JP2013169030A - Switching element control circuit and switching element control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching element control circuit which can detect a reflux current with a simple configuration without imparting hysteresis characteristics.SOLUTION: A resistive element 9 and a comparator 10 detect a reflux current in a freewheel diode 4 connected in antiparallel with an IGBT 1. When the reflux current is detected in the freewheel diode 4 while the IGBT 1 is on, a latch 12 forcibly puts the IGBT 1 in the OFF state from the time of detection at least until a timer 13 counts to a prescribed time.

Description

  The present invention relates to a switching element control circuit and a control method applied to a power conversion circuit having an arm composed of a semiconductor device in which a switching element and a freewheel diode connected in antiparallel are mounted on the same semiconductor substrate. .

  A free wheel diode is connected in parallel between the collector and emitter of an IGBT (Insulated Gate Bipolar Transistor) used as a power semiconductor switching element constituting the inverter circuit. Then, a diode built-in IGBT module in which an IGBT and a free wheel diode are mounted on the same substrate, or an inverter module formed by bridging them is put into practical use.

  In the diode built-in IGBT, it is known that the amount of voltage drop when a forward current flows through a freewheel diode increases when a voltage is applied to the gate of the IGBT. For this reason, when IGBT switching control is performed on the inverter circuit, a power loss generated when a forward current flows through the freewheeling diode increases, which may increase the amount of heat generated by the IGBT module.

  In order to deal with such a problem, for example, Patent Document 1 discloses that a forward current flowing in a freewheeling diode is detected by being shunted, and if it is determined that the forward current has flowed, the IGBT is forcibly turned off. A technique for suppressing an increase in power loss is disclosed. Specifically, the forward current flowing through the external resistor 9 is detected by the comparator 7a in comparison with the reference voltage Vs. Further, FIGS. 3 to 5 of the cited document 1 disclose a configuration in which a hysteresis characteristic is given to the comparator 7a. Thus, the reason for providing the hysteresis characteristic is to prevent chattering from occurring in the control response.

  Moreover, although there is no clear description in Patent Document 1, as another reason for imparting hysteresis characteristics, as shown in FIG. 4 of Patent Document 2, depending on the level of the voltage Vge applied to the gate of the IGBT, There is a point that the amount of voltage drop generated in the current detecting shunt resistor changes. When the forward current is detected (reflux mode) and the IGBT is turned off, the voltage drop amount decreases and falls below the determination value, so that the IGBT is turned on again. Then, the sequence of determining again the reflux mode and turning off the IGBT is repeated. In order to prevent such chattering from occurring, it is necessary to consider the amount of voltage drop in the shunt resistor according to the on / off state of the IGBT as the hysteresis width. When the determination value is increased by providing the hysteresis characteristic, the generation of loss increases accordingly.

  Moreover, in order to reduce the influence accompanying the provision of hysteresis characteristics, it is conceivable to change the shunt ratio of the current detection element associated with the IGBT or to increase the resistance value of the shunt resistor. However, since overcurrent detection is also performed for the IGBT with the same configuration, if the above adjustment is performed, the influence on overcurrent detection is exerted. Therefore, in Patent Document 3, a configuration is adopted in which the detection path is separated between the current flowing through the IGBT and the case where the return current flows through the freewheel diode.

JP 2008-72848 A JP 2010-246175 A JP 2010-183765 A

However, even in the configuration of Patent Document 3, there is a problem that the determination of the current flowing to the IGBT side varies and the number of detection terminals increases due to variations in temperature characteristics of the diode inserted to divide the current path.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a switching element control circuit and a switching element control method capable of detecting a return current with a simple configuration without providing hysteresis characteristics. It is to provide.

According to the switching element control circuit of the first aspect, the return current detecting means detects that the return current flows through the free wheel diode connected in antiparallel to the switching element. Then, when it is detected that the return current flows through the free wheel diode connected to the element during the period when the switching element is turned on, the forced-off setting means sets the switching element to a predetermined value from the time of the detection. Turn off for more than an hour.
With this configuration, in order to prevent chattering in which the switching element is repeatedly turned on and off, there is no need to add hysteresis characteristics to the determination value for detecting the return current as in Patent Document 1, and thus the determination value is set low. This makes it possible to suppress the occurrence of loss. Further, since there is no need to divide the current path as in Patent Document 3, the determination accuracy does not decrease and the number of detection terminals does not increase.

  According to the switching element control circuit according to claim 2, the semiconductor device includes a current output terminal that outputs a smaller current having a correlation with a current flowing through the switching element and a free wheel diode connected to the element, The return current detection means performs detection based on a change in voltage according to the current flowing through the current output terminal. Therefore, the return current detecting means can be constituted by an element having a smaller current capacity.

  According to the control circuit for the switching element of the third aspect, the return current detection means performs the detection based on the voltage between the conduction terminals of the switching element. That is, when a return current flows through the freewheeling diode, the voltage between the conduction terminals is reduced by a forward voltage with respect to the anode side of the diode, so that the return current can be detected by detecting the voltage drop.

  According to the control circuit of the switching element of the fourth aspect, the return current detecting means compares the change in the voltage with a reference voltage by the comparator. Therefore, the return current can be detected using the reference voltage as a single determination value.

  According to the control circuit for a switching element according to claim 5, the period of the current flowing through the switching element is detected by the current period detecting means, and the forced-off setting means is set for a predetermined time according to the length of the period of the current. Change to lengthen. That is, if the period of the current is short, the interval at which the polarity of the current is reversed is shortened. Accordingly, by shortening the predetermined time accordingly, the minimum period for turning off the switching element is appropriately set to set the reflux current. It can be reliably detected.

  According to the switching element control circuit of the sixth aspect, the amplitude of the current flowing through the switching element is detected by the current amplitude detecting means, and the forced-off setting means has a predetermined time corresponding to the magnitude of the amplitude of the current. Change to shorten. That is, as the amplitude of the current increases, the current change per time increases, so by shortening the predetermined time accordingly, the minimum period during which the switching element is turned off can be set appropriately to ensure the return current. Can be detected.

The figure which is a 1st Example and shows the structure of a drive control circuit Timing chart showing each signal waveform FIG. 1 equivalent view showing the second embodiment FIG. 1 equivalent view showing the third embodiment FIG. 1 equivalent view showing the fourth embodiment

(First embodiment)
The first embodiment will be described below with reference to FIGS. FIG. 1 shows a configuration of a drive control circuit provided in association with a drive circuit that drives one of IGBTs (switching elements) constituting a power conversion circuit such as an inverter circuit. The IGBT 1 constitutes, for example, a lower arm of an inverter circuit that outputs AC power to a motor. When an IGBT drive signal (IN) is given by a control device (not shown), the IGBT 1 is driven via the drive circuit 2 and the pre-driver 3. The

  A free wheel diode 4 is connected in the reverse direction between the collector and emitter of the IGBT 1. The IGBT 1 is also provided with a sense IGBT 5 for current detection (only the emitter thereof is shown in FIG. 1). The sense IGBT 5 allows a current flowing through the IGBT 1 to flow from the emitter (current output terminal) with a small current ratio. Output. The IGBT 1, the free wheel diode 4 and the sense IGBT 5 are mounted on the same substrate, and constitute an IGBT module 6 (semiconductor device). The collector of the IGBT 1 is connected to the emitter of the upper arm IGBT (not shown) and one end of the motor winding.

  The pre-driver 3 is illustrated as a series circuit of two switches 7 and 8 connected between the gate driving power source and the emitter of the IGBT 1 (hereinafter referred to as a reference potential point). Is composed of a MOSFET or the like. Then, the drive circuit 2 exclusively turns on one of the switches 7 and 8 in accordance with the input IGBT drive signal, thereby setting the gate of the IGBT 1 connected to the common connection point between the two to the high level and low level. Drive to level.

  The emitter of the sense IGBT 5 is connected to the input terminal of the drive circuit 2 and is connected to the reference potential point via the resistance element 9 (reflux current detection means). Further, the inverting input terminal of the comparator 10 (reflux current detection means). It is connected to the. A reference voltage Vref is applied to a non-inverting input terminal of the comparator 10, and an output terminal is connected to an input terminal of a latch 12 (forced off setting means) via a filter 11.

  The filter 11 is a low-pass filter for removing noise. The comparator 10 sets the output signal to a high level when the terminal voltage VSE of the resistance element 9 falls below the reference voltage Vref. The latch 12 latches the rising edge of the signal, and outputs the latched high level signal to the drive circuit 2 as an IGBT forced off signal. Further, when the drive circuit 2 monitors the terminal voltage VSE and detects that an overcurrent has flowed through the IGBT 1, the drive circuit 2 performs an overcurrent protection operation for forcibly turning off the IGBT1. Note that the reference voltage Vref is a threshold for detecting that the terminal voltage VSE exhibits negative polarity as described later, and therefore may be a voltage slightly higher than the reference potential point.

  The timer 13 (forced off setting means) starts a counting operation when a high level signal is given from the latch 12, and outputs a reset signal to the latch 12 when the predetermined time is counted up. The predetermined time is set to 20% of the PWM carrier cycle, for example, and is 50 μs when the carrier frequency is 5 kHz. In the above configuration, the portion consisting of reference numerals 9 to 13 constitutes the drive control circuit 14.

  Next, the operation of this embodiment will be described with reference to FIG. FIG. 2 is a timing chart showing each signal waveform. For example, the U-phase IGBT 1 on the lower arm side is turned off if the upper arm side IGBT of the same phase is turned on, and the U-phase is turned on if another phase, for example, the W-phase lower arm side IGBT is turned on. A positive current flows through and a negative current flows through the W phase. When the U-phase upper arm IGBT is turned off from this state, the lower-arm IGBT 1 is turned on, but the W-phase current flows as a return current through the free wheel diode 4.

  When the return current flows as described above, the current also flows through the free wheel diode of the sense IGBT 5 (not shown), so that a voltage drop occurs in the resistance element 9, and the polarity of the terminal voltage VSE is that the reference potential point is ground; Then it becomes negative. Then, the output signal level of the comparator 10 changes from low to high.

  When the IGBT drive signal indicates a low level (on), the drive circuit 2 turns on the IGBT 1 by turning on the on-side switch 7 and turning off the off-side switch 8 (see (A)). Conversely, when the IGBT drive signal indicates a high level (off), the on-side switch 7 is turned off and the off-side switch 8 is turned on to turn off the IGBT 1. Even if the IGBT 1 is turned on, if no collector current flows, no current flows in the sense IGBT 5, so the terminal voltage VSE becomes 0V.

  When a freewheeling diode 4 flows into the freewheeling diode and the terminal voltage VSE becomes negative (see (B)), an IGBT forced-off signal is output from the latch 12 (there is a delay due to the filter 11), and an IGBT drive signal IGBT1 is turned off even if indicates a low level (see (C)). When the timer 13 counts a predetermined time after the IGBT forced-off signal is output, a reset signal is output to the latch 12 (indicated by a broken-line arrow in FIG. 2D. Refer to FIG. 2D), but at this time, the IGBT is driven. Since the signal indicates a high level, there is substantially no influence.

  Next, also when the IGBT 1 is turned on at the timing when the IGBT drive signal falls, the polarity of the terminal voltage VSE becomes negative (see (E)), and after the delay by the filter 11, the IGBT forced-off signal is output and the IGBT 1 Is turned off (see (F)). Here, if the period in which the polarity of the terminal voltage VSE is negative (up to (G) in FIG. 2B) is longer than the predetermined time counted by the timer 13, the IGBT is output even if the reset signal is output to the latch 12. The forced off signal continues to be output.

Next, when the IGBT 1 is turned on at the timing when the IGBT drive signal falls, the polarity of the terminal voltage VSE becomes negative for a short period (that is, a period shorter than the predetermined period) (see (H)). After the IGBT forced-off signal is output, the IGBT forced-off signal becomes inactive when the timer 13 counts a predetermined time and outputs a reset signal (see (I)). Therefore, the driving state according to the IGBT driving signal is thereafter performed.
2 (b) to 2 (d) show a signal state when the latch 12 is not reset by the timer 13, and as a result of the IGBT forced-off signal maintaining the active state, It becomes impossible to turn on in the period to be turned on.

  As described above, according to the present embodiment, it is detected by the resistance element 9 and the comparator 10 that the return current flows through the free wheel diode 4 connected in antiparallel to the IGBT 1. Then, when it is detected that the return current flows through the freewheel diode 4 during the period when the IGBT 1 is on, the latch 12 forces the IGBT 1 to be at least a predetermined time counted by the timer 13 from the time of the detection. To turn it off.

  Therefore, in order to prevent chattering in which the IGBT 1 is repeatedly turned on and off, it is not necessary to add hysteresis characteristics to the determination value for detecting the return current as in Patent Document 1, so that the determination value given to the comparator 10; the reference voltage Vref is lowered. It can be set and the occurrence of loss can be suppressed. In addition, since the drive circuit 2 uses the same path as the current detection path for performing the overcurrent protection operation and does not divide the path as in Patent Document 3, the determination accuracy does not decrease and the number of detection terminals increases. There is nothing. Furthermore, since the IGBT module 6 includes the sense IGBT 5 and the detection is performed based on a change in voltage according to the current flowing through the emitter of the IGBT module 6, the resistance element 9 can be configured with an element having a smaller current capacity.

(Second embodiment)
FIG. 3 shows a second embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted. Hereinafter, different parts will be described. The drive control circuit 21 of the second embodiment is obtained by adding a cycle detection unit 22 (forced off setting means) to the drive control circuit 14 of the first embodiment and replacing the timer 13 with a timer 23 (forced off setting means). is there. The input terminal of the period detection unit 22 is connected to the output terminal of the filter 11, and the period detection unit 22 counts the edge interval of the signal output from the comparator 10 via the filter 11, thereby passing through the IGBT 1. The period of the flowing current is detected. For example, in FIG. 2, the intervals between the time points (C) to (F) are counted.

  The period detection unit 22 also includes a register, a comparator, and the like in which the comparison value is stored. When the count value of the period detection unit 22 exceeds the comparison value, the timer 23 switches the timer value switching signal to a high level. The timer 23 is configured to be able to change the count value counted as a predetermined time. When the timer value switching signal becomes high level, the count value is switched to a high value, and when the signal becomes low level, the count value is changed. It is designed to switch to a lower value.

  That is, if the cycle of the current flowing through the IGBT 1 is short, the interval at which the polarity of the current is reversed is shortened. Accordingly, the predetermined time counted by the timer 23 is shortened accordingly, and if the current cycle is long, the interval is reversed. The predetermined time counted by the timer 23 is shortened. As a result, a minimum period (predetermined time) during which the IGBT 1 is turned off can be appropriately set to reliably detect the reflux current.

(Third embodiment)
FIG. 4 shows a third embodiment, and only differences from the second embodiment will be described. In the drive control circuit 31 of the third embodiment, a comparator 32 (forced off setting means) is arranged in place of the cycle detector 22 of the drive control circuit 21 of the second embodiment. The inverting input terminal of the comparator 32 is connected to one end of the resistor element 9 in common with the inverting input terminal of the comparator 10, and the reference voltage Vref2 is applied to the non-inverting input terminal. The output terminal of the comparator 32 outputs a timer value switching signal to the timer 23. The reference voltage Vref2 is set to a voltage higher than the reference voltage Vref.

  That is, the comparator 32 sets the timer value switching signal to a low level when the terminal voltage VSE becomes larger than the reference voltage Vref2. Thereby, the timer 23 switches the count value corresponding to the predetermined time to a low value. That is, if the amplitude of the current flowing through the IGBT 1 increases, the current change per time increases. Accordingly, by shortening the predetermined time accordingly, the minimum period for turning off the IGBT 1 is appropriately set to set the return current. It can be reliably detected.

(Fourth embodiment)
FIG. 5 shows the fourth embodiment, and the differences from the first embodiment will be described. In the fourth embodiment, instead of the IGBT module 6, an IGBT module 42 (semiconductor device) that does not include the sense IGBT 5 is used. The resistance element 9 is omitted, and the inverting input terminal of the comparator 10 is connected to the collector of the IGBT 1 via the diode 43 (return current detection means). The inverting input terminal of the comparator 44 is connected to the anode of the diode 43, and the non-inverting input terminal is supplied with a reference voltage Vref2 (however, a value different from the reference voltage Vref2 of the third embodiment). ing. The output terminal of the comparator 44 is connected to the input terminal of the drive circuit 2A, and the comparator 44 outputs an overcurrent detection signal to the drive circuit 2A.

Next, the operation of the fourth embodiment will be described. The cathode and anode potentials of the diode 43 are V1 and V2, respectively. When the current is flowing with the IGBT 1 turned on, the voltage V1 (the voltage between the conducting terminals of the IGBT 1) becomes the ON voltage Von of the IGBT 1 with respect to the emitter. The voltage V2 at the input terminal is
V2 = Von + VD1
become. When an overcurrent flows through the IGBT 1, the ON voltage Von is higher than usual. Therefore, the reference voltage Vref2 is
Vref2> Von (normal voltage) + VD1
By setting to, the comparator 44 changes the output signal level from high to low when an overcurrent is detected.

When a freewheeling current flows through the freewheeling diode 4, the voltage V1 decreases by the forward voltage VD2 of the diode 4 with respect to the emitter. At this time, the voltage V2 is
V2 = VD1-VD2
Therefore, the reference voltage Vref is
Von (minimum value) + VD1>Vref> VD1-VD2
By setting in this range, the comparator 10 can detect that the return current flows.

  As described above, according to the fourth embodiment, detection is performed based on the collector-emitter voltage V1 of the IGBT 1 using the comparator 10 and the diode 43. That is, when the return current flows through the freewheeling diode 4, it is understood that the voltage V1 has decreased by the forward voltage VD1 with respect to the anode side voltage V2 of the freewheeling diode 43, and the return current is the same as in the first embodiment. Can be detected.

The present invention is not limited to the embodiments described above or shown in the drawings, and the following modifications or expansions are possible.
In the first to third embodiments, the IGBT module of the fourth embodiment may be used, and the return current may be detected by inserting the resistance element 9 into the emitter of the IGBT instead of the sense MOS 5.
The fourth embodiment may be implemented by combining the configuration for changing the predetermined time of the timer 23 as in the second and third embodiments.
The timer may perform a down count operation.

The predetermined time of the timer may be changed in three stages or more.
The PWM carrier frequency may be appropriately changed according to the individual design.
You may apply to the switching element arrange | positioned at the upper arm side of a bridge circuit.
The switching element is not limited to the IGBT but may be a MOSFET, a bipolar transistor, or the like.

  In the drawings, 1 is an IGBT (switching element), 4 is a free wheel diode, 5 is a sense IGBT (current output terminal), 6 is an IGBT module (semiconductor device), 9 is a resistance element (reflux current detection means), and 10 is a comparator. (Reflux current detection means), 12 is a latch (forced OFF setting means), 13 is a timer (forced OFF setting means), 14 and 21 are drive control circuits, 22 is a period detection unit (forced OFF setting means), and 23 is a timer. (Forced off setting means), 31 is a drive control circuit, 32 is a comparator (forced off setting means), 41 is a drive control circuit, 42 is an IGBT module (semiconductor device), and 43 is a diode (return current detection means).

Claims (7)

The switching element and a free wheel diode connected in reverse parallel to the switching element are applied to a power conversion circuit having an arm composed of a semiconductor device mounted on the same semiconductor substrate.
A return current detecting means for detecting that a return current flows through the freewheel diode;
When it is detected that a return current flows through a freewheeling diode connected to the switching element while the switching element is on, the switching element is turned off for a predetermined time or more from the time of the detection. A switching element control circuit comprising: a forced-off setting unit. The semiconductor device includes a current output terminal that outputs a smaller current having a correlation with a current flowing through the switching element and a free wheel diode connected to the element,
2. The switching element control circuit according to claim 1, wherein the return current detection means performs the detection based on a change in voltage according to a current flowing through the current output terminal.   2. The switching element control circuit according to claim 1, wherein the return current detection means performs the detection based on a voltage between conduction terminals of the switching element.   4. The switching element control circuit according to claim 2, wherein the return current detecting means includes a comparator that compares the change in the voltage with a reference voltage. A current period detecting means for detecting a period of a current flowing through the switching element;
5. The switching element control circuit according to claim 1, wherein the forced-off setting unit changes the predetermined time in accordance with a length of the cycle of the current. 6. Current amplitude detecting means for detecting the amplitude of the current flowing through the switching element;
5. The switching element control circuit according to claim 1, wherein the forced-off setting unit changes the predetermined time in accordance with the amplitude of the current. 5. The switching element and a free wheel diode connected in reverse parallel to the switching element are applied to a power conversion circuit having an arm composed of a semiconductor device mounted on the same semiconductor substrate.
When it is detected that a return current flows through a freewheeling diode connected to the switching element while the switching element is on, the switching element is turned off for a predetermined time or more from the time of the detection. A method for controlling a switching element.

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