JP2011030396A - Parallel connection dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of effectively suppressing surge voltages and noises, while utilizing superior characteristics of a lateral GaN MOS high electron mobility transistor. <P>SOLUTION: A parallel connection DC-DC converter 100a is provided which is used for a moving-body mounting type power supply system to supply an electric power to a device to drive a moving body, and has a boosting ratio of 4 or more. The parallel connection DC-DC converter 100a includes three DC-DC converter units 111, 112, 113 connected in parallel with one another. Each DC-DC converter unit includes switching elements 511, 512, 513 including a lateral type high electron mobility transistor using GaN as a material and reactors 121, 122, 123 connected in series to the switching elements thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a DC-DC converter used in a power supply system that supplies power to a device that drives a vehicle or other moving body. In particular, the present invention relates to a DC-DC converter used in a power supply system mounted on a moving body. The mobile body includes a hybrid system that uses an internal combustion engine and a motor as a drive device, an electric vehicle that uses a motor as a drive device, a fuel cell vehicle that drives a motor with electric power supplied from a fuel cell and a storage battery, and the like. included.

  In Patent Document 1, as a power supply source for a mobile body, a power supply system that realizes efficient driving by boosting the voltage of a direct current power source with a DC-DC converter and supplying high-voltage and small-current power to a motor. Has been proposed. The reason why efficient driving is realized by power supply with high voltage and small current is that copper loss or the like in the motor or wiring system can be reduced (for example, paragraph 0029). On the other hand, in Patent Document 2, as a power supply source for a microprocessor, a power supply system that realizes efficient driving at a low voltage and a large current by connecting a plurality of DC-DC converters in parallel and shifting the phase. Has been proposed. The reason why efficient driving is realized by power supply with low voltage and large current is that the supply power can be reduced by decreasing the voltage while supplying a large current to drive the logic circuit of the microprocessor. is there. The low-voltage, high-current power supply system can be grasped as a power supply system in which the output impedance is reduced by connecting a plurality of DC-DC converters in parallel.

  FIG. 1 is an explanatory diagram showing an example of a conventional power drive system mounted on a moving body (not shown) such as a hybrid system or a fuel cell vehicle. A conventional power drive system includes a storage battery 400, a DC-DC converter 100 that boosts DC power supplied from the storage battery 400, a capacitor 700 that smoothes the boosted DC power, and a smoothed DC power. Is converted to three-phase alternating current, and a three-phase motor 300 driven by the three-phase alternating current is provided. The hybrid system is generally configured by mechanically connecting an internal combustion engine (not shown) to the output shaft of the three-phase motor 300 with a planetary gear or the like. The fuel cell vehicle is generally configured by electrically connecting a fuel cell (not shown) to the inverter 200 via another DC-DC converter or the like.

  The conventional DC-DC converter 100 includes a reactor 120 having an inductance L, two insulated gate bipolar transistors (IGBT) 131 and 141, and two diodes 132 and 142. One electrode of the reactor 120 is connected to the positive electrode of the storage battery 400. The other electrode of reactor 120 is connected to the collector electrode of IGBT 131 and the emitter electrode of IGBT 141. The collector electrode of IGBT 141 is connected to the positive electrode of inverter 200 and one electrode of capacitor 700. The negative electrode of inverter 200 and the other electrode of capacitor 700 are connected to the emitter electrode of IGBT 131 and the negative electrode of storage battery 400. The anode of the diode 132 is connected to the emitter electrode of the IGBT 131. The cathode of the diode 132 is connected to the collector electrode of the IGBT 131. The anode of the diode 142 is connected to the emitter electrode of the IGBT 141. The cathode of the diode 142 is connected to the collector electrode of the IGBT 141.

FIG. 2 is an explanatory diagram showing the operating state of the DC-DC converter 100 of the prior art. FIG. 2A shows the operating state of the DC-DC converter 100 during the step-up operation. In FIG. 2A, illustration of elements that are not involved in the boosting operation is omitted for easy understanding. The DC-DC converter 100 can boost the voltage of the DC power supplied from the storage battery 400 by turning on and off the IGBT 131 with a predetermined duty ratio. Specifically, the IGBT 131 is turned off after the current energy is stored in the reactor 120 by turning on the IGBT 131 and causing the current I ₁ to flow through the reactor 120. Then, the reactor 120 generates a voltage so as to maintain the current value flowing through the reactor 120 with the current energy. On the other hand, since the positive electrode of the storage battery 400 is connected to one electrode of the reactor 120, a voltage obtained by adding the voltage of the storage battery 400 and the voltage generated by the reactor 120 is generated at the other electrode of the reactor 120. . Thus, a voltage higher than the power supply voltage of the storage battery 400 is applied between the electrodes of the capacitor 700.

As shown in FIG. 2A, the reactor 120 generates a voltage equal to the product of the time differential value of the current and the inductance L of the reactor 120 (= L × di / dt). As a result, the current I ₂ flows into one electrode of the capacitor 700 via the diode 142, so that electric power is stored in the capacitor 700 and can be supplied to the positive electrode of the inverter 200 with a stable voltage (smoothing). .

FIG. 2B shows the operating state of the DC-DC converter 100 during the regenerative operation. In FIG. 2B, illustration of elements not involved in the regenerative operation is omitted for easy understanding. The regenerative operation is an operation mode in which, for example, the current I ₃ is returned to the storage battery 400 and charged in accordance with the electric power generated by the three-phase motor 300 during the deceleration of the moving body (not shown). The DC-DC converter 100 can regenerate (reflux) the electric power generated by the three-phase motor 300 via the inverter 200 by turning on the IGBT 141. The diode 132 is equipped to prevent an excessively high voltage from being generated between the collector and emitter of the IGBT 131 when the IGBT 141 is turned off.

JP 2008-125257 A JP 2009-5467 A

  As a switching element of a DC-DC converter, the inventors of the present application employ a lateral type high electron mobility transistor (High Electron) of gallium nitride (GaN), which is a wide gap semiconductor having characteristics of lower switching loss and lower on-resistance than IGBT. The use of Mobility Transistor (HEMT) was examined. The high electron mobility transistor is a field effect transistor having a two-dimensional electron gas (2DEG) induced in a semiconductor heterojunction (described later) as a channel.

  FIG. 3 is an explanatory diagram showing an example of the structure of a GaN lateral MOS high electron mobility transistor (insulated gate lateral HEMT) which the inventors have attempted to use. The GaN lateral MOS high electron mobility transistor 500 includes a sapphire substrate 510, an i-GaN layer 520 that is an undoped GaN layer provided on the sapphire substrate 510, and an undoped GaN 520 provided on the undoped GaN 520. i-AlGaN layer 540. The junction surface between the i-AlGaN layer 540 and the i-GaN layer 520 constitutes a heterojunction that creates a new effect by connecting different kinds of semiconductors. In the heterojunction, the i-AlGaN layer 540 and the i-GaN layer 520 are different in forbidden band width (band gap) and electron affinity, so that discontinuity of the conductor energy occurs and a kind of quantum well is formed. Can effectively confine electrons. The electrons thus confined form a two-dimensional electron gas (2DEG) 530 that functions as an efficient channel.

  In the GaN lateral MOS high electron mobility transistor 500, two contact layers 551 and 552 are provided at both ends of a two-dimensional electron gas (2DEG) 530. The contact layer 551 is provided with an emitter electrode 571 with a titanium layer 561 interposed therebetween. The contact layer 552 is provided with a collector electrode 573 through a titanium layer 563. On the other hand, the i-AlGaN layer 540 is provided with a gate electrode 572 with a silicon oxide insulating layer 562 interposed therebetween. Since the two-dimensional electron gas (2DEG) 530 includes a large amount of carriers supplied from the i-AlGaN layer 540 to the undoped i-GaN layer 520 with few impurities that hinder electron transfer, smooth electron transfer and abundant A low on-resistance is realized by realizing a carrier. The GaN lateral MOS high electron mobility transistor 500 has an advantage that the loss during high-speed operation is low because the capacitance is further small.

However, when the present inventors configured a DC-DC converter using the GaN lateral MOS high electron mobility transistor 500 and conducted a driving experiment thereof, as shown in FIG. It has been found that surge voltage and noise are generated, which is not practical. Such a phenomenon becomes prominent when the cycle for turning on and off the transistor is set to a high frequency. According to the analysis of the inventors of the present application, the cause of this is not only that the fluctuation speed of the current value (temporal differentiation of the current value) is increased due to the increase of the driving frequency, but also the modularization of the DC-DC converter. It has been found that the generation of voltage due to the parasitic inductance Lp (see FIG. 1) such as the printed pattern and the mounting wiring accompanying this becomes obvious. That is, the superior switching characteristics of the lateral high-electron mobility transistor 500 of GaN, as shown in FIG. 5, because the rate of decrease in the current value I _d at turn-off is extremely large, the parasitic inductance Lp of such printed pattern It has been found that a large peak and noise occur in the collector-emitter voltage _Vds .

  The present invention was created to solve the above-mentioned new problem found by the inventors of the present invention, and suppresses surge voltage and noise while utilizing the excellent characteristics of the GaN lateral MOS high electron mobility transistor. Provide technology for effective suppression.

The present invention can provide techniques exemplified as the following configurations and modes.
The first configuration example provides a parallel-connected DC-DC converter that is used in a mobile unit-mounted power supply system that supplies power to a device that drives the mobile unit and has a step-up ratio of 4 or more. This parallel connection type DC-DC converter includes three DC-DC converter units connected in parallel to each other. Each DC-DC converter unit has a switching element which is a lateral high electron mobility transistor made of GaN, and a reactor connected in series to the switching element.

  Since the parallel connection type DC-DC converter of the first configuration example includes three DC-DC converter units connected in parallel to each other, the current flowing through the parallel connection type DC-DC converter is supplied to the three DC-DC converters. It can be distributed in the converter unit. Thereby, the current which flows into each DC-DC converter unit can be reduced, and as a result, the surge voltage can be reduced by suppressing the time differentiation (fluctuation) of the current value.

  According to the analysis by the present inventors, the generation factor of the surge voltage and the mechanism of reduction are as follows. The surge voltage is generated by the parallel inductance type DC-DC converter being modularized (print pattern), the parasitic inductance Lp (see FIG. 1) accompanying the mounting wiring and the like. This parasitic inductance generates a voltage that suppresses fluctuations in the current value caused by turning on and off the switching element, so that the switching element has excellent response characteristics and the current value drop rate at turn-off (current value) As the time derivative of () is faster, a larger voltage is generated. In this configuration, the time differentiation of the current value is reduced by distributing the current to the three DC-DC converter units and reducing the current value flowing through each DC-DC converter unit.

  According to the common general knowledge of those skilled in the art at the time of filing, the parallel connection type DC-DC converter reduces the output impedance by connecting a plurality of DC-DC converter units in parallel, which makes it efficient at a low voltage and a large current. It is used as a configuration that realizes simple driving. On the other hand, the power source for moving bodies has a technology direction of suppressing a large current that causes a high voltage and causes copper loss. Furthermore, the parallel connection of a plurality of DC-DC converter units increases the number of reactors and semiconductor elements due to the increase in the number of DC-DC converter units to be connected in parallel, thereby increasing the total weight and cost of the DC-DC converter. Will cause the problem. In particular, unlike a power supply to a logic circuit or the like, a power source for a mobile body using a large reactor becomes a big problem.

  The present inventors have proposed that a configuration in which a plurality of DC-DC converter units developed in order to increase the current by stepping down are connected in parallel to a power source for a mobile body that needs to be stepped up and reduced in current. We found it advantageous. In the case of a DC-DC converter that boosts and reduces current, it is not necessary to divide into multiple units and connect them in parallel. If such a thing is done, it will be necessary to use several large-sized reactors, and it is disadvantageous. The present invention was born from an idea contrary to this common sense.

By optimizing the number of DC-DC converter units connected in parallel, the inventors of the present application have an excessive surge voltage even when using a lateral high electron mobility transistor made of GaN having high-speed switching characteristics. In addition, we focused on the possibility of realizing a high step-up ratio using high-speed switching characteristics. This study was performed on a trial and error basis with the following as parameters because of its low predictability.
(1) Driving frequency and loss of a DC-DC converter unit using a specific device (2) Mounting cost, weight, and size of a storage battery or a reactor included in a mobile object (3) DC-DC converter unit using a specific device Mounting Cost Specifically, the lateral high electron mobility transistor made of GaN has doubled the driving frequency in the range where the loss does not increase excessively (practical area) compared to the insulated gate bipolar transistor (IGBT). It was confirmed that it was possible. It has also been confirmed that if the drive frequency can be doubled, a step-up ratio of 4 or more, which is twice that when an IGBT is used, is realized while adjusting the inductance and duty ratio of the reactor as necessary. Furthermore, it was confirmed that the optimal configuration is to divide and connect in parallel to three DC-DC converter units.

  As a result of such trial and error, the present inventors have found that since the output voltage of the storage battery can be halved in accordance with the increase in the step-up ratio, the number of stacked cells of the storage battery can be halved. . Furthermore, the present inventors have found that an increase in the total weight due to an increase in the number of reactors can be suppressed by downsizing the reactor due to an increase in driving frequency. As a result, even if the weight of the DC-DC converter increases, it has been found that there is a region where the weight and cost are remarkably reduced in the entire power supply system.

  The present inventors have found that three parallel connections of DC-DC converter units are the optimum configuration based on the following study. That is, halving the output voltage of the storage battery means that the input voltage of the DC-DC converter is halved. In order to maintain the input power from the storage battery, the input current of the DC-DC converter is It means to double. Therefore, it has been found that in order not to increase the current value of the DC-DC converter unit, it is necessary to connect two DC-DC converter units in parallel. On the other hand, it has been found that an increase in driving frequency causes a surge voltage to increase by, for example, manifesting a parasitic inductance of a printed pattern and mounting wiring accompanying modularization. The inventors have found that a surge voltage increase caused by such parasitic inductance can be sufficiently absorbed by connecting a third DC-DC converter unit in parallel. Based on such experiments and analysis, the present inventors have made the DC-DC converter into three units in order to fully demonstrate the performance of a lateral high electron mobility transistor made of GaN. It was found that the optimal configuration is to divide and connect in parallel.

The DC-DC converter related to the first configuration uses a lateral high electron mobility transistor made of GaN as the DC-DC converter unit divided into three parts in parallel and uses the following results. Can be realized.
(1) Since the switching speed of the high electron mobility transistor made of GaN is high, a high step-up ratio of 4 or more can be realized.
(2) As a result, the output voltage of the storage battery can be kept low, and the number of cells connected in series can be reduced.
(3) The DC-DC converter itself is divided into a plurality of parts, which is disadvantageous in terms of weight, size, cost, and the like.
(4) However, the disadvantage of (3) is fully compensated by the advantage of (2). In particular, when divided into three DC-DC converter units and connected in parallel, the effect of (2) surpassing the disadvantage of (3) becomes significant.

  The second configuration example further includes a capacitor connected between the gate electrode and the emitter electrode of the switching element in the first configuration example. In this way, it is possible to easily reduce or adjust the surge voltage according to the design application by manipulating the delay time of the gate electrode and suppressing excessive fluctuation of the potential of the emitter electrode.

  The third configuration example further includes a Schottky barrier diode made of GaN and connected in parallel to the switching element in the first or second configuration example. Since the Schottky barrier diode is excellent in high-speed operation and has a low forward voltage drop, high-speed driving can be realized with high efficiency together with a lateral high electron mobility transistor made of GaN. As a result, it is possible to realize mounting that fully utilizes the performance of a lateral high electron mobility transistor made of GaN.

  The parallel-connected DC-DC converter of the first configuration can realize a high-efficiency power supply system that takes advantage of the excellent characteristics of a lateral high electron mobility transistor made of GaN, and the output of the storage battery. Since the voltage can be significantly reduced (for example, half), the mounting cost, weight, and size of the power supply system can be significantly reduced. The parallel-connected DC-DC converter having the second configuration can easily realize the reduction and adjustment of the surge voltage according to the design application. The parallel-connected DC-DC converter having the third configuration can be mounted so as to sufficiently utilize the performance of a lateral high electron mobility transistor made of GaN.

Explanatory drawing which shows an example of the prior art electric power drive system mounted in moving bodies, such as a hybrid system and a fuel cell vehicle. (A) And (b) is explanatory drawing which shows the operation state of the DC-DC converter 100 of a prior art. Explanatory drawing which shows an example of the structure of a GaN lateral type | mold MOS high electron mobility transistor. FIG. 3 is an explanatory diagram showing an excessive surge voltage generated between the collector and emitter in the DC-DC converter 100. Illustration depicting the current value I _d and the collector-emitter voltage V _ds at the turn-off of the switching element. Explanatory drawing which shows the structure of the parallel connection type DC-DC converter 100a which concerns on the Example of this invention. Explanatory drawing which shows the structure of the Schottky barrier diode 600 which concerns on the Example of this invention. Explanatory drawing which shows a mode that the control part 900 which concerns on the Example of this invention controls three DC-DC converter units 101,102,103 in a pressure | voltage rise mode. Explanatory drawing which shows the mode of the surge voltage which generate | occur | produces in the parallel connection type DC-DC converter 100a which concerns on the Example of this invention. Explanatory drawing which shows the comparison with the case where the switching device of another kind is used for the loss of the DC-DC converter unit 101 which concerns on the Example of this invention. Explanatory drawing which shows the structure of the parallel connection type DC-DC converter 100b which concerns on the modification of this invention. Explanatory drawing which shows the Schottky gate type | mold lateral high electron mobility transistor which is a diode of a modification. Explanatory drawing which shows the horizontal type Schottky barrier diode which is a switching element of a modification.

This invention can also implement | achieve a preferable form, for example by providing the following characteristics individually or in combination.
(Feature 1) The parallel-connected DC-DC converter has an operation mode in which it is driven at a drive frequency of 20 kHz or more. Since the drive frequency of 20 kHz or more is out of the human audible band, it has an advantage that generation of unpleasant sound caused by, for example, reactor vibration can be suppressed.
(Feature 2) The parallel connection type DC-DC converter includes a GaN lateral high electron mobility transistor connected in parallel with a boosting Schottky barrier diode as a switching element for regeneration. Thereby, the electric power regenerated can be efficiently recirculated to the storage battery.

In the following, embodiments of the present invention will be described in the following order in order to clearly describe the operation and effects of the present invention based on the above-described features.
A. Configuration of a parallel-connected DC-DC converter according to an embodiment of the present invention:
B. Variation:

A. Configuration of a parallel-connected DC-DC converter according to an embodiment of the present invention:
FIG. 6 is an explanatory diagram showing the configuration of the parallel connection type DC-DC converter 100a according to the embodiment of the present invention. The parallel connection type DC-DC converter 100a includes a pair of input terminals Tin, a pair of output terminals Tout, and three DC- connected in parallel between the pair of input terminals Tin and the pair of output terminals Tout. DC converter units 101, 102, and 103, and a control unit 900 that controls the three DC-DC converter units 101, 102, and 103 are provided. A storage battery 400a is connected between the pair of input terminals Tin. A capacitor 700 is connected between the pair of output terminals Tout. Since the storage battery 400a is configured to supply half the output voltage of the storage battery 400, a reduction in size and weight and a reduction in cost are realized.

  Since the parallel-connected DC-DC converter 100a has the following parasitic inductance, it causes a surge voltage. In FIG. 6, parasitic inductances Lp1, Lp2, and Lp3 resulting from the printed pattern and the like are illustrated between the three DC-DC converter units 101, 102, and 103 and the negative electrode of the storage battery 400a. There is also a parasitic inductance in the part. Parasitic inductances Lp1, Lp2, and Lp3 cause a surge voltage by increasing the collector-emitter voltage by lowering the potential of the emitter electrode when the GaN lateral high electron mobility transistors 511, 512, and 513 are turned off. . On the other hand, the parasitic inductance of the wiring between the GaN lateral high electron mobility transistors 511, 512, 513 and the reactors 121, 122, 123 similarly increases the potential of the collector electrode and generates a surge voltage.

  The three DC-DC converter units 101, 102, and 103 all have the same configuration. The DC-DC converter unit 101 includes two GaN lateral high electron mobility transistors 511 and 521, a reactor 121, and two Schottky barrier diodes 611 and 621. The DC-DC converter unit 102 includes two GaN lateral high electron mobility transistors 512 and 522, a reactor 122, and two Schottky barrier diodes 612 and 622. The DC-DC converter unit 103 includes two GaN lateral type high electron mobility transistors 513 and 523, a reactor 123, and two Schottky barrier diodes 613 and 623.

  Each component of the DC-DC converter unit 101 is connected as follows in the same manner as the DC-DC converter 100 of the prior art. That is, one electrode of the reactor 121 is connected to the positive electrode of the storage battery 400. The other electrode of the reactor 121 is connected to the collector electrode of the GaN lateral high electron mobility transistor 511 and the emitter electrode of the GaN lateral high electron mobility transistor 521. The collector electrode of the GaN lateral high electron mobility transistor 521 is connected to one output terminal Tout and one electrode of the capacitor 700. The other output terminal Tout and the other electrode of the capacitor 700 are connected to the emitter electrode of the GaN lateral high electron mobility transistor 511 and the negative electrode of the storage battery 400. The anode of the Schottky barrier diode 611 is connected to the emitter electrode of the GaN lateral high electron mobility transistor 511. The cathode of the Schottky barrier diode 611 is connected to the collector electrode of the GaN lateral high electron mobility transistor 511. The anode of the Schottky barrier diode 621 is connected to the emitter electrode of the GaN lateral high electron mobility transistor 521. The cathode of the Schottky barrier diode 621 is connected to the collector electrode of the GaN lateral high electron mobility transistor 521.

  FIG. 7 is an explanatory diagram showing the structure of a Schottky barrier diode 600 according to an embodiment of the present invention. The Schottky barrier diode 600 is used as the six Schottky barrier diodes 611, 621, 612, 622, 613, and 623 described above. The Schottky barrier diode 600 includes a gallium nitride (GaN) substrate 610 having a Ti / Al electrode (not shown) as a cathode, an n-type GaN layer 620 provided on the GaN substrate 610, and a GaN layer 620. A nickel (Ni) electrode 630 serving as an anode, and insulating films 631 and 632.

  The Schottky barrier diode 600 is a diode using a Schottky barrier having a rectifying action formed by a Schottky junction between the Ni electrode 630 and the GaN layer 620. The Schottky junction is advantageous in that it is superior in high-speed operation and has a low forward voltage drop because current transport is performed by majority carriers as compared with the PN junction.

  FIG. 8 is an explanatory diagram illustrating a state in which the control unit 900 according to the embodiment of the present invention controls the three DC-DC converter units 101, 102, and 103 in the boost mode. The controller 900 has two operation modes, a regeneration mode and a boost mode. In the step-up mode, the controller 900 can control the output voltage generated at the pair of output terminals Tout by performing on / off operations of the three GaN lateral high electron mobility transistors 511, 512, and 513. In the regeneration mode, the control unit 900 can turn on the three GaN lateral type high electron mobility transistors 621, 622, and 623 to return the power returned from the pair of output terminals Tout to the pair of input terminals Tin.

The controller 900 operates by sequentially shifting the phases of the three DC-DC converter units 101, 102, and 103 by 120 °. Specifically, the control unit 900, the phase 0 °, the GaN lateral high electron mobility transistor 511 included in the DC-DC converter unit 101 turns off _{T off,} turned _{T on} after a predetermined time has elapsed. As a result, the voltage V _ds1 is generated between the collector and emitter of the GaN lateral high electron mobility transistor 511 by the current energy accumulated in the reactor 121.

When the voltage V _ds1 exceeds the voltage across the capacitor 700, the current I _d (see FIG. 6) passes through the Schottky barrier diode 621 and flows into the output terminal Tout and the capacitor 700 separately. Current _{I c} flowing into the capacitor 700 would raise the voltage across the capacitor 700. Current _{I t} flowing to the output terminal Tout is supplied to the outside as an output current. The sum of the current _{I c} and the current _{I t} is equal to the current _{I d} which passes through the Schottky barrier diode 621. Such an operation, for three of the DC-DC converter units 111 to 113 are executed in sequence with a phase difference of 120 °, and the voltage _{V ds2} and the voltage _{V ds3} generated respectively, current _{I c} is generated It will be. Thus, the current I _c is the flow three times in the capacitor 700 in each cycle.

  The controller 900 controls the output voltage by operating the duty ratios of the three DC-DC converter units 101, 102, and 103 so that the voltage across the capacitor 700 approaches the reference voltage Vref while repeating such operations. To do.

  FIG. 9 is an explanatory diagram showing a state of a surge voltage generated in the parallel connection type DC-DC converter 100a according to the embodiment of the present invention. The solid line shows a normalized surge voltage generated in the parallel connection type DC-DC converter 100a of the present embodiment. The dotted line shows a normalized surge voltage generated in the conventional DC-DC converter 100. As can be seen from the figure, in the parallel-connected DC-DC converter 100a of the example, the peak of the surge voltage is remarkably reduced. The peak of the surge voltage is reduced by distributing the output current of the parallel-connected DC-DC converter 100a to the three DC-DC converter units 101, 102, and 103, thereby reducing the time differential value of the current. Because.

  FIG. 10 is an explanatory diagram showing a comparison between the loss of the DC-DC converter unit 101 according to the embodiment of the present invention and the case where another type of switching device is used. This figure normalizes the comparison of losses when switching elements of silicon (Si), silicon carbide (SiC), vertical gallium nitride (GaN), and lateral gallium nitride (GaN) are used in the DC-DC converter unit 101. It shows. This figure shows a loss when the DC-DC converter unit 101 is driven at a driving frequency of 10 kHz and a loss when the DC-DC converter unit 101 is driven at a driving frequency of 20 kHz.

  As can be seen from this figure, the GaN lateral high electron mobility transistor has a smaller loss than other types of devices, and the loss does not increase excessively even when the drive frequency is increased to 20 kHz. The reason why the loss is small even at such a high frequency is that the GaN lateral high electron mobility transistor has the property that all of the collector-gate capacitance Cdg, the emitter-gate capacitance Csg, and the collector-emitter capacitance Cds are extremely small. Because. As a result, the parallel-connected DC-DC converter 100a of the embodiment can be driven with low loss at 20 kHz where the driving frequency is out of the human audible band. As a result, the parallel-connected DC-DC converter 100a according to the embodiment also has an advantage that it is possible to suppress generation of unpleasant sound due to, for example, reactor vibration.

  As described above, the parallel-connected DC-DC converter 100a according to the embodiment can realize a high-efficiency power supply system utilizing the excellent characteristics of the lateral high electron mobility transistor made of GaN. Since the output voltage of the storage battery can be halved, the mounting cost, weight, and size of the power supply system can be significantly reduced. Furthermore, it is possible to drive while suppressing unpleasant noise within the human audible band.

  FIG. 11 is an explanatory diagram showing a configuration of a parallel connection type DC-DC converter 100b according to a modification of the present invention. The parallel-connected DC-DC converter 100b of the modification is an adjustment capacitor between the gate emitters of the GaN lateral high electron mobility transistors 511, 512, and 513 included in the three DC-DC converter units 101a, 102a, and 103a. It differs from the parallel connection type DC-DC converter 100a of an Example by the point provided with 521,522,523. The adjusting capacitors 521, 522, and 523 manipulate the delay time of the gate electrodes of the GaN lateral type high electron mobility transistors 511, 512, and 513 (deliberately slow down an excessively fast response characteristic) and also adjust the potential of the emitter electrode. By suppressing the excessive fluctuation of the surge voltage, the surge voltage can be easily reduced or adjusted according to the design application.

B. Variation:
Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. In addition, the technical elements described in the present specification or drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in the present specification or the drawings can achieve a plurality of objects at the same time, and has technical utility by achieving one of the objects. Specifically, for example, the following modifications can be implemented.

B-1: In the above-described embodiments and modifications, an insulating gate type lateral high electron mobility transistor (HEMT) is used as a switching element. For example, a Schottky gate type lateral type as shown in FIG. A high electron mobility transistor (HEMT) may be used. The Schottky gate type lateral high electron mobility transistor is a transistor in which a Ni / Au gate electrode 572a is Schottky-bonded to the AlGaN layer 540. Thus, the switching element that can be used in the present invention may be a lateral high electron mobility transistor generally made of GaN.

B-2: In the above-described embodiments and modifications, a vertical Schottky barrier diode made of gallium nitride is used as the diode. For example, a horizontal Schottky barrier diode as shown in FIG. 13 is used. May be used. In the lateral Schottky barrier diode, a buffer layer 615 is provided on a silicon substrate 610a, an N-type gallium nitride layer 620a is provided thereon, and a Ti / Al electrode as a cathode is provided on the N-type gallium nitride layer 620a. 661, 662, a nickel electrode 640a as an anode, and insulating films 671, 672 that insulate the electrodes from each other. As described above, the diode that can be used as a preferable embodiment in the present invention may be a Schottky barrier diode generally made of GaN.

B-3: In the above-described embodiments and modifications, the DC-DC converter unit is configured as a non-insulated boost converter. For example, a converter capable of a non-insulating step-up / step-down operation such as SEPIC, Zeta, or Cuk. Further, it may be configured as an isolated boost converter using a transformer, for example. The isolated boost converter includes, for example, a flyback converter and a forward converter. The circuit configuration of the DC-DC converter unit that can be used in the present invention is a DC-DC converter including a circuit having a reactor that stores current energy for boosting and a switching element connected in series to the reactor. It only has to be configured.

120-123 ... Reactors 132, 142 ... Diode 200 ... Inverter 300 ... Three-phase motor 400, 400a ... Storage battery 510 ... Sapphire substrate 521, 522, 523 ... Adjustment capacitor 551, 552 ... Contact layer 561, 563 ... Titanium layer 562 ... Insulating layer 571 ... Emitter electrode 572, 572a ... Gate electrode 573 ... Collector electrode 600 ... Schottky barrier diode 610 ... GaN substrate 610a ... Silicon substrate 611, 612, 613, 621 ... Schottky barrier diode 615 ... Buffer layer 620a ... Gallium nitride Layers 630, 640a ... Ni electrodes 631, 671 ... Insulating film 700 ... Capacitor 900 ... Control unit 100a, 100b ... Parallel connection type DC-DC converter

Claims (3)

A parallel-connected DC-DC converter that is used in a mobile unit-mounted power supply system that supplies power to a device that drives a mobile unit and has a step-up ratio of 4 or more,
Comprising three DC-DC converter units connected in parallel to each other;
A DC-DC converter in which each DC-DC converter unit includes a switching element that is a lateral high electron mobility transistor made of GaN, and a reactor connected in series to the switching element. The parallel-connected DC-DC converter according to claim 1, further comprising:
A DC-DC converter comprising a capacitor connected between a gate electrode and an emitter electrode of a switching element. The parallel connection type DC-DC converter according to claim 1, further comprising:
A DC-DC converter including a Schottky barrier diode made of GaN and connected in parallel to a switching element.

Images