Gate drive device, switch device

Abstract

If the change speed of the gate voltage is uniformly reduced, the turn-off loss may increase. The present invention provides a gate driving device, comprising: a gate driving unit driving the gate of a switching element; a measuring unit measuring a parameter that changes according to a current flowing through the switching element; and a switching unit switching the change speed of the gate voltage of the switching element based on the gate driving unit after a first reference time from the turn-off of the switching element based on the parameter.

Description

Technical Field

[0001] The invention relates to a gate driving device and a switch device. Background Art

[0002] Conventionally, in a gate driving device that drives the gate of a switching element, the change speed of the gate voltage is reduced in order to reduce a surge voltage at the time of turn-off (for example, refer to Patent Documents 1 to 3).

[0003] Patent Document 1: Japanese Patent No. 6290118

[0004] Patent Document 2: Japanese Patent No. 6266478

[0005] Patent Document 3: Japanese Patent No. 4935266

[0006] Technical problem to be solved by the invention

[0007] If the gate voltage change speed is uniformly reduced, the turn-off loss may increase. Summary of the invention

[0008] A first aspect of the present invention provides a gate drive device. The gate drive device may include a gate drive unit that drives the gate of a switching element. The gate drive device may include a measuring unit that measures a parameter that changes according to a current flowing through the switching element. The gate drive device may include a switching unit that switches the speed of change of the gate voltage of the switching element based on the gate drive unit after a first reference time has passed since the switching element was turned off, based on the parameter.

[0009] The switching unit may switch a change speed of the gate voltage after a first reference time has elapsed since the switching element was turned off during the off period of the switching element.

[0010] The switching unit may reduce a change speed of the gate voltage after a first reference time has elapsed from the turn-off of the switching element during the turn-off period of the switching element.

[0011] The switching unit can change the gate voltage change speed after the first reference time has passed since the switching element was turned off in one off period of the switching element relative to the gate voltage change speed after the first reference time has passed since the switching element was turned off in the other off periods.

[0012] The switching unit may switch the change speed of the gate voltage after a first reference time has elapsed from the turn-off of the switching element in the next and subsequent turn-off periods of the switching element based on the parameter measured in the previous switching cycle of the switching element.

[0013] The first reference time may be the time from the start of turning off the switching element to the timing when the voltage generated between the main terminals of the switching element reaches the peak value at the latest.

[0014] The first reference time may be a time from when the switching element is turned off to when the mirror period of the gate voltage ends.

[0015] The switching unit may include a switching determination unit that determines whether to switch the change speed of the gate voltage based on a comparison result between the parameter and the reference value.

[0016] The parameter may represent a current when the switching element is in an on state.

[0017] The parameter may represent the time from when the switching element is turned off to when the voltage applied between the main terminals of the switching element becomes the reference voltage.

[0018] The parameter may represent a voltage applied to the switching element after a second reference time has elapsed since the switching element was turned off.

[0019] The parameter may represent a surge voltage generated when the switching element is turned off. The switching unit may switch the change speed of the gate voltage based on the parameter and whether to switch the change speed of the gate voltage in a switching cycle in which the parameter is measured.

[0020] A second aspect of the present invention provides a switching device. The switching device may include the gate driving device according to the first aspect. The switching device may include a switching element whose gate is driven by the gate driving device.

[0021] The switching element may be a wide bandgap semiconductor element.

[0022] The above invention summary does not list all the features of the present invention. In addition, sub-combinations of these feature groups may also constitute inventions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A switch device 100 according to this embodiment is shown.

[0024] Figure 2 The operation of the switch device 100 is shown.

[0025] Figure 3 The operation waveform when the main switching element 2 is turned off is shown.

[0026] Figure 4 The operation waveform when the switching device 100 is turned off is shown.

[0027] Figure 5 Other operation waveforms when the switching device 100 is turned off are shown.

[0028] Figure 6 A switch device 100A according to a modified example is shown. DETAILED DESCRIPTION

[0029] The present invention is described below by way of the embodiments of the invention, but the following embodiments do not limit the invention involved in the claims. In addition, the combination of features described in the embodiments is not necessarily a technical means for solving the technical problem of the present invention. In addition, the same reference numerals are given to the common structures throughout the embodiments, and repeated descriptions are omitted.

[0030] [1. Structure of switch device 100]

[0031] Figure 1 The switch device 100 according to the present embodiment is shown. In the figure, blank arrows indicate voltages.

[0032] As an example, the switching device 100 shows one phase of a power conversion device used for driving or supplying a motor, and switches the connection between the positive power line 101 and the negative power line 102 and the power output terminal 105 to output the converted voltage from the power output terminal 105.

[0033] Here, for example, a DC voltage Ed of 600 to 800 V is applied between the positive power line 101 and the negative power line 102, and the negative power line 102 is connected to the reference potential (for example, the ground potential) of the entire switching device 100. The inductive load 106 can be connected to the power output terminal 105. The switching device 100 includes: a main switching element 1 on the positive side and a main switching element 2 on the negative side, return diodes 3 and 4 connected in reverse parallel to the main switching elements 1 and 2, and a gate driving device 5 on the positive side and a gate driving device 6 on the negative side.

[0034] [1-1. Main switching elements 1, 2]

[0035] The main switch elements 1 and 2 are each an example of a switch element, and electrically connect or disconnect the drain terminal and the source terminal. For example, the main switch elements 1 and 2 are switched to be turned on (also called connected) / off (also called disconnected) by the gate drive devices 5 and 6 described later. Here, in this embodiment, as an example, the main switch elements 1 and 2 are connected in series between the negative power supply line 102 and the positive power supply line 101 in sequence, forming the upper arm and the lower arm in the power conversion device. The power output terminal 105 is connected to the midpoint of the main switch elements 1 and 2.

[0036] The main switch elements 1 and 2 are silicon semiconductor elements using silicon as a substrate. At least one of the main switch elements 1 and 2 may also be replaced by a wide bandgap semiconductor element. The so-called wide bandgap semiconductor element is a semiconductor element having a larger bandgap than a silicon semiconductor element, and is a semiconductor element including, for example, SiC, GaN, diamond, gallium nitride materials, gallium oxide materials, AlN, AlGaN, or ZnO. Wide bandgap semiconductor elements can make the switching speed faster than that of silicon semiconductor elements. In addition, in the present embodiment, the main switch elements 1 and 2 may be MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), having a parasitic diode (not shown) with the cathode on the positive side power supply phase 101 side.

[0037] [1-2. Reflux diodes 3, 4]

[0038] The return diodes 3 and 4 are connected in antiparallel to the main switch elements 1 and 2. The return diodes 3 and 4 may be Schottky barrier diodes or parasitic diodes of MOSFET. The return diodes 3 and 4 may be silicon semiconductor elements or wide bandgap semiconductor elements.

[0039] [1-3. Gate driving devices 5, 6]

[0040] The gate driving devices 5 and 6 drive the gates of the corresponding main switch elements 1 and 2 based on the input signal input from the outside. The input signal can control the main switch elements 1 and 2 through PWM control, and output a substantially sinusoidal AC current from the power supply output terminal 105. The input signal can be input to the main switch element 1 and the main switch element 2, respectively. In addition, in the present embodiment, as an example, the input signal indicates that the main switch element 2 becomes the on state when it is at a high level (on command signal), and indicates that the main switch element 2 becomes the off state when it is at a low level (off command signal).

[0041] The positive side gate driving device 5 drives the gate of the main switch element 1, and the negative side gate driving device 6 drives the gate of the main switch element 2. In addition, the gate driving devices 5 and 6 have the same structure, so in this embodiment, the negative side switch driving device 6 is described, and the description of the positive side gate driving device 5 is omitted.

[0042] The gate driving device 6 includes a gate driving unit 61, a measuring unit 62, and a switching unit 63. In the present embodiment, each unit of the gate driving device 6 is described as an analog circuit as an example.

[0043] [1-3-1. Gate driving unit 61]

[0044] The gate driving unit 61 drives the gate of the main switching element 2 based on the on signal and the off signal included in the input signal from the outside. The gate driving unit 61 provides a gate driving signal (on command signal / off command signal) that instructs the gate terminal of the main switching element 2 to be on / off. The gate driving unit 61 can also provide the gate driving signal to the measuring unit 62 and the switching unit 63. The gate driving unit 61 can also be connected to the source terminal of the main switching element 2, and use the potential of the source terminal as a reference potential of the gate driving signal.

[0045] [1-3-2. Measurement unit 62]

[0046] The measuring unit 62 measures the current flowing through the main switching element 2 (for example, the current I flowing through the drain terminal). d In this embodiment, as an example, the parameter may represent the voltage V applied between the source terminal and the drain terminal from the time when the main switch element 2 is turned off to the time when the main terminal of the main switch element 2 is applied (in this embodiment, as an example, the voltage V applied between the source terminal and the drain terminal) ds ) becomes the reference voltage V ref If the current I flowing through the main switching element 2 d As the reference voltage V ref It can also be the DC voltage Ed and the source-drain voltage V ds The measuring unit 62 includes a voltage detection circuit 620, a comparison unit 621, and a parameter measuring unit 623.

[0047] [1-3-2-1. Voltage detection circuit 620]

[0048] The voltage detection circuit 620 detects the voltage V ds For example, the voltage detection circuit 620 has a voltage V ds Resistors 6201 and 6202 for voltage division. The midpoint of the resistors 6201 and 6202 is connected to the comparison unit 621, and the detected voltage is provided to the comparison unit 621. In this embodiment, the detection voltage is a positive voltage when the potential on the drain terminal side is higher than that on the source terminal side.

[0049] [1-3-2-2. Comparison unit 621]

[0050] The comparison unit 621 compares the voltage V detected by the voltage detection circuit 620 with the voltage V ds With reference voltage V ref For example, the comparison unit 621 may be a comparator, and a voltage V may be input to the non-inverting input terminal. ds, the inverting input terminal can input a reference voltage V ref The comparison unit 621 can be configured to compare the voltage V ds becomes greater than the reference voltage V ref To prevent this situation, a trigger signal is provided to the parameter measuring unit 623.

[0051] [1-3-2-3. Parameter measurement unit 623]

[0052] The parameter measuring unit 623 measures the parameter based on the comparison result obtained by the comparing unit 621. The measuring unit 62 can measure the parameter during the off period of the main switching element 2. For example, the parameter measuring unit 623 can detect the reception timing of the off instruction signal included in the gate driving signal from the gate driving unit 61 as the start timing of the off of the main switching element 2. The parameter measuring unit 623 can measure the elapsed time from the detected start timing to the reception of the trigger signal as the parameter. The parameter measuring unit 623 provides a parameter signal indicating the measured parameter to the switching determination unit 632. The parameter measuring unit 623 can be reset every time the off instruction signal is received.

[0053] [1-3-3. Switching unit 63]

[0054] The switching unit 63 determines the first reference time ΔT after the main switching element 2 is turned off based on the parameter signal supplied from the measuring unit 62. ref1 The switching unit 63 can switch the gate voltage change speed of the main switching element 2 by the gate driving unit 61. The switching unit 63 can change the gate voltage of the main switching element 2 by the first reference time ΔT during the off period of the main switching element 2. ref1 The change speed of the gate voltage is subsequently switched, and as an example the change speed can be reduced.

[0055] First reference time ΔT ref1 It can be the voltage V from the main switch element 2 to the main switch element 2 at the latest. ds The switching unit 63 includes a gate resistor 630, a connection switching unit 631, and a switching determination unit 632. In addition, the first reference time ΔT ref1 The end timing of may be the same as the end timing of the mirror period of the gate voltage.

[0056] [1-3-3-1. Gate resistor 630]

[0057] The gate resistor 630 includes two gate resistors 6301 and 6302 having different resistance values. The resistance value of the gate resistor 6301 may be larger than the resistance value of the gate resistor 6302. In the present embodiment, as an example, one end of each of the gate resistors 6301 and 6302 is connected to the gate of the main switch element 2, and the other end is connected to the connection switching unit 631. In addition, the gate resistor 630 may have other structures as long as the resistance value can be changed during the off period of the main switch element 2.

[0058] [1-3-3-2. Connection switching unit 631]

[0059] The connection switching unit 631 switches the resistance value of the gate resistor 630. Thus, the speed of change of the gate voltage is switched. In the present embodiment, as an example, the connection switching unit 631 electrically connects one of the two gate resistors 6301 and 6302 to the gate. The connection switching unit 631 can electrically connect the other end (the end on the side opposite to the gate side) of either gate resistor 6301 or 6302 to the gate driving unit 61 according to the instruction signal from the switching determination unit 632. In addition, the connection switching unit 631 can also be a structure with switches that can turn on and off the gate resistors 6301 and 6302, respectively. In this case, the on and off of each switch can also be controlled by the switching determination unit 632. As an example, when the speed of change of the gate voltage is switched, the switches corresponding to the gate resistors 6301 and 6302 can be changed from being turned on to either one of them being turned off.

[0060] [1-3-3-3. Switching determination unit 632]

[0061] The switching determination unit 632 determines the switching time from the start of the main switching element 2 turning off to the voltage V ds becomes the reference voltage V ref The comparison result of the time ΔT from the cut-off of the main switching element 2 to ... ds becomes the reference voltage V ref The time until (also called the third reference time ΔT ref3 ). The switching determination unit 632 may determine that the time ΔT is shorter than the third reference time ΔT. ref3In this case, it is determined that the gate voltage change speed is switched. Thus, switching is performed when a surge voltage greater than the element withstand voltage is generated. In addition, the third reference time ΔT ref3 Can be compared with the first reference time ΔT ref1 The same or different. ref3 ΔT ref1 In different cases, the third reference time ΔT ref3 Can be compared with the first reference time ΔT ref1 Longer, or shorter.

[0062] The switching determination unit 632 provides an instruction signal indicating whether to switch to the connection switching unit 631. The switching determination unit 632 may determine whether to switch based on the gate drive signal from the gate drive unit 61 after a first reference time ΔT has elapsed since the main switching element 2 was turned off. ref1 The timing output indication signal.

[0063] In addition, when the connection object connected to the gate is switched to the gate resistor 6301, the switching determination unit 632 may restore the connection object connected to the gate to the gate resistor 6302 at the latest before the next cutoff starts. As an example, the switching determination unit 632 may restore the connection object connected to the gate to the gate resistor 6302 after a predetermined time has passed since the completion of the cutoff, or may restore the connection object connected to the gate to the gate resistor 6302 in response to the fact that a conduction instruction signal included in the gate drive signal is received.

[0064] According to the above switching device 100, based on the current I flowing through the main switching element 2 d The parameter that changes is the first reference time ΔT after the main switching element 2 is turned off. ref1 The gate voltage change speed of the main switch element 2 is switched. Therefore, when a surge voltage higher than the element withstand voltage is generated due to the cut-off of the main switch element 2, the change of the gate voltage can be slowed down, thereby preventing the element from being destroyed by the surge voltage. In addition, when a surge voltage lower than the element withstand voltage is generated due to the cut-off of the main switch element 2, the change of the gate voltage can be accelerated, thereby reducing the cut-off loss. Therefore, unlike the case where the gate voltage is uniformly slowed down, the increase of the cut-off loss caused by the unnecessary reduction of the surge voltage can be prevented.

[0065] In addition, the time from when the main switching element 2 is turned off to when the voltage V ds becomes the reference voltage V ref The time ΔT until the end of the switching operation is used as a parameter, so the current I flowing through the main switching element 2 can be indirectly measured. d Therefore, it is different from directly measuring the current I flowing through the main switching element 2.d Compared with the case of FIG. 1 , the cost of the switching element 100 can be reduced.

[0066] In addition, during the off period of the main switching element 2, the first reference time ΔT elapses from the off time of the main switching element 2. ref1 Since the change speed of the gate voltage thereafter is switched, it is possible to reliably prevent element destruction due to a surge voltage at the time of turn-off and reduce turn-off loss.

[0067] In addition, the first reference time ΔT ref1 It can be from the time when the main switching element 2 is turned off to the voltage V ds The time until the peak value is reached or the time until the mirror period of the gate voltage ends is reduced, thereby reducing the peak voltage generated between the main terminals and further reducing the surge voltage. Therefore, it is possible to reliably prevent the destruction of the element due to the surge voltage.

[0068] Furthermore, since either of the two gate resistors 6301 and 6302 having different resistance values ​​is alternatively connected to the gate of the main switching element 2 , the change speed of the gate voltage can be reliably switched.

[0069] [2.Action]

[0070] Figure 2 1 shows the operation of the switch device 100. The switch device 100 changes the driving conditions during the off period of the main switching element 2 by performing the processing of steps S101 to S111.

[0071] In step S101, the gate driving unit 61 receives a turn-off instruction signal included in an input signal from the outside. In step S103, the gate driving unit 61 outputs a gate driving signal instructing turn-off, and starts turning off the main switching element 2.

[0072] In step S105, the switching determination unit 632 determines whether to switch the change speed of the gate voltage based on the comparison result of the parameter provided by the measuring unit 62 and the reference value. The switching determination unit 632 can determine whether to switch the change speed of the gate voltage in the next off period based on the parameter measured in the previous switching cycle. In this embodiment, as an example, the switching determination unit 632 determines to maintain the connection object connected to the gate at the gate resistor 6301 when the parameter is larger than the reference value, and determines to switch the connection object connected to the gate from the gate resistor 6302 to the gate resistor 6301 when the parameter is smaller than the reference value. When the switching determination unit 632 determines to switch (step S105; "Yes"), the processing is transferred to step S107, and when it is determined not to switch (step S105; "No"), the processing is transferred to step S109.

[0073] In step S107, the switching unit 63 switches the speed of change of the gate voltage. In the present embodiment, as an example, the switching determination unit 632 outputs an instruction signal to switch to reduce the speed of change of the gate voltage, that is, an instruction signal to switch the connection object connected to the gate from the gate resistor 6302 to the gate resistor 6301, so that the connection switching unit 631 performs the switching. As a result, compared with the case where the gate resistor 6302 is connected to the gate, the injection speed of the charge into the gate of the main switching element 2 becomes smaller, and the speed of change of the gate becomes smaller, and the surge voltage accompanying the cutoff is reduced. The switching unit 63 can switch to the gate of the main switching element 2 after the first reference time ΔT has passed since the cutoff. ref1 As an example, the switching unit 63 can switch the voltage V of the main switch element 2 from the start timing of the current cut-off to the current cut-off period. ds The switching is performed at any timing within the period until the timing at which the peak value is reached.

[0074] Thus, when the determination result in step S105 is positive (step S105; "Yes"), the change speed of the gate voltage during the off period of the main switch element 2 is changed, and when the determination result is negative (step S105; "No"), the change speed remains unchanged. Therefore, in one off period of the main switch element 2, the first reference time ΔT elapses from the start of the off period. ref1 The gate voltage change rate thereafter is relatively fast compared to the first reference time ΔT after the OFF start in other OFF periods. ref1 The subsequent change speed of the gate voltage changes.

[0075] In step S109, the measuring unit 62 measures the parameter. In the present embodiment, as an example, the measuring unit 62 measures the voltage V ds becomes the reference voltage V ref The time ΔT until the end is taken as a parameter.

[0076] Then, in step S111, when the main switch element 2 is turned off, the switch device 100 ends the operation related to the turn-off. In addition, the process of step S109 for measuring the parameter can also be performed at any timing between step S103 and step S107. In addition, when the change speed of the gate resistance is switched in step S107, the switch unit 63 can also return to the state before the change speed is switched before the next turn-off starts.

[0077] According to the above operation, the gate voltage change rate in one off period of the main switching element 2 is changed relative to the gate voltage change rate in other off periods, thereby preventing element destruction due to surge voltage in each off period and reducing off loss.

[0078] Furthermore, the change speed of the gate voltage in the next off period is switched based on the parameters measured in the previous switching cycle of the main switching element 2. Therefore, unlike the case where the change speed of the gate voltage is switched based on the parameters measured in the same switching cycle, reliable switching can be performed even when the switching cycle is short.

[0079] [3. Action waveform]

[0080] [3-1. Current I d Relationship with time ΔT] Figure 3 FIG. 2 shows the operation waveform when the main switch element 2 is turned off. In the figure, the gate-source voltage V gs1 , drain-source voltage V ds1 , drain current I d1 The diagram shows the current I flowing through the main switching element 2 d The gate-source voltage V represented by the dotted line is gs2 , drain-source voltage V ds2 , drain current I d2 The diagram shows the current I flowing through the main switching element 2 d The horizontal axis in the figure represents time, and the vertical axis represents the gate-source voltage V of the main switching element 2. gs , drain-source voltage V ds , drain current I d Alternatively, the drain current I d If the value is 50% or more of the rated current value of the main switch element 2, it is large, and if it is 50% or less, it is small, but it is not limited to this. In addition, relative to the rated current value, the drain current I d It can also be determined based on the surge voltage value during actual operation.

[0081] When the input signal of the main switch element 2 is switched from high level (on command) to low level (off command), the gate drive signal from the gate drive unit 61 becomes low level, and the negative gate current Ig starts to flow, and the gate charge starts to be injected into the main switch element 2 in the reverse bias direction. Then, the gate input capacitance Cgs of the main switch element 2 is charged in the reverse bias direction, and the gate-source voltage V gs Starts to decrease (time t1).

[0082] Next, when the gate-source voltage V gs When the voltage is reduced to the mirror voltage (time t2), the feedback capacitor (gate-drain capacitor) Cgd starts to charge, the change of the gate-source voltage Vgs becomes gentle (the so-called mirror period), and the drain-source voltage V ds With this, the drain-source voltage V of the main switch element 1 relative to the main switch element 2 increases sharply. ds The drain current Id of the main switching element 2 decreases, and a discharge current flows from the parasitic capacitance Cds. Therefore, the drain current Id of the main switching element 2 decreases.

[0083] Next, at time t3 and t3', the mirror period ends in the main switch element 2, and the drain current Id decreases sharply. As a result, the voltage applied to the wiring inductance of the positive power supply line 101 increases instantaneously, and the drain-source voltage V ds At time t4, t4', the reference voltage V ref , increasing to the peak voltage Vp, Vp'. Thereafter, the drain-source voltage V ds Decreases to a DC voltage Ed, and the gate-source voltage V gs The gate input capacitance Cgs of the main switch element 2 is charged in the reverse bias direction, and the main switch element 2 is turned off.

[0084] Here, from the cutoff to the voltage V ds2 becomes the reference voltage V ref The time ΔT2 from the start of cutoff to the voltage V ds1 becomes the reference voltage V ref Therefore, if the current I flowing through the main switch element 2 is d is smaller, then from the cut-off of the main switch element 2 to the voltage V ds becomes the reference voltage V ref The time ΔT until the switching element 2 is longer. d The smaller the value, the smaller the peak voltage.

[0085] [3-2. Operation waveform of the switch device 100 according to the embodiment (1)]

[0086] Figure 4 The operation waveform when the switching device 100 is turned off is shown.

[0087] If the input signal of the main switch element 2 is switched from high level (on command) to low level (off command) at time t11 in the nth switching cycle, the voltage V ds becomes the reference voltage V ref Time ΔT n(In this operation example, it is the period from time t11 to time t12) as a parameter. In this operation example, the current I d The surge voltage is large enough to generate a surge voltage larger than the component withstand voltage, and the time ΔT n becomes shorter than the third reference time ΔT ref3 Therefore, in the n+1th switching cycle, according to the instruction signal from the switching determination unit 632, the first reference time ΔT after the first reference time ΔT is elapsed from the start of the cut-off ref1 The gate voltage change rate is then switched to be smaller. In this way, when a surge voltage higher than the device withstand voltage is generated due to the cutoff, the gate voltage change is slowed down, thus preventing the device from being destroyed by the surge voltage.

[0088] In this operation example, as an example, the instruction signal is output after the first reference time ΔT has elapsed. ref1 The timing is maintained at a high level until the cutoff is completed. In addition, in the n-1th cycle and the n+1th cycle, the time ΔT as a parameter n-1 , ΔT n+1 It also becomes longer than the third reference time ΔT ref3 Keep it short.

[0089] [3-2. Operation waveform of the switch device 100 according to the embodiment (2)]

[0090] Figure 5 Other operation waveforms when the switching device 100 is turned off are shown.

[0091] If the input signal of the main switch element 2 is switched from high level (on command) to low level (off command) at time t11 in the nth switching cycle, the voltage V ds becomes the reference voltage V ref Time ΔT n (In this operation example, it is the period from time t11 to time t12') as a parameter. In this operation example, the current I d The surge voltage is small enough not to exceed the withstand voltage of the component, and the time ΔT n becomes shorter than the third reference time ΔT ref3 Therefore, in the n+1th switching cycle, the first reference time ΔT elapses from the start of the cutoff. ref1 After that, the gate voltage change speed is also maintained at a large speed without switching. In this way, when the turn-off does not cause a surge voltage higher than the component withstand voltage, the gate voltage change is maintained at a fast speed, reducing the turn-off loss. In addition, in this operation example, as an example, in the n-1th cycle and the n+1th cycle, the time ΔT as a parameter n-1 , ΔT n+1 It also becomes longer than the third reference time ΔTref3 It should be long.

[0092] [4. Modifications]

[0093] Figure 6 A switch device 100A according to a modification example is shown. The switch device 100A includes a measuring unit 62 and a switching unit 63A. In the present embodiment, as an example, each part of the measuring unit 62A and the switching unit 63A is described as a simulation circuit.

[0094] The measuring unit 62A measures the current I indicating that the main switching element 2 is in the on state. d The value of I flowing through the main switching element 2 is used as d The measuring unit 62A includes a current sensor 620A, a parameter measuring unit 623A, and a voltage detection circuit 620A.

[0095] Current sensor 620A measures current I d In this modification, as an example, the current sensor 620A is provided on the drain terminal side of the main switching element 2, but it may be provided on the source terminal side. The current sensor 620A may provide the measured current value to the parameter measuring unit 623A.

[0096] The parameter measuring unit 623A measures the parameter based on the current value from the current sensor 620A. For example, the parameter measuring unit 623A may measure the current I at the timing when the off instruction signal included in the gate drive signal is received. d as a parameter.

[0097] The voltage detection circuit 620A has the same resistors 6201 and 6202 as the voltage detection circuit 620. The voltage detection circuit 620A supplies the voltage detected by the resistors 6201 and 6202 to the switching unit 63A.

[0098] The switching determination unit 632A of the switching unit 63A determines the current I when the main switching element 2 is in the on state based on the parameter provided by the measuring unit 62 (in this modification, as an example, the current I d ) and the reference value to determine whether to switch the gate voltage change speed. The reference value may be a parameter (current I d The switching unit 63A may be configured to switch the switch after a first reference time ΔT has elapsed since the cut-off. ref1 As an example, the switching unit 63A can switch the voltage V of the main switch element 2 from the start timing of this cut-off to the voltage V of the main switch element 2 during this cut-off period based on the voltage provided by the slave voltage detection circuit 620A. dsThe switching is performed at any timing between the timing at which the peak value is reached and the timing at which the peak value is reached.

[0099] According to the switching device 100A described above, it is also possible to prevent element destruction due to a surge voltage and reduce turn-off loss.

[0100] [5. Other Modifications]

[0101] In addition, in the above embodiment, the switching unit 63 switches the change speed of the gate voltage by switching the resistance value of the gate resistor 630, but the switching can also be performed by other methods. For example, the switching unit 63 can also reduce the current of the gate drive signal. In order to reduce the current of the gate drive signal, for example, the internal path of the gate drive signal toward the gate can be branched to perform shunting.

[0102] In addition, the current I d The parameter to be changed is described as the time ΔT, etc., but may be another value. For example, the parameter may represent the time from the turn-off of the main switching element 2 to the second reference time ΔT. ref2 The voltage applied to the main switching element 2 after the second reference time ΔT ref2 In this case, the switching unit 63 may set the first reference time ΔT from the start of the switching element to the end of the switching element, based on the fact that the parameter representing the voltage is greater than the reference value. ref1 The speed of change of the gate voltage thereafter is switched. In this case, it is also possible to prevent the destruction of the element due to the surge voltage and reduce the turn-off loss. In addition, the second reference time ΔT ref2 Can be compared with the first reference time ΔT ref1 The same or different. ref2 ΔT ref1 In different cases, the second reference time ΔT ref2 Can be compared with the first reference time ΔT ref1 It can be longer or shorter.

[0103] In addition, the parameter may also represent a surge voltage generated when the main switch element 2 is turned off. As an example, the surge voltage may be detected by the voltage detection circuit 620. In this case, the switching unit 63 may switch the gate voltage change speed based on the parameter representing the surge voltage and whether to switch the gate voltage change speed in the switching cycle in which the parameter is measured. For example, as shown in Table 1 below, the switching unit 63 may switch the gate voltage change speed after the first reference time ΔT from the start of the cutoff in the next switching cycle based on whether the parameter representing the surge voltage in the previous switching cycle is greater than the reference value and whether to switch the gate voltage change speed. ref1In this case, it is also possible to prevent component damage caused by surge voltage and reduce turn-off loss. In addition, unlike the case where whether to perform switching is determined based only on the parameter representing the surge voltage, it is possible to prevent the generation of a surge voltage exceeding the component withstand voltage in each switching cycle.

[0104] [Table 1]

[0105]

[0106] In addition, the case where the gate voltage change speed in the next off period is switched based on the parameter measured in the previous switching cycle is described, but the change speed in the next off period after the next may be switched based on the parameter measured in the previous and previous switching cycles. In this case, the measuring unit 62 may have n parameter storage units that latch the parameters measured by the parameter measuring unit 623. The n parameter storage units store the measured parameters in sequence and provide them to the switching determination unit 632. The number n of the parameter storage units may be equal to the number of cycles from the cycle of measuring the parameters to the cycle of switching the change speed.

[0107] Furthermore, the case where the gate voltage change speed is reduced or maintained based on the parameters has been described, but the change speed may be increased instead of being maintained. In this case, the turn-off loss can be further reduced.

[0108] Furthermore, the switch device 100 , 100A is described as including a set of the positive-side main switch element 1 and the gate drive device 5 and a set of the negative-side main switch element 2 and the gate drive device 6 , but may include only one set.

[0109] In addition, although the various parts of the gate driving device 6 are described as analog circuits, at least one of the comparison unit 621, the parameter measurement unit 623, and the switching determination unit 632 may be a digital circuit. Similarly, although the various parts of the measurement unit 62A and the switching unit 63A are described as analog circuits, at least one of the parameter measurement unit 623A and the switching determination unit 632A may be a digital circuit.

[0110] The present invention has been described above using 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 changes or improvements can be made to the above embodiments. According to the claims, the various changes or improvements described above may also be included in the technical scope of the present invention.

[0111] Please note that the execution order of the actions, processes, steps, and stages of the devices, systems, programs, and methods shown in the claims, specifications, and drawings can be implemented in any order unless "before", "previously", etc. are specifically stated, and the output of the previous processing is not used in the subsequent processing. In the action flow in the claims, specifications, and drawings, "first", "then", etc. are used for convenience of explanation, but it does not mean that it must be implemented in this order.

[0112] Description of symbols

[0113] 1 Main switching element, 2 Main switching element, 3 Freewheeling diode, 4 Freewheeling diode, 5 Gate driving device, 6 Gate driving device, 61 Gate driving unit, 62 Measuring unit, 63 Switching unit, 100 Switching device, 101 Positive power supply line, 102 Negative power supply line, 105 Power supply output terminal, 106 Inductive load, 620 Voltage detection circuit, 621 Comparing unit, 623 Parameter measuring unit, 630 Gate resistor, 631 Connection switching unit, 632 Switching determination unit, 6201 Resistor, 6202 Resistor, 6301 Gate resistor, 6302 Gate resistor.

Claims

1. A gate driving device, characterized in that: include: a gate driving unit that drives a gate of the switching element; a measuring unit that measures a parameter that changes according to a current flowing through the switching element before the switching element is turned off; as well as A switching unit switches, based on the parameter, a change speed of the gate voltage of the switching element by the gate driving unit after a first reference time has passed since the switching element was turned off, until the switching element is completely turned off.

2. The gate driving device according to claim 1, wherein: The switching unit switches a change speed of the gate voltage after a first reference time has elapsed since the switching element was turned off during an off period of the switching element.

3. The gate driving device according to claim 2, wherein: The switching unit reduces a change rate of the gate voltage after a first reference time has elapsed since the switching element was turned off during an off period of the switching element.

4. The gate driving device according to claim 2 or 3, characterized in that: The switching unit changes a change rate of the gate voltage after a first reference time has passed since the switching element was turned off in one off period of the switching element relative to a change rate of the gate voltage after a first reference time has passed since the switching element was turned off in the other off period.

5. The gate driving device according to any one of claims 1 to 3, characterized in that: The switching unit switches the change speed of the gate voltage after a first reference time has passed since the switching element was turned off in the next and subsequent off periods of the switching element based on the parameter measured in the previous switching cycle of the switching element.

6. The gate driving device according to any one of claims 1 to 3, characterized in that: The first reference time is the time from the start of turning off the switching element to the timing when the voltage generated between the main terminals of the switching element reaches a peak value at the latest.

7. The gate driving device according to any one of claims 1 to 3, characterized in that: The first reference time is a time from when the switching element is turned off to when the mirror period of the gate voltage ends.

8. The gate driving device according to any one of claims 1 to 3, characterized in that: The switching unit includes a switching determination unit that determines whether to switch the change speed of the gate voltage based on a comparison result between the parameter and a reference value.

9. The gate driving device according to any one of claims 1 to 3, characterized in that: The parameter represents the current when the switching element is in an on state.

10. The gate driving device according to any one of claims 1 to 3, characterized in that: The parameter indicates the time from when the switching element is turned off to when the voltage applied between the main terminals of the switching element reaches the reference voltage.

11. The gate driving device according to any one of claims 1 to 3, characterized in that: The parameter indicates a voltage applied to the switching element after a second reference time has elapsed since the switching element was turned off.

12. The gate driving device according to any one of claims 1 to 3, characterized in that: The parameter represents the surge voltage generated when the switching element is turned off. The switching unit switches the change speed of the gate voltage based on the parameter and whether the change speed of the gate voltage is switched in a switching cycle in which the parameter is measured.

13. A switch device, characterized in that: include: The gate driving device according to any one of claims 1 to 12; as well as The switching element has its gate driven by the gate driving device.

14. The switch device according to claim 13, characterized in that The switching element is a wide bandgap semiconductor element.

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