Gate drive device and power conversion device

Abstract

A gate driving device is provided, which can simultaneously suppress a turn-off surge voltage and reduce a switching loss by changing a switching speed at an appropriate timing. The gate driving device comprises: a gate driving unit that drives a gate of a switching element according to an input signal that instructs the switching element to turn on or off; a timing determination unit that measures an on-time width from when the input signal switches to an on-command to when it switches to an off-command, and determines a mid-time timing before the turn-off surge voltage of the switching element reaches a peak value based on the measured on-time width; and a driving condition changing unit that changes a gate driving condition of the switching element at the mid-time determined by the timing determination unit.

Description

Technical Field

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

[0002] Conventionally, an active gate drive method is known, which changes the switching speed at an appropriate timing according to the drain current or collector current (hereinafter also referred to as the main current) flowing through the switching element in order to suppress the surge voltage and reduce the switching loss. For example, Patent Document 1 discloses a gate drive circuit that stores the surge period from the timing of the shutdown instruction to the timing of the surge voltage generation, and determines the change timing of the effective gate resistance value of the switching element based on the surge period stored at the last shutdown at the time of the current shutdown.

[0003] On the other hand, in power conversion devices such as chopper circuits, there is known a technology that uses a current continuous mode for making the current flowing through a reactor continuous and a current discontinuous mode for making the current flowing through the reactor intermittent, depending on the purpose (see, for example, Patent Document 2).

[0004] <Prior Art Literature>

[0005] <Patent Documents>

[0006] Patent Document 1: Japanese Patent No. 4935266

[0007] Patent Document 2: Japanese Patent No. 6398537 Summary of the invention

[0008] <Problems to be Solved by the Invention>

[0009] In the conventional active gate drive method, it is assumed that the current value of the main current at the start time of the shutdown is the same between the last time and this time. However, in a drive mode (e.g., a current discontinuous mode) in which the current value of the main current at the start time of the shutdown may be different between the last time and this time, the appropriate timing of changing the switching speed for achieving surge voltage suppression and switching loss reduction will change each time. Therefore, it is impossible to perform active gate drive at an appropriate timing, and it may be difficult to achieve both shutdown surge voltage suppression and switching loss reduction at the same time.

[0010] Therefore, the present disclosure provides a gate driving device and a power conversion device which can simultaneously suppress a turn-off surge voltage and reduce a switching loss by changing a switching speed at an appropriate timing.

[0011] <Methods used to solve the problem>

[0012] The present disclosure provides a gate driving device, comprising: a gate driving unit, which drives the gate of the switching element according to an input signal indicating the on or off of the switching element; a timing determination unit, which measures the on-time width from the input signal switching to the on-time instruction to the off-time instruction, and determines the mid-time timing before the off-time surge voltage of the switching element reaches a peak value based on the measured on-time width; and a driving condition changing unit, which changes the gate driving condition of the switching element at the mid-time determined by the timing determination unit.

[0013] In addition, the present disclosure provides a power conversion device, including the gate driving device.

[0014] <Effects of the Invention>

[0015] According to the technology disclosed in the present invention, it is possible to provide a gate driving device and a power conversion device that can simultaneously suppress a turn-off surge voltage and reduce a switching loss by changing a switching speed at an appropriate timing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a block diagram showing a structural example of a gate driving device.

[0017] Figure 2 is a circuit diagram showing a structure of a chopper circuit as an example of a power conversion device.

[0018] Figure 3 1 is a diagram showing examples of operation waveforms in the current continuous mode and the current discontinuous mode.

[0019] Figure 4 1 is a timing chart showing a first operation example of the gate driving device.

[0020] Figure 5 It is a timing chart showing a second operation example of the gate driving device. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0022] Figure 1 is a block diagram showing a structural example of a gate driving device. Figure 1 The gate driving device 1 shown is a circuit that supplies a positive or negative voltage to the gate of the switching element 11 to drive the gate of the switching element 11 to turn on or off. The gate driving device 1 drives the gate of the switching element 11 by an active gate driving method that adjusts the switching speed of the switching element 11 during the off period of the switching element 11.

[0023] The switch element 11 is a voltage-driven semiconductor element and has a control electrode (gate), a first main electrode (collector or drain), and a second main electrode (emitter or source). Specific examples of the switch element 11 include MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), etc. Figure 1 The case where the switch element 11 is an N-channel MOSFET is exemplified.

[0024] The switch element 11 may be a semiconductor such as Si (silicon), or a wide bandgap device such as SiC (silicon carbide), GaN (gallium nitride), Ga2O3 (gallium oxide), or diamond. By applying a wide bandgap device to the switch element 11, the loss reduction effect of the switch element 11 is improved.

[0025] The gate driving device 1 includes, for example, a gate driving unit 200 , a timing determination unit 241 , and a driving condition change unit 231 .

[0026] The gate driving unit 200 is a circuit unit that drives the gate of the switching element 11 according to an input signal from outside the gate driving device 1. The input signal is a signal that instructs the switching of the switching element 11, for example, a pulse width modulated signal (PWM signal). When the input signal is a PWM signal, when the input signal is an active level (for example, a high level), it indicates a turn-on instruction for the switching element 11, and when the input signal is an inactive level (for example, a low level), it indicates a turn-off instruction for the switching element 11.

[0027] The timing determination unit 241 determines the on-time width T from when the input signal is switched to the on-command to when it is switched to the off-command. ON The measured conduction time width T ON The intermediate timing tm before the turn-off surge voltage of the switching element 11 reaches the peak is determined. The intermediate timing tm is a condition change timing for changing the gate drive condition of the switching element 11 during the turn-off period so that the switching speed of the switching element 11 changes during the turn-off period.

[0028] The timing determination unit 241 includes, for example, a time width measurement unit 211 and a timing output unit 221 .

[0029] The time width measuring unit 211 measures the on time width T from when the input signal is switched to the on command to when it is switched to the off command. ONThe time width measuring unit 211 may be a counter or a filter that measures the conduction time width T ON The structure for performing the measurement may be a structure for converting the pulse width of the input signal into a voltage value.

[0030] The timing output unit 221 outputs the conduction time width T measured by the time width measuring unit 211. ON , outputs a timing signal S for causing the driving condition changing section 231 to change the gate driving condition of the switching element 11 at the midway timing tm.

[0031] The driving condition changing section 231 changes the gate driving condition of the switching element 11 at the intermediate timing tm determined by the timing determining section 241 based on the timing signal S output from the timing output section 221. Figure 1 Although driving conditions a1 and a2 having different condition contents are exemplarily shown in FIG. 1 , three or more driving conditions having different condition contents may be set.

[0032] The driving condition changing section 231 selects one of the driving conditions a1 and a2 according to the timing signal S. For example, the driving condition changing section 231 selects the driving condition a1 while the timing signal S is output from the timing determining section 241 , and selects the driving condition a2 while the timing signal S is not output from the timing determining section 241 .

[0033] The driving condition changing unit 231 includes, for example, two gate resistors having different resistance values ​​and a switch circuit for switching whether to connect each gate resistor to the gate of the switching element 11. The resistance value of the gate resistor connected to the gate of the switching element 11 is smaller when the driving condition a1 is selected than when the driving condition a2 is selected.

[0034] Therefore, during the period when the switching element 11 is turned off by the gate driving unit 200, the switching speed (turn-off speed) of the switching element 11 is accelerated by selecting the driving condition a1 that reduces the resistance value of the gate resistor. Therefore, the switching loss at the time of turning off can be reduced. On the other hand, during the period when the switching element 1 is turned off by the gate driving unit 200, the switching speed (turn-off speed) of the switching element 11 is slowed down by selecting the driving condition a2 that increases the resistance value of the gate resistor. Therefore, the time change rate (dI / dt) of the drain current flowing through the switching element 11 is reduced, and the turn-off surge voltage can be suppressed.

[0035] In addition, the driving condition changing unit 231 may be a structure having two gate current sources with different current values ​​and a switch circuit for switching whether to connect each gate current source to the gate of the switching element 11. The current value of the gate current source connected to the gate of the switching element 11 is greater when the driving condition a1 is selected than when the driving condition a2 is selected.

[0036] Therefore, during the period when the switching element 11 is turned off by the gate driving unit 200, the switching speed (turn-off speed) of the switching element 11 is accelerated by selecting the driving condition a1 that increases the current value of the gate current. Therefore, the switching loss at the time of turning off can be reduced. On the other hand, during the period when the switching element 11 is turned off by the gate driving unit 200, the switching speed (turn-off speed) of the switching element 11 is slowed down by selecting the driving condition a2 that reduces the current value of the gate current. Therefore, the time change rate (dI / dt) of the drain current flowing through the switching element 11 is reduced, and the turn-off surge voltage can be suppressed.

[0037] Here, refer to Figure 2 , Figure 3 , the intermediate timing tm before the turn-off surge voltage of the switching element 11 reaches the peak value is described.

[0038] Figure 2 is a circuit diagram showing a structure of a chopper circuit as an example of a power conversion device. Figure 3 The operation waveforms of the current continuous mode and the current discontinuous mode are shown. In the current continuous mode and the current discontinuous mode, the main current (drain current or collector current) flowing through the semiconductor element S1 is determined in proportion to the input signal (e.g., duty cycle command) of the gate drive device that drives the semiconductor element S1 in the power conversion device. Figure 2 In the example, when E1 is the input voltage, E2 is the output voltage, L is the reactor, and I L When the reactor current is , in the case of this boost circuit, since the drain current is consistent with the reactor current, the drain current changes according to the following formula.

[0039] When S1 is on:

[0040] Δi L =E1 / L×T ON

[0041] When S1 is off:

[0042] Δi L =(E1-E2) / L×T OFF

[0043] Δi L is the change in drain current, TON is the conduction time of semiconductor element S1, T OFF is the turn-off time of semiconductor element S1. However, due to the diode D, i L It will not fall below 0.

[0044] In the discontinuous current mode, if Figure 3 As shown, in one carrier cycle, due to the reactor current i L becomes 0, so the reactor current i immediately before shutdown (in other words, at the shutdown start time point) L The current value of the drain current depends on the on-time width T ON Therefore, the peak arrival time from the turn-off start timing of the semiconductor element S1 to the timing when the turn-off surge voltage reaches the peak value is roughly determined by the on-time width T ON .

[0045] Therefore, the timing determination unit 241 uses the conduction time width T ON , thereby being able to determine the midway timing tm before the turn-off surge voltage of the semiconductor element S1 reaches its peak. The driving condition changing unit 231 changes the gate driving condition of the switching element 11 at the midway timing tm determined by the timing determining unit 241. In other words, the timing determining unit 241 is able to determine an appropriate midway timing tm for changing the switching speed to achieve surge voltage suppression and switching loss reduction. Furthermore, since the gate driving condition can be changed at the appropriate midway timing tm, surge voltage suppression and switching loss reduction can be achieved simultaneously. Since surge voltage suppression and switching loss reduction can be achieved simultaneously, for example, miniaturization and cost reduction of magnetic elements such as transformers or reactors can be achieved, and miniaturization of the cooling body of the switching element can be achieved.

[0046] In particular, in the current discontinuous mode, since the current value of the main current at the shutdown start time point may be different between the previous time and the current time, it is beneficial to be able to determine the appropriate intermediate timing tm as described above.

[0047] Figure 4 1 is a timing chart showing a first operation example of the gate driving device 1. The gate driving unit 200 provides a control signal (gate driving signal) to the control terminal (gate) of the switching element 11 via the driving condition changing unit 231 according to an input signal for switching the switching element 11 in the current discontinuous mode. In this example, a high-level input signal indicates an on command of the switching element 11, and a low-level input signal indicates an off command of the switching element 11.

[0048] When the input signal changes from a shutdown command to an on command, the switch element 11 starts to conduct according to the control signal input to its control terminal (time point t1). The voltage VDS between the drain and source of the switch element 11 decreases, and the drain current Id starts to increase. At the same time when the input signal changes to an on command, the time width measuring unit 211 starts to measure the on time width T of the input signal. ON For example, during the period when the input signal becomes the conduction instruction, the time width measurement unit 211 counts down from the preset count start value as the starting point, and measures the conduction time width T of the input signal. ON Convert to digital or voltage value.

[0049] At this time, the time width measuring unit 211 can measure the conduction time width T ON The counting speed of the time width measuring unit 211 is converted to a counting speed of an appropriate intermediate timing tm that can simultaneously achieve the suppression of the surge voltage and the reduction of the switching loss. ON The value is set in advance in the form of a relationship X with an appropriate intermediate timing tm that can simultaneously achieve suppression of surge voltage and reduction of switching loss.

[0050] It should be noted that the time width measuring unit 211 may also be configured to measure the conduction time width T ON The count start value of the time width measuring unit 211 is converted to the appropriate intermediate timing tm that can simultaneously achieve the suppression of the surge voltage and the reduction of the switching loss, and the count is started. ON The value is set in advance in the form of a relationship X with an appropriate intermediate timing tm that can simultaneously achieve suppression of surge voltage and reduction of switching loss.

[0051] Then, when the input signal changes from an on command to an off command, the switch element 11 starts to turn off according to the control signal input to its control terminal (time point t2). At the same time when the input signal changes to an off command, the time width measuring unit 211 stops counting and outputs the on time width T representing the input signal to the timing output unit 221. ON The size of the signal.

[0052] The timing output unit 221 outputs a timing signal S based on the output of the time width measuring unit 211. Figure 4In the example, the count value of the time width measuring unit 211 at the time point t2 when the input signal becomes the shutdown command is used as the count start value of the timing output unit 221. The timing output unit 221 counts down at a preset constant counting speed, and outputs the timing signal S during the period Δt0 until the time point t3 when the count value becomes 0. t3 corresponds to the appropriate intermediate timing tm that can simultaneously achieve the suppression of the surge voltage and the reduction of the switching loss.

[0053] In other words, at the time point t2 when the shutdown action starts, the output of the timing signal S starts, thereby switching from the driving condition a2 to the driving condition a1, and the voltage VDS between the drain and the source starts to increase. Since the driving condition a2 is switched to the driving condition a1, the switching speed in the first half of the shutdown period is increased, and the switching loss is reduced. For example, the driving condition changing unit 231 reduces the resistance value of the gate resistor connected to the gate of the switching element 11 at the time point t2, or increases the current value of the gate current flowing through the gate of the switching element 11 at the time point t2.

[0054] Next, when the mirror period of the switch element 11 ends (time point t3), when the drain current begins to decrease sharply, a surge voltage corresponding to the time rate of change of the drain current is generated. However, since the count value of the timing output unit 221 becomes 0, the output of the timing signal S stops. Thus, since the gate driving condition is switched from the driving condition a1 to the driving condition a2 at the time point t3, the switching speed in the second half of the shutdown period is slowed down, and the shutdown surge voltage can be suppressed. For example, the driving condition changing unit 231 increases the resistance value of the gate resistor connected to the gate of the switch element 11 at the time point t3, or reduces the current value of the gate current flowing through the gate of the switch element 11 at the time point t3.

[0055] As described above, the time width measuring unit 211 counts the time from when the input signal switches to the on command to when it switches to the off command, thereby outputting the same value as the on time width T. ON The timing output unit 221 changes the length of the period Δt0 for outputting the timing signal S according to the count value. ON The length of tm varies at each turn-off timing, and an appropriate intermediate timing tm that can simultaneously suppress surge voltage and reduce switching loss can be set. Figure 4 As shown, even if the next ((n+1)th) switch timing has an on-time width T ON The length is longer than the conduction time width T of the current (nth) switch timing. ON The length of Δt1 for outputting the timing signal S can be shortened. Thus, an appropriate intermediate timing tm can be set.

[0056] In addition, since the intermediate timing tm is the same as the measured conduction time width T ON The timing t3 during the period of the adjacent turn-off command can be used to make use of the previous on-time width T even in the current discontinuous mode. ON To set the intermediate timing tm suitable for the size of the drain current flowing.

[0057] Figure 5 1 is a timing chart showing a second operation example of the gate driving device 1. Since the operations other than the processing between the time width measuring unit 211 and the timing output unit 221 are the same as those of the first operation example, the description thereof is omitted or simplified by citing the above description. In the first operation example, the time width measuring unit 211 counts based on the relationship X, whereas in the second operation example, the timing output unit 221 counts based on the relationship X. The two are different in this respect.

[0058] When the input signal changes from the off command to the on command, the switch element 11 starts to conduct according to the control signal input to its control terminal (time point t1). At the same time when the input signal changes to the on command, the time width measuring unit 211 starts to measure the on time width T of the input signal. ON For example, during the period when the input signal becomes the conduction instruction, the time width measurement unit 211 counts up from the preset count start value (0 in this case) as the starting point, and measures the conduction time width T of the input signal. ON Convert to digital or voltage value.

[0059] At this time, the time width measuring unit 211 may not be able to measure the conduction time width T ON The counting speed is converted to a suitable intermediate timing tm that can simultaneously achieve suppression of surge voltage and reduction of switching loss. For example, the counting speed of the time width measuring unit 211 may be a value preset so as to conform to the actual passage of time.

[0060] Then, when the input signal changes from an on command to an off command, the switch element 11 starts to turn off according to the control signal input to its control terminal (time point t2). At the same time when the input signal changes to an off command, the time width measuring unit 211 stops counting and outputs the on time width T representing the input signal to the timing output unit 221. ON The size of the signal.

[0061] The timing output unit 221 outputs the timing signal S based on the output of the time width measuring unit 211. For example, the timing output unit 221 refers to the conduction time width T ONThe on-time width T measured by the time width measuring unit 211 is determined based on the relationship between the on-time width T and the appropriate intermediate timing tm that can simultaneously achieve the suppression of the surge voltage and the reduction of the switching loss. ON , output timing signal S.

[0062] exist Figure 5 In the example 1, the count value of the time width measuring unit 211 at the time point t2 when the input signal becomes a shutdown command is used as the count start value of the timing output unit 221. The timing output unit 221 counts down at a counting speed corresponding to the count value of the time width measuring unit 211 at the time point t2 when the input signal becomes a shutdown command, and outputs the timing signal S during the period Δt0 until the time point t3 when the count value becomes 0. t3 corresponds to the appropriate intermediate timing tm that can simultaneously achieve the suppression of the surge voltage and the reduction of the switching loss. In other words, the timing output unit 221 outputs the timing signal S from the on time width T measured by the time width measuring unit 211. ON The timing signal S is output during the period from the start of counting to the end of counting at the corresponding counting speed.

[0063] At this time, the counting speed of the timing output unit 221 is in accordance with the conduction time width T ON The relationship X between the surge voltage suppression and the appropriate intermediate timing tm that can simultaneously achieve the reduction of the switching loss is determined based on the on-time width T measured in each on-operation. ON For example, the timing output unit 221 determines the conduction time width T measured by the time width measuring unit 211 based on the relationship X. ON The corresponding counting speed is determined, and the timing signal S is output during the period from the start of counting to the end of counting at the determined counting speed.

[0064] In addition, Figure 5 As a second example, the timing output unit 221 may count down from the count start value corresponding to the count value of the time width measuring unit 211 at the time point t2 when the input signal becomes off as the starting point. In this case, the counting speed of the timing output unit 221 is a predetermined constant value, for example, a value predetermined in a manner consistent with the actual passage of time. In other words, the timing output unit 221 counts down from the count start value corresponding to the on time width T measured by the time width measuring unit 211. ON The corresponding counting start value is the period from the start of counting to the end of counting, and the timing signal S is output.

[0065] At this time, the counting start value of the timing output unit 221 is based on the conduction time width T ONThe relationship X between the surge voltage suppression and the appropriate intermediate timing tm that can simultaneously achieve the reduction of the switching loss is determined based on the on-time width T measured in each on-operation. ON For example, the timing output unit 221 determines the conduction time width T measured by the time width measuring unit 211 based on the relationship X. ON The corresponding count start value is determined, and the timing signal S is output during the period from when counting starts with the determined count start value to when counting ends.

[0066] In other words, at the time point t2 when the shutdown operation starts, the voltage VDS between the drain and the source starts to increase by starting to output the timing signal S, thereby switching from the driving condition a2 to the driving condition a1. Since the driving condition a2 is switched to the driving condition a1, the switching speed in the first half of the shutdown period is increased, and the switching loss is reduced.

[0067] Next, when the mirror period of the switching element 11 ends (time point t3), when the drain current begins to decrease sharply, a surge voltage corresponding to the time change rate of the drain current is generated. However, since the count value of the timing output unit 221 becomes 0, the output of the timing signal S stops. Therefore, since the gate driving condition is switched from the driving condition a1 to the driving condition a2 at the time point t3, the switching speed in the second half of the turn-off period is slowed down, and the turn-off surge voltage can be suppressed.

[0068] As described above, when the counting speed of the time width measuring unit 211 is not a value preset so as to satisfy the above relationship X, the conduction time width T measured by the time width measuring unit 211 can be used as the basis for the calculation. ON , to change the count start value or count speed of the timing output unit 221. At this time, the timing output unit 221 can be based on the conduction time width T measured by the time width measuring unit 211. ON The counting start value or the counting speed is determined each time in accordance with the appropriate intermediate timing tm for changing the driving condition. It should be noted that the method of referring to the above relationship X may also be other methods.

[0069] The gate drive device and the power conversion device are described above by using the embodiments, but the present invention is not limited to the above embodiments. Various modifications and improvements such as combination or replacement with part or all of other embodiments can be made within the scope of the present invention.

[0070] For example, the power conversion device including at least one gate driving device is not limited to a DC-DC converter that converts direct current into direct current. Specific examples thereof include an inverter that converts direct current into alternating current, a boost converter that boosts and outputs an input voltage, a buck converter that steps down and outputs an input voltage, a buck-boost converter that steps up or steps down an input voltage and outputs the same, and the like.

[0071] Explanation of symbols

[0072] 1 Gate drive device

[0073] 11 Switching elements

[0074] 200 Gate drive unit

[0075] 211 Time width measurement unit

[0076] 221 Timing output unit

[0077] 231 Driving Condition Change Department

[0078] 241 Timing determination unit

Claims

1. A gate driving device, comprising: a gate driving unit that drives the gate of the switching element according to an input signal that instructs the switching element to turn on or off, Characterized in that, the gate driving device also includes: a timing determination unit that measures an on-time width from when the input signal is switched to an on-command to when it is switched to an off-command, and determines a midway timing before a turn-off surge voltage of the switching element reaches a peak value based on the measured on-time width; and The driving condition changing unit changes the gate driving condition of the switching element so as to slow down the switching speed of the switching element at the intermediate timing determined by the timing determining unit.

2. The gate driving device according to claim 1, wherein: The timing determination unit has: a time width measuring unit for measuring the conduction time width; and The timing output unit outputs a timing signal for causing the driving condition changing unit to change the gate driving condition at the midway timing, based on the on-time width measured by the time width measuring unit.

3. The gate driving device according to claim 2, wherein: The time width measuring unit counts the time from when the input signal switches to the on command to when it switches to the off command, thereby outputting a count value corresponding to the on time width. The timing output unit changes the length of a period for outputting the timing signal according to the count value.

4. The gate driving device according to claim 3, wherein: The time width measuring unit counts at a counting speed capable of converting the on-time width into the intermediate timing or with a counting start value capable of converting the on-time width into the intermediate timing as a starting point.

5. The gate driving device according to claim 2 or 3, wherein: The timing output unit outputs the timing signal from the start of counting to the end of counting, starting from a counting speed corresponding to the on-time width measured by the time width measuring unit or a counting start value corresponding to the on-time width measured by the time width measuring unit.

6. The gate driving device according to claim 2 or 3, wherein: The timing output unit refers to the relationship between the on-time width and the change timing of the gate driving condition, and outputs the timing signal according to the on-time width measured by the time width measuring unit.

7. The gate driving device according to claim 6, wherein: The timing output unit determines a counting speed or a counting start value corresponding to the conduction time width measured by the time width measuring unit based on the relationship, and outputs the timing signal from the start of counting to the end of counting, starting from the determined counting speed or the determined counting start value.

8. The gate driving device according to any one of claims 2 to 4, wherein: When the input signal is switched to a shutdown command, the timing output unit starts outputting the timing signal.

9. The gate driving device according to any one of claims 1 to 4, wherein: The driving condition changing section reduces a current value of a gate current flowing through a gate of the switching element at the intermediate timing.

10. The gate driving device according to any one of claims 1 to 4, wherein: The switch element is a wide bandgap device.

11. A power conversion device, characterized in that: The power conversion device comprises: The gate driving device according to any one of claims 1 to 10; and The switching element.

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