JP2016086511A - Switching element drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching element drive device which can appropriately execute switching element cutoff processing when an abnormality such as short-circuit or overcurrent occurs in the switching element.SOLUTION: A switching element drive device includes: a gate voltage monitoring circuit 22 which detects the drive voltage of an IGBT 11; a current monitoring circuit 24 which detects the current flowing through the IGBT 11;an abnormality detection circuit 25 which determines whether or not short-circuit or overcurrent abnormality occurs in the IGBT 11 on the basis of the current detection result; and an overcurrent protection circuit 26 which forcibly makes the IGBT 11 into a cutoff state on determination that an abnormality occurs in the IGBT 11. The switching element drive device sets a cutoff speed when the IGBT 11 is set to be the cutoff state, on the basis of a drive voltage detection value when the abnormality detection circuit 25 determines the occurrence of abnormality in the IGBT 11.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a switching element driving apparatus for driving a semiconductor switching element such as an IGBT.

  When an abnormality such as a short circuit or an overcurrent occurs in a semiconductor switching element such as an IGBT, an excessive current flows through the switching element, which may cause problems such as overheating or damage to the switching element. Therefore, when the current of the switching element exceeds a predetermined threshold value, the switching element is switched to the OFF state, so that the switching element is protected from an excessive current. However, when the switching element is cut off, a surge voltage is generated. Since the surge voltage becomes larger as the switching element cut-off speed becomes faster, there is a concern that the surge voltage may exceed the withstand voltage due to the surge voltage.

  Therefore, conventionally, the blocking speed of the switching element is limited. Specifically, the cutoff speed is reduced as the applied voltage (collector-emitter voltage) between the input and output terminals of the switching element increases. This suppresses an increase in surge voltage caused by shutting off the switching element when the applied voltage between the input and output terminals is large (see Patent Document 1).

JP, 2014-140280, A

  By the way, when the switching element is turned on, the gate voltage rises to a predetermined full on voltage value. At this time, there are cases where an abnormality occurs when the gate voltage is relatively small, and cases where an abnormality occurs when the gate voltage is relatively large. Of these, an abnormality occurs when the gate voltage is relatively large. In such a case, if the interruption speed of the switching element is limited as described above, there may be a disadvantage associated with a further increase in current before the switching element is turned off. However, in the prior art, this point is not taken into consideration, and it can be said that there is room for improvement in order to more appropriately perform the switching element blocking process.

  The present invention has been made in view of the above, and it is a main object of the present invention to provide a switching element drive device that can more appropriately perform switching element shut-off processing when an abnormality such as a short circuit or overcurrent occurs in the switching element. It is what.

  The present invention is based on the voltage detection means (22) for detecting the drive voltage of the switching element (11), the current detection means (24) for detecting the current flowing through the switching element, and the detection result of the current. An abnormality determination means (25) for determining whether a short circuit or an overcurrent abnormality has occurred in the switching element, and forcibly shutting off the switching element when it is determined that an abnormality has occurred in the switching element A shut-off means (26) for setting a state, and a shut-off when the switching element is put into a shut-off state based on a detected value of the drive voltage when it is determined by the abnormality determining means that an abnormality has occurred in the switching element And a shut-off speed setting means (26) for setting the speed.

  According to the present invention, the cutoff speed of the switching element is set according to the drive voltage when it is determined that a short circuit or overcurrent abnormality has occurred in the switching element. In this case, a more appropriate blocking process can be performed according to the state at the time of occurrence of the abnormality of the switching element.

The schematic block diagram of an inverter apparatus. Explanatory drawing of the drive device of a switching element. Explanatory drawing of the drive device of a switching element. The figure which shows the execution example of the operation | movement of the drive device of a switching element. The figure which shows the execution example of the operation | movement of the drive device of a switching element. The figure which shows the execution example of the operation | movement of the drive device of a switching element. Explanatory drawing of the abnormality determination process of a modification example. The flowchart of the abnormality determination process of the example of a change by a control apparatus.

  Embodiments of a switching element driving apparatus according to the present invention will be described below with reference to the drawings. In the following description, the switching element driving device is applied to a vehicle including a rotating machine as an in-vehicle main machine.

  As shown in FIGS. 1 and 2, a motor generator 10 as an in-vehicle main machine is connected to drive wheels of a vehicle (not shown). The inverter IV connected to the motor generator 10 includes a plurality of IGBTs 11 serving as switching elements, and a gate driving device 12 that drives each IGBT 11, and is driven by power of a supply voltage VS from a power supply unit (not shown). The Each IGBT 11 is configured as an individual module including a reflux diode 13 and a current sensing circuit. The inverter IV in FIG. 1 is composed of three IGBTs 11 on the upper arm and three IGBTs 11 on the lower arm connected by a three-phase bridge.

  As shown in FIG. 2, the gate driving device 12 includes a gate driving IC 20 that is a one-chip semiconductor integrated circuit, a photocoupler 15, and the like. The gate driving IC 20 is connected to the control device 14 via the photocoupler 15. It is connected. The control device 14 outputs a PWM control signal (hereinafter referred to as a control signal D) for switching the IGBT 11 between an on state (drive state) and an off state (cut-off state). The gate drive IC 20 includes the control device 14. The state of the IGBT 11 is switched based on the control signal D received from.

  In addition to switching on and off the IGBT 11, the gate drive IC 20 of the present embodiment forcibly switches the IGBT 11 to an off state regardless of the control signal D when a short circuit or overcurrent abnormality occurs in the IGBT 11. .

  The gate drive IC 20 includes a gate drive circuit 21, a gate voltage monitoring circuit 22, a gate clamp circuit 23, a current monitoring circuit 24, an abnormality detection circuit 25, and an overcurrent protection circuit 26.

  The gate drive circuit 21 switches the IGBT 11 on and off according to the level of the control signal D. The gate drive circuit 21 of the present embodiment turns on the IGBT 11 when the control signal D is at L level. That is, by supplying a constant gate current Ig to the gate G which is an open / close control terminal, the gate voltage VG is raised, thereby turning on the IGBT 11. In the following description, turning on the IGBT 11 in the saturation region of the gate voltage VG is referred to as a full-on state. On the other hand, when the control signal D is at the H level, the IGBT 11 is turned off. In this case, the supply of the gate current Ig is stopped.

  The gate voltage monitoring circuit 22 detects the gate voltage VG applied to the gate G of the IGBT 11. The gate clamp circuit 23 performs clamp processing for temporarily limiting (clamping) the gate voltage VG to a predetermined clamp voltage Vc (limit voltage) or less when the gate voltage VG rises when the IGBT 11 is in an on state. For example, an N-channel MOS transistor is provided.

  Here, the clamp process will be described. This process is a process of clamping the gate voltage VG to a clamp voltage that is lower than the full-on voltage while raising the gate voltage VG of the IGBT 11 to the full-on voltage (voltage in the full-on state). is there. According to this process, the collector current Ic flowing through the IGBT 11 can be limited until the IGBT 11 is switched to the OFF state.

  The current monitoring circuit 24 detects the collector current Ic that flows through the collector C that is the output terminal of the IGBT 11. The current monitoring circuit 24 of this embodiment acquires the collector current Ic based on the voltage (sense voltage) applied to the sense resistor Rs connected to the sense terminal St of the IGBT 11. The current monitoring circuit 24 may acquire the amount of change in the collector current Ic based on the amount of change in the sense voltage.

  The abnormality detection circuit 25 determines the presence / absence of an abnormality due to a short circuit or overcurrent in the IGBT 11 based on the collector current Ic acquired by the current monitoring circuit 24. That is, the IGBT 11 is determined to be in an abnormal state when the collector current Ic is larger than the predetermined threshold value Ith. When the collector current Ic is less than the threshold value Ith, the IGBT 11 is determined to be in a normal state. The threshold value Ith may be set based on the maximum value of the collector current Ic when the IGBT 11 is normal.

  The overcurrent protection circuit 26 is forcibly switching the IGBT 11 to the OFF state when the abnormality detection circuit 25 determines that the IGBT 11 is in an abnormal state. In the present embodiment, the overcurrent protection circuit 26 According to the magnitude | size, the interruption | blocking speed at the time of interrupting IGBT11 shall be set. Here, the cutoff speed is switched according to whether or not the gate voltage VG is equal to or higher than a predetermined second threshold value Vth. Note that the second threshold Vth may be set to a predetermined value between the clamp voltage of the IGBT 11 and the full-on voltage.

  Here, switching of the breaking speed by the overcurrent protection circuit 26 will be described in detail. FIG. 3 is a diagram illustrating the interruption circuit 30 provided in the overcurrent protection circuit 26. In FIG. 3, the cutoff circuit 30 includes a first cutoff path 31 that sets the cutoff speed of the IGBT 11 as a first cutoff speed, and a second cutoff path 32 that sets the cutoff speed of the IGBT 11 to a second cutoff speed that is higher than the first cutoff speed. And have. The first blocking path 31 includes a series connection body of a blocking resistor 31a and a switching element 31b. The second blocking path 32 includes a series connection body of a blocking resistor 32a and a switching element 32b.

  The resistor 31a and the resistor 32a connected to the gate G of the IGBT 11 are for making the resistance value of the interruption path of the gate G higher, and here, the resistance of the resistor 32a is higher than that of the resistor 31a. The value is smaller.

  With the above configuration, the overcurrent protection circuit 26 turns on the switching element 32b of the second cutoff path 32 when the gate voltage VG when the abnormality is detected by the abnormality detection circuit 25 is equal to or higher than the second threshold value Vth. To. In this case, the charge of the gate G is discharged relatively quickly via the resistor 32a. On the other hand, when the gate voltage VG is less than the second threshold value Vth, the switching element 31b of the first cutoff path 31 is turned on. In this case, the charge of the gate G is discharged relatively slowly through the resistor 31a.

  As described above, when the gate voltage VG is high, that is, when the IGBT 11 is quickly cut off when the gate voltage VG is equal to or higher than the second threshold value Vth, the overcurrent further increases until the IGBT 11 is cut off because the gate voltage VG is high. Can be preferentially suppressed. On the other hand, when the gate voltage VG is small, that is, when the IGBT 11 is gently shut off when the gate voltage VG is less than the second threshold value Vth, an increase in the gate voltage VG caused by the IGBT 11 being shut off can be preferentially suppressed.

  Next, an execution example of the above processing will be described with reference to FIGS. FIG. 4 shows an example when the IGBT 11 is normal. FIG. 5 shows an example in which a short circuit occurs before the IGBT 11 is clamped. FIG. 6 shows an example in which a short circuit occurs after the clamping operation of the IGBT 11.

  In the case of FIG. 4, when the control signal D becomes L level at time t1, the gate voltage VG and the collector current Ic of the IGBT 11 increase due to the energization of the gate current Ig. When the gate voltage VG reaches the clamp voltage Vc at time t2, the gate voltage VG is held at the clamp voltage Vc. Then, after the state where the gate voltage VG is held at the clamp voltage Vc is continued until time t3, the gate voltage VG is increased again. When the gate voltage VG reaches a predetermined drive voltage at time t4, the IGBT 11 is in a full-on state.

  In the case of FIG. 5, when the control signal D becomes L level at time t11, the gate voltage VG of the IGBT 11 increases with the increase of the gate current Ig as in FIG. At this time, since the short circuit abnormality has occurred in the IGBT 11, the collector current Ic rapidly increases. When the collector current Ic reaches the threshold value Ith at time t12, the gate voltage VG at this time is less than the second threshold value Vth, so that the first cutoff process is performed. In this case, the gate voltage VG is decreased at the first cutoff speed, and the IGBT 11 is turned off at time t14 after the time ΔT1 has elapsed from time t13.

  In the case of FIG. 6, when the control signal D becomes L level at time t21, the gate voltage VG and the collector current Ic of the IGBT 11 increase with the increase of the gate current Ig as in FIG. Then, after the gate voltage VG is clamped at time t22, the rise of the gate voltage VG starts again at time t23, and when a short circuit abnormality occurs at time t24, the collector current Ic increases rapidly. When the collector current Ic reaches the threshold value Ith at time t25, the gate voltage VG at this time is equal to or higher than the second threshold value Vth, whereby the second cutoff process is performed. In this case, the gate voltage VG is decreased at the second cutoff speed. The IGBT 11 is turned off at time t26 of a predetermined time ΔT2 (<ΔT1) from time t25.

  According to the above, the following excellent effects can be achieved.

  When an abnormality such as a short circuit or an overcurrent occurs in a switching element such as an IGBT, the switching element is switched off to protect the switching element from an excessive current, but at this time, a surge voltage is generated. The surge voltage increases as the speed when switching the switching element to the OFF state increases. Therefore, conventionally, when an abnormality occurs in the switching element, a process for limiting the cutoff speed for switching the switching element to the OFF state is performed, so that the influence due to the increase of the surge voltage can be suppressed. However, if a process for limiting the cut-off speed is performed when an abnormality occurs when the driving voltage of the switching element is high, the current may increase further until the switching element is turned off. Therefore, the switching element cutoff speed is set in accordance with the drive voltage when it is determined that a short circuit or overcurrent abnormality has occurred in the switching element (IGBT 11). In this case, a more appropriate blocking process can be performed according to the state at the time of occurrence of the abnormality of the switching element.

  ・ The larger the detected value of the drive voltage when it is determined that the IGBT 11 is short-circuited or overcurrent is abnormal, the higher the cutoff speed is set, the overcurrent when an abnormality occurs at a high drive voltage. Can be suppressed.

  The present invention is not limited to the description of the above embodiment, and may be implemented as follows. In the following description, the same components as those described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  A plurality of second threshold values Vth may be set between the clamp voltage Vc and the full-on voltage of the IGBT 11. In this case, the accuracy of setting the cutoff speed of the IGBT 11 can be increased according to the gate voltage VG when the short circuit abnormality occurs.

  The clamp voltage Vc may be set to the second threshold value Vth. In this case, when the gate voltage VG at the time of occurrence of abnormality is lower than the clamp voltage, the overcurrent protection circuit 26 sets the cutoff speed of the IGBT 11 to the first cutoff speed, and the gate voltage VG at the time of occurrence of abnormality is the clamp voltage. If it is higher, the cutoff speed of the IGBT 11 is set to the second cutoff speed.

  In the above description, the present embodiment can be applied to a configuration in which the gate driving device 12 does not include the gate clamp circuit 23. In this case, at least one second threshold value Vth may be set in a voltage range (VG = 0 to full-on voltage) that can be taken by the gate voltage VG. For example, the second threshold value Vth can be set to the middle value of the voltage range that the gate voltage VG can take.

  As shown in the example of FIG. 7, the overcurrent protection circuit 26 is configured so that the gate when the short circuit abnormality occurs is based on the map showing the relationship between the gate voltage VG when the short circuit abnormality occurs and the cutoff speed of the IGBT 11. The cutoff speed may be set linearly according to the voltage VG. In this case, the overcurrent protection circuit 26 having a configuration that can arbitrarily set the cutoff speed according to the gate voltage VG at the time of abnormality determination is used.

  In the above, the abnormality detection circuit 25 determines the presence or absence of abnormality by comparing the collector current Ic and the threshold value Ith. In addition, the abnormality detection circuit 25 may determine an abnormal state based on the change amount ΔIc (increase amount) of the collector current Ic. For example, in this case, a normal state is determined when the change amount ΔIc of the collector current Ic is less than a predetermined value, and an abnormal state is determined when the change amount ΔIC of the collector current Ic is equal to or greater than a predetermined value.

  The abnormality detection circuit 25 may perform abnormality determination based on the sense voltage detected by the sense resistor Rs. In this case, the presence / absence of abnormality may be determined based on whether the sense voltage is equal to or higher than a predetermined value.

  -You may implement the interruption | blocking process of IGBT11 based on the command signal from the control apparatus 14. FIG. For example, the control device 14 takes in a signal from the gate drive IC 20 and performs the processing shown in the example of FIG. 8 below. First, it is determined whether or not the control signal D is at L level (S11). If a negative determination is made in S11, the process ends. When an affirmative determination is made in S11, it is determined whether or not the collector current Ic is greater than or equal to a threshold value Ith (S12). If it is determined in S12 that the collector current Ic is less than the threshold value Ith, the process ends. When it is determined that the collector current Ic is greater than or equal to the threshold value Ith, it is determined whether or not the gate voltage VG at that time is less than the second threshold value Vth (S13). When an affirmative determination is made in S13, a command signal for setting the cutoff speed of the IGBT 11 to the first cutoff speed is output (S14). If a negative determination is made, a command signal for setting the cutoff speed of the IGBT 11 to the second cutoff speed is output (S15).

  22 ... Gate voltage monitoring circuit, 24 ... Current monitoring circuit, 25 ... Abnormality detection circuit, 26 ... Overcurrent protection circuit.

Claims (6)

Voltage detection means (22) for detecting the drive voltage of the switching element (11);
Current detection means (24) for detecting a current flowing through the switching element;
An abnormality determining means (25) for determining whether a short circuit or an overcurrent abnormality has occurred in the switching element based on the detection result of the current;
Shut-off means (26) for forcibly turning off the switching element when it is determined that an abnormality has occurred in the switching element;
An interruption speed setting means (26) for setting an interruption speed when the switching element is in an interruption state based on a detected value of the drive voltage when it is determined by the abnormality determination means that an abnormality has occurred in the switching element. )When,
A drive device for a switching element, comprising:   2. The switching element according to claim 1, wherein the cutoff speed setting unit sets the cutoff speed of the drive voltage to be larger as a detected value of the drive voltage when it is determined that an abnormality has occurred in the switching element. Drive device.   The shut-off speed setting means sets the shut-off speed of the switching element to a first shut-off speed when the detected value of the drive voltage when it is determined that an abnormality has occurred in the switching element is less than a predetermined threshold value. 3. The switching element drive device according to claim 1, wherein when the detected value of the voltage is equal to or greater than the threshold value, the switching element is set to a second cutoff speed larger than the first cutoff speed. . Clamping means (23) for clamping the drive voltage to a clamp voltage lower than the full-on voltage in the middle of raising the drive voltage of the switching element to the full-on voltage,
The switching element driving device according to claim 3, wherein the threshold is set between the clamp voltage and the full-on voltage. Clamping means (23) for clamping the drive voltage to a clamp voltage lower than the full-on voltage in the middle of raising the drive voltage of the switching element to the full-on voltage,
The shutoff speed setting means sets the shutoff speed of the switching element to a first shutoff speed when an abnormality occurs in the switching element and before the drive voltage is clamped by the clamp means, and the switching element malfunctions. 3. The switching element drive device according to claim 1, wherein when the generation occurs after the clamp of the driving voltage, the switching element is set to a second cutoff speed larger than the first cutoff speed.   The abnormality determination unit determines that an abnormality has occurred in the switching element when a detected value of the current exceeds a predetermined determination value or when a change speed of the detected value of the current is higher than a predetermined value. The switching element drive device according to any one of 1 to 5.

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