JP2009254034A - Current detector for power inverter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that power loss increases when a power switching element Sw is switched on when a current is flowing to a free wheel diode FD. <P>SOLUTION: The cathode potential of the free wheel diode FD is raised by a specified voltage Vp by a power source 74, and it is applied to the anode of a diode 70 for detection. The cathode side of the diode 70 for detection is connected to the cathode side of the free wheel diode FD. A shunt resistor 72 is connected to the anode of the diode 70 for detection, and when determined that a current is flowing to the free wheel diode FD, based on the voltage drop of the shunt resistor 72, it compulsively switches off the power switching element Sw. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power conversion circuit including a power switching element and a free wheel diode connected to an input / output terminal thereof, and relates to a current detection device for a power conversion circuit that detects a current flowing through the power conversion circuit.

  As this type of power conversion circuit, a circuit (inverter) including a series connection body of a high potential side switching element and a low potential side switching element for connecting each terminal of a DC power source and a terminal of a rotating machine is well known. It is. The inverter includes a free wheel diode connected to the input / output terminal of the switching element. Here, when operating the high-potential side switching element and the low-potential side switching element to flow a sinusoidal current to the rotating machine, the high-potential side switching element and the low-potential side switching element are alternately turned on and off. Generally, a method of driving these pair of switching elements in a complementary manner by setting the state is used.

  On the other hand, an insulated gate bipolar transistor (IGBT) may be used as the switching element of the inverter. In recent years, for example, as can be seen in Patent Document 1 below, as a semiconductor element constituting such an inverter, a so-called diode built-in IGBT in which a free wheel diode is provided on the same substrate as the IGBT has been proposed and put into practical use. ing.

However, since the IGBT has a forward direction from the collector to the emitter, no current flows on the reverse side. For this reason, when a pair of switching elements of the inverter are driven in a complementary manner, depending on the flow direction of the sine wave current, the current may not flow to the switching element that is in the on state. In this case, a current flows through a freewheeling diode connected in antiparallel to this.
JP 2007-214541 A

  By the way, in the diode built-in IGBT, it is known that the amount of voltage drop when a forward current flows through the freewheeling diode increases when a voltage is applied to the gate of the IGBT. For this reason, when operating a switching element complementarily, there exists a possibility that the power loss by a free wheel diode when a forward current may flow into a free wheel diode may become large.

  In addition to the above example, in a power conversion circuit including a power switching element and a freewheel diode connected between its input and output terminals, power loss is caused when a forward current flows through the freewheel diode. This fact that increases when the switching element is turned on is also generally common.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to operate a power conversion circuit including a power switching element and a free wheel diode connected between input and output terminals. It is an object of the present invention to provide a current detection device for a power conversion circuit that can detect with high accuracy whether or not a current is flowing in the circuit. Another object of the present invention is to provide a current detection device for a power conversion circuit capable of reducing the power loss when it is detected that a current flows through a freewheel diode.

  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 current detection device for a power conversion circuit that detects a current flowing through a power conversion circuit including a power switching element and a freewheel diode connected in antiparallel to an input / output terminal of the power switching element. A detection diode connected in parallel to the freewheel diode, and a current flows through the freewheel diode depending on whether a forward current flows through the detection diode connected to the anode side of the detection diode. And a judging means for judging whether or not it is present.

  The direction of current flow differs between the case where current flows through the freewheeling diode and the case where current flows through the power switching element without current flowing through the freewheeling diode. The anode potential fluctuates. For this reason, it is possible to set so that when a current flows through the freewheeling diode, a current flows through the detection diode, and when no current flows through the power switching element, no current flows through the detection diode. Become. In the above invention, in view of this point, it is possible to detect with high accuracy whether or not current flows through the freewheel diode, depending on whether or not forward current flows through the detection diode.

  Further, in the above invention, by making the detection diode a high breakdown voltage element, it is not necessary to configure the judging means with a high breakdown voltage element, and the configuration can be simplified or configured.

  According to a second aspect of the present invention, in the first aspect of the invention, the voltage drop amount of the detection diode can be larger than the voltage drop amount of the freewheel diode, and the anode of the freewheel diode is used as a reference. A power supply for raising the potential of the anode of the detection diode as a potential is further provided.

  If the voltage drop of the detection diode is larger, even if the current flows through the freewheeling diode and the potential on the anode side relative to the cathode side of the detection diode rises, this potential is There is a possibility that the potential is lower than the potential on the cathode side of the diode. In this respect, in the above-described invention, by using the power supply, the potential on the anode side of the detection diode when the current flows through the freewheel diode can be reliably made higher than the potential on the cathode side.

  According to a third aspect of the present invention, in the second aspect of the present invention, the voltage of the power source is variable according to temperature.

  Freewheel diodes, detection diodes, and power switching elements generally have temperature characteristics. For this reason, the amount of voltage drop when current flows through these depends on temperature. Therefore, the voltage of the power supply for making it possible to distinguish whether the current is flowing in the free wheel diode or not depending on whether the current is flowing in the detection diode depends on the temperature. There is a fear. In this regard, in the above invention, the identification can be performed accurately by making the power supply voltage variable according to the temperature.

  According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the voltage Vp of the power source includes the voltage drop amount vf1 of the freewheel diode, the voltage drop amount vf2 of the detection diode, and the power switching element. An inequality “vf2−vf1 <Vp <vf2 + Vt” using the voltage Vt between the input and output terminals is satisfied.

  In the above invention, when a current flows through the freewheel diode, a current flows through the detection diode, and when a current flows through the power switching element without flowing through the freewheel diode, a current flows through the detection diode. It is possible to suitably realize a setting that does not flow.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the judging means includes a resistor provided on the anode side of the detection diode, and both ends of the resistor. A differential amplifier circuit that generates a voltage signal corresponding to the voltage, and a comparison unit that compares the voltage signal output from the differential amplifier circuit with the threshold voltage.

  When a current flows through the detection diode, a current flows through the resistor, and when no current flows through the detection diode, no current flows through the resistor. For this reason, the voltage drop amount of the resistor is a parameter indicating whether or not current is flowing through the detection diode. Then, the threshold voltage is set to a value for determining that a current is flowing through the detection diode based on the voltage drop amount of the resistor, thereby comparing the output of the differential amplifier circuit with the threshold voltage. Based on this, it can be determined whether or not a current flows through the detection diode.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the determination means includes a collector connected to the anode side of the freewheel diode and the anode side of the detection diode. A bipolar transistor having a base connected thereto, a power source for raising the potential of the emitter of the bipolar transistor relative to the anode potential of the freewheel diode, and whether the freewheel is based on whether or not current flows through the bipolar transistor Means for determining whether or not a current is flowing through the diode.

  The potential of the emitter of the bipolar transistor relative to the potential of the cathode of the detection diode differs depending on whether current is flowing through the freewheeling diode or current is flowing through the power switching element without flowing through the freewheeling diode. That is, when the current is flowing through the freewheel diode, the current is higher than when the current is flowing through the power switching element without flowing the current. Therefore, only in this case, it is possible to apply a forward bias for turning on the transistor between the base and emitter of the bipolar transistor. With such a setting, it is possible to identify whether or not current is flowing through the free wheel diode according to whether or not current is flowing through the bipolar transistor.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, further comprising variable means for changing a driving mode of the power switching element based on a determination result of the determination means. Features.

  In the said invention, it becomes possible to perform more suitable switching operation according to a condition by driving a switching element based on the information whether the electric current is flowing into the freewheel diode.

  According to an eighth aspect of the present invention, in the invention according to the seventh aspect, when the variable means determines that a forward current is flowing through the free wheel diode by the determining means, the power switching element is turned on. A stop means for stopping voltage application to the control terminal is provided.

  When the power switching element connected in antiparallel with the current flowing through the freewheel diode is turned on, the power loss of the freewheel diode tends to increase. In the above invention, in view of this point, the conduction loss can be reduced by providing the stopping means.

  The invention according to claim 9 is the invention according to claim 8, wherein the power conversion circuit includes a series connection body of a switching element on a high potential side and a switching element on a low potential side as the power switching element, and The pair of switching elements are characterized in that an ON state is commanded alternately.

  In the above invention, since the pair of power switching elements are driven in a complementary manner, the power switching elements connected to the pair of power switching elements are turned on even when a current flows through the freewheel diode. For this reason, when a forward current flows through the freewheeling diode, there is a possibility that the power loss of the freewheeling diode increases due to unnecessary switching. For this reason, the utility value of the invention specific matter of claim 8 is particularly high.

  The invention according to claim 10 is the invention according to claim 8 or 9, wherein the power conversion circuit constitutes an in-vehicle high voltage system insulated from the in-vehicle low voltage system, and the stop means is provided in the in-vehicle high voltage system. It is provided in that.

  In the above invention, by providing the stop means in the high pressure system, the number of means for insulating between the high pressure system and the low pressure system can be reduced as compared with the case where the stop means is provided on the low pressure system side.

  The invention according to claim 11 is the invention according to any one of claims 1 to 10, characterized in that the power switching element and the free wheel diode are provided on the same semiconductor substrate.

  When a power switching element and a freewheel diode connected between its input / output terminals are provided on the same semiconductor substrate, power loss when a forward current flows through the freewheel diode increases due to the ON state of the switching element. This phenomenon becomes particularly prominent. For this reason, the above invention has a particularly high utility value of the invention specific matters of claims 7 and 8.

(First embodiment)
Hereinafter, an embodiment in which a drive device for a power conversion circuit according to the present invention is applied to a drive device for a power conversion circuit of a hybrid vehicle will be described with reference to the drawings.

  FIG. 1 shows the system configuration of this embodiment. As shown in the figure, a motor generator 10 as an in-vehicle rotating machine is connected to a high voltage battery 12 via an inverter IV and a converter CV. The converter CV is a booster circuit that boosts the voltage of the high-voltage battery 12 (for example, “288V”) within a predetermined upper limit voltage (for example, “660V”). Specifically, the converter CV includes a series connection body of the high-potential side power switching element Swp and the low-potential side power switching element Swn, a coil L that connects the connection point of the series connection body to the high-voltage battery 12, and the power switching element. A high-potential-side freewheel diode FDp and a low-potential-side freewheel diode FDn connected between the input / output terminals of the Swp and the power switching element Swn are provided. The voltage of the converter CV is taken into the inverter IV as an input voltage.

  The inverter IV is configured by connecting three series-connected bodies of a high-potential side power switching element Swp and a low-potential side power switching element Swn in parallel. The connection points of these series connection bodies are connected to the respective phases of the motor generator 10. A high-potential-side freewheel diode FDp and a low-potential-side freewheel diode FDn are connected between the input / output terminals of the high-potential-side power switching element Swp and the low-potential-side power switching element Swn. .

  A drive circuit DC is connected to the conduction control terminals (gates) of the power switching elements Swp and Swn constituting the inverter IV and the converter CV. Thereby, the power switching elements Swp and Swn are driven by the microcomputer (microcomputer 20) using the low voltage battery 16 as a power source via the drive circuit DC and the interface 14. Here, the interface 14 includes an insulating means such as a photocoupler that insulates the high voltage system including the inverter IV and the converter CV from the low voltage system including the microcomputer 20.

  FIG. 1 schematically shows a part of the process for operating the power switching elements Swp and Swn among the processes performed in the microcomputer 20. Here, the PWM signal generation unit 22 is a signal gu for operating each of the U-phase, V-phase, and W-phase of the inverter IV and the power switching element of the converter CV as a PWM signal modulated at a predetermined frequency. , Gv, gw, gcv are generated. Based on these signals gu, gv, gw, and gcv, the complementary signal generation unit 24 generates an operation signal for alternately turning on the high-potential-side power switching element Swp and the low-potential-side power switching element Swn. To do. That is, the operation signals gup, gvp, gwp, gcp for operating the power switching elements Swp on the high potential side of the U phase, V phase, W phase of the inverter IV and the converter CV, and the U phase, V phase, Operation signals gun, gvn, gwn, and gcn for operating the low-phase power switching elements Swn of the W phase and the converter CV are generated.

  Each of the power switching elements Swp and Swn is a switching element that has an input terminal and an output terminal that are uniquely defined and prevents a current from flowing from the output terminal to the input terminal. Specifically, these are constituted by insulated gate bipolar transistors (IGBT). In particular, in the present embodiment, an IGBT with a built-in diode is used. That is, in this embodiment, the high-potential side power switching element Swp and the high-potential side freewheel diode FDp are formed adjacent to each other on the same semiconductor substrate. The freewheel diodes FDn on the side are formed adjacent to the same semiconductor substrate in parallel with each other.

  FIG. 2 shows a cross-sectional structure of the diode built-in IGBT according to the present embodiment. As shown in the figure, the IGBT cell 30 and the diode cell 32 are provided on the same semiconductor substrate. Specifically, a P-type layer 36 is formed on the main surface side of the N-type semiconductor substrate 34. A main surface side N-type layer region 38 and a main surface side P-type layer region 40 are formed on the upper surface of the P-type layer 36. Then, a trench 42 is formed so as to penetrate the main surface side N-type layer region 38, the main surface side P-type layer region 40, and the P-type layer 36, and the trench 42 has an electrode constituting the gate of the IGBT cell. 44 is embedded. On the other hand, a back side P-type layer 46 and a back side N-type layer 48 are formed on the back side of the N-type semiconductor substrate 34.

  An upper surface of the electrode 44 protruding from the trench 42 is covered with an interlayer insulating film 49. On the upper surface of the interlayer insulating film 49, the P-type layer 36, the main surface side N-type layer region 38, and the main surface side P-type layer region 40, the electrode 50 is a region of both the IGBT cell 30 and the diode cell 32. It is formed so as to cover. The electrode 50 is shared between the emitter of the IGBT cell 30 and the anode of the diode cell 32. On the other hand, the back side P-type layer 46 and the back side N-type layer 48 are covered with an electrode 52. The electrode 52 is shared between the collector of the IGBT cell 30 and the cathode of the diode cell 32.

  By the way, as described above, since the high-potential side power switching element Swp and the low-potential side power switching element Swn are turned on complementarily, no current flows through them, and these are in antiparallel. Even when a forward current flows through the connected freewheeling diodes FDp and FDn, the ON operation is performed. However, in this case, the power loss when the forward current flows through the freewheeling diodes FDp and FDn is greater than when the power switching elements Swp and Swn are in the off state.

  Therefore, in the present embodiment, it is determined whether or not forward current flows through the free wheel diodes FDp and FDn. If it is determined that current flows, the power switching elements Swp and Swn connected in reverse parallel to the free wheel diodes FDp and FDn are determined. The operation signals gup, gvp, gwp, gun, gvn, gwn, gcp, gcn are forcibly turned off. However, it is difficult to detect the current flowing through the freewheel diodes FDp and FDn by connecting a shunt resistor to the anode. Next, this will be described.

  FIG. 3 shows the relationship between the voltage Vg between the gate and the emitter of the IGBT, the current of the diode provided therewith, and the voltage drop amount. Here, the diode current shown on the vertical axis in FIG. 3 is detected based on the voltage drop when a shunt resistor having a resistance value of “2 kΩ” is connected to the anode of the diode. Here, since the current and voltage drop of the IGBT are considered as a reference, the diode current and the voltage drop amount are negative. As shown in the figure, the change in the voltage drop amount of the shunt resistor with respect to the change in the amount of current flowing through the diode is very small. This is due to the fact that the current flowing through the diode becomes “several hundred A”. That is, in order to keep the amount of voltage drop when the current flowing through the diode changes in the range of “0 to several hundred A” within the allowable voltage range (several V) of the current detection circuit, the current flowing through the diode is The amount of voltage drop at “A” must be “1V” or less. In this case, in order to determine whether or not a current of “several A to 20 A” or more flows through the diode, the voltage detection circuit is required to have very high accuracy. Furthermore, as shown in FIG. 3, the amount of voltage drop varies according to the voltage Vg and temperature between the gate and emitter of the IGBT. For this reason, it is particularly preferable to set two threshold values with hysteresis so as to avoid hunting in which the determination that current is flowing in the diode and the determination that current is not flowing are frequently switched based on the voltage drop amount. It becomes difficult.

  Therefore, in the present embodiment, it is determined whether or not a current flows through the free wheel diodes FDp and FDn using the circuit shown in FIG. FIG. 4 shows a circuit configuration of the drive circuit DC. Hereinafter, the power switching elements Swp and Swn on the high potential side and the low potential side are referred to as power switching elements Sw, and the free wheel diodes FDp and FDn on the high potential side and the low potential side are referred to as free wheel diodes FD. Further, the operation signals gup, gvp, gwp, gun, gvn, gwn, gcp, and gcn are expressed as an operation signal g.

  As shown in the figure, the drive circuit DC includes a series connection body of a switching element 64 and a switching element 66 between the anode of the freewheel diode FD and the power source 62, and these connection points are conduction control of the power switching element Sw. Connected to terminal (gate). On the other hand, the operation signal g taken into the drive circuit DC via the interface 14 is taken into the drive IC 60, and the drive IC 60 operates the switching elements 64 and 66 based on this. Here, when the switching element 64 is turned on and the switching element 66 is turned off, the gate of the power switching element Sw is charged with the electric charge from the power supply 62. In contrast, when the switching element 64 is turned off and the switching element 66 is turned on, the charge of the gate of the power switching element Sw is discharged.

  Here, the cathode of the detection diode 70 is connected to the connection point between the input terminal (collector) of the power switching element and the cathode of the freewheel diode FD. Specifically, the cathode of the detection diode 70 is connected to the wiring L1 in the current detection circuit (drive circuit DC) connected to the wiring of the power conversion circuit (inverter IV, converter CV). The detection diode 70 has a rated current smaller than that of the freewheel diode FD (for example, “less than 1 A to several A”), but has a breakdown voltage of about the freewheel diode FD (for example, “several hundreds V”). It is a rectifying element. The detection diode 70 has a function of preventing a high voltage from being applied to the current detection circuit when the current detection circuit is connected to the cathode side of the freewheel diode FD so as to detect the current flowing through the freewheel diode FD. Accordingly, the anode side component of the detection diode 70 is not required to have a high breakdown voltage, and can be configured with a small current and low breakdown voltage component.

  A shunt resistor 72 is connected to the anode side of the detection diode 70. The shunt resistor 72 is connected to the positive electrode of the power supply 74, and the negative electrode of the power supply 74 is connected to the anode side of the freewheel diode FD. Specifically, the negative electrode of the power source 74 is connected to the wiring L2 in the current detection circuit (drive circuit DC) connected to the wiring of the power conversion circuit (inverter IV, converter CV). A capacitor 76 is connected to both ends of the shunt resistor 72 in parallel. The capacitor 76 has a function as a filter for preventing voltage noise (surge) applied between the input / output terminals of the power switching element Sw and the free wheel diode FD from affecting current detection.

  A differential amplifier circuit 80 is provided at both ends of the shunt resistor 72 (capacitor 76). The differential amplifier circuit 80 includes an operational amplifier 80a. A resistor 80b connecting the inverting input terminal and the output terminal of the operational amplifier 80a, a resistor 80c connected to the inverting input terminal, and a resistor 80d connected to the non-inverting input terminal are provided.

  The output voltage of the differential amplifier circuit 80 according to the voltage drop amount of the shunt resistor 72 is applied to the non-inverting input terminal of the comparator 82. The inverting input terminal of the comparator 82 is connected to the positive electrode of the reference power supply 84, and the negative electrode of the reference power supply 84 is connected to the wiring L2. As a result, the threshold voltage Vth of the reference power supply 84 is applied to the non-inverting input terminal of the comparator 82. This threshold voltage Vth is used to determine whether or not a forward current flows through the detection diode 70.

  The voltage Vp of the power supply 74 includes a voltage drop amount vf1 when a forward current flows through the freewheeling diode FD, a voltage drop amount Vce between the collector and emitter of the power switching element Sw, and a forward current applied to the detection diode 70. Is set to a value that satisfies the relationship of “vf2−vf1 <Vp <vf2 + Vce”. This is because the forward current flows through the detection diode 70 when the forward current flows through the freewheeling diode FD, and the forward current does not flow through the detection diode 70 when the current flows through the power switching element Sw. It is a setting to be. Here, the power source 74 is provided because the voltage drop amount vf2 of the detection diode 70 is larger than the voltage drop amount vf1 of the freewheel diode FD. That is, in this case, if the detection diode 70 is connected in parallel to the freewheel diode FD without providing the power supply 74, the anode potential of the detection diode 70 is detected even when a forward current flows through the freewheel diode FD. Cannot be made higher than the cathode potential by a voltage drop amount vf2.

  According to the above setting, when a current flows through the free wheel diode FD, a current flows through the detection diode 70 and a voltage drop occurs in the shunt resistor 72. Accordingly, since the output voltage of the differential amplifier circuit 80 exceeds the threshold voltage Vth, the comparator 82 outputs a signal having a logical value “H” as an off command signal for the power switching element Sw. Thereby, in the drive IC 60, the power switching element Sw is forcibly turned off regardless of the value of the operation signal g. On the other hand, when a current flows through the power switching element Sw, no current flows through the detection diode 70, so that no voltage drop occurs in the shunt resistor 72. For this reason, the output voltage of the differential amplifier circuit 80 becomes lower than the threshold voltage Vth, and the output signal of the comparator 82 becomes logic “L”. As a result, the drive IC 60 turns the power switching element Sw on and off according to the operation signal g.

  As a result, when a current flows through the freewheel diode FD, the power switching element Sw is turned off, so that the power loss of the freewheel diode FD can be reduced.

  In the shunt resistor 72, when a current flows through the free wheel diode FD, the current flows from the power conversion circuit (inverter IV, converter CV) side to the anode side of the detection diode 70 via the wiring L2. It is set to a value that can be avoided. That is, the shunt resistor 72 according to the present embodiment not only constitutes a current detection circuit but also has a function as blocking means for blocking current inflow from the power conversion circuit.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) A circuit is provided on the anode side of the detection diode 70 to determine whether or not current is flowing through the free wheel diode according to whether or not forward current flows through the detection diode 70. Thereby, it is possible to detect with high accuracy whether or not a current flows through the freewheeling diode FD. In addition, since the detection diode 70 is a high-breakdown-voltage element, it is not necessary to configure the above-described determination circuit with a high-breakdown-voltage element.

  (2) A power source 74 is further provided for increasing the potential of the anode of the detection diode 70 using the anode of the freewheel diode FD as a reference potential. As a result, the potential on the anode side of the detection diode 70 when a current is flowing through the freewheel diode FD can be reliably made higher than the potential on the cathode side.

  (3) The voltage Vp of the power source 74 is set to satisfy “vf2−vf1 <Vp <vf2 + Vce”. As a result, setting is made such that when current flows through the freewheeling diode FD, current flows through the detection diode 70, and when current flows through the power switching element Sw, no current flows through the detection diode 70. Can be suitably realized.

  (4) A resistor provided on the anode side of the detection diode 70 (shunt resistor 72: a resistor as a linear element for quantifying the current to be detected as a voltage drop), and a shunt A current detection circuit includes a differential amplifier circuit 80 that generates a voltage signal corresponding to the voltage across the resistor 72, and a comparator 82 that compares the voltage signal output from the differential amplifier circuit 80 with the threshold voltage Vth. Configured. Thereby, it can be determined whether or not a current flows through the detection diode 70.

  (5) When it is determined that a forward current flows through the freewheeling diode FD, voltage application to the conduction control terminal (gate) of the power switching element Sw is stopped. Thereby, conduction loss can be reduced.

  (6) A command was made to alternately turn on the series connection body of the power switching element Swp on the high potential side and the power switching element Swn on the low potential side. As a result, even when a current flows through the freewheel diode FD, the power switching element Sw connected in antiparallel to the freewheel diode FD is turned on. Therefore, when a forward current flows through the freewheel diode FD, it is useless. This may increase the power loss of the freewheeling diode FD, despite being switched. For this reason, the utility value of the function to stop the voltage application is particularly high.

  (7) The function of stopping the voltage application is provided in an in-vehicle high voltage system including the inverter IV and the converter CV. Thereby, compared with the case where this function is provided on the low pressure system side, the number of means for insulating between the high pressure system and the low pressure system can be reduced.

  (8) The power switching element Sw and the free wheel diode FD are provided on the same semiconductor substrate. Thereby, the phenomenon that the power loss when the forward current flows through the freewheeling diode FD increases when the power switching element Sw is turned on becomes particularly remarkable. For this reason, the utility value of the function to stop voltage application is particularly high.

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

  FIG. 5 shows a circuit configuration of the drive circuit DC according to the present embodiment. In FIG. 5, members corresponding to those shown in FIG. 4 are given the same reference numerals for convenience.

  As shown in the figure, the present embodiment includes a temperature sensitive diode SD that senses the temperature in the vicinity of the free wheeling diode FD and the power switching element Sw. However, the temperature sensitive diode SD is externally attached to the drive circuit DC. Specifically, the temperature-sensitive diode SD has its cathode connected to the anode of the freewheel diode FD, and its anode is connected to the output terminal of the constant current source 90 using the power source 92 as a power supply means. Thereby, the voltage on the anode side of the temperature sensitive diode SD becomes a value corresponding to the temperature in the vicinity of the free wheel diode FD and the power switching element Sw.

  The voltage on the anode side of the temperature sensitive diode SD is taken into the adjusting circuit 94. The adjustment circuit 94 adjusts the voltage of the variable power source 74a having a voltage variable function for increasing the anode potential of the detection diode 70 according to the voltage on the anode side of the temperature sensitive diode SD. In other words, the temperature is adjusted according to the temperature in the vicinity of the free wheel diode FD and the power switching element Sw.

  This is done in view of the fact that the voltage drop amount vf1 of the freewheel diode FD, the voltage drop amount vf2 of the detection diode 70, and the voltage drop amount Vce of the power switching element Sw vary depending on the temperature. . That is, as shown in FIG. 6, as the temperature increases, the voltage drop amount vf1 of the freewheeling diode FD increases, the voltage drop amount vf2 of the detection diode 70 decreases, and the voltage drop amount Vce of the power switching element Sw is Increase. For this reason, in this embodiment, the voltage of the variable power source 74a is lowered as the temperature is higher.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects of the first embodiment.

  (9) The voltage Vp of the variable power source 74a is variably set according to the temperature. Accordingly, the condition “vf2−vf1 <Vp <vf2 + Vce” can be surely satisfied regardless of the temperature variation of the voltage drop amounts vf1, vf2, and Vce.

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

  FIG. 7 shows a circuit configuration of the drive circuit DC according to the present embodiment. In FIG. 7, members corresponding to those shown in FIG. 5 are given the same reference numerals for the sake of convenience.

  As illustrated, in the present embodiment, the base of a PNP bipolar transistor 100 is connected to the anode of the detection diode 70. The collector of the bipolar transistor 100 is connected to the wiring L2 so as to have the same potential as the anode of the freewheel diode FD. Further, the positive electrode of the variable power source 74 a is connected to the emitter of the bipolar transistor 100 through the resistor 102. The variable power source 74a is configured to increase the positive electrode potential by the voltage Vp with respect to the potential on the anode side of the freewheel diode FD by connecting the negative electrode side to the wiring L2. This voltage Vp is adjusted by the adjustment circuit 94. The voltage Vp of the variable power source 74 a is divided by the resistor 104 and the resistor 106. The divided voltage is applied to the non-inverting input terminal of the comparator 82, and the emitter voltage of the bipolar transistor 100 is applied to the inverting input terminal of the comparator 82.

  Again, the voltage Vp of the variable power source 74a is set so as to reliably satisfy the condition “vf2−vf1 <Vp <vf2 + Vce”. As a result, the output voltage of the comparator 82 differs depending on whether a current flows through the free wheel diode FD or a current flows through the power switching element Sw.

  That is, when a current flows through the power switching element Sw, the emitter potential of the bipolar transistor 100 is higher than the cathode potential of the detection diode 70 by “−Vce + Vp”. However, from the above conditions, this value is smaller than the voltage drop amount vf2 of the detection diode 70. For this reason, a forward bias cannot be applied between the emitter and base of the bipolar transistor 100. Therefore, when a current flows through the power switching element Sw, the bipolar transistor 100 is turned off. Therefore, the emitter voltage of the bipolar transistor 100 based on the anode potential of the freewheel diode FD is about the voltage Vp of the variable power source 74a, and is higher than the voltage Vp divided by the resistors 104 and 106. For this reason, when a current flows through the power switching element Sw, the output voltage of the comparator 82 is logic “L”.

  On the other hand, when a current flows through the freewheel diode FD, the potential of the emitter of the bipolar transistor 100 is higher than the cathode potential of the detection diode 70 by “vf1 + Vp”. From this condition, this value is larger than the voltage drop amount vf2 of the detection diode 70. Therefore, a forward bias is applied between the emitter and base of the bipolar transistor 100, and the bipolar transistor 100 is turned on. For this reason, the potential of the emitter of the bipolar transistor 100 is lowered to about the anode potential of the free wheel diode FD due to the voltage drop caused by the current flowing through the resistor 102. Therefore, the potential of the emitter of bipolar transistor 100 is lower than the divided value of voltage Vp by resistors 104 and 106. Therefore, when a current flows through the freewheeling diode FD, the output voltage of the comparator 82 is logic “H”. For this reason, the case where the output voltage of the comparator 82 is logic “H” is defined as the case where the off command signal is output, thereby forcing the power switching element Sw when the current flows through the freewheeling diode FD. Can be turned off automatically.

  According to this embodiment described above, the effects (1) to (3) and (5) to (8) of the previous first embodiment and the above (9) of the previous second embodiment. In addition to the above effects, the following effects can be obtained.

  (10) Based on whether or not current is flowing through the bipolar transistor 100, it is determined whether or not current is flowing through the freewheeling diode FD. This makes it possible to identify whether current is flowing through the freewheeling diode FD or current is flowing through the power switching element Sw.

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

  In the second embodiment, the voltage of the power source 74a is decreased as the temperature is higher, but the present invention is not limited to this. In short, the variable voltage voltage setting mode may be adjusted in accordance with the temperature characteristics of the power switching element, the freewheel diode, the detection diode 70, and the like.

  In the first and second embodiments, the input side of the differential amplifier circuit 80 is used as a filter for preventing a surge from being superimposed on the current detection system via a parasitic capacitor parallel to the detection diode 70. However, the present invention is not limited to this. For example, a CR filter may be provided on the output side of the differential amplifier circuit 80.

  In the first and second embodiments, the shunt resistor 72 is provided between the anode of the detection diode 70 and the positive terminal of the power source 74, but the present invention is not limited to this. For example, you may provide between the wiring L2 and the negative electrode terminal of the power supply 74. FIG.

  In the first and second embodiments, the shunt resistor 72 is also provided with a function as a limiting unit that limits the current flowing from the power conversion circuit (inverter IV, converter CV) side to the current detection system. However, it is not limited to this. For example, a current limiting resistor may be provided separately from the shunt resistor 72. Further, for example, a constant current output means such as a constant current diode may be provided between the anode of the detection diode 70 and the positive terminal of the power source 74.

  In the second and third embodiments, the sensing means for sensing the temperature in the vicinity of the power switching element and the free wheel diode is not limited to the temperature sensitive diode SD, and may be a thermistor, for example.

  In the third embodiment, instead of the variable power source 74a, a power source 74 having a fixed voltage value may be used as in the first embodiment.

  As a means for determining whether or not a current flows through the free wheel diode based on whether or not a current flows through the bipolar transistor, the voltage of the emitter of the bipolar transistor 100 is set as a threshold value as illustrated in the third embodiment. The present invention is not limited to means for determining whether or not a current is flowing through the bipolar transistor 100 by comparing with the voltage. For example, a means for providing a shunt resistor between the collector of the bipolar transistor and the free wheel diode FDp (FDn) and determining whether or not a current flows through the bipolar transistor 100 based on the voltage drop amount may be used.

  In each of the above embodiments, the forward current is detected in order to forcibly turn off the power switching elements Swp and Swn when the forward current flows through the freewheeling diodes FDp and FDn of the inverter IV and the converter CV. Not limited to this. For example, the present invention may be applied when detecting the current flowing through the freewheel diode so as to determine whether the motor generator 10 is powered or regenerated. According to this, for example, in the control setting in which the high-potential side power switching element Swp and the low-potential side power switching element Swn are not driven in a complementary manner, the side that is required in the control of power running and regeneration and the actual Can be corrected based on the current detection result of the freewheeling diode, the driving mode of the power switching elements Swp and Swn can also be corrected.

  The free wheel diode is not limited to the one formed on the same semiconductor substrate as the IGBT as illustrated in FIG. For example, as described in “RC-IGBT for motor control Hideki Takahashi, 2 others 7 (315) Mitsubishi Electric Technical Report, Vol 81, No. 5, 2007”, the IGBT and the free wheel diode are formed separately. It may be what was done. Even in this case, as shown in FIG. 5 of the same technical report, since the forward voltage of the freewheeling diode is increased by turning on the IGBT, the application of the present invention is effective.

  The power conversion circuit is not limited to the inverter IV and the converter CV as a boost converter. For example, a step-down converter that steps down the voltage of the high voltage battery 12 and applies it to the low voltage battery 16 may be used.

  -As a power converter circuit, not only what is mounted in a hybrid vehicle, For example, you may mount in an electric vehicle.

1 is a system configuration diagram according to a first embodiment. FIG. Sectional drawing which shows the cross-sectional structure of IGBT and diode concerning the embodiment. The figure which shows the characteristic of the diode concerning the embodiment. The circuit diagram which shows the detection process circuit of the electric current of the diode concerning the embodiment. The circuit diagram which shows the detection process circuit of the electric current of the diode concerning 2nd Embodiment. The figure which shows the variable setting aspect of the voltage concerning the embodiment. The circuit diagram which shows the detection process circuit of the electric current of the diode concerning 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Motor generator, 12 ... High voltage battery, 24 ... Complementary signal production | generation part, 70 ... Detection diode, 72 ... Shunt resistance, 74 ... Power supply, 80 ... Differential amplifier circuit, 82 ... Comparator, Swp, Swn, Sw ... Power Switching element, FDp, FDn, FD ... Freewheel diode, IV ... Inverter, CV ... Converter, DC ... Drive circuit.

Claims (11)

For a power conversion circuit comprising a power switching element and a freewheeling diode connected in antiparallel to its input / output terminal, in a current detection device of the power conversion circuit for detecting a current flowing therethrough,
A detection diode connected in parallel to the freewheel diode;
Determining means connected to the anode side of the detection diode and determining whether or not a current flows in the free wheel diode according to whether or not a forward current flows in the detection diode; A current detection device for a power conversion circuit. The voltage drop amount of the detection diode may be larger than the voltage drop amount of the freewheel diode,
2. The current detection device for a power conversion circuit according to claim 1, further comprising a power supply for raising the anode potential of the detection diode with the anode of the freewheeling diode as a reference potential.   The current detection device for a power conversion circuit according to claim 2, wherein the voltage of the power supply is variable according to temperature.   The voltage Vp of the power supply is expressed by an inequality “vf2−vf1 <Vp <using the voltage drop amount vf1 of the freewheel diode, the voltage drop amount vf2 of the detection diode, and the voltage Vt between the input and output terminals of the power switching element. 4. The current detection device for a power conversion circuit according to claim 2, wherein vf2 + Vt is satisfied.   The determination means includes a resistor provided on the anode side of the detection diode, a differential amplifier circuit that generates a voltage signal corresponding to a voltage across the resistor, and a voltage output from the differential amplifier circuit The current detection device for a power conversion circuit according to any one of claims 1 to 4, further comprising a comparison means for comparing the magnitude of the signal and the threshold voltage.   The determination means includes: a bipolar transistor having a collector connected to the anode side of the freewheel diode and a base connected to the anode side of the detection diode; and the potential of the emitter of the bipolar transistor to the anode of the freewheel diode The power supply for raising with respect to electric potential, The means to determine whether the electric current is flowing into the said freewheel diode based on whether the electric current flows through the said bipolar transistor, The 1st aspect is characterized by the above-mentioned. The electric current detection apparatus of the power converter circuit of any one of -4.   The current detection device for a power conversion circuit according to claim 1, further comprising a variable unit that changes a driving mode of the power switching element based on a determination result of the determination unit.   The variable means includes stop means for stopping voltage application to the conduction control terminal of the power switching element when the determination means determines that a forward current flows through the freewheeling diode. The current detection device for a power conversion circuit according to claim 7.   The power conversion circuit includes a series connection body of a high-potential side switching element and a low-potential side switching element as the power switching element, and the pair of switching elements are instructed to be turned on alternately. The current detection device for a power conversion circuit according to claim 8, wherein the current detection device is provided. The power conversion circuit constitutes an in-vehicle high voltage system insulated from an in-vehicle low voltage system,
The current detecting device for a power conversion circuit according to claim 8 or 9, wherein the stop means is provided in an in-vehicle high voltage system.   The current detection device for a power conversion circuit according to any one of claims 1 to 10, wherein the power switching element and the freewheel diode are provided on the same semiconductor substrate.

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