JP7540291B2 - Power switching element driver - Google Patents

Description

This invention relates to a power switching element driver suitable for power conversion devices, etc.

In a power conversion device such as an inverter, a drive device drives a power switching element to turn on and off, and this power switching element switches the DC input power to generate AC power.

Here, when the power switching element is turned off, the current flowing through the power switching element changes abruptly. This can cause an excessive surge voltage to occur when the power switching element is turned off, which can lead to the destruction of the power switching element. For this reason, active gate control is sometimes used in the drive device that drives the power switching element.

For example, in the case of a power conversion device equipped with a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as a power switching element, the driver changes the input resistance connected to the gate of the MOSFET in the process of generating a gate voltage waveform that turns off the MOSFET, thereby changing the transition speed of the gate voltage waveform and keeping the time gradient of the change in the drain current within a specified limit.

By performing this type of active gate control, it is possible to reduce the surge voltage applied to the MOSFET and protect the MOSFET from destruction. In addition, by performing this type of active gate control, it is possible to shorten the time required for the MOSFET to turn off and reduce turn-off losses compared to when active gate control is not performed. This type of active gate control is disclosed, for example, in Patent Document 1.

JP 2018-153007 A

The surge voltage generated in a power conversion device is not constant, but changes depending on the operating state of the power conversion device, such as the value of the current flowing through the power switching element before turn-off. When the surge voltage that may occur is large, it is necessary to slow down the transition speed of the gate voltage waveform for turn-off in order to sufficiently suppress the surge voltage. However, when the surge voltage that may occur is small, slowing down the transition speed of the gate voltage waveform for turn-off unnecessarily lengthens the time required for turn-off, resulting in an unnecessarily increased turn-off loss.

Therefore, Patent Document 1 proposes a technology in which a circuit is provided that generates multiple types of turn-off gate voltage waveforms with different transition speeds, and the multiple types of turn-off gate voltage waveforms are switched and applied to the power switching element.

However, when generating multiple types of turn-off gate voltage waveforms with different transition speeds, resistors and other components must be connected to the gate to generate each gate voltage waveform, which increases the number of parts and increases the cost and volume of the device.

This invention was made in consideration of the above-described circumstances, and aims to provide a drive device that can perform appropriate drive control to suppress surge voltages according to the operating state of the power switching element without increasing the number of parts.

The present invention relates to a drive device for driving a power switching element having a first main terminal (D) and a second main terminal (Sp), and a first control terminal (G) and a second control terminal (Sd), in which a current flowing in a current path between the first main terminal and the second main terminal is controlled by a control voltage applied between the first control terminal and the second control terminal, the drive device having a turn-off control unit that controls the current flowing in the power switching element in response to a command to turn off the power switching element and generates a turn-off control voltage to turn off the power switching element, the turn-off control unit being: A drive device is provided that includes a control voltage path selection unit that selects, as a path for applying the turn-off control voltage based on an index related to a surge voltage applied to the power switching element, one of a first path between the first control terminal and the second control terminal of the power switching element, a control current passing through the first control terminal (G) of the power switching element, and a second path in which a common section through which a current passing through a path between the first main terminal (D) and the second main terminal (Sp) of the power switching element commonly passes is longer than the common section of the first path.

In a preferred embodiment, the second path is a path that passes through a path between the first control terminal (G) and the second main terminal (Sp) of the power switching element, and then reaches a third control terminal (Sdp) that is provided at a location where a current passes through a path between the first main terminal (D) and the second main terminal (Sp).

In this embodiment, the common section of the first path is mainly the channel region directly below the gate electrode of the power switching element. On the other hand, the common section of the second path includes, in addition to this channel region, a section in which the current passing through the channel region passes through the second main terminal and reaches the third control terminal. Therefore, the common section of the second path is longer than the common section of the first path.

In a preferred embodiment, the turn-off control unit generates a first turn-off control voltage as the turn-off control voltage, the first turn-off control voltage being intended to suppress a surge voltage applied to the power switching element.

In another preferred embodiment, the turn-off control unit is capable of generating, as the turn-off control voltage, a first turn-off control voltage that has the effect of suppressing a surge voltage applied to the power switching element, and a second turn-off control voltage that has a lower effect of suppressing a surge voltage applied to the power switching element than the first turn-off control voltage, and selects and generates either the first turn-off control voltage or the second turn-off control voltage based on an index related to the surge voltage.

In another preferred embodiment, the turn-off control unit switches the voltage value of the first turn-off control voltage in response to a change in the state of the power switching element.

In another preferred embodiment, the drive device has a DC intermediate capacitor that supplies a DC intermediate voltage to the power switching element, and a first voltage detection means that detects a DC intermediate voltage value of the DC intermediate capacitor, and the control voltage path selection unit selects the second path when the DC intermediate voltage value is equal to or greater than a first threshold value.

In another preferred embodiment, the drive device has a second voltage detection means for detecting a voltage value between the first main terminal and the second main terminal of the power switching element, and the control voltage path selection unit selects the second path when the voltage value detected by the second voltage detection means is equal to or greater than a second threshold value.

In another preferred embodiment, the drive device has a current detection means for detecting the value of a current flowing through the power switching element, and the control voltage path selection unit selects the second path when the current value detected by the current detection means is equal to or greater than a third threshold value.

In another preferred embodiment, the drive device includes a DC intermediate capacitor that supplies a DC intermediate voltage to the power switching element, a first voltage detection means that detects a DC intermediate voltage value of the DC intermediate capacitor, a second voltage detection means that detects a voltage value between a first main terminal and a second main terminal of the power switching element, and a current detection means that detects a current value flowing through the power switching element, and the control voltage path selection unit selects the second path when at least one of the following conditions is satisfied: a first condition that the DC intermediate voltage value is equal to or greater than a first threshold value, a second condition that the voltage value detected by the second voltage detection means is equal to or greater than a second threshold value, and a third condition that the current value detected by the current detection means is equal to or greater than a third threshold value.

In another preferred embodiment, the power switching element is a wide-gap semiconductor element.

This invention can also be implemented as a power conversion device that includes the drive device described above.

According to this invention, either the first path or the second path is selected as a path for applying a turn-off control voltage based on an index related to a surge voltage. Here, in the second path, a common section through which the control current passing through the first control terminal (G) of the power switching element and the current flowing through the path between the first main terminal (D) and the second main terminal (Sp) of the power switching element pass in common is longer than the common section of the first path. Therefore, the floating inductance present in the common section of the second path is larger than the floating inductance present in the common section of the first path. Therefore, when the second path is selected as a path for applying a turn-off control voltage, when the turn-off control voltage is applied to the power switching element and the current flowing between the first main terminal and the second main terminal of the power switching element decreases, the floating inductance present in the common section generates a back electromotive force. The electromotive force generated in this common section is greater than the electromotive force generated in the common section when the first path is selected, and prevents the charge in the first control terminal of the power switching element from moving in a direction that reduces the current flowing through the power switching element. Therefore, the transition speed at which the power switching element is turned off can be made slower than when the first path is selected. Therefore, according to this invention, appropriate drive control can be performed to suppress surge voltages according to the operating state of the power switching element without increasing the number of parts.

1 is a circuit diagram showing a configuration of a power conversion device including a drive device according to an embodiment of the present invention. 5 is a time chart showing an operation in the embodiment when a DC intermediate voltage is equal to or lower than a threshold value. 5 is a time chart showing an operation in the embodiment when a DC intermediate voltage is equal to or higher than a threshold value. 4 is a circuit diagram showing a state of a power switching element when a first path is selected as a control voltage transmission path. FIG. FIG. 11 is a circuit diagram showing a state of the power switching element when a second path is selected as the control voltage transmission path. 1 is a circuit diagram showing a configuration of an electric circuit that selects a control voltage transmission path using an output voltage value of a power switching element as an index related to a surge voltage. 1 is a circuit diagram showing a configuration of an electric circuit that selects a control voltage transmission path using an output current value of a power switching element as an index related to a surge voltage. 1 is a circuit diagram showing a configuration of an electric circuit that uses both an output voltage value and an output current value as indicators related to a surge voltage and selects a control voltage transmission path.

The following describes an embodiment of the invention with reference to the drawings.

<Embodiment>
FIG. 1 is a circuit diagram showing the configuration of a power conversion device 100 including driving devices 2a and 2b according to an embodiment of the present invention.

The power conversion device 100 has power switching elements 3a and 3b connected in series between a high-potential power line 101 and a low-potential power line 102. The common connection point of the power switching elements 3a and 3b is connected to an output terminal 103 of the power conversion device 100, and a load (not shown) such as a motor winding is connected to this output terminal 103. A DC intermediate capacitor 4 is connected between the high-potential power line 101 and the low-potential power line 102. A DC intermediate voltage is applied to this DC intermediate capacitor 4 from a DC power source (not shown). The power switching elements 3a and 3b output AC power from an output node 103 by switching the DC intermediate power stored in the DC intermediate capacitor 4. The voltage detector 7 is a first voltage detection means for detecting the DC intermediate voltage value Vdc stored in the DC intermediate capacitor 4.

In this embodiment, the power switching elements 3a and 3b are power MOSFETs. Specifically, the power switching elements 3a and 3b are wide-gap semiconductor elements made of materials such as silicon carbide compound semiconductor (SiC) and gallium nitride compound semiconductor (GaN). The power switching elements 3a and 3b have the same configuration. Therefore, in the following, when there is no need to distinguish between the two, they will be collectively referred to as the power switching element 3.

The power switching element 3 has a drain terminal D, which is a first main terminal, a power source terminal Sp, which is a second main terminal, a gate terminal G, which is a first control terminal, and a driver source terminal Sd, which is a second control terminal. In the power switching element 3, the current flowing in the current path (channel of the MOSFET) between the drain terminal D and the power source terminal Sp is controlled by the voltage Vgsd between the gate terminal G and the driver source terminal Sd. There is a current path between the driver source terminal Sd, which is the second control terminal, and the power source terminal Sp, which is the second main terminal, and a floating inductance is interposed in this current path.

Current detectors 5a and 5b are current detection means for detecting the current value (specifically, source current value) Is flowing between drain terminal D, which is the first main terminal, and power source terminal Sp, which is the second main terminal, in power switching elements 3a and 3b. One end of each of current detectors 5a and 5b is connected to the power source terminal Sp of power switching elements 3a and 3b. The other end of current detector 5a is connected to output terminal 103, and the other end of current detector 5b is connected to low potential power line 102. Voltage detectors 6a and 6b are second voltage detection means for detecting the voltage value Vds between drain terminal D and power source terminal Sp of power switching elements 3a and 3b, respectively.

Drivers 2a and 2b are devices that drive power switching elements 3a and 3b, respectively, under the control of control unit 1. Drivers 2a and 2b have the same configuration. For this reason, in FIG. 1, only the detailed configuration of drive unit 2b is shown, and the detailed configuration of drive unit 2a is not shown.

The detailed configuration of the drive device 2b will be described below with reference to Figure 1. The drive device 2b controls the drive of the power switching element 3b based on the drive signal sent from the control unit 1, the current value Is detected by the current detector 5b, the voltage value Vds detected by the voltage detector 6b, and the DC intermediate voltage value Vdc detected by the voltage detector 7.

The drive unit 2b includes a drive control unit 10 that calculates a drive command, an ON drive control unit 11 that performs ON control to transition the power switching element 3b from the OFF state to the ON state, and an OFF drive control unit 12 that performs OFF control to transition the power switching element 3b from the ON state to the OFF state.

A drive signal is given to the drive control unit 10 from the control unit 1. When the power switching element 3b should be switched from OFF to ON, the drive signal changes from OFF to ON, and when the power switching element 3b should be switched from ON to OFF, the drive signal changes from ON to OFF. When the drive signal changes from OFF to ON, the drive control unit 10 outputs an ON command to the ON drive control unit 11. As a result, the ON drive control unit 11 generates a turn-on control voltage that transitions the power switching element 3b from the OFF state to the ON state and supplies it to the power switching element 3b. Also, when the drive signal changes from ON to OFF, the drive control unit 10 outputs an active drive OFF command to the OFF drive control unit 12. As a result, the OFF drive control unit 12 generates a turn-off control voltage VGD that turns off the power switching element 3b and supplies it to the power switching element 3b. The relationship between the active drive OFF command and the turn-off control voltage VGD will be described in detail later.

The drive control unit 10 includes a gate voltage path selection unit 13. The gate voltage path selection unit 13 is a control voltage path selection unit that selects either a first path or a second path as a path for applying the turn-off control voltage VGD. Here, the first path is a path between the gate terminal G (first control terminal) of the power switching element 3b and the driver source terminal Sd (second control terminal). The second path is a path in which a common section through which the gate current (control terminal) passing through the gate terminal G of the power switching element 3b and the current flowing through the path between the drain terminal D (first main terminal) and the power source terminal Sp (second main terminal) pass in common is longer than the common section of the first path. Specifically, the second path is a path that passes through a path between the gate terminal G (first control terminal) and the power source terminal Sp (second main terminal) of the power switching element 3b, and further passes through a path between the drain terminal D (first main terminal) and the power source terminal Sp (second main terminal) to a third control terminal Sdp provided at a location where a current passes. The common section of the first path is mainly a channel region directly below the gate electrode of the power switching element 3b. On the other hand, the common section of the second path is a section that passes through this channel region, passes through the power source terminal Sp (second main terminal), and reaches the third control terminal Sdp. Therefore, the stray inductance intervening in the common section of the second path is larger than the stray inductance intervening in the common section of the first path. In this embodiment, the stray inductance intervening in the common section of the first path is negligibly small compared to the stray inductance intervening in the common section of the second path. Hereinafter, the stray inductance present in the common section of the second path is referred to as the common inductance Ls.

In this embodiment, the gate voltage path selection unit 13 selects the path to which the turn-off control voltage VGD is applied based on an index related to the surge voltage applied to the power switching element 3b. When the gate voltage path selection unit 13 selects the first path as the path to which the turn-off control voltage VGD is applied, the first path selection command is turned ON and the second path selection command is turned OFF, and when the gate voltage path selection unit 13 selects the second path, the first path selection command is turned OFF and the second path selection command is turned ON. As indexes related to the surge voltage, the current value Is detected by the current detector 5b, the voltage value Vds detected by the voltage detector 6b, and the DC intermediate voltage value Vdc detected by the voltage detector 7 are suitable, but in this embodiment, the gate voltage path selection unit 13 uses the DC intermediate voltage value Vdc detected by the voltage detector 7 as an index related to the surge voltage. Specifically, the gate voltage path selection unit 13 selects the first path when the DC intermediate voltage value Vdc is less than the first threshold th1, and selects the second path when the DC intermediate voltage value Vdc is equal to or greater than the first threshold th1. Here, the first threshold th1 is the limit value of the DC intermediate voltage value Vdc at which the surge voltage applied to the power switching element 3 falls within a predetermined limit even if the first path is selected.

The OFF drive control unit 12 includes an active drive unit 30 that performs active gate control in response to an active drive OFF command from the drive control unit 10, a reverse bias power supply 31 that is a DC power supply, a first switch 20 that turns ON/OFF in response to a first path selection command from the gate voltage path selection unit 13, and a second switch 21 that turns ON/OFF in response to a second path selection command from the gate voltage path selection unit 13. Here, active gate control is control that generates a turn-off control voltage VGD that reduces the output current of the power switching element 3b so that the time gradient of the decrease in the output current of the power switching element 3b falls within a predetermined limit.

In the OFF drive control unit 12, the first switch 20 is connected between the driver source terminal Sd of the power switching element 3b and the positive electrode of the reverse bias power supply 31. The second switch 21 is connected between the end of the current detector 5b on the low potential power supply line 102 side and the positive electrode of the reverse bias power supply 31.

The active drive unit 30 is connected between the gate terminal G of the power switching element 3b and the negative electrode of the reverse bias power supply 31. Here, the active drive unit 30 is composed of a series-connected switch 40 and resistor 45, and a series-connected switch 41 and resistor 46, which are connected in parallel. The resistors 45 and 46 generate a turn-off control voltage VGD when the voltage of the reverse bias power supply 31 is applied via the switches 40 and 41, respectively. For this reason, the resistors 45 and 46 are called OFF resistors 45 and 46. In this embodiment, the OFF resistor 45 has a larger resistance value than the OFF resistor 46.

The switches 40 and 41 of the active drive unit 30 are turned on/off by an active drive OFF command output by the drive control unit 10. The active drive OFF command is either a set of an open command for switch 40 and a close command for switch 41, or a set of a close command for switch 40 and an open command for switch 41.

In this embodiment, the drive control unit 10 outputs an open command to the switch 40 and an on command to the switch 41 as an active drive OFF command in response to the drive signal switching from ON to OFF. After that, the drive control unit 10 outputs a on command to the switch 40 and an open command to the switch 41 as an active drive OFF command in response to the state of the power switching element 3b, specifically, the voltage value Vds becoming a predetermined value. Further thereafter, the drive control unit 10 outputs an open command to the switch 40 and an on command to the switch 41 as an active drive OFF command in response to the state of the power switching element 3b, specifically, the voltage value Vds decreasing.

In this way, the drive control unit 10 and the active drive unit 30 switch the input resistance to the gate terminal G of the power switching element 3b by switching the switches 40 and 41 ON/OFF depending on the state of the power switching element 3b, thereby changing the voltage value of the turn-off control voltage VGD. This suppresses the surge voltage that occurs during turn-off. In this embodiment, the drive control unit 10 and the active drive unit 30 constitute a turn-off control unit that controls the current flowing through the power switching element 3b in response to a command (drive signal) to turn off the power switching element 3b, and generates the turn-off control voltage VGD, which is the control voltage that turns off the power switching element 3b.

Next, the operation of the drive unit 2b when the DC intermediate voltage value Vdc is less than the first threshold value th1 will be described with reference to FIG. 2.

In the example shown in FIG. 2, at time t1, the drive signal from the control unit 1 changes from ON to OFF, and the drive control unit 10 is instructed to turn off the switching element 3b.

If the DC intermediate voltage value Vdc from the voltage detector 7 is less than the first threshold value th1, for example at time t0 prior to time t1, the gate voltage path selection unit 13 turns the first path selection command ON and the second path selection command OFF. The first switch 20 is turned ON when the first path selection command (ON) is given. The second switch 21 is turned OFF when the second path selection command (OFF) is given.

As a result, the first path is selected as the path for applying the turn-off control voltage VGD to the power switching element 3b, and a closed loop is formed from the reverse bias power supply 31-active drive unit 30-gate terminal G of the power switching element 3b-driver source terminal Sd of the power switching element 3b-first switch 20-reverse bias power supply 31.

In this embodiment, it is necessary to select a path for applying the turn-off control voltage VGD at time t0, which is before time t1, when the operation of generating the turn-off control voltage VGD is started. Various methods can be considered for this purpose, but for example, a path for applying the turn-off control voltage VGD may be selected based on the result of comparing the DC intermediate voltage value Vdc with the threshold value th1 in a short period, and the last selected path may be maintained after time t1. Alternatively, when the drive signal changes from ON to OFF, a path for applying the turn-off control voltage may be selected based on the result of comparing the DC intermediate voltage value Vdc with the threshold value th1, and the operation of generating the turn-off control voltage VGD may be started after a very short delay.

Next, at time t1, the drive signal output from the control unit 1 to the drive control unit 10 changes from ON to OFF, commanding the power switching element 3b to be turned OFF. As a result, the drive control unit 10 outputs an open command for switch 40 and an open command for switch 41 to the active drive unit 30 as an active drive OFF command. In addition, the gate voltage path selection unit 13 of the drive control unit 10 maintains the first path selection command (ON) and the second path selection command (OFF).

The active drive unit 30, which has received an active drive OFF command from the drive control unit 10, opens the switch 40 and closes the switch 41. As a result, the output voltage of the reverse bias power supply 31 passes through the OFF resistor 46, which has a low resistance value, and is applied between the gate terminal G and the driver source terminal Sd of the power switching element 3b as the turn-off control voltage VGD. As a result, the power switching element 3b starts to turn off, and the voltage value Vds between the drain terminal D and the driver source terminal Sd of the power switching element 3b starts to rise at a certain rate of change (dVds/dt)_1. At this time, the voltage Vgsd (=VGD) applied between the gate terminal G and the driver source terminal Sd of the power switching element 3b becomes, for example, -6V. This voltage Vgsd is the voltage applied between the gate terminal G and the driver source terminal Sd of the power switching element 3b via the OFF resistor 46.

At time t2, when the voltage value Vds between the first and second main terminals of the power switching element 3b reaches, for example, 95% of the withstand voltage of the power switching element 3b, the drive control unit 10 determines that surge suppression is required and outputs an active drive OFF command (surge suppression) to the active drive unit 30, including a command to close switch 40 and a command to open switch 41.

When the active drive unit 30 receives an active drive OFF command (surge suppression) from the drive control unit 10, it closes the switch 40 and opens the switch 41. This switches the input resistance to the gate terminal G of the power switching element 3b from the low resistance OFF resistor 46 to the high resistance OFF resistor 45.

As a result, the voltage Vgsd between the gate terminal G of the power switching element 3b and the driver source terminal Sd becomes lower (for example, -3V), the discharge rate of the gate charge decreases, and the increase in the voltage value Vds is suppressed. In this case, the voltage Vgsd = -3V is the voltage applied between the gate terminal G of the power switching element 3b and the driver source terminal Sd via the OFF resistor 46. In this embodiment, the OFF resistor 45 has a larger resistance value than the OFF resistor 46, so the voltage Vgsd = -3V output through the OFF resistor 45 is smaller than the voltage Vgsd = -6V output through the OFF resistor 46.

At time t3, when the voltage value Vds between the first and second main terminals of the power switching element 3b drops, the drive control unit 10 determines that surge suppression should be stopped, and outputs an active drive OFF command (surge suppression stop) to the active drive unit 30, as well as a command to open switch 40 and a command to close switch 41.

When the active drive unit 30 receives an active drive OFF command (surge suppression stop) from the drive control unit 10, it opens switch 40 and closes switch 41. This switches the input resistance to the gate terminal G of the power switching element 3b from the high resistance OFF resistor 45 to the low resistance OFF resistor 46. As a result, the voltage Vgsd applied between the gate terminal G of the power switching element 3b and the driver source terminal Sd becomes high (-6V), the discharge rate of the gate charge increases, and the discharge of the gate input capacitance is completed in a short time.

As described above, by switching the resistance value of the input resistor for the gate terminal G of the power switching element 3b to change the voltage value of the turn-off control voltage VGD, and varying the rate of change dVds/dt of the voltage value Vds between the first and second main terminals of the power switching element 3b and the rate of change dIs/dt of the current value Is flowing through the power switching element 3b, it is possible to reduce turn-off loss and protect the power switching element 3b.

Next, the operation of the drive unit 2b when the DC intermediate voltage Vdc is equal to or greater than the first threshold th1 will be described with reference to FIG. 3.

At a time before time t1 (for example, time t0), when the gate voltage path selection unit 13 determines that the DC intermediate voltage value Vdc detected by the voltage detector 7 is equal to or greater than the first threshold th1, it turns the first path selection command OFF and the second path selection command ON. As a result, the first switch 20 is OFF and the second switch 21 is ON. As a result, the path for transmitting the turn-off control voltage VGD to the power switching element 3b becomes the second path, and a closed loop is formed from the reverse bias power supply 31-active drive unit 30-gate terminal G of the power switching element 3b-power source terminal Sp of the power switching element 3b-current detector 5b-third control terminal Sdp-second switch 21-reverse bias power supply 31.

At time t1, the drive signal from the control unit 1 changes from ON to OFF, and the drive control unit 10 is instructed to turn off the power switching element 3b.

The drive control unit 10, which receives this command, outputs an open command for switch 40 and an open command for switch 41 to the active drive unit 30 as an active drive OFF command. In addition, the gate voltage path selection unit 13 maintains the first path selection command (OFF) and the second path selection command (ON).

When the active drive unit 30 receives an active drive OFF command from the drive control unit 10, it opens the switch 40 and closes the switch 41, supplying the turn-off control voltage VGD to the power switching element 3b via the low-resistance OFF resistor 46. As a result, the voltage value Vds between the first and second main terminals of the power switching element 3b starts to rise at a certain rate of change (dVds/dt)_2. In this case, the rate of change (dVds/dt)_2 of the voltage value Vds is slower than the rate of change (dVds/dt)_1 of the voltage value Vds when the first path is selected.

The reason for this is explained below. Figure 4 is a circuit diagram showing the state of the power switching element 3b when the first path is selected as the control voltage transmission path. Also, Figure 5 is a circuit diagram showing the state of the power switching element 3b when the second path is selected as the control voltage transmission path. In these figures, the inductance Ls connected to the power source terminal Sp of the power switching element 3b is a common inductance Ls that combines the floating inductance intervening in the current path between the driver source terminal Sd and the power source terminal Sp of the power switching element 3b and the floating inductance intervening in the current detector 5b.

When the DC intermediate voltage Vdc is less than the first threshold value Th1 before turning off and the first path is selected as the control voltage transmission path, as shown in FIG. 4, the active drive unit 30 applies a turn-off control voltage VGD between the gate terminal G of the power switching element 3b and the driver source terminal Sd. This turn-off control voltage VGD is a voltage applied between the gate terminal G of the power switching element 3b and the driver source terminal Sd via the OFF resistor 46 as described above.

In contrast, when the DC intermediate voltage value Vdc is equal to or higher than the first threshold value Th1 before turn-off and the second path is selected as the control voltage transmission path, as shown in Fig. 5, the turn-off control voltage VGD output by the active drive unit 30 is applied between the gate terminal G of the power switching element 3b and the third control terminal Sdp on the low potential power line 102 side of the current detector 5b. The section where this gate voltage VGD is applied includes a common inductance Ls, and the current Is flowing through the power switching element 3b flows through this common inductance Ls. Therefore, when the current Is flowing through the power switching element 3b decreases due to the application of the turn-off control voltage VGD, a counter electromotive force that opposes the decrease in the current Is is generated in the common inductance Ls, and this counter electromotive force has a polarity that prevents current from being drawn from the gate of the power switching element 3b. Specifically, if the current flowing through the power switching element 3b at this time is Is, then the voltage Vgsd between the gate terminal G of the power switching element 3b and the driver source terminal Sd is given by the following equation.
Vgsd=VGD-Ls(dIs/dt)...(1)

In this way, when the second path is selected, the voltage Vgsd (see FIG. 4) between the gate terminal G and the driver source terminal Sd of the power switching element 3b at the start of turn-off is a voltage obtained by shifting the voltage Vgsd (see FIG. 3) at the start of turn-off to the positive side by ΔV=-Ls (dIs/dt) when the first path is selected. Therefore, the rate of change (dVds/dt)_2 of the voltage Vds between the first and second main terminals of the power switching element 3b when the second path is selected is slower than the rate of change (dVds/dt)_1 of the voltage Vds when the first path is selected.

After that, at time t2, when the voltage value Vds between the first and second main terminals of the power switching element 3b reaches, for example, 95% of the withstand voltage of the power switching element 3b, the drive control unit 10 determines that surge suppression is necessary and outputs an active drive OFF command (surge suppression) to the active drive unit 30, including a command to close switch 40 and a command to open switch 41.

By receiving this active drive OFF command (surge suppression), the active drive unit 30 closes switch 40 and opens switch 41. As a result, the input resistance to the gate terminal G of the power switching element 3b switches from the low resistance OFF resistor 46 to the high resistance OFF resistor 45.

As a result, the turn-off control voltage VGD applied between the gate terminal G of the power switching element 3b and the third control terminal Sdp becomes lower, the discharge rate of the gate charge decreases, and the increase in the output voltage value Vds is suppressed.

In this case, the common inductance Ls is also included in the section where the turn-off control voltage VGD is applied, and the back electromotive force ΔV generated in this common inductance Ls acts with a polarity that prevents current from being drawn from the gate of the power switching element 3b. Therefore, the surge voltage suppression amount is greater than when the first path is selected. At this time, the voltage Vgsd applied between the gate terminal G of the power switching element 3b and the driver source terminal Sd is -3V + ΔV = -3V - Ls (dIs/dt).

At time t3, when the voltage value Vds between the first and second main terminals of the power switching element 3b drops, the drive control unit 10 determines that surge suppression should be stopped, and outputs an active drive OFF command (surge suppression stop) to the active drive unit 30, including a command to open switch 40 and a command to close switch 41.

By receiving this active drive OFF command (surge suppression stop), the active drive unit 30 opens switch 40 and closes switch 41. This causes the input resistance to the gate terminal G of the power switching element 3b to switch from the high resistance OFF resistor 45 to the low resistance OFF resistor 46.

As a result, the voltage Vgsd applied between the gate terminal G of the power switching element 3b and the driver source terminal Sd becomes higher, the discharge rate of the gate charge increases, and at time t4, the discharge of the charge of the gate input capacitance is completed in a short time.

Then, when the discharge of the charge in the gate input capacitance of the power switching element 3b is completed and the interruption of the current Is is completed, no back electromotive force is generated in the common inductance Ls, and the voltage Vgsd between the gate terminal G of the power switching element 3b and the driver source terminal Sd becomes -6 V.

The above describes the operation of drive unit 2b as an example, but the operation of drive unit 2a is similar to that of drive unit 2b.

As described above, in this embodiment, the gate voltage path selection unit 13, which is a control voltage path selection unit, selects, as a path to apply the turn-off control voltage VGD, either the first path between the gate terminal G (first control terminal) and the driver source terminal Sd (second output terminal) of the power switching element 3, or the second path in which the common section through which the gate current (control terminal) passing through the gate terminal G of the power switching element 3b and the current flowing through the path between the drain terminal D (first main terminal) and the power source terminal Sp (second main terminal) pass in common is longer than the common section of the first path. Therefore, when the second path is selected, the back electromotive force generated in the common inductance Ls of the common section causes the rate of change of the voltage Vds between the first and second main terminals of the power switching element 3 to become gentle, and the surge voltage is suppressed. Thus, according to this embodiment, the surge voltage suppression effect can be varied depending on whether the first path or the second path is selected as the path for applying the turn-off control voltage. Therefore, according to this embodiment, appropriate drive control for suppressing the surge voltage can be performed according to the operating state of the power switching element 3 without increasing the number of parts, such as by providing a circuit that generates multiple types of turn-off control voltage waveforms with different transition speeds.

Furthermore, according to this embodiment, the effect of increasing the reduction rate of turn-off loss is obtained. In the technology disclosed in the above-mentioned Patent Document 1, the drain-source voltage of the power switching element before turn-off is compared with a threshold value, and if it is equal to or greater than the threshold value, it is determined that the surge voltage generated by turn-off is high, and active gate control is performed. In addition, if the drain-source voltage of the power switching element before turn-off is equal to or less than the threshold value, it is determined that the surge voltage generated by turn-off is low, and active gate control is not performed. With this technology, if active gate control is not performed, the time required for turn-off is longer, which hinders an increase in the reduction rate of turn-off loss.

In contrast, in this embodiment, active gate control (generation of a turn-off control voltage) is always performed regardless of whether the surge voltage applied to the power switching element 3 is large or small. Therefore, the reduction rate of turn-off loss can be increased compared to the technology of Patent Document 1.

<Other embodiments>
Although one embodiment of the present invention has been described above, other embodiments of the present invention are also possible. For example, the following embodiments are possible.

(1) In the above embodiment, regardless of the magnitude of the index related to the surge voltage, the turn-off control unit, which is composed of the drive control unit 10 and the active drive unit 30, generates a turn-off control voltage that has the effect of suppressing the surge voltage always given to the power switching element 3 as a turn-off control voltage. However, instead of doing so, as in Patent Document 1, it is also possible to switch whether or not to suppress the surge voltage based on the index related to the surge voltage. Specifically, the turn-off control unit is configured to be able to generate a first turn-off control voltage that has the effect of suppressing the surge voltage given to the power switching element 3, and a second turn-off control voltage (a turn-off control voltage generated in inactive gate control) that has a lower effect of suppressing the surge voltage than the first turn-off control voltage. Then, for example, the entire range that the index related to the surge voltage can take is divided into, for example, three ranges. Then, when the index belongs to the smallest range, the second turn-off control voltage is generated at the time of turn-off. Also, when the index belongs to the second smallest range or the largest range, the first turn-off control voltage is generated at the time of turn-off. Furthermore, when the index is in the second smallest range, the first path is selected as the path for applying the turn-off control voltage. When the index is in the largest range, the second path is selected as the path for applying the turn-off control voltage. This aspect also provides the same effect as the above embodiment. Furthermore, this aspect can provide more types of surge suppression levels than the above embodiment.

(2) In the above embodiment, the DC intermediate voltage value is used as an index related to the surge voltage, but other detection values may be used as an index related to the surge voltage. For example, FIG. 6 is a circuit diagram showing the configuration of an electric circuit that uses the voltage value Vds between the drain terminal D and the power source terminal Sp of the power switching element 3 as an index related to the surge voltage and selects a control voltage transmission path. In this electric circuit, the comparator 300a compares the voltage value Vds with the second threshold th2, and outputs a signal "1" if Vds≧th2, and outputs a signal "0" if Vds<th2. The NOT operator 303 changes the output signal from "1" to "0" when an OFF command, that is, an event in which the drive signal changes from ON to OFF, occurs. The flip-flop 302 is reset when a signal "1" is given from the NOT operator 303, and is set when a signal "1" is given from the comparator 300a. The non-inverted output signal Q of the flip-flop 302 becomes the second path selection command. In addition, the signal obtained by inverting this non-inverted output signal Q by the NOT operator 304 becomes the first path selection command.

According to the electric circuit shown in FIG. 6, when an OFF command is generated and the flip-flop 302 is released from the reset state, if Vds≧th2 and the flip-flop 302 is set, the second path selection command is "1" and the first path selection command is "0". Also, when an OFF command is generated and the flip-flop 302 is released from the reset state, if Vds<th2 and the flip-flop 302 is not set, the second path selection command is "0" and the first path selection command is "1". Thus, according to the embodiment shown in FIG. 6, the voltage value Vds between the drain terminal D and the power source terminal Sp of the power switching element 3 can be used as an index related to the surge voltage to select a control voltage transmission path.

FIG. 7 is a circuit diagram showing the configuration of an electric circuit that uses the source current value Is, which is the current value flowing through the power switching element 3, as an index related to the surge voltage and selects a control voltage transmission path. In FIG. 7, the comparator 300a in FIG. 6 is replaced with a comparator 300b that compares the source current value Is with a third threshold value th3. Other points are the same as the configuration shown in FIG. 6.

According to the electric circuit shown in FIG. 7, when an OFF command is generated and the flip-flop 302 is released from the reset state, if Is≧th3 and the flip-flop 302 is set, the second path selection command is "1" and the first path selection command is "0". Also, when an OFF command is generated and the flip-flop 302 is released from the reset state, if Is<th3 and the flip-flop 302 is not set, the second path selection command is "0" and the first path selection command is "1". Thus, according to the aspect shown in FIG. 6, the source current value Is, which is the current value flowing through the power switching element 3, can be used as an index related to the surge voltage to select a control voltage transmission path.

(3) Two or more types of detection values may be used as an index related to the surge voltage. That is, a DC intermediate capacitor that supplies a DC intermediate voltage to the power switching element 3, a first voltage detection means that detects the DC intermediate voltage value Vdc, a second voltage detection means that detects the voltage value Vds between the drain terminal D (first main terminal) and the power source terminal Sp (second main terminal) of the power switching element 3, and a current detection means that detects the value of the current flowing through the power switching element 3 are provided, and the gate voltage path selection unit 13, which is a control voltage path selection unit, selects the second path when at least two of the following conditions are satisfied: a first condition that the DC intermediate voltage value Vdc is equal to or greater than a first threshold value th1, a second condition that the voltage value Vds is equal to or greater than a second threshold value th2, and a third condition that the current value Is is equal to or greater than a third threshold value th3.

Figure 8 is a circuit diagram showing one example of this embodiment. In the circuit shown in Figure 8, a comparator 300b that compares the source current value Is with a third threshold value th3 and an OR operator 301 that supplies the logical sum of the output signal of comparator 300a and the output signal of comparator 300b to the set terminal S of flip-flop 302 are added to the circuit shown in Figure 6.

According to the electric circuit shown in FIG. 8, when an OFF command is generated and the flip-flop 302 is released from the reset state, if at least one of the conditions Vds≧th2 or Is≧th3 is satisfied and the flip-flop 302 is set, the second path selection command becomes "1" and the first path selection command becomes "0". Also, when an OFF command is generated and the flip-flop 302 is released from the reset state, if neither of the conditions Vds≧th2 or Is≧th3 is satisfied and the flip-flop 302 is not set, the second path selection command becomes "0" and the first path selection command becomes "1".

In this way, according to the embodiment shown in FIG. 8, the voltage value Vds between the first and second main terminals of the power switching element 3 and the source current value Is, which is the value of the current flowing through the power switching element 3, are used as indices related to the surge voltage, and the control voltage transmission path can be selected.

(4) The form of active gate control that generates the turn-off control voltage VGD is arbitrary. In the above embodiment, the voltage value of the turn-off control voltage VGD is changed in response to changes in the voltage value Vds between the first and second main terminals of the power switching element 3, but the turn-off control voltage VGD may be generated with a predetermined waveform.

(5) In the above embodiment, the third control terminal Sdp is provided at a position where the current passes through the path between the drain terminal D (first main terminal) and the power source terminal Sp (second main terminal). However, if the section from where the current passes through the channel region of the power switching element 3 reaches the power source terminal Sp (second main terminal) is long and the inductance in the common section of the second path is sufficiently large, the power source Sp (second main terminal) may be the third control terminal Sdp.

(6) In the above embodiment, a MOSFET is used as the power switching element 3, but a power switching element 3 other than a MOSFET, such as an IGBT (Insulated Gate Bipolar Transistor), may also be used.

1...control unit, 2a, 2b...drive device, 3a, 3b...power switching element, 4...DC intermediate capacitor, 5a, 5b...current detector, 6a, 6b, 7...voltage detector, 10...drive control unit, 11...ON drive control unit, 12...OFF drive control unit, 13...gate voltage path selection unit, 20, 21...switch, 30...active drive unit, 31...reverse bias power supply, 40, 41...switch, 45, 46...OFF resistor, 100...power conversion device, 300a, 300b...comparator, 301...OR operator, 302...flip-flop, 303, 304...NOT operator.

Claims (7)

A drive device for driving a power switching element having first and second main terminals and first and second control terminals, in which a current flowing through a current path between the first and second main terminals is controlled by a control voltage applied between the first and second control terminals, comprising:
a turn-off control unit that controls a current flowing through the power switching element in response to a command to turn off the power switching element and generates a turn-off control voltage to turn off the power switching element,
the turn-off control unit includes a control voltage path selection unit that selects, as a path to which the turn-off control voltage is applied, one of a first path between the first control terminal and the second control terminal of the power switching element, a control current passing through the first control terminal of the power switching element, and a second path in which a common section through which a current passing through a path between the first main terminal and the second main terminal of the power switching element commonly passes is longer than a common section of the first path , based on an index related to a surge voltage applied to the power switching element;
the turn-off control section is capable of generating, as the turn-off control voltage, a first turn-off control voltage having an effect of suppressing a surge voltage applied to the power switching element, and a second turn-off control voltage having a lower effect of suppressing a surge voltage applied to the power switching element than the first turn-off control voltage;
A range in which the index of the surge voltage can be taken is divided into a first range in which the index is the smallest, a second range in which the index is the second smallest, and a third range in which the index is the largest,
When the index of the surge voltage falls within the first range, the turn-off control unit outputs the second turn-off control voltage;
When the index of the surge voltage falls within the second range or the third range, the turn-off control unit outputs the first turn-off control voltage;
When the index of the surge voltage falls within the second range, the control voltage path selection unit selects the first path;
When the index of the surge voltage falls within the third range, the control voltage path selection unit selects the second path.
A drive device characterized by: 2. The drive device according to claim 1, wherein the turn-off control unit switches a voltage value of the first turn-off control voltage in response to a change in a voltage value between a first main terminal and a second main terminal of the power switching element. a DC intermediate capacitor for supplying a DC intermediate voltage to the power switching element;
a first voltage detection means for detecting a DC intermediate voltage value of the DC intermediate capacitor as an index related to the surge voltage,
3. The drive device according to claim 1, wherein the control voltage path selection unit selects the second path when the DC intermediate voltage value is equal to or higher than a first threshold value. a second voltage detection means for detecting a voltage value between a first main terminal and a second main terminal of the power switching element when the turn-off command is generated as an index related to the surge voltage;
3. The drive device according to claim 1, wherein the control voltage path selection unit selects the second path when the voltage value detected by the second voltage detection means is equal to or higher than a second threshold value. 3. The drive device according to claim 1, further comprising a current detection means for detecting a current value flowing through the power switching element when the turn-off command is generated as an index related to the surge voltage, and the control voltage path selection unit selects the second path when the current value detected by the current detection means is equal to or greater than a third threshold value. 6. The drive device according to claim 1, wherein the power switching element is a wide gap semiconductor element. A power conversion device comprising the drive device according to any one of claims 1 to 6.

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