阅读说明：本技术 栅极驱动装置、开关装置和栅极驱动方法 (Gate driving device, switching device and gate driving method ) 是由 松原邦夫 于 2021-03-23 设计创作，主要内容包括：对想要抑制浪涌电压并降低开关损耗这样的期望不断提高。本发明提供一种栅极驱动装置,包括：栅极驱动部,该栅极驱动部驱动开关元件的栅极；以及切换部,该切换部在开关元件的接通期间中电流开始流过该开关元件的定时以后的至少一部分的期间内,将该开关元件的栅极电流切换为比该至少一部分的期间之前要小的电流。(There is an increasing desire to suppress surge voltages and reduce switching losses. The present invention provides a gate driving device, including: a gate driving section that drives a gate of the switching element; and a switching unit that switches the gate current of the switching element to a current smaller than that before at least a part of a period after a timing at which the current starts to flow through the switching element during an on period of the switching element.)

1. A gate driving apparatus, comprising:

a gate driving part driving a gate of the switching element; and

and a switching unit that switches the gate current of the switching element to a current smaller than that before at least a part of a period after a timing at which the current starts to flow through the switching element in an on period of the switching element.

2. The gate drive apparatus of claim 1,

the switching unit changes a rate of change of the gate current of the switching element in the at least one part of the period so that the gate current is smaller than before the at least one part of the period.

3. A gate drive apparatus as claimed in claim 1 or 2,

the period of the at least a part starts after the timing when the current starts to flow through the switching element.

4. A gate drive apparatus as claimed in claim 3,

further comprising a first detection section that detects an elapse of a first reference time from a first reference timing after an on signal is input to the switching element to a timing after a current starts to flow through the switching element, and supplies a signal to the switching section.

5. A gate drive apparatus as claimed in claim 4,

the first reference timing is after an input timing at which an on signal is input to the switching element,

the switching element is connected in series with an opposing switching element connected in anti-parallel with the reflux diode,

the gate driving apparatus further includes:

a first acquisition unit that acquires at least one of a parameter indicating a gate voltage of the switching element, a parameter indicating an element voltage of the switching element, a parameter indicating a current flowing through the switching element, and a parameter indicating a current flowing through the free wheeling diode; and

a second detection section that detects the first reference timing based on the parameter acquired by the first acquisition section and supplies a signal to the first detection section.

6. A gate drive apparatus as claimed in claim 4,

the first reference timing is an input timing at which an on signal is input to the switching element.

7. A gate drive apparatus as claimed in any one of claims 1 to 6,

the switching element is connected in series with an opposing switching element connected in anti-parallel with the reflux diode,

the period of the at least one portion includes a timing at which the current flowing through the reflux diode becomes zero.

8. The gate drive apparatus of claim 7, further comprising:

a second acquisition unit that acquires at least one of a parameter indicating a current flowing through the free wheeling diode and a parameter indicating a current flowing through the switching element; and

a third detection section that detects that the current flowing through the free wheeling diode becomes zero and supplies a signal to the switching section, based on the parameter acquired by the second acquisition section.

9. A gate drive apparatus as claimed in claim 7,

further comprising a fourth detection section that detects an elapse of a second reference time from a second reference timing after an on signal is input to the switching element to a timing after a current flowing through the free wheeling diode becomes zero, and supplies a signal to the switching section.

10. A gate drive apparatus as claimed in any one of claims 1 to 9,

the switching unit switches the gate current of the switching element to a current larger than the at least one partial period after the at least one partial period in the on period.

11. A gate drive apparatus as claimed in any one of claims 1 to 10,

the switching unit has a gate resistor connected to the gate of the switching element, and switches a resistance value of the gate resistor.

12. A gate drive apparatus as claimed in any one of claims 1 to 10,

the switching unit has a power supply connected to a gate of the switching element, and switches a voltage of the power supply.

13. A gate drive apparatus as claimed in any one of claims 1 to 12,

the switching unit switches the gate current of the switching element in a stepwise manner a plurality of times during the at least one part of the period.

14. A switching device, comprising:

a gate drive apparatus as claimed in any one of claims 1 to 13; and

and the switching element of which the gate is driven by the gate driving device.

15. The switching device according to claim 14,

the switching element is a wide bandgap semiconductor element.

16. A method for driving a gate electrode of a semiconductor device,

a gate driving method for driving a gate of a switching element,

in at least a part of a period after a timing at which a current starts to flow through the switching element in an on period of the switching element, a gate current of the switching element is switched to a current smaller than that before the at least a part of the period.

Technical Field

The invention relates to a gate driving device, a switching device and a gate driving method.

Background

Various techniques have been proposed to suppress a surge voltage when a switching element is turned on (see, for example, patent document 1).

Patent document 1: japanese patent No. 5186095

Disclosure of Invention

Technical problem to be solved by the invention

In recent years, there has been an increasing desire to suppress surge voltage and reduce switching loss.

Means for solving the problems

In order to solve the above problem, a first aspect of the present invention provides a gate driving device. The gate driving device may include a gate driving unit that drives the gate of the switching element. The gate driving device may include a switching unit that switches the gate current of the switching element to a current smaller than that before at least a part of a period after a timing at which the current starts to flow through the switching element during an on period of the switching element.

The switching unit may change a rate of change of the gate current of the switching element for at least a part of the period, and may reduce the gate current to be smaller than before the at least a part of the period.

At least a part of the period may start after the timing when the current starts to flow through the switching element.

The gate driving device further includes a first detection section that detects an elapse of a first reference time from a first reference timing after the on signal is input to the switching element to after the current starts to flow through the switching element, and supplies the signal to the switching section.

The first reference timing may be after an input timing of inputting the on signal to the switching element. The switching element may be connected in series with an opposing switching element connected in anti-parallel with the reflux diode. The gate driving device may further include a first acquisition section that acquires at least one of a parameter indicating a gate voltage of the switching element, a parameter indicating an element voltage of the switching element, a parameter indicating a current flowing through the switching element, and a parameter indicating a current flowing through the free wheeling diode. The gate driving device further includes a second detection section that detects the first reference timing based on the parameter acquired by the first acquisition section and supplies a signal to the first detection section.

The first reference timing may be an input timing at which an on signal is input to the switching element.

The switching element may be connected in series with an opposing switching element connected in anti-parallel with the reflux diode. At least a part of the period may include a timing at which the current flowing through the reflux diode becomes zero.

The gate driving device may further include a second acquisition unit that acquires at least one of a parameter indicating a current flowing through the free wheeling diode and a parameter indicating a current flowing through the switching element. The gate driving device further includes a third detection section that detects a case where the current flowing through the free wheeling diode becomes zero and supplies a signal to the switching section based on the parameter acquired by the second acquisition section.

The gate driving device further includes a fourth detection section that detects an elapse of a second reference time from a second reference timing after the on signal is input to the switching element to a timing after a current flowing through the free wheeling diode becomes zero, and supplies a signal to the switching section.

The switching unit may switch the gate current of the switching element to a current larger than at least a part of the on period after the at least a part of the on period.

The switching unit has a gate resistor connected to the gate of the switching element, and can switch the resistance value of the gate resistor.

The switching unit has a power supply connected to the gate of the switching element, and can switch the voltage of the power supply.

The switching unit may switch the gate current of the switching element in a stepwise manner a plurality of times during at least a part of the period.

In a second aspect of the present invention, a switching device is provided. The switching device may include the gate driving device of the first aspect. The switching device may include a switching element for driving the gate by the gate driving device.

The switching element may be a wide bandgap semiconductor element.

In a third aspect of the present invention, a gate driving method for driving a gate of a switching device is provided. The gate driving method may include a switching phase in which the gate current of the switching element is switched to a current smaller than that before at least a part of a period after a timing at which the current starts to flow through the switching element in the on period of the switching element.

The summary of the present invention does not list all necessary features of the present invention. Furthermore, sub-combinations of these feature sets may also constitute the invention.

Drawings

Fig. 1 shows a switchgear 100 according to the present embodiment.

Fig. 2 shows the operation of the switching device 100.

Fig. 3 shows an operation waveform in a case where the main switching element 2 is turned on by the switching device of the comparative example.

Fig. 4 shows an operation waveform in a case where the main switching element 2 is turned on by the switching device 100.

Detailed Description

The present invention will be described below with reference to embodiments thereof, but the following embodiments do not limit the invention according to the claims. In addition, the combination of the features described in the embodiments is not all necessary for technical means for solving the technical problems of the present invention.

[1. Structure of switching device 100 ]

Fig. 1 shows a switchgear 100 according to the present embodiment. In the figure, white arrows indicate voltages.

As an example, the switching device 100 shows 1 phase of a power conversion device used for driving a motor or feeding power, and switches the connection between the positive power supply line 101 and the negative power supply line 102 and the power output terminal 105, thereby outputting the converted voltage from the power output terminal 105.

Here, a dc voltage Ed of, for example, 600 to 800V is applied between the positive power line 101 and the negative power line 102, and the negative power line 102 is connected to a reference potential (ground potential, as an example) of the entire switching device 100. Inductive load 106 may be connected to power output terminal 105. The switching device 100 includes: a positive side main switching element 1 and a negative side main switching element 2, reflux diodes 3, 4 connected in anti-parallel with the main switching elements 1, 2, and a positive side gate drive device 5 and a negative side gate drive device 6.

[1-1. Main switching elements 1, 2]

The main switching elements 1 and 2 are examples of switching elements, and electrically connect or disconnect the drain terminal and the source terminal. For example, the main switching elements 1 and 2 are switched on (also referred to as connected) and off (also referred to as disconnected) by gate driving devices 5 and 6 described later. Here, in the present embodiment, main switching elements 1 and 2 are connected in series in this order between negative power supply line 102 and positive power supply line 101, and constitute an upper arm and a lower arm in the power converter, as an example. The power supply output terminal 105 is connected to the midpoint of the main switching elements 1 and 2.

The main switching elements 1 and 2 are silicon semiconductor elements having silicon as a base material. Alternatively, at least one of the main switching elements 1 and 2 may be a wide bandgap semiconductor element. The wide bandgap semiconductor device is a semiconductor device having a bandgap larger than that of a silicon semiconductor device, and includes, for example, SiC, GaN, diamond, gallium nitride based materials, gallium oxide based materials, AlN, AlGaN, ZnO, or the like. Wide bandgap semiconductor devices enable faster switching speeds than silicon semiconductor devices. In the present embodiment, the main switching elements 1 and 2 may be MOSFETs (Metal Oxide Semiconductor Field Effect transistors) having a parasitic diode (not shown) with the positive power supply line 101 side serving as a cathode.

[1-2. reflux diodes 3, 4]

The free wheeling diodes 3, 4 are connected in anti-parallel with the main switching elements 1, 2. The free wheeling diodes 3, 4 may be schottky barrier diodes or parasitic diodes of MOSFETs. The free wheeling diodes 3, 4 may be silicon semiconductor devices or wide band gap semiconductor devices.

[1-3. Gate driver 5, 6]

The gate driving devices 5 and 6 drive the gates (also referred to as gate terminals) of the corresponding main switching elements 1 and 2 based on an input signal input from the outside. The input signal can control the main switching elements 1 and 2 by PWM control, and an ac current having a substantially sine wave is output from the power supply output terminal 105. The input signal may be input to the main switching element 1 and the main switching element 2, respectively. In addition, in the present embodiment, as an example, the input signal instructs to set the main switching element 2 to the on state in the case of high (on command signal) and instructs to set the main switching element 2 to the off state in the case of low (off command signal). When the input signal is to alternately turn on the main switching elements 1 and 2, after both the main switching elements 1 and 2 are turned off, either one of the main switching elements 1 and 2 may be turned on.

The positive side gate driver 5 drives the gate of the main switching element 1, and the negative side gate driver 6 drives the gate of the main switching element 2. Since the gate driving devices 5 and 6 have the same configuration, the negative-side switching driving device 6 will be described in the present embodiment, and the positive-side gate driving device 5 will not be described.

The gate driving device 6 includes a gate driving unit 61, an acquisition unit 62, detection units 63 to 65, and a switching unit 67. In the present embodiment, each part of the gate driver 6 is described as an analog circuit as an example.

[1-3-1. Gate driver 61]

The gate driving device 61 drives the gate of the main switching element 2 based on an on signal (rising signal) and an off signal (falling signal) included in an input signal from the outside. The gate driving section 61 supplies a gate driving signal (on command signal/off command signal) for instructing on/off of the gate terminal of the main switching element 2. In the present embodiment, as an example, the gate drive signal may become high in a case where conduction of the main switching element 2 is instructed. The gate driving section 61 may be connected to the source terminal of the main switching element 2, and may use the potential of the source terminal as the reference potential of the gate driving signal.

[1-3-2 ] acquisition part 62

The acquisition unit 62 is an example of a first acquisition unit and a second acquisition unit, and acquires a parameter related to the switching timing of the switching unit 67. For example, the acquisition section 62 may acquire a parameter indicating a current flowing through the main switching element 2. In the present embodiment, as an example, the acquisition section 62 may acquire the drain current Id from the current sensor 621. The acquisition unit 62 may acquire the parameter during the on period of the main switching element 2. The acquisition section 62 may supply the acquired parameters to the detection sections 63, 65.

[1-3-3. detecting part 63]

The detection unit 63 is an example of a second detection unit, and detects the first reference timing. The detection section 63 may detect the first reference timing based on the parameter acquired by the acquisition section 62. For example, the detection unit 63 may be a comparator that compares the parameter with a reference value. The detection section 63 may supply a signal indicating the first reference timing to the detection section 64.

Here, the first reference timing is a start timing of the first reference time for switching the switching mode of the switching unit 67. The first reference timing may be a timing after the on signal is input to the main switching element 2, and in the present embodiment, as an example, may be a timing after an input timing when the on signal is input to the main switching element 2.

Further, the first reference time may be a time from the first reference timing to a timing after the current starts to flow through the main switching element 2. The end of the first reference time may be any timing after the timing when the current starts to flow through the main switching element 2 and before the timing when the current flowing through the free wheeling diode 3 becomes zero. The first reference time may be measured in advance before shipment of the switch device 100 and set by the detection unit 63.

[1-3-4. detecting part 64]

The detection unit 64 is an example of a first detection unit, and detects the passage of a first reference time from a first reference timing. For example, the detection section 64 may have an integration circuit that outputs a voltage corresponding to an elapsed time from the first reference timing, and a comparator that compares the voltage from the integration circuit with a reference value. The detection section 64 may supply a signal indicating the elapse of the first reference timing to the switching section 67.

[1-3-5. detecting part 65]

The detection unit 65 is an example of a third detection unit, and detects that the current flowing through the free wheeling diode 3 becomes zero. The detection unit 65 can perform detection based on the parameter acquired by the acquisition unit 62 (in the present embodiment, as an example, a parameter indicating the current flowing through the main switching element 2). For example, the detection unit 65 can detect that the current flowing through the free wheeling diode 3 becomes zero by detecting that the current flowing through the main switching element 2 reaches the current in the constant on state of the main switching element 2. The detection section 65 may be a comparator that compares the parameter with a reference value. The detection section 65 may supply a signal indicating that the current flowing through the free wheeling diode 3 becomes zero to the switching section 67.

[1-3-6. switching part 67]

The switching unit 67 switches the gate current of the main switching element 2 to a current smaller than that before the fall period in at least a part of a period (also referred to as the fall period) after the timing when the current starts flowing through the main switching element 2 in the on period of the main switching element 2. The switching section 67 can reduce the gate current by switching of the connection. The switching unit 67 may change the rate of change of the gate current of the main switching element 2 in the fall period so that the gate current is smaller than before the fall period.

The reduction period may be started at the timing when the current starts to flow through the main switching element 2, but in the present embodiment, the reduction period is started after the timing, as an example. The beginning of the lowering period can be detected by the detection section 64.

The lowering period may include a timing at which the current flowing through the free wheeling diode 3 becomes zero. In other words, the end section of the lowering period may be after the timing at which the current flowing through the reflux diode 3 becomes zero. The end of the lowering period can be detected by the detection section 65.

The switching unit 67 includes an amplification circuit 670, a connection switching unit 671, and a switching control unit 672.

[1-3-6-1. amplifier circuit 670]

The amplifier circuit 670 amplifies the gate drive signal from the gate drive section 61 and supplies the amplified signal to the gate terminal of the main switching element 2. The amplifier circuit 670 includes positive side switching elements 6701 and 6702, positive side resistors 6705 and 6706, a negative side switching element 6703, and a negative side resistor 6707 between a positive side power supply line 6711 and a negative side power supply line 6712.

The positive side switching elements 6701 and 6702 are elements for turning on the main switching element 2, and are connected in parallel between the positive side power supply line 6711 and the gate terminal of the main switching element 2. The positive side switching elements 6701 and 6702 are npn bipolar transistors, and are turned on when the gate drive signal inputted to the base terminal becomes high, and supply a current from the positive side power supply line 6711 to the gate terminal of the main switching element 2.

The positive side resistors 6705, 6706 are an example of gate resistors, and are connected to the gate of the main switching element 2. For example, the resistors 6705, 6706 may be connected in parallel between the positive side power supply line 6711 and the gate terminal of the main switching element 2, and connected in series with the positive side switching elements 6701, 6702, respectively. The resistors 6705, 6706 have resistance values different from each other. In this embodiment, as an example, the resistance value of the resistor 6705 is smaller than that of the resistor 6706.

The negative-side switching element 6703 is an element for turning off the main switching element 2, and is connected between the negative-side power supply line 6712 and the gate terminal of the main switching element 2. The negative side switch element 6703 is a pnp bipolar transistor, and turns on when the gate drive signal input to the base terminal becomes low, and captures electric charges from the gate terminal of the main switch element 2 to the negative side power supply line 6712.

The negative-side resistor 6707 is connected in series with the negative-side switching element 6703 between the gate terminal of the main switching element 2 and the negative-side power supply line 6712.

[1-3-6-2. connection switching part 671]

The connection switching portion 671 switches the resistance value of the gate resistor between the resistance value of the resistor 6705 and the resistance value of the resistor 6706. Thereby, the gate current is switched.

The connection switching portion 671 may alternatively electrically connect any one of the 2 resistors 6705, 6706 to the gate. In the present embodiment, as an example, the connection switching portion 671 connects either one of the base terminal of the switching element 6701 and the base terminal of the switching element 6702 to the gate driving portion 61.

[1-3-6-3. switching control section 672]

The switching control unit 672 controls the connection switching unit 671 in accordance with signals supplied from the detection units 64 and 65, thereby controlling the gate current during the on period. The switching control section 672 can connect the resistance 6706 to the gate terminal during a fall period in the on period of the main switching element 2 and connect the resistance 6705 to the gate before and after the fall period by using a switching signal to the connection switching section 671. Thus, the gate current of the main switching element 2 is switched to a current smaller than that before the fall period in the fall period, and the gate current of the main switching element 2 is switched to a current larger than that in the fall period after the fall period. When the main switching element 2 is turned on, the switching control unit 672 may connect the resistor 6705 to the gate terminal at the latest until the next turn-on.

According to the switching device 100 described above, in the fall period after the timing at which the current starts to flow through the main switching element 2 in the on period of the main switching element 2, the gate current of the main switching element 2 is switched to a current smaller than that before the fall period. Therefore, the rate of change of the current flowing through the free wheeling diode 3 can be reduced, and therefore, the surge voltage generated by the reverse recovery of the free wheeling diode 3 can be reduced, and the element breakdown due to the surge voltage can be prevented. Further, since the reduction period is started after the timing when the current starts to flow through the main switching element 2, the rate of change of the gate current is reduced and the rate of change of the gate voltage is reduced, unlike the case where the reduction period is started before the timing when the current starts to flow, and thus the on period can be prevented from being lengthened and the switching loss can be reduced.

Further, since the reduction period is started after the timing when the current starts to flow through the main switching element 2, the on period can be further shortened and the switching loss can be reduced as compared with the case where the reduction period is started before the timing when the current starts to flow.

Further, the elapse of the first reference time from the first reference timing after the on signal is input to the main switching element 2 to after the current starts to flow through the main switching element 2 is detected, and the decreasing period is started, so that the decreasing period can be reliably set to be after the timing at which the current starts to flow through the main switching element 2.

Further, since the first reference timing is detected based on the parameter acquired by the acquisition unit 62, the first reference timing can be detected without being affected by the state of the switching device 100, unlike the case where the elapsed timing of the fixed time is detected as the first reference timing.

Further, since the fall period includes a timing at which the current flowing through the free wheeling diode 3 becomes zero, it is possible to reliably reduce the surge voltage generated by the reverse recovery of the free wheeling diode 3 and prevent the element breakdown due to the surge voltage.

Further, since the current flowing through the free wheeling diode 3 is detected to be zero based on the acquired parameter, unlike the case where the current is detected to be zero at the elapsed timing of the fixed time, the timing at which the current flowing through the free wheeling diode 3 becomes zero can be reliably included in the reduction period without being affected by the state of the switching device 100.

Further, since the rate of change of the gate current changes during the fall period and the gate current becomes smaller than before the fall period, the gate current can be reduced rapidly, the surge voltage generated by the reverse recovery of the free wheeling diode 3 can be reduced reliably, and element destruction due to the surge voltage can be prevented.

[2. action ]

Fig. 2 shows the action of the switching device 100. The switching device 100 drives the gate of the main switching element 2 and turns on the main switching element 2 by performing the processing of steps S101 to S115.

In step S101, the gate driving unit 61 receives an on command signal included in an input signal from the outside. In step S103, the gate driving unit 61 outputs a gate driving signal instructing to turn on, and starts to turn on the main switching element 2. In the present embodiment, as an example, when the main switching element 2 starts to be turned on, the resistor 6705 is connected to the gate terminal of the main switching element 2, and a current corresponding to the resistance value of the resistor 6705 starts to flow through the gate in accordance with the gate drive signal. Further, the acquisition unit 62 starts acquiring a parameter indicating the current flowing through the main switching element 2.

In step S105, the detection unit 63 detects the first reference timing. The detection unit 63 may detect the first reference timing based on the parameter acquired by the acquisition unit 62, and in the present embodiment, as an example, may detect a timing at which the current flowing through the main switching element 2 reaches a threshold value larger than zero as the first reference timing. Thereby, the first reference timing after the input timing at which the on signal is input to the main switching element 2 is detected.

In step S107, the detection unit 64 detects the timing at which the first reference time has elapsed since the first reference timing. Thereby, the timing after the specific current starts flowing through the main switching element 2 is detected, and the fall period starts. The detected timing may be a timing at which the current flowing through the free wheeling diode 3 becomes zero or a timing before the current starts to flow through the main switching element 2. In the present embodiment, as an example, the detected timing may be immediately before the timing at which the current flowing through the free wheeling diode 3 becomes zero.

In step S109, the switching unit 67 switches the gate current of the main switching element 2 to a current smaller than that before the fall period. In the present embodiment, the switching unit 67 switches the gate resistance from the resistance 6705 to the resistance 6706, changes the rate of change of the gate current, and reduces the gate current. The gate current may be discontinuously decreased from before the decreasing period.

In step S111, the detection unit 65 detects that the current flowing through the free wheeling diode 3 becomes zero. The detection unit 65 may detect that the current flowing through the free wheeling diode 3 becomes zero based on the parameter acquired by the acquisition unit 62, and in the present embodiment, as an example, detects that the current flowing through the main switching element 2 reaches the current in the constant on state of the main switching element 2, and detects that the current flowing through the free wheeling diode 3 becomes zero. This ends the reduction period.

In step S113, the switching unit 67 switches the gate current of the main switching element 2 to a current larger than the fall period. In the present embodiment, the switching unit 67 switches the gate resistance from the resistance 6706 to the resistance 6705 to increase the gate current, as an example. Thus, the gate current during the set-down period becomes smaller than that before the set-down period, and the gate current after the set-down period becomes larger than that during the set-down period.

Then, in step S115, when the main switching element 2 is turned on, the switching device 100 ends the operation related to the turning on.

[3. operation waveform ]

[3-1 ] operating waveform of switching device of comparative example ]

Fig. 3 shows an operation waveform when the main switching element 2 is turned on by the switching device of the comparative example of the present embodiment. The switching device of the comparative example reduces the gate current of the main switching element 2 by increasing the gate resistance before the gate voltage Vg of the main switching element 2 exceeds the threshold voltage Vth, thereby suppressing the rate of change of the element current Id, further suppressing the rate of change of the current flowing through the free wheeling diode 3, and reducing the surge voltage due to the reverse recovery of the free wheeling diode 3.

In fig. 3 and fig. 4 described later, the horizontal axis represents time, and the vertical axis represents an input signal to the main switching element 2, a switching signal from the switching control unit 672, a gate voltage Vg, a gate current Ig, an element current (drain current) Id, an element voltage (drain-source voltage) Vds of the main switching element 2, a current IF flowing through the free wheeling diode 3, an element voltage (anode-cathode voltage) VAK of the free wheeling diode 3, and a mode of the switching device. Here, the switching signal is illustrated as "Rg small" in the case where the resistor 6705 having a small resistance value is connected to the gate terminal, and "Rg large" in the case where the resistor 6706 having a large resistance value is connected to the gate terminal. The switching device is illustrated in a mode in which the on command signal is input to the main switching element 2, the mode (1) is set before the increase of the element current Id of the main switching element 2 and the decrease of the current IF of the free wheeling diode 3 start, the mode (2) is set after the mode (1) and before the zero crossing of the current IF flowing through the free wheeling diode 3, and the mode (3) is set after the mode (2).

If the input signal for driving the main switching element 2 is switched from low (off command) to high (on command) at time t1 in a state where the resistor 6705 is connected to the gate terminal of the main switching element 2, the gate drive signal from the gate drive section 61 becomes high, and the gate current Ig corresponding to the resistance value of the resistor 6705 (in the present comparative example, a resistance value smaller than the resistor 6706) starts to flow. Further, the gate voltage Vg starts to rise.

At time t2, when switching control unit 672 connects resistor 6706 to the gate terminal by the switching signal, gate current Ig decreases. Further, the rate of change in the gate voltage Vg becomes small.

When the gate voltage Vg reaches the threshold voltage Vth at time t3, the element current Id starts to flow through the main switching element 2, and the current IF flowing through the free wheeling diode 3 starts to drop. The element voltage Vds is lowered by a voltage Δ V1 (L × d (Id)/dt) obtained by multiplying the change rate of the element current Id by the inductance L of the wiring connected to the main switching element 2.

At time t4, the current IF flowing through the free wheeling diode 3 becomes zero, and at time t5 thereafter, the switching control unit 672 connects the resistor 6705 to the gate terminal by the switching signal, thereby increasing the gate current Ig. Thereby, the switch-on is made earlier. The reflux diode 3 is reversely restored, the surge voltage reaches the peak voltage Vp, and the on period ends at time t 6.

In the above modification, in the on period of the time t1 to t6, the gate current Ig is reduced and the rate of change in the current flowing through the free wheeling diode 3 is suppressed during the time t2 to t5, so that the surge voltage generated by the reverse recovery is reduced. However, the longer the period for reducing the gate current Ig, the longer the on period, and the larger the switching loss.

[3-2 ] operation waveform of switching device 100 of the embodiment ]

Fig. 4 shows an operation waveform when the main switching element 2 is turned on by the switching device 100 of the present embodiment.

In the switching device 100 according to the present embodiment, as in the comparative example, if the input signal is switched from low (off command) to high (on command) at time t1, the gate current Ig corresponding to the resistance value of the resistor 6705 (in the comparative example, a resistance value smaller than the resistor 6706) flows, and the gate voltage Vg starts to rise.

When the gate voltage Vg reaches the threshold voltage Vth at time t3, the element current Id starts to flow through the main switching element 2, and the current IF flowing through the free wheeling diode 3 starts to drop.

Here, in the switching device 100 according to the present embodiment, the resistor 6705 is connected to the gate terminal of the main switching element 2 at time t3 when the gate voltage Vg reaches the threshold voltage Vth. Therefore, the gate current Ig is maintained large and the rate of change of the element current Id is maintained large as compared with the comparative example, and as a result, the element voltage Vds is dropped by the voltage Δ V2 larger than the voltage Δ V1. Further, the rate of change of the current IF flowing through the free wheeling diode 3 is maintained large as compared with the comparative example.

At time t10, the detector 63 detects the first reference timing at which the element current Id reaches the threshold current Ith, and at time t 2', the start timing of the fall period, which is the timing at which the first reference time Δ t elapses from time t10 detected as the first reference timing by the detector 64.

When the start timing is detected, the switching control unit 672 connects the resistor 6706 to the gate terminal by a switching signal. This changes the rate of change of the gate current Ig, and reduces the gate current Ig. Further, the rate of change in the gate voltage Vg becomes small. Here, the time t2 'may be after the time t3 at which the gate voltage Vg reaches the threshold voltage Vth, or before the time t 4' at which the current IF flowing through the free wheeling diode 3 becomes zero. IF time t2 'is before time t 4', the change in the element current Id and the current IF of the free wheeling diode 3 becomes gentle, and as a result, the magnitude of the current flowing from the cathode terminal side to the anode terminal side of the free wheeling diode 3 due to reverse recovery becomes small, and the surge voltage due to reverse recovery is reduced.

IF the detection unit 65 detects that the current IF flowing through the free wheeling diode 3 becomes zero at time t4 ', the switching control unit 672 connects the resistor 6705 to the gate terminal by the switching signal at the immediately subsequent time t 5'. As a result, the rate of change of the gate current changes, the gate current Ig increases, and the turn-on is advanced. Further, the reflux diode 3 recovers in the reverse direction, and the surge voltage reaches the peak voltage Vp ', and at time t 6', the on period ends. In the present operation example, the rate of change of the current IF flowing through the free wheeling diode 3 is large between the times t3 and t2 ', and therefore the time t 4' at which the current IF crosses zero is earlier than the time t4 of the comparative example.

As described above, according to the present operation example, in the period from time t2 'to t 5' of the on period from time t1 to t6 ', the gate current Ig is reduced and the rate of change in the current flowing through the free wheeling diode 3 is suppressed, so that the peak voltage Vp' of the surge voltage generated by the reverse recovery becomes smaller than the peak voltage Vp of the comparative example. In addition, as the period for reducing the gate current Ig is shorter than the period from time t2 to time t5 in the comparative example, the on period t1 to time t 6' is shorter, and the switching loss is reduced.

[4. modification ]

In the above-described embodiment, the acquisition unit 62 has been described as acquiring the parameter indicating the current flowing through the main switching element 2, but in addition to or instead of this, at least one of the parameter indicating the gate voltage Vg of the main switching element 2, the parameter indicating the element voltage Vds of the main switching element 2, and the parameter indicating the current IF flowing through the free wheeling diode 3 may be acquired. When acquiring the parameter indicating the gate voltage Vg, the detecting section 63 may detect, as the first reference timing, the timing at which the gate voltage Vg reaches the threshold voltage Vth. When acquiring the parameter indicating the element voltage Vds, the detection section 63 may detect, as the first reference timing, a timing at which the element voltage Vds falls and reaches the reference voltage. When outputting the parameter indicating the current IF, the detecting section 63 may detect, as the first reference timing, a timing at which the current IF falls and reaches the reference current.

Note that, although the first reference timing is detected based on the parameter acquired by the acquisition unit 62, the input timing at which the on signal is input to the main switching element 2 may be detected as the first reference timing. In this case, the gate driving device 6 may not include the detection unit 63 for detecting the first reference timing based on the parameter.

The description has been given of the period of decrease starting after the timing when the current starts to flow through the main switching element 2, but the period of decrease may also start at the timing when the current starts to flow through the main switching element 2. In this case, the gate driving device 6 may not include the detection unit 63 for detecting the first reference timing. Further, the detection portion 64 for detecting the start timing of the fall period may detect the timing at which the current Id becomes larger than zero when the parameter indicating the current Id flowing through the main switching element 2 is acquired. When acquiring the parameter indicating the gate voltage Vg, the detection unit 64 can detect the timing at which the gate voltage Vg reaches the threshold voltage Vth. When acquiring the parameter indicating the element voltage Vds, the detection unit 64 may detect the timing at which the element voltage Vds starts to decrease. When outputting a parameter indicating the current IF flowing through the free wheeling diode 3, the detector 64 may detect the timing at which the current IF starts to fall.

Further, the case where the detection unit 65 detects that the current flowing through the free wheeling diode 3 becomes zero based on the parameter indicating the current Id flowing through the main switching element 2 has been described, but detection may be performed based on a parameter indicating the current flowing through the free wheeling diode 3 in addition to or instead of this. The detection unit 65 may detect the elapse of a second reference time from a second reference timing after the on signal is input to the main switching element 2 to a timing after the current IF flowing through the free wheeling diode 3 becomes zero. The second reference time may be measured in advance before shipment of the switch device 100 and set by the detection unit 65. The second reference timing may be the same as or different from the first reference time. For example, the second reference timing may be an input timing of the on signal, may be an increase timing of the gate current Ig, may be a timing at which the gate voltage Vg exceeds the threshold voltage Vth, may be a decrease timing of the element voltage Vds of the main switching element 2, may be an increase timing of the current Id flowing through the main switching element 2, or may be a decrease timing of the current IF flowing through the free wheeling diode 3.

Further, although the switching section 67 has 2 resistors 6705 and 6706 connected in parallel between the positive power supply line 6711 and the gate terminal and one of the resistors 6705 and 6706 is connected to the gate terminal alternatively, it may have another configuration as long as the gate current of the main switching element 2 can be reduced during the on period. For example, the switching unit 67 may have 2 resistors connected in parallel between the gate driving unit 61 and the gate terminal, and one of the resistors may be alternatively connected to the gate terminal. Further, the switching portion 67 may have 3 resistors having different resistance values, and each of the resistors may be connected to the gate terminal before, during, and after the fall period. In this case, the resistance connected to the gate terminal during the pull-down period may have the largest resistance value, and any one of the resistance connected to the gate terminal before the pull-down period and the resistance connected to the gate terminal after the pull-down period may have a larger resistance value. The switching unit 67 may have a single variable resistor, and the gate current may be reduced by switching the resistance value of the variable resistor.

Further, although the switching unit 67 reduces the gate current of the main switching element 2 by switching the gate resistance, the gate current may be reduced by another method. For example, the switching unit 67 may include one or more power supplies connected to the gate terminal of the main switching element 2, and the gate current may be reduced by switching the voltage of the power supplies.

Further, although the switching unit 67 switches the gate current once to decrease the gate current during the lowering period, the switching may be performed a plurality of times in a stepwise manner. In this case, the gate current can be changed more gently than in the case where the gate current is switched once, and therefore, the surge voltage can be reliably reduced.

Further, the description has been given of the switching device 100 including the group of the positive-side main switching element 1 and the gate driving device 5 and the group of the negative-side main switching element 2 and the gate driving device 6, but it may be configured to include only one of the groups.

Further, each part of the gate driving device 6 is described as an analog circuit, but at least one of the detection units 63 to 65 and the switching control unit 672 may be a digital circuit.

The present invention has been described above with reference to the embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. Those skilled in the art will appreciate that various modifications or improvements can be made to the above-described embodiments. It is clear from the description of the scope of the claims that the embodiment to which such a change or improvement is applied is also included in the technical scope of the present invention.

It should be noted that the execution order of the respective processes of the actions, the sequence, the steps, the stages, and the like in the apparatus, the system, the program, and the method shown in the claims, the description, and the drawings may be realized in any order as long as the execution order is not specifically explicitly shown as "before", and the like, and further, as long as the output of the previous process is not used in the subsequent process. In the operation flows in the claims, the specification, and the drawings, the terms "first", "next", and the like are used for convenience of description, but the terms do not necessarily mean that the operations are performed in this order.

Description of the reference symbols

1 main switching element

2 main switching element

3 reflux diode

4 reflux diode

5 grid driving device

6 grid driving device

61 gate driving part

62 acquisition part

63 detection part

64 detection part

65 detection part

67 switching part

100 switching device

101 positive side power supply line

102 negative side power supply line

105 power supply output terminal

106 inductive load

621 Current sensor

670 amplifying circuit

671 connection switching part

672 switching control part

6701 switching element

6702 switching element

6703 switching element

6705 electric resistance

6706 electric resistance

6707 resistance

6711 Positive side Power line

6712 negative side power supply line.