Electric motor vehicle

Abstract

To suppress oscillation of the output voltage of a DC / DC converter during a discharge process performed by the DC / DC converter.SOLUTION: An electric motor vehicle comprises: an inverter which drives a motor; a power storage device connected with a first power line with the inverter; a relay provided in the first power line; a capacitor connected on the inverter side of the relay of the first power line; a DC / DC converter which steps down voltage on the inverter side of the relay of the first power line to be supplied to a second power line; and a control device which turns the relay off to execute discharge processing by the DC / DC converter when discharge of the capacitor is requested. The control device controls the DC / DC converter so that the output current of the DC / DC converter is restricted to a value not exceeding the upper limit in the discharge processing.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to electric vehicles. [Background technology]

[0002] Conventionally, as this type of technology, a system interconnection device has been proposed that includes a power generation device, a converter that converts the DC voltage of the power generation device, an inverter that converts the DC voltage of the converter into AC voltage and outputs it to multiple phase electric wires of a system power source, a capacitor provided between busbars of the inverter, a voltage sensor that detects the voltage of the capacitor, relays provided on each of the multiple phase electric wires, and a power supply circuit that supplies power using the DC voltage between the busbars (see, for example, Patent Document 1). In this system interconnection device, after setting a target voltage of the capacitor to a first voltage that is equal to or higher than the peak value of the system voltage and controlling the converter, one of the relays is controlled to be turned off and the other relays are controlled to be turned on, and the target voltage is set to a second voltage lower than the first voltage to control the converter. Then, when the capacitor voltage does not become equal to or lower than a threshold value lower than the peak value or does not decrease by a predetermined amount or more, it is determined that the one relay is welded. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-48269 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an electric vehicle including an inverter for driving a motor, a power storage device connected to a first power line together with the inverter, a relay provided on the first power line, a capacitor connected to the first power line on the inverter side of the relay, and a DC / DC converter capable of stepping down the voltage on the first power line on the inverter side of the relay and supplying it to a second power line, it is considered that when a discharge of the capacitor is requested, the relay is turned off and a discharge process is performed by the DC / DC converter. Here, when the input voltage of the DC / DC converter drops, the resistance to oscillation of the output voltage (increase in pulsating components) tends to decrease. For this reason, when the input voltage (voltage of the capacitor) drops due to the discharge process by the DC / DC converter, oscillation of the output voltage is induced, which may affect the life of parts, etc. The electric vehicle disclosed herein has a main object to suppress oscillation of the output voltage of the DC / DC converter when the discharge process by the DC / DC converter is performed. [Means for solving the problem]

[0005] The electric vehicle of the present disclosure employs the following means to achieve the above-mentioned primary object. The electric vehicle of the present disclosure is an electric vehicle including an inverter that drives a motor, a power storage device connected together with the inverter to a first power line, a relay provided on the first power line, a capacitor connected to the first power line on the inverter side of the relay, a DC / DC converter capable of stepping down a voltage on the first power line on the inverter side of the relay and supplying the voltage to a second power line, and a control device that turns off the relay and executes a discharge process by the DC / DC converter when a discharge of the capacitor is requested, and the control device controls the DC / DC converter so that an output current of the DC / DC converter is limited to an upper limit value or less during the discharge process.

[0006] In the electric vehicle disclosed herein, the DC / DC converter is controlled so that the output current of the DC / DC converter is limited to an upper limit value or less during the discharge process. Here, the upper limit value is determined in advance through analysis, experiment, or the like as a current at which the output voltage of the DC / DC converter does not oscillate until the end of the discharge process. This makes it possible to suppress oscillation of the output voltage of the DC / DC converter during the discharge process by the DC / DC converter. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of an electric vehicle 20 according to the present disclosure. [Diagram 2] 4 is a flowchart showing an example of a processing routine executed by an electronic control unit 70. [Diagram 3] 11 is an explanatory diagram showing an example of the relationship between the voltage Vc1 of the capacitor 31, the voltage Vc2 of the capacitor 44, the output current Io, and the output oscillation region. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic configuration diagram of an electric vehicle 20 of the present disclosure. As shown in the figure, the electric vehicle 20 of the present disclosure includes a motor 22, an inverter 24, a high-voltage battery 26 (electricity storage device), a system main relay 28, a capacitor 31, an auxiliary battery 32, a DC / DC converter 40, and an electronic control unit 70.

[0009] The motor 22 is configured as, for example, a synchronous generator motor, and includes a rotor with a permanent magnet embedded in the rotor core, and a stator with a three-phase coil wound around the stator core. The rotor of the motor 22 is connected to a drive shaft connected to the drive wheels. The inverter 24 has a plurality of switching elements, is used to drive the motor 22, and is connected to the power line 30.

[0010] The high-voltage battery 26 is configured as, for example, a lithium-ion secondary battery or a nickel-hydrogen secondary battery with a rated voltage of several hundred volts. The positive terminal of the high-voltage battery 26 is connected to a power line (positive line) 30, and the negative terminal is connected to a ground (common negative line). For example, the metallic vehicle body is used as the ground.

[0011] System main relay 28 is provided on power line 30, and is turned on and off to connect and disconnect inverter 24 and high-voltage battery 26. Capacitor 31 is connected to the inverter 24 side of power line 30 relative to system main relay 28 and to ground.

[0012] The auxiliary battery 32 is configured as, for example, a lead-acid battery with a rated voltage of 12 V. The positive terminal of the auxiliary battery 32 is connected to a power line (positive line) 34, and the negative terminal is connected to ground (common negative line).

[0013] The DC / DC converter 40 is connected to the power line 30, the power line 34, and the ground. The DC / DC converter 40 includes switching elements 41, 42, a reactor 43, and a capacitor 44. For example, a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) is used as the switching elements 41, 42. Diodes are connected in parallel to the switching elements 41, 42 in the reverse direction. The switching element 41 is connected to the power line 30. The switching element 42 is connected to the switching element 41 and the ground. The reactor 43 is connected to the connection point of the switching elements 41, 42 and the power line 34. The capacitor 44 is connected to the power line 34 and the ground. The DC / DC converter 40 is configured to step down the power on the inverter 24 or capacitor 31 side of the system main relay 28 of the power line 30 by switching the switching elements 41, 42, and supply the power to the power line 34.

[0014] The electronic control unit 70 includes a microcomputer, and the microcomputer includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a flash memory, an input / output port, a communication port, and the like. Signals are input to the electronic control unit 70 from various sensors. Examples of signals input to the electronic control unit 70 include a rotational position θm from a rotational position sensor that detects the rotational position of the rotor of the motor 22, and phase currents Iu, Iv, and Iw from a current sensor that detects the current of each phase of the motor 22. Examples of signals input to the electronic control unit 70 include a voltage Vb1 from a voltage sensor attached to the output terminal of the high-voltage battery 26, a current Ib from a current sensor attached to the output terminal of the high-voltage battery 26, and a voltage Vb2 from a voltage sensor attached to the output terminal of the auxiliary battery 32. Examples of the voltage Vc1 of the capacitor 31 (between the power line 30 and ground) from a voltage sensor 31v attached between the terminals of the capacitor 31, i.e., the input voltage of the DC / DC converter 40, and the voltage Vc2 of the capacitor 44 (between the power line 34 and ground) from a voltage sensor 44v attached between the terminals of the capacitor 44, i.e., the output voltage of the DC / DC converter 40, can also be mentioned. Examples of the output current Io from a current sensor 46 attached in series to the reactor 43 can also be mentioned. Examples of the start signal from the start switch 72, the shift position from a shift position sensor that detects the operation position of the shift lever, the accelerator opening from an accelerator pedal position sensor that detects the amount of depression of the accelerator pedal, the brake pedal position from a brake pedal position sensor that detects the amount of depression of the brake pedal, and the vehicle speed from a vehicle speed sensor can also be mentioned. Various control signals are output from the electronic control unit 70. Examples of the signal output from the electronic control unit 70 include control signals to the inverter 24 and the DC / DC converter 40, for example.

[0015] Next, the operation of the electric vehicle 20 of this embodiment, particularly the operation when the start switch 72 is turned off (discharging of the capacitor 31 is requested), will be described. Fig. 2 is a flowchart showing an example of a processing routine executed by the electronic control unit 70. This routine is executed when the start switch 72 is turned off.

[0016] When this routine is executed, the electronic control unit 70 first turns off the system main relay 28 (step S100). Next, the electronic control unit 70 sets an output current upper limit value Iolim in the discharge process by the DC / DC converter 40 (step S110), and starts the discharge process by the DC / DC converter 40 using the set output current upper limit value Iolim (step S120).

[0017] Here, in the discharge process by DC / DC converter 40, DC / DC converter 40 is controlled so that output current Io from current sensor 46 is limited to be equal to or less than output voltage upper limit value Iolim. For example, a target voltage command Vo* is set so that the difference between output current Io and target value Io* less than output current upper limit value Iolim is cancelled out, and a duty command D* is set so that voltage Vc2 of capacitor 44 from voltage sensor 44v and target voltage command Vo* are cancelled out, and switching control of switching elements 41, 42 is performed using the set duty command D*.

[0018] The output current upper limit Iolim is determined in advance as follows. FIG. 3 is an explanatory diagram showing an example of the relationship between the voltage Vc1 of the capacitor 31, the voltage Vc2 of the capacitor 44, the output current Io, and the output oscillation region. Here, the output oscillation region is a region in which the voltage Vc2 of the capacitor 44 (the output voltage of the DC / DC converter 40) may oscillate (the pulsating component may increase). The impedance Zdcdc of the DC / DC converter 40 can be expressed by equation (1) using the voltage Vc1 of the capacitor 31, the voltage Vc2 of the capacitor 44, the output current Io, and the step-down efficiency η. In equation (1), when the voltage Vc1 of the capacitor 31 decreases, the impedance Zdcdc of the DC / DC converter 40 decreases rapidly, and the voltage Vc2 of the capacitor 44 is more likely to oscillate. Through analysis and experiments by the inventors, it has been found that the lower limit of the output current Io of the output oscillation region becomes lower as the voltage Vc1 of the capacitor 31 decreases, and becomes lower as the voltage Vc2 of the capacitor 44 increases, as shown in the figure. In light of this, in the embodiment, when the system main relay 28 is normally turned off, the output current upper limit value Iolim is set in advance by analysis, experiment, or the like so that the relationship between the voltage Vc1 of the capacitor 31, the voltage Vc2 of the capacitor 44, and the output current Io does not enter the output oscillation region until the voltage Vc1 of the capacitor 31 becomes less than the threshold value Vcref described later. For example, the output current upper limit value Iolim is set to a value somewhat lower than the lower limit of the output current Io in the output oscillation region when the voltage Vc1 of the capacitor 31 is the threshold value Vcref and the voltage Vc2 of the capacitor 44 is at the upper limit of the expected voltage range (for example, about 15V to 15.5V). By setting the output current upper limit value Iolim in this way and using it for the discharge process by the DC / DC converter 40, it is possible to suppress the voltage Vc2 of the capacitor 44 (the output voltage of the DC / DC converter 40) from oscillating during the discharge process by the DC / DC converter 40. As a result, it is possible to suppress the occurrence of inconveniences due to the oscillation of the voltage Vc2 of the capacitor 44, such as the effect on the life of parts.

[0019] Zdcdc=Vc1 2 / (Vc2×Io)×η (1)

[0020] Then, it is determined whether the voltage Vc1 of the capacitor 31 (the input voltage of the DC / DC converter 40) is less than the threshold value Vcref (step S130), and if it is determined that the voltage Vc1 of the capacitor 31 is equal to or greater than the threshold value Vcref, it is determined whether a predetermined time Tref has elapsed since the start of the discharge process by the DC / DC converter 40 (step S140). If it is determined that the predetermined time has not elapsed since the start of the discharge process by the DC / DC converter 40, the process returns to step S130. Here, the threshold value Vcref is predetermined as a voltage at which the discharge process by the DC / DC converter 40 may be terminated. The predetermined time Tref is predetermined as a time that is somewhat longer than the time required for the voltage Vc of the capacitor 31 to become less than the threshold value Vcref by the discharge process by the DC / DC converter 40 when the system main relay 28 is normally turned off.

[0021] When it is determined in step S130 that the voltage Vc1 of the capacitor 31 is less than the threshold value Vcref, or when it is determined in step S140 that a predetermined time Tref has elapsed since the start of the discharge process by the DC / DC converter 40, the discharge process by the DC / DC converter 40 is terminated (step S150). Then, a welding check of the system main relay 28 is performed (step S160), and this routine is terminated. Here, in the welding check of the system main relay 28, for example, when the voltage Vc1 of the capacitor 31 becomes less than the threshold value Vcref and the discharge process by the DC / DC converter 40 is terminated, it may be determined that the system main relay 28 is normal, and when the predetermined time Tref has elapsed since the start of the discharge process by the DC / DC converter 40 and the discharge process is terminated, the system main relay 28 may be determined to be welded. Also, it may be determined whether the system main relay 28 is welded or not using the voltage Vc1 of the capacitor 31 when the system main relay 28 is on / off controlled.

[0022] In the electric vehicle 20 of the present embodiment described above, the DC / DC converter 40 is controlled so that the output current Io of the DC / DC converter 40 is limited to be equal to or less than the output current upper limit value Iolim during the discharge process by the DC / DC converter 40. This makes it possible to suppress oscillation of the voltage Vc2 of the capacitor 44 (the output voltage of the DC / DC converter 40) during the discharge process by the DC / DC converter 40.

[0023] In the above-described embodiment, the high-voltage battery 26, the capacitor 31, the auxiliary battery 32, the switching element 42, and the capacitor 44 are connected to ground as a common negative line, but the common negative line does not have to be grounded.

[0024] In the above-described embodiment, the electric vehicle 20 is provided with the system main relay 28 on the positive electrode side (power line 30) of the high-voltage battery 26, but the electric vehicle 20 may also be provided with a system main relay on the negative electrode side of the high-voltage battery 26.

[0025] In the above-described embodiment, the electric vehicle 20 includes the high-voltage battery 26 and the auxiliary battery 32 as power storage devices, but at least one of these may be replaced with a capacitor.

[0026] In the above-described embodiment, the electric vehicle 20 is described as including the motor 22, the inverter 24, the high-voltage battery 26, the auxiliary battery 32, and the DC / DC converter 40. However, the present invention is not limited to this, and may be implemented as a hybrid vehicle including an engine in addition to a hardware configuration similar to that of the electric vehicle 20, or as a fuel cell vehicle including a fuel cell in addition to a hardware configuration similar to that of the electric vehicle 20.

[0027] The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on Means for Solving the Problems will be described below. In the embodiment, the inverter 24 corresponds to the "inverter", the high voltage battery 26 corresponds to the "electricity storage device", the system main relay 28 corresponds to the "relay", the capacitor 31 corresponds to the "capacitor", the DC / DC converter 40 corresponds to the "DC / DC converter", and the electronic control unit 70 corresponds to the "control device".

[0028] The above describes embodiments for implementing the present disclosure, but the present disclosure is not limited to these embodiments, and it goes without saying that the present disclosure can be implemented in various forms without departing from the gist of the present disclosure. [Industrial Applicability]

[0029] The present disclosure can be used in the electric vehicle manufacturing industry and the like. [Explanation of symbols]

[0030] 20 electric vehicle, 22 motor, 24 inverter, 26 high voltage battery, 28 system main relay, 30 power line, 31 capacitor, 31v voltage sensor, 32 auxiliary battery, 34 power line, 40 DC / DC converter, 41 switching element, 42 switching element, 43 reactor, 44 capacitor, 44v voltage sensor, 46 current sensor, 70 electronic control unit, 72 start switch.

Claims

[Claim 1] an inverter that drives a motor; a power storage device that is connected together with the inverter to a first power line; a relay provided on the first power line; a capacitor that is connected to the first power line on the inverter side of the relay; a DC / DC converter that can step down a voltage on the first power line on the inverter side of the relay and supply the voltage to a second power line; and a control device that turns off the relay and executes a discharge process by the DC / DC converter when a discharge of the capacitor is requested, the control device controls the DC / DC converter during the discharge process so that an output current of the DC / DC converter is limited to an upper limit value or less. Electric car.

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