JP6365278B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a protection circuit that protects a semiconductor switching element from an overcurrent.

  As a power conversion device that performs power conversion between a DC voltage and an AC voltage, a pair of semiconductor switching elements (hereinafter referred to as switching elements) of an upper arm circuit and a lower arm circuit for one phase between power lines. What was comprised by connecting in series is known. In this type of power conversion device, the switching elements of the upper arm circuit and the lower arm circuit are alternately driven to convert power between, for example, a DC voltage and an AC voltage.

  By the way, the switching element may cause a short circuit abnormality due to its switching operation or the like. When a short circuit abnormality occurs in one of the upper arm circuit and the lower arm circuit, an inconvenience that an overcurrent exceeding the rated current flows in the driving state of the other switching element occurs.

  Therefore, conventionally, when an overcurrent flows in a state where a drive voltage is applied to one of the switching elements, the switching element is forcibly switched to a cutoff state to protect from the overcurrent (see Patent Document 1). ).

JP 2004-357463 A

  When a short circuit abnormality of a switching element results from a failure of the other switching element before the drive voltage is applied to one switching element (hereinafter referred to as a first case), one switching element There is a case (hereinafter referred to as a second case) due to the failure of the other switching element when a drive voltage is applied to the other.

  In the case of the first case, the overcurrent is relatively small because the switching element is forcibly cut off before the drive voltage in the switching element reaches a full-on voltage that saturates. On the other hand, in the case of the second case, when the drive voltage of the switching element becomes a full-on voltage, the switching element may be forcibly cut off, and the overcurrent tends to be relatively large.

  Thus, since the magnitude of the overcurrent when the switching element is shut off differs between the case of the first case and the case of the second case, the first case and the second case are different from each other. It is preferable that the switching element is forcibly cut off at a speed. However, in this case, if the first case and the second case are erroneously determined, there may be a problem that the switching element is not properly cut off.

  The present invention has been made in view of the above, and a main object of the present invention is to provide a power conversion circuit capable of more appropriately protecting a switching element from an overcurrent.

  The present invention is a power conversion device that performs power conversion by a switching operation by a pair of semiconductor switching elements (11) provided in an upper arm circuit and a lower arm circuit that are connected in series with each other. A driving voltage detecting means (21) for detecting a driving voltage; a driving voltage holding means (30) for holding the driving voltage detected by the driving voltage detecting means as a past value; and one of the pair of semiconductor switching elements. When a drive voltage is applied to the semiconductor switching element, the short-circuit abnormality determining means (30) for determining whether or not there is a short-circuit abnormality in which an overcurrent flows, and when the short-circuit abnormality is determined, Drive state determination means (3) for determining the drive state of the semiconductor switching element when the short circuit abnormality occurs based on the past value of the voltage ) And, characterized in that it comprises a.

  According to the present invention, the driving voltage of the switching element is held as a past value. And when the short circuit abnormality of the switching element is determined, the drive state of the switching element when the short circuit abnormality occurs is determined based on the held past value of the drive voltage. Can be used to accurately determine the driving state of the switching element when a short circuit abnormality occurs.

The schematic block diagram of a power conversion system. The schematic block diagram of an inverter. Explanatory drawing of the relationship between a short circuit abnormality and the drive state of a switching element. Explanatory drawing of the interruption | blocking process.

  As shown in FIG. 1, the power conversion system 10 includes a motor generator MG as an in-vehicle main machine, an inverter IV, and an MPU 40.

  Motor generator MG is a three-phase rotating machine and is connected to high voltage battery 15 via inverter IV. The inverter IV is configured by a three-phase bridge, and the IGBT 11 for the upper arm circuit and the IGBT 11 for the lower arm circuit are connected in series for each phase. Each IGBT 11 is provided with a reflux diode 13 and a current sensing circuit (not shown) and is configured as an individual module.

  As shown in FIG. 2, a control circuit 20 is connected to each IGBT 11 constituting the inverter IV. The control circuit 20 is connected to the MPU 40. The MPU 40 is a known microcomputer that includes a CPU, a ROM, a RAM, and the like, and includes a control signal output unit 41.

  The control signal output unit 41 outputs a PWM control signal (hereinafter referred to as a control signal) that switches between the driving state (ON state) and the blocking state (OFF state) of each IGBT 11. Specifically, based on a command signal from a host ECU (not shown), the control signal output unit 41 sets the control signal to L level when driving the IGBT 11, and sets the control signal to H level when cutting the IGBT 11. To do.

  The control circuit 20 includes a drive circuit 21, a drive voltage monitoring circuit 22, a current monitoring circuit 23, and a protection circuit 30.

  The drive circuit 21 switches the drive state of the IGBT 11 based on a control signal from the MPU 40. That is, when the control signal is at the L level, the drive circuit 21 increases the drive voltage (gate voltage Vg) of the IGBT 11 to switch the IGBT 11 to the drive state. When the control signal is at the H level, the drive voltage (gate voltage Vg) of the IGBT 11 is lowered, and the IGBT 11 is switched to the cutoff state.

  The drive voltage monitoring circuit 22 detects the drive voltage applied to the IGBT 11. In this embodiment, the gate voltage Vg applied to the gate G is detected. In addition to this, the drive voltage monitoring circuit 22 may detect, as the drive voltage, the emitter-collector voltage Vce of the IGBT 11, the sense voltage Vs detected by a current sensing circuit (not shown), and the like.

  The current monitoring circuit 23 detects a collector current Ice that flows between the emitter and collector of the IGBT 11. The detection results of the drive voltage (gate voltage Vg) and the collector current Ice are output to the MPU 40.

  The protection circuit 30 has functions of an abnormality determination unit 31, a cutoff processing unit 32, a cutoff speed setting unit 33, and a drive voltage holding unit 34.

  Abnormality determination unit 31 determines whether or not a short circuit abnormality has occurred in IGBT 11 based on whether or not an overcurrent greater than or equal to the rated current flows in IGBT 11 using the detection result of collector current Ice. That is, when the detected value of the collector current Ice is equal to or larger than the predetermined threshold Th1, it is determined that there is a short circuit abnormality. When the collector current Ice is less than the threshold value Th1, it is determined to be normal (not a short circuit abnormality). The threshold value Th1 is determined in advance as a value equal to or higher than the rated current.

  The cutoff processing unit 32 forcibly switches the IGBT 11 to the cutoff state when a short circuit abnormality is determined in a state where the gate voltage Vg is applied to the IGBT 11.

  The shut-off speed setting unit 33 determines the shut-off speed when a short-circuit abnormality occurs in a saturation region (full-on state) where the change amount of the gate voltage Vg is less than a predetermined value and when a short-circuit abnormality occurs outside the full-on state. Switch.

  Here, the short-circuit abnormality of the IGBT will be described. The short-circuit abnormality of the IGBT 11 means that in the pair of IGBTs 11 in the upper arm circuit and the lower arm circuit, the other IGBT 11 fails before the drive voltage is applied to the one IGBT 11. When the drive voltage is applied to one IGBT 11 and when the other IGBT 11 fails (hereinafter referred to as the second case) There is.

  In the case of the first case, since the short circuit abnormality is detected before the drive voltage of the IGBT 11 becomes the full-on voltage, the overcurrent when the IGBT 11 is forcibly cut off is relatively small. On the other hand, in the case of the second case, there is a possibility that a short-circuit abnormality may be detected when the drive voltage of the IGBT 11 is a full-on voltage. In this case, an overcurrent when the IGBT 11 is forcibly cut off is detected. growing.

  Here, the short circuit abnormality of the IGBT 11 will be described in detail with reference to FIG. Of the upper arm circuit and the lower arm circuit, the switching driven arm is referred to as a self arm, and the non-switching arm is referred to as an opposing arm. It should be noted that a delay inherent to the switching operation of the IGBT 11 occurs after the detection of the short-circuit abnormality of the IGBT 11 until the IGBT 11 is shut off.

  First, in the first case shown in FIG. 3A, after applying the gate voltage Vg to its own arm, a short circuit abnormality is determined at time t1 when the collector current Ice becomes equal to or higher than the threshold Th1. In this case, since the short circuit abnormality is detected before the gate voltage Vg reaches the full-on voltage, the overcurrent (collector current Ice) that flows when the own arm is cut off is relatively small.

  On the other hand, in the case of the second case shown in FIG. 3B, the opposing arm is out of order when the self arm reaches the full-on voltage. In this case, if a short circuit abnormality is determined at time t11 when the collector current Ice is equal to or greater than the threshold Th1, the collector current Ice increases rapidly due to the high gate voltage Vg. Therefore, the overcurrent (collector current Ice) when the IGBT 11 is cut off increases.

  In other words, the first case and the second case have different effects of overcurrent when the interruption process is performed, so that the IGBT 11 is forcibly interrupted depending on whether the short circuit abnormality is the first case or the second case. It is preferable to set a shut-off speed when performing processing. However, if the first case and the second case are not correctly determined, there will be inconveniences caused by the IGBT 11 not being properly shut off.

  Therefore, in the present embodiment, the drive voltage holding unit 34 is used to hold the drive voltage of the IGBT 11 as a past value. Then, when a short circuit abnormality is determined by the abnormality determination unit 31, it is determined whether the short circuit abnormality is the first case or the second case using the past value of the drive voltage held in the drive voltage holding unit 34. To do.

  Returning to the description of FIG. 2, the drive voltage holding unit 34 includes a delay circuit that holds a detected value of the drive voltage of the IGBT 11 as a past value in a predetermined delay period T. The delay circuit can be composed of, for example, a well-known CR filter, a serial connection body of buffers, an analog circuit such as an even number of serial connection bodies of logic inversion elements, a digital circuit using a timer, or the like.

  As shown in FIG. 3A, the delay period T in the delay circuit according to the present embodiment is saturated from the time ta when the application of the gate voltage Vg to the IGBT 11 is started (full-on voltage Vgf). Is set to a period ΔT1 that is longer than the period ΔT up to time tb by a predetermined period α.

  Therefore, when the short circuit abnormality of the IGBT 11 shown in FIG. 3A is the first case, the past value Vgb of the drive voltage of the IGBT 11 held by the delay circuit goes back by the period ΔT1 from the time t1 when the short circuit abnormality occurs. The gate voltage Vg = 0 at time t0. On the other hand, when the short-circuit abnormality of the IGBT 11 in FIG. 3B is the second case, the past value Vgb of the drive voltage of the IGBT 11 held by the delay circuit goes back by a period ΔT1 from the time t11 when the short-circuit abnormality occurs. The gate voltage Vg> 0 at time t10.

  Therefore, when a short circuit abnormality is determined by the abnormality determination unit 31, the first case is obtained when the past value Vgb = 0 of the gate voltage Vg held in the drive voltage holding unit 34, and the second case when Vgb> 0. It can be determined as a case.

  Here, the operation of the control circuit 20 having the above configuration will be described. First, after the drive of the IGBT 11 by the drive circuit 21 (after the start of energization), the collector current Ice is monitored by the current monitoring circuit 23. When the abnormality determination unit 31 determines that the collector current Ice is equal to or greater than the threshold value Th1, the cutoff processing unit 32 stores the past value of the gate voltage Vg (drive voltage) held by the drive voltage holding unit 34. Based on Vgb, the driving state of the IGBT 11 when the short circuit abnormality occurs is determined. That is, it is determined whether the current short circuit abnormality corresponds to the first case or the second case.

  At this time, during operation of the power conversion system 10, the drive voltage is always held by the drive voltage holding unit 34. Based on the past value Vgb of the gate voltage before ΔT1 from the present time, the first case or the first A determination is made as to whether there are two cases. Specifically, if the past value Vgb of the gate voltage at the time of occurrence of the short-circuit abnormality is 0V, it is determined that it corresponds to the first case, and if the past value Vgb of the gate voltage is greater than 0V, it corresponds to the second case. Then, it is determined. Moreover, in the interruption | blocking process part 32, if this short circuit abnormality corresponds to a 1st case, it will be set to the 1st cutoff speed V1 with a low interruption speed, and if this short circuit abnormality corresponds to a 2nd case. The second cutoff speed V2 (> V1) is set to a higher cutoff speed.

  The present invention has the following excellent effects.

  • Hold the switching element drive voltage as a past value. Then, when the short circuit abnormality of the switching element is determined, the driving state of the switching element when the short circuit abnormality occurs is determined based on the past value of the held drive voltage. In this case, it is possible to accurately determine the driving state of the switching element when the short circuit abnormality occurs using the past value of the driving voltage.

  Hold the drive voltage as a past value for a predetermined period. And when it is determined that there is a short circuit abnormality, the drive state when the short circuit abnormality occurs is determined based on the past value of the drive voltage that goes back the predetermined period, so the difference in the past value of the drive voltage Can be used to accurately determine the state of the switching element when a short circuit abnormality occurs.

  ・ If the past value of the drive voltage is maintained for a predetermined period based on the period from the start of energization of the switching element to the full-on voltage, the short-circuit abnormality is switched based on the drive voltage when a short-circuit abnormality occurs. It can be determined whether or not it has occurred at the time of the full on voltage of the element.

  -The interruption | blocking speed | rate of a switching element can be set appropriately based on the drive state of the switching element when a short circuit abnormality generate | occur | produces.

  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.

  In the above, the drive voltage holding unit 34 uses the control signal of the control signal output unit 41 to set the upper limit from the previous time when the IGBT 11 is switched from the drive state to the cutoff state until the next time when the IGBT 11 is in the full-on state. The delay period T may be set as follows.

  In the above, the drive voltage holding unit 34 uses the level of the command signal of the host ECU (not shown), and the next time the drive voltage is the full on voltage from the time when the command signal level of the host ECU is switched to the L level. The delay period T may be set up to the upper limit of time.

  In the above, the drive voltage holding unit 34 may hold a plurality of parameters related to the drive voltage. For example, a first delay circuit that holds the past value Vgb of the gate voltage and a second delay circuit that holds the past value of the sense voltage Vs are provided. When the short-circuit abnormality of the IGBT 11 is generated by the abnormality determination unit 31, it is determined whether the case is the first case or the second case using both the first delay circuit and the second delay circuit. Also good.

  In the above, in order to improve the determination accuracy of the short circuit abnormality, a mask period from when the collector current Ice ≧ Th1 until the occurrence of the short circuit abnormality is determined may be set. In this case, when Ice ≧ Th1 temporarily due to the influence of noise or the like, it is possible to reduce the accuracy of erroneously determining that a short circuit abnormality has occurred, and to further increase the determination accuracy of a short circuit abnormality.

  In the above, the driving state of the IGBT 11 when a short circuit abnormality has occurred may be determined by arithmetic processing by the control circuit 20 or the MPU 40. For example, as shown in the flowchart of FIG. 4, first, it is determined whether or not the drive state is such that the drive voltage is applied to the IGBT 11 (S11). This process makes an affirmative determination when the gate voltage Vg> 0. If a positive determination is made in S11, it is determined whether or not a short circuit abnormality has occurred (S12). This process is determined based on whether or not the collector current Ice ≧ Th1. When Ice ≧ Th1, it is determined that there is a short circuit abnormality. When Ice <Th1, it is determined that a short circuit abnormality has not occurred (it is normal). If there is a short circuit abnormality, it is determined whether the current case is the first case or the second case using the past value Vgb of the drive voltage held by the drive voltage holding unit 34 (S13). That is, when the past value Vgb = 0 of the drive voltage, it is determined that the current case is the first case (S14). If Vgb> 0, it is determined as the second case (S15). If a negative determination is made in S11 and S12, the process is terminated.

  In the above, the case where an insulated gate bipolar transistor (IGBT) is used as a switching element constituting the inverter IV is exemplified. However, other than this, an N channel MOS field effect transistor, a P channel MOS field effect are used as a switching element. Transistors may be used. Further, the switching element is not limited to the voltage control type switching element, and may be a current control type switching element such as a bipolar transistor that performs conduction control by a base current.

  DESCRIPTION OF SYMBOLS 10 ... Power conversion system, 21 ... Drive circuit, 30 ... Protection circuit, 31 ... Abnormality determination circuit, 32 ... Cut-off processing circuit, 33 ... Cut-off speed setting circuit, 34 ... Drive voltage holding circuit

Claims (5)

A power conversion device that performs power conversion by a switching operation by a pair of semiconductor switching elements (11) provided in an upper arm circuit and a lower arm circuit connected in series with each other,
Drive voltage detection means (21) for detecting a drive voltage of the semiconductor switching element;
Drive voltage holding means (30) for holding the drive voltage detected by the drive voltage detection means as a past value;
A short circuit abnormality determining means (30) for determining whether or not there is a short circuit abnormality in which an overcurrent flows when a drive voltage is applied to one of the pair of semiconductor switching elements;
Driving state determining means (30) for determining a driving state of the semiconductor switching element when the short circuit abnormality occurs based on the past value of the driving voltage when it is determined that the short circuit abnormality is present;
A power conversion device comprising: The drive voltage holding means holds the drive voltage detected by the drive voltage detection means as a past value in a predetermined period;
When it is determined that the short circuit abnormality is present, the driving state determination unit is configured to switch the semiconductor switching when the short circuit abnormality occurs based on the past value that is a drive voltage that goes back the predetermined period from that time point. The power conversion device according to claim 1, wherein the drive state of the element is determined. The drive voltage holding means holds a past value of the drive voltage in a predetermined period determined based on a period from the start of energization of the semiconductor switching element to a full-on voltage,
The drive state determination means determines that the short-circuit abnormality has occurred in a full-on state of the semiconductor switching element when the past value of the drive voltage is greater than or equal to a predetermined value , and when the past value of the drive voltage is less than a predetermined value The power converter according to claim 1, wherein it is determined that the short-circuit abnormality has occurred before the semiconductor switching element is fully turned on.   4. The power conversion device according to claim 1, further comprising: a cut-off speed setting unit configured to set a cut-off speed of the semiconductor switching element based on the drive state determined by the drive state determination unit. .   5. The power conversion device according to claim 1, wherein the drive voltage includes at least one of a gate voltage, a sense voltage, and a collector-emitter voltage of a semiconductor switching element.

Images