JP2013110838A - Electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of preventing discharge time of a capacitor from elongating due to current produced by counter-electromotive force of a motor at collision.SOLUTION: An electric vehicle 100 includes an inverter 4 for supplying power to the motor 6, the capacitor 12, a discharge device 20, a short-circuit relay circuit 5, and a controller 2. The capacitor 12 is connected to an input terminal of the inverter 4. The discharge device 20 is a device for discharging the capacitor 12. The short-circuit relay circuit 5 switches a connection destination of a motor line 14 of UVW-three phase extruded from the motor 6 from the inverter 4 to mutual short circuiting. The controller 2 switches the connection destination of the motor line 14 from the inverter 4 to mutual short-circuiting if a signal indicating that the vehicle has collided, and causes the discharge device 20 to operate. Induction current due to counter-electromotive force of the motor does not flows into the discharge device 20, and the capacitor 12 is quickly discharged.

Description

  The present invention relates to an electric vehicle provided with an electric motor (motor) for driving wheels. The “electric vehicle” in the present specification includes a fuel cell vehicle and a hybrid vehicle including both a wheel driving motor and an engine.

  An electric vehicle includes an inverter that converts DC power of a battery into AC power suitable for driving a motor. The inverter is provided with a capacitor in order to suppress current pulsation accompanying the switching operation of the inverter. Hereinafter, such a capacitor is referred to as a smoothing capacitor. The wheel driving motor consumes a large amount of power, and the current handled by the inverter is large. Therefore, a smoothing capacitor having a large capacity is also provided. Therefore, when the vehicle collides with an obstacle, it is preferable to quickly release the charge remaining in the smoothing capacitor for safety.

  As an example of a technique for discharging a smoothing capacitor, Patent Document 1 and Patent Document 2 propose a technique for using a switching loss of an inverter to discharge electrical energy stored in the capacitor. In addition, as another technique for discharging the smoothing capacitor, it is considered to use a discharge resistor (a device that has a large electric resistance and generates heat when a current is passed to dissipate electric energy). It has been proposed to use an existing electrical device, for example, a headlight or a horn, as a discharge device instead of the discharge resistor. The techniques of Patent Document 1 and Patent Document 2 utilize the inverter itself as a discharge device.

JP 2010-130845 A JP 2005-20952 A

  If the impact of the collision is large, the drive wheels may float and the motor may remain rotating. If the motor continues to rotate, current generated by the counter electromotive force of the motor flows into the inverter. If the current generated by the back electromotive force flows into the discharge device even while the electric energy stored in the smoothing capacitor is being discharged by the discharge device, the time required for the discharge becomes long. The present specification provides a technique for preventing a discharge time of a smoothing capacitor from becoming long due to a current generated by a counter electromotive force of a motor at the time of a collision.

  The technology disclosed in the present specification disconnects the inverter and the motor (three-phase AC motor) when the vehicle collides (more precisely, when a signal indicating that the vehicle has collided is transmitted from some device). The technology disclosed in this specification not only disconnects the motor from the inverter, but also short-circuits the UVW three-phase motor wires (power supply wires connected to the motor windings) from the motor. By short-circuiting the motor wires, a circuit in which the motor windings are closed is formed. Then, an induced current (alternating current) is generated by the back electromotive force of the motor, and the induced current generates a force (Lorentz force) by electromagnetic action. Lorentz force acts in a direction to stop the rotation of the motor. That is, by disconnecting a plurality of motor wires from the inverter and short-circuiting each other, it is possible to prevent inductive current from flowing into the inverter and simultaneously apply braking by Lorentz force to the motor.

  The technology disclosed in this specification can be embodied in an electric vehicle. The electric vehicle includes an inverter that supplies electric power to a wheel driving motor (three-phase AC motor), a capacitor (smoothing capacitor), a discharge device, a relay, and a controller. The capacitor is connected in parallel to the input terminal of the inverter. The discharge device is connected in parallel with the capacitor and discharges the capacitor. The relay switches the connection destination of the UVW three-phase motor wire coming out of the motor so as to short-circuit each other from the inverter. In the following, such a relay is referred to as a “short-circuit relay” and distinguished from other relays. When a signal indicating that the vehicle has collided is input, the controller controls the short-circuit relay so that the connection destination of the motor line is switched from the inverter to the mutual short circuit, and activates the discharge device. The discharge device may be, for example, a discharge resistor. In this case, operating the discharge device corresponds to connecting the discharge resistance to the smoothing capacitor.

  When the rotation of the motor is low, the induced current due to the counter electromotive force is small, and there is no need to consider this. Therefore, the controller may operate the discharge device without switching the connection destination of the motor line from the inverter to the mutual short-circuit when the rotational speed of the motor is equal to or lower than a predetermined rotational speed threshold. However, when the rotational speed of the motor exceeds the rotational speed threshold, the controller switches the connection destination of the motor line from the inverter to the mutual short circuit and operates the discharge device.

  Alternatively, if it is not necessary to consider the induced current due to the counter electromotive force of the motor, the motor itself can be used as a discharge device. That is, the controller releases the electric power stored in the capacitor to the motor without switching the connection destination of the motor line from the inverter to the mutual short circuit when the motor rotation speed is equal to or less than a predetermined rotation speed threshold. Also good. However, when the rotational speed of the motor exceeds the rotational speed threshold, the controller switches the connection destination of the motor line from the inverter to the mutual short circuit and operates the discharge device.

  Considering the reliable operation of the short-circuit relay, the short-circuit relay is preferably connected so that the motor wires are short-circuited to each other when no power is supplied and the motor wires are connected to the inverter when power is supplied.

  Furthermore, when operating the discharge device, it is also undesirable for current to flow from the battery into the discharge device. Therefore, in a further improvement of the electric vehicle disclosed in this specification, the controller further includes an input cutoff relay for connecting or disconnecting a battery to a circuit in which a capacitor, a discharge device, and an inverter are connected in parallel. It is preferable to control the input cut-off relay so that the connection between the circuit and the battery is cut off when a signal indicating that the operation has been performed is input. In this case, the input cut-off relay may be a normally open type that disconnects the circuit and the battery when power is not supplied and connects the battery to the circuit when power is supplied.

It is a circuit diagram of the drive system of the electric vehicle of an Example. It is a flowchart figure of a discharge process (1st Example). It is a flowchart figure of a discharge process (2nd Example). It is a flowchart figure of a discharge process (3rd Example). It is a flowchart figure of a discharge process (4th Example).

  (First Embodiment) FIG. 1 is a circuit diagram of a drive system of an electric vehicle 100 according to the embodiment. The electric vehicle 100 is a one-motor vehicle having wheel driving motors 6. The motor 6 is a three-phase AC motor. It should be noted that FIG. 1 shows only the units necessary for explaining the present invention, and does not show all the units that the electric vehicle should have.

  The drive system of the electric vehicle 100 mainly includes a battery 9, an input cutoff relay 3, a discharge device 20, a smoothing capacitor 12, an inverter 4, a short-circuit relay circuit 5, a motor 6, and a controller 2. The battery 9 is typically a high voltage, high output lithium ion battery with an output voltage of 300 [V]. In addition to the battery 9, the electric vehicle 100 also has a sub-battery (not shown) for driving a low-power device such as an audio and navigation system and the controller 2. The output voltage of the sub battery is typically 12 [V] or 24 [V].

  In addition, the electric vehicle 100 includes, as sensors, a current sensor 13 that measures a current flowing through each of the UVW three-phase motor wires 14 that supply power to the motor 6, and a rotation speed sensor 15 that measures the rotation speed of the motor 6. Prepare. In addition, a voltage sensor that measures the input voltage of the inverter 4 and a voltage sensor that measures the output voltage of the inverter 4 are included, but these are not shown.

  First, the inverter 4 will be described. The inverter 4 is composed of six switching circuits Sw1 to Sw6. That is, here, six switching circuit groups that generate three-phase AC power from the DC power of the battery 9 are referred to as inverters 4. Each of the switching circuits Sw1 to Sw6 has a circuit configuration in which an IGBT and a diode (freewheeling diode) are connected in antiparallel. In order to configure a switching circuit that allows a large current with an IGBT having a small allowable current value, a single switching circuit may be configured by connecting a plurality of IGBTs in parallel. The controller 2 supplies a PWM signal for turning on (conducting) / OFF (opening) each switching circuit (IGBT).

  In the inverter 4, three sets in which two switching circuits are connected in series are connected in parallel, and an inverter output line extends from the connection point of the two switching circuits in series to the motor 6. The output of the inverter 4 is three UVWs, and the three output lines are connected to each UVW line (motor line 14) of the motor through the short-circuit relay circuit 5. Each of the three output lines and a set of switching circuits corresponding to the output lines are called “arms”.

  The short-circuit relay circuit 5 is a switch for switching the connection destination of each of the UVW three-phase motor wires 14 coming out of the motor so as to short-circuit each other from the corresponding output terminal of the inverter. The short-circuit relay circuit 5 includes three relays 5a, 5b, and 5c, and can switch the connection destination of each line of the motor line 14 from the inverter output to the common conduction line 5d. The three relays 5 a to 5 c are switched at the same time according to a command from the controller 2. The short circuit relay circuit 5 is a general term for the three relays 5a to 5c. The relays 5a to 5c are connected so that the motor wire 14 is connected to the inverter 4 when voltage is supplied to the coil that drives the contacts, and the plurality of motor wires 14 are short-circuited to each other when no power is supplied. Has been. Hereinafter, for convenience of expression, short-circuiting a plurality of motor wires 14 may be simply referred to as mutual short-circuiting.

  Input terminals 4 a and 4 b of the inverter 4 are connected to the battery 9 via the input cutoff relay 3. The input cutoff relay 3 is incorporated in both the positive electrode line 10 a connected to the positive electrode of the battery 9 and the negative electrode line 10 b connected to the negative electrode of the battery 9, and both relays are opened and closed at the same time by a command from the controller 2. The relay incorporated in the positive electrode wire 10a and the relay incorporated in the negative electrode wire 10b are collectively referred to as the input cutoff relay 3. The input cutoff relay 3 is closed while the voltage is supplied to the coil that drives the contact (that is, the battery 9 and the inverter 4 are connected), and is opened when no power is supplied (that is, the battery 9 and the inverter 4 are cut off). ). That is, the input cutoff relay 3 is a so-called normally open type.

  On the input side (DC side) of the inverter 4, a smoothing capacitor 12 is connected between the positive electrode line 10a and the negative electrode line 10b. That is, the smoothing capacitor 12 is connected in parallel to the input terminal of the inverter (DC power input terminal). In other words, the smoothing capacitor 12 is connected between the two input terminals 4 a and 4 b of the inverter 4. The smoothing capacitor 12 is inserted to suppress the pulsation of the input current due to the influence of the switching operation of the inverter 4. The smoothing capacitor 12 has a large capacity in order to smooth a large current flowing from the battery 9 to the inverter 4. In the event of a collision, it is not preferable that the electrical energy stored in the smoothing capacitor 12 flow into other devices carelessly. Therefore, it is preferable that the electric energy accumulated in the smoothing capacitor 12 is quickly released when the vehicle collides. The electric vehicle 100 includes a discharge device 20 for that purpose.

  The discharge device 20 is a combination of a discharge resistor 22 and a switch relay 21, and is connected in parallel with the smoothing capacitor 12. The discharge resistor 22 is a metal having high resistance and high heat resistance, and generates heat when a current flows. The discharge resistor 22 is a device that converts electric energy into heat energy and dissipates it. The switch relay 21 is opened and closed according to a command from the controller 2. The controller 2 driving the switch relay 21 and connecting the discharge resistor 22 to the smoothing capacitor 12 corresponds to an example of “actuating the discharge device”. The switch relay 21 closes the contact (i.e., connects the discharge resistor 22 to the smoothing capacitor 12) while the voltage is supplied to the coil that drives the contact, and opens when the power is not supplied (i.e., the discharge resistor). 22 is disconnected from the smoothing capacitor 12). The switch relay 21 is also a so-called normally open type.

  In addition, the electric vehicle 100 includes an acceleration sensor 24. The acceleration sensor 24 is a part of an airbag system (not shown), and outputs a signal when the detected acceleration is greater than or equal to a predetermined magnitude. “When the detected acceleration is greater than or equal to a predetermined magnitude” means that the vehicle has collided. Therefore, the signal received from the acceleration sensor 24 by the controller 2 corresponds to a “signal indicating that the vehicle has collided”. Hereinafter, the “signal indicating that the vehicle has collided” output from the acceleration sensor 24 is simply referred to as a “collision signal”. In addition to the signal from the acceleration sensor 24, a “signal indicating that the vehicle has collided” may be sent from another device. For example, a signal indicating that communication between electronic devices has been interrupted can also be one of the “signals indicating that the vehicle has collided”. Strictly speaking, the “signal indicating that the vehicle has collided” is a “signal for notifying an event assumed to occur when the vehicle collides in the vehicle design stage”.

  When the controller 2 receives the collision signal, the controller 2 executes a process of releasing the electric energy (charge) accumulated in the smoothing capacitor 12. FIG. 2 shows a flowchart of a process (discharge process) executed by the controller 2 when a collision signal is received. As shown in FIG. 2, when receiving a collision signal, the controller 2 first stops the inverter 4 (S2). Next, the controller 2 switches the short-circuit relay circuit 5 to short-circuit the motor wires 14 (S4). Then, the controller 2 operates the discharge device 20 (S6). As described above, “driving the discharge device” is an example of closing the switch relay 21 and connecting the discharge resistor 22 to the smoothing capacitor 12.

  The above operation has the following advantages. First, the plurality of motor wires 14 are short-circuited to each other and the motor 6 is disconnected from the inverter 4, thereby preventing the induced current caused by the counter electromotive force from flowing back to the inverter 4. On the inverter side, the discharge device 20 (discharge resistor 22) dissipates the electrical energy of the smoothing capacitor 12, but the induction current is prevented from being applied thereto. Addition of the induced current prevents delay of the smoothing capacitor 12 from completing the discharge. Second, even if the motor 6 continues to rotate due to inertia after the collision, a braking force can be applied to the motor 6 by short-circuiting the motor wires 14. This is because the winding of the motor is closed due to the mutual short circuit, and the induced current caused by the counter electromotive force induces a Lorentz force, and the Lorentz force acts as a braking force on the motor.

  There are several improvement patterns in the discharge process executed by the controller 2. Hereinafter, another discharge process will be described. Since the hardware configuration may be the same as that shown in FIG. 1, an improved discharge process will be described below with reference to the configuration shown in FIG.

  (Second Embodiment) FIG. 3 shows a flowchart of the discharge process of the second embodiment. In the discharge process of the second embodiment, it is determined whether or not to switch the short-circuit relay according to the rotational speed of the motor. When receiving the collision signal, the controller 2 first stops the inverter 4 (S12). Next, the controller 2 determines whether or not the rotational speed of the motor 6 is equal to or less than a predetermined rotational speed threshold Nth based on the sensor data of the rotational speed sensor 15 (S14). When the rotation speed of the motor 6 is equal to or less than the threshold value Nth (S14: YES), the controller 2 immediately activates the discharge device 20 without switching the short-circuit relay 5 circuit (without mutually short-circuiting the motor line 14) ( S18). On the other hand, when the motor rotational speed exceeds the threshold value Nth, the controller 2 operates the discharge device 20 after switching the short circuit relay circuit 5 to mutually short the motor wires 14 (S14: NO, S16, S18).

  The rotation speed threshold Nth of the motor is set to a value such that the induced current due to the back electromotive force does not significantly affect the discharge of the smoothing capacitor 12. For example, the rotation speed threshold Nth is set to 1000 [rpm]. If the rotation is so low, the influence of the back electromotive force on the discharge of the smoothing capacitor 12 is small. In the discharge process of the second embodiment, since the discharge device 20 is driven immediately when the rotational speed of the motor is low, the smoothing capacitor 12 is quickly discharged.

  (Third Embodiment) FIG. 4 shows a flowchart of the discharge process of the third embodiment. In the discharge process of the third embodiment, when the rotational speed of the motor is low, the smoothing capacitor 12 is discharged using the motor 6 instead of the discharge device 20. When receiving the collision signal, the controller 2 first stops the inverter 4 (S22). Next, the controller 2 determines whether or not the rotational speed of the motor 6 is equal to or less than a predetermined rotational speed threshold Nth based on the sensor data of the rotational speed sensor 15 (S24). When the rotational speed of the motor 6 is equal to or less than the threshold value Nth (S24: YES), the controller 2 uses the motor 6 to smooth the capacitor without switching the short circuit relay 5 circuit (without mutually shorting the motor line 14). 12 is discharged (S29). Specifically, the controller 2 gives an appropriate switching command (PWM signal) to the switching circuit of the inverter 4. Then, the electric energy stored in the smoothing capacitor 12 flows to the motor 6 through the inverter 4, and the electric energy is consumed by the switching loss of the inverter 4 and the movement of the motor 6. On the other hand, when the motor rotation speed exceeds the threshold value Nth, the controller 2 operates the discharge device 20 after switching the short circuit relay circuit 5 to mutually short the motor wires 14 (S24: NO, S26, S28). The magnitude of the motor rotation speed threshold Nth is determined in the same manner as in the second embodiment.

  In the case of the third embodiment, when the number of rotations of the motor is low at the time of receiving a collision signal, the motor 6 and the inverter 4 are used as discharge devices. Since the discharge resistor 22 dissipates electrical energy due to heat generation, it is heavily consumed. In the third embodiment, when the smoothing capacitor 12 can be discharged by other than the discharge resistor, it is not necessary to use the discharge resistor. Therefore, the consumption of the discharge resistor 22 can be reduced.

  (Fourth Embodiment) FIG. 5 shows a flowchart of the discharge process of the fourth embodiment. In the discharge process of the fourth embodiment, the battery 9 is disconnected when the discharge device 20 is operated. The current from the battery 9 is prevented from flowing into the discharge device 20, and the smoothing capacitor 12 is discharged quickly. When receiving the collision signal, the controller 2 stops the inverter 4 (S32). Next, the controller 2 switches the short circuit relay circuit 5 to mutually short the motor wires 14 (S34). Next, the controller 2 opens the input cutoff relay 3, and disconnects the battery 9 from the circuit of the discharge device 20 and the smoothing capacitor 12 (S36). Thereafter, the controller 2 operates the discharge device 20 (S38).

  In the case of the fourth embodiment, since no current flows from the battery 9 into the discharge device 20 during the discharge of the smoothing capacitor 12, the discharge of the smoothing capacitor 12 is completed quickly.

  Points to be noted regarding the embodiment will be described. It is also preferable to incorporate the process for opening the input cutoff relay 3 (step S36 in FIG. 5) into the discharge process in the second embodiment or the third embodiment. For example, in the process of step S12 (see FIG. 3), it is also preferable that the controller 2 stops the inverter 4 and opens the input cutoff relay 3. Alternatively, in the process of step S22 (see FIG. 4), the controller 2 may stop the inverter 4 and open the input cutoff relay 3. In any case, the discharge of the smoothing capacitor 12 can be completed quickly by disconnecting the battery 9 from the circuit of the discharge device 20 and the smoothing capacitor 12.

  The discharge device 20 is not limited to the discharge resistor 22. Vehicle audio, headlights, or horns may be used as discharge devices.

  The electric vehicle 100 of the example was a one-motor vehicle. The technique disclosed in this specification is also preferably applied to a hybrid vehicle having both a wheel driving motor and an engine.

  In the embodiment, several flowcharts have been described. The order of processing in the flowchart may be changed within a range not exceeding the technical idea disclosed in the present specification. For example, in the flowchart of FIG. 2, after switching the short circuit relay (S4), the discharge device is activated (S6). Instead of such processing order, the discharge device may be operated simultaneously with switching the short-circuit relay. The short-circuit relay may be switched after operating the discharge device. However, it should be noted that the switching of the short-circuit relay after the discharge device is operated needs to be performed within a time period in which the current caused by the back electromotive force of the motor does not exceed the allowable discharge time of the discharge device.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Controller 3: Input cutoff relay 4: Inverter 5: Short-circuit relay circuits 5a, 5b, 5c: Relay 5d: Common conduction line 6: Motor 9: Battery 10a: Positive line 10b: Negative line 12: Smoothing capacitor 13: Current Sensor 14: Motor wire 15: Rotational speed sensor 20: Discharge device 21: Switch relay 22: Discharge resistor 24: Acceleration sensor 100: Electric vehicle Sw: Switching circuit

Claims (6)

An inverter that supplies power to the wheel drive motor;
A capacitor connected in parallel to the input end of the inverter;
A discharge device connected in parallel to the capacitor and discharging the capacitor;
A short-circuit relay that switches the connection destination of the UVW three-phase motor wires coming out of the motor so as to short-circuit each other from the inverter;
When a signal indicating that the vehicle has collided is input, the controller that controls the short-circuit relay to switch the connection destination of the motor line from the inverter to the mutual short-circuit, and operates the discharge device;
An electric vehicle comprising: The controller
If the motor rotation speed is less than or equal to a predetermined rotation speed threshold, the discharge device is operated without switching the connection destination of the motor wire from the inverter to the mutual short circuit,
When the rotational speed of the motor exceeds the rotational speed threshold value, the connection destination of the motor wire is switched from the inverter to the mutual short circuit and the discharge device is operated.
The electric vehicle according to claim 1. The controller
When the motor speed is less than or equal to a predetermined speed threshold value, the power stored in the capacitor is discharged to the motor without switching the connection destination of the motor line from the inverter to the mutual short circuit.
When the rotational speed of the motor exceeds the rotational speed threshold value, the connection destination of the motor wire is switched from the inverter to the mutual short circuit and the discharge device is operated.
The electric vehicle according to claim 1.   The electric circuit according to any one of claims 1 to 3, wherein the short-circuit relay short-circuits the motor wires when no power is supplied, and connects the motor wires to the inverter when electric power is supplied. Automobile. The battery is further provided with an input cutoff relay that is provided at the output end of the battery and connects or disconnects the battery to a circuit in which a capacitor, a discharge device and an inverter are connected in parallel.
5. The controller according to claim 1, wherein the controller controls the input cutoff relay so as to cut off the connection between the battery and the inverter when a signal indicating that the vehicle has collided is input. The electric vehicle described in 1.   The said input interruption | blocking relay is a normally open type which cuts the connection of the said circuit and a battery at the time of no power supply, and connects a battery and an inverter when electric power is supplied. Electric car.

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