JP6268140B2 - Electric motor drive circuit - Google Patents

Description

  The present invention relates to an electric motor drive circuit, and more particularly to an electric motor drive circuit including a load protection circuit for protecting a load even when electrodes of a DC power supply are connected in reverse.

  2. Description of the Related Art Conventionally, a protection circuit for protecting a load (for example, an in-vehicle electronic device) is known even when an electrode of a DC power source such as a battery mounted on a vehicle is connected in reverse.

  For example, Patent Document 1 discloses a protection circuit that is intended to protect an electronic device from a state in which battery electrodes are reversely connected, and to realize an inexpensive and small size. In this protection circuit, an n-type MOS field effect transistor having a substrate connected to the ground line is connected between the ground terminal of the electronic device to which the negative electrode of the battery is connected and the ground line of the electronic device. A resistor is connected in series between the power supply terminal of the electronic device and the ground line, and the divided voltage is applied to the gate of the n-type MOS field effect transistor. As a result, the ground line and the ground terminal are electrically connected only when the battery is correctly connected, and when the battery is connected reversely, it is not electrically connected, so that the load circuit is protected.

  Further, Patent Document 2 has a problem that a junction in an IC generated by reversely connecting a battery is forward-biased, and minority carriers flow to the base layer to prevent a latch-up phenomenon or heat generation. A protection circuit for a reverse connected battery is disclosed. The protection circuit includes a battery, a load, and a device for protecting the load against a reversely connected battery. The device includes a first means for biasing the MOSFET to a conductive state when the battery is in series with a MOSFET connected in series with the battery and a load, and sourcing the gate of the MOSFET when the battery is reverse connected. And a second means for biasing the MOSFET to a non-conducting state by short-circuiting. Thereby, the load circuit is protected.

Further, Patent Document 3 discloses a protection circuit for an electronic device in order to protect a circuit when a DC power source is connected with reverse polarity and to realize a configuration that is resistant to noise. In this protection circuit, a P-channel FET is provided to protect the reverse connection of the power supply, its drain is connected to the positive power supply terminal, its source is connected to the power input terminal of the electronic device, and the FET gate is connected to the ground line. Connect to. In this protection circuit, when the power supply is reversely connected, the P-channel FET is turned off, and the ground is shared between the circuit of the electronic device and the power supply, so that the circuit of the electronic device is protected when reversely connected.
It is also known that an electric motor drive circuit for an electric motor that drives an electric power steering or the like is provided with an FET that protects the circuit when a battery that supplies power to the electric motor is reversely connected.

  For example, Patent Document 4 discloses an electric power steering device with the object of realizing miniaturization and ensuring reliability. This electric power steering apparatus is provided with a power supply relay that conducts / cuts off the energization path in the energization path from the DC power source to the motor drive unit. This power supply relay is arranged in a back-to-back manner in which two MOSFETs are connected in series so that bidirectional current can be cut off. A thermistor is disposed in the vicinity of the MOSFET to detect the temperature in the vicinity of the MOSFET. When the electrodes of the DC power supply are reversely connected, the temperature of the MOSFET rises. Therefore, when the temperature is equal to or higher than a preset reference temperature, it is determined that the DC power supply is reversely connected.

  Further, the following techniques have been proposed in order to detect a failure of a protection circuit that protects an electronic device when battery electrodes are connected in reverse polarity.

  For example, Patent Document 5 discloses a motor control device with the object of diagnosing whether or not the reverse connection protection means has failed. This motor control device has a reverse connection protection means having a switching element for connecting or disconnecting between the battery and the motor and a reverse current prevention element for preventing a reverse current flow when the battery is reversely connected, and a failure of the reverse connection protection means. It has a failure diagnosis means for diagnosing. The failure diagnosis means calculates the difference between the cut-off potential difference before connecting the reverse connection protection means and the connection potential difference when the reverse connection protection means is connected, and when the difference is greater than or equal to a preset threshold value Determines that the reverse connection protection means has not failed, and determines that the reverse connection protection means has failed when the difference is smaller than the threshold value.

  Patent Document 6 discloses a drive control device for an electric actuator in order to improve the fault diagnosis accuracy of the reverse connection protection circuit. In this drive control device, a relay circuit, a reverse connection protection circuit, and a drive circuit that drives a brake actuator are disposed on an electric circuit that connects a power supply line that supplies the voltage V1 and the ground. These circuits are composed of FETs each having a parasitic diode, and the parasitic diodes of the reverse connection protection circuit are opposite to those of other circuits. In addition, a voltage V2 lower than the voltage V1 is supplied to an electric circuit located between the reverse connection protection circuit and the drive circuit. The drive control device appropriately controls the relay circuit, the reverse connection protection circuit, and the drive circuit, and diagnoses the failure of the reverse connection protection circuit based on the voltage on the source side of the reverse connection protection circuit.

JP 2002-095159 A Japanese Patent Application Laid-Open No. 07-184318 JP 2003-037933 A JP 2014-162423 A JP 2012-065405 A Japanese Patent Laying-Open No. 2015-061338

  However, the failure detection of reverse connection protection disclosed in Patent Document 5 is based on the presence or absence of a voltage drop (potential difference) that occurs when a current flows through a diode. Since the potential difference caused by the voltage drop is small, the potential difference is detected. A high-precision voltmeter is required for detection. In the first place, in this failure detection, a failure cannot be detected unless a current flows. Further, the failure detection disclosed in Patent Document 6 requires a power supply circuit for generating the voltage V2, which increases costs.

  The electric motor may rotate due to an external force applied to the tire or the like during traveling in the power steering control device, or due to an external force applied to the door or the like during opening / closing in the power slide door control device or the power tailgate control device. In such a drive circuit for driving an electric motor, a counter electromotive force is generated when the electric motor is rotated by an external force. Such a control device for driving an electric motor is also provided with an FET for protecting the circuit when the battery is reversely connected (Patent Document 4).

  The inventors of the present invention provide a drive circuit for driving a power steering or the like, and includes a reverse connection protection FET. The reverse connection protection FET is an off failure (a failure in which the switch does not turn on, and is always As a result of diligent research on the case of a failure that would result in a disconnection, the following was discovered. In other words, when the reverse connection protection FET is turned off and an external force is applied to the drive target and a back electromotive force is generated in the drive circuit of the electric motor, a high voltage is applied across the reverse connection protection FET. It was found to be detected.

  Therefore, in the present invention, in the drive circuit of the electric motor that drives the driven object to which an external force is easily applied, an additional power source for detecting a failure and a high-accuracy voltmeter are not required. Provided is an electric motor drive circuit that detects a failure of a reverse connection protection circuit regardless of non-drive time.

In order to solve the above-mentioned problem, a bridge circuit that includes a plurality of switching elements having a freewheeling diode and drives an electric motor, a negative connection terminal that connects the bridge circuit to the negative electrode of the battery, a bridge circuit and a negative connection terminal thereof A reverse connection protection switching element provided between and an anode connected to the bridge circuit side, a cathode connected to the negative connection terminal side, and a reverse connection protection diode connected in parallel with the reverse connection protection switching element, A potential difference detection unit that detects a potential difference between both ends of the reverse connection protection diode, a control unit that controls ON / OFF of the plurality of switching elements and the reverse connection protection switching element, and the control unit controls OFF of all the switching elements of the bridge circuit. When the reverse connection protection switching element is on-controlled, If part detects any potential difference, an electric motor driving circuit comprising: a determining malfunction determining unit and the reverse connection protection switching elements is faulty, is provided.
According to this, even when the bridge circuit is not driven and no current flows, an electric motor drive circuit that detects a failure of the reverse connection protection switching element based on the counter electromotive force of the electric motor can be provided. .

In order to solve the above-described problem, a bridge circuit that includes a plurality of switching elements having a reflux diode and drives an electric motor, a negative connection terminal that connects the bridge circuit to the negative electrode of the battery, a bridge circuit and a negative connection terminal, A reverse connection protection switching element, an anode connected to the bridge circuit side, a cathode connected to the negative connection terminal side, a reverse connection protection diode connected in parallel with the reverse connection protection switching element, and reverse connection protection A potential difference detection unit that detects a potential difference between both ends of the diode, a control unit that controls on / off of the plurality of switching elements and the reverse connection protection switching element, and the control unit controls on / off of the plurality of switching elements of the bridge circuit. When the electric motor is being driven, the reverse connection protection switching element is turned on. When the potential difference detection unit detects a potential difference larger than the voltage drop of the reverse connection protection diode, a failure determination unit that determines that the reverse connection protection switching element is faulty is provided. The
According to this, when the bridge circuit is driven and a potential difference larger than the voltage drop of the reverse connection protection diode is detected, it is determined as an off-fault, so that a highly accurate voltmeter is not required and the reverse of the electric motor is performed. An electric motor drive circuit that detects a failure of the reverse connection protection switching element based on the electromotive force can be provided.

  According to the present invention, in an electric motor drive circuit that drives an object to which a drive force is easily applied, an additional power source for failure detection and a highly accurate voltmeter are not required. It is possible to provide an electric motor drive circuit that detects a failure of the reverse connection protection circuit regardless of when it is not driven.

The circuit diagram which shows the electric motor drive circuit of the 1st Example which concerns on this invention. In the electric motor drive circuit of the first embodiment according to the present invention, an explanatory circuit diagram in a case where a DC power source is positively connected to drive a bridge circuit and the reverse connection protection switching element has no failure. In the electric motor drive circuit of the first embodiment according to the present invention, an explanatory circuit diagram in the case where a back electromotive force is generated when a bridge circuit is driven and there is no failure in the reverse connection protection switching element. In the electric motor drive circuit of the first embodiment according to the present invention, when the bridge circuit is not driven and the reverse electromotive force is generated when there is no failure in the reverse connection protection switching element, FIG. In the electric motor drive circuit of the first embodiment according to the present invention, explanation is given when a back electromotive force is generated when the bridge circuit is driven and an off-failure occurs in the reverse connection protection switching element. circuit diagram. In the electric motor drive circuit of the first embodiment according to the present invention, explanation is given when a back electromotive force is generated when the bridge circuit is not driven and an OFF failure occurs in the reverse connection protection switching element. circuit diagram. FIG. 7 is an explanatory circuit diagram in a case where a bridge circuit is not driven in the conventional electric motor drive circuit and an OFF failure has occurred in the reverse connection protection switching element. FIG. 7 is an explanatory circuit diagram in a case where a bridge circuit is driven in an electric motor drive circuit according to the prior art, and an OFF failure has occurred in a reverse connection protection switching element.

Embodiments according to the present invention will be described below with reference to the drawings.
<First Example>
With reference to FIG. 1, the electric motor drive circuit 100 in a present Example is demonstrated. The electric motor drive circuit 100 includes a bridge circuit 10 that drives the electric motor M, a motor switching element MF that turns on and off the three phases of the electric motor M, and a negative electrode connection terminal that connects the bridge circuit 10 to the negative electrode / positive electrode of the battery BAT. 60 / positive electrode connection terminal 70. The electric motor M is a power steering device that applies steering assist force to the steering of the vehicle, a power sliding door that automatically opens and closes the side and rear doors of the vehicle, and a three-phase (U phase) that serves as a power source for the power tailgate. , V phase, W phase) brushless motor. Since the electric motor M drives the steering and the door in both forward and reverse directions, the rotation direction is switched between forward rotation and reverse rotation, and the rotation speed is controlled by PWM control. In addition, although the electric motor M in this specification is a three-phase, it may be a two-phase electric motor.

  The motor switching element MF is a field effect transistor (FET), and is used when each phase of the electric motor M is turned on and off. The negative electrode connection terminal 60 / positive electrode connection terminal 70 are terminals for electrically connecting / disconnecting the electric motor drive circuit 100 and the battery BAT of the DC power source. When the battery BAT is attached or detached, the electric motor drive circuit 100 is electrically connected / disconnected by this terminal.

  The bridge circuit 10 includes six switches SW <b> 1 to SW <b> 6 having a reflux diode 12. The bridge circuit 10 is connected to the positive electrode side of the battery BAT via the positive electrode connection terminal 70 and connected (grounded) to the negative electrode side of the battery BAT via the negative electrode connection terminal 60. Each phase circuit of the bridge circuit 10 includes high potential side switches SW1 to SW3 provided on the positive electrode connection terminal 70 side and low potential side switches SW4 to SW6 provided on the negative electrode connection terminal 60 side in series. In the present embodiment, FETs are used as the switching elements 11 of the switches SW1 to SW6. Each free-wheeling diode 12 has an anode connected to the source side, a cathode connected to the drain side, and is connected in a forward direction from the source to the drain.

  The drains of the high potential side switches SW <b> 1 to SW <b> 3 are connected to the positive electrode connection terminal 70. The sources of the high potential side switches SW1 to SW3 are connected to the drains of the low potential side switches SW4 to SW6. The sources of the low potential side switches SW4 to SW6 are connected to the negative electrode connection terminal 60 side. In the switching element 11 of the switches SW1 to SW6, a PWM signal from the control unit 50 described later is input to the gate, and the source-drain is turned on / off.

  The electric motor drive circuit 100 further includes a reverse connection protection switching element 20, a reverse connection protection diode 30 connected in parallel with the reverse connection protection switching element 20, and a potential difference detection unit that detects a potential difference between both ends of the reverse connection protection diode 30. 40, a control unit 50 that controls on / off of the switching element 11 and the like, and a failure determination unit 80 that determines a failure of the reverse connection protection switching element 20. In this embodiment, the reverse connection protection switching element 20 is an FET. The reverse connection protection switching element 20 is provided between the bridge circuit 10 and the negative electrode connection terminal 60, and has a source connected to the bridge circuit 10 side and a drain connected to the negative electrode connection terminal 60 side. The reverse connection protection diode 30 has an anode connected to the bridge circuit 10 side and a cathode connected to the negative electrode connection terminal 60 side, and is connected in parallel with the reverse connection protection switching element 20.

  When the battery BAT is positively connected, the source of the reverse connection protection switching element 20 is connected to the positive side of the battery BAT, the drain is connected to the negative side, and a voltage that always turns on the reverse connection protection switching element 20 is applied to the gate. It is configured to be. On the other hand, when the battery BAT is reversely connected, the source of the reverse connection protection switching element 20 is connected to the negative electrode side of the battery BAT and the drain is connected to the positive electrode side. The protective switching element 20 is configured to be turned off. Further, the reverse connection protection diode 30 connected in parallel with the reverse connection protection switching element 20 has the anode connected to the bridge circuit 10 side and the cathode connected to the negative electrode connection terminal 60 side, so that the battery BAT is reversely connected. Is reverse biased, so no current flows. With such a configuration, even if the battery BAT is reversely connected, the load included in the electric motor drive circuit 100 is protected.

  The potential difference detection unit 40 detects the voltage on the anode side of the diode 30 for reverse connection protection as V2 and the voltage on the cathode side as V1, and detects a potential difference between both ends thereof. The voltage V1 is a ground level voltage when the battery BAT is positively connected. In the present embodiment, the potential difference detection unit 40 is a PIC microcomputer (Peripheral Interface Controller) incorporating an AD converter, but may be any device having an equivalent function and capable of detecting a potential difference.

  The control unit 50 controls on / off of the six switching elements 11 (a plurality of switching elements 11) and the reverse connection protection switching element 20 of the bridge circuit 10. The control unit 50 controls the rotation direction (forward rotation and reverse rotation) and the rotation speed of the electric motor M by switching (turning on and off) the six switching elements 11 of the bridge circuit 10 to an energized state or a cut-off state in a predetermined combination. To do. For example, as shown in FIG. 2, when SW1 is turned on, SW2 is turned off, SW3 is turned off, SW4 is turned off, SW5 is turned on, and SW6 is turned on, the electric motor M rotates normally. Conversely, when SW1 is turned off, SW2 is turned on, SW3 is turned on, SW4 is turned on, SW5 is turned off, and SW6 is turned off, the electric motor M is reversed.

  The control unit 50 performs control so that the gate of the reverse connection protection switching element 20 is always on when the battery BAT is normally connected, and the gate is off when the battery BAT is reversely connected. Further, the control unit 50 performs PWM control (Pulse Width Modulation, pulse width modulation) on the six switching elements 11 so that the steering assist force of the power steering, the driving speed of the power slide door, the power tailgate, and the like coincide with the target. Control as follows. As the control unit 50, a microcomputer including a CPU (Central Processing Unit), a driver IC, a memory, and the like is used.

  The failure determination unit 80 detects the failure of the reverse connection protection switching element 20 based on the switching state of the six switching elements 11 of the bridge circuit 10, the switching state of the reverse connection protection switching element 20, and the potential difference detected by the potential difference detection unit 40. The presence or absence of is determined. First, with reference to FIG. 7 and FIG. 8, the case where the off-failure has occurred in the reverse connection protection switching element in the electric motor drive circuit of the prior art will be described. Note that an off-failure is a failure in which the switch does not turn on, and means a failure that is always in a disconnected state.

  FIG. 7 shows a case where the bridge circuit is not driven. When the bridge circuit is not driven, all the switching elements of the bridge circuit are in the off state. Then, no current flows through the circuit shown in the figure including the bridge circuit. In this case, even if an attempt is made to detect a potential difference between both ends of the reverse connection protection diode of the reverse connection protection circuit, it cannot be detected (V1, V2: not detectable).

  FIG. 8 shows a case where the bridge circuit is driven. When the bridge circuit is driven, a current flows in the circuit shown in the figure. In this figure, SW1 is turned on, SW2 is turned off, SW3 is turned off, SW4 is turned off, SW5 is turned on, and SW6 is turned on, and a current flows as shown by a one-dot chain line. Then, the current tends to flow through the reverse connection protection circuit. Since an OFF fault has occurred in the reverse connection protection switching element of the reverse connection protection circuit, the current does not flow through the reverse connection protection switching element.

  However, since the reverse connection protection diode of the reverse connection protection circuit is forward-biased, the current flows through the reverse connection protection diode. As a result, the voltages V1 and V2 across the reverse connection protection diode can be detected, and the potential difference Vd can be detected as Vd = V1−V2. However, this potential difference Vd is the voltage drop (Vf) of the reverse connection protection diode, and is a slight voltage drop. Therefore, a highly accurate voltmeter is required to detect this.

  With reference to FIG. 2 to FIG. 6, a method in which the failure determination unit 80 determines whether or not the reverse connection protection switching element 20 has an off failure will be described. FIG. 2 shows that when an off failure has not occurred in the reverse connection protection switching element 20, the control unit 50 turns on SW1, turns off SW2, turns off SW3, turns off SW4, turns on SW5, turns on SW6, and reversely connects. The state which turned on the protection switching element 20 is shown. Note that all the motor switching elements MF are in the on state in this embodiment.

  In the electric motor drive circuit 100, a current flows as shown by a one-dot chain line. That is, since the battery BAT is positively connected, the current flows from the positive electrode connection terminal 70 to the bridge circuit 10, the motor switching element MF, the electric motor M, the motor switching element MF, the bridge circuit 10, and the reverse connection protection switching element 20. Via, it reaches the negative electrode connection terminal 60. Since SW1, SW5, and SW6 are turned on in the bridge circuit 10, the current is switched by the switching element 11 of SW1, the U phase of the electric motor M, the V phase and W phase of the electric motor M, and the switching of SW5 and SW6. It passes through the element 11. In this case, the electric motor M is rotating forward. Since the current passes through the reverse connection protection switching element 20, the potential difference Vd of the reverse connection protection diode 30 detected by the potential difference detection unit 40 is substantially equal to zero (Vd = V1-V2≈0). When the potential difference Vd of the reverse connection protection diode 30 detected by the potential difference detection unit 40 is substantially equal to zero (Vd = V1−V2≈0), the failure determination unit 80 determines that the reverse connection protection switching element 20 is conductive. Judgment is not made and it is not determined that there is an off failure.

  FIG. 3 shows a state similar to FIG. That is, FIG. 3 shows that the control unit 50 turns on SW1, turns off SW2, turns off SW3, turns off SW4, turns on SW5, and turns on SW6 when there is no off failure in the reverse connection protection switching element 20. 2 shows a state in which the reverse connection protection switching element 20 is turned on. FIG. 3 shows a case where an external force (a dotted arrow) for reverse rotation is further applied to the electric motor M in this state. For example, when the electric motor M is used for the power tailgate, the external force is a case where a force for preventing the tail motor is applied during the closing operation of the tailgate. The external force is, for example, when the electric motor M is used for power steering and when the tire rides on the curb while steering the steering.

  In this case, electromotive forces Ve1, Ve2, and Ve3 having a relationship of Ve1 + Ve2 + Ve3 = 0 are generated in each phase of the electric motor M, respectively. Then, in the electric motor drive circuit 100, a current flows as shown by a one-dot chain line. That is, since an electromotive force is generated in the reverse direction, the current due to the electromotive force is supplied from the negative connection terminal 60 to the reverse connection protection switching element 20, the bridge circuit 10, the motor switching element MF, the electric motor M, the motor switching element MF, the bridge. The positive electrode connection terminal 70 is reached via the circuit 10.

  In this case, the current is reverse-biased in the reverse connection protection diode 30 and passes through the reverse connection protection switching element 20, so that the potential difference Vd of the reverse connection protection diode 30 detected by the potential difference detection unit 40 is substantially equal to zero (Vd = V1). −V2≈0). Even when an electromotive force is generated, the failure determination unit 80 detects a reverse connection protection switching element when the potential difference Vd of the reverse connection protection diode 30 detected by the potential difference detection unit 40 is substantially equal to zero (Vd = V1−V2≈0). 20 is determined to be conductive and is not determined to be off-failed.

  FIG. 4 shows a case where the bridge circuit 10 is not driven and an external force (a dotted arrow) is applied to the electric motor M shown in FIG. When an electromotive force is generated, the current shown in FIG. 3 tends to flow. When the bridge circuit 10 is not driven, the switching elements 11 of all the switches SW <b> 1 to SW <b> 6 of the bridge circuit 10 are in an off state, so that current does not flow through the switching element 11. However, since the free-wheeling diode 12 of the switches SW1 to SW6 is forward biased, a current flows through the free-wheeling diode 12. Although this figure shows that a current flows through the freewheeling diodes 12 of SW1, SW5, and SW6, the present invention is not limited to this, and other freewheeling diodes 12 also pass.

  In this case, the current is reverse-biased in the reverse connection protection diode 30 and passes through the reverse connection protection switching element 20, so that the potential difference Vd of the reverse connection protection diode 30 detected by the potential difference detection unit 40 is substantially equal to zero (Vd = V1). −V2≈0). Even when an electromotive force is generated, the failure determination unit 80 detects a reverse connection protection switching element when the potential difference Vd of the reverse connection protection diode 30 detected by the potential difference detection unit 40 is substantially equal to zero (Vd = V1−V2≈0). 20 is determined to be conductive and is not determined to be off-failed.

  FIG. 5 shows a state where the control unit 50 is driving the bridge circuit 10 when the reverse connection protection switching element 20 is off, and the reverse connection protection switching element 20 is on-controlled. The case where an external force for reverse rotation is applied to is shown. Note that ON control (same for OFF control) refers to outputting a control signal so as to be in an ON state. As a result of this ON control, the ON state is actually turned on or the OFF state is maintained depending on the situation (normal / failure) of the reverse connection protection switching element 20. In this case, as described with reference to FIG. 3, electromotive forces Ve1, Ve2, and Ve3 are generated in the respective phases of the electric motor M, and in the electric motor driving circuit 100, a current flows as shown by a one-dot chain line. And However, generally, an off-failure has occurred in the reverse connection protection switching element 20, and no current flows because the reverse connection protection diode 30 is reverse biased.

  However, it has been found that a large potential difference Vd is detected across the reverse connection protection diode 30 when a reverse electromotive force is generated in the state where the reverse connection protection switching element 20 is in an off-failure state. That is, the potential difference detection unit 40 detects that the potential difference Vd of the reverse connection protection diode 30 is almost zero (Vd = V1−V2≈0) in a state where the reverse connection protection switching element 20 is not turned off. When a failure occurs, a large potential difference Vd, that is, a potential difference (Vd = V1-V2 >> Vf) greater than the voltage drop Vf of the reverse connection protection diode 30 is detected. The potential difference Vd measured by the inventors is slightly smaller than the voltage of the battery BAT (for example, 12 V), and is a potential difference considerably larger than the voltage drop Vf of the reverse connection protection diode 30.

  Therefore, the failure determination unit 80 is when the control unit 50 is driving the electric motor M by turning on and off the six switching elements 11 of the bridge circuit 10 and turning on the reverse connection protection switching element 20. Sometimes, when the potential difference detection unit 40 detects a potential difference that is larger than the voltage drop Vf of the reverse connection protection diode 30, it is determined that the reverse connection protection switching element 20 has an off failure. According to this, when the bridge circuit is driven and a potential difference larger than the voltage drop of the reverse connection protection diode is detected, it is determined as an off-fault, so that a highly accurate voltmeter is not required and the reverse of the electric motor is performed. Fault detection of the reverse connection protection switching element can be performed based on the electromotive force.

  FIG. 6 shows a state where the control unit 50 is not driving the bridge circuit 10 and the reverse connection protection switching element 20 is on-controlled when the reverse connection protection switching element 20 has an off-failure. A case where an external force for reverse rotation is applied to M is shown. In this case, as described with reference to FIG. 4, electromotive forces Ve1, Ve2, and Ve3 are generated in the respective phases of the electric motor M, and in the electric motor drive circuit 100, the free wheel diode 12 is provided as shown by a one-dot chain line. The current is going to flow through. However, generally, an off-failure has occurred in the reverse connection protection switching element 20, and no current flows because the reverse connection protection diode 30 is reverse biased.

  However, it has been found that a large potential difference Vd is detected across the reverse connection protection diode 30 when a reverse electromotive force is generated in the state where the reverse connection protection switching element 20 is in an off-failure state. That is, the potential difference detection unit 40 detects that the potential difference Vd of the reverse connection protection diode 30 is almost zero (Vd = V1−V2≈0) in a state where the reverse connection protection switching element 20 is not turned off. Even if a failure occurs, the potential difference Vd (Vd = | V1−V2 |> 0) is detected.

  Therefore, in the failure determination unit 80, when the control unit 50 turns off all the switching elements 11 of the bridge circuit 10 and turns on the reverse connection protection switching element 20, the potential difference detection unit 40 sets some potential difference Vd. If it is detected, it is determined that the reverse connection protection switching element 20 has an off-failure. According to this, even when the bridge circuit is not driven and no current is flowing, the failure detection of the reverse connection protection switching element can be performed based on the counter electromotive force of the electric motor M.

  In addition, this invention is not limited to the illustrated Example, The implementation by the structure of the range which does not deviate from the content described in each item of a claim is possible. That is, although the present invention has been particularly illustrated and described with respect to particular embodiments, it should be understood that the present invention has been described in terms of quantity, quantity, and amount without departing from the scope and spirit of the present invention. Various modifications can be made by those skilled in the art in application examples and other detailed configurations.

DESCRIPTION OF SYMBOLS 1 Vehicle M Electric motor MF Motor switching element BAT Power supply 100 Electric motor drive circuit 10 Bridge circuit 11 Switching element 12 Reflux diode 20 Reverse connection protection switching element 30 Reverse connection protection diode 40 Potential difference detection unit 50 Control unit 60 Negative connection terminal 70 Positive connection Terminal 80 Failure determination part SW1-SW6 switch

Claims (2)

A bridge circuit including a plurality of switching elements having a reflux diode and driving an electric motor;
A negative connection terminal for connecting the bridge circuit to a negative electrode of a battery;
A reverse connection protection switching element provided between the bridge circuit and the negative electrode connection terminal;
An anode connected to the bridge circuit side, a cathode connected to the negative electrode connection terminal side, and a reverse connection protection diode connected in parallel with the reverse connection protection switching element;
A potential difference detection unit for detecting a potential difference between both ends of the reverse connection protection diode;
A controller for controlling on / off of the plurality of switching elements and the reverse connection protection switching element;
When the control unit controls all of the switching elements of the bridge circuit to be OFF and controls the reverse connection protection switching element to be ON, the reverse connection protection is performed when the potential difference detection unit detects some potential difference. A failure determination unit that determines that the switching element for failure is in failure;
An electric motor drive circuit comprising: A bridge circuit including a plurality of switching elements having a reflux diode and driving an electric motor;
A negative connection terminal for connecting the bridge circuit to a negative electrode of a battery;
A reverse connection protection switching element provided between the bridge circuit and the negative electrode connection terminal;
An anode connected to the bridge circuit side, a cathode connected to the negative electrode connection terminal side, and a reverse connection protection diode connected in parallel with the reverse connection protection switching element;
A potential difference detection unit for detecting a potential difference between both ends of the reverse connection protection diode;
A controller for controlling on / off of the plurality of switching elements and the reverse connection protection switching element;
When the control unit is driving the electric motor by turning on and off the plurality of switching elements of the bridge circuit, the potential difference detecting unit is controlling the reverse connection protection switching element. Detects a potential difference larger than the voltage drop of the reverse connection protection diode, a failure determination unit that determines that the reverse connection protection switching element is defective, and
An electric motor drive circuit comprising:

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