JP7243156B2 - Drive circuit for switching element - Google Patents

Description

The present invention relates to a switching element drive circuit for driving a plurality of switching elements connected in parallel.

As this type of drive circuit, there is known one that includes a current detection section and a switching section, as disclosed in Patent Document 1, for example. The current detection unit detects a current flowing through each of a plurality of switching elements connected in parallel. The switching unit determines a switching element to be turned off first from among the plurality of switching elements based on the magnitude relationship between the value detected by the current detection unit and the threshold. When turning off the plurality of switching elements, the switching element to be turned off first is switched to off drive, and then the other switching elements are switched to off drive.

JP 2018-29259 A

As shown in Patent Document 1, when turning off a plurality of switching elements connected in parallel with each other, after switching a reference switching element which is at least one switching element among the plurality of switching elements to off drive, the remaining switching elements are turned off. Other switching elements, which are the switching elements of , may be switched to off drive. In this way, in a plurality of switching elements connected in parallel with each other, if the switching elements are switched to off-drive at different timings, it is not possible to properly turn off the other switching elements that are switched to off-drive with a delay.

For example, when driving a plurality of switching elements in a predetermined switching cycle, if the on-drive period from when the reference switching element is switched to on-drive to when it is switched to off-drive is long, the other switching elements are off-driven. The switching timing is delayed. Accordingly, if the other switching elements cannot be turned off until the reference switching element is turned on next time, the charge accumulated in the other switching elements cannot be discharged until the reference switching element is turned on. . As a result, there arises a problem that a relatively large surge voltage is generated when turning on the reference switching element. A technique is desired that can properly turn off a plurality of switching elements connected in parallel with each other.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching element driving circuit capable of properly turning off a plurality of switching elements connected in parallel.

The present invention provides a switching element driving circuit for driving a plurality of switching elements connected in parallel with each other in a predetermined switching period, wherein at least one of the switching elements is used as a reference switching element, and the remaining switching elements are A determination unit that determines whether an on-drive period from when the reference switching element is switched to on-drive to when it is switched to off-drive is longer than a reference period when the switching element is another switching element and the reference switching element is turned off until the next reference switching element is turned on when the determination unit determines that the on-driving period is longer than the reference period. a switching unit that switches the element and the other switching element to off drive.

In the present invention, when turning off a plurality of switching elements connected in parallel, it is determined whether or not the ON drive period of the reference switching element is longer than the reference period. When it is determined that the on-drive period is longer than the reference period, the reference switching element and the other switching elements are turned off until the reference switching element is turned on next time. switch. Therefore, even if the on-driving period is longer than the reference period, other switching elements can be turned off before the next reference switching element is turned on. As a result, the plurality of switching elements connected in parallel can be properly turned off.

FIG. 1 is an overall configuration diagram of a control system for a rotating electrical machine; The figure which shows the current voltage characteristic of a 1st, 2nd switching element. 2 is a diagram showing a drive circuit according to the first embodiment; FIG. 4 is a flowchart of drive control processing according to the first embodiment; 4 is a time chart showing changes in drive states of first and second switching elements according to the first embodiment; 8 is a flowchart of drive control processing according to the second embodiment; FIG. 10 is a time chart showing the transition of the drive state in the first drive of the first and second switching elements according to the second embodiment; FIG. FIG. 11 is a time chart showing the transition of the drive state in the second drive of the first and second switching elements according to the second embodiment; FIG. The figure which shows the drive circuit which concerns on 3rd Embodiment. 10 is a flowchart of drive control processing according to the third embodiment; FIG. 11 is a time chart showing the transition of the drive state in the first drive of the first and second switching elements according to the third embodiment; FIG. FIG. 11 is a time chart showing the transition of the drive state in the second drive of the first and second switching elements according to the third embodiment; FIG. 14 is a flowchart of drive control processing according to the fourth embodiment; FIG. 11 is a time chart showing the transition of the drive state in the second drive of the first and second switching elements according to the fourth embodiment; FIG.

<First Embodiment>
DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment embodying a drive circuit according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the control system includes a DC power supply 10, an inverter 20, a rotating electrical machine 30, and a control device 40. The rotary electric machine 30 is, for example, an in-vehicle main machine. Rotating electric machine 30 is electrically connected to DC power supply 10 via inverter 20 . In this embodiment, a three-phase rotating electric machine is used as the rotating electric machine 30 . As the rotary electric machine 30, for example, a permanent magnet synchronous machine can be used. Also, the DC power supply 10 is, for example, a storage battery having a terminal voltage of 100 V or higher. The DC power supply 10 is, for example, a secondary battery such as a lithium-ion battery or a nickel-metal hydride battery. A capacitor 11 is connected in parallel with the DC power supply 10 .

The inverter 20 includes upper and lower arm switching element sections 20H and 20L corresponding to each phase. In each phase, the upper arm switching element section 20H and the lower arm switching element section 20L are connected in series. In each phase, one end of winding 31 of rotary electric machine 30 is connected to a connection point between upper arm switching element section 20H and lower arm switching element section 20L. The other end of each phase winding 31 is connected at a neutral point.

Each switching element section 20H, 20L includes a parallel connection of a first switching element SW1 and a second switching element SW2. In each phase, the positive electrode side of the DC power supply 10 is connected to the input terminals of the first and second switching elements SW1 and SW2 of the upper arm switching element section 20H. In each phase, the negative electrode side of the DC power supply 10 is connected to the output terminals of the first and second switching elements SW1 and SW2 of the lower arm switching element section 20L. In each phase, the input terminals of the first and second switching elements SW1 and SW2 of the lower arm switching element section 20L are connected to the output terminals of the first and second switching elements SW1 and SW2 of the upper arm switching element section 20H. It is connected.

In this embodiment, the first switching element SW1 is an N-channel MOSFET as a SiC device. Therefore, in the first switching element SW1, the output terminal is the source and the input terminal is the drain. Also, the second switching element SW2 is an IGBT as a Si device. Therefore, in the second switching element SW2, the output terminal is the emitter and the input terminal is the collector. A freewheel diode is connected in anti-parallel to each of the second switching elements SW2.

The reason why the switching element units 20H and 20L are configured with parallel-connected bodies of IGBTs and MOSFETs is that by connecting IGBTs having a large current capacity in parallel to MOSFETs, a large amount of current flows through the windings 31 of the rotary electric machine 30. be. When attempting to increase the current capacity of the MOSFET, there is concern that the size of the inverter 20 will increase due to the increase in size of the MOSFET. By connecting the IGBT in parallel with the MOSFET, it is possible to suppress an increase in size of the inverter 20 .

Another reason is to reduce the loss in the small current region by allowing more current to flow through the MOSFET with lower on-resistance in the small current region. A description will be given below with reference to FIG. FIG. 2 is a diagram showing the relationship between the current flowing through the switching element and the voltage Von between the input/output terminals of the switching element. Specifically, FIG. 2 shows the voltage-current characteristics of the drain-source voltage Vds and the drain current Id of the MOSFET, and the voltage-current characteristics of the collector-emitter voltage Vce and the collector current Ic of the IGBT.

As shown in FIG. 2, in the small current region where the current is smaller than the predetermined current Iα, the drain-source voltage Vds with respect to the drain current Id is lower than the collector-emitter voltage Vce with respect to the collector current Ic. That is, in the small current region, the on-resistance of the MOSFET is smaller than the on-resistance of the IGBT. Therefore, in the small current region, more current flows through the MOSFET out of the MOSFET and IGBT connected in parallel with each other. On the other hand, in a large current region where the current is greater than the predetermined current Iα, the collector-emitter voltage Vce with respect to the collector current Ic is lower than the drain-source voltage Vds with respect to the drain current Id. That is, in the large current region, the on-resistance of the IGBT is smaller than the on-resistance of the MOSFET. Therefore, in the large current region, more current flows through the IGBT out of the MOSFET and IGBT connected in parallel with each other.

Control device 40 drives inverter 20 to control the control amount of rotating electric machine 30 to the command value. The controlled variable is, for example, torque. In order to drive the switching elements SW1 and SW2 of the inverter 20, the control device 40 supplies drive signals IN corresponding to the switching elements SW1 and SW2 to the driving circuits provided individually for the switching element sections 20H and 20L. Output to Dr. For example, the control device 40 generates a drive signal IN corresponding to each drive circuit Dr by PWM processing based on a magnitude comparison between a three-phase command voltage having an electrical angle difference of 120° and a carrier signal such as a triangular wave. . The drive signal IN switches between an ON command for instructing ON drive of the switching element and an OFF command for instructing OFF drive for each predetermined switching period TW (see FIG. 5). In each phase, the drive signal IN on the upper arm side and the corresponding drive signal IN on the lower arm side are alternately turned on. Therefore, in each phase, the switching elements SW1 and SW2 of the upper arm switching element section 20H and the switching elements SW1 and SW2 of the lower arm switching element section 20L are alternately turned on.

Next, the configuration of the drive circuit Dr will be described with reference to FIG. Each drive circuit Dr corresponding to each switching element unit 20H, 20L in the present embodiment basically has the same configuration. The functions provided by the drive circuit Dr can be provided by, for example, software recorded in a physical memory device, a computer executing the software, hardware, or a combination thereof.

The drive circuit Dr is a circuit that drives a plurality of switching elements SW1 and SW2 connected in parallel with each other at a predetermined switching cycle TW, and includes a drive IC 50 that is a one-chip semiconductor integrated circuit. The driving IC 50 is connected via a first terminal T1 of the driving IC 50 to a constant voltage power supply 80 having a predetermined output voltage Vom (eg 15V). A constant-voltage power supply 80 is connected to the source of a P-channel MOSFET (hereinafter referred to as a first charging switching element) 52 via a first terminal T1. The drain of the first charging switching element 52 is connected to the gate, which is the opening/closing control terminal of the first switching element SW1, via the second terminal T2 of the drive IC50.

A gate of the first switching element SW1 is connected to the third terminal T3 of the drive IC 50 via the first discharge resistor 54 . The third terminal T3 is connected to the source of the first switching element SW1 via the N-channel MOSFET (hereinafter referred to as first discharge switching element) 56 and the fifth terminal T5 of the drive IC50.

The first switching element SW1 has a first sense terminal St1 that outputs a very small current correlated with the collector current Ic. A first sense terminal St1 is connected to the source via a first sense resistor 58 . As a result, a minute current output from the first sense terminal St1 causes a voltage drop across the first sense resistor 58, and the voltage on the first sense terminal St1 side of the first sense resistor 58 (hereinafter referred to as first sense voltage) Vse1 can be an electrical state quantity correlated with the drain current Id. The first sense voltage Vse1 is input to the control section 60 via the fourth terminal T4 of the drive IC50.

Also, the constant voltage power supply 80 is connected to the source of the P-channel MOSFET (hereinafter referred to as the second charging switching element) 62 via the first terminal T1. The drain of the second charging switching element 62 is connected to the gate, which is the opening/closing control terminal of the second switching element SW2, via the sixth terminal T6 of the drive IC50.

The gate of the second switching element SW2 is connected to the seventh terminal T7 of the driving IC 50 via the second discharge resistor 64. As shown in FIG. The seventh terminal T7 is connected to the emitter of the second switching element SW2 via the N-channel MOSFET (hereinafter referred to as second discharge switching element) 66 and the ninth terminal T9 of the drive IC50.

The second switching element SW2 has a second sense terminal St2 that outputs a very small current correlated with the collector current Ic. A second sense terminal St2 is connected to the emitter via a second sense resistor 68 . As a result, a small current output from the second sense terminal St2 causes a voltage drop across the second sense resistor 68, causing a voltage drop on the second sense terminal St2 side of the second sense resistor 68 (hereinafter referred to as a second sense voltage Vse2). ) can be an electrical state quantity correlated with the collector current Ic. The second sense voltage Vse2 is input to the control section 60 via the eighth terminal T8 of the drive IC50.

The control unit 60 drives the first and second switching elements SW1 and SW2 based on the drive signal IN input from the control device 40 via the tenth terminal T10 of the drive IC50. The control unit 60 acquires the drive signal IN, and when the acquired drive signal IN is an ON command, switches the second charging switching element 62 to the ON state, thereby switching the second switching element SW2 to the ON drive. As a result, the gate of the second switching element SW2 is charged through the sixth terminal T6 of the drive IC50. When the gate voltage (hereinafter referred to as the second gate voltage) Vg2 of the second switching element SW2 becomes equal to or higher than the second threshold voltage Vth2 due to the ON drive, the second switching element SW2 is turned on, that is, switched from the OFF state to the ON state. The ON state is a state that allows current to flow through the switching element. The OFF state is a state in which current flow through the switching element is blocked. The second threshold voltage Vth2 is a voltage for switching the second switching element SW2 from one of the ON state and the OFF state to the other state.

The control unit 60 switches the first charging switching element 52 to the ON state at the timing when the ON transition period TN has passed since the drive signal IN, which is the ON command, is acquired, thereby turning the first switching element SW1 to the ON drive. switch. Here, the on-transition period TN is a period required from switching the second switching element SW2 to on-driving until the second switching element SW2 is turned on. As a result, the gate of the first switching element SW1 is charged through the second terminal T2 of the drive IC50. When the gate voltage (hereinafter referred to as first gate voltage) Vg1 of the first switching element SW1 becomes equal to or higher than the first threshold voltage Vth1 due to ON drive, the first switching element SW1 is turned on. The first threshold voltage Vth1 is a voltage for switching the first switching element SW1 from one of the ON state and the OFF state to the other state.

Further, when the control unit 60 determines that the acquired drive signal IN is an OFF command, it switches the second switching element SW2 to the OFF drive by switching the second discharge switching element 66 to the ON state. As a result, electric charges are discharged from the gate of the second switching element SW2 through the seventh terminal T7 of the drive IC50. When the second gate voltage Vg2 becomes less than the second threshold voltage Vth2 due to off-driving, the second switching element SW2 is turned off, that is, the second switching element SW2 is switched from the on state to the off state.

The control unit 60 switches the first discharge switching element 56 to the ON state at the timing when the OFF transition period TF has passed since the drive signal IN, which is the OFF command, is acquired, thereby turning the first switching element SW1 to the OFF drive. switch. Here, the off-transition period TF is a period required from switching the second switching element SW2 to off drive until the second switching element SW2 is turned off. As a result, electric charges are discharged from the gate of the first switching element SW1 through the third terminal T3 of the drive IC50. When the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 due to the off drive, the first switching element SW1 is turned off.

In the present embodiment, the second switching element SW2 is selected as the reference switching element, and is switched to the ON drive in synchronization with the drive signal IN being the ON command, and the drive signal IN is the OFF command. is switched to OFF drive in synchronization with . The first switching element SW1 is another switching element that is switched to ON driving after the second switching element SW2 is turned on, and is switched to OFF driving after the second switching element SW2 is turned off. Therefore, the first switching element SW1 is turned off after the second switching element SW2 is turned off.

The reason why the first switching element SW1 is turned off after the second switching element SW2 is turned off is to suppress the power loss of the inverter 20. FIG. If the second switching element SW2 is turned off after the first switching element SW1 is turned off, a tail current flows when the second switching element SW2, which is an IGBT, is turned off, increasing power loss. Since the first switching element SW1 is turned off after the second switching element SW2 is turned off, it is possible to suppress the generation of the tail current, and the power loss of the inverter 20 can be suppressed.

By the way, when the first and second switching elements SW1 and SW2 connected in parallel are turned off, if the switching elements are switched to off-driving at different timings, the first switching element SW1, which is switched to off-driving with a delay, is appropriately selected. may not be able to turn off at

For example, if the on-drive period TM (see FIG. 5) from when the second switching element SW2 is switched to on-drive to when it is switched to off-drive is long, the timing at which the first switching element SW1 is switched to off-drive is delayed. Accordingly, if the first switching element SW1 cannot be turned off until the second switching element SW2 is turned on next time, the power stored in the first switching element SW1 is accumulated until the second switching element SW2 is turned on. the charge cannot be discharged. As a result, there arises a problem that a relatively large surge voltage is generated when turning on the second switching element SW2.

The control unit 60 of the present embodiment performs drive control processing when turning off the first and second switching elements SW1 and SW2. In the drive control process, it is determined whether or not the ON drive period TM is longer than the reference period TK (see FIG. 5). When it is determined that the on-driving period TM is longer than the reference period TK, the first switching element SW1 is turned off before the second switching element SW2 is next turned on. A second drive is performed to switch SW1 and SW2 to OFF drive. Therefore, even if the on-driving period TM is longer than the reference period TK, the first switching element SW1 can be turned off before the second switching element SW2 is next turned on. As a result, the first and second switching elements SW1 and SW2 connected in parallel can be properly turned off.

FIG. 4 shows a flowchart of the drive control process of this embodiment. While the rotating electric machine 30 is operating, the control unit 60 repeatedly executes the drive control process at predetermined time intervals.

When the drive control process is started, first, in step S10, it is determined whether or not the second switching element SW2 is ON drive. Whether or not the second switching element SW2 is ON-driven is determined by the drive signal IN.

If a negative determination is made in step S10, the drive control process is terminated. On the other hand, if an affirmative determination is made in step S10, in step S12, the elapsed period TP after the second switching element SW2 is switched to ON drive is acquired. The control unit 60 measures the elapsed period TP from the switching of the drive signal IN to the ON command. It should be noted that in the present embodiment, the process of step S12 corresponds to the "elapsed period acquisition unit".

In step S14, it is determined whether or not the elapsed period TP acquired in step S12 is longer than the reference period TK. If a negative determination is made in step S14, it is determined in step S16 whether the drive signal IN has been switched to the OFF command. In addition, in this embodiment, the process of step S14 corresponds to a "judgment part."

If a negative determination is made in step S16, the drive control process is terminated. On the other hand, if an affirmative determination is made in step S16, that is, if the second switching element SW2 is switched to OFF drive before the elapsed period TP reaches the reference period TK, it is determined that the ON drive period TM is equal to or shorter than the reference period TK. In this case, the first driving (S18 to S22) is performed to turn off the first and second switching elements SW1 and SW2 so that the first switching element SW1 is turned off after the second switching element SW2 is turned off. .

Specifically, when the drive signal IN is switched to the OFF command, in step S18, the second switching element SW2 is switched to OFF drive. In subsequent step S20, it is determined whether or not the off transition period TF has elapsed after switching the second switching element SW2 to the off drive. If a negative determination is made in step S20, step S20 is repeated. On the other hand, when an affirmative determination is made in step S20, in step S22, the first switching element SW1 is switched to OFF drive, and the drive control process ends.

On the other hand, if an affirmative determination is made in step S14, that is, if the second switching element SW2 has not been switched to off-driving before the elapsed period TP reaches the reference period TK, it is determined that the on-driving period TM is longer than the reference period TK. do. In this case, the second drive (S24 to S28) for switching the first and second switching elements SW1 and SW2 to off drive is performed so that the first switching element SW1 is turned off before the second switching element SW2 is turned on next time. )I do. It should be noted that in the present embodiment, the processing of steps S18 to S28 corresponds to the "switching section".

Specifically, in step S24, the first switching element SW1 is switched to OFF drive. In other words, the first switching element SW1 is switched to OFF drive before the OFF transition period TF elapses after switching the second switching element SW2 to OFF drive. In the present embodiment, the first switching element SW1 is switched to OFF drive before switching the second switching element SW2 to OFF drive. In subsequent step S26, it is determined whether the drive signal IN has been switched to the OFF command. If a negative determination is made in step S26, step S26 is repeated. On the other hand, if an affirmative determination is made in step S26, in step S28, the second switching element SW2 is switched to OFF drive, and the drive control process ends.

Next, FIG. 5 shows changes in the drive states of the first and second switching elements SW1 and SW2 in the drive control process. Here, FIG. 5(a) shows the transition of the command state of the driving signal IN, FIG. 5(b) shows the transition of the second gate voltage Vg2, and FIG. 5(c) shows the transition of the second switching element SW2. shows the transition of the driving state of FIG. 5(d) shows transition of the first gate voltage Vg1, and FIG. 5(e) shows transition of the driving state of the first switching element SW1. FIGS. 5D and 5E show the transition of each value (solid line) in the present embodiment and the transition of each value (broken line) in the comparative example. The comparative example differs from the present embodiment in which only the first drive is performed, in which the first drive and the second drive are performed.

FIG. 5 also shows transitions of the drive states of the first and second switching elements SW1 and SW2 for two cycles, with the switching cycle TW as one cycle. Hereinafter, the switching period TW from time t1 to time t8 is called a first period TD1, and the switching period TW from time t8 to time t15 is called a second period TD2.

As shown in FIG. 5, at time t1 in the first period TD1, when the drive signal IN is turned on, the second switching element SW2 is switched to the on drive. When the second gate voltage Vg2 becomes equal to or higher than the second threshold voltage Vth2 at time t2 after the ON transition period TN has passed from time t1, the second switching element SW2 is turned on.

At time t2, when the second gate voltage Vg2 is turned on, the first switching element SW1 is switched to ON drive. When the first gate voltage Vg1 becomes equal to or higher than the first threshold voltage Vth1 at time t3 by the ON drive, the first switching element SW1 is turned on.

The control unit 60 measures the elapsed period TP from the time t1 when the drive signal IN is turned on. Then, it is determined whether or not the driving signal IN is turned off before the measured elapsed period TP reaches the reference period TK.

In the first period TD1, the drive signal IN is instructed to be turned off by time t6 when the elapsed period TP reaches the reference period TK. That is, it shows a form in which the on-drive period TM is equal to or shorter than the reference period TK. In this case, the first drive is performed. Specifically, at time t4 before the reference period TK elapses from time t1, when the drive signal IN is turned off, the second switching element SW2 is switched to off drive. When the second gate voltage Vg2 becomes less than the second threshold voltage Vth2 at time t5 when the off-transition period TF has passed from time t4 due to the off drive, the second switching element SW2 is turned off.

At time t5, when the second gate voltage Vg2 is turned off, the first switching element SW1 is switched to off drive. When the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 at time t7 by the off drive, the first switching element SW1 is turned off. As a result, the first switching element SW1 is turned off by time t9 when the second gate voltage Vg2 is next turned on.

In the second period TD2, at time t8, when the drive signal IN is turned on, the second switching element SW2 is switched to ON drive. When the second gate voltage Vg2 becomes equal to or higher than the second threshold voltage Vth2 at time t9 due to the ON drive, the second switching element SW2 is turned on. At time t9, when the second gate voltage Vg2 is turned on, the first switching element SW1 is switched to ON drive. When the first gate voltage Vg1 becomes equal to or higher than the first threshold voltage Vth1 at time t10 by the ON drive, the first switching element SW1 is turned on.

In the second period TD2, the drive signal IN is not turned on by the time t11 when the elapsed period TP reaches the reference period TK. That is, it shows a form in which the on-driving period TM is longer than the reference period TK. In this case, when the first drive is performed, the first switching element SW1 cannot be turned off by time t16 when the second gate voltage Vg2 is next turned on. Specifically, as indicated by the dashed line in FIG. 5, when the driving signal IN is turned off at time t12 after time t11 after the reference period TK has passed from time t8, at time t12 The second switching element SW2 is switched to off drive. When the second gate voltage Vg2 becomes less than the second threshold voltage Vth2 at time t14 when the OFF transition period TF has passed from time t12 due to the OFF drive, the second switching element SW2 is turned off.

At time t14, when the second gate voltage Vg2 is turned off, the first switching element SW1 is switched to off drive. However, at time t15 before the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 due to the off drive, the drive signal IN is turned on, and the first gate voltage Vg1 becomes less than the first threshold voltage Vth1. At time t16, the second switching element SW2 is turned on. Therefore, the first switching element SW1 cannot be turned off by time t16 when the second gate voltage Vg2 next turns on.

In this embodiment, the second drive is performed in the second period TD2. Specifically, at time t11 when the reference period TK has passed from time t8, the first switching element SW1 is switched to OFF drive. When the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 at time t13 before time t16 due to the off drive, the first switching element SW1 is turned off. Therefore, the first switching element SW1 can be turned off by time t16 when the second gate voltage Vg2 next turns on.

According to this embodiment detailed above, the following effects can be obtained.

In the present embodiment, when it is determined that the on-drive period TM is equal to or shorter than the reference period TK, the first switching element SW1 is turned on at the timing when the off-transition period TF has passed after switching the second switching element SW2 to the off-drive. First drive is performed to switch to OFF drive. Further, when it is determined that the on-drive period TM is longer than the reference period TK, the first switching element SW1 is switched to off-drive before the off-transition period TF elapses after switching the second switching element SW2 to off-drive. A second drive is performed. That is, when it is determined that the on-drive period TM is longer than the reference period TK, the first switching element SW1 is switched to off-drive at an earlier timing than when it is determined that the on-drive period TM is equal to or shorter than the reference period TK. Therefore, when it is determined that the on-driving period TM is longer than the reference period TK, the first switching element SW1 can be quickly switched to off-driving. As a result, the first switching element SW1 can be turned off before the second switching element SW2 is turned on next time.

- In this embodiment, when determining whether or not the on-drive period TM is longer than the reference period TK, the elapsed period TP after the second switching element SW2 is switched to the on-drive is used. By using the elapsed period TP, it is possible to determine whether the on-drive period TM is longer than the reference period TK before the second switching element SW2 is switched to off-drive and the on-drive period TM is determined. can. As a result, when it is determined that the on-driving period TM is longer than the reference period TK, the first switching element SW1 can be quickly switched to off-driving.

<Second embodiment>
The second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

In this embodiment, the first switching element SW1 is selected as the reference switching element and the second switching element SW2 is the other switching element. Therefore, the second switching element SW2 is turned off after the first switching element SW1 is turned off.

Further, in the present embodiment, the total current amount IS, which is the sum of the current amount of the collector current Ic flowing through the first switching element SW1 and the current amount of the drain current Id flowing through the second switching element SW2, is It may be larger than the current capacity Itg of one switching element SW1. When the total current amount IS is larger than the current capacity Itg, if the second switching element SW2 is turned off first, a collector current Ic larger than the current capacity Itg flows through the first switching element SW1, and the first switching element SW1 problems occur. Therefore, in the drive control process of the present embodiment, when it is determined that the ON drive period TM is longer than the reference period TK and the total current amount IS is larger than the current capacity Itg, the first switching element SW1 is turned off. After that, the second switching element SW2 is switched to off drive so that the second switching element SW2 is turned off.

FIG. 6 shows the drive control process of this embodiment. In the present embodiment, the reference switching element and the other switching element are switched with respect to the first embodiment, so the order of steps S18 and S22 and the order of steps S24 and S28 are switched. 6, for the sake of convenience, the same step numbers are assigned to the same processes as those shown in FIG. 4, and descriptions thereof are omitted.

In the drive control process of the present embodiment, when affirmative determination is made in step S14, the second drive (S24 to S52) is performed. In the second drive, first, in step S30, the total current amount IS is acquired. The control unit 60 acquires the total current amount IS using the first sense voltage Vse1 and the second sense voltage Vse2. It should be noted that in the present embodiment, the process of step S30 corresponds to the "current amount acquisition unit".

In subsequent step S32, it is determined whether or not the total current amount IS acquired in step S30 is greater than the current capacity Itg of the first switching element SW1. If a negative determination is made in step S32, the processing of steps S24 to S28 is performed. Note that in the present embodiment, the current capacity Itg corresponds to the "threshold".

On the other hand, if an affirmative determination is made in step S32, that is, if the total current amount IS is greater than the current capacity Itg, the second switching element SW2 is turned off after the first switching element SW1 is turned off. The element SW2 is switched to OFF drive.

Specifically, in step S34, the first OFF transition period TF1 of the first switching element SW1 and the second OFF transition period TF2 of the second switching element SW2 are obtained. The off-transition period TF for each switching element is stored in advance in the storage section 60a of the control section 60, and the control section 60 acquires the first off-transition period TF1 and the second off-transition period TF2 from the storage section 60a. Note that the storage unit 60a is, for example, a non-transitional substantive recording medium other than a ROM (for example, a non-volatile memory other than a ROM).

In subsequent step S36, it is determined whether or not the first OFF transition period TF1 is longer than or equal to the second OFF transition period TF2. If a negative determination is made in step S30, that is, if the first off-transition period TF1 is shorter than the second off-transition period TF2, the first switching element SW1 and the second switching element SW2 are switched to off driving substantially simultaneously.

Specifically, in step S38, it is determined whether the drive signal IN has been switched to the OFF command. If a negative determination is made in step S38, the drive control process ends. On the other hand, if an affirmative determination is made in step S38, the first switching element SW1 is switched to OFF drive in step S40, the second switching element SW2 is switched to OFF drive in step S42, and the drive control process ends.

On the other hand, if an affirmative determination is made in step S30, that is, if the first OFF transition period TF1 is equal to or longer than the second OFF transition period TF2, the 1 switching element SW1 and the second switching element SW2 are switched to OFF drive.

Specifically, in step S44, it is determined whether the drive signal IN has been switched to the OFF command. If a negative determination is made in step S44, the drive control process is terminated. On the other hand, if an affirmative determination is made in step S44, the first switching element SW1 is switched to OFF drive in step S46.

In subsequent step S48, the difference period ΔTF is calculated. The differential period ΔTF is obtained by subtracting the second OFF-transition period TF2 from the first OFF-transition period TF1 and adding the delay period TA. In the delay period TA, the timing at which the second switching element SW2 is turned off is set earlier than the timing at which the first switching element SW1 is turned off, in order to suppress problems caused by the simultaneous turning off of the first and second switching elements SW1 and SW2. It is a period of delay. The difference period ΔTF is expressed as in (Equation 1).

ΔTF = TF1 - TF2 + TA (Formula 1)
In subsequent step S50, it is determined whether or not the differential period ΔTF has elapsed since the first switching element SW1 was switched to OFF drive.

If a negative determination is made in step S50, step S50 is repeated. On the other hand, if an affirmative determination is made in step S50, in step S52 the second switching element SW2 is switched to OFF drive, and the drive control process ends.

Next, FIGS. 7 and 8 show changes in the drive states of the first and second switching elements SW1 and SW2 in the drive control process of this embodiment. FIG. 7 shows changes in the drive states of the first and second switching elements SW1 and SW2 when the first OFF transition period TF1 is shorter than the second OFF transition period TF2. Also, FIG. 8 shows transition of the drive states of the first and second switching elements SW1 and SW2 when the first OFF transition period TF1 is longer than or equal to the second OFF transition period TF2. Here, in FIGS. 7 and 8, (a) shows transition of the first gate voltage Vg1, and (b) shows transition of the drive state of the first switching element SW1. (c) shows transition of the second gate voltage Vg2, and (d) shows transition of the driving state of the second switching element SW2. In FIGS. 7 and 8, (c) and (d) show the transition of each value (solid line) in the present embodiment and the transition (broken line) of each value in the comparative example.

As shown in FIG. 7, when the first OFF-transition period TF1 is shorter than the second OFF-transition period TF2, the first switching element SW1 is switched to OFF drive when the drive signal IN is turned off at time t21. Substantially at the same time, the second switching element SW2 is switched to OFF drive. When the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 at time t22 after the first OFF transition period TF1 has passed from time t21, the first switching element SW1 is turned off. Further, when the second gate voltage Vg2 becomes less than the second threshold voltage Vth2 at time t23 when the second OFF transition period TF2 has elapsed from time t21, the second switching element SW2 is turned off.

In the form shown in FIG. 7, the first switching element SW1 and the second switching element SW2 are switched to the off drive substantially simultaneously. Accordingly, the first switching element SW1 can be turned off earlier than the second switching element SW2 based on the difference between the first off-transition period TF1 and the second off-transition period TF2. In addition, the second switching element SW2 is switched to OFF driving substantially simultaneously with the first switching element SW1. Therefore, as indicated by the dashed line in FIG. 7, when the second switching element SW2 is switched to the OFF drive at time t24 when the first OFF transition period TF1 has passed since the first switching element SW1 was switched to the OFF drive. , the second switching element SW2 can be turned off earlier.

On the other hand, as shown in FIG. 8, when the first OFF-transition period TF1 is equal to or longer than the second OFF-transition period TF2, the first switching element SW1 is turned off when the drive signal IN is turned off at time t31. can be switched to When the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 at time t33 when the first OFF transition period TF1 has passed from time t31, the first switching element SW1 is turned off. Further, at time t32 when the difference period ΔTF has elapsed from time t31, the second switching element SW2 is switched to OFF drive. When the second gate voltage Vg2 becomes less than the second threshold voltage Vth2 at time t34 when the second OFF transition period TF2 has passed from time t32 due to the ON drive, the second switching element SW2 is turned off.

In the form shown in FIG. 8, based on the difference between the first OFF transition period TF1 and the second OFF transition period TF2, the second switching element SW2 is switched to OFF drive with a delay of the difference period ΔTF from the first switching element SW1. . As a result, the first switching element SW1 can be turned off before the second switching element SW2. Also, the delay period TA can be set shorter than the second off-transition period TF2. Therefore, as indicated by the dashed line in FIG. 8, when the second switching element SW2 is switched to the OFF drive at time t35 when the first OFF transition period TF1 has passed since the first switching element SW1 was switched to the OFF drive. , the second switching element SW2 can be turned off earlier.

According to the present embodiment described above, in the second drive, when the total current amount IS is larger than the current capacity Itg, the first switching element SW1, which is a MOSFET, is turned off, and then the second switching element, which is an IGBT, is turned off. The second switching element SW2 is switched to off drive so that SW2 is turned off. As a result, it is possible to prevent a collector current Ic larger than the current capacity Itg from flowing through the first switching element SW1, thereby preventing the first switching element SW1 from malfunctioning.

Specifically, when the total amount of current IS is greater than the current capacity Itg, the second switching element SW2 is switched to off drive based on the difference between the first off-transition period TF1 and the second off-transition period TF2. . For example, when the first off-transition period TF1 is shorter than the second off-transition period TF2, the first switching element SW1 and the second switching element SW2 are switched to the off drive substantially simultaneously. Further, when the first OFF transition period TF1 is equal to or longer than the second OFF transition period TF2, the second switching element SW2 is switched to the OFF drive with a delay of the difference period ΔTF from the first switching element SW1. Accordingly, it is possible to turn off the second switching element SW2 after properly turning off the first switching element SW1.

<Third Embodiment>
The third embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

The present embodiment differs in that the drive circuit Dr includes a third discharge resistor 74 and an N-channel MOSFET (hereinafter referred to as a third discharge switching element) 76 . A gate of the first switching element SW1 is connected to the eleventh terminal T11 of the drive IC 50 via the third discharge resistor 74 . The eleventh terminal T11 is connected to the drain of the first switching element SW1 via the third discharge switching element 76 and the fifth terminal T5 of the driving IC 50 . Also, the resistance value Rb of the third discharge resistor 74 is smaller than the resistance value Ra of the first discharge resistor 54 . In FIG. 9, the same reference numerals are assigned to the same contents as those shown in FIG. 3, and the description thereof will be omitted.

This embodiment differs in that the charge discharge speed of the gate of the first switching element SW1 is switched in the drive control process. The charge discharge speed is switched by the discharge resistor used for discharging the charge, and by using the third discharge resistor 74 with a small resistance value, it is possible to reduce In comparison, the charge discharge rate can be increased.

FIG. 10 shows the drive control process of this embodiment. In FIG. 10, the same steps as those shown in FIG. 4 are given the same step numbers for convenience, and descriptions thereof will be omitted.

In the drive control process of this embodiment, if a negative determination is made in step S14, in step S60, the first discharge resistor 54 is selected as the discharge resistor of the first switching element SW1, and the process proceeds to step S16. That is, in the first drive (S18 to S22), the first discharge resistor 54 having a large resistance value is used to discharge the electric charge of the gate of the first switching element SW1.

On the other hand, if an affirmative determination is made in step S14, the third discharge resistor 74 is selected as the discharge resistor of the first switching element SW1 in step S62, and the process proceeds to step S66. It should be noted that the processing of steps S66 to S74 is the same as that of steps S16 to S22, and redundant description will be omitted. As a result, in the second drive (S68 to S72), the third discharge resistor 74 having a small resistance value is used to discharge the electric charge of the gate of the first switching element SW1. As a result, in the second drive, the charge discharging speed of the gate of the first switching element SW1 can be made higher than in the first drive, and the first off transition period TF1 can be shortened.

Next, FIGS. 11 and 12 show changes in the drive states of the first and second switching elements SW1 and SW2 in the drive control process of this embodiment. FIG. 11 shows changes in the driving states of the first and second switching elements SW1 and SW2 when the second switching element SW2 is switched to OFF driving before the elapsed period TP reaches the reference period TK. Also, FIG. 12 shows the transition of the drive states of the first and second switching elements SW1 and SW2 when the second switching element SW2 is not switched to the off drive before the elapsed period TP reaches the reference period TK. Here, in FIGS. 11 and 12, (a) shows transition of the second gate voltage Vg2, and (b) shows transition of the driving state of the second switching element SW2. (c) shows transition of the first gate voltage Vg1, and (d) shows transition of the driving state of the first switching element SW1. FIGS. 12C and 12D show the transition of each value (solid line) in the present embodiment and the transition of each value (broken line) in the comparative example.

As shown in FIG. 11, when the time t41 at which the drive signal IN is turned off is before the time tk at which the elapsed period TP reaches the reference period TK, the first drive is performed. In the first drive, the second switching element SW2 is switched to OFF drive at time t41. When the second gate voltage Vg2 becomes less than the second threshold voltage Vth2 at time t42 after the second OFF transition period TF2 has elapsed from time t41, the second switching element SW2 is turned off by the off drive. At time t42, when the second gate voltage Vg2 is turned off, the first switching element SW1 is switched to off drive. When the first gate voltage Vg1 becomes less than the first threshold voltage Vth1 at time t44 when the 1a-th OFF transition period TF1a corresponding to the first discharge resistor 54 has elapsed from time t42 by the off drive, the first gate voltage Vg1 becomes less than the first threshold voltage Vth1. The switching element SW1 is turned off.

On the other hand, as shown in FIG. 12, when the time t41 at which the drive signal IN is turned off is after the time tk at which the elapsed period TP reaches the reference period TK, the second drive is performed. In the second drive, the first gate voltage Vg1 is set at time t43 when the 1b-th OFF transition period TF1b corresponding to the third discharge resistor 74 has elapsed from time t42 by the off-driving of the first switching element SW1. When the voltage becomes less than the first threshold voltage Vth1, the first switching element SW1 is turned off. As a result, as shown by the dashed line in FIG. 12, the first switching element SW1 is turned off earlier than when the first switching element SW1 is turned off at time t44 when the 1a-th OFF transition period TF1a has elapsed from time t42. can be turned off at

According to the present embodiment described above, in the off-drive of the first switching element SW1, the first discharge resistor 54 is used to discharge the gate charge of the first switching element SW1 in the first drive. Also, in the second drive, the third discharge resistor 74 is used to discharge the electric charge of the gate of the first switching element SW1. That is, in the second drive, the charge discharging speed of the gate of the first switching element SW1 is made higher than in the first drive. Therefore, when it is determined that the on-driving period TM is longer than the reference period TK, the first switching element SW1 can be quickly switched to off-driving. As a result, the first switching element SW1 can be turned off before the second switching element SW2 is turned on next time.

<Fourth Embodiment>
The fourth embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

This embodiment differs in that the on-drive period TM is limited to be shorter than the upper limit period TL in the second drive of the drive control process. The upper limit period TL is obtained by subtracting the first OFF transition period TF1 and the second OFF transition period TF2 from the switching period TW. The upper limit period TL is represented by (Equation 2).

TL=TW-(TF1+TE2) (Formula 2)
FIG. 13 shows the drive control process of this embodiment. In addition, in FIG. 13, for convenience, the same step numbers are assigned to the same processes as those shown in FIG. 4, and descriptions thereof are omitted.

In the drive control process of the present embodiment, when affirmative determination is made in step S14, the second drive (S24 to S92) is performed. Specifically, in step S80, the first OFF transition period TF1 of the first switching element SW1 and the second OFF transition period TF2 of the second switching element SW2 are acquired.

In step S82, the upper limit period TL is obtained by calculation using the first off-transition period TF1 and the second off-transition period TF2 obtained in step S80. In subsequent step S84, it is determined whether or not the elapsed period TP is longer than the upper limit period TL obtained in step S82. If a negative determination is made in step S14, the process proceeds to step S86. It should be noted that the processing of steps S86 to S92 is the same as that of steps S16 to S22, and redundant description will be omitted. On the other hand, if an affirmative determination is made in step S84, the process proceeds to step S24.

Next, FIG. 14 shows changes in drive states of the first and second switching elements SW1 and SW2 in the drive control process of this embodiment. Here, FIG. 14(a) shows transition of the second gate voltage Vg2, and FIG. 14(b) shows transition of the driving state of the second switching element SW2. FIG. 14(c) shows transition of the first gate voltage Vg1, and FIG. 14(d) shows transition of the driving state of the first switching element SW1. FIG. 14 shows the transition (solid line) of each value in the present embodiment and the transition (broken line) of each value in the comparative example.

In FIG. 14, in the second drive, the time t52 at which the drive signal IN is instructed to be turned off is later than the time tk when the elapsed period TP reaches the reference period TK and the time tl when the elapsed period TP reaches the upper limit period TL. showing morphology. In this case, as indicated by the dashed line in FIG. 14, the second switching element SW2 is turned off at time t52, and the first switching element SW1 is turned off at time t54 when the second gate voltage Vg2 turns off. After switching, the first switching element SW1 is switched to OFF drive at time t55. As a result, the timing at which the first switching element SW1 is switched to off drive is delayed.

In the present embodiment, in the second drive, if the time t52 at which the drive signal IN is turned off is later than the time tl, the second switching element SW2 is switched to the off drive at the time tl. Specifically, at time tl, the second switching element SW2 is switched to off-drive, and at time t51 when the second gate voltage Vg2 is turned off, when the first switching element SW1 is switched to off-drive, at time t53, The first switching element SW1 is switched to OFF drive.

According to the present embodiment described above, in the second drive, the second switching element SW2 is switched to off drive so that the on drive period TM is shorter than the upper limit period TL. Therefore, even when the on-driving period TM is longer than the upper limit period TL, the first switching element SW1 can be turned off before the second switching element SW2 is next turned on. As a result, the first switching element SW1 can be turned off before the second switching element SW2 is turned on next time.

Specifically, the upper limit period TL is obtained by subtracting the first OFF transition period TF1 and the second OFF transition period TF2 from the switching period TW. Therefore, even if the first switching element SW1 is switched to the OFF drive at the timing when the second OFF transition period TF2 has passed after the second switching element SW2 is switched to the OFF drive, the second switching element SW2 is switched to the OFF drive within the switching period TW. SW2 can be turned off.

<Other embodiments>
It should be noted that each of the above-described embodiments may be modified as follows.

- Switching between the first drive and the second drive is not limited to being based on the elapsed period TP. For example, when the control device 40 can determine whether the on-drive period TM is longer than the reference period TK, the drive circuit Dr receives a signal indicating the determination result from the control device 40, The signal may be used to switch between the first drive and the second drive.

・The combination of switches is not limited to the combination of MOSFET and IGBT.

- The number of switches connected in parallel is not limited to two, and may be three or more. For example, two MOSFETs and one IGBT may be connected in parallel. In this case, two MOSFETs may be selected as the reference switching element, or one IGBT may be selected as the reference switching element.

When the reference switching element is selected in advance and the first OFF-transition period TF1 and the second OFF-transition period TF2 are predetermined, the first OFF-transition period TF1 and the second OFF-transition period TF2 The size relationship is also determined in advance. Therefore, it is not necessary to compare the first OFF transition period TF1 and the second OFF transition period TF2 in the drive control process. Moreover, the upper limit period TL is also predetermined. Therefore, it is not necessary to calculate the upper limit period TL in the drive control process.

- The inverter is not limited to a three-phase inverter, and may be, for example, a two-phase inverter or a four-phase or more inverter. Moreover, the power converter provided with the switch is not limited to the inverter.

Dr... drive circuit, SW1... first switching element, SW2... second switching element, TM... ON drive period, TK... reference period.

Claims (6)

In a switching element driving circuit (Dr) that drives a plurality of switching elements (SW1, SW2) connected in parallel with each other in a predetermined switching cycle (TW),
When at least one switching element among the plurality of switching elements is used as a reference switching element and the remaining switching elements are used as other switching elements, the reference switching element is switched to ON drive and then to OFF drive. a determination unit that determines whether an on-drive period (TM) until switching is longer than a reference period (TK);
When the determination unit determines that the on-driving period is longer than the reference period, the reference switching element is turned off until the reference switching element is turned on next time. A switching unit that switches the other switching element to off drive,
The switching unit is configured to switch the reference switching element to an off-drive state until the reference switching element is turned off when the determination unit determines that the on-drive period is equal to or shorter than the reference period. At the timing when the period (TF) has passed, switching the other switching element to off drive,
When the determination unit determines that the on-drive period is longer than the reference period, the other switching element is off-driven before the off-transition period elapses after switching the reference switching element to off-drive. The drive circuit for the switching element that switches to When the determination unit determines that the on-drive period is longer than the reference period, the switching section is configured to provide a difference between the off-transition period of the reference switching element and the off-transition period of the other switching element. 2. The driving circuit of a switching element according to claim 1, wherein the other switching element is switched to off driving such that the other switching element is turned off after the reference switching element is turned off. the reference switching element has a smaller current capacity than the other switching element;
A current amount acquisition unit that acquires the amount of current (IS) flowing through the plurality of switching elements,
When the determination unit determines that the on-driving period is longer than the reference period and the amount of current is greater than a threshold value (Itg), the switching unit performs the switching operation after the reference switching element is turned off. 3. The driving circuit of the switching element according to claim 2, wherein the other switching element is turned off so that the other switching element is turned off. When the determining unit determines that the on-drive period is longer than the reference period, the switching unit is configured to set the switching unit to the other period than when the determining unit determines that the on-drive period is equal to or shorter than the reference period. 4. A driving circuit for a switching element according to any one of claims 1 to 3, wherein the charge discharge speed of the switching control terminal of the switching element is increased. In a switching element driving circuit (Dr) that drives a plurality of switching elements (SW1, SW2) connected in parallel with each other in a predetermined switching cycle (TW),
When at least one switching element among the plurality of switching elements is used as a reference switching element and the remaining switching elements are used as other switching elements, the reference switching element is switched to ON drive and then to OFF drive. a determination unit that determines whether an on-drive period (TM) until switching is longer than a reference period (TK);
When the determination unit determines that the on-driving period is longer than the reference period, the reference switching element is turned off until the reference switching element is turned on next time. A switching unit that switches the other switching element to off drive,
The switching unit adjusts the reference switching period so that the on-drive period becomes shorter than a predetermined upper limit period (TL) when the determination unit determines that the on-drive period is longer than the reference period. A drive circuit for a switching element that switches the element to off-drive. The switching unit switches the other switching element to off drive at a timing when an off transition period (TF) required from switching the reference switching element to off drive to turning off of the reference switching element elapses. ,
6. The switching element drive circuit according to claim 5 , wherein the upper limit period is a period obtained by subtracting the off-transition period of the reference switching element and the off-transition period of the other switching element from the switching period.

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