JP2006314154A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive a normally-on semiconductor switching element through a simple composition. <P>SOLUTION: Normally-on high side and low side semiconductor switching elements 15 and 17 are connected in series (totem-pole type) and when each semiconductor switching element 15, 17 is driven on/off, respectively, by drive circuit 19, 21, a negative voltage for the high side drive circuit 19 is generated by a constant voltage diode 35 through floating operation. A positive voltage is generated by a bootstrap circuit through floating operation. As compared with normally-off type, the high side semiconductor switching element 15 can be turned off easily by simply adding the constant voltage diode 35 and a negative voltage source 25, and a normally-on power converter can be constituted easily. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power converter in which at least a pair of semiconductor switching elements are connected in series between a high-voltage side and a low-voltage side of a power supply and are driven on and off by a drive circuit.

  In recent years, attention has been paid to a hybrid vehicle (HEV) using both a gasoline engine and a motor as power sources due to an increase in environmental awareness. Inverters are used to drive motors in electric vehicles including these HEVs.

  FIG. 3 is a block diagram showing a general inverter device 1. The inverter device 1 shown in FIG. 3 is a three-phase inverter that drives a motor 2 that is a three-phase AC motor for running a vehicle. For example, six inverter devices using N-channel power MOSFETs (N-MOS) are used. The semiconductor switching elements 3a to 3c and 4a to 4c are configured.

  The drains of the high-side semiconductor switching elements 3a, 3b, and 3c are connected together to the plus (+) side of the power source B, and their sources are connected to the drains of the low-side semiconductor switching elements 4a, 4b, and 4c, respectively. Yes. The sources of the low-side semiconductor switching elements 4a, 4b, and 4c are all connected to the negative (−) side of the power supply B. The voltages at the connection points between the sources of the high-side semiconductor switching elements 3a, 3b, and 3c and the drains of the low-side semiconductor switching elements 4a, 4b, and 4c are the phases of the U phase, V phase, and W phase of the motor 2, respectively. Connected to.

  The semiconductor switching elements 3a to 3c and 4a to 4c are turned on and off at a timing corresponding to a control signal given from the gate drive circuit 5 to each gate terminal.

  Each semiconductor switching element 3a, 3b, 3c, 4a, 4b, 4c is not limited to the power MOSFET as shown in FIG. 3 as long as it is used in a general inverter, but is a power junction transistor or IGBT. Other semiconductor switching elements may be used. A semiconductor switching element using a SiC semiconductor or a GaN semiconductor may be used.

  FIG. 4 is a block diagram illustrating a part of a conventional inverter device 1 using a normally-off type semiconductor device. In the example of FIG. 4, each of the high-side and low-side semiconductor switching elements 3a, 4a is normally-off type, and becomes conductive when a positive voltage is applied to the control terminal 6 of each semiconductor switching element 3a, 4a. When the voltage is not applied to the terminal 6 (that is, zero voltage), the circuit is cut off.

  In FIG. 4, as the gate drive circuit 5, a high side drive circuit 7a and a low side drive circuit 7b are illustrated separately. The positive power supply terminal of the low-side drive circuit 7b is directly connected to the power supply 8c, whereas the positive power supply terminal of the high-side drive circuit 7a is connected to the power supply 8c via the backflow prevention diode 8a and the resistor 8b. . Further, the source of the high-side semiconductor switching element 3a serving as the output terminal to the motor 2 is connected to the plus power supply terminal of the high-side drive circuit 7a via the capacitor 8d. In this case, the capacitor 8d, the backflow prevention diode 8a, and the resistor 8b constitute a bootstrap circuit for applying a positive voltage to the high side drive circuit 7a.

  In the circuit of FIG. 4, the low-side drive circuit 7b operates with the voltage from the power supply 8c. As for the high-side drive circuit 7a, the capacitor 8d is charged when the low-side semiconductor switching element 4a is on and the high-side semiconductor switching element 3a is off, and the high-side drive circuit 7a operates with the charged charge.

  Specifically, complementary PWM pulses are input to both drive circuits 7a and 7b in FIG. In this case, when the low-side semiconductor switching element 4a is on, the source of the high-side semiconductor switching element 3a (that is, the output to the motor 2) falls to the ground level. At this time, since the voltage across the capacitor 8d increases, the capacitor 8d is charged. If the capacitor 8d is sufficiently charged, when the low-side semiconductor switching element 4a is subsequently turned off, the charge stored in the capacitor 8d is applied to the high-side drive circuit 7a, and the high-side semiconductor switching element 3a is driven. After that, if the complementary PWM pulse is switched before the voltage of the capacitor 8d drops below a certain level, both the semiconductor switching elements 3a and 4a are continuously turned on and off.

  In this way, by using the charged state of the capacitor 8d of the bootstrap circuit as a voltage source, in particular, the switching operation of the high side drive circuit 7a can be easily performed.

  By the way, in recent years, as semiconductor switching elements 3a, 3b, 3c, 4a, 4b, and 4c used in the inverter device 1, many compound semiconductor devices capable of large current and high withstand voltage have been developed. Type) semiconductor devices have been developed. Unlike the normally-off semiconductor device, a drain current flows even when a gate voltage is not applied to this normally-on type semiconductor device. Since a normally-on type semiconductor device is relatively easy to manufacture, it is very meaningful to configure the inverter device 1 using this semiconductor device.

  Here, as an inverter device using a normally-on type semiconductor device, for example, Patent Literature 1 and Patent Literature 2 are disclosed.

JP 2002-335681 A JP 2004-072942 A

  In an inverter device using a normally-on type semiconductor switching element, a conductive state is established when a positive voltage is applied to the control terminals of the semiconductor switching elements 3a, 4a, and a cutoff state is established when a negative voltage is applied. In this case, it is necessary to configure the drive circuits 7a and 7b that operate using both the positive voltage and the negative voltage, but a negative voltage is generated only by using a general bootstrap circuit as shown in FIG. The high-side drive circuit 7a cannot be configured as it is.

  In this regard, Patent Documents 1 and 2 disclose a configuration in which a negative voltage can be input to the semiconductor switching elements 3a and 4a.

  However, in Patent Documents 1 and 2, it is necessary to provide floating (independent) positive voltage sources and negative voltage sources corresponding to the number of semiconductor switching elements.

  For example, in Patent Document 1, it is necessary to prepare power supplies for generating a positive bias voltage that operates independently (floating) from a semiconductor switching element, as many as the number of switching elements. At times, a method of generating a voltage source by charging a capacitor with a charge is used, so that the power charged in the capacitor on the high side is used for the negative voltage generation circuit on the low side, and the voltage drops. There is.

  Further, Patent Document 2 discloses a configuration that protects the high voltage IC of the high-side switching drive circuit from a negative surge generated by the self-inductance of the wiring. There are disadvantages in that it is necessary to provide a voltage source and a negative voltage source, and it is necessary to provide high voltage ICs as many as the number of high side semiconductor switching elements.

  Therefore, an object of the present invention is to provide a power converter that can drive a normally-on type semiconductor switching element with a simple configuration.

  In order to solve the above-mentioned problem, the invention according to claim 1 is connected in series between a high-side semiconductor switching element connected to a high voltage source and the high-side semiconductor switching element and a predetermined reference voltage. A low-side semiconductor switching element; a high-side drive circuit that drives the high-side semiconductor switching element on and off; a low-side drive circuit that drives the low-side semiconductor switching element on and off; and a first voltage based on the reference voltage as the low-side drive A first voltage source applied to the drive circuit; a second voltage source applied to the low-side drive circuit with a second voltage having a polarity opposite to the first voltage with reference to the reference voltage; and the high-side semiconductor switching The first voltage with reference to the voltage at the connection point between the device and the low-side semiconductor switching device. A bootstrap circuit that applies a voltage to the high-side drive circuit, and a constant that applies to the high-side drive circuit the second voltage based on a voltage at a connection point between the high-side semiconductor switching element and the low-side semiconductor switching element. And a voltage diode.

  The power converter according to claim 2, wherein the high-side semiconductor switching element and the low-side semiconductor switching element are normally-on type semiconductor switching elements.

  The invention according to claim 3 is the power converter according to claim 1 or 2, wherein a resistor is connected in series to the constant voltage diode.

  The invention according to claim 4 is the power converter according to claim 1 or 2, wherein a constant current circuit is connected in series to the constant voltage diode.

  The power converter according to claim 1, wherein the bias voltage of the high-side semiconductor switching element is operated based on the voltage at the connection point with the low-side semiconductor switching element. The high-side semiconductor switching element and the low-side semiconductor switching element Since the voltage at the connection point between the first and second semiconductor switching elements changes depending on the ON / OFF operation of both semiconductor switching elements, the first voltage and the second voltage generated by the floating operation (independent operation not depending on the source potential) are used as the bias voltage. Need to be generated. Therefore, the first voltage is generated by the bootstrap circuit and the second voltage is generated by the constant voltage diode, respectively, in a floating operation, and is supplied to the high side drive circuit. Accordingly, for example, when the circuit is configured with the normally-on type semiconductor switching element according to the second aspect, the high-side semiconductor switching element can be driven on and off with a simple circuit configuration.

  In the power converter according to the third aspect of the present invention, the current flowing through the constant voltage diode can be easily adjusted by a resistor.

  In the power converter according to the fourth aspect of the present invention, the second voltage applied to the high side drive circuit can be easily adjusted by the constant voltage diode and the constant current circuit. Furthermore, since the second voltage in the floating state can be generated with less power consumption than in the case of using a resistor as in claim 3, a power converter meeting the demand for power saving can be provided.

{First embodiment}
<Configuration>
FIG. 1 is a circuit block diagram showing a power converter 11 according to a first embodiment of the present invention. However, in FIG. 1, only the structure of any one of the three phases is shown, and the other phases are not shown because of the same structure.

  The power converter 11 is, for example, a three-phase inverter device for driving a motor for driving an electric vehicle such as a hybrid vehicle (HEV) (see reference numeral 2 in FIG. 3), and U, V, In each of the phases of W, as shown in FIG. 1, a normally-on (depletion-type) high-side semiconductor switching element 15 (for example, an FET) and a normally-on (depletion-type) low-side semiconductor switching element 17 ( For example, FETs and the like are connected in series (totem pole type), and driving circuits 19 and 21 for driving the semiconductor switching elements 15 and 17 on and off are provided.

  The drain of the high-side semiconductor switching element 15 is connected to the high voltage source 18, and the source of the low-side semiconductor switching element 17 is connected to the ground (reference voltage). Further, the source of the high-side semiconductor switching element 15 and the drain of the low-side semiconductor switching element 17 are connected, and the voltage at this connection point becomes the output voltage to the motor (see reference numeral 2 in FIG. 3).

  Further, between the source of the high-side semiconductor switching element 15 and the positive voltage source (first voltage source) 23, as in the conventional normally-off type inverter device shown in FIG. 4, a resistor 29, a forward diode 27 and a capacitor 31 are connected, and a connection point between the forward diode 27 and the capacitor 31 is connected to a positive power supply terminal (VCC +) of a high side drive circuit 19 to be described later.

  The gate of the high side semiconductor switching element 15 is connected to the high side drive circuit 19, and the gate of the low side semiconductor switching element 17 is connected to the low side drive circuit 21.

  Each of the drive circuits 19 and 21 uses each voltage applied to the positive power supply terminal (VCC +) and the negative power supply terminal (VCC−) with reference to the voltage applied to the ground terminal (GND), and each semiconductor switching element 15. , 17 are driven on and off.

  A positive voltage source (V +) 23 and a negative voltage source (second voltage source: V−) 25 are applied as voltage sources of the drive circuits 19 and 21, and a relative positive voltage source (V +) 23 is applied. Both voltage sources 23 and 25 are connected in series so that is located on the high side and the negative voltage source (V−) 25 is located on the low side.

  The positive power supply terminal (VCC +) of the low side drive circuit 21 is directly connected to the positive terminal (V +) of the positive voltage source 23.

  The ground terminal (GND) of the low-side drive circuit 21 is connected to the ground (reference voltage) together with the source of the low-side semiconductor switching element 17.

  The negative power supply terminal (VCC−) of the low side drive circuit 21 is connected to the negative terminal (V−) of the negative voltage source 25.

  On the other hand, the positive power supply terminal (VCC +) of the high side drive circuit 19 is connected to the positive side terminal of the positive voltage source 23 via the backflow prevention diode 27 and the resistor 29. The capacitor 31 is interposed between the positive power supply terminal (VCC +) of the high side drive circuit 19 and the source of the high side semiconductor switching element 15. A connection point between the forward diode 27 and the capacitor 31 is connected to a positive power supply terminal (VCC +) of the high side drive circuit 19. In this case, the capacitor 31, the backflow prevention diode 27, and the resistor 29 constitute a bootstrap circuit for generating a positive voltage (first voltage) applied to the high-side drive circuit 19 by a floating operation.

  The ground terminal (GND) of the high-side drive circuit 19 is connected to the source of the high-side semiconductor switching element 15 that serves as an output terminal to the motor.

  Further, the negative power supply terminal (VCC−) of the high side drive circuit 19 is connected to the negative terminal (V−) of the negative voltage source 25 through the resistor 33 and is connected to the high side semiconductor through the constant voltage diode (zener diode) 35. The source of the switching element 15 is connected.

  Here, the anode of the constant voltage diode 35 is connected to the negative terminal (V−) of the negative voltage source 25 through the resistor 33, and the cathode of the constant voltage diode 35 is connected to the ground terminal (GND) of the high side drive circuit 19. It is connected. Thereby, the negative power supply terminal (VCC−) of the high side drive circuit 19 is set lower than the ground terminal (GND) of the high side drive circuit 19 by the reverse voltage of the constant voltage diode 35. That is, when the voltage at the ground terminal (GND) is used as a reference, a negative voltage (second voltage) generated by the floating operation by the constant voltage diode 35 is applied to the negative power supply terminal (VCC−). Become. The constant voltage generated by the constant voltage diode 35 includes the voltage applied to the negative power supply terminal (VCC−) of the high side drive circuit 19 and the high side semiconductor switching element 15 when the low side semiconductor switching element 17 is off. Is set to be equivalent to the negative terminal (V−) of the negative voltage source 25.

<Operation>
The operation of the power converter having the above configuration will be described. Here, an operation example of only one of the three phases will be described, and the same description will be omitted for the other phases.

  In this power converter, complementary PWM pulses are sequentially input to the drive circuits 19 and 21 for each of the three phases, and the high-side semiconductor switching element 15 and the low-side semiconductor connected to each other in series (totem pole type). By alternately turning on and off the switching elements 17, the DC current from the high voltage source 18 is converted into power to generate AC power.

  In this power conversion operation, the low-side semiconductor switching element 17 can be turned on and off by the low-side drive circuit 21 as a normal bias drive circuit because the reference source is connected to the ground (reference voltage).

  In this case, in this embodiment, the low-side drive circuit 21 is supplied from the positive voltage source 23 to the positive power supply terminal (VCC +) and from the negative voltage source 25 to the negative power supply terminal (VCC−). The low side semiconductor switching element 17 is driven on and off using the negative voltage (V−) as it is.

  Specifically, by applying a positive voltage (V +) given from the positive voltage source 23 to the positive power supply terminal (VCC +) to the gate of the low side semiconductor switching element 17, the low side semiconductor switching element 17 is turned on and a negative voltage is applied. By applying a negative voltage (V−) applied from the source 25 to the negative power supply terminal (VCC−) to the gate of the low side semiconductor switching element 17, the low side semiconductor switching element 17 is turned off.

  On the other hand, the bias voltage of the high-side semiconductor switching element 15 is operated based on the potential on the source side. However, since the source potential varies depending on the output, it is necessary to generate a positive voltage and a negative voltage generated by a floating operation (independent operation independent of the source potential) as the bias voltage.

  Therefore, with respect to the high side drive circuit 19, the charge charged in the capacitor 31 of the bootstrap circuit is used as a positive voltage source, and the anode side voltage of the constant voltage diode 35 is used as a negative voltage source. The switching element 15 is driven on and off.

  Specifically, when complementary PWM pulses are input to both drive circuits 19 and 21, when the low-side semiconductor switching element 17 is on, the source of the high-side semiconductor switching element 15 (ie, the output to the motor) is ground (reference). Voltage) falls to the level. At this time, since the voltage across the capacitor 31 of the bootstrap circuit increases, the capacitor 31 is charged. If the capacitor 31 is sufficiently charged, the charge stored in the capacitor 31 of this bootstrap circuit is applied to the high side drive circuit 19 as a positive voltage when the low side semiconductor switching element 17 is subsequently turned off. The high side semiconductor switching element 15 is turned on using this positive voltage as a voltage source. Then, the power supply from the high voltage source 18 causes the source of the high-side semiconductor switching element 15 (that is, the output to the motor) to be high, and this high voltage is output to the motor.

  When the high-side semiconductor switching element 15 is turned off by the high-side drive circuit 19, the negative voltage generated on the anode side of the constant voltage diode 35 applied to the negative power supply terminal (VCC-) is used. Input to the gate of the high-side semiconductor switching element 15. More specifically, the anode of the constant voltage diode 35 is connected to the negative terminal (V−) of the negative voltage source 25 through the resistor 33, and the cathode of the constant voltage diode 35 is connected to the ground terminal ( Therefore, the negative power supply terminal (VCC−) of the high side drive circuit 19 is lower than the ground terminal (GND) of the high side drive circuit 19 by the reverse voltage of the constant voltage diode 35. Is set. This is because the negative voltage (V−) corresponding to the reverse voltage of the constant voltage diode 35 is applied to the negative power supply terminal (VCC−) of the high side drive circuit 19 when the voltage of the ground terminal (GND) is used as a reference. Is applied. By inputting this negative voltage to the gate of the high-side semiconductor switching element 15 through the high-side drive circuit 19, the high-side semiconductor switching element 15 is turned off. At this time, since the low-side semiconductor switching element 17 is turned on by the low-side drive circuit 21, the source of the high-side semiconductor switching element 15 (that is, the output to the motor) falls to the ground (reference voltage) level.

  As described above, as compared with the normally-off circuit shown in FIG. 4, only the negative voltage source 25 and the constant voltage diode 35 are added, so that not only the low-side drive circuit 21 but also the high-side drive circuit 19 can be easily floated. A negative voltage power supply can be generated, and thus a normally-on power converter can be easily configured.

  Further, there is an advantage that the current flowing through the constant voltage diode 35 can be easily adjusted by the resistor 33.

{Second Embodiment}
FIG. 2 is a circuit block diagram showing a power converter 41 according to the second embodiment of the present invention. However, in FIG. 2, only the structure of any one of the three phases is shown, and the other phases are not shown because of the same structure. In this embodiment, elements having the same functions as those in the first embodiment are denoted by the same reference numerals.

  In this embodiment, instead of the series circuit of the constant voltage diode 35 and the resistor 33 in the first embodiment, a constant voltage diode 35a and a constant current circuit 37 are used, and in the first embodiment, This is different from the first embodiment in that the resistor 33 is omitted.

  Other configurations are the same as those of the first embodiment.

  The operation of the power converter having such a configuration will be described. Here, an operation example of only one of the three phases will be described, and the same description will be omitted for the other phases.

  The low-side drive circuit 21 receives the positive voltage (V +) supplied from the positive voltage source 23 to the positive power supply terminal (VCC +) and the negative voltage (V−) supplied from the negative voltage source 25 to the negative power supply terminal (VCC−) as they are. The low-side semiconductor switching element 17 is driven on and off.

  Specifically, by applying a positive voltage (V +) given from the positive voltage source 23 to the positive power supply terminal (VCC +) to the gate of the low side semiconductor switching element 17, the low side semiconductor switching element 17 is turned on and a negative voltage is applied. By applying a negative voltage (V−) applied from the source 25 to the negative power supply terminal (VCC−) to the gate of the low side semiconductor switching element 17, the low side semiconductor switching element 17 is turned off.

  On the other hand, the high-side drive circuit 19 turns the high-side semiconductor switching element 15 on and off using the electric charge charged in the capacitor 31 as a positive voltage source and the anode voltage of the constant voltage diode 35a as a negative voltage source. To drive.

  Specifically, when complementary PWM pulses are input to both drive circuits 19 and 21, when the low-side semiconductor switching element 17 is on, the source of the high-side semiconductor switching element 15 (ie, the output to the motor) is ground (reference). Voltage) falls to the level. At this time, since the voltage across the capacitor 31 increases, the capacitor 31 is charged. If the capacitor 31 is sufficiently charged, the charge stored in the capacitor 31 is applied as a positive voltage to the high-side drive circuit 19 when the low-side semiconductor switching element 17 is subsequently turned off. Is used as a voltage source to turn on the high-side semiconductor switching element 15. As a result, the source of the high-side semiconductor switching element 15 becomes high due to the power supply from the positive voltage source 18, and this high voltage is output to the motor.

  When the high-side semiconductor switching element 15 is turned off by the high-side drive circuit 19, the constant current from the constant-current circuit 37 causes the anode of the constant voltage diode 35 a to be closer to the anode than the source of the high-side semiconductor switching element 15. A voltage lower by the reverse voltage of the constant voltage diode 35a is formed. The high side drive circuit 19 inputs the negative voltage (V−) generated by the constant voltage diode 35 a to the gate of the high side semiconductor switching element 15.

  In this way, as compared with the normally-off circuit shown in FIG. 4, only the negative voltage source 25, the constant voltage diode 35a, and the constant current circuit 37 are added to the high side drive circuit 19 as well as the low side drive circuit 21. A floating negative voltage power supply can be easily generated, and thus a normally-on power converter can be easily configured.

  Compared to the first embodiment in which the resistor 33 is used, the high-side drive circuit 19 is connected to the anode side of the constant voltage diode 35a with power consumption smaller than that generated in the resistor 33. Therefore, it is possible to provide a power converter that meets the demand for power saving.

  In each of the above embodiments, the power converter has been described by taking a three-phase inverter device as an example. However, the present invention is not limited to this.

1 is a circuit block diagram showing a power converter according to a first embodiment of the present invention. It is a circuit block diagram which shows the power converter which concerns on the 2nd Embodiment of this invention. It is a circuit block diagram which shows the conventional power converter. It is the block diagram which illustrated some conventional normally-off type power converters.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11,41 Power converter 15 High side semiconductor switching element 17 Low side semiconductor switching element 18 High voltage source 19 High side drive circuit 21 Low side drive circuit 23 Positive voltage source 25 Negative voltage source 27 Backflow prevention diode 29 Resistance 31 Capacitor 33 Resistance 35 , 35a Constant voltage diode 37 Constant current circuit

Claims (4)

A high-side semiconductor switching element connected to a high voltage source;
A low-side semiconductor switching element connected in series between the high-side semiconductor switching element and a predetermined reference voltage;
A high-side drive circuit for driving the high-side semiconductor switching element on and off;
A low-side driving circuit for driving the low-side semiconductor switching element on and off;
A first voltage source that provides the low-side drive circuit with a first voltage based on the reference voltage;
A second voltage source that provides the low-side drive circuit with a second voltage having a polarity opposite to the first voltage with respect to the reference voltage;
A bootstrap circuit that applies the first voltage to the high-side drive circuit based on a voltage at a connection point between the high-side semiconductor switching element and the low-side semiconductor switching element;
A power converter comprising: a constant voltage diode that applies the second voltage to the high-side drive circuit based on a voltage at a connection point between the high-side semiconductor switching element and the low-side semiconductor switching element. The power converter according to claim 1,
The power converter in which the high-side semiconductor switching element and the low-side semiconductor switching element are normally-on type semiconductor switching elements. The power converter according to claim 1 or 2, wherein
A power converter in which a resistor is connected in series to the constant voltage diode. The power converter according to claim 1 or 2, wherein
A power converter in which a constant current circuit is connected in series to the constant voltage diode.

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