JP5799902B2 - Switching element drive circuit - Google Patents

Description

  The present invention relates to a driving circuit for a switching element including a sense terminal that outputs a minute current having a correlation with a current flowing between its input / output terminals.

  As this type of drive circuit, for example, as shown in Patent Document 1 below, one having an overcurrent protection function for protecting a semiconductor switching element (for example, IGBT) from overcurrent is known. This circuit will be described. The emitter of the switching element is connected to a sense terminal provided in the switching element via a resistor. Then, assuming that the potential at the connection point of the sense terminal and the resistor is referred to as a sense voltage, when it is determined that the state in which the sense voltage exceeds the threshold voltage is continued for a predetermined time under the condition that the switching element is turned on, The gate charge of the switching element is discharged to inhibit the switching element from being driven. Thereby, the fall of the reliability of a switching element is aimed at.

JP-A-5-275999

  Here, the present inventors faced a problem that, despite the overcurrent flowing through the switching element, the switching element cannot be promptly prohibited by the overcurrent protection function. Hereinafter, this problem will be described.

  Under the condition that the switching element is turned on, the sense voltage basically increases as the collector current increases, but a phenomenon may occur in which the sense voltage becomes smaller than the initial expected value corresponding to the collector current. . In this case, the time until the actual sense voltage exceeds the threshold voltage becomes longer. That is, there is a problem that it takes a long time from the start of overcurrent to the switching element until the switching element is inhibited from being driven by the overcurrent protection function. This may reduce the reliability of the switching element.

  In order to avoid such a problem, there is a technique that can accurately determine whether or not an overcurrent flows through the switching element even in a situation where the sense voltage becomes smaller than the initial value corresponding to the collector current. Required.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a new switching element drive circuit capable of determining that an overcurrent flows through the switching element.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  The invention according to claim 1 is a switching element (S * #; * = c, u, v) having a sense terminal (St) for outputting a minute current having a correlation with a current (Ice) flowing between its input / output terminals. , W: # = p, n), detected by the current detection means (42) for detecting the output current (Vse) of the sense terminal, and the current detection means in a situation where the switching element is turned on. On the basis of the fact that the absolute value of the change rate of the output current after the timing at which the generated output current starts to rise is below a specified value (| Vα |, Vβ) greater than 0, it is determined that an overcurrent flows through the switching element. And determining means.

  The present inventors have a phenomenon in which an overcurrent flow path of the switching element is formed and the output current detected by the current detection means becomes smaller than the initial assumed value corresponding to the current flowing between the input / output terminals. It has been noted that the occurrence state of is a situation in which the absolute value of the change rate of the output current becomes small. In view of this point, the above invention includes a determination unit. For this reason, it is possible to accurately determine that an overcurrent flows through the switching element in a situation in which a phenomenon occurs in which the output current becomes smaller than the initial assumed value. Thereby, it is possible to take appropriate measures to avoid a decrease in the reliability of the switching element thereafter.

  The invention according to claim 2 is the invention according to claim 1, wherein the switching element is a high-potential side switching element (S ¥ p; ¥ = u, v, w) connected in parallel to a DC power supply (CV). And a low-potential-side switching element (S ¥ n) connected in series, and both the high-potential-side switching element and the low-potential-side switching element are turned on so that the overcurrent of the switching element Is defined as a short circuit between the upper and lower arms, and the specified value (| Vα |) increases the output current in a situation where the switching element is turned on and the short circuit between the upper and lower arms occurs. It is set to a value equal to or lower than the rate of decrease of the output current after the start timing, and the determination means that the overcurrent flows based on the rate of decrease of the output current being less than the specified value. Characterized by disconnection.

  The inventors of the present invention basically increase the output current as the current flowing between the input / output terminals rises in a situation where the phenomenon that the output current becomes smaller than the initial assumed value occurs. In addition, attention was paid to the fact that the output current temporarily decreases during the increase. And it discovered that it was possible to correlate that the reduction | decrease speed and an overcurrent flow into a switching element. Therefore, in the above invention, the specified value is set in the above manner.

  According to a third aspect of the present invention, in the first aspect of the invention, the switching element is a high-potential side switching element (S ¥ p; ¥ = u, v, w) connected in parallel to a DC power source (CV). And a low-potential-side switching element (S ¥ n) connected in series, and both the high-potential-side switching element and the low-potential-side switching element are turned on so that the overcurrent of the switching element Is defined as a short circuit of the upper and lower arms, and the specified value (Vβ) is equal to or less than the rate of increase of the output current in a situation where the switching element is turned on and the short circuit of the upper and lower arms occurs. It is set to a value, and the determination means determines that the overcurrent flows based on the increase rate of the output current being lower than the specified value.

  The inventors of the present invention have noted that the phenomenon in which the output current becomes smaller than the initial assumed value is a situation in which the rate of increase in the output current is low. Therefore, in the above invention, the specified value is set in the above manner.

The block diagram of the control system concerning 1st Embodiment. The block diagram of the drive unit concerning the embodiment. The time chart which shows an example of the overcurrent protection process at the time of the upper-lower arm short circuit concerning the embodiment. The figure which shows the outline | summary of the short circuit between phases concerning the embodiment. The time chart which shows an example of the overcurrent protection process at the time of the short circuit between phases concerning the embodiment. The time chart which shows transition of collector current etc. when the overcurrent concerning the embodiment flows. The time chart which shows transition of the collector current etc. when the overcurrent concerning the embodiment does not flow. The flowchart which shows the procedure of the short circuit detection process between phases concerning the embodiment. The flowchart which shows the procedure of the short circuit detection process between phases concerning 2nd Embodiment.

(First embodiment)
Hereinafter, a first embodiment in which a switching element drive circuit according to the present invention is applied to a hybrid vehicle including a rotating machine and an internal combustion engine as an in-vehicle main engine will be described with reference to the drawings.

  FIG. 1 shows an overall configuration of a control system according to the present embodiment.

  The motor generator 10 is an in-vehicle main machine and is connected to drive wheels (not shown). The motor generator 10 is connected to the high voltage battery 12 via an inverter IV and a converter CV as a DC power source. Here, converter CV includes capacitor C, a pair of switching elements Scp and Scn connected in parallel to capacitor C, and a reactor L that connects a connection point between the pair of switching elements Scp and Scn and the positive electrode of high-voltage battery 12. And. Specifically, converter CV has a function of boosting the voltage of high-voltage battery 12 (for example, 100 V or more) up to a predetermined voltage (for example, “666 V”) by turning on / off switching elements Scp, Scn.

  On the other hand, the inverter IV includes a series connection body of the switching elements Sup and Sun, a series connection body of the switching elements Svp and Svn, and a series connection body of the switching elements Swp and Swn. The points are connected to the U, V, and W phases of the motor generator 10, respectively.

  Incidentally, in the present embodiment, a voltage control type is used as the switching element S * # (* = c, u, v, w; # = p, n), more specifically, an insulated gate bipolar. A transistor (IGBT) is used. In addition, a diode D * # is connected in antiparallel to each of these.

  The control device 14 uses the low voltage battery 16 as a power source, and operates the inverter IV and the converter CV to control the control amount (for example, torque) of the motor generator 10 as desired. Specifically, the control device 14 outputs the operation signals gcp and gcn to the drive unit DU to operate the switching elements Scp and Scn of the converter CV, and the switching elements Sup, Sun, Svp, Svn, Swp, and the inverter IV. In order to operate Swn, operation signals gup, gun, gvp, gvn, gwp, gwn are output to the drive unit DU. Here, the high-potential side operation signal g * p and the corresponding low-potential side operation signal g * n are complementary to each other. In other words, the high-potential side switching element S * p and the corresponding low-potential side switching element S * n are alternately turned on.

  Note that the high-voltage system including the high-voltage battery 12 and the low-voltage system including the low-voltage battery 16 are insulated from each other, and transmission and reception of signals between them is an interface 18 including an insulating element such as a photocoupler. Is done through.

  Next, the configuration of the drive unit DU will be described with reference to FIG.

  As shown in the figure, the drive unit DU includes a drive IC 20 that is a one-chip semiconductor integrated circuit. The drive IC 20 includes a constant voltage power source 22 having a terminal voltage VH (for example, 15 V). The constant voltage power source 22 is a constant current circuit 24, a P-channel MOS field effect transistor (constant current switching element 26), and a terminal of the drive IC 20. The switching element S * # is connected to the switching control terminal (gate) of the switching element S * # via T1. In FIG. 2, the free wheel diode D * # is not shown.

  The gate of the switching element S * # is connected to the terminal T3 of the drive IC 20 via the discharge resistor 28, the terminal T2 of the drive IC 20 and the N-channel MOS field effect transistor (discharge switching element 30). The terminal T3 is connected to the output terminal (emitter) of the switching element S * #.

  The gate of the switching element S * # is also connected to the terminal T3 via the terminal T4 of the drive IC 20, the Zener diode 34, and the N-channel MOS field effect transistor (clamping switching element 36). Here, the breakdown voltage of the zener diode 34 (hereinafter referred to as the clamp voltage Vclamp) is, for example, a voltage (for example, 12V) that does not flow a current that causes the reliability of the switching element S * # to decrease excessively in a short time. Is set to a voltage that limits the applied voltage (gate voltage Vge) of the switching control terminal of the switching element S * #. In the present embodiment, the clamp voltage Vclamp is set to a voltage that is higher than the mirror voltage of the switching element S * # and lower than the upper limit value of the gate voltage (terminal voltage VH of the constant voltage power supply 22).

  The gate of the switching element S * # is further connected to the terminal T3 via the soft cutoff resistor 38, the terminal T5 of the drive IC 20 and the N-channel MOS field effect transistor (soft cutoff switching element 40).

  The switching element S * # is a sense terminal that outputs a minute current (for example, “1/10000” of the collector current Ice) having a correlation with a current flowing between the input terminal (collector) and the emitter (hereinafter referred to as a collector current Ice). St is provided. The sense terminal St is connected to the emitter via a resistor (sense resistor 42). As a result, a voltage drop occurs in the sense resistor 42 due to a small current output from the sense terminal St. Therefore, the potential on the sense terminal St side of the sense resistor 42 (hereinafter, the sense voltage Vse) has a correlation with the collector current Ice. It can be an electrical state quantity.

  Incidentally, in the present embodiment, the sense voltage Vse when the potential on the sense terminal St side of both ends of the sense resistor 42 is higher than the potential of the emitter is defined as positive. The emitter potential is set to “0”.

  The sense terminal St side of both ends of the sense resistor 42 is connected to the non-inverting input terminal of the comparator 44 via the terminal T6 of the drive IC 20. The inverting input terminal of the comparator 44 is connected to the power source 46. Here, the terminal voltage (hereinafter referred to as threshold voltage Vth) of the power supply 46 is determined from the viewpoint of maintaining the reliability of the switching element S * #. Specifically, for example, the reliability of the switching element S * # is maintained. The upper limit value of the possible collector current Ice is set to the sense voltage Vse when it flows through the switching element S * #. The output signal of the comparator 44 is input to the drive control unit 48 provided in the drive IC 20.

  The terminal T6 is connected to the input side of the differentiation circuit 50. The differentiating circuit 50 has a function of outputting a change speed of the sense voltage Vse (hereinafter, voltage change speed Sse). The output signal of the differentiation circuit 50 is input to the drive control unit 48.

  The constant current switching element 26 and the discharge switching element 30 are operated by the drive control unit 48. The drive control unit 48 alternately turns on / off the constant current switching element 26 and the discharge switching element 30 based on the operation signal g * # input via the terminal T7 of the drive IC 20 to thereby switch the switching element S. * Drive #. Specifically, when the operation signal g * # is an on operation command, the discharge switching element 30 is turned off, and the constant current switching element 26 is turned on. On the other hand, when the operation signal g * # is an off operation command, the constant current switching element 26 is turned off, and the discharge switching element 30 is turned on.

  In the present embodiment, since the constant current circuit 24 is provided, the charging current of the gate can be set to a constant value during the period in which the constant current switching element 26 is turned on. That is, the gate charging process of the switching element S * # can be performed by constant current control.

  Next, the overcurrent protection process executed by the drive control unit 48 will be described.

  In this process, when it is determined that the logic of the output signal of the comparator 44 is “H”, the clamp switching element 36 is turned on, and the logic of the output signal of the comparator 44 is “H”. This is a process of turning off the constant current switching element 26 and the discharging switching element 30 and turning on the soft cutoff switching element 40 when it is determined that the predetermined time has been continued. Hereinafter, the overcurrent protection process will be described with reference to FIG.

  FIG. 3 is a diagram illustrating an example of the overcurrent protection process when the upper and lower arms are short-circuited. Specifically, FIG. 3A shows a gate voltage Vge, a sense voltage Vse, a collector-emitter voltage Vce, a collector current Ice, and a loss in the switching element S * # (collector-emitter voltage Vce and The transition of the collector current Ice is shown. FIG. 3B shows the transition of the operating state of the constant current switching element 26, FIG. 3C shows the transition of the operating state of the discharging switching element 30, and FIG. FIG. 3E shows the transition of the operating state of the soft shut-off switching element 40. FIG.

  Note that the upper and lower arm short circuit is an overcurrent (short circuit current) of the switching element S * # when both the high potential side switching element S * p and the low potential side switching element S * n are turned on. A distribution channel is formed. This short circuit between the upper and lower arms occurs, for example, when one of the high-potential side switching element S * p and the low-potential side switching element S * n is short-circuited and the other is switched to the ON state.

  As shown in the figure, at time t1, the discharge switching element 30 is switched to the off operation, and the constant current switching element 26 is switched to the on operation, whereby the gate voltage Vge starts to rise. As a result, the collector current Ice begins to flow, and the sense voltage Vse also begins to rise.

  Thereafter, at time t2 when it is determined that the sense voltage Vse exceeds the threshold voltage Vth and the logic of the output signal of the comparator 44 becomes “H”, the clamp switching element 36 is turned on. As a result, the gate voltage Vge is then limited by the clamp voltage Vclamp. The reason why the sense voltage Vse becomes higher than the threshold voltage Vth immediately after the time t2 is that it takes a certain time from when the on operation of the clamp switching element 36 is started until this element is actually turned on. Because.

  Thereafter, the state in which the logic of the output signal of the comparator 44 is “H” is continued for a predetermined time Tcut from time t2. Therefore, at time t3, the constant current switching element 26 is turned off, and the soft cutoff switching element 40 is turned on. Thereby, switching element S * # is forcibly turned off.

  Here, the soft blocking resistor 38 shown in FIG. 2 is for increasing the resistance value of the discharge path of the gate charge, and the resistance value Ra of the soft blocking resistor 38 is the discharge value. The resistance value Rb of the working resistor 28 is set higher. This is because, under a situation where the collector current Ice is excessive, if the speed at which the switching element S * # is switched from the on state to the off state, in other words, the cutoff speed between the collector and the emitter is increased, the surge voltage is increased. This is in view of the possibility of being excessive.

  Incidentally, when the soft cutoff switching element 40 is turned on, the drive control unit 48 performs a process of outputting the fail signal FL and a process of prohibiting the driving of the constant current switching element 26 and the discharge switching element 30. Perform together. The fail signal FL is output to the low voltage system (control device 14) via the terminal T8 of the drive IC 20, as shown in FIG. By the fail signal FL, the fail processing unit 18a shown in FIG. 1 shuts down the inverter IV and the converter CV. In addition, the control device 14 evacuates the vehicle using only the engine as the driving power source, for example. Processing is performed. Here, the configuration of the fail processing unit 18a may be, for example, that shown in FIG. 3 of Japanese Patent Application Laid-Open No. 2009-60358.

  By the way, the present inventors have found that an overcurrent is generated in the switching element S * # in a situation where the collector-emitter voltage Vce is low when a short circuit between the phases occurs and the switching element S * # is turned off. In spite of the current flow, the overcurrent protection process faced a problem that the switching element S * # could not be quickly switched to the OFF state. Hereinafter, the interphase short circuit will be described first, and then the above problem will be described.

  First, the interphase short circuit will be described.

  The phase-to-phase short circuit is, for example, a short circuit of two of the three-phase electrical paths (for example, a bus bar or a motor cable) connecting the inverter IV and the motor generator 10, or a three-phase electrical path provided in the inverter IV. In a situation where two of the connected output terminal blocks are short-circuited or two of the three-phase electrical paths in the motor generator 10 are short-circuited, a switching element on the high potential side corresponding to one of the short-circuited phases In addition, an overcurrent flow path is formed by turning on the low-potential side switching element corresponding to the other.

  FIG. 4 shows the V and W phase arms of inverter IV and motor generator 10 in the overall configuration of the system shown in FIG.

  In the illustrated example, the V-phase high-potential side switching element Svp and the W-phase low-potential side switching element Swn are turned on in a situation where the electrical paths of the V and W phases are short-circuited. This indicates a short circuit between phases in which an overcurrent flow path is formed.

  Next, the above problem will be described with reference to FIG. Specifically, FIG. 5 shows the switching element S ¥ # (¥ = u, v, w) of the inverter IV when the input voltage VL of the inverter IV is lower than that of FIG. 3 and a short circuit between the phases occurs. This is an example of the overcurrent protection process. 5A to 5E correspond to the previous FIG. 3A to FIG. 3E. FIG. 5 also shows a horizontal scale HS1 (time scale) and a vertical scale VS1 (scale such as voltage) corresponding to FIG.

  In the illustrated example, the broken line in FIG. 5A indicates the initial assumed value Vdl of the sense voltage Vse according to the collector current Ice. The rising speed of the initial assumed value Vdl is lower than the rising speed of the sense voltage Vse when the upper and lower arm short circuit shown in FIG. This is because the overcurrent distribution path in the case where the short circuit between the phases occurs due to the fact that the distribution path of the overcurrent when the short circuit between the phases occurs is longer than the distribution path of the overcurrent when the short circuit between the upper and lower arms occurs. This is because the inductance is larger than the inductance of the overcurrent flow path when the upper and lower arms are short-circuited.

  Further, when a short circuit between the phases occurs, the collector-emitter voltage Vce when the switching element S ¥ # is in the on state is lower than when the upper and lower arms are short circuited. This is because the resistance value of the path (for example, the bus bar) from the emitter of the switching element on the high potential side to the collector of the switching element on the low potential side among the resistance values of the overcurrent distribution path when the short circuit between the phases occurs. This is due to the fact that the occupying ratio is higher than in the case of the upper and lower arm short circuit, and the amount of voltage drop in the path is increased. The reason why the ratio increases is mainly that the overcurrent distribution path when the short circuit between the phases occurs is longer than the overcurrent distribution path when the upper and lower arm short circuits occur.

  When the collector-emitter voltage Vce when the switching element S ¥ # is in the on state is low, the actual sense under the situation where the switching element S ¥ # is in the transient state that is shifted from the off state to the on state The voltage Vse becomes lower than the initial assumed value Vdl corresponding to the collector current Ice (see the sense voltage Vse at times t2 to t4 in FIG. 5A). That is, while the switching element S ¥ # is turned on, the sense voltage Vse basically increases as the collector current Ice increases, but the sense voltage Vse becomes lower than the initial assumed value Vdl.

  In particular, the lower the input voltage of the inverter IV, the lower the collector-emitter voltage Vce when the switching element S ¥ # is in the on state, and the degree to which the sense voltage Vse is lower than the initial assumed value Vdl. large. Here, the situation where the input voltage of the inverter IV becomes low can occur, for example, by diverting the control system of the motor generator 10 designed for a specific vehicle type to another vehicle type. This is because the operating voltage range of the inverter IV can be different depending on the vehicle type.

  When the sense voltage Vse becomes lower than the initial assumed value Vdl for the reason described above, there arises a problem that the switching element S ¥ # cannot be quickly switched to the OFF state by the overcurrent protection process. That is, the time TL (time t2 to t5) from when the sense voltage Vse exceeds the threshold voltage Vth to when the soft cutoff switching element 40 is turned on when the phase short-circuit occurs is the time when the upper and lower arms are short-circuited. It becomes longer than the time TH (time t2 to t3 in FIG. 3) from when the voltage Vse exceeds the threshold voltage Vth until the soft cutoff switching element 40 is turned on. As a result, the time during which an overcurrent flows through the switching element S ¥ # becomes longer, and the reliability of the switching element S ¥ # may be reduced.

  Note that the above-described problem can also occur in the switching elements Scp and Scn included in the converter CV.

  Here, the present inventors basically use the sense voltage Vse as the collector current Ice increases in a situation where a short circuit between the phases occurs and a phenomenon occurs in which the sense voltage Vse becomes smaller than the initial assumed value Vdl. In particular, while focusing on the increase, as shown in the vicinity of time t2 in FIG. 5, it was noted that the sense voltage Vse temporarily decreased during the increase. Then, it has been found that it is possible to relate the decrease rate of the sense voltage Vse under the situation where the sense voltage Vse is temporarily decreased and the occurrence of a short circuit between the phases. Hereinafter, this will be described with reference to FIGS. Here, FIG. 6 (a) corresponds to FIG. 3 (a), and FIG. 6 (b) corresponds to FIG. 5 (a).

  As shown in FIG. 6, the decrease rate ΔVb1 (for example, 0.5 V / μsec) of the sense voltage Vse when the short circuit between the phases occurs is the decrease rate ΔVa1 (for example, 5 V / μs) of the sense voltage Vse when the upper and lower arm short circuit occurs. sufficiently lower than μsec).

  In addition, when the switching element S * # is turned on when the overcurrent flow path is not formed, the decrease rate ΔVn1 of the sense voltage Vse is higher than the decrease rate ΔVa1 of the sense voltage Vse when the upper and lower arms are short-circuited. High enough. This will be described with reference to FIG. Specifically, FIG. 7A to FIG. 7C correspond to FIG. 3A to FIG. 3C, and “Varm” in FIG. 7A represents the input of the inverter IV. It is the transition of voltage. Further, the horizontal axis scale HS2 (for example, 80 nsec) in FIG. 7A is sufficiently smaller than the horizontal axis scale HS1 (for example, 1 μsec) in FIG. 3A, and the collector current Ice in FIG. The vertical axis scale VS2 (for example, 100 A) for is smaller than the vertical axis scale VS1 (for example, 500 A) for the collector current Ice in FIG.

  Since the collector current Ice and the sense voltage Vse have a correlation, and the horizontal axis HS2 in FIG. 7A is sufficiently smaller than the horizontal axis HS1 in FIG. 3A, FIG. The decrease rate ΔVn1 of the sense voltage Vse when the switching element S * # shown in a) is turned on is sufficiently higher than the decrease rate ΔVa1 of the sense voltage Vse when the upper and lower arms are short-circuited.

  As described above, in view of the fact that the decrease rate of the sense voltage Vse in the case where the short circuit between the phases occurs, the case where the upper and lower arms are short circuited, and the case where the overcurrent distribution path is not formed is in the above relationship, the sense voltage The rate of decrease in Vse is a parameter for determining whether or not an overcurrent flows through the switching element S * #. Therefore, in the present embodiment, the inter-phase short-circuit detection process using the decrease rate of the sense voltage Vse is performed.

  FIG. 8 shows the procedure of the interphase short-circuit detection process. Since the drive control unit 48 according to the present embodiment is hardware, the processing shown in FIG. 8 is actually executed by a logic circuit.

  In this series of processing, first, in step S10, it is determined whether or not the logical product of the condition that the operation signal g * # is an ON operation command and the condition that the voltage change rate Sse is negative is true. To do.

  When an affirmative determination is made in step S10, the process proceeds to step S12, and it is determined whether or not the voltage change rate Sse exceeds the specified voltage Vα (<0). This process is a process for determining whether or not a short circuit between phases has occurred. Here, the specified voltage Vα is set to a value capable of discriminating between the upper and lower arm short circuit and the inter-phase short circuit. In this embodiment, the upper and lower arm short circuit occurs and the switching element S * # is turned on. The maximum value of the voltage change rate Sse (<0) is set. That is, the situation in which an affirmative determination is made in this step is that the maximum value of the decrease rate (> 0) of the sense voltage Vse under the situation where the switching element S * # is turned on is less than the absolute value | Vα | Is the situation.

  In addition, in order to improve the determination accuracy of whether or not an inter-phase short-circuit has occurred, the process of this step may be a process of determining whether or not the state where the voltage change rate Sse exceeds the specified voltage Vα is continued for a specified time. .

  If an affirmative determination is made in step S12, it is determined that a short circuit between phases has occurred, and the process proceeds to step S14. In step S14, the soft cutoff switching element 40 is turned on, and both the constant current switching element 26 and the discharge switching element 30 are turned off. Thereby, switching element S * # is switched to an OFF state, and driving of switching element S * # is prohibited. In addition to the process of this step, the process of outputting the fail signal FL may be performed together.

  If a negative determination is made in steps S10 and S12 described above, or if the process in step S14 is completed, the series of processes is temporarily terminated.

  As described above, in the present embodiment, when it is determined that the voltage change rate Sse exceeds the specified voltage Vα in a state where the switching element S * # is turned on, the soft cutoff switching element 40 is turned on. Both the constant current switching element 26 and the discharge switching element 30 were turned off. According to such a configuration, when the upper and lower arms are short-circuited, the switching element S * # can be protected by the overcurrent protection process, and when the inter-phase short circuit occurs, the switching element S * # can be protected by the inter-phase short circuit detection process. . As a result, even under a situation where a short circuit between the phases occurs, the driving of the switching element S * # can be promptly prohibited, and as a result, a decrease in the reliability of the switching element S * # can be avoided.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the present embodiment, the processing method of the interphase short-circuit detection process is changed. Specifically, as the parameter used in this process, the rising speed of the sense voltage Vse under the condition where the switching element S * # is turned on is used instead of the decreasing speed of the sense voltage Vse. Here, the rising speed of the sense voltage Vse can be used because, as shown in FIG. 6, the rising speed ΔVb2 (for example, 0.625 V / μsec) of the sense voltage Vse when a short-circuit between phases occurs. This is in view of the fact that it is sufficiently lower than the rate of increase ΔVa2 (eg, 4 V / μsec) of the sense voltage Vse when the upper and lower arms are shorted. Further, as shown in FIG. 7, when the overcurrent flow path is not formed, the rising speed ΔVn2 of the sense voltage Vse under the condition where the switching element S * # is turned on is the case where the upper and lower arms are short-circuited. This is in view of the fact that it is sufficiently higher than the rising speed ΔVa2 of the sense voltage Vse.

  FIG. 9 shows the procedure of the interphase short-circuit detection process executed by the drive control unit 48. In FIG. 9, the same processing as in FIG. 8 is given the same step number for convenience.

  In this series of processing, first, in step S10a, it is determined whether or not the logical product of the condition that the operation signal g * # is an ON operation command and the condition that the voltage change rate Sse is positive is true. To do.

  When an affirmative determination is made in step S10, the process proceeds to step S12a to determine whether or not the voltage change rate Sse is lower than the second specified voltage (> 0). Here, the second specified voltage Vβ is set to a value capable of discriminating between the upper and lower arm short circuit and the phase short circuit, and in this embodiment, the upper and lower arm short circuit occurs and the switching element S * # is turned on. The minimum voltage change speed Sse (> 0) below is set. That is, the situation in which an affirmative determination is made in this step is a situation in which the maximum value of the increase rate (> 0) of the sense voltage Vse is less than the second specified voltage Vβ under the condition where the switching element S * # is turned on. .

  In addition, in order to improve the determination accuracy of whether or not an inter-phase short-circuit has occurred, the voltage change speed Sse is lower than the second specified voltage Vβ in the same manner as the process in step S12 of FIG. It may be a process for determining whether or not is continued for a specified time.

  If a positive determination is made in step S12a, the process proceeds to step S14.

  When a negative determination is made in steps S10a and S12a described above, or when the process of step S14 is completed, this series of processes is temporarily terminated.

  Thus, the effect similar to the effect acquired by the said 1st Embodiment can be acquired also by the interphase short circuit detection process concerning this embodiment.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  The first limiting unit and the second limiting unit are not limited to those that switch the switching element S * # to the off state and prohibit the driving of the switching element S * # and prevent the collector current Ice from flowing. For example, the collector current Ice is reduced while allowing the collector current Ice to flow by reducing the gate voltage Vge to a voltage higher than the mirror voltage of the switching element S * # and lower than the clamp voltage Vclamp. It may be.

  In the first embodiment, the voltage change rate Sse is calculated using the differentiating circuit 50. However, the present invention is not limited to this. For example, the voltage change rate Sse may be calculated by dividing the difference between the sense voltages Vse at two different timings by the time difference between the two timings without providing the differentiating circuit 50. .

  The method for setting the specified voltage Vα is not limited to the method exemplified in the first embodiment. For example, the specified voltage Vα may be set to a value slightly higher than the maximum value of the voltage change rate Sse (<0) in a situation where the upper and lower arms are short-circuited and the switching element S * # is turned on. In this case, the situation in which an affirmative determination is made in step S12 of FIG. 8 is that the maximum value of the decrease rate (> 0) of the sense voltage Vse under the condition where the switching element S * # is turned on is the absolute value of the specified voltage Vα. The situation is slightly lower than the value | Vα |.

  Further, the method of setting the second specified voltage Vβ is not limited to the one exemplified in the second embodiment. For example, even if the second specified voltage Vβ is set to a value slightly lower than the minimum value of the voltage change rate Sse (> 0) in a situation where the upper and lower arms are short-circuited and the switching element S * # is turned on. Good. In this case, the situation in which an affirmative determination is made in step S12a of FIG. 9 is that the maximum value of the increase rate (> 0) of the sense voltage Vse under the condition where the switching element S * # is turned on is the second specified voltage. The situation is slightly lower than Vβ.

  -The DC power supply is not limited to the converter CV. For example, in the above embodiment, when the converter CV is not provided or when the operation of the converter CV is stopped, the high voltage battery 12 is a DC power source.

  The current detection means is not limited to the one provided with the sense resistor 42 that detects the output current of the sense terminal St as the sense voltage Vse. For example, as long as the current flowing through the electrical path from the sense terminal St to the emitter can be detected, other current detection means such as one equipped with a Hall element may be used. In this case, it is desirable to provide a certain resistance to the electrical path so that the sense terminal and the emitter are not short-circuited.

  The switching element is not limited to the IGBT but may be a MOSFET, for example.

  -As a vehicle to which this invention is applied, an electric vehicle provided with only a rotary machine as a vehicle-mounted main machine may be sufficient, for example.

  -The application object of the present invention is not limited to a switching element provided in a power conversion circuit (inverter IV or converter CV) for driving an in-vehicle main machine, for example, a power conversion circuit for driving a compressor for air conditioning May be a switching element. The application object of the present invention is not limited to the switching element provided in the in-vehicle power conversion circuit, and is not limited to the switching element provided in the power conversion circuit. In this case, the flow path of the overcurrent is not limited to the one formed by the upper and lower arm short circuit or the phase short circuit. If there are other situations in which an overcurrent flows through the switching element and a plurality of overcurrent flow paths having different inductances are assumed, for example, an inductor among the overcurrent flow paths having different inductances may be used. The application of the present invention is effective in the configuration in which the overcurrent protection function is designed corresponding to the one having the lowest dance.

  42... Sense resistor, St... Sense terminal, S * # (* = c, u, v, w: # = p, n).

Claims (6)

Switching element (S * #; * = c, u, v, w: # = p, n) having a sense terminal (St) that outputs a minute current correlated with the current (Ice) flowing between its input / output terminals )
Current detection means (42) for detecting an output current (Vse) of the sense terminal;
Under the condition that the switching element is turned on, the absolute value of the change rate of the output current after the timing at which the output current detected by the current detection means starts to rise is greater than the specified value (| Vα |, Vβ ) And a determination means for determining that an overcurrent flows through the switching element,
A switching element drive circuit comprising: The switching device, the switching element having a high potential side; of (S ¥ p ¥ = u, v, w), and the high-potential side of the low potential side of the switching elements connected in series to the switching element (S ¥ n) Each
A DC power source (CV) is connected in parallel to the series connection body of the high potential side switching element and the low potential side switching element,
The upper and lower arm short circuit is defined as the overcurrent flow path of the switching element is formed by turning on both the high potential side switching element and the low potential side switching element,
The specified value (| Vα |) is set to a value equal to or less than the rate of decrease in the output current after the timing at which the output current starts to rise in a situation where the switching element is turned on and the upper and lower arms are short-circuited. ,
The switching element drive circuit according to claim 1, wherein the determination unit determines that the overcurrent flows based on a decrease rate of the output current being lower than the specified value. The switching device, the switching element having a high potential side; of (S ¥ p ¥ = u, v, w), and the high-potential side of the low potential side of the switching elements connected in series to the switching element (S ¥ n) Each
A DC power source (CV) is connected in parallel to the series connection body of the high potential side switching element and the low potential side switching element,
The upper and lower arm short circuit is defined as the overcurrent flow path of the switching element is formed by turning on both the high potential side switching element and the low potential side switching element,
The specified value (Vβ) is set to a value equal to or less than the increase rate of the output current under a situation where the switching element is turned on and the upper and lower arms are short-circuited,
The switching element drive circuit according to claim 1, wherein the determination unit determines that the overcurrent flows based on an increase rate of the output current being lower than the specified value.   And a limiting unit that performs a process of limiting the driving of the switching element by discharging electric charge from the switching control terminal of the switching element based on the determination that the overcurrent flows by the determining unit. The drive circuit of the switching element according to any one of claims 1 to 3.   5. The switching element driving circuit according to claim 4, wherein the limiting means performs the limiting process by prohibiting driving of the switching element. The limiting means is a first limiting means,
A second restriction for performing a process of restricting driving of the switching element by discharging electric charges from the switching control terminal based on the state where the output current exceeds the threshold value (Vth) for a predetermined time (Tcut). 6. The switching element drive circuit according to claim 4, further comprising means.