Discharge circuit of a smoothing capacitor

Abstract

This invention provides a discharge circuit for smoothing capacitors that can reduce the number of high-voltage switches required. [Solution] The signal processing circuit 70 comprises a connection path 71, a path resistor 72, a first path switch Q1, a parallel path 73, and a voltage divider 74. The connection path 71 connects the smoothing capacitor 24 to the emitters of the lower arm switches SWL for each phase. The series connection of the path resistor 72 and the first path switch Q1 is provided in the connection path 71. The parallel path 73 connects the part of the connection path 71 that is at a higher potential than the series connection of the path resistor 72 and the first path switch Q1 to the emitters of the lower arm switches SWL for each phase. The voltage divider 74 is provided in the parallel path 73 and divides the voltage of the smoothing capacitor 24. The divided voltage generated by the voltage divider 74 is input to the gate of the first path switch Q1.

Description

Technical Field

[0001] This disclosure relates to a discharge circuit for a smoothing capacitor.

Background Art

[0002] As this type of discharge circuit, one provided with a discharge resistor and a discharge switch is known. A series connection of the discharge resistor and the discharge switch is provided in a connection path connecting the smoothing capacitor and the ground portion. When the discharge switch is turned on, a path for discharging the smoothing capacitor is secured. As an example of such a technique, the technique disclosed in Patent Document 1 can be cited.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As the discharge switch, a high-voltage withstand switch capable of withstanding the voltage of the smoothing capacitor is used. In the discharge circuit, a high-voltage withstand switch may also be used in addition to the discharge switch. In this case, there is a concern that the number of high-voltage withstand switches installed in the discharge circuit will increase.

[0005] For example, the discharge circuit described in Patent Document 1 includes an abnormal power supply. The abnormal power supply includes a control switch connected to the smoothing capacitor. The control switch is a voltage adjustment switch for reducing the voltage of the smoothing capacitor. When the control switch for voltage adjustment is turned on, power for driving the discharge switch is generated. In this case, due to the use of high-voltage withstand switches as the discharge switch and the control switch, there is a concern that the number of high-voltage withstand switches installed in the discharge circuit will increase.

[0006] The purpose of this disclosure is to provide a discharge circuit for a smoothing capacitor that can reduce the number of high-voltage switches that need to be installed. [Means for solving the problem]

[0007] This disclosure relates to a discharge circuit for discharging a smoothing capacitor, A connection path connecting the smoothing capacitor and the ground portion which serves as the discharge destination for the smoothing capacitor, A series connection of a path resistor and a path switch provided in the aforementioned connection path, A parallel path connecting the connection path to the ground portion, which is at a higher potential than the series connection of the path resistor and the path switch, A voltage divider unit is provided in the parallel path and divides the voltage of the smoothing capacitor, Equipped with, The divided voltage generated by the voltage divider is input to the control terminal of the path switch.

[0008] In the discharge circuit described above, the voltage across the smoothing capacitor is divided by the voltage divider, and the divided voltage is input to the control terminal of the path switch. In this case, it is possible to step down the voltage across the smoothing capacitor without using a high-voltage switch, and it is possible to secure the voltage required to turn on the path switch. This makes it possible to secure the discharge path for the smoothing capacitor while avoiding the addition of a high-voltage switch to the discharge circuit. Therefore, compared to the comparative example in which a high-voltage switch is used to generate the voltage applied to the control terminal of the path switch, the number of high-voltage switches installed in the discharge circuit can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] Overall configuration diagram of the control system according to the first embodiment. [Figure 2] A diagram showing the control circuit and its peripheral configuration. [Figure 3] A diagram illustrating the configuration of a signal processing circuit. [Figure 4]A flowchart illustrating the procedure performed by the switch control unit. [Figure 5] A time chart showing an example of the operation in which a smoothing capacitor discharges. [Figure 6] A diagram illustrating the configuration of a signal processing circuit according to the second embodiment. [Figure 7] A diagram illustrating the configuration of a signal processing circuit according to the third embodiment. [Figure 8] A flowchart illustrating the operation procedure of a signal processing circuit. [Modes for carrying out the invention]

[0010] Multiple embodiments will be described with reference to the drawings. In multiple embodiments, functionally and / or structurally corresponding and / or related parts may be given the same reference numeral, or reference numerals that differ by hundreds or more digits. For corresponding and / or related parts, refer to the descriptions of other embodiments.

[0011] <First Embodiment> A first embodiment of the discharge circuit described herein will be described below with reference to the drawings. The discharge circuit according to this embodiment is applied to a control system equipped with an inverter. In this embodiment, the control system is installed in an electric vehicle such as an electric car or a hybrid vehicle.

[0012] As shown in Figure 1, the control system 100 includes a rotating electric machine 10 and an inverter 15. In this embodiment, the rotating electric machine 10 is a synchronous machine, more specifically, a permanent magnet synchronous machine. The rotating electric machine 10 has armature windings 11 for three phases. Each phase armature winding 11 is connected in a star configuration and is positioned with an electrical angle offset of 120°. The rotating electric machine 10 is a vehicle-mounted main machine. Although not shown in the figure, the rotor of the rotating electric machine 10 is capable of transmitting power to the drive wheels.

[0013] The inverter 15 includes a switching device section 20. The switching device section 20 includes three sets of series-connected bodies of an upper arm switch SWH and a lower arm switch SWL. In each phase, the first end of the armature winding 11 is connected to the connection point of the upper and lower arm switches SWH and SWL. The second ends of the armature windings 11 of each phase are connected at the neutral point. In this embodiment, as each switch SWH and SWL, a voltage-controlled semiconductor switching element is used, and more specifically, an IGBT is used. In this case, in each switch SWH and SWL, the high-potential side terminal is the collector, the low-potential side terminal is the emitter, and the control terminal is the gate. Freewheeling diodes, i.e., upper and lower arm diodes DH and DL, are connected in anti-parallel to the upper and lower arm switches SWH and SWL.

[0014] The positive terminal of the high-voltage power supply 30 is connected to the collector of each upper arm switch SWH via a high-potential side electrical path 22H. The negative terminal of the high-voltage power supply 30 is connected to the emitter of each lower arm switch SWL via a low-potential side electrical path 22L. In this embodiment, the high-voltage power supply 30 is a secondary battery such as a lithium-ion battery, and its output voltage (rated voltage) is, for example, 100 V or more.

[0015] A first cutoff switch 23a is provided in the high-potential side electrical path 22H, and a second cutoff switch 23b is provided in the low-potential side electrical path 22L. Each switch 23a and 23b is, for example, a relay or a semiconductor switching element. In this embodiment, each cutoff switch 23a and 23b is driven by a control circuit 50. Note that each switch 23a and 23b may be driven by an upper ECU (not shown). The upper ECU is a control device superior to the control circuit 50.

[0016] The inverter 15 includes a smoothing capacitor 24. The first terminal of the smoothing capacitor 24 is connected to the side of the switching device unit 20 closer to the first cutoff switch 23a in the high-potential-side electrical path 22H. The second terminal of the smoothing capacitor 24 is connected to the side of the switching device unit 20 closer to the second cutoff switch 23b in the low-potential-side electrical path 22L.

[0017] The control system 100 includes an in-vehicle electrical device 25. The in-vehicle electrical device 25 is, for example, an electric compressor and a DCDC converter. The electric compressor constitutes an in-vehicle air conditioner and is driven by being supplied with power from the high-voltage power source 30 to circulate the refrigerant in the in-vehicle refrigeration cycle. The DCDC converter steps down the output voltage of the high-voltage power source 30 and supplies it to an in-vehicle low-voltage load. The low-voltage load includes the low-voltage power source 31 shown in FIG. 2. In the present embodiment, the low-voltage power source 31 is a secondary battery having an output voltage (rated voltage) lower than the output voltage (rated voltage) of the high-voltage power source 30 (for example, 12V), and is, for example, a lead-acid battery.

[0018] Subsequently, the configuration of the control circuit 50 will be described using FIG. 2. The control circuit 50 includes a microcomputer 51 and a power supply circuit 52. The microcomputer 51 and the power supply circuit 52 are provided in the low-voltage region of the control circuit 50. The positive terminal of the low-voltage power source 31 is connected to the power supply circuit 52. A ground as a grounding portion is connected to the negative terminal of the low-voltage power source 31. The power supply circuit 52 generates a power supply voltage VB (for example, 6V) by stepping down the voltage of the low-voltage power source 31.

[0019] The microcomputer 51 is made operable by being supplied with the power supply voltage VB. The microcomputer 51 includes a CPU and other peripheral circuits. The peripheral circuits include an input / output unit for exchanging signals with the outside and an AD conversion unit.

[0020] The control system 100 includes a voltage sensor 26, an angle sensor 27, a start switch 28, and a power switch 29. The voltage sensor 26 detects the terminal voltage VH of the smoothing capacitor 24. The angle sensor 27 detects the electrical angle of the rotor of the rotating electric machine 10. The values ​​detected by the voltage sensor 26 and the angle sensor 27 are input to the microcontroller 51.

[0021] The start switch 28 is, for example, an ignition switch or a push-button start switch, and is operated by the vehicle user. When the higher-level ECU determines that the start switch 28 has been switched to the ON state, it switches the power switch 29 to the ON state. This starts the supply of power from the low-voltage power supply 31 to the power supply circuit 52. On the other hand, when the higher-level ECU determines that the start switch 28 has been switched to the OFF state, it switches the power switch 29 to the OFF state. This stops the supply of power from the low-voltage power supply 31 to the power supply circuit 52. A signal indicating whether the start switch 28 is ON or OFF is input to the microcontroller 51. Based on the signal indicating the state of the start switch 28, the microcontroller 51 controls the first and second cutoff switches 23a and 23b.

[0022] The microcontroller 51 generates switching commands for the upper and lower arm switches SWH and SWL to control the controlled quantity of the rotating electric machine 10 to a commanded value. The controlled quantity is, for example, torque. The microcontroller 51 generates switching commands based on the detected values ​​of the voltage sensor 26 and the angle sensor 27. The switching command is either an ON command that instructs the switch to be turned ON, or an OFF command that instructs the switch to be turned OFF. The microcontroller 51 generates switching commands such that the upper arm switch SWH and the lower arm switch SWL are alternately turned ON in each phase.

[0023] The control circuit 50 includes an isolated power supply 60, an upper arm driver 61, and a lower arm driver 62. In this embodiment, the upper arm driver 61 is provided individually for each phase upper arm switch SWH, and the lower arm driver 62 is provided individually for each phase lower arm switch SWL. Therefore, a total of six drivers 61 and 62 are provided.

[0024] The isolated power supply 60 generates an upper arm drive voltage VdH to supply to the upper arm driver 61 and a lower arm drive voltage VdL to supply to the lower arm driver 62, based on the power supply voltage VB supplied from the power supply circuit 52. The isolated power supply 60 and each driver 61, 62 are provided in the control circuit 50, straddling the boundary between the low-voltage region and the high-voltage region. The high-voltage region is electrically isolated from the low-voltage region.

[0025] For example, the isolated power supply 60 includes an upper arm isolated power supply provided individually for each of the three phases of upper arm drivers 61, and a lower arm isolated power supply common to the three phases of lower arm drivers 62. The lower arm isolated power supply may also be provided individually for each of the three phases of lower arm drivers 62.

[0026] Each driver 61, 62 receives a switching command output from the microcontroller 51. Based on the input switching command, each driver 61, 62 turns the corresponding switches SWH and SWL on or off. Specifically, each driver 61, 62 includes an isolation transmission section provided in the low-voltage and high-voltage regions, straddling the boundary between the low-voltage and high-voltage regions, and a drive section provided in the high-voltage region. The high-voltage region side of the drive section and isolation transmission section of each driver 61, 62 is configured to operate when the drive voltages VdH and VdL of the isolation power supply 60 are supplied. The low-voltage region side of the isolation transmission section of each driver 61, 62 is configured to operate when the power supply voltage VB is supplied.

[0027] In each driver 61, 62, the isolated transmission unit electrically isolates the low-voltage region from the high-voltage region while transmitting the switching command from the microcontroller 51 to the drive unit. The isolated transmission unit of each driver 61, 62 is, for example, a photocoupler, a photoMOS relay, or a magnetic coupler.

[0028] The drive unit of each driver 61, 62 supplies a charging current to the gate of the corresponding switch SWH, SWL when the switching command transmitted by the isolation transmission unit is an ON command. This causes the gate voltage of the corresponding switch SWH, SWL to be equal to or greater than the threshold voltage Vth, and the corresponding switch SWH, SWL is turned ON. On the other hand, the drive unit of each driver 61, 62 flows a discharge current from the gate to the emitter side of the corresponding switch SWH, SWL when the input switching command is an OFF command. This causes the gate voltage of the corresponding switch SWH, SWL to be less than the threshold voltage Vth, and the corresponding switch SWH, SWL is turned OFF.

[0029] The microcontroller 51 determines whether or not an abnormality has occurred in the control circuit 50. In this embodiment, the microcontroller 51 determines whether or not a power failure abnormality has occurred. Power failure abnormalities include abnormalities in which power cannot be supplied from the low-voltage power supply 31 to the power supply circuit 52, and abnormalities in which power cannot be supplied from the power supply circuit 52 to the microcontroller 51. Power failure abnormalities occur, for example, when an abnormality occurs in the power supply circuit 52, or when the electrical path from the low-voltage power supply 31 to the microcontroller 51 is broken. For example, the microcontroller 51 determines that a power failure abnormality has occurred when the input power supply voltage VB is lower than a predetermined value. Note that power failure abnormalities can occur, for example, due to a vehicle collision.

[0030] When the microcontroller 51 determines that a power failure has occurred, it switches off the respective cutoff switches 23a and 23b and switches the discharge command CmdAD from logic H to logic L. The discharge command CmdAD is a signal used to communicate that a power failure has occurred. Specifically, a logic H discharge command CmdAD communicates that no power failure has occurred, and a logic L discharge command CmdAD communicates that a power failure has occurred. The discharge command CmdAD is input to a signal processing circuit 70 (corresponding to the "discharge circuit") located in the high-voltage region of the control circuit 50. When a logic H discharge command CmdAD is input to the signal processing circuit 70, it does not perform any control to discharge the smoothing capacitor 24. When a logic L discharge command CmdAD is input to the signal processing circuit 70, it performs control to discharge the smoothing capacitor 24. The control performed by the signal processing circuit 70 will be described later.

[0031] The control circuit 50 includes a command transmission unit 63. The command transmission unit 63 is located in both the low-voltage and high-voltage regions, straddling the boundary between the two regions. The command transmission unit 63 electrically isolates the low-voltage and high-voltage regions while transmitting the discharge command CmdAD output from the microcontroller 51 to the signal processing circuit 70 located in the high-voltage region. The command transmission unit 63 is, for example, a photocoupler, a photoMOS relay, or a magnetic coupler. In this embodiment, the high-voltage region side of the command transmission unit 63 is configured to operate when the lower arm drive voltage VdL of the isolated power supply 60 is supplied. The low-voltage region side of the command transmission unit 63 is configured to operate when the power supply voltage VB is supplied.

[0032] Next, we will explain in detail the configuration of the signal processing circuit 70.

[0033] As shown in Figure 3, the signal processing circuit 70 includes a connection path 71, a path resistor 72, and a first path switch Q1. The first end of the connection path 71 is connected to the first end of the smoothing capacitor 24. The second end of the connection path 71 is connected to the emitter of the lower arm switch SWL, which serves as the ground. The series connection of the path resistor 72 and the first path switch Q1 is provided in the connection path 71.

[0034] Here, the first path switch Q1 is a high-voltage switch capable of withstanding the voltage VH of the smoothing capacitor 24. In this embodiment, an N-channel MOSFET is used as the first path switch Q1. More specifically, the first path switch Q1 is an N-channel MOSFET made of SiC (silicon carbide) material. In this case, the high-potential terminal is the drain, the low-potential terminal is the source, and the control terminal is the gate. The withstand voltage of the first path switch Q1 is the upper limit of the voltage that can be applied between the drain and source of the first path switch Q1 (for example, the absolute maximum rating). For example, the withstand voltage between the drain and source of the first path switch Q1 is set higher than the maximum value of the voltage value assumed to be the voltage VH of the smoothing capacitor 24, and is several hundred volts. Specifically, with Vds1 being the withstand voltage between the drain and source in the first path switch Q1, the following conditions apply: 100[V]≦Vds1≦1000[V], 100[V]≦Vds1≦200[V], 200[V]≦Vds1≦300[V], 300[V]≦Vds1≦400[V], 400[V]≦Vds1≦500[V], 500[V]≦Vds1≦600[V], 600[V]≦Vds1≦700[V], 700[V]≦Vds1≦800[V], 800[V]≦Vds1≦900[V], or 900[V]≦Vds1≦1000[V].

[0035] In Figure 3, the first end of the path resistor 72 is connected to the first end of the smoothing capacitor 24. The second end of the path resistor 72 is connected to the drain of the first path switch Q1. In other words, the first path switch Q1 is located at a lower potential than the path resistor 72 in the connection path 71. Alternatively, the first path switch Q1 may be located at a higher potential than the path resistor 72 in the connection path 71.

[0036] Incidentally, if high-voltage switches are used in the signal processing circuit 70 in addition to the first path switch Q1, there is a concern that the number of high-voltage switches to be installed will increase. In this case, there is a concern that the cost of the control circuit 50 will increase due to the large number of high-voltage switches installed in the signal processing circuit 70.

[0037] Therefore, in this embodiment, the signal processing circuit 70 is configured to minimize the use of high-voltage switches. The characteristic configuration of the signal processing circuit 70 will be described below.

[0038] The signal processing circuit 70 includes a parallel path 73 and a voltage divider 74 as a configuration for turning on the first path switch Q1. The first end of the parallel path 73 is connected to the side of the connection path 71 that is at a higher potential than the series connection of the path resistor 72 and the first path switch Q1. The second end of the parallel path 73 is connected to the emitter of the lower arm switch SWL.

[0039] The voltage divider 74 is located in the parallel path 73. The voltage divider 74 divides the voltage VH of the smoothing capacitor 24. The voltage divided by the voltage divider 74 is input to the gate of the first path switch Q1. Specifically, the voltage divider 74 comprises a voltage divider resistor 74a and a Zener diode 74b. The voltage divider resistor 74a corresponds to the "first voltage divider element," and the Zener diode 74b corresponds to the "second voltage divider element."

[0040] The Zener diode 74b is positioned on the lower potential side relative to the voltage divider resistor 74a in the parallel path 73. Specifically, the first end of the voltage divider resistor 74a is connected to the first end of the smoothing capacitor 24. The second end of the voltage divider resistor 74a is connected to the cathode of the Zener diode 74b and the gate of the first path switch Q1. The anode of the Zener diode 74b is connected to the emitter of the lower arm switch SWL. In this case, the voltage VH across the smoothing capacitor 24 is divided by the voltage divider resistor 74a and the Zener diode 74b, generating a divided voltage Vg. The divided voltage Vg generated by the voltage divider 74 is input to the gate of the first path switch Q1.

[0041] The voltage divider unit 74 generates a divided voltage Vg that can turn on the first path switch Q1. In this embodiment, the divided voltage Vg is a Zener voltage generated by the Zener diode 74b. The Zener voltage of the Zener diode 74b is set so that the gate-source voltage of the path switch Q1 is higher than the threshold voltage Vth. The divided voltage Vg generated by the voltage divider unit 74 is input to the gate of the first path switch Q1, thereby turning on the first path switch Q1. By using the Zener diode 74b in the voltage divider unit 74, a configuration suitable for outputting a constant voltage as the divided voltage Vg can be realized. Therefore, the voltage required to turn on the first path switch Q1 can be accurately secured.

[0042] The source voltage of the first path switch Q1 in connection path 71 is lower than the voltage VH of the smoothing capacitor 24 due to the voltage drop across the path resistor 72 and the first path switch Q1. In this case, a low-voltage switch can be used on the side of the connection path 71 that is lower than the series connection of the path resistor 72 and the first path switch Q1.

[0043] Therefore, in this embodiment, the signal processing circuit 70 is equipped with a second path switch Q2. The second path switch Q2 is a switch for controlling the discharge of the smoothing capacitor 24. The second path switch Q2 is located on the lower potential side of the connection path 71 than the series connection of the path resistor 72 and the first path switch Q1. In this embodiment, an N-channel MOSFET is used as the second path switch Q2. More specifically, the second path switch Q2 is an N-channel MOSFET made of a Si (silicon)-based material. The drain of the second path switch Q2 is connected to the source of the first path switch Q1. The source of the second path switch Q2 is connected to the emitter of the lower arm switch SWL. The withstand voltage between the drain and source of the second path switch Q2 is a voltage lower than the withstand voltage Vds1 of the first path switch Q1. For example, the withstand voltage between the drain and source of the second path switch Q2 is a value lower than 100[V].

[0044] The signal processing circuit 70 includes a switch control unit 75 and an auxiliary power supply unit 76 for driving the second path switch Q2. The auxiliary power supply unit 76 includes an auxiliary diode 76a and a backup capacitor 76b. The anode of the auxiliary diode 76a is connected to the connection path 71 between the source of the first path switch Q1 and the drain of the second path switch Q2. The cathode of the auxiliary diode 76a is connected to the first terminal of the backup capacitor 76b. The second terminal of the backup capacitor 76b is connected to the emitter of the lower arm switch SWL. In other words, the series connection of the auxiliary diode 76a and the backup capacitor 76b is connected in parallel to the second path switch Q2.

[0045] When the first path switch Q1 is ON and the second path switch Q2 is OFF, a charging path is formed that includes the smoothing capacitor 24, the path resistor 72, the first path switch Q1, the auxiliary diode 76a, and the backup capacitor 76b. In this case, power is supplied from the smoothing capacitor 24 to the backup capacitor 76b via the formed charging path, and the backup capacitor 76b is charged.

[0046] The rated voltage of the backup capacitor 76b is set higher than the lower limit of the operating voltage of the switch control unit 75. The switch control unit 75 is made operational by being powered by the backup capacitor 76b.

[0047] The switch control unit 75 controls the discharge of the smoothing capacitor 24 by driving the second path switch Q2. The discharge control of the smoothing capacitor 24 will be described below. Some or all of the functions of the switch control unit 75 may be configured in hardware, for example, by one or more integrated circuits (ICs). Also, some or all of the functions of the switch control unit 75 may be configured by software recorded on a non-transitional physical recording medium and a computer that executes it. Some or all of the functions of the switch control unit 75 may be configured by both hardware and software.

[0048] The switch control unit 75 receives the discharge command CmdAD output from the command transmission unit 63. When the switch control unit 75 receives the logical low discharge command CmdAD, it generates an ON command for the second path switch Q2. On the other hand, when the switch control unit 75 receives the logical high discharge command CmdAD, it generates an OFF command for the second path switch Q2. The ON or OFF command generated by the switch control unit 75 is input to the gate of the second path switch Q2. As a result, the second path switch Q2 is set to an ON state or an OFF state based on the command generated by the switch control unit 75.

[0049] When the second path switch Q2 is turned ON, a discharge path is formed that includes the smoothing capacitor 24, the path resistor 72, the first path switch Q1, and the second path switch Q2. Current flows through the formed discharge path, and the smoothing capacitor 24 is discharged.

[0050] Furthermore, the voltage divider 74 is configured to prevent excessive discharge of the smoothing capacitor 24 via the parallel path 73. Specifically, the resistance value of the voltage divider resistor 74a is set to be greater than the resistance value of the path resistor 72.

[0051] Figure 4 shows the discharge control process performed by the switch control unit 75. This control is repeatedly performed at a predetermined control cycle.

[0052] In step S10, the discharge command CmdAD is obtained from the command transmission unit 63. In step S11, it is determined whether the logic of the obtained discharge command CmdAD is L or not.

[0053] If a negative result is obtained in step S11, the process proceeds to step S12. In step S12, an off command for the second path switch Q2 is generated. In this case, the second path switch Q2 is turned off. This allows the backup capacitor 76b to be charged.

[0054] On the other hand, if a positive determination is made in step S11, the process proceeds to step S13. In step S13, an ON command for the second path switch Q2 is generated. In this case, each path switch Q1 and Q2 is turned ON, and the smoothing capacitor 24 is discharged.

[0055] Figure 5 shows an example of discharge control performed by the switch control unit 75. In Figure 5, (a) shows the logic of the discharge command CmdAD, (b) shows the driving state of the first path switch Q1, (c) shows the driving state of the second path switch Q2, (d) shows the change in the voltage VH of the smoothing capacitor 24, and (e) shows the change in the voltage VL of the backup capacitor 76b. Here, we will explain assuming a situation where, after the control system 100 is started, the smoothing capacitor 24 has finished charging and the divided voltage Vg of the voltage divider unit 74 is input to the gate of the first path switch Q1.

[0056] Before time t1, the gate-source voltage of the first path switch Q1 is higher than the threshold voltage Vth, so the first path switch Q1 is ON. Also, the second path switch Q2 is OFF. For example, if a normally-off switch is used as the second path switch Q2, the second path switch Q2 is OFF before time t1. When the first path switch Q1 is ON and the second path switch Q2 is OFF, a charging path is formed for the backup capacitor 76b, and the backup capacitor 76b is charged. As a result, the voltage VL of the backup capacitor 76b rises.

[0057] At time t1, the voltage VL across the backup capacitor 76b reaches a first predetermined value VLa. The first predetermined value VLa is higher than the lower limit voltage at which the switch control unit 75 can operate, for example, 5V. After the voltage VL across the backup capacitor 76b exceeds the first predetermined value VLa, the switch control unit 75 becomes operational. In this case, the switch control unit 75 generates an off command for the second path switch Q2 based on the input of a logic H discharge command CmdAD. As a result, the off state of the second path switch Q2 is maintained.

[0058] At time t2, the voltage VL of the backup capacitor 76b reaches the second predetermined value VLb. The second predetermined value VLb is higher than the first predetermined value VLa. During the period from time t2 to time t3, the first path switch Q1 is repeatedly switched on and off. This is because the source voltage of the first path switch Q1 fluctuates with the charging and discharging of the backup capacitor 76b. When the gate-source voltage of the first path switch Q1 is lower than the threshold voltage Vth, the first path switch Q1 is in the off state. When the gate-source voltage of the first path switch Q1 is higher than the threshold voltage Vth, the first path switch Q1 is in the on state.

[0059] At time t3, a power failure occurs, and the logic of the discharge command CmdAD is switched from H to L. In this case, the switch control unit 75 generates an ON command for the second path switch Q2. As a result, each path switch Q1 and Q2 are turned ON, and the smoothing capacitor 24 is discharged via the connection path 71. Therefore, the voltage VH of the smoothing capacitor 24 decreases after time t3.

[0060] In this embodiment, the voltage VH of the smoothing capacitor 24 is divided by the voltage divider 74, and the divided voltage Vg is input to the gate of the first path switch Q1. In this case, it is possible to step down the voltage of the smoothing capacitor 24 without using a high-voltage switch, and it is possible to secure a voltage necessary to turn on the first path switch Q1. This makes it possible to secure a discharge path for the smoothing capacitor 24 while avoiding the addition of a high-voltage switch to the signal processing circuit 70. Therefore, compared to a comparative example in which a high-voltage switch is used to generate the voltage applied to the gate of the first path switch Q1, the number of high-voltage switches installed in the signal processing circuit 70 can be reduced.

[0061] The switch control unit 75, powered by the auxiliary power supply unit 76, drives the second path switch Q2, enabling discharge control of the smoothing capacitor 24. Specifically, when the first path switch Q1 is turned ON and the second path switch Q2 is turned OFF, a charging path is formed including the smoothing capacitor 24, the path resistor 72, the first path switch Q1, and the auxiliary power supply unit 76. This enables power supply from the smoothing capacitor 24 to the auxiliary power supply unit 76. On the other hand, when the first and second path switches Q1 and Q2 are turned ON, the smoothing capacitor 24 is discharged via the connection path 71. Here, the voltage applied to the second path switch Q2 and the auxiliary power supply unit 76 is stepped down by the series connection of the path resistor 72 and the first path switch Q1, and is a voltage lower than the voltage VH of the smoothing capacitor 24. Therefore, it is possible to use lower voltage components for the second path switch Q2 and the auxiliary power supply unit 76 rather than high voltage components that can withstand the voltage of the smoothing capacitor 24. Therefore, in the signal processing circuit 70, it is possible to realize a configuration that allows for discharge control of the smoothing capacitor 24 while avoiding the need to add high-voltage components.

[0062] Incidentally, if a power failure occurs, the drive voltages VdH and VdL output from the isolated power supply 60 may decrease. In this case, the upper and lower arm switches SWH and SWL for the three phases may be turned off (hereinafter referred to as the shutdown state). In the shutdown state, if a back electromotive force is generated in each phase armature winding 11, the line voltage of the armature winding 11 may become higher than the voltage VH of the smoothing capacitor 24.

[0063] When the armature winding 11 is shut down, if the line voltage is higher than the voltage VH of the smoothing capacitor 24, the induced current generated in the armature winding 11 flows through the closed circuit including the diodes DH, DL, the armature winding 11, and the smoothing capacitor 24. In this case, the voltage VH of the smoothing capacitor 24 rises significantly, raising concerns that at least one of the smoothing capacitor 24, the inverter 15, and the on-board electrical equipment 25 may fail.

[0064] Therefore, in this embodiment, the switch control unit 75 is configured to drive the lower arm switches SWL for each phase in addition to the second path switch Q2. The reason for enabling the switch control unit 75 to drive the lower arm switches SWL for each phase is to enable three-phase short-circuit control that turns on the lower arm switches SWL for each phase (corresponding to the "on-side switches") even when a power supply failure occurs.

[0065] Specifically, the switch control unit 75 receives the lower arm drive voltage VdL output from the isolated power supply 60 as a signal to determine whether or not a power failure abnormality has occurred. When the switch control unit 75 determines that the input lower arm drive voltage VdL has fallen below a predetermined voltage, it generates an ON command for the lower arm switch SWL of each phase. The predetermined voltage is set to a value that allows it to determine that a sufficient period of time has elapsed before the upper arm switch SWH turns off, and for example, it may be set to the same value as the threshold voltage Vth of the upper arm switch SWH or to a value less than the threshold voltage Vth. The ON command generated by the switch control unit 75 is input to the gate of the lower arm switch SWL of each phase. In this case, regardless of the switching command output from the microcontroller 51, the lower arm switch SWL of each phase is turned ON. This protects the smoothing capacitor 24, inverter 15, and on-board electrical equipment 25 in the event of a power failure abnormality.

[0066] The switch control unit 75 can perform discharge control to generate an ON command for the second path switch Q2 and three-phase short-circuit control in the event of a power failure. In this case, compared to a configuration in which only the discharge control among the two three-phase short-circuit controls can be performed by the switch control unit, there is a significant advantage in being able to operate the switch control unit 75 with the power of the auxiliary power supply unit 76.

[0067] <Modified form of the first embodiment> The switch control unit 75 may be configured to drive the upper arm switch SWH for each phase instead of the lower arm switch SWL for each phase. In this case, the switch control unit 75 can perform three-phase short-circuit control by turning on the upper arm switch SWH (corresponding to the "on-side switch") for each phase when a power failure occurs.

[0068] The switch control unit 75 does not necessarily have to be configured to drive the upper arm switch SWH or the lower arm switch SWL for each phase. In other words, in the event of a power failure, the switch control unit 75 may only be able to perform discharge control among the three-phase short-circuit control and discharge control.

[0069] The switch control unit 75 may generate on and off commands for the second path switch Q2 based on the output voltage of the isolation power supply 60 (for example, the lower arm drive voltage VdL) instead of the discharge command CmdAD. Specifically, in step S10 of Figure 4, the lower arm drive voltage VdL output from the isolation power supply 60 may be acquired. In step S11, it may be determined whether the acquired lower arm drive voltage VdL has fallen below a predetermined voltage.

[0070] <Second Embodiment> The second embodiment will now be described, focusing on the differences from the first embodiment, with reference to the drawings. In this embodiment, as shown in Figure 6, the signal processing circuit 70 includes a parallel switch 77. The parallel switch 77 is connected in parallel to the Zener diode 74b. The parallel switch 77 is a low-voltage switch, such as a semiconductor switching element or a mechanical relay. For example, an N-channel MOSFET made of Si-based material can be used as the parallel switch 77. The parallel switch 77 is controlled by the switch control unit 75.

[0071] When the parallel switch 77 is in the off state, the divided voltage Vg is set to the Zener voltage of the Zener diode 74b. In this case, the first path switch Q1 is set to the on state. On the other hand, when the parallel switch 77 is in the on state, the divided voltage Vg is set to a voltage lower than the Zener voltage (for example, 0V). In this case, the first path switch Q1 is set to the off state.

[0072] The switch control unit 75 turns the parallel switch 77 on and off at predetermined intervals so that the output voltage of the auxiliary power supply unit 76 is maintained at a level higher than a predetermined voltage (for example, a first predetermined value VLa).

[0073] For example, the switch control unit 75 has a timer function that turns the parallel switch 77 on and off based on the elapsed time since the timing of switching the parallel switch 77 on or off. Specifically, the switch control unit 75 generates an on command for the parallel switch 77 when the elapsed time since the generation of the off command for the parallel switch 77 reaches a predetermined off time. The switch control unit 75 generates an off command for the parallel switch 77 when the elapsed time since the generation of the on command for the parallel switch 77 reaches a predetermined on time. The off time and on time can be determined based on at least one of the following: the voltage of the smoothing capacitor 24 (e.g., rated voltage), the resistance value of the path resistor 72, the on resistance of the first path switch Q1, and the capacitance of the backup capacitor 76b, so as to maintain a state in which the output voltage of the auxiliary power supply unit 76 is higher than a first predetermined value VLa.

[0074] Furthermore, for example, the switch control unit 75 has a voltage monitoring function that monitors the voltage VL of the backup capacitor 76b. When the detected value of the voltage VL of the backup capacitor 76b is greater than or equal to a predetermined threshold, the switch control unit 75 generates an ON command for the parallel switch 77. On the other hand, when the detected value of the voltage VL of the backup capacitor 76b is less than the threshold, the switch control unit 75 generates an OFF command for the parallel switch 77. The threshold is higher than a first predetermined value VLa and lower than a second predetermined value VLb.

[0075] In this embodiment, the parallel switch 77 is turned on and off so that the output voltage of the auxiliary power supply unit 76 is maintained at a level higher than a first predetermined value VLa. In this case, a configuration in which power is supplied from the smoothing capacitor 24 to the auxiliary power supply unit 76 can be suitably realized compared to a configuration in which the parallel switch 77 is not provided.

[0076] For example, the switch control unit 75 can verify the operation of the auxiliary power supply unit 76 based on the change in the voltage VL of the backup capacitor 76b when the parallel switch 77 is switched on or off. Therefore, it is possible to verify the operation of the auxiliary power supply unit 76 while suppressing the occurrence of a situation in which the output voltage of the auxiliary power supply unit 76 drops excessively.

[0077] Furthermore, in a configuration where the parallel switch 77 is not provided, for example, the divided voltage Vg is constantly input to the gate of the first path switch Q1, causing the first path switch Q1 to be turned on and off as needed. In this case, the backup capacitor 76b may be overcharged. In this embodiment, however, the voltage input to the gate of the first path switch Q1 can be controlled according to the on / off state of the parallel switch 77, thereby controlling the charging of the backup capacitor 76b. As a result, it is possible to suppress the occurrence of overcharging of the backup capacitor 76b while also suppressing the occurrence of an excessive drop in the output voltage of the auxiliary power supply unit 76.

[0078] Furthermore, among the functions of the switch control unit 75, the function for controlling the second path switch Q2 and the function for controlling the parallel switch 77 (specifically, the timer function or the voltage monitoring function) may be configured as a single IC chip. In this case, it is possible to suppress an increase in the number of IC chips provided in the signal processing circuit 70. Alternatively, the function for controlling the second path switch Q2 and the function for controlling the parallel switch 77 may be configured as separate IC chips.

[0079] <Third Embodiment> The third embodiment will now be described, focusing on the differences from the first embodiment, with reference to the drawings. In this embodiment, the signal processing circuit does not include the second path switch Q2, auxiliary power supply unit 76, and switch control unit 75 described in the first embodiment.

[0080] As shown in Figure 7, the signal processing circuit 170 includes an abnormality detection unit 80, a bypass path 81, and a low-voltage side resistor 82. In this embodiment, the first path switch Q1 described in the first embodiment is referred to as "path switch Q1". The source of path switch Q1 is connected to the emitter of the lower arm switch SWL of each phase, instead of the drain of the second path switch Q2.

[0081] The bypass path 81 is located in the high-voltage region. The bypass path 81 is connected in parallel to the Zener diode 74b. In Figure 7, the first end of the bypass path 81 is connected between the second end of the voltage divider resistor 74a and the cathode of the Zener diode 74b in the parallel path 73. The second end of the bypass path 81 is connected to the anode side of the Zener diode 74b in the parallel path 73.

[0082] The abnormality detection unit 80 is located in both the low-voltage and high-voltage regions, straddling the boundary between the high-voltage and low-voltage regions. The abnormality detection unit 80 detects power failure abnormalities in the low-voltage region, such as an excessive drop in the power supply voltage VB. Figure 7 shows an example where a photocoupler is used as the abnormality detection unit 80. Note that the abnormality detection unit 80 may also be a photoMOS relay or a magnetic coupler.

[0083] The abnormality detection unit 80 includes a photodiode 80a located in the low-voltage region and a phototransistor 80b located in the high-voltage region. A series connection of the photodiode 80a and a low-voltage side resistor 82 is connected to the power supply circuit 52. Specifically, the first end of the low-voltage side resistor 82 is connected to the power supply circuit 52. The second end of the low-voltage side resistor 82 is connected to the anode of the photodiode 80a. The cathode of the photodiode 80a is connected to the ground in the low-voltage region. As a result, the power supply voltage VB is supplied to the photodiode 80a of the abnormality detection unit 80. When the power supply voltage VB is supplied normally to the photodiode 80a, the phototransistor 80b is turned ON. If the voltage supplied to the photodiode 80a drops excessively, the phototransistor 80b is turned OFF.

[0084] The phototransistor 80b is located in the bypass path 81. Specifically, the phototransistor 80b is located in the bypass path 81 such that its collector is at the first end of the bypass path 81 and its emitter is at the second end of the bypass path 81. When the phototransistor 80b is ON, the bypass path 81 is open. When the phototransistor 80b is OFF, the bypass path 81 is closed.

[0085] Figure 8 shows the operation sequence of the signal processing circuit 170. This operation is performed after the user turns on the start switch 28.

[0086] In step S20, the abnormality detection unit 80 detects a power failure abnormality. The state in which the power supply voltage VB is supplied to the photodiode 80a of the abnormality detection unit 80 corresponds to a normal state. The state in which the voltage supplied to the photodiode 80a of the abnormality detection unit 80 drops excessively corresponds to the occurrence of a power failure abnormality.

[0087] If a negative result is obtained in step S20, the phototransistor 80b of the abnormality detection unit 80 is turned ON, and the bypass path 81 is opened (step S21). In this case, the divided voltage Vg is set to a voltage lower than the Zener voltage (for example, 0V), and the path switch Q1 is turned OFF (step S22). When the path switch Q1 is OFF, the discharge of the smoothing capacitor 24 is stopped. After the operation of step S22, the operation of step S20 is performed again.

[0088] If a positive result is obtained in step S20, the phototransistor 80b of the abnormality detection unit 80 is turned off, and the bypass path 81 is blocked (step S23). In this case, the voltage divider voltage Vg is set to the Zener voltage of the Zener diode 74b, and the path switch Q1 is turned on (step S24). When the path switch Q1 is turned on, the smoothing capacitor 24 is discharged.

[0089] In this embodiment, the abnormality detection unit 80 detects whether or not there is a power failure abnormality in the low-voltage region. If no power failure abnormality is detected, the bypass path 81 in the high-voltage region is electrically connected. In this case, the divided voltage Vg of the voltage divider unit 74 decreases compared to when the bypass path 81 is electrically disconnected. On the other hand, if a power failure abnormality is detected, the bypass path 81 is electrically disconnected. In this case, the divided voltage Vg of the voltage divider unit 74 increases compared to when the bypass path 81 is electrically connected. Therefore, it is possible to change the voltage applied to the gate of the path switch Q1 and turn the path switch Q1 on and off depending on whether or not there is a power failure abnormality. As a result, it is possible to realize a configuration that can control the discharge of the smoothing capacitor 24 while avoiding the need to add high-voltage components.

[0090] The abnormality detection unit 80 switches the path switch Q1 on or off. In this case, the configuration provided in the high-voltage region can be simplified compared to the first embodiment. Therefore, a configuration that enables discharge control of the smoothing capacitor 24 can be realized with a simpler configuration compared to the first embodiment.

[0091] <Other Embodiments> Furthermore, each of the above embodiments may be implemented with the following modifications.

[0092] The voltage divider may include a resistor instead of the Zener diode 74b. In other words, the voltage divider may be a series connection of multiple voltage divider resistors. Even in this case, a configuration can be achieved in which the divided voltage of the voltage divider is input to the gate of the first path switch Q1, thereby turning on the first path switch Q1.

[0093] The second-path switch Q2 may be an IGBT instead of an N-channel MOSFET made of a silicon-based material. In this case as well, the second-path switch Q2 can be a low-voltage switch. For example, the collector-emitter breakdown voltage of the second-path switch Q2 can be as low as a few tens of volts.

[0094] In the configuration shown in Figure 1, a boost converter may be provided between the smoothing capacitor 24 and each of the cutoff switches 23a and 23b.

[0095] The switches that make up the inverter are not limited to IGBTs; for example, an N-channel MOSFET with a built-in body diode may also be used.

[0096] The rotating electric machine may have three or more phases. Furthermore, the rotating electric machine is not limited to permanent magnet synchronous machines, but may also be, for example, a wound-field synchronous machine. Furthermore, the rotating electric machine is not limited to synchronous machines, but may also be, for example, an induction machine. In addition, the rotating electric machine is not limited to those used as vehicle main engines, but may also be used for other purposes such as electric motors that make up electric power steering systems or electric compressors for air conditioning.

[0097] The mobile device on which the control system is mounted is not limited to a vehicle; for example, it could be an aircraft or a ship. Furthermore, the mounting location of the control system is not limited to a mobile device; it could be a stationary device.

[0098] The smoothing capacitor is not limited to that provided by the inverter 15. For example, it may be provided by a power conversion circuit such as a DC-DC converter and a rectifier circuit. In this case as well, it is possible to configure a signal processing circuit that discharges the smoothing capacitor. [Explanation of Symbols]

[0099] 24...Smoothing capacitor, 70, 170...Signal processing circuit (discharge circuit), 71...Connection path, 72...Path resistor, 73...Parallel path, 74...Voltage divider, Q1, Q2...First and second path switches.

Claims

1. In a discharge circuit (70, 170) for discharging a smoothing capacitor (24), A connection path (71) connecting the smoothing capacitor and the ground portion which serves as the discharge destination for the smoothing capacitor, A series connection of a path resistor (72) and a path switch (Q1) provided in the aforementioned connection path, A parallel path (73) connects the connection path to the ground portion, with the side of the connection path that is at a higher potential than the series connection of the path resistor and the path switch. A voltage divider (74) is provided in the parallel path and divides the voltage of the smoothing capacitor, Equipped with, A discharge circuit for a smoothing capacitor, to which the divided voltage generated by the voltage divider is input to the control terminal of the path switch.

2. The aforementioned route switch is a first route switch, Of the aforementioned connection paths, a second path switch (Q2) is provided on the lower potential side than the series connection of the path resistor and the first path switch, An auxiliary power supply unit (76) connected in parallel to the second path switch, A switch control unit (75) which is powered by the auxiliary power supply unit and controls the on / off state of the second path switch, A discharge circuit for a smoothing capacitor according to claim 1, comprising:

3. The aforementioned pressure dividing section is A first voltage dividing element (74a) is provided in the parallel path, Of the parallel paths, a second voltage divider element (74b) is provided on the lower potential side than the first voltage divider element, It has, The system includes a parallel switch (77) connected in parallel to the second voltage dividing element, The discharge circuit for a smoothing capacitor according to claim 2, wherein the switch control unit turns the parallel switch on and off at predetermined intervals so that the output voltage of the auxiliary power supply unit is maintained at a state higher than a predetermined voltage.

4. A rotating electric machine (10) having multiple phase armature windings, An inverter (15) having a series connection of upper arm switches (SWH) and lower arm switches (SWL) for each phase, wherein in each phase, the low-potential terminal of the upper arm switch and the high-potential terminal of the lower arm switch are connected to the armature winding, In a discharge circuit for a smoothing capacitor applied to a system (100) comprising the following: The smoothing capacitor connects the high-potential terminal of the upper arm switch for each phase to the low-potential terminal of the lower arm switch for each phase. When a signal indicating that an abnormality has occurred in the system is input to the switch control unit, Discharge control that turns on the second path switch, Short-circuit control that turns on the ON-side switches of each phase, with either the upper arm switch or the lower arm switch as the ON-side switch, A discharge circuit for a smoothing capacitor according to claim 2 or 3, which is capable of performing the following.

5. The aforementioned pressure dividing section is A first voltage dividing element (74a) is provided in the parallel path, Of the parallel paths, a second voltage divider element (74b) is provided on the lower potential side than the first voltage divider element, It has, The smoothing capacitor, the connection path, the path resistor, the path switch, the parallel path, the first voltage divider element, and the second voltage divider element are provided in the high-voltage region. An abnormality detection unit (80) is provided in the low-voltage region and the high-voltage region, straddling the boundary between the high-voltage region and the low-voltage region which is electrically insulated from the high-voltage region. A bypass path (81) provided in the high-voltage region and connected in parallel to the second voltage divider element, Equipped with, The abnormality detection unit, An abnormality in the low-pressure region is detected, A discharge circuit for a smoothing capacitor according to claim 1, wherein the bypass path is electrically connected when the abnormality is not detected, and the bypass path is electrically disconnected when the abnormality is detected.

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