of the first embodiment of the present invention.

FIG. 5 is an operation explanatory diagram of the fourth mode of the first embodiment of the present invention.

6 is an explanatory diagram of an operation when a short-circuit fault occurs according to the first embodiment of the present invention.

FIG. 7 is a diagram illustrating a second embodiment of the present invention.

FIG. 8 is a diagram illustrating a third embodiment of the present invention.

FIG. 9 is a diagram for explaining a fourth embodiment of the present invention.

FIG. 10 is a diagram illustrating a fifth embodiment of the present invention.

FIG. 11 is a diagram illustrating a sixth embodiment of the present invention.

FIG. 12 is a diagram illustrating a seventh embodiment of the present invention.

FIG. 13 is a diagram illustrating an eighth embodiment of the present invention.

FIG. 14 is a diagram illustrating a ninth embodiment of the present invention.

FIG. 15 is a diagram illustrating a tenth embodiment of the present invention.

FIG. 16 is a diagram illustrating an eleventh embodiment of the present invention.

FIG. 17 is a circuit diagram of the prior art described in Patent Document 1. FIG.

Detailed ways

Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of a DC-DC converter according to a first embodiment, and corresponds to claims 1 to 4 . In FIG. 1 , the positive pole of the DC power supply 1 is connected to one end of the circuit breaker 2 through the input terminal IN1 , and the other end of the circuit breaker 2 is connected to one end of the reactor 3 . The other end of the reactor 3 is connected to the connection point of the switching element 5 and the diode 7 .

On the other hand, the negative electrode of the DC power supply 1 is connected to one end of the reactor 4 through the input terminal IN2 , and the other end of the reactor 4 is connected to the connection point of the switching element 6 and the diode 9 .

The switching elements 5 and 6 are connected in series, the capacitor 8 is connected between the series connection point and the cathode of the diode 7 , and the capacitor 10 is connected between the series connection point and the anode of the diode 9 . That is, the capacitors 8 and 10 are also connected in series, and both ends of the capacitor series circuit are connected to the positive and negative output terminals OUT1 and OUT2, respectively.

Further, voltage detectors 11 and 12 are connected to both ends of the capacitors 8 and 10 , respectively, and output signals (voltage detection values) thereof are input to the control circuit 20 . The control circuit 20 is configured to generate on/off signals to the switching elements 5 and 6 based on the voltage detection values of the capacitors 8 and 10, and to generate an opening and closing command (opening (opening) command/ turn-on command).

In the above structure, the switching elements 5 and 6 correspond to the first and second switching elements in the claims, respectively, the diodes 7 and 9 correspond to the first and second diodes, respectively, and the capacitors 8 and 10 correspond to the first and second diodes, respectively. Two capacitors, the voltage detectors 11 and 12 correspond to the first and second voltage detectors, respectively.

In FIG. 1 , although IGBTs are used for the switching elements 5 and 6 , it is of course possible to use power transistors or FETs. In particular, elements using wide-bandgap semiconductors such as SiC (Silicon Carbide) and GaN (Gallium Nitride) can be used, and it is expected that a compact three-level boost chopper circuit can be constructed with higher efficiency by using these elements. In addition, any one of the reactors 3 and 4 may be provided at least.

In addition, if the circuit breaker 2 , the voltage detectors 11 and 12 , the control circuit 20 , and the like are removed from the circuit of FIG. 1 , the circuit is substantially the same as the three-level boost chopper circuit of FIG. 17 .

Next, the operation of this embodiment will be described with reference to FIGS. 2 to 6 .

The DC-DC converter of FIG. 1 controls on/off of the switching elements 5 and 6 by the control circuit 20, and sequentially executes the same operation modes as those of the prior art in FIG. 17 (the first to fourth modes described below) , so that the capacitors 8 and 10 are boosted.

(1) The first mode (Fig. 2)

This is a state in which both the switching elements 5 and 6 are turned on. In this state, the current flows along the path of DC power source 1→breaker 2→reactor 3→switching element 5→switching element 6→reactor 4→DC power source 1, and energy is stored in the reactors 3 and 4.

(2) The second mode (Fig. 3)

This is a state in which the switching element 5 is continuously turned on and the switching element 6 is turned off. In this state, the current flows along the path of DC power source 1→breaker 2→reactor 3→switching element 5→capacitor 10→diode 9→reactor 4→DC power source 1, and the energy stored in the reactors 3 and 4 is utilized. Capacitor 10 is charged.

(3) The third mode (Fig. 4)

In contrast to the second mode, this is a state in which the switching element 5 is turned off and the switching element 6 is turned on. In this state, the current flows along the path of DC power source 1→breaker 2→reactor 3→diode 7→capacitor 8→switching element 6→reactor 4→DC power source 1, and the energy stored in the reactors 3 and 4 is utilized. Charge capacitor 8.

(4) Fourth mode (Figure 5)

This is a state in which both the switching elements 5 and 6 are turned off. In this state, the current flows along the path of DC power source 1→breaker 2→reactor 3→diode 7→capacitor 8→capacitor 10→diode 9→reactor 4→DC power source 1, and is stored in the DC power source 1 and the reactor. The energy in 3,4 charges capacitors 8,10.

In this way, the capacitors 8 and 10 are boosted while being repeatedly charged, and are kept stable at a constant voltage according to the ON/OFF ratio of the switching elements 5 and 6 .

Next, an operation when a short-circuit fault occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described.

When the switching element 6 is short-circuited and the other switching element 5 is intact, the current-carrying operation is alternately and repeatedly performed along the paths shown in Figs.

That is, in FIG. 6( a ) when the switching element 5 is in the ON state, the current flows along the lines of DC power source 1 → circuit breaker 2 → reactor 3 → switching element 5 → switching element 6 (short-circuit state) → reactor 4 → DC power source 1 The path flows through, and the energy is stored in the reactors 3 and 4.

In addition, in FIG. 6( b ) with the switching element 5 in the OFF state, the stored energy of the reactors 3 and 4 and the power of the DC power supply 1 are used, and the current flows along the DC power supply 1 → the circuit breaker 2 → the reactor 3 → the diode 7 → The path of capacitor 8→switching element 6 (short-circuited state)→reactor 4→DC power supply 1 flows.

When the above-described operations of FIGS. 6( a ) and ( b ) are repeated, only the step-up chopper operation for the capacitor 8 is performed. Therefore, when the switching elements 5 and 6 are intact, the energy of the reactors 3 and 4 shared by the two capacitors 8 and 10 using the normal operations of the first to fourth modes is all supplied to one capacitor 8 . As a result, the voltage of the capacitor 8 rises higher than the normal value.

The voltage of the capacitor 8 is detected by the voltage detector 11 , and the detected value of the voltage is input to the control circuit 20 , so that the control circuit 20 determines that an overvoltage is applied to the capacitor 8 .

Further, the voltages of the capacitors 8 and 10 are detected by the voltage detectors 11 and 12 , and these voltage detection values are input to the control circuit 20 . The control circuit 20 determines that the voltage of the capacitor 8 is higher than the voltage of the capacitor 10 and that the voltage values of the two capacitors have a deviation of a predetermined value or more.

When the control circuit 20 determines that an overvoltage is applied to the capacitor 8, or determines that the voltage of the capacitor 8 is higher than the voltage of the capacitor 10 and the voltage values of the capacitors 8 and 10 vary by a predetermined value or more, it is estimated that the switching element 6 has occurred. Short circuit fault.

When it is estimated that the switching element 6 has a short-circuit fault, the control circuit 20 outputs a signal for opening the circuit breaker 2 as a protective action. However, there is a slight delay before the circuit breaker 2 actually opens, and the boosting action of the capacitor 8 may continue. Therefore, the control circuit 20 turns on the switching element 5 at the point of time when it is estimated that the switching element 6 has a short-circuit fault, in other words, before the circuit breaker 2 is actually opened. In this way, until the DC power supply 1 is completely disconnected from the device, the operation of the device is fixed in the mode shown in FIG. 6( a ), and the voltage of the capacitor 8 can be prevented from rising continuously.

The above example is an example when the switching element 6 has a short-circuit fault. When the switching element 5 has a short-circuit fault, the switching element 6 is repeatedly turned on and off, so that the capacitor 10 becomes an overvoltage. In addition, since the switching element 6 repeats the on and off operations, the voltage of the capacitor 10 is higher than the voltage of the capacitor 8 and the voltage values of the two capacitors vary by a predetermined value or more.

Therefore, based on the voltage detection values of the voltage detectors 11 and 12, the control circuit 20 turns on the switching element 6 before the circuit breaker 2 is actually opened, thereby preventing the voltage of the capacitor 10 from rising continuously.

The control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6, and the same effect can be achieved in this case.

According to the first embodiment, when the control circuit 20 determines that an overvoltage is applied to the capacitor 8 , it is estimated that the switching element 6 has a short-circuit failure. Similarly, when the control circuit 20 determines that an overvoltage is applied to the capacitor 10 , it is estimated that the switching element 5 has a short-circuit failure.

In addition, the control circuit 20 estimates that the switching element 6 has a short-circuit failure when the voltage of the capacitor 8 is higher than the voltage of the capacitor 10 and the voltage values of the two capacitors 8 and 10 vary by a predetermined value or more. Similarly, when the voltage of the capacitor 10 is higher than the voltage of the capacitor 8 and the voltage values of the two capacitors 8 and 10 vary by a predetermined value or more, the control circuit 20 infers that the switching element 5 is short-circuited.

Therefore, when the control circuit 20 deduces the occurrence of the above-mentioned short-circuit fault, it is preferable to perform a protective operation to open the circuit breaker 2, and at the same time, issue an alarm in an appropriate manner to prompt maintenance and inspection work including replacement of switching elements.

Next, a second embodiment of the present invention corresponding to claim 5 will be described with reference to FIG. 7 .

In the second embodiment, current detectors 13 and 14 are connected in series with the switching elements 5 and 6 , respectively, and the current detection values output by these current detectors 13 and 14 are input to the control circuit 20 . The control circuit 20 is configured to generate ON/OFF signals for the switching elements 5 and 6 based on the current detection values of the switching elements 5 and 6 and to generate an opening and closing command for the circuit breaker 2 .

Here, when a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example), the switching on the first embodiment described with reference to FIGS. 6( a ) and ( b ) is repeated. flow action. As a result, the current flowing to the switching element 6 gradually increases, and an excessive current, ie, an overcurrent, flows as compared with the normal operation.

In the present embodiment, the current flowing in the switching element 6 is detected by the current detector 13 , and the detected current value is input to the control circuit 20 , so that the control circuit 20 determines that an overcurrent is flowing in the switching element 6 . Therefore, when the control circuit 20 determines that an overcurrent flows in the switching element 6, it is estimated that the switching element 6 has a short-circuit failure.

The control circuit 20 , which infers that the switching element 6 has a short-circuit fault, turns on the switching element 5 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 from rising continuously.

The above example is an example when the switching element 6 has a short-circuit fault. When the switching element 5 has a short-circuit fault, the switching element 6 repeatedly conducts on and off operations, so that an overcurrent flows in the switching element 5 .

Therefore, according to the current detection value of the current detector 14, the control circuit 20 turns on the switching element 6 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 10 from rising continuously.

The control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6, and the same effect can be achieved in this case.

Next, a third embodiment of the present invention corresponding to claims 6 and 7 will be described with reference to FIG. 8 .

In the third embodiment, voltage detectors 11 and 12 are connected to both ends of the switching elements 5 and 6 , respectively, and voltage detection values output by these voltage detectors 11 and 12 are input to the control circuit 20 . The control circuit 20 is configured to generate on/off signals for the switching elements 5 and 6 based on voltage detection values of the switching elements 5 and 6 and to generate an opening and closing command for the circuit breaker 2 .

Here, when a short-circuit fault occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example), as an example, the voltage across the switching element 6 is compared with the voltage during the normal ON period. Sometimes too small. This is because the internal resistance of the switching element 6 becomes extremely low as compared with the normal state when the channel serving as the main current path is short-circuited inside the switching element 6 .

In addition, as another form, the voltage between both ends of the switching element 6 may be excessively larger than the voltage during the normal ON period. This is due to the failure of the gate of the switching element 6, and the switching element 6 cannot be transferred to the OFF state. At this time, the current flowing through the switching element 6 gradually increases because the current-carrying operation described with reference to FIGS. 6( a ) and ( b ) is repeated. As a result, in the period in which the gate command issued to the switching element 6 is turned on, the element voltage is excessively larger than that during the conduction period during the normal operation.

In addition, in any of the above-described modes, the switching element 6 cannot be shifted to the normal OFF state while the gate command to the switching element 6 is OFF. Therefore, even if the gate command is turned off, the voltage across the switching element 6 is an excessively small voltage compared with the voltage during the normal off period.

Therefore, in the present embodiment, when the control circuit 20 detects that the gate command of the switching element 6 is turned on, the voltage across both ends of the switching element 6 is too large or too small compared to the voltage in the normal on-period, and it is estimated that The switching element 6 has a short-circuit failure.

Alternatively, when the gate command of the switching element 6 is detected to be OFF, the voltage across both ends of the switching element 6 is too small compared with the voltage during the OFF period in a normal state, and it is estimated that the switching element 6 has a short-circuit failure.

Then, the control circuit 20 which infers the short-circuit failure of the switching element 6 prevents the voltage of the capacitor 8 from rising continuously by turning on the switching element 5 before the circuit breaker 2 is opened.

The above-mentioned example is an example when the switching element 6 has a short-circuit fault, and the same estimation is made also when the switching element 5 has a short-circuit fault. Then, the control circuit 20 that has estimated the short-circuit failure of the switching element 5 prevents the voltage of the capacitor 10 from continuing to rise by turning on the switching element 6 before the circuit breaker 2 is opened.

In addition, the control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6 , and the same effect can be achieved in this case.

Next, a fourth embodiment of the present invention corresponding to claim 8 will be described with reference to FIG. 9 .

In the fourth embodiment, current detectors 13 and 14 are connected in series with the diodes 7 and 9 , respectively, and the current detection values output by these current detectors 13 and 14 are input to the control circuit 20 . The control circuit 20 is configured to generate ON/OFF signals for the switching elements 5 and 6 based on the current detection values of the diodes 7 and 9 , and to generate an opening and closing command for the circuit breaker 2 .

Here, a case in which a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described. At this time, the flow-through operation described with reference to FIGS. 6( a ) and ( b ) as the first embodiment is repeated. As a result, the current flowing to the diode 7 gradually increases, and an excessive current, ie, an overcurrent, flows as compared with the normal operation.

In the present embodiment, the control circuit 20 determines that an overcurrent flows in the diode 7 based on the current detection value of the diode 7 .

When the control circuit 20 determines that an overcurrent flows in the diode 7 , it is estimated that the switching element 6 has a short-circuit failure.

The control circuit 20 , which infers that the switching element 6 has a short-circuit fault, turns on the switching element 5 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 from rising continuously.

When a short-circuit failure occurs in the switching element 5 , the switching element 6 repeats the on and off operations, so that an overcurrent flows through the diode 9 . The control circuit 20 determines that an overcurrent flows in the diode 9 based on the current detection value of the diode 9 .

When the control circuit 20 determines that an overcurrent flows in the diode 9 , it is estimated that the switching element 5 has a short-circuit failure.

The control circuit 20 , which infers that the switching element 5 has a short-circuit fault, turns on the switching element 6 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 10 from rising continuously.

In addition, the control circuit 20 may issue a gate-on command to both of the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6, and the same effect can be achieved in this case.

Next, a fifth embodiment of the present invention corresponding to claim 9 will be described with reference to FIG. 10 .

In the fifth embodiment, voltage detectors 11 and 12 are connected to both ends of the diodes 7 and 9 , respectively, and voltage detection values output by these voltage detectors 11 and 12 are input to the control circuit 20 . The control circuit 20 is configured to generate ON/OFF signals for the switching elements 5 and 6 based on the voltage detection values of the diodes 7 and 9 , and to generate an opening and closing command for the circuit breaker 2 .

Here, a case in which a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described. At this time, the flow-through operation described in the first embodiment using FIGS. 6( a ) and ( b ) is repeated. As a result, the current flowing to the diode 7 gradually increases, and an excessive current, ie, an overcurrent, flows as compared with the normal operation.

Therefore, the voltage of the diode 7 is excessively larger than the voltage during the diode-on period (period during which the gate command to the switching element 5 is turned off) during normal operation. Here, the voltage of the diode 7 depends on the forward current-voltage characteristic.

In the present embodiment, the control circuit 20 determines that there is an overcurrent in the diode 7 when the voltage across the diode 7 is excessively higher than the voltage in the above-mentioned period during the normal period when the gate command of the switching element 5 is detected to be OFF. flow.

When the control circuit 20 determines that an overcurrent flows in the diode 7 , it is estimated that the switching element 6 has a short-circuit failure.

The control circuit 20 , which infers that the switching element 6 has a short-circuit fault, turns on the switching element 5 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 from rising continuously.

When a short-circuit failure occurs in the switching element 5 , the switching element 6 repeats the on and off operations, so that an overcurrent flows through the diode 9 . Therefore, the voltage of the diode 9 is excessively higher than the voltage during the diode-on period (the period during which the gate command to the switching element 6 is turned off) during normal operation.

When the control circuit 20 determines that an overcurrent flows in the diode 9, it is estimated that the switching element 6 has a short-circuit failure. Furthermore, the control circuit 20 prevents the voltage of the capacitor 10 from rising continuously by turning on the switching element 6 before the circuit breaker 2 is opened.

Here, the control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6, and the same effect can be achieved in this case. .

Next, a sixth embodiment of the present invention corresponding to claim 10 will be described with reference to FIG. 11 .

In the sixth embodiment, a current detector 15 is connected in series to the reactor 3 , and a current detection value output by the current detector 15 is input to the control circuit 20 . In the following, the case where the current detector 15 is connected in series to the reactor 3 will be described. However, a current detector may be connected to either or both of the reactors 3 and 4, and the detected current value thereof may be input to the control circuit 20. .

The control circuit 20 is configured to generate on/off signals to the switching elements 5 and 6 based on the current detection value of the reactor 3 and to generate an opening and closing command to the circuit breaker 2 .

Here, a case in which a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described. At this time, the flow-through operation described in the first embodiment using FIGS. 6( a ) and ( b ) is repeated. As a result, the current flowing to the reactor 3 gradually increases, and an excessive current, that is, an overcurrent, flows as compared with the normal operation.

The above example is an example when the switching element 6 has a short-circuit fault. When the switching element 5 has a short-circuit fault, the switching element 6 is repeatedly turned on and off, so that an overcurrent still flows in the reactor 3 .

The control circuit 20 determines that an overcurrent flows in the reactor 3 based on the current detection value of the reactor 3 .

When the control circuit 20 determines that an overcurrent flows in the reactor 3 , it infers that a short-circuit failure has occurred in either one of the switching elements 5 or 6 .

The control circuit 20, which infers that either one of the switching elements 5 or 6 has a short-circuit fault, issues a gate-on command to both the switching elements 5 and 6 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 or 10 from continuing. rise.

Next, a seventh embodiment of the present invention corresponding to claim 11 will be described with reference to FIG. 12 .

In the seventh embodiment, a voltage detector 16 is connected in parallel to the reactor 3 , and a voltage detection value output by the voltage detector 16 is input to the control circuit 20 . In the following, the case where the voltage detector 16 is connected in parallel to the reactor 3 will be described. However, a voltage detector may be connected to either or both of the reactors 3 and 4, and the detected voltage value may be input to the control circuit 20. .

The control circuit 20 is configured to generate on/off signals to the switching elements 5 and 6 based on the voltage detection value of the reactor 3 and to generate an opening and closing command to the circuit breaker 2 .

Here, a case in which a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described. At this time, the flow-through operation described in the first embodiment using FIGS. 6( a ) and ( b ) is repeated. As a result, the current flowing to the reactor 3 gradually increases, and an excessive current flows compared with the normal operation. Therefore, the voltage across the reactor 3 is excessively larger than that during the normal operation. Alternatively, while the gate command issued to the switching element 5 is ON and the gate command issued to the switching element 6 is OFF, the reactor 3 receives the voltage that should have been received by the failed switching element 6 . Therefore, the voltage across the reactor 3 is excessively larger than the value of the period in the normal case.

When a short-circuit failure occurs in the switching element 5, the voltage across the reactor 3 is also excessively higher than the voltage during normal operation, as described above.

Therefore, the control circuit 20 determines that an overcurrent is flowing in the reactor 3 based on the voltage detection values at both ends of the reactor 3 .

When the control circuit 20 determines that an overcurrent flows in the reactor 3 , it infers that a short-circuit failure has occurred in either one of the switching elements 5 or 6 .

The control circuit 20 , which infers that either one of the switching elements 5 or 6 has a short-circuit fault, can prevent the voltage of the capacitor 8 or 10 by issuing a gate-on command to both the switching elements 5 and 6 before the circuit breaker 2 is opened. continuously rising.

Next, an eighth embodiment of the present invention corresponding to claim 12 will be described with reference to FIG. 13 .

In the eighth embodiment, the current detector 17 is connected to a wiring (hereinafter referred to as an intermediate wiring) connecting the connection point between the switching elements 5 and 6 to the connection point between the capacitors 8 and 10, and the The current detection value output by the current detector 17 is input to the control circuit 20 . The control circuit 20 is configured to generate ON/OFF signals for the switching elements 5 and 6 based on the current detection value of the intermediate wiring, and to generate an opening/closing command for the circuit breaker 2 .

Here, a case in which a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described. At this time, the flow-through operation described in the first embodiment using FIGS. 6( a ) and ( b ) is repeated. As a result, the current flowing to the intermediate wiring gradually increases, and an excessive current, that is, an overcurrent, flows as compared with the normal operation.

The above example is an example when the switching element 6 has a short-circuit fault. When the switching element 5 has a short-circuit fault, the switching element 6 repeatedly conducts on and off operations, so that an overcurrent still flows in the intermediate wiring.

The control circuit 20 determines that an overcurrent flows in the intermediate wiring based on the current detection value of the current detector 17 .

Then, when the control circuit 20 determines that an overcurrent flows in the intermediate wiring, it is estimated that a short-circuit failure has occurred in either one of the switching elements 5 or 6 .

The control circuit 20, which infers that either one of the switching elements 5 or 6 has a short-circuit fault, issues a gate-on command to both the switching elements 5 and 6 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 or 10 from continuing. rise.

Next, a ninth embodiment of the present invention corresponding to claim 13 will be described with reference to FIG. 14 .

In the present embodiment, voltage detectors are connected between the gates serving as control electrodes of the switching elements 5 and 6 (base regions serving as control electrodes in bipolar transistors. The gates will be described below) and the emitters, respectively. 11 and 12, the voltage detection value thereof is input to the control circuit 20. In addition, if the gate voltage can be successfully detected, the voltage detectors 11 and 12 may be connected between the gates and collectors of the switching elements 5 and 6, respectively.

The control circuit 20 is configured to generate on/off signals for the switching elements 5 and 6 based on voltage detection values of the gates of the switching elements 5 and 6 and to generate an opening and closing command for the circuit breaker 2 .

Here, the case where the gate of any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) is always short-circuited or the gate potential is always at a high level will be described. At this time, in the present embodiment, the control circuit 20 determines from the gate voltage detection value that the gate of the switching element 6 is always short-circuited or the gate potential is always high.

When the control circuit 20 determines that the gate of the switching element 6 is always short-circuited or the gate potential is always high, it is estimated that the switching element 6 is short-circuited.

The control circuit 20 , which has estimated that the switching element 6 has a short-circuit fault, turns on the switching element 5 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 from rising continuously.

In addition, when the control circuit 20 determines that the gate of the switching element 5 is always short-circuited or the gate potential is always high, it is estimated that the switching element 5 has a short-circuit failure.

The control circuit 20 , which has estimated that the switching element 5 has a short-circuit fault, turns on the switching element 6 based on the gate voltage detection value before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 10 from rising continuously.

In addition, the control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6 , and the same effect can be achieved in this case.

Next, a tenth embodiment of the present invention corresponding to claim 14 will be described with reference to FIG. 15 .

In the present embodiment, current detectors 13 and 14 are connected to gates of the switching elements 5 and 6 serving as control electrodes (base regions serving as control electrodes in bipolar transistors. The gates will be described below), respectively. The current detection value is input to the control circuit 20 .

The control circuit 20 is configured to generate on/off signals for the switching elements 5 and 6 based on current detection values of the gates of the switching elements 5 and 6 and to generate an opening and closing command for the circuit breaker 2 .

Here, the case where the gate current of any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) is an overcurrent or an always-on current will be described. At this time, in the present embodiment, the control circuit 20 determines whether the gate current of the switching element 6 is an overcurrent or an always-on current based on the gate current detection value.

When the control circuit 20 determines that the gate current of the switching element 6 is an overcurrent or is always flowing, it is estimated that the switching element 6 has a short-circuit failure.

The control circuit 20 , which infers that the switching element 6 has a short-circuit fault, turns on the switching element 5 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 from rising continuously.

In addition, when the control circuit 20 determines that the gate current of the switching element 5 is an overcurrent or is always flowing, it is estimated that a short-circuit failure has occurred in the switching element 5 .

The control circuit 20 , which infers that the switching element 5 has a short-circuit fault, turns on the switching element 6 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 10 from rising continuously.

In addition, the control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6 , and the same effect can be achieved in this case.

Next, an eleventh embodiment of the present invention corresponding to claim 15 will be described with reference to FIG. 16 .

In the eleventh embodiment, current detectors 13 and 14 are connected in series to the capacitors 8 and 10 , respectively, and current detection values output by these current detectors 13 and 14 are input to the control circuit 20 . The control circuit 20 is configured to generate ON/OFF signals for the switching elements 5 and 6 based on the current detection values of the capacitors 8 and 10 , and to generate an opening and closing command for the circuit breaker 2 .

Here, a case in which a short-circuit failure occurs in any one of the switching elements 5 and 6 (here, the switching element 6 is taken as an example) will be described. When a short-circuit failure occurs in the switching element 6 , an excessive current, that is, an overcurrent flows, in the capacitor 8 compared with the normal operation. In particular, an overcurrent flows during the steady state period, that is, during the period after the switching element 6 has passed the transition period and before the next switching starts.

The control circuit 20 determines that an overcurrent flows in the capacitor 8 based on the current detection value of the capacitor 8 output from the current detector 13 . When the control circuit 20 determines that an overcurrent flows in the capacitor 8, it is estimated that the switching element 6 has a short-circuit failure.

When it is concluded that the switching element 6 has a short-circuit fault, the control circuit 20 turns on the switching element 5 before the circuit breaker 2 is opened, thereby preventing the voltage of the capacitor 8 from rising continuously.

The above-mentioned example is an example when the switching element 6 has a short-circuit fault, and when the switching element 5 has a short-circuit fault, an overcurrent flows in the capacitor 10 . When the control circuit 20 determines that an overcurrent is flowing in the capacitor 10 based on the current detection value of the capacitor 10 output from the current detector 14 , the control circuit 20 estimates that the switching element 5 has a short-circuit failure.

The control circuit 20 inferring that the switching element 5 has a short-circuit failure can prevent the voltage of the capacitor 10 from rising continuously by turning on the switching element 6 before the circuit breaker 2 is opened.

The control circuit 20 may issue a gate-on command to both the switching elements 5 and 6 when it is estimated that a short-circuit failure has occurred in either the switching element 5 or the switching element 6, and the same effect can be achieved in this case.

In addition, as mentioned in the first embodiment, the delay time from the output of the opening command of the circuit breaker by the control circuit to the actual opening of the circuit breaker is different from the output of the on-gate command to the switching element to the actual opening of the switching element. The turn-on delay time is usually longer than that. Therefore, regardless of the timing of outputting the opening command of the circuit breaker, the control circuit of the present invention needs to output the conduction gate command, so that the predetermined switching element completes the conduction action before the actual opening of the circuit breaker.

That is, the basic idea of the present invention is to turn on a predetermined switching element before performing the protective action of opening the circuit breaker when it is estimated that a short-circuit fault has occurred in the switching element, thereby suppressing the voltage rise of the capacitor and preventing low withstand voltage. The switching element or the capacitor with low withstand voltage is damaged.

Label description

1: DC power supply

2: circuit breaker

3, 4: Reactor

5, 6: Semiconductor switching elements

7, 9: Diode

8, 10: Capacitors

11, 12, 16: Voltage detector

13, 14, 15, 17: Current detectors

20: Control circuit

IN1, IN2: input terminals

OUT1, OUT2: output terminals

Claims (16)

1. A dc-dc conversion apparatus comprising:

a switching element series circuit in which a first switching element and a second switching element are connected in series and connected to both ends of a direct current power supply;

a reactor connected between the dc power supply and the switching element series circuit;

a circuit breaker between the direct-current power supply and the switching element series circuit;

a capacitor series circuit in which first and second capacitors are connected in series;

first and second diodes connected between both ends of the switching element series circuit and both ends of the capacitor series circuit, respectively; and

a control circuit for controlling on/off of the first and second switching elements,

the connection point of the first and second switching elements is connected to the connection point of the first and second capacitors,

a step-up circuit for stepping up a voltage of the DC power supply and outputting the voltage from both ends of the capacitor series circuit by performing an on/off chopping operation of the first and second switching elements,

when it is estimated that at least one of the first and second switching elements has a short-circuit fault, the control circuit issues a conduction command to the other switching element or both switching elements before opening the circuit breaker.

2. The DC-DC converting apparatus according to claim 1,

the control circuit sends a conduction command to the switching element and a brake-off command to the circuit breaker,

and the breaker is switched off after the switching element is switched on.

3. The DC-DC converting apparatus according to claim 1,

includes first and second voltage detectors for detecting voltages of the first and second capacitors, respectively,

the control circuit infers that a short-circuit fault has occurred in the second switching element when it is determined that an overvoltage is applied to the first capacitor, and infers that a short-circuit fault has occurred in the first switching element when it is determined that an overvoltage is applied to the second capacitor.

4. The DC-DC converting apparatus according to claim 1,

includes first and second voltage detectors for detecting voltages of the first and second capacitors, respectively,

the control circuit estimates that a short-circuit failure has occurred in the second switching element when it is determined that the voltage of the first capacitor is higher than the voltage of the second capacitor and that a deviation between the voltage values of the two capacitors is equal to or greater than a predetermined value, and estimates that a short-circuit failure has occurred in the first switching element when it is determined that the voltage of the second capacitor is higher than the voltage of the first capacitor and that a deviation between the voltage values of the two capacitors is equal to or greater than a predetermined value.

5. The DC-DC converting apparatus according to claim 1,

includes first and second current detectors for detecting currents of the first and second switching elements, respectively,

the control circuit estimates that a short-circuit fault has occurred in the first switching element when it is determined that an overcurrent flows in the first switching element, and estimates that a short-circuit fault has occurred in the second switching element when it is determined that an overcurrent flows in the second switching element.

6. The DC-DC converting apparatus according to claim 1,

includes first and second voltage detectors for detecting voltages of the first and second switching elements, respectively,

the control circuit estimates that a short-circuit failure has occurred in the first switching element when it is determined that a voltage across the first switching element is equal to or higher than a predetermined value or equal to or lower than a predetermined value during a period in which an on command is issued to the first switching element, and estimates that a short-circuit failure has occurred in the second switching element when it is determined that a voltage across the second switching element is equal to or higher than a predetermined value or equal to or lower than a predetermined value during a period in which an on command is issued to the second switching element.

7. The DC-DC converting apparatus according to claim 1,

includes first and second voltage detectors for detecting voltages of the first and second switching elements, respectively,

the control circuit estimates that a short-circuit failure has occurred in the first switching element when it is determined that a voltage across the first switching element is equal to or lower than a predetermined value during a period in which an off command is issued to the first switching element, and estimates that a short-circuit failure has occurred in the second switching element when it is determined that a voltage across the second switching element is equal to or lower than a predetermined value during a period in which an off command is issued to the second switching element.

8. The DC-DC converting apparatus according to claim 1,

comprises a first current detector and a second current detector, which respectively detect the current of the first diode and the second diode,

the control circuit estimates that a short-circuit fault has occurred in the second switching element when it is determined that an overcurrent flows in the first diode, and estimates that a short-circuit fault has occurred in the first switching element when it is determined that an overcurrent flows in the second diode.

9. The DC-DC converting apparatus according to claim 1,

comprises a first and a second voltage detector for detecting the voltage of the first and the second diodes respectively,

the control circuit estimates that a short-circuit failure has occurred in the second switching element when the voltage across the first diode is determined to be equal to or greater than a predetermined value during a period in which an off command is issued to the first switching element, and estimates that a short-circuit failure has occurred in the first switching element when the voltage across the second diode is determined to be equal to or greater than a predetermined value during a period in which an off command is issued to the second switching element.

10. The DC-DC converting apparatus according to claim 1,

includes a current detector that detects a current of the reactor,

the control circuit infers that at least one of the first and second switching elements has a short-circuit fault when it is determined that an overcurrent flows through the reactor.

11. The DC-DC converting apparatus according to claim 1,

includes a voltage detector that detects a voltage of the reactor,

the control circuit estimates that at least one of the first and second switching elements has a short-circuit fault when it is determined that the voltage across the reactor is equal to or higher than a predetermined value.

12. The DC-DC converting apparatus according to claim 1,

a current detector for detecting a current of a wiring connecting a connection point between the first and second switching elements and a connection point between the first and second capacitors,

the control circuit infers that at least one of the first and second switching elements has a short-circuit failure when it is determined that an overcurrent flows through the wiring.

13. The DC-DC converting apparatus according to claim 1,

the control circuit estimates that a short-circuit failure has occurred in the first switching element when it is determined that the control electrode of the first switching element is always short-circuited or the potential of the control electrode is always high, and estimates that a short-circuit failure has occurred in the second switching element when it is determined that the control electrode of the second switching element is always short-circuited or the potential of the control electrode is always high.

14. The DC-DC converting apparatus according to claim 1,

the control circuit estimates that a short-circuit failure has occurred in the first switching element when it is determined that the current flowing through the control electrode of the first switching element is an overcurrent or always flows, and estimates that a short-circuit failure has occurred in the second switching element when it is determined that the current flowing through the control electrode of the second switching element is an overcurrent or always flows.

15. The DC-DC converting apparatus according to claim 1,

comprises a first current detector and a second current detector, which respectively detect the current of the first capacitor and the second capacitor,

the control circuit estimates that a short-circuit fault has occurred in the second switching element when it is determined that an overcurrent flows in the first capacitor, and estimates that a short-circuit fault has occurred in the first switching element when it is determined that an overcurrent flows in the second capacitor.

16. The DC-DC converting apparatus according to claim 1,

the control circuit generates an alarm when it is inferred that the first or second switching element has a short-circuit fault.

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