JP6914399B1 - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power conversion device which suppresses a recirculation current flowing through a body diode while reducing a surge voltage generated when a switch element turns off at the time of overcurrent. SOLUTION: A converter unit 5 in which a switching element 8 and a switching element 9 are connected in series, a current sensor 11 for detecting a current flowing through a connection point between the switching element 8 and the switching element 9, and a current detected by the current sensor 11 are excessive. It is provided with overcurrent detection units 19a and 19b for detecting that it is a current, and one of the switching element 8 and the switching element 9 is transitioned from an off state to an on state at a specified turn-on time, and the other is specified. The turn-off time is longer than the turn-off time to transition from the on state to the off state. [Selection diagram] Fig. 1

Description

The present application relates to a power converter.

Recently, automobiles equipped with electric power trains such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (EV), and fuel cell vehicles (FCV) (hereinafter referred to as electric vehicles) have become widespread. There is. In addition to the configuration of a conventional gasoline engine vehicle, these electrified vehicles are equipped with a motor for propelling the vehicle, a power conversion device for driving the motor, and a power conversion device for filling a high-voltage battery or an auxiliary battery. ing.

It is known that a surge voltage is generated when a switch element provided in a power conversion device is turned off. The magnitude of this surge voltage depends on the inductance component of the bus, which is a DC power supply line, and the value of the current flowing through the bus at turn-off. The withstand voltage of each switch element and the insulation distance between metal members such as a bus bar to which a voltage is applied are determined in consideration of the surge voltage.

When an abnormality is detected, the switch element in the ON state is turned off as a protective operation. When the bus current is overcurrent, if the turn-off is suddenly performed during the protection operation, the surge voltage becomes excessive and the switch element may be destroyed. Therefore, it is desirable to softly shut off the switch element.

Soft cutoff refers to gradually transitioning the state of the switch element from the on state to the off state, that is, lowering the gate voltage of the switch element over time, as compared with the case of turning off during normal operation. ..

For example, Patent Document 1 discloses an inverter circuit that generates a signal that softly shuts off a switch element when an overcurrent of a load current is detected, and softly shuts off the corresponding drive circuit.

Japanese Unexamined Patent Publication No. 2016-181986

However, in the inverter circuit disclosed in Patent Document 1, although the generation of surge voltage due to soft cutoff can be suppressed when the load current is overcurrent, the return current after soft cutoff of the switch element is not mentioned. The return current is a current that tries to continue flowing to the inductive load when trying to cut off the current flowing to the inductive load having a coil component such as a motor, and passes through the body diode of the switch element.

Like a general diode, a body diode has a short-time rated current that is a permissible current value that is larger than the continuously energizable current for a short time, but the overcurrent determines the short-time rated current of the body diode. If it exceeds the limit, the switch element may be destroyed. In order to increase the rated current for a short period of time, it is necessary to reduce the current density flowing through the switch element, that is, it is necessary to increase the chip area of the switch element, resulting in an increase in the cost of the switch element and an increase in the size of the power conversion device. Challenges arise.

The present application discloses a technique for solving the above-mentioned problems, and is a power that suppresses a return current flowing through a body diode while reducing a surge voltage generated when a switch element turns off during an overcurrent. It is an object of the present invention to provide a conversion device.

The power conversion device disclosed in the present application includes a first switch element pair composed of a series circuit of a first switch constituting a lower arm and a second switch forming an upper arm, and the first switch and the second switch. A first inductive load connected to a connection point with the switch, a first current detecting means for detecting the current flowing through the first inductive load, and a control unit for controlling the first switch and the second switch. , With
The control unit includes a control signal generation unit that generates a control signal that controls the first switch and the second switch, and a first overcurrent that detects that the detection current of the first current detection means is an overcurrent. When the detection unit and the first overcurrent detection unit detect the overcurrent, either one of the first switch and the second switch is changed from the off state to the on state at a specified turn-on time, and the other. It is characterized by having an on / off drive unit that transitions from an on state to an off state in a turn-off time longer than a specified turn-off time.

According to the power conversion device disclosed in the present application, it is possible to obtain a power conversion device capable of suppressing the return current flowing through the body diode while reducing the surge voltage generated when the switch element is turned off.

It is a block diagram which shows the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure explaining the switching mode of the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure explaining the switching mode of the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure explaining the switching mode of the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure explaining the switching mode of the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the increase / decrease of the reactor current at the time of power running in the power conversion apparatus which concerns on Embodiment 1, and the on / off relationship of a semiconductor switch element. It is a figure which shows the increase / decrease of the reactor current at the time of regeneration in the power conversion apparatus which concerns on Embodiment 1, and the on / off relationship of a semiconductor switch element. It is a block diagram which shows the control part in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the current sensor output in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the reactor current and the on / off state of the semiconductor switch element at the time of the positive side overcurrent detection in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the reactor current at the time of the negative side overcurrent detection in the power conversion apparatus which concerns on Embodiment 1, and the on / off state of a semiconductor switch element. It is a figure which shows the current immediately before and immediately after the detection of the positive side overcurrent in the conventional power conversion apparatus. It is a figure which shows the current immediately before and immediately after the negative side overcurrent detection in the conventional power conversion apparatus. It is a figure which shows the state transition of the positive side overcurrent detection immediate current and the immediate current, and the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the state transition of the negative side overcurrent detection immediate current and immediate current, and the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the switching characteristic of a general MOSFET. It is a circuit diagram of a general MOSFET. It is a block diagram which shows the power conversion apparatus which concerns on Embodiment 2. It is a block diagram which shows the control part in the power conversion apparatus which concerns on Embodiment 2. It is a figure which shows the state transition of the positive side overcurrent detection immediate current and the immediate current, and the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 2. FIG. It is a figure which shows the state transition of the negative side overcurrent detection immediate current and immediate current, and the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 2. FIG. It is a figure which shows the state transition of the positive side overcurrent detection immediate current and the immediate current, and the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 2. FIG. It is a figure which shows the state transition of the negative side overcurrent detection immediate current and immediate current, and the semiconductor switch element in the power conversion apparatus which concerns on Embodiment 2. FIG. It is a block diagram which shows the other embodiment of the power conversion apparatus which concerns on Embodiment 2. FIG. It is a figure explaining the operation of the power conversion apparatus shown in FIG. It is a figure explaining the operation of the power conversion apparatus shown in FIG.

Hereinafter, embodiments of the power conversion device according to the present application will be described with reference to the drawings. In each figure, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted.

Embodiment 1.
FIG. 1 is a configuration diagram showing a power conversion device according to the first embodiment. In the present embodiment, a case where the power conversion device is composed of a boost converter will be described as an example.
In FIG. 1, the power storage unit 1 is connected to the input terminals Pi and Ni of the boost converter. The power storage unit 1 outputs a DC voltage. The power storage unit 1 is composed of, for example, a battery. Here, when the power conversion device according to the present embodiment is applied to an electric vehicle or a hybrid vehicle, the power storage unit 1 is typically composed of a secondary battery such as nickel hydrogen or lithium ion.

Next, the circuit configuration of the boost converter will be described.
As shown in FIG. 1, the boost converter constituting the power conversion device includes an input voltage detection circuit 2, an input capacitor 3, a reactor 4a as a first inductive load, a converter unit 5, a smoothing capacitor 6, and an output voltage detection circuit. 7 is provided. Hereinafter, these components will be described.

Input voltage detection circuit 2 detects the value of the input voltages V ₁ from the electric storage unit 1, and outputs a voltage detection value of the input voltages V _1. The input capacitor 3 is connected in parallel to the power storage unit 1. The input capacitor 3 functions as a ripple current suppression capacitor that removes the ripple current from the direct current input from the power storage unit 1.

A reactor 4a is connected to the subsequent stage of the input capacitor 3. A converter unit 5 as a switch circuit is connected to the rear stage of the reactor 4a. The converter unit 5 includes a first semiconductor switch element 8 and a second semiconductor switch element 9. The second semiconductor switch element 9 is an upper arm switch, and the first semiconductor switch element 8 is a lower arm switch. The second semiconductor switch element 9 which is a switch of the upper arm and the first semiconductor switch element 8 which is a switch of the lower arm form a first switch element pair. The second semiconductor switch element 9 of the upper arm and the first semiconductor switch element 8 of the lower arm forming the first switch element pair are connected in series to form a series circuit.

A smoothing capacitor 6 is connected to the subsequent stage of the converter unit 5. Smoothing capacitor 6, by smoothing the DC voltage outputted from the converter section 5, and generates an output voltage V ₂ output terminal Po, between No. Here, the output voltage V ₂ is a DC voltage. Further, the output voltage detection circuit 7 detects the value _{of the output voltage V 2} from the smoothing capacitor 6 and outputs the voltage detection value of the output _{voltage V 2.} The output voltage detection circuit 7 functions as a voltage detection unit that detects voltage values across the converter unit 5 as a switch circuit.

Here, the first semiconductor switch element 8 and the second semiconductor switch element 9 are MOSFETs (Metal-Oxide-Semiconductor Field-Effective Transistor) having a body diode built in and parasitic on the transistor. The drain terminal of the second semiconductor switch element 9 is connected to the positive electrode side of the smoothing capacitor 6, and the source terminal of the first semiconductor switch element 8 is connected to the negative electrode side of the smoothing capacitor 6. Further, the source terminal of the second semiconductor switch element 9 and the drain terminal of the first semiconductor switch element 8 are connected to each other at the connection point 10.

The reactor 4a is an inductive load having an inductance L1 and is connected between the connection point 10 and the positive electrode side of the input capacitor 3. The current sensor 11, which is a current detecting means, detects the reactor current I ₁ flowing through the reactor 4a, which is an inductive load. The detected reactor current I ₁ is input to the control unit 13 via the signal line 12a. The current flowing from the positive electrode side of the input capacitor 3 toward the connection point 10 is defined as a positive current, and the current flowing from the connection point 10 toward the positive electrode side of the input capacitor 3 is defined as a negative current.

Next, the control unit 13 will be described.
The control unit 13 controls the operation of the boost converter. Specifically, the control unit 13 transmits a gate signal to the first semiconductor switch element 8 and the second semiconductor switch element 9 via the control line 14, and the first semiconductor switch element 8 and the second semiconductor switch element 9 are used. On / off control. The MOSFET of the first semiconductor switch element 8 transitions from the off state to the on state over a specified turn-on time by the gate signal Gate1a output from the control unit 13, and changes from the on state to the off state over a specified turn-off time. Transition to. The MOSFET of the second semiconductor switch element 9 transitions from the off state to the on state over a specified turn-on time by the gate signal Gate1b output from the control unit 13, and changes from the on state to the off state over a specified turn-off time. Transition to. _{Further, the control unit 13 acquires the voltage detection value of the input voltage V 1} from the input voltage detection circuit 2 via the signal line 12b, and _{the voltage of the output voltage V 2} from the output voltage detection circuit 7 via the signal line 12c. Get the detected value. Both the input voltage V ₁ and the output voltage V ₂ are DC voltages. _{Further, the output voltage command value V 2} * is input to the control unit 13 via the external signal line 15.

Next, the outline of the control by the control unit 13 will be described.
The control unit 13 has a function of controlling the _{output voltage V 2 output from the boost converter.} The control unit 13 controls the gate signals Gate1a and Gate1b of the boost converter so that _{the output voltage V 2} becomes equal to the output voltage command value V _{2 *.} The operation in which electric power is output from the output side of the boost converter is called power running, and a positive current flows through the reactor 4a. The operation in which power is input to the output side of the boost converter is called regeneration, and a negative current flows through the reactor 4a.

Hereinafter, the operation of the boost converter as the power conversion device according to the first embodiment will be described. In the power conversion device according to the first embodiment, the four operation modes shown in FIGS. 2 to 5 are set according to the states of the first semiconductor switch element 8 and the second semiconductor switch element 9 during power running, regeneration, and so on. exist. Since FIGS. 2 to 5 are views for explaining the operation mode, the control unit 13 shown in FIG. 1 is not shown. In addition, the current change of the _{reactor current I 1} will be described with reference to FIGS. 6 and 7. The horizontal axis represents time t in FIG. 6 and FIG. 7, the vertical axis represents the reactor current I _1.

In mode 1 shown in FIG. 2, the first semiconductor switch element 8 is on and the second semiconductor switch element 9 is off during power running. At this time, the reactor current I ₁ shown in FIG. 6 is flowing through the reactor 4a, and the reactor current I ₁ increases with a _{slope determined by ΔI / Δt = V 1} / L1 at the time shown in FIG. 6a.

In mode 2 shown in FIG. 3, the first semiconductor switch element 8 is off and the second semiconductor switch element 9 is on during power running. At this time, the reactor 4a, and flows reactor current _{I 1} shown in FIG. _{6, ΔI / Δt = (V} 2 -V 1) / L1 reactor current _{I 1} at a slope determined by the time indicated by b in FIG. 6 Decreases.

In mode 3 shown in FIG. 4, the first semiconductor switch element 8 is on and the second semiconductor switch element 9 is off during regeneration. At this time, the reactor current I ₁ shown in FIG. 7 is flowing through the reactor 4a, and the reactor current I ₁ increases with a _{slope determined by ΔI / Δt = V 1} / L1 at the time shown in b in FIG.

In mode 4 shown in FIG. 5, the first semiconductor switch element 8 is off and the second semiconductor switch element 9 is on during regeneration. At this time, the reactor 4a, and flows reactor current _{I 1} shown in FIG. _{7, ΔI / Δt = (V} 2 -V 1) / L1 reactor current _{I 1} at a slope determined by the time indicated by a in FIG. 7 Decreases.

Next, the details of the control unit 13 will be described with reference to FIG.
As shown in FIG. 8, the control unit 13 includes a control signal generation unit 16, a first drive unit 17, a second drive unit 18, a first positive side overcurrent detection unit 19a, and a first negative side overcurrent detection unit 19b. Consists of. The first drive unit 17 outputs the gate signal Gate1a that drives the first semiconductor switch element 8 via the control line 14. The second drive unit 18 outputs the gate signal Gate1b that drives the second semiconductor switch element 9 via the control line 14. The first drive unit 17 and the second drive unit 18 form an on / off drive unit.

The first drive unit 17 includes a first on / off unit 20a, a first soft cutoff unit 21a, and a first forced on unit 22a. The second drive unit 18 includes a second on / off unit 20b, a second soft cutoff unit 21b, and a second forced on unit 22b. Control signal generating unit 16, a first positive overcurrent detection unit 19a, and the first negative overcurrent detection unit 19b, a current detection value of the reactor current I ₁ through the signal line 12a is input. The determination signal 23a from the first positive side overcurrent detection unit 19a is input to the first soft cutoff unit 21a, the second forced on unit 22b, and the control signal generation unit 16. The determination signal 23b from the first negative side overcurrent detection unit 19b is input to the second soft cutoff unit 21b, the first forced on unit 22a, and the control signal generation unit 16. The control signal 24a from the control signal generation unit 16 is input to the first on / off unit 20a, and the control signal 24b is input to the second on / off unit 20b.

As shown in FIG. 9, the current sensor 11 outputs a voltage of 2.5 V at a current value of 0 A, 4.5 V at the rated sensor current value on the positive side, and 0.5 V at the rated sensor current value on the negative side. Output voltage. The first positive side overcurrent detection unit 19a _{constantly monitors the output voltage of the current sensor 11 corresponding to the current detection value of the reactor current I 1} , and the voltage value corresponding to the current detection value sets a preset positive current threshold value. When it exceeds, it is determined that the positive current is overcurrent, and the determination signal 23a is switched from, for example, high “H” to low “L”. The first negative side overcurrent detection unit 19b _{constantly monitors the output voltage of the current sensor 11 corresponding to the current detection value of the reactor current I 1} , and the voltage value corresponding to the current detection value sets a preset negative current threshold value. When it exceeds, it is determined that the negative current is overcurrent, and the determination signal 23b is switched from, for example, high “H” to low “L”.

The control signal generation unit 16 generates control signals 24a and 24b so that the _{output voltage V 2} becomes equal to the output voltage command value V _{2 *.} The control signal generation unit 16 is realized by, for example, a microcomputer. The microcomputer has a processor and a memory. The function of the control signal generation unit 16 is realized by the processor reading and executing the program stored in the memory. The microcomputer generates control signals 24a and 24b for controlling the first semiconductor switch element 8 and the second semiconductor switch element 9 according to a preset modulation method. As the modulation method, for example, PWM (Pulse Width Modulation) by comparing the triangular wave serving as the reference wave with the duty is used. Here, the duty is a command value corresponding to a time ratio indicating the ratio of the time length during which the semiconductor switch element is turned on to the total time length.

The first on / off unit 20a and the second on / off unit 20b turn on the first semiconductor switch element 8 and the second semiconductor switch element 9 from the off state over a specified turn-on time according to the control signals 24a and 24b. It outputs Gate1a and Gate1b that transition to the state and transition from the on state to the off state at the specified turn-off time. Here, the specified turn-on time and the specified turn-off time are referred to as a normal turn-on time and a normal turn-off time, respectively. The loss of the switch element or the surge voltage generated by the switching operation is set to be within the allowable range. Generally, when the turn-on time and turn-off time are short, the loss of the switch element decreases and the surge voltage increases, and when the turn-on time and turn-off time are long, the loss of the switch element increases and the surge voltage decreases.

In many cases, one time is set for each of the normal turn-on time and the normal turn-off time, but two or more turn-on time and turn-off time are switched depending on the reactor current value, the converter output power, the heat generation condition of the switch element, etc., respectively. You may.

The first soft cutoff unit 21a and the second soft cutoff unit 21b give priority to the first on / off unit 20a and the second on / off unit 20b according to the determination signals 23a and 23b, and the first semiconductor switch element 8 , And the gate signals Gate1a and Gate1b that cause the second semiconductor switch element 9 to transition from the on state to the off state over a turnoff time longer than the normal turnoff time are output. Here, a turn-off time longer than the normal turn-off time is referred to as a soft cutoff time, and transitioning from an on state to an off state over a soft cutoff time is referred to as a soft cutoff time. In order to suppress the surge voltage generated when a large current value at the time of overcurrent detection is turned off, the time is usually set longer than the turn-off time, and the surge voltage is set to be within the allowable range. If the gate signals Gate1a and Gate1b in the on state are being output by the first on / off section 20a and the second on / off section 20b, the gate signals Gate1a and Gate1b to softly shut off are output, and the gate signal in the off state is output. If Gate1a and Gate1b are being output, the off state is continued as it is.

The first forced on section 22a and the second forced on section 22b have priority over the first on / off section 20a and the second on / off section 20b according to the determination signals 23b and 23a, and the first semiconductor switch element 8 , And the gate signals Gate1a and Gate1b for transitioning the second semiconductor switch element 9 from the off state to the on state in the normal turn-on time are output. If the gate signals Gate1a and Gate1b in the off state are being output by the first on / off section 20a and the second on / off section 20b, the gate signals Gate1a and Gate1b that change from the off state to the on state in the normal turn-on time are generated. If it is output and the gate signals Gate1a and Gate1b in the ON state are being output, the ON state is continued as it is.

Hereinafter, the operation when an overcurrent occurs in the power conversion device according to the first embodiment will be described with reference to FIGS. 10 to 15. Here, too, a boost converter will be described as an example of the power conversion device.

Overcurrent during power running occurs when the output load becomes overloaded or the output load is short-circuited. When the output load becomes overloaded, the reactor current I ₁ increases as shown in FIG. 10, and when it exceeds the positive overcurrent threshold value as shown by X in the figure, it is determined that an overcurrent has occurred. At this time, the first semiconductor switch element 8 which is the lower arm switch is in the ON state, and the current is flowing along the path indicated by the solid arrow in FIG.

Conventionally, when the positive side overcurrent threshold is exceeded, the first positive side overcurrent detection unit 19a switches the determination signal 23a to low “L”, and when the negative side overcurrent threshold is exceeded, the first negative side overcurrent is exceeded. The detection unit 19b switches the determination signal 23b to low "L", and the control signal generation unit 16 outputs control signals 24a and 24b for turning off the first semiconductor switch element 8 and the second semiconductor switch element 9 accordingly. do. As a result, the first on / off section 20a and the second on / off section 20b are gate signals that cause the first semiconductor switch element 8 and the second semiconductor switch element 9 to transition from the on state to the off state in the normal turn-off time. Outputs Gate1a and Gate1b.

Further, a logic circuit is provided between the control signal generation unit 16, the first on / off unit 20a, and the second on / off unit 20b, and when the determination signals 23a and 23b are low “L”, the control signal 24a, There is also a method of outputting the gate signals Gate1a and Gate1b for transitioning the first semiconductor switch element 8 and the second semiconductor switch element 9 from the on state to the off state in the normal turn-off time by setting the 24b to the off logic.

In this way, if the first semiconductor switch element 8 transitions from the on state to the off state in the normal turn-off time when the positive side overcurrent occurs, an excessive surge voltage may be generated and the first semiconductor switch element 8 may be destroyed. .. When the first semiconductor switch element 8 is turned off, the current flows through the body diode of the second semiconductor switch element 9 along the path indicated by the dotted arrow, and when the current exceeds the rated current of the body diode, the body diode is destroyed. There is a fear.

On the other hand, in the first embodiment, when the positive side overcurrent threshold value is exceeded, the first positive side overcurrent detection unit 19a switches the determination signal 23a to low “L”, and the first soft cutoff unit 21a and the second forced on unit 21a. 22b becomes active. Accordingly, as shown in FIG. 14, the first semiconductor switch element 8 is softly shut off, and the second semiconductor switch element 9 is turned on. As a result, the first semiconductor switch element 8 can suppress the generation of surge voltage and transition to the off state, and can prevent destruction due to surge voltage. Further, the second semiconductor switch element 9 can pass a current without energizing the body diode, and can prevent the body diode from being destroyed by an excessive current.

The overcurrent at the time of regeneration is generated by the input of excessive regenerative energy from the output side. When the regenerative energy is input, the reactor current I ₁ decreases as shown in FIG. 11, and when the negative overcurrent threshold is exceeded as shown by Y in the figure, it is determined that an overcurrent has occurred. At this time, the second semiconductor switch element 9 which is the upper arm switch is in the ON state, and the current is flowing along the path indicated by the solid arrow in FIG.

Similar to the above, if the second semiconductor switch element 9 transitions from the on state to the off state in the normal turn-off time when an overcurrent occurs, an excessive surge voltage may be generated and the second semiconductor switch element 9 may be destroyed. When the second semiconductor switch element 9 is turned off, the current flows through the body diode of the first semiconductor switch element 8 along the path indicated by the dotted arrow, and when the current exceeds the rated current of the body diode, the body diode is destroyed. There is a fear.

When the negative side overcurrent threshold value is exceeded, the first negative side overcurrent detection unit 19b switches the determination signal 23b to low “L”, and the second soft cutoff unit 21b and the first forced on unit 22a become active. Accordingly, as shown in FIG. 15, the second semiconductor switch element 9 is softly shut off, and the first semiconductor switch element 8 is turned on. As a result, the second semiconductor switch element 9 can suppress the generation of surge voltage and transition to the off state, and can prevent destruction due to surge voltage. The first semiconductor switch element 8 can pass a current without energizing the body diode, and can prevent the body diode from being destroyed by an excessive current.

By the way, the MOSFETs which are the first semiconductor switch element 8 and the second semiconductor switch element 9 have the switching characteristics as shown in FIG. As shown in FIG. 17, assuming that the voltage between the gate G and the source S is Vgs, the voltage between the drain D and the source S is Vds, and the current flowing between the drain D and the source S is Id, the MOSFETs are generated by the gate signals Gate1a and Gate1b. When transitions from on to off, the voltage Vgs between the gate G and the source S first drops to the mirror voltage Vgs_pl. The voltage Vgs between the gate G and the source S becomes a substantially constant voltage during the mirror period, and the voltage Vds between the drain D and the source S increases during this period. When the mirror period ends, the voltage Vgs between the gate G and the source S begins to decrease, and the current Id flowing between the drain D and the source S also begins to decrease. When the voltage Vgs between the gate G and the source S drops to the threshold voltage Vgs_th, the current Id flowing between the drain D and the source S decreases to 0, and the MOSFET is turned off. The time from when the voltage Vgs between the gate G and the source S starts to drop until the current Id flowing between the drain D and the source S becomes 0 corresponds to the normal turn-off time and the soft cutoff time.

When the MOSFET transitions from the off state to the on state, looking at the switching characteristics of FIG. 16 in the opposite direction, first, the voltage Vgs between the gate G and the source S starts to rise, and when the voltage Vgs rises to the threshold voltage Vgs_th, the drain D and the source The current Id flowing between S begins to increase. When the voltage Vgs between the gate G and the source S rises to the mirror voltage Vgs_pl, the voltage Vgs between the gate G and the source S becomes a substantially constant voltage during the mirror period, and the voltage Vds between the drain D and the source S decreases during this period. do. At the end of the mirror period, the MOSFET is turned on. The time from when the voltage Vgs between the gate G and the source S starts to rise until the voltage Vds between the drain D and the source S becomes 0 corresponds to the normal turn-on time.

Considering the above switching characteristics, when the soft cutoff of one semiconductor switch element and the normal turn-on of the other semiconductor switch element start at the same time, the other before the current Id flowing between the drain D and the source S during the soft cutoff starts to decrease. The current Id flowing between the drain D and the source S of the above starts to increase, and in this case, a short-circuit current far larger than the overcurrent flows to both switch elements, which may lead to destruction.

Therefore, the first forced on section 22a and the second forced on section 22b usually start the turn-off after the end of the mirror period during the transition to the off state of the semiconductor switch element during soft interruption. As a result, the current Id flowing between the drain D and the source S of the semiconductor switch element transitioning to the off state is decreasing, or flows between the drain D and the source S of the semiconductor switch element transitioning to the on state after the decrease is completed. By starting to increase the current Id, it is possible to prevent the generation of an excessive short-circuit current.

The end of the mirror period during the transition to the off state of the semiconductor switch element during soft cutoff can be determined by the voltage Vgs between the gate G and the source S falling below the mirror voltage Vgs_pl. The voltage Vgs between the gate G and the source S is monitored, compared with the mirror voltage Vgs_pl, and when the voltage falls below the voltage Vgs, the first forced on section 22a and the second forced on section 22b are notified, and the notification is received. After that, the first forced on section 22a and the second forced on section 22b may output the gate signals Gate1a and Gate1b that are turned on during the normal turn-on time.

Alternatively, the end of the mirror period during the transition to the off state of the semiconductor switch element during soft cutoff can be determined by the time from the start of the voltage Vgs between the gate G and the source S decreasing to the mirror voltage Vgs_pl. From the switching characteristics of the semiconductor switch element and the soft cutoff time, it is possible to estimate in advance the time from the start of the voltage Vgs between the gate G and the source S decreasing to the mirror voltage Vgs_pl. The first forced on section 22a and the second forced on section 22b may output the gate signals Gate1a and Gate1b that are turned on during the normal turn-on time after waiting for the estimated time.

Next, the operation after the semiconductor switch element is turned off due to soft cutoff or turned on over a normal turn-off time will be described.
After the overcurrent is detected during power running, the current indicated by the dotted arrow in FIG. 14 is flowing. The current decreases with a slope determined by ΔI / Δt = (V _2- V _{1) / L1.} After the overcurrent is detected during regeneration, the current indicated by the dotted arrow in FIG. 15 is flowing. The current decreases with a slope determined by ΔI / Δt = V _{1 / L1.}

If the current value decreases below a certain current value, for example, to the current value flowing during normal operation, even if the semiconductor switch element in the on state is turned off, the current value flowing through the body diode is within the allowable range. Since it is considered that there is no risk of destruction, it is turned off. After that, the control unit 13 confirms the presence or absence of an abnormal signal or the like, and restarts the operation as a converter, or performs an operation such as waiting for a user's instruction to enter a standby state.

A function is provided to detect that the current value is below a certain value from the output of the current sensor 11 and notify the first forced on section 22a and the second forced on section 22b, and after receiving the notification, the first forced on section 22a is provided. The on unit 22a and the second forced on unit 22b may output the gate signals Gate1a and Gate1b that change the on state to the off state in the normal turn-off time. Further, if the current value is reduced to 0 A, it can be turned off without fear of destruction.

Since the current decreases with ΔI / Δt = (V _2- V ₁ ) / L1 or ΔI / Δt = V ₁ / L1, if ΔI is set to the overcurrent threshold of −0A, the input voltage V ₁ is the input voltage detection. _{Since the output voltage V 2} is acquired from the circuit 2 and the output voltage V 2 is acquired from the output voltage detection circuit 7 and the value of the inductance L1 is fixed as a circuit constant, the time to be 0A can be calculated. The first forced on section 22a and the second forced on section 22b can be turned off at the timing when the current becomes 0 A if the first forced on section 22a and the second forced on section 22b are turned off during the normal turn-off time after continuing the on state for this time.

As described above, according to the power conversion device according to the first embodiment, it is possible to avoid the generation of a large surge voltage and suppress the energization of the body diode. As a result, it is not necessary to expand the chip area of the switch element, and it is possible to solve the problems of increasing the cost of the switch element and increasing the size of the power conversion device.

Embodiment 2.
Next, the power conversion device according to the second embodiment will be described.
FIG. 18 is a configuration diagram showing a power conversion device according to the second embodiment. In the present embodiment, a case where the power conversion device is composed of a multi-phase DC / DC converter will be described as an example.
The multi-phase DC / DC converter switches one DC input voltage using a multi-phase switch and supplies one DC output voltage to one load. In FIG. 18, the case where the number of phases is 2 is shown as an example, but the number of phases is not particularly limited as long as it is 2 or more.

The power conversion device according to the first embodiment is a one-phase converter, and the power conversion device according to the second embodiment has a configuration in which a switch is added thereto. Therefore, detailed description of the same parts as those described in the first embodiment will be omitted.

As shown in FIG. 18, the multi-phase DC / DC converter constituting the power conversion device has a reactor 4b as a second inductive load, a third semiconductor switch element 25, and a fourth semiconductor switch element in addition to the configuration of FIG. 26, and a current sensor 27 which is a current detecting means are provided. The third semiconductor switch element 25 and the fourth semiconductor switch element 26 are MOSFETs like the first semiconductor switch element 8 and the second semiconductor switch element 9.
The reactor 4b is connected to the subsequent stage of the input capacitor 3. The converter unit 5 as a switch circuit further includes a third semiconductor switch element 25 and a fourth semiconductor switch element 26. The fourth semiconductor switch element 26 is a semiconductor switch element of the upper arm. Further, the third semiconductor switch element 25 is a semiconductor switch element of the lower arm. The fourth semiconductor switch element 26 of the upper arm and the third semiconductor switch element 25 of the lower arm form a second switch element pair. The fourth semiconductor switch element 26 of the upper arm and the third semiconductor switch element 25 of the lower arm forming the second switch element pair are connected in series to form a series circuit.

The drain terminal of the fourth semiconductor switch element 26 is connected to the positive electrode side of the smoothing capacitor 6. Further, the source terminal of the third semiconductor switch element 25 is connected to the negative electrode side of the smoothing capacitor 6. Further, the source terminal of the fourth semiconductor switch element 26 and the drain terminal of the third semiconductor switch element 25 are connected to each other at a connection point 28.

The reactor 4b has an inductance L2 and is connected between the connection point 28 and the positive electrode side of the input capacitor 3. The current sensor 27 detects the _{reactor current I 2} flowing through the reactor 4b. The detected reactor current I ₂ is input to the control unit 13 via the signal line 12d. The current flowing from the positive electrode side of the input capacitor 3 toward the connection point 28 is defined as a positive current, and the current flowing from the connection point 28 toward the positive electrode side of the input capacitor 3 is defined as a negative current.

The control unit 13 further controls the third semiconductor switch element 25 on / off by transmitting the gate signal Gate2a via the control line 14, and turns on / off the fourth semiconductor switch element 26 by transmitting the gate signal Gate2b. Control off. Control unit 13, the output voltage _{V 2,} so as to be equal to the output voltage command value _{V 2} *, gate signal GATE1A, gate signal GATE1B, controls the gate signals Gate2a, and the gate signal Gate2b.

The first semiconductor switch element 8 and the third semiconductor switch element 25, the second semiconductor switch element 9 and the fourth semiconductor switch element 26 may be turned on / off synchronously or may be turned on / off asynchronously. Ripple generated in the smoothing capacitor 6 by turning on / off the first semiconductor switch element 8 and the third semiconductor switch element 25, the second semiconductor switch element 9 and the fourth semiconductor switch element 26 so that the phase shifts by 180 degrees. The current can be suppressed, which contributes to the miniaturization of the capacitor.

Next, the details of the connection of the control unit 13 will be described with reference to FIG.
As shown in FIG. 19, in addition to the configuration shown in FIG. 8, the control unit 13 includes a third drive unit 29, a fourth drive unit 30, a second positive overcurrent detection unit 19c, and a second negative overcurrent detection unit. It is composed of 19d. The third drive unit 29 outputs the gate signal Gate 2a that drives the third semiconductor switch element 25 via the control line 14. The fourth drive unit 30 outputs the gate signal Gate 2b that drives the fourth semiconductor switch element 26 via the control line 14. The third drive unit 29 includes a third on / off unit 20c, a third soft cutoff unit 21c, and a third forced on unit 22c. The fourth drive unit 30 includes a fourth on / off unit 20d, a fourth soft cutoff unit 21d, and a fourth forced on unit 22d. The first drive unit 17, the second drive unit 18, the third drive unit 29, and the fourth drive unit 30 form an on / off drive unit.

The current detection value of _{the reactor current I 2} is input to the control signal generation unit 16, the second positive side overcurrent detection unit 19c, and the second negative side overcurrent detection unit 19d via the signal line 12d. The determination signal 23c from the second positive side overcurrent detection unit 19c is input to the third soft cutoff unit 21c, the fourth forced on unit 22d, and the control signal generation unit 16. The determination signal 23d from the second negative side overcurrent detection unit 19d is input to the fourth soft cutoff unit 21d, the third forced on unit 22c, and the control signal generation unit 16. The control signal 24c from the control signal generation unit 16 is input to the third on / off unit 20c, and the control signal 24d is input to the fourth on / off unit 20d.

Hereinafter, the operation when an overcurrent occurs in the power conversion device according to the second embodiment will be described with reference to FIGS. 20 to 23.
FIG. 20 shows the operation when the _{reactor current I 1 exceeds the positive overcurrent.} Similar to the first embodiment, the first semiconductor switch element 8 of the lower arm switch in which the overcurrent is generated is softly shut off, and the second semiconductor switch element 9 of the upper arm switch is normally turned on from the off state over a turn-on time. Transition to. The third semiconductor switch element 25 and the fourth semiconductor switch element 26 in which no overcurrent is generated transition from the on state to the off state in the normal turn-off time. As a result, while preventing the destruction of the second semiconductor switch element 9 of the upper arm switch and the first semiconductor switch element 8 of the lower arm switch in which an overcurrent is generated, the other third semiconductor switch element 25 and the fourth semiconductor switch element 26 are prevented. By turning off, it is possible to suppress the occurrence of a similar overcurrent.

FIG. 21 shows the operation when the _{reactor current I 1 exceeds the negative overcurrent.} Similar to the first embodiment, the second semiconductor switch element 9 of the upper arm switch in which the overcurrent is generated is softly shut off, and the first semiconductor switch element 8 of the lower arm switch is normally turned on from the off state over a turn-on time. Transition to. The third semiconductor switch element 25 and the fourth semiconductor switch element 26 in which no overcurrent is generated transition from the on state to the off state in the normal turn-off time. As a result, while preventing the destruction of the second semiconductor switch element 9 of the upper arm switch and the first semiconductor switch element 8 of the lower arm switch in which an overcurrent is generated, the other third semiconductor switch element 25 and the fourth semiconductor switch By turning off the element 26, it is possible to suppress the occurrence of a similar overcurrent.

In the third semiconductor switch element 25 and the fourth semiconductor switch element 26, the control signal generation unit 16 outputs control signals 24c and 24d that turn off the third semiconductor switch element 25 and the fourth semiconductor switch element 26. By doing so, the transition from the on state to the off state is made in the normal turn-off time.

Alternatively, a logic circuit is provided between the control signal generation unit 16, the third on / off unit 20c, and the fourth on / off unit 20d, and when the determination signals 23c and 23d are low “L”, the control signals 24c and 24d May be set to the off logic so that the third semiconductor switch element 25 and the fourth semiconductor switch element 26 are transitioned from the on state to the off state in the normal turn-off time.

When the reactor current I ₂ causes a positive side overcurrent and a negative side overcurrent, the fourth semiconductor switch element 26 of the upper arm switch and the third semiconductor switch element 25 of the lower arm switch, in which currents are similarly generated, are softly cut off or cut off. By turning the other first semiconductor switch element 8 and the second semiconductor switch element 9 into the off state, it is possible to prevent the same overcurrent from occurring while preventing the destruction by turning it on.

_{Further, when either one of} the reactor current I 1 and the reactor current I ₂ causes an overcurrent, the reactor current of the other may also be a current close to the overcurrent threshold value. In that case, even if the semiconductor switch element does not generate an overcurrent, if the transition from the on state to the off state in the normal turn-off time, the surge voltage may exceed the permissible value.

As shown in FIG. 22, during power running, both the reactor current I ₁ and the reactor current I ₂ are flowing in the positive direction. Therefore, when either of the overcurrents occurs, the first semiconductor switch element of the lower arm switch is used. 8. The third semiconductor switch element 25 is softly shut off, and the second semiconductor switch element 9 and the fourth semiconductor switch element 26 of the upper arm switch usually transition from the off state to the on state over a turn-on time. This makes it possible to prevent the semiconductor switch element from being destroyed.

As shown in FIG. 23, during regeneration, both the reactor current I ₁ and the reactor current I ₂ are flowing in the negative direction. Therefore, when either of the overcurrents occurs, the second semiconductor switch element of the upper arm switch is used. 9. The fourth semiconductor switch element 26 is softly shut off, and the first semiconductor switch element 8 and the third semiconductor switch element 25 of the lower arm switch usually transition from the off state to the on state over a turn-on time. This makes it possible to prevent the semiconductor switch element from being destroyed.

In the above, the determination signal 23a is also input to the third soft cutoff unit 21c and the fourth forced on unit 22d, the determination signal 23b is also input to the fourth soft cutoff unit 21d and the third forced on unit 22c, and the determination signal 23c Is also input to the first soft cutoff unit 21a and the second forced on unit 22b, and the determination signal 23d is also input to the second soft cutoff unit 21b and the first forced on unit 22a.

In the above, the second switch element pair composed of the fourth semiconductor switch element 26 of the upper arm and the third semiconductor switch element 25 of the lower arm, the reactor 4b as the second inductive load, and the current detecting means. The case where one of the current sensor 27, the second positive side overcurrent detection unit 19c, and the second negative side overcurrent detection unit 19d is used has been illustrated and described, but in these cases, n is a positive integer of 1 or more. In this case, it is possible to configure the power conversion device provided with n pieces in the same manner as described above.

Further, as shown in FIG. 24, the power conversion device according to the second embodiment may be a full bridge converter including a full bridge circuit.
The power conversion device in FIG. 24 includes an isolation transformer 33 provided between the primary side circuit 31, the secondary side circuit 32, the primary side circuit 31 and the secondary side circuit 32, and a current sensor which is a current detecting means. It is composed of 34. The isolation transformer 33 is composed of a first winding M ₁ and a second winding M ₂ . The first winding M ₁ is provided on the primary side circuit 31 side, and the second winding M ₂ is provided on the secondary side circuit 32 side. Current sensor 34, the current I _Tr that flows in the first winding M ₁ of the isolation transformer 33 is measured and the current flowing through the current flowing in the direction of the arrow shown in FIG. 24 positive current, in a direction opposite to that of the negative current.

Primary circuit 31 includes a _{Q 4} from the semiconductor switching element to _{Q 1} MOSFET, and a DC power supply 35. The semiconductor switch element Q ₁ and the semiconductor switch element Q ₂ , the semiconductor switch element Q ₃ and the semiconductor switch element Q ₄ are connected in series, and the series connectors are connected in parallel. DC power supply 35 is a power to the parallel-connected series connection, the semiconductor switching element Q _1, the semiconductor switching element Q ₃ are connected to the positive electrode of the DC power source 35 constitute a upper arm, the semiconductor switch The element Q ₂ and the semiconductor switch element Q _{4 form} a lower arm and are connected to the negative electrode of the DC power supply 35.

The secondary circuit 32 includes diodes D ₁ to D ₄ , a capacitor 36, and a reactor 37, and the capacitor 36 and the reactor 37 are connected in series. The diode D ₁ and the diode D ₂ , the diode D ₃ and the diode D ₄ are connected in series, and the series connectors of each other are connected in parallel. The series connection of the capacitor 36 and the reactor 37 is connected in parallel to _{the series connection of the diode D 1} and the diode D ₂ , and the diode D ₃ and the diode D _4.

As shown in FIG. 25, when the semiconductor switch element Q ₁ and the semiconductor switch element Q ₄ are in the ON state, a current flows along the path indicated by the solid line arrow, and the current sensor 34 detects a positive current. When the semiconductor switch element Q ₁ and the semiconductor switch element Q ₄ are turned off, a reflux current flows along the path indicated by the dotted arrow. Therefore, when the positive-side overcurrent occurs, the semiconductor switching element Q _1, the semiconductor switching element Q ₄ is soft blocked, the on state of the semiconductor switching element Q ₂ and the semiconductor switching element Q ₃ at turn-on time of the specified By doing so, the semiconductor switch element Q ₁ and the semiconductor switch element Q ₄ can suppress the generation of surge voltage and transition to the off state, and can prevent destruction due to surge voltage. Semiconductor switching element Q _2, the semiconductor switching element Q ₃ are, it is possible to flow electric current without energizing the body diode, it is possible to prevent the destruction of the body diode due to excessive current.

Similarly, when the semiconductor switch element Q ₂ and the semiconductor switch element Q ₃ are in the ON state, as shown in FIG. 26, a current flows along the path indicated by the solid line arrow, and the current sensor 34 detects a negative current. When the semiconductor switch element Q ₂ and the semiconductor switch element Q ₃ are turned off, a reflux current flows along the path indicated by the dotted arrow. Therefore, when the negative side of the overcurrent occurs, the semiconductor switching element Q ₂ and the semiconductor switching element Q ₃ is soft blocked, the on state of the semiconductor switching element Q _1, the semiconductor switching element Q ₄ at turn-on time of the specified by the semiconductor switch element Q _2, the semiconductor switching element Q ₃ are able to transition to the off state by suppressing a surge voltage generated can be prevented from being damaged by the surge voltage. The semiconductor switch element Q ₁ and the semiconductor switch element Q ₄ can pass a current without energizing the body diode, and can prevent the body diode from being destroyed by an excessive current.

Although the semiconductor switch element has been described as a MOSFET in the first and second embodiments, it is more suitable when a wide bandgap semiconductor is used. A power semiconductor switch element made of a wide bandgap semiconductor has a high withstand voltage, good heat dissipation, and high-speed switching is possible. Specifically, it is a MOSFET using a SiC (silicon carbide, silicon carbide) -based material, a GaN (gallium nitride) -based material, or a diamond-based material.

Conventional switch elements made of Si (silicon) semiconductors cannot be used in the high voltage region where unipolar operation is difficult, but power semiconductor switch elements made of wide bandgap semiconductors can also be used in such high voltage regions. .. Further, the wide bandgap semiconductor has a small power loss and is suitable for high frequency switching operation. Therefore, when a power semiconductor switch element made of a wide bandgap semiconductor is applied to a converter that requires a high frequency, the reactor and the capacitor in the converter can be miniaturized by increasing the switching frequency.

However, wide bandgap semiconductors are expensive. Therefore, in order to make the power conversion device inexpensive and compact, it is necessary to miniaturize the wide bandgap semiconductor, increase the switching speed, and reduce the power loss. Increasing the switching speed means that the normal turn-on time and the normal turn-off time are used in a short time setting, and the surge voltage becomes a larger value.

Further, miniaturization of the reactor means reducing the inductance value, and reducing the inductance value increases the amount of change in the current of the reactor. That is, when the reactor is miniaturized by using the wide bandgap semiconductor, the current value at the time of overcurrent becomes more excessive, and the surge voltage at the time of overcurrent detection becomes more excessive.

Further, in particular, it is known that the SiC-MOSFET undergoes crystal deterioration when the body diode is energized. If crystal deterioration progresses, the on-voltage of the body diode rises, and the SiC-MOSFET itself may be destroyed. It is possible to make it so as to cope with an excessive current such as an overcurrent, but it will increase the cost.

The power conversion device according to the first embodiment and the second embodiment can set a normal turn-off time without being bound by the surge voltage at the time of overcurrent by performing a soft cutoff at the time of overcurrent, and has characteristics of a wider bandgap semiconductor. Can be utilized. Further, since the energization of the body diode is suppressed, crystal deterioration in the SiC-MOSFET can be prevented. By using the wide bandgap semiconductor, the generation of surge voltage and the energization of the body diode become more problems, but by applying this embodiment, it works more usefully and compared with the conventional power conversion device. , The switching speed can be increased, the wide bandgap semiconductor can be miniaturized, and the power conversion device can be miniaturized at low cost.

Although the present application describes various exemplary embodiments and examples, the various features, embodiments, and functions described in one or more embodiments are applications of a particular embodiment. It is not limited to, but can be applied to embodiments alone or in various combinations.
Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed in the present application. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

1 Power storage unit, 2 Input voltage detection circuit, 3 Input capacitor, 4a, 4b, 37 reactor, 5 Converter unit, 6 Smoothing capacitor, 7 Output voltage detection circuit, 8 1st semiconductor switch element, 9 2nd semiconductor switch element, 10 , 28 Connection points, 11, 27, 34 Current sensor, 12a, 12b, 12c, 12d Signal line, 13 Control unit, 14 Control line, 15 External signal line, 16 Control signal generator, 17 1st drive unit, 18th 2 Drive unit, 19a 1st positive side overcurrent detection unit, 19b 1st negative side overcurrent detection unit, 19c 2nd positive side overcurrent detection unit, 19d 2nd negative side overcurrent detection unit, 20a 1st on / off Unit, 20b 2nd on / off section, 21a 1st soft blocking section, 21b 2nd soft blocking section, 22a 1st forced on section, 22b 2nd forced on section, 23a, 23b, 23c, 23d determination signal, 24a, 24b, 24c, 24d control signal, 25 3rd semiconductor switch element, 26 4th semiconductor switch element, 29 3rd drive unit, 30 4th drive unit, 31 primary side circuit, 32 secondary side circuit, 33 isolated transformer, 35 DC power supply, 36 capacitor, M ₁ 1st winding, M ₂ 2nd winding, Q ₁ , Q ₂ , Q ₃ , Q ₄ semiconductor switch element, D ₁ , D ₂ , D ₃ , D ₄ diode, Pi , Ni input terminal, Po, No output terminal, V ₂ * Output voltage command value, V ₁ input voltage, V ₂ output voltage, Gate 1a, Gate 1b, Gate 2a, Gate 2b gate signal, I ₁ reactor current, G gate, S source, D drain, Vgs_pl mirror voltage, Vgs_th threshold voltage.

Claims (14)

A first switch element pair composed of a series circuit of a first switch constituting the lower arm and a second switch constituting the upper arm, and
The first inductive load connected to the connection point between the first switch and the second switch,
The first current detecting means for detecting the current flowing through the first inductive load, and
A control unit that controls the first switch and the second switch is provided.
The control unit
A control signal generator that generates a control signal that controls the first switch and the second switch,
A first overcurrent detection unit that detects that the detection current of the first current detection means is an overcurrent, and
When the first overcurrent detection unit detects the overcurrent, either one of the first switch and the second switch is changed from the off state to the on state in the specified turn-on time, and the other is changed to the specified turn-off. A power conversion device including an on / off drive unit that transitions from an on state to an off state with a turn-off time longer than the time. Equipped with an input terminal to which input voltage is supplied and an output terminal
The second switch is connected to the positive electrode of the output terminal, and the first switch is connected to the negative electrode of the output terminal.
The first current detecting means is configured to detect the current flowing from the input terminal to the connection point as a positive current.
When the first overcurrent detector detects the overcurrent of the positive current, the second switch is changed from the off state to the on state at the specified turn-on time, and the first switch is longer than the specified turn-off time. The power conversion device according to claim 1, wherein a transition from an on state to an off state is performed at a turn-off time. Equipped with an input terminal to which input voltage is supplied and an output terminal
The second switch is connected to the positive electrode of the output terminal, and the first switch is connected to the negative electrode of the output terminal.
The first current detecting means is configured to detect the current flowing from the connection point to the input terminal as a negative current.
When the first overcurrent detection unit detects the overcurrent of the negative current, the second switch is changed from the on state to the off state with a turn-off time longer than the specified turn-off time, and the first switch is changed to the above-specified The power conversion device according to claim 1, wherein a transition from an off state to an on state is performed at a turn-on time. It is composed of a series circuit of a switch connected to the negative electrode of the output terminal to form a lower arm and a switch connected to the positive electrode of the output terminal to form an upper arm, and each is connected in parallel to the first switch element pair. N second switch element pairs (n is a positive integer of 1 or more) and
The n second inductive loads connected to the connection points between the switches constituting each of the n second switch element pairs, and the n second inductive loads.
The current flowing from the input terminal to the connection point between the switches constituting each of the n second switch element pairs is detected as a positive current, and the current flowing from the connection point between the switches to the input terminal is negative. N second current detecting means for detecting as current, and
It is provided with n second overcurrent detection units for detecting that the detection current of each of the n second current detection means is an overcurrent.
When either the first overcurrent detection unit or the second overcurrent detection unit detects an overcurrent, the upper arm switch and the lower arm are not connected to the inductive load through which the current for which the overcurrent is detected flows. The power conversion device according to claim 2 or 3, wherein the switch is changed from an on state to an off state over a specified turn-off time. It is composed of a series circuit of a switch connected to the negative electrode of the output terminal to form a lower arm and a switch connected to the positive electrode of the output terminal to form an upper arm, and each is connected in parallel to the first switch element pair. N second switch element pairs (n is an integer of 1 or more) and
The n second inductive loads connected to the connection points between the switches constituting each of the n second switch element pairs, and the n second inductive loads.
The current flowing from the input terminal to the connection point between the switches constituting each of the n second switch element pairs is detected as a positive current, and the current flowing from the connection point between the switches to the input terminal is negative. N second current detecting means for detecting as current, and
It is provided with n second overcurrent detection units for detecting that the detection current of each of the n second current detection means is an overcurrent.
When the overcurrent of the positive current is detected, the upper arm switch that is not connected to the inductive load through which the current that detects the overcurrent flows is changed from the off state to the on state over a specified turn-on time, and the lower arm is changed. The power conversion device according to claim 2, wherein the switch is transitioned from an on state to an off state over a turn-off time longer than a specified turn-off time. It is composed of a series circuit of a switch connected to the negative electrode of the output terminal to form a lower arm and a switch connected to the positive electrode of the output terminal to form an upper arm, and each is connected in parallel to the first switch element pair. N second switch element pairs (n is an integer of 1 or more) and
The n second inductive loads connected to the connection points between the switches constituting each of the n second switch element pairs, and the n second inductive loads.
The current flowing from the input terminal to the connection point between the switches constituting each of the n second switch element pairs is detected as a positive current, and the current flowing from the connection point between the switches to the input terminal is negative. N second current detecting means for detecting as current, and
It is provided with n second overcurrent detection units for detecting that the detection current of each of the n second current detection means is an overcurrent.
When the overcurrent of the negative current is detected, the upper arm switch that is not connected to the inductive load through which the current that detects the overcurrent flows is changed from the on state to the off state with a turnoff time longer than the specified turnoff time. The power conversion device according to claim 3, wherein the lower arm switch is changed from an off state to an on state at a specified turn-on time. A first switch element pair composed of a series circuit of a first switch connected to the positive electrode of the DC power supply to form an upper arm and a second switch connected to the negative electrode of the DC power supply to form a lower arm.
It is composed of a series circuit of a third switch connected to the positive electrode of the DC power supply to form an upper arm and a fourth switch connected to the negative electrode of the DC power supply to form a lower arm. With the second switch element pair connected in parallel,
A transformer having a first winding provided on the primary side and a second winding provided on the secondary side,
A current detecting means for detecting the current flowing through the first winding and
The overcurrent detection unit for detecting that the detection current of the current detection means is an overcurrent is provided.
One end of the first winding is connected to the connection point between the first switch and the second switch, and the other end is connected to the connection point between the fourth switch and the third switch.
The current detecting means is configured to detect the current flowing from one end of the first winding to the other end as a positive current and the current flowing from the other end to the other end as a negative current.
When the overcurrent detection unit detects the overcurrent of the positive current, the first switch and the fourth switch are changed from the on state to the off state in a turn-off time longer than the specified turn-off time, and the second switch is changed. The switch and the third switch are changed from the off state to the on state at the specified turn-on time.
When the overcurrent detection unit detects the overcurrent of the negative current, the second switch and the third switch are changed from the on state to the off state in a turn-off time longer than the specified turn-off time, and the first switch is changed. A power conversion device characterized by transitioning a switch and the fourth switch from an off state to an on state at a specified turn-on time. A switch that transitions from the off state to the on state at the specified turn-on time when an overcurrent is detected transitions to the on state after the mirror period of the switch that transitions from the on state to the off state at a turn-off time longer than the specified turn-off time ends. The power conversion device according to any one of claims 1 to 7, wherein the power conversion device is characterized by the above. The power conversion device according to claim 8, wherein the end of the mirror period is determined by the gate voltage of the switch. The power conversion device according to claim 8, wherein the end of the mirror period is determined by time. When an overcurrent is detected, the switch that transitions from the off state to the on state at the specified turn-on time continues to be on until the current value falls below the specified current value, and then changes from the on state to the off state at the specified turn-off time. The power conversion device according to any one of claims 1 to 7, wherein the transition is performed. When an overcurrent is detected, the switch that transitions from the off state to the on state at the specified turn-on time continues to be on until the current value reaches 0A, and then transitions from the on state to the off state at the specified turn-off time. The power conversion device according to any one of claims 1 to 7, wherein the power conversion device is characterized. A claim characterized in that a switch that transitions from an off state to an on state at a specified turn-on time when an overcurrent is detected continues to be on for a specified time and then transitions from an on state to an off state at a specified turn-off time. Item 2. The power conversion device according to any one of Items 1 to 7. The power conversion according to any one of claims 1 to 13, wherein at least one of the switch constituting the lower arm and the switch constituting the upper arm is composed of a wide bandgap semiconductor. Device.

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