JP2018152973A - Power conversion circuit, motor control device and power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge electric charge remaining in a capacitor without damaging a switching element even when a power supply and a power conversion circuit are disconnected from each other.SOLUTION: A power conversion circuit 60 comprises: an inverter 40; a driver circuit D that drives the inverter 40; a line L3 connecting between a line L1 and a power supply input part of the driver circuit D; a normally-on type power supply relay T7 provided on the line L3; and a smoothing capacitor C1. The power supply relay T7 is turned on and thereby, the driver circuit D is driven by residual electric charge of the smoothing capacitor C1 when supply of power to the driver circuit D is blocked. The driver circuit D controls an upper-stage switching element T1 and a lower-stage switching element T6 of the inverter 40 to be in an ON state, and controls the switching elements T2, T3, T4 and T5 to be in an off state.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power conversion circuit, and a motor control device and a power steering device using the power conversion circuit. Specifically, the present invention relates to a power conversion circuit having a discharge path for residual charges of a smoothing capacitor, and a motor control device and a power steering device using the power conversion circuit.

  A power conversion circuit including an inverter is used for controlling a motor, for example. The power conversion circuit converts DC power from the power source into AC and supplies it to the motor. A smoothing capacitor is provided between the inverter and the power source. There are cases where the power supply and the power conversion circuit are interrupted due to various factors, such as when the power supply is removed for reasons of repair or when the power cable is disconnected due to an external impact. When the power source and the power conversion circuit are interrupted, it is preferable to quickly discharge the charge of the smoothing capacitor.

  Japanese Patent Laying-Open No. 2008-094342 (Patent Document 1) discloses a technique for discharging electric charge accumulated in a capacitor for absorbing current ripple without using a dedicated circuit. In Japanese Patent Application Laid-Open No. 2008-094342, when the power is turned off, the drive control unit controls the motor drive circuit to discharge the capacitor charge through a part of the current path necessary for the rotation of the motor.

  In Japanese Patent Laying-Open No. 2006-152634 (Patent Document 2), a resistor is provided for reducing the inrush current to the smoothing capacitor. In Japanese Patent Application Laid-Open No. 2006-152634, the residual charge of the smoothing capacitor is discharged by flowing it through a resistor for reducing inrush current.

  In Japanese Patent Application Laid-Open No. 2011-239608 (Patent Document 3), the power conversion device includes a backup power source separately from the power source. The power converter is configured to discharge the electric charge of the smoothing capacitor by controlling the switching element with a backup power source.

JP 2008-094342 A Japanese Patent Laid-Open No. 2006-152634 JP 2011-239608 A

  With the configuration described in Japanese Patent Application Laid-Open No. 2008-094342, the capacitor charge can be discharged without using a dedicated circuit. However, in the configuration described in Japanese Patent Application Laid-Open No. 2008-094342, the drive control unit cannot be controlled when the power source is cut off, such as when the in-vehicle battery is removed. If a situation in which the drive control unit cannot be controlled occurs, the motor drive circuit cannot be controlled, so that the MOS-FET element cannot be turned on. If the MOS-FET element cannot be turned on, the charge of the capacitor cannot be passed through the current path necessary for the rotation of the motor.

  In JP-A-2006-152634 (Patent Document 2), when the residual charge of the smoothing capacitor is discharged, the discharge path of the residual charge is secured by controlling the upper arm and the lower arm of the DC-AC converter. . However, in a state where the power supply is stopped and the DC-AC converter cannot be controlled, it is not possible to secure a discharge path for residual charges.

  In Japanese Patent Laid-Open No. 2011-239608 (Patent Document 3), a separate backup power source is required to discharge the residual charge of the smoothing capacitor.

  The present application is intended to discharge the electric charge remaining in the capacitor even when the power supply and the power conversion circuit are interrupted, such as when the power supply cable is disconnected due to an external impact when the power supply is removed. Let it be an issue.

  An electric power conversion circuit according to an embodiment of the present invention drives an inverter having a plurality of bridge circuits connected in parallel between a first line to which a power supply voltage is applied and a second line. A driver circuit, a third line connecting the first line and the driver circuit, a normally-on type power relay provided on the third line, and between the power source and the inverter And a smoothing capacitor connected between the first line and the second line. Each of the plurality of bridge circuits includes an upper switching element connected to the first line, and a lower switching element connected in series to the upper switching element and connected to the second line. When the power supply from the power supply to the driver circuit is cut off, the power supply relay is turned on, so that the driver circuit is driven by the residual charge of the smoothing capacitor. The driver circuit controls at least one of the upper switching elements of each bridge circuit to an on state and controls at least one to an off state. The driver circuit controls a lower switching element connected in series with an upper switching element controlled in an on state to an off state, and a lower switching element connected in series with a switching element controlled in an off state. One of the switching elements is controlled to be on.

  According to the power conversion circuit of the embodiment of the present invention, even if the power supply and the power conversion circuit are shut off, the charge remaining in the capacitor is discharged without damaging the switching element of the inverter. be able to.

It is a block diagram which shows the structure of the power converter circuit which concerns on 1st Embodiment. It is a figure which shows the path | route by which the residual charge of an electrolytic capacitor is discharged at the time of power supply interruption | blocking in the power converter circuit which concerns on 1st Embodiment. It is a figure which shows the path | route by which the residual charge of an electrolytic capacitor is discharged at the time of power supply interruption | blocking in the power converter circuit which concerns on 2nd Embodiment. It is a figure which shows the path | route by which the residual charge of an electrolytic capacitor is discharged at the time of power interruption in the power converter circuit which concerns on 3rd Embodiment. It is an equivalent circuit diagram when an electrolytic capacitor is connected to a switching element. It is a graph which shows the example of the current waveform which flows when an electrolytic capacitor is connected to a switching element. It is an equivalent circuit diagram when an electrolytic capacitor is connected to a motor via a switching element. It is a graph which shows the example of the electric current waveform which flows when an electrolytic capacitor is connected to a motor via a switching element. It is a block diagram which shows the structure of a power steering apparatus.

  A power conversion circuit including an inverter is used for controlling a motor, for example. A smoothing capacitor is provided between the inverter and the power source. The smoothing capacitor is composed of, for example, an electrolytic capacitor. The smoothing capacitor smoothes the DC voltage supplied from the power source. The voltage supplied from the power source to the inverter is stabilized by the smoothing capacitor.

  Here, there are cases where the power source and the power conversion circuit are interrupted due to various factors, such as when the power source is removed for reasons of repair or when the power cable is disconnected due to an external impact. When the power source and the power conversion circuit are interrupted, it is preferable to quickly discharge the charge of the smoothing capacitor.

  The inventor of the present application studied discharging the residual charge of the smoothing capacitor in a load supplied with power from the inverter. During this study, when the power supply was shut off, the problem was that the driver circuit of the inverter could not be controlled.

  Therefore, the inventor of the present application has studied a configuration in which the residual charge of the smoothing capacitor is discharged at the load connected to the inverter even when the power supply is shut off and the driver circuit of the inverter cannot be controlled. Then, the inventor of the present application has come up with the use of a normally-on type relay in which the conduction state is turned on while the power supply is cut off. By using a normally-on type relay, the remaining charge of the capacitor is supplied to the driver circuit of the inverter, and the driver circuit is driven. Further, the inventors have come up with the idea that a normally-on type switching element is used as an inverter switching element. The normally-on type element has an advantage in terms of cost. However, if normally-on type switching elements are used for both the upper and lower arms connected in series, a through current may flow through the upper and lower arms, possibly destroying the switching elements. Therefore, the inventor of the present application has come up with the following configuration.

  The power conversion circuit according to the present embodiment includes an inverter having a plurality of bridge circuits connected in parallel between a first line and a second line to which a power supply voltage is applied, and a driver circuit that drives the inverter A third line connecting the first line and the power input unit of the driver circuit, a normally-on type power relay provided on the third line, and between the power source and the inverter And a smoothing capacitor connected between the first line and the second line.

  Each of the plurality of bridge circuits includes an upper switching element connected to the first line, and a lower switching element connected in series to the upper switching element and connected to the second line.

  When the power supply from the power supply to the driver circuit is cut off, the power supply relay is turned on, whereby the driver circuit is driven by the residual charge of the smoothing capacitor, and the driver circuit is connected to each bridge circuit. At least one of the upper switching elements is controlled to be on, and at least one of the upper switching elements is controlled to be off. The lower switching element connected in series with the upper switching element that is controlled to be on is turned off. And controlling one of the lower switching elements connected in series with the switching element whose upper stage is controlled to be in the off state.

  According to the power conversion circuit having the above configuration, even when the power supply and the power conversion circuit are cut off, the driver circuit of the inverter is driven using the charge remaining in the capacitor, and the remaining charge in the capacitor is discharged. It is possible.

  One of the upper and lower switching elements connected in series in one bridge circuit is controlled to be in an off state. As a result, no through current flows through the upper and lower switching elements in one bridge circuit, and the charge remaining in the capacitor can be discharged without damaging the switching elements of the inverter.

  In the power conversion circuit according to the embodiment of the present invention, the inverter has three bridge circuits, the driver circuit controls two of the three upper switching elements to an ON state, and one of them Control to off state.

  According to the power conversion circuit having the above configuration, the residual charge of the capacitor can be discharged in the load connected to the inverter by way of the switching element controlled to be in the ON state.

  In the power conversion circuit according to the embodiment of the present invention, the inverter has three bridge circuits, the driver circuit controls two of the three lower switching elements to an on state, and one of them Control to off state.

  According to the power conversion circuit having the above configuration, the residual charge of the capacitor can be discharged in the load connected to the inverter by way of the switching element controlled to be in the ON state.

  In the power conversion circuit according to the embodiment of the present invention, all the switching elements constituting the plurality of bridge circuits are normally-on switching elements.

  According to the power conversion circuit having the above configuration, since all the switching elements constituting the bridge circuit are normally on, the circuit cost can be reduced.

  In the power conversion circuit according to the embodiment of the present invention, the driver circuit controls the upper or lower switching element to an OFF state by a pull-down resistor.

  According to the power conversion circuit having the above configuration, the on / off state of the switching element can be controlled by the hardware configuration.

  A motor control device including the power conversion circuit having any one of the above configurations is also an object of the present invention. In the motor control device according to the embodiment of the present invention, a node between the upper switching element and the lower switching element of each of the plurality of bridge circuits is connected to the motor.

  According to the motor control device having the above configuration, even if the power source and the power conversion circuit are shut off, the electric charge remaining in the capacitor is discharged using the motor without damaging the switching element of the inverter. be able to.

  In the motor control apparatus according to the embodiment of the present invention, the inverter and the motor constitute a discharge path for residual charge of the smoothing capacitor, and the residual charge flows through the discharge path as a oscillating discharge current.

  A power steering device that applies a steering assist force to a vehicle steering mechanism is also an object of the present invention. A power steering apparatus according to an embodiment of the present invention includes the motor control apparatus configured as described above and the motor that is controlled by the motor control apparatus and applies the steering assist force to the steering mechanism.

{First embodiment}
Hereinafter, embodiments will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same reference numerals, and the same description is not repeated. For convenience of explanation, in each drawing, the configuration may be simplified or schematically illustrated, or a part of the configuration may be omitted.

  FIG. 1 is a block diagram showing the configuration of the power conversion circuit 60 of the present embodiment. As an example, the power conversion circuit 60 illustrated in FIG. 1 supplies power to the motor of the power steering apparatus. In the example shown in FIG. 1, the power conversion circuit 60 converts the DC power supplied from the power supply 51 into a three-phase AC and supplies the converted power to the motor 20. The power conversion circuit 60 is connected between the power source 51 and the motor 20. The power source 51 of the present embodiment is a battery.

  In the example of FIG. 1, a power supply relay unit 52 is provided between the power supply 51 and the power conversion circuit 60. The power relay unit 52 is turned off when the power supply from the power source 51 is stopped. When the power supply relay unit 52 is turned off, the power supply 51 and the power conversion circuit 60 are electrically disconnected.

  The power conversion circuit 60 includes an inverter 40, a smoothing capacitor C1, a ceramic capacitor C2, resistors R4, R5, and R6, and a power supply relay T7. The power conversion circuit 60 is connected to the two lines L1 and L2 to which the voltage of the power source 51 is applied. In the example shown in FIG. 1, the two lines L <b> 1 and L <b> 2 are respectively connected to the positive electrode and the negative electrode of the battery that is the power source 51. In the present embodiment, of the two lines, one L1 is a positive bus and the other L2 is a negative bus. One of the two lines, L1, is a power line, and the other L2 is a ground line (ground line).

(Inverter)
The inverter 40 has three bridge circuits connected in parallel between the two lines L1 and L2. Each bridge circuit has an upper arm and a lower arm connected in series. The upper arm includes a switching element T1, a switching element T3, and a switching element T5. The lower arm includes a switching element T2, a switching element T4, and a switching element T6. That is, the three upper arms of the inverter 40 shown in FIG. 1 include upper switching elements T1, T3, T5 connected to the positive bus, and the three lower arms are lower switching elements T2 connected to the negative bus. , T4, T6. The upper switching elements T1, T3, and T5 may be referred to as high-side transistors, and the lower switching elements T2, T4, and T6 may be referred to as low-side transistors.

  In the present embodiment, the switching elements T1 to T6 are all normally-on type switching elements. That is, when the power supply from the power supply 51 to the power conversion circuit 60 is interrupted, such as when the power supply is turned off, when the power supply 51 is removed, or when the connection cable of the power supply 51 is disconnected, the switching elements T1 to T1. T6 is turned on.

  Two switching elements (T1, T2) connected in series constitute a bridge circuit corresponding to the U phase. Two switching elements (T3, T4) connected in series constitute a bridge circuit corresponding to the V phase. Two switching elements (T5, T6) connected in series constitute a bridge circuit corresponding to the W phase. That is, the bridge circuit is connected in parallel by the number of phases.

  In each bridge circuit, nodes (also referred to as midpoints or connection points) Pu, Pv, Pw between the upper switching elements T1, T3, T5 and the lower switching elements T2, T4, T6 are respectively The U-phase, V-phase, and W-phase output terminals are connected to the phase coils 20u, 20v, and 20w of the motor 20, respectively.

  In the pair of switching elements T1 and T2, the drain of the upper switching element T1 is connected to the line L1 on the positive side of the power supply 51, and the voltage corresponding to the control signal b1 output from the driver circuit D1 is input to the gate. The source is connected to the node Pu. The node Pu is connected to the drain of the lower switching element T2 and the coil 20u of the motor 20. The gate of the lower switching element T2 is connected to a terminal to which a voltage corresponding to the control signal b2 output from the driver circuit D2 is input, and the source is connected to the line L2 (ground) on the negative side of the power supply 51.

  In the pair of switching elements T3 and T4, the drain of the upper switching element T3 is connected to the line L1 on the positive side of the power supply 51, and the voltage corresponding to the control signal b3 output from the driver circuit D3 is input to the gate. The source is connected to the node Pv. The node Pv is connected to the drain of the lower switching element T4 and the coil 20v of the motor 20. The gate of the lower switching element T4 is connected to a terminal to which a voltage corresponding to the control signal b4 output from the driver circuit D4 is input, and the source is connected to the line L2 (ground) on the negative side of the power supply 51.

  In the pair of switching elements T5 and T6, the drain of the upper switching element T5 is connected to the line L1 on the positive side of the power supply 51, and the voltage corresponding to the control signal b5 output from the driver circuit D5 is input to the gate. The source is connected to the node Pw. The node Pw is connected to the drain of the lower switching element T6 and the coil 20w of the motor 20. The gate of the lower switching element T6 is connected to a terminal to which a voltage corresponding to the control signal b6 output from the driver circuit D6 is input, and the source is connected to the line L2 (ground) on the negative side of the power supply 51.

  The driver circuit D includes six driver circuits D1 to D6. The driver circuits D1 to D6 output voltages corresponding to the control signals b1 to b6, respectively. Voltages corresponding to the control signals b1 to b6 output from the driver circuits D1 to D6 are applied to the gates of the switching elements T1 to T6 of the inverter 40, respectively. For example, the first voltage or the second voltage is selectively applied to the gates of the switching elements T1 to T6. The second voltage is higher than the first voltage. When the gate voltage of the switching elements T1 to T6 is switched between the first voltage and the second voltage, the on / off of the switching elements T1 to T6 is switched.

  The switching elements T1 to T6 can be formed by, for example, semiconductor transistors. For example, the switching elements T1 to T6 can be formed by FETs such as MOSFETs or bipolar transistors such as IGBTs.

(Smoothing capacitor)
The smoothing capacitor C1 is connected between the two lines L1 and L2 to which the voltage of the power supply 51 is applied, between the power supply 51 and the inverter 40. That is, the smoothing capacitor C1 is connected in parallel with the inverter 40 between the two lines L1 and L2. The smoothing capacitor C1 is formed by an electrolytic capacitor, for example. The smoothing capacitor C <b> 1 smoothes the DC voltage supplied from the power supply 51. The voltage supplied from the power supply 51 to the inverter 40 is stabilized by the smoothing capacitor C1. For example, when the voltage supplied from the power supply 51 varies depending on the connected load, the variation range can be suppressed.

(Ceramic capacitor)
A ceramic capacitor C2 is connected between the two lines L1 and L2 between the smoothing capacitor C1 and the inverter 40. The ceramic capacitor C2 is connected in parallel with the smoothing capacitor C1 and each bridge circuit of the inverter 40. Specifically, the ceramic capacitor C2 is connected between the drains of the upper switching elements T1, T3, and T5 of the inverter 40 and the sources of the lower switching elements T2, T4, and T6.

  The surge voltage of the switching elements T1 to T6 is suppressed by the ceramic capacitor C2. The surge voltage of the switching elements T1 to T6 is generated when the path of the current flowing through the switching elements T1 to T6 is changed.

(resistance)
Reference is again made to FIG. Two resistors R4 and R5 are connected in series between the two lines L1 and L2 between the smoothing capacitor C1 and the ceramic capacitor C2. Two resistors R4 and R5 connected in series are connected in parallel to the smoothing capacitor C1. The resistors R4 and R5 are for discharging the residual charge of the smoothing capacitor C1 when the power relay unit 52 is turned off. The resistors R4 and R5 may be disposed between the smoothing capacitor C1 and the power relay unit 52. That is, a resistor can be connected in parallel with the smoothing capacitor C1 between the power source 51 and the ceramic capacitor C2. Thereby, the electric charge of the smoothing capacitor C1 when the power supply of the power supply 51 is stopped can be discharged to the resistor. As will be described later, in the present embodiment, since the electric charge of the smoothing capacitor C1 can be discharged by the motor 20 and the driver circuit D, the resistors R4 and R5 may be omitted.

  In the example shown in FIG. 1, a shunt resistor R6 is connected in series to the line L2 on the negative electrode bus (ground side) of the two lines L1 and L2.

(Power relay)
The power supply relay unit 52 includes two power supply relays T9 and T10 connected in series to one (positive bus) line L1 of the one lines L1 and L2, and a power supply connected to the other (negative bus) line L2. Relay T8. Between the two power supply relays T9 and T10 on the line L1, a plurality of resistors R1, R2, and R3 connected in series with each other are connected between the two lines L1 and L2. A node between two resistors R2, R3 among the plurality of resistors R1, R2, R3 is connected to an electrode on the negative electrode bus side of the smoothing capacitor C1.

  When power supply from the power supply 51 is stopped, the power supply relays T8, T9, and T10 are turned off. Thereby, the two lines L1 and L2 connecting the power source 51 and the power conversion circuit 60 are cut off. That is, the power supply 51 and the power conversion circuit 60 are electrically disconnected. The resistors R1 and R2 are used to check whether the power supply relays T9 and T10 are not broken at the time of startup. The resistor R3 is used as a limiting resistor when charging the smoothing capacitor C1.

  A line L3 is connected to the line L1 between the capacitor C1 and the inverter 40. The line L3 is connected to the power input portion of the driver circuit D. A power supply relay T7 is provided on the line L3. The power supply relay T7 is configured by a normally-on type switching element. A line L4 is connected to the line L3 between the power supply relay T7 and the driver circuit D. The line L4 is connected to the power source 51. A regulator 53 is provided on the line L4.

  In such a configuration, in a state where the power source 51 and the power conversion circuit 60 are connected, the power of the power source 51 is supplied to the driver circuit D via the regulator 53. However, when the power supply from the power supply 51 to the power conversion circuit 60 is stopped, such as when the power supply 51 is removed, the operation of the regulator 53 is also stopped and the power supply to the driver circuit D is also stopped. When power supply from the power supply 51 to the power conversion circuit 60 is stopped, the normally-on type power supply relay T7 is turned on. As a result, the residual charge of the smoothing capacitor C1 is supplied to the driver circuit D via the power supply relay T7 that is turned on.

  A power conversion circuit 60 illustrated in FIG. 1 is included in the motor control device 4. FIG. 1 also shows a configuration example of the motor control device 4. The motor control device 4 includes a power conversion circuit 60 and a control unit 41.

(Control unit and driver circuit)
When the switching elements T1 to T6 are switched, the DC voltage supplied from the power supply 51 is converted into a three-phase (U-phase, V-phase, W-phase) AC voltage. The converted three-phase AC voltage is supplied to the phase coils 20u to 20w of the motor 20 through the nodes Pu, Pv, and Pw, so that the motor 20 rotates.

  The control unit 41 is constituted by a microcomputer, for example. The control unit 41 outputs control signals b1 to b6 to the driver circuit D as PWM drive signals. Specifically, the control unit 41 outputs control signals b1 to b6 corresponding to the switching elements T1 to T6 to the driver circuits D1 to D6 as PWM drive signals. The driver circuits D1 to D6 output voltages corresponding to the PWM drive signals to the switching elements T1 to T6. As a result, voltages corresponding to the PWM drive signals output from the driver circuits D1 to D6 are applied to the gates of the switching elements T1 to T6 of the inverter 40, respectively.

  The driver circuits D1 to D6 output voltages corresponding to the control signals b1 to b6 to the switching elements T1 to T6, thereby driving the inverter 40 by PWM (pulse width modulation). Each of the switching element pairs (T1 and T2, T3 and T4, T5 and T6) corresponding to each of the U-phase, V-phase, and W-phase has a pair of PWMs corresponding to each phase. Controlled by drive signals (b1 and b2, b3 and b4, b5 and b6). A pair of PWM drive signals in each phase are in an inverted relationship with each other. Thereby, the voltages obtained at the nodes Pu, Pv, and Pw of the respective phases are applied to the motor 20 as the U-phase voltage, the V-phase voltage, and the W-phase voltage, respectively. Thereby, the U-phase current, the V-phase current, and the W-phase current are supplied to the motor 20.

  Current sensors 8 for detecting the respective phase current values Iu to Iw in the power supply line between the nodes Pu, Pv, Pw and the motor 20 are provided. Information of the detected phase current values Iu to Iw is taken into the control unit 41. The control unit 41 takes in the steering torque τ from the torque sensor 5, the vehicle speed V from the vehicle speed sensor 7, and the rotation angle θma that is the rotation angle of the motor 20 from the rotation angle sensor 6.

  The control unit 41 receives the phase current values Iu to Iw, the steering torque τ, the vehicle speed V, and the rotation angle θma of the motor, and generates a control signal based on these. For example, the control unit 41 generates voltage command values Vu *, Vv *, and Vw * for each phase of the motor 20 based on the steering torque τ, the vehicle speed V, the rotation angle θma, and the phase current values Iu to Iw. The control unit 41 generates PWM drive signals b1, b3, and b5 and negative signals b2, b4, and b6 as control signals based on the voltage command values Vu *, Vv *, and Vw *.

  As a specific example, the control unit 41 determines a target value It of current to be passed through the motor 20 based on the steering torque τ and the vehicle speed V, and determines the q-axis component of the current target value It and the phase current values Iu to Iw. The difference between the obtained current detection value from the q-axis component and the difference between the d-axis component of the current target value It and the d-axis component of the current detection value obtained from the phase current values Iu to Iw are calculated. The controller 41 calculates the voltage to be applied to the motor 20 as the voltage command values Vu *, Vv *, Vw * in order to cancel these differences. Thereby, the control part 41 drives the motor 20 by electric current feedback control.

  In the present embodiment, pull-down resistors Rd2, Rd3, Rd4 and Rd5 are connected to the driver circuits D2, D3, D4 and D5 among the driver circuits D1 to D6. There are cases where the power source 51 and the power conversion circuit 60 are cut off due to various factors, such as when the power source is removed for reasons such as repair or when the power cable is disconnected due to an external impact. When the power supply 51 and the power conversion circuit 60 are cut off, the power supply to the control unit 41 is also stopped. Thereby, the supply of the PWM drive signal from the control unit 41 to the driver circuits D1 to D6 is also stopped. At this time, since the pull-down resistors Rd2, Rd3, Rd4, and Rd5 are provided, grounded signals are input to the driver circuits D2, D3, D4, and D5. Thus, the first voltage is applied to the switching elements T2, T3, T4, and T5 by the driver circuits D2, D3, D4, and D5, respectively. As described above, the first voltage is lower than the second voltage.

  Switching elements T1 to T6 of the present embodiment are controlled to be turned off when the first voltage is applied. Thereby, switching elements T2, T3, T4 and T5 are controlled to be in an off state. In other words, the power supply from the power supply 51 to the power conversion circuit 60 is cut off, so that all of the normally-on type switching elements T1 to T6 are normally turned on. However, since the driver circuits D2, D3, D4, and D5 are provided with the pull-down resistors Rd2, Rd3, Rd4, and Rd5, the switching elements T2, T3, T4, and T5 are controlled to be in the off state.

(Operation when power supply from the power supply to the power conversion circuit is cut off)
When the power source 51 is removed due to maintenance work such as repair, or when the power cable connecting the power source 51 is disconnected due to an impact from the outside, the power source 51 and the power conversion circuit 60 may be shut off. When the power supply 51 and the power conversion circuit 60 are cut off, the normally-on switching elements T1 to T6 included in the inverter 40 are turned on (conductive state).

  Further, when the power supply 51 and the power conversion circuit 60 are cut off, the normally-on type power supply relay T7 is turned on. As a result, the residual charge of the smoothing capacitor C1 is supplied to the driver circuit D via the relay T7, and the driver circuit D is driven. Since the driver circuits D2, D3, D4 and D5 included in the driver circuit D are provided with pull-down resistors Rd2, Rd3, Rd4 and Rd5, the first voltage is supplied to the switching elements T2, T3, T4 and T5. Is done. Thereby, switching elements T2, T3, T4, and T5 are controlled to be in an off state. Since the first voltage is not applied to switching elements T1 and T6, switching elements T1 and T6 maintain the on state.

  FIG. 2 is a diagram illustrating a discharge path of residual charges of the smoothing capacitor C1 when power supply from the power source 51 to the power conversion circuit 60 is interrupted. As described above, when the power supply 51 and the power conversion circuit 60 are shut off, the switching element T1 is turned on and the switching elements T3 and T5 are turned off, so that the residual charge of the smoothing capacitor C1 passes through the line L1. Flow into the switching element T1. Further, when the power source 51 and the power conversion circuit 60 are cut off, the switching element T6 is turned on and the switching elements T2 and T4 are turned off, so that the residual charges flowing into the switching element T1 are the coil 20u and the coil 20w. And then flows to the switching element T6. Most of the residual charges are discharged in the coil 20u and the coil 20w.

  As described above, in the power conversion circuit 60 of the present embodiment, when the power supply from the power source 51 is cut off, the residual charge of the smoothing capacitor C1 is discharged in the motor 20 that is a load that receives power supply from the inverter 40. Is done. In the driver circuit D, the residual charge of the smoothing capacitor C1 is discharged. Thereby, the residual charge of the smoothing capacitor C1 can be discharged without providing a special dedicated circuit. Moreover, even if it is a case where the control part 41 (drive control part of an inverter) cannot be controlled by interrupting | blocking the electric power supply from the power supply 51, the residual charge of the smoothing capacitor C1 can be discharged in the motor 20. FIG.

  As described above, the residual charge of the smoothing capacitor C1 is discharged through a path that passes through the switching element T1 and the switching element T6. If a through current flows through the upper-limit switching element ((T1, T2), (T3, T4) or (T5, T6)) constituting one bridge circuit, the switching element may be destroyed. However, in the inverter 40 of the present embodiment, since the switching elements T1 and T6 included in different bridge circuits are turned on, no through current flows through any of the bridge circuits. Thereby, the residual charge of the smoothing capacitor C1 can be discharged without damaging the switching element of the inverter 40.

(Modification of the first embodiment)
In the first embodiment, the switching elements T1 and T6 are controlled to be turned on when the power source 51 and the power conversion circuit 60 are cut off, and the switching elements T2, T3, T4, and T5 are turned off. It was configured to be controlled by the state. However, the above configuration is an example. Any configuration may be adopted as long as a path capable of discharging the residual charge of the smoothing capacitor C1 to the motor 20 is ensured and no through current flows in any bridge circuit.

  For example, the switching elements T1 and T4 are controlled to be turned on when the power source 51 and the power conversion circuit 60 are cut off, and the switching elements T2, T3, T5, and T6 are controlled to be turned off. May be. Alternatively, the switching elements T3 and T2 are controlled to be turned on when the power source 51 and the power conversion circuit 60 are cut off, and the switching elements T1, T4, T5, and T6 are controlled to be turned off. May be. Alternatively, the switching elements T3 and T6 are controlled to be turned on when the power source 51 and the power conversion circuit 60 are cut off, and the switching elements T1, T2, T4, and T5 are controlled to be turned off. May be. Alternatively, the switching elements T5 and T2 are controlled to be turned on when the power source 51 and the power conversion circuit 60 are cut off, and the switching elements T1, T3, T4, and T6 are controlled to be turned off. May be. Alternatively, the switching elements T5 and T4 are controlled to be turned on when the power source 51 and the power conversion circuit 60 are cut off, and the switching elements T1, T2, T3, and T6 are controlled to be turned off. May be. In any of these configurations, all the switching elements T1 to T6 are configured as normally-on switching elements, and a driver circuit corresponding to a switching element that is controlled to be turned off when the power source 51 and the power conversion circuit 60 are shut off. A pull-down resistor may be connected to.

{Second Embodiment}
FIG. 3 is a diagram illustrating a power conversion circuit 60A according to the second embodiment of the present invention. In the power conversion circuit 60A of the second embodiment, the configuration of the driver circuit DA is different from the configuration of the driver circuit D of the first embodiment. The other configuration is the same as that of the first embodiment. That is, as in the first embodiment, the switching elements T1 to T6 are normally-on type switching elements.

  Pull-down resistors Rd2, Rd4, and Rd5 are connected to the driver circuits D2, D4, and D5. No pull-down resistor is connected to the driver circuits D1, D3, and D6. In this configuration, when the power supply 51 and the power conversion circuit 60A are shut off, the switching elements T2, T4, and T5 are controlled to be in an off state. Switching elements T1, T3, and T6 maintain the on state. That is, in the second embodiment, the upper two switching elements T1 and T3 are controlled to be turned on. The residual charge of the smoothing capacitor C1 is discharged by the coil 20u and the coil 20v via the switching elements T1 and T3. Further, the residual charge is discharged by the coil 20w in the process of flowing toward the switching element T6.

  As described above, also in the power conversion circuit 60A of the second embodiment, when the power supply from the power source 51 is interrupted, the residual charge of the smoothing capacitor C1 in the motor 20 that is a load that receives the power supply from the inverter 40. Is discharged. Further, the residual charge of the smoothing capacitor C1 is discharged in the driver circuit DA. Thereby, the residual charge of the smoothing capacitor C1 can be discharged without providing a special dedicated circuit. Even when the control unit 41 (inverter drive control unit) cannot be controlled by shutting off the power supply from the power source 51, the motor 20 and the driver circuit DA discharge residual charges in the smoothing capacitor C1. be able to.

  In inverter 40, since switching elements T1, T3, and T6 included in different bridge circuits are controlled to be in an on state, no through current flows through any of the bridge circuits. Thereby, the residual charge of the smoothing capacitor C1 can be discharged without damaging the switching element of the inverter 40.

(Modification of the second embodiment)
In the second embodiment, when the power supply 51 and the power conversion circuit 60A are shut off, the switching elements T1, T3, and T6 are controlled to be in the on state, and the switching elements T2, T4, and T5 are controlled to be in the off state. However, the above configuration is an example. Any configuration may be adopted as long as a path capable of discharging the residual charge of the smoothing capacitor C1 to the motor 20 is ensured and no through current flows in any bridge circuit.

  For example, the switching elements T1, T5, and T4 may be turned on when the power supply 51 and the power conversion circuit 60A are cut off, and the switching elements T2, T3, and T6 may be turned off. Alternatively, the switching elements T3, T5, and T2 may be turned on when the power supply 51 and the power conversion circuit 60A are cut off, and the switching elements T1, T4, and T6 may be turned off. In any of these configurations, all the switching elements T1 to T6 are configured as normally-on type switching elements, and a driver circuit corresponding to a switching element that is controlled to be turned off when the power source 51 and the power conversion circuit 60A are shut off. A pull-down resistor may be connected to.

{Third embodiment}
FIG. 4 is a diagram illustrating a power conversion circuit 60B according to the third embodiment of the present invention. In the power conversion circuit 60B of the third embodiment, the configuration of the driver circuit DB is different from the configuration of the driver circuit D of the first embodiment. The other configuration is the same as that of the first embodiment. That is, as in the first embodiment, the switching elements T1 to T6 are normally-on type switching elements.

  Pull-down resistors Rd2, Rd3, and Rd5 are connected to the driver circuits D2, D3, and D5. No pull-down resistor is connected to the driver circuits D1, D4, and D6. In this configuration, when the power supply 51 and the power conversion circuit 60B are cut off, the switching elements T2, T3, and T5 are controlled to be in an off state. Switching elements T1, T4, and T6 maintain the on state. That is, in the third embodiment, the lower two switching elements T4 and T6 are controlled to be in the ON state. The residual charge of the smoothing capacitor C1 is discharged by the coil 20u via the switching element T1. Further, the residual charge is discharged by the coil 20v and the coil 20w in the process of flowing toward the switching elements T4 and T6.

  As described above, also in the power conversion circuit 60B according to the third embodiment, when the power supply from the power source 51 is cut off, the residual charge of the smoothing capacitor C1 in the motor 20 that is a load that receives the power supply from the inverter 40. Is discharged. Further, the residual charge of the smoothing capacitor C1 is discharged in the driver circuit DB. Thereby, the residual charge of the smoothing capacitor C1 can be discharged without providing a special dedicated circuit. Further, even if the control unit 41 (inverter drive control unit) cannot be controlled by cutting off the power supply from the power supply 51, the residual charge of the smoothing capacitor C1 is discharged in the motor 20 and the driver circuit DB. be able to.

  In inverter 40, switching elements T1, T4, and T6 included in different bridge circuits are controlled to be in an on state, so that no through current flows through any of the bridge circuits. Thereby, the residual charge of the smoothing capacitor C1 can be discharged without damaging the switching element of the inverter 40.

(Modification of the third embodiment)
In the third embodiment, when the power supply 51 and the power conversion circuit 60B are cut off, the switching elements T1, T4, and T6 are controlled to be in the on state, and the switching elements T2, T3, and T5 are controlled to be in the off state. However, the above configuration is an example. Any configuration may be adopted as long as a path capable of discharging the residual charge of the smoothing capacitor C1 to the motor 20 is ensured and no through current flows in any bridge circuit.

  For example, the switching elements T3, T2, and T6 may be turned on when the power supply 51 and the power conversion circuit 60B are cut off, and the switching elements T1, T4, and T5 may be turned off. Alternatively, the switching elements T5, T2, and T4 may be turned on when the power source 51 and the power conversion circuit 60B are cut off, and the switching elements T1, T3, and T6 may be turned off. In any of these configurations, all the switching elements T1 to T6 are configured as normally-on type switching elements, and a driver circuit corresponding to a switching element that is controlled to be turned off when the power source 51 and the power conversion circuit 60B are cut off. A pull-down resistor may be connected to.

{Verification of effect by equivalent circuit}
With reference to FIGS. 5 to 8, effects of the power conversion circuits 60, 60 </ b> A, and 60 </ b> B of the above-described embodiment will be described. FIG. 5 is a diagram showing a circuit in which an electrolytic capacitor, a pattern L, two normally-on switching elements, and a shunt resistor are connected in series. That is, in the circuit of FIG. 5, unlike the power conversion circuits 60, 60A, 60B of the present embodiment described above, normally-on type switching elements are connected in series without a motor interposed therebetween. The pattern L is the inductance of the copper foil that electrically connects the electrolytic capacitor and the switching element (FET) on the substrate.

  FIG. 6 is a diagram illustrating a current flowing through a normally-on type switching element when the residual charge of the electrolytic capacitor is discharged in the circuit of FIG. As can be seen from the figure, a large current exceeding 900 A at the maximum flows through the switching element.

  FIG. 7 is a circuit of FIG. 5 in which two motor reluctances (motor L) and two motor resistors (motor R) are further connected. Two motor reluctances (motor L) and two motor resistors (motor R) are connected in series between two normally-on switching elements. That is, in the circuit of FIG. 7, a motor load is interposed between normally-on type switching elements as in the power conversion circuits 60, 60A, 60B of the present embodiment described above.

FIG. 8 is a diagram showing a current flowing through a normally-on type switching element when the residual charge of the electrolytic capacitor is discharged in the circuit of FIG. As can be seen from the drawing, a maximum current of about 30 A flows through the switching element. 7 is a discharge circuit in which two motors L and R are added to the discharge path as compared with FIG. If a resistance value of the discharge path in FIG. 7 is r, an electrolytic capacitor capacity is c, and an inductance is l, FIG. 7 forms a known lcr discharge circuit. Here, it can be considered that r = (electrolytic C ESR) + (shunt resistance) + 2 × (motor R), l = (pattern L) + 2 × (motor L). Now, by selecting r, c, and l so as to satisfy r ² << (4l / c), the discharge current flows while oscillating, and the initial voltage value of the capacitor is V0 and the maximum value of the discharge current Becomes V0 · √ (c / l). Here, if a capacity in which c is not too larger than l is selected, the maximum value of the discharge current can be made smaller than in the case of FIG. Of r, c, and l, r and l are determined by the substrate on which the circuit is mounted and the motor, so it is preferable to adjust the value of c. For example, when a GaN element or SiC element is used as a normally-on type switching element, the PWM frequency when operating as an inverter can be set high, so that the value of c can be reduced (relative to c relative to l). The maximum value of the discharge current can be effectively suppressed.

  Thus, a large current does not flow through the power conversion circuits 60, 60A, and 60B of the present embodiment even when the residual charge of the capacitor flows, and the switching element can be protected.

{Configuration example of power steering device}
The motor control device 4 shown in FIG. 1 can be used for controlling the motor in the power steering device. FIG. 9 is a block diagram illustrating a configuration example of the power steering apparatus. The power steering apparatus shown in FIG. 9 includes a steering mechanism 1 that steers the steered wheels 3 based on an operation of the driver's steering wheel 10 and an assist mechanism 2 that assists the driver's steering operation.

  The steering mechanism 1 includes a steering shaft 11 that serves as a rotating shaft of the steering wheel 10 and a rack shaft 13 that is coupled to a lower end portion thereof via a rack and pinion mechanism 12. Tie rods 14 are connected to both ends of the rack shaft 13. The steered wheel 3 is connected to the tie rod 14. In the steering mechanism 1, when the steering shaft 11 rotates in accordance with the driver's operation of the steering wheel 10, the rotational motion is converted into a reciprocating linear motion in the axial direction of the rack shaft 13 via the rack and pinion mechanism 12. The reciprocating linear motion of the rack shaft 13 is transmitted to the steered wheels 3 through tie rods 14 connected to both ends thereof. Thereby, the turning angle of the steered wheels 3 is changed, and the traveling direction of the vehicle is changed.

  The assist mechanism 2 includes a motor 20 that applies assist torque to the steering shaft 11. The motor 20 is a three-phase brushless motor. The rotation of the motor 20 is transmitted to the steering shaft 11 via the gear mechanism 21 so that motor torque is applied to the steering shaft 11 and the steering operation is assisted.

  This power steering apparatus is provided with various sensors for detecting the operation amount of the steering wheel 10 and the state amount of the vehicle. For example, the steering shaft 11 is provided with a torque sensor (torque detector) 5 that detects torque (steering torque) τ applied to the steering shaft 11 when the driver performs a steering operation. The motor 20 is provided with a rotation angle sensor 6 that detects its rotation angle (electrical angle) θma. The vehicle is provided with a vehicle speed sensor 7 for detecting the vehicle speed (traveling speed) V. Outputs of these sensors 5 to 7 are taken into the motor control device 4. The motor control device 4 controls the drive of the motor 20 based on the outputs of the sensors 5-7.

(Modification)
The configuration of the power conversion circuit is not limited to the example shown in FIG. For example, the ceramic capacitor C2 may be omitted. Further, since the residual charge of the smoothing capacitor C1 can be discharged by the motor 20, the resistors R4 and R5 may be omitted. Other elements may be added to the power conversion circuit 60 shown in FIG.

  The power source 51 is not limited to a battery. For example, the form which converts the alternating current power supplied from alternating current power supply into direct current power, and supplies it to a power converter circuit may be sufficient.

  The power conversion circuit of the present invention is not limited to that used for motor control. For example, the power conversion circuit of the present invention can be applied to an inverter of a converter that is connected to a battery and converts the direct current power of the battery into alternating current and outputs the alternating current. Further, the motor control device of the present invention is not limited to that used in the power steering device. For example, the present invention can be applied to consumer motors such as motors for home appliances, industrial motors, and any other motor control devices.

  The motor targeted by the motor control device of the present invention is not limited to the three-phase brushless motor of the above example. The present invention is also applicable to a motor control device for driving other types of electric motors such as a brushless motor having a number of phases other than three phases and a motor with brushes.

  The present invention is not limited to the above-described column assist type electric power steering device, but can also be applied to other types of electric power steering devices such as a pinion assist type or rack assist type electric power steering device.

DESCRIPTION OF SYMBOLS 1 Steering mechanism 4 Motor control apparatus 20 Motor 40 Inverter 41 Control part 51 Power supply T1, T2, T3, T4, T5, T6 Switching element C1 Smoothing capacitor D, DA, DB Driver circuit 60 Power conversion circuit

Claims (8)

An inverter having a plurality of bridge circuits connected in parallel between a first line to which a voltage of a power supply is applied and a second line;
A driver circuit for driving the inverter;
A third line connecting the first line and the power input part of the driver circuit;
A normally-on type power relay provided on the third line;
A smoothing capacitor connected between the first line and the second line between the power source and the inverter;
With
Each of the plurality of bridge circuits is
An upper switching element connected to the first line;
A lower switching element connected in series with the upper switching element and connected to the second line;
Have
When the power supply from the power supply to the driver circuit is cut off, the power supply relay is turned on, whereby the driver circuit is driven by the residual charge of the smoothing capacitor, and the driver circuit is connected to each bridge circuit. At least one of the upper switching elements is controlled to be on, and at least one of the upper switching elements is controlled to be off. The lower switching element connected in series with the upper switching element that is controlled to be on is turned off. A power conversion circuit that controls one of the lower switching elements connected in series with the switching element that is controlled in a state and whose upper stage is controlled in the off state. The power conversion circuit according to claim 1,
The inverter has three bridge circuits,
The driver circuit is a power conversion circuit that controls two of the three upper-stage switching elements to an on state and controls one to an off state. The power conversion circuit according to claim 1,
The inverter has three bridge circuits,
The driver circuit is a power conversion circuit that controls two of the three lower-stage switching elements to an on state and controls one to an off state. The power conversion circuit according to any one of claims 1 to 3,
All the switching elements that constitute the plurality of bridge circuits are normally-on type switching elements. The power conversion circuit according to any one of claims 1 to 4, wherein
The driver circuit is a power conversion circuit that controls an upper or lower switching element to an OFF state by a pull-down resistor. A motor control device including the power conversion circuit according to any one of claims 1 to 5,
A node between the upper switching element and the lower switching element of each of the plurality of bridge circuits is connected to a motor. The motor control device according to claim 6,
The motor control device, wherein the inverter and the motor constitute a discharge path of residual charge of the smoothing capacitor, and the residual charge flows through the discharge path as a oscillating discharge current. A power steering device that applies a steering assist force to a steering mechanism of a vehicle,
A motor control device according to claim 6;
The motor controlled by the motor control device and providing the steering assist force to the steering mechanism;
A power steering apparatus comprising:

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