POWER CONVERSION CIRCUIT, POWER CONVERSION APPARATUS, AND CONTROL SYSTEM

Provided is a power conversion circuit, including: a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, wherein a current value at a cross point of current-voltage characteristics when a forward current flows through the first switching element and current-voltage characteristics when a current flows through the second switching element is greater than a rated current value of the power conversion circuit.

1. TECHNICAL FIELD

The present disclosure relates to a power conversion circuit, a power conversion apparatus, and a control system.

2. DESCRIPTION OF THE RELATED ART

In recent years, it is studied in a power conversion circuit to connect a first semiconductor element and a second semiconductor element in parallel and to cause these semiconductor elements to perform switching operation. It is sturdied to use, for example, an MOSFET as the first semiconductor element and to use, for example, an IGBT as the second semiconductor element. It is studied to improve characteristics of the entire power conversion circuit by connecting the switching elements having different characteristics in parallel as described above.

On the other hand, as next-generation switching elements that enable realization of high withstand voltage, low loss, and high heat resistance, semiconductor devices using gallium oxide (Ga2O3) having a wide bandgap has attracted attention, and are expected to be applied to a power semiconductor device such as inverters and converters. In addition, because of the wide bandgap, application of the semiconductor devices to light emitting/receiving devices such as LEDs and sensors is also expected. Such gallium oxide may control the bandgap by forming a mixed crystal with indium or aluminum singly or in combination, and configure an extremely attractive family of materials as InAlGaO-based semiconductors. Here, InAlGaO-based semiconductors indicate InXAlYGaZO3(0≤X≤2, 0≤Y≤2, 0≤Z≤2, and X+Y+Z=1.5 to 2.5), and may be regarded as a family of materials including gallium oxide.

The first switching element and the second switching element connected in parallel are used for protection from a short-circuit current, for optimization of an on-resistance, and the like. For example, there is a control apparatus configured to, when driving of an IGBT and an MOSFET connected in parallel is controlled and an on-resistance per unit area of the IGBT is greater than an on-resistance per unit area of the MOSFET, turn off the IGBT and then turn off the MOSFET, and to, when the on-resistance per unit area of the IGBT is less than the on-resistance per unit area of the MOSFET, turn off the MOSFET and then turn off the IGBT. Further, there is a power conversion apparatus including: a switching circuit including a first switching element and a second switching element connected in parallel to each other; and a control apparatus configured to selectively perform first switching control for driving the first switching element and second switching control for driving the second switching element based on a current instruction value to the switching circuit and an actual current flowing through the switching circuit, in which, when at least one of the current instruction value and the actual current flowing exceeds a predetermined threshold during the first switching control, the control apparatus changes the switching control to the second switching control.

SUMMARY OF THE INVENTION

According to an example of the present disclosure, there is provided a power conversion circuit, including: a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, wherein a current value at a cross point of current-voltage characteristics when a forward current flows through the first switching element and current-voltage characteristics when a current flows through the second switching element is greater than a rated current value of the power conversion circuit.

According to an example of the present disclosure, there is provided a power conversion circuit, at least comprising, a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, wherein the power conversion circuit comprises a reactor connected in series to the second switching element.

Thus, a power conversion circuit according to the present disclosure enables improvement in short-circuit withstand time while maintaining the switching characteristics.

DETAILED DESCRIPTION

Note that issues and the like in a case where a switching element actually using gallium oxide is applied to a circuit have not been studied. Further, the control apparatus or the power conversion apparatus has an issue that a plurality of gate drivers is necessary, or control itself is complicated.

The present inventors have found that a power conversion circuit including: a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, in which a current value at a cross point of current-voltage characteristics when a forward current flows through the first switching element and current-voltage characteristics when a current flows through the second switching element is greater than a rated current value of the power conversion circuit enables improvement in short-circuit withstand time without impairing an improvement effect of switching characteristics by the wide bandgap semiconductor such as gallium oxide. Further, the present inventors have found that a power conversion circuit at least including: a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, in which the power conversion circuit includes a reactor connected in series to the second switching element enables improvement in short-circuit withstand time without impairing an improvement effect of switching characteristics by a wide bandgap semiconductor such as gallium oxide. Furthermore, the present inventors have found that such a power conversion circuit makes it possible to solve the above-described existing issues.

Power conversion circuit and Power conversion apparatuses according to embodiments of the present disclosure are described below. Note that the present disclosure is not limited to the embodiments described below.

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. In the following description, the same parts and components are designated by the same reference numerals. The present embodiment includes, for example, the following disclosures.

A power conversion circuit, including: a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, wherein a current value at a cross point of current-voltage characteristics when a forward current flows through the first switching element and current-voltage characteristics when a current flows through the second switching element is greater than a rated current value of the power conversion circuit.

The power conversion circuit according to [Structure 1], wherein a voltage value at the cross point is twice or more a rated current value of the power conversion circuit.

The power conversion circuit according to [Structure 1] or [Structure 2], wherein the second switching element is a switching element including a wide bandgap semiconductor.

The power conversion circuit according to any of [Structure 1] to [Structure 3], wherein the second switching element includes a gallium oxide-based MOSFET, a gallium oxide-based IGBT, a gallium nitride-based HEMT, a SiC-based MOSFET, or a SiC-based IGBT.

The power conversion circuit according to any of [Structure 1] to [Structure 4], wherein the second switching element is a gallium oxide-based MOSFET.

The power conversion circuit according to any of [Structure 1] to [Structure 5], wherein the second switching element is a trench MOSFET.

The power conversion circuit according to any of [Structure 1] to [Structure 6], wherein the first switching element includes a silicon-based MOSFET or a silicon-based IGBT.

The power conversion circuit according to any of [Structure 1] to [Structure 7], further comprising a diode connected in series to the first switching element.

A power conversion circuit, at least including: a first switching element and a second switching element connected in parallel to each other; and a control unit configured to control turn-on/off of each of the switching elements, wherein the power conversion circuit includes a reactor connected in series to the second switching element.

The power conversion circuit according to [Structure 9], wherein the second switching element is a switching element including a wide bandgap semiconductor.

The power conversion circuit according to [Structure 9] or [Structure 10], wherein the second switching element includes a gallium oxide-based MOSFET, a gallium oxide-based IGBT, a gallium nitride-based HEMT, a SiC-based MOSFET, or a SiC-based IGBT.

The power conversion circuit according to any of [Structure 9] to [Structure 11], wherein the second switching element is a gallium oxide-based MOSFET.

The power conversion circuit according to any of [Structure 9] to [Structure 12], wherein the first switching element includes a silicon-based MOSFET or a silicon-based IGBT.

The power conversion circuit according to any of [Structure 9] to [Structure 13], wherein inductance of the reactor is adjusted to a value causing a voltage applied to the first switching element when a predetermined short-circuit current is generated in the power conversion circuit not to exceed an allowable withstand voltage value of the first switching element.

A power conversion apparatus performing power conversion between a power supply and a load, the power conversion apparatus comprising a power conversion circuit provided on a power supply path from the power supply to the load, wherein as the power conversion circuit, the power conversion circuit according to any of [Structure 1] to [Structure 14] is used.

A control system using the power conversion circuit according to any of [Structure 1] to [Structure 14] or the power conversion apparatus according to [Structure 15].

A control system inFIG.1is mounted on an automobile such as a hybrid vehicle, a fuel-cell vehicle, and an electric vehicle, and performs power conversion between a battery1and a motor5driving wheels. However, the technique disclosed in the present embodiment is applicable not only to a control system using a power conversion apparatus mounted on an automobile but also to a control system using any of various power conversion apparatuses. A system including the battery1, the power conversion apparatus3, and the motor5inFIG.1configures a control system of the present disclosure.

The motor5functions as an electric motor and as a power generator in some cases. When the motor5functions as an electric motor, power is supplied from the battery1to the motor5through the power conversion apparatus3. In this case, the battery1serves as a power supply, and the motor5serves as a load. In contrast, when the motor functions as a power generator, power is supplied from the motor5to the battery1through the power conversion apparatus3. In this case, the motor5serves as a power supply, and the battery1serves as a load.

As illustrated inFIG.1, the power conversion apparatus3includes a DC-DC converter2, an inverter4, and a control unit6. The DC-DC converter2is provided between the battery1and the inverter4. The DC-DC converter2is a step-up/down DC-DC converter, and may step up and down direct-current power between the battery1and the inverter4. The inverter4is provided between the DC-DC converter2and the motor5. The inverter4is a three-phase inverter, and may perform conversion from direct-current power to three-phase alternating-current power and inverse conversion thereof, between the DC-DC converter2and the motor1.

For example, in the case where the motor5functions as an electric motor, the direct-current power supplied from the battery1is stepped up by the DC-DC converter2, the resultant direct-current power is converted into the three-phase alternating-current power by the inverter4, and the three-phase alternating-current power is then supplied to the motor5. As a result, the three-phase alternating-current motor5is driven by the direct-current power supplied from the battery1. In contrast, in the case where the motor5functions as a power generator, the three-phase alternating-current power supplied from the motor5is converted into direct-current power by the inverter4, the direct-current power is stepped down by the DC-DC converter2, and the resultant direct-current power is then supplied to the battery1. As a result, power generated by the motor5is charged in the battery1.

FIG.2illustrates an example of circuit configurations of the DC-DC converter2and the inverter4according to a first embodiment of the present disclosure. As illustrated inFIG.2, the DC-DC converter2and the inverter4are configured using a plurality of switching circuits10. The switching circuits10are provided on a power supply path between the battery1and the motor5, and operation of each of the switching circuits10is controlled by the control unit6. Each of the switching circuits10includes a first switching element11and a second switching element12. A configuration of each of the switching circuits10is described in detail below.

The other configurations of the DC-DC converter2and the inverter4except for the configurations of the switching circuits10are common to configurations of a well-known DC-DC converter and a well-known inverter. For example, the DC-DC converter includes the switching circuit10, an inductor, and a smoothing capacitor. The inverter4includes six switching circuits10. The switching circuits10are provided on a U-phase upper arm13a, a U-phase lower arm13b, a V-phase upper arm13c, a V-phase lower arm13d, a W-phase upper arm13e, and a W-phase lower arm13fThe configurations of the DC-DC converter2and the inverter4inFIG.2are illustrative, and are appropriately changeable depending on an application. Furthermore, the power conversion apparatus3may include only a step-up (or step-down) DC-DC converter. As illustrated by dotted lines inFIG.2, a calculation unit7including a CPU (Central Processing Unit) and a storage unit8including a non-volatile memory are provided in the control unit6. A signal input to the driving control unit6is provided to the calculation unit7, and the calculation unit7generates a feedback signal for each of the switching elements by performing necessary calculation. The storage unit8temporarily holds a calculation result of the calculation unit7and stores physical constants, functions, and the like necessary for driving control in a format of a table, and appropriately outputs the physical constants, the functions, and the like to the calculation unit7. Well-known configurations are applicable to the calculation unit7and the storage unit8, and processing capabilities and the like of the calculation unit7and the storage unit8are also optionally selectable.

Each of the switching circuits10includes the first switching element11and the second switching element12. The first switching element11and the second switching element12are connected in parallel to each other. The first switching element11includes, for example, a silicon-based MOSFET or a silicon-based IGBT. The second switching element12is not particularly limited unless it interferes with the present disclosure. In the embodiment of the present disclosure, the second switching element is preferably a switching element including a wide bandgap semiconductor (for example, gallium nitride, silicon carbide, gallium oxide, or diamond). For example, the switching element is not particularly limited unless it interferes with the present disclosure, and may be an MOSFET or an IGBT. Examples of the second switching element include a gallium oxide-based MOSFET, a gallium oxide-based IGBT, a gallium nitride-based HEMT, a SiC-based MOSFET or SiC-based IGBT, and a Si-based MOSFET or Si-based IGBT. In the embodiment of the present disclosure, the second switching element is preferably a gallium oxide-based MOSFET, a gallium oxide-based IGBT, a gallium nitride-based HEMT, a SiC-based MOSFET, or a SiC-based IGBT. Further, in the embodiment of the present disclosure, the second switching element preferably includes a reflux diode (not illustrated). The reflux diode may be incorporated in the switching element or may be externally provided.

FIG.3illustrates relationship between current-voltage characteristics when a forward current flows through the first switching element inFIG.2and current-voltage characteristics when a current flows through the second switching element inFIG.2.FIG.3illustrates an example in a case where the first switching element is a silicon-based IGBT and the second switching element is a gallium oxide-based MOSFET. As illustrated inFIG.3, a current value at a cross point of the current-voltage characteristics of the first switching element and the current-voltage characteristics of the second switching element is greater than a rated current value of the power conversion circuit of the power conversion apparatus. Therefore, in a case where the power conversion circuit of the power conversion apparatus3operates within a range of a rated current, the current flows through the second switching element (gallium oxide-based MOSFET). At the time of short-circuit, the Si-based IGBT having a longer short-circuit withstand time bears the current, which makes it possible to prevent the gallium oxide-based MOSFET from being broken by a short-circuit current. Accordingly, it is possible to realize the power conversion apparatus excellent in the short-circuit current resistance while maximizing advantages of the gallium oxide-based MOSFET excellent in switching characteristics such as switching speed within the range of the rated current. Further, in the embodiment of the present disclosure, using the first switching element (silicon-based IGBT) and the second switching element (gallium oxide-based MOSFET) in combination makes it possible to minimize the number of gate drivers corresponding to the switching elements. Moreover, according to the embodiment of the present disclosure, since it is unnecessary to separately control the first switching element and the second switching element, it is possible to achieve the above-described effects without complicating the control programs and the like.

The configuration for making the current value at the cross point of the current-voltage characteristics of the first switching element and the current-voltage characteristics of the second switching element greater than the rated current value of the power conversion circuit of the power conversion apparatus as illustrated inFIG.3is not particularly limited unless it interferes with the present disclosure. In the embodiment of the present disclosure, appropriately combining the characteristics of the first switching element and/or the second switching element makes it possible to make the current value at the cross point greater than the rated current value of the power conversion circuit of the power conversion apparatus. In the embodiment of the present disclosure, the current value at the cross point may be increased by, for example, shifting a graph of the current-voltage characteristics of the first switching element inFIG.3rightward or reducing a gradient of the graph. Alternatively, the current value at the cross point may be increased by, for example, increasing a gradient of a graph of the current-voltage characteristics of the second switching element. As the configuration for increasing a rising voltage of the first switching element, for example, arrangement of a diode (for example, PN diode) in series to the first switching element as illustrated inFIG.4AandFIG.4Bis considered. Further, as a method of increasing the gradient of the graph of the current-voltage characteristics of the second switching element, for example, use of a device having lower on-resistance as the second switching element is considered. In the embodiment of the present disclosure, for example, a trench MOSFET is preferably used as the second switching element.

FIG.5illustrates an example of circuit configurations of the DC-DC converter2and the inverter4according to a second embodiment of the present disclosure. As illustrated inFIG.5, the DC-DC converter2and the inverter4are configured using the plurality of switching circuits10. The switching circuits10are provided on a power supply path between the battery1and the motor5, and operation of each of the switching circuits10is controlled by the control unit6. Each of the switching circuits10includes the first switching element11and the second switching element12. A configuration of each of the switching circuits10is described in detail below.

The other configurations of the DC-DC converter2and the inverter4except for the configurations of the switching circuits10are common to configurations of a well-known DC-DC converter and a well-known inverter. For example, the DC-DC converter includes the switching circuit10, an inductor, and a smoothing capacitor. The inverter4includes six switching circuits10. The switching circuits10are provided on the U-phase upper arm13a, the U-phase lower arm13b, the V-phase upper arm13c, the V-phase lower arm13d, the W-phase upper arm13e, and the W-phase lower arm13fThe configurations of the DC-DC converter2and the inverter4inFIG.5are illustrative, and are appropriately changeable depending on an application. Furthermore, the power conversion apparatus3may include only a step-up (or step-down) DC-DC converter. As illustrated by dotted lines inFIG.5, the calculation unit7including a CPU (Central Processing Unit) and the storage unit8including a non-volatile memory are provided in the control unit6. A signal input to the driving control unit6is provided to the calculation unit507, and the calculation unit7generates a feedback signal for each of the switching elements by performing necessary calculation. The storage unit8temporarily holds a calculation result of the calculation unit7and stores physical constants, functions, and the like necessary for driving control in a format of a table, and appropriately outputs the physical constants, the functions, and the like to the calculation unit7. Well-known configurations are applicable to the calculation unit7and the storage unit8, and processing capabilities and the like of the calculation unit7and the storage unit8are also optionally selectable.

Each of the switching circuits10includes the first switching element11and the second switching element12. The first switching element11and the second switching element12are connected in parallel to each other. Further, a reactor15is connected in series to the second switching element12. The first switching element11includes, for example, a silicon-based MOSFET or a silicon-based IGBT. The second switching element12is not particularly limited unless it interferes with the present disclosure. In the embodiment of the present disclosure, the second switching element is preferably a switching element including a wide bandgap semiconductor (for example, gallium nitride, silicon carbide, gallium oxide, or diamond). The switching element is not particularly limited unless it interferes with the present disclosure, and may be an MOSFET or an IGBT. More specifically, examples of the second switching element include a gallium oxide-based MOSFET, a gallium oxide-based IGBT, a gallium nitride-based HEMT, a SiC-based MOSFET or SiC-based IGBT, and a Si-based MOSFET or Si-based IGBT. In the embodiment of the present disclosure, the second switching element is preferably a gallium oxide-based MOSFET, a gallium oxide-based IGBT, a gallium nitride-based HEMT, a SiC-based MOSFET, or a SiC-based IGBT. Further, in the embodiment of the present disclosure, the second switching element preferably includes a reflux diode (not illustrated). The reflux diode may be incorporated in the switching element or may be externally provided. In addition, the reactor is not particularly limited, and may be a well-known reactor.

FIG.6schematically illustrates one switching circuit10inFIG.5, namely, a circuit in which the first switching element11and the second switching element12are connected in parallel, and the reactor15is connected in series to the second switching element12. In the switching circuit10, during normal operation, the first switching element bears the voltage applied to the first switching element11side, and the second switching element12and the reactor15bear the voltage applied to the second switching element12side. At a time when a short-circuit current is generated, a time rate of change in the current flowing through the switching circuit10is drastically increased; however, the reactor15bears a predetermined voltage of the increased amount, which makes it possible to reduce the voltage applied to the second switching element to the predetermined voltage or less. In other words, connecting the second switching element12and the reactor15in series to each other makes it possible to suppress the short-circuit current flowing through the second switching element when the short-circuit current is generated in the switching circuit10, and to protect the second switching element from being broken by the short-circuit current. Here, inductance of the reactor15is adjusted to a value causing the voltage applied to the first switching element when the predetermined short-circuit current is generated in the switching circuit10not to exceed an allowable withstand voltage value of the first switching element. Accordingly, it is possible to realize the power conversion apparatus excellent in the short-circuit current resistance while maximizing advantages of the gallium oxide-based MOSFET excellent in switching characteristics such as switching speed within the range of the rated current. Further, in the embodiment of the present disclosure, using the first switching element (silicon-based IGBT) and the second switching element (gallium oxide-based MOSFET) in combination makes it possible to minimize the number of gate drivers corresponding to the switching elements. Moreover, according to the embodiment of the present disclosure, since it is unnecessary to separately control the first switching element and the second switching element, it is possible to achieve the above-described effects without complicating the control programs and the like.

Note that the plurality of embodiments according to the present disclosure may be combined, and some components may be applied to other embodiments. In addition, the number of some components may be increased/decreased, and may be further combined with other well-known technique. Modifications such as partial omission may be made unless it interferes with the present disclosure, and such modifications are also included in the embodiments of the present disclosure.

The embodiments of the present invention are exemplified in all respects, and the scope of the present invention includes all modifications within the meaning and scope equivalent to the scope of claims.

REFERENCE SIGNS LIST