Electric motor car

Abstract

To suppress step-up function degradation of a step-up converter in an electric motor car.SOLUTION: An electric motor car comprises: at least one motor for driving a wheel; a battery pack for supplying electric power to the motor; and a power control unit which controls supply power from the battery pack to the motor. The battery pack has at least one battery cell, a first step-up converter which boosts output power from the battery cell, and a first controller which controls operation of the first step-up converter. The power control unit has a second set-up converter which boosts output power from the battery pack, and a second controller which controls operation of the second step-up converter. At least one of the first controller and the second controller execute processing for determining each set-up width by the first set-up converter and the second set-up converter on the basis of each loss predicted in the first set-up converter and the second set-up converter.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed in this specification relates to electric vehicles. The electric vehicle referred to herein broadly means a vehicle driven by a motor, including, for example, battery electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and fuel cell electric vehicles.

Background Art

[0002] Patent Document 1 describes an electric vehicle. This electric vehicle includes a motor that drives the wheels, a battery pack that supplies power to the motor, and a power control unit that controls the power supplied from the battery pack to the motor. The power control unit is provided with a boost converter that boosts the output power from the battery pack.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an electric vehicle as described above, in order to improve the cruising performance of the electric vehicle, it is conceivable to adopt a large-capacity battery. However, there is an antagonistic relationship between the capacity of the battery and the output voltage. Therefore, when a large-capacity battery is adopted, the output voltage of the battery may be insufficient for the system voltage required for the motor or the like. To avoid this, it is conceivable to provide a boost converter also in the battery pack. In this case, the boost converter of the battery pack and the boost converter of the power control unit are connected in series. Therefore, it is important to appropriately determine the boost width of each of these two boost converters with respect to the required system voltage. In particular, in the power control unit, when a temperature abnormality occurs in its boost converter, the operation of the boost converter is often restricted, and as a result, there is a possibility that the required system voltage cannot be obtained.

[0005] In view of the above, this specification provides a technique for appropriately determining the boost width of each of the two boost converters while avoiding a temperature abnormality in the boost converter.

Means for Solving the Problem

[0006] The technique disclosed in this specification is embodied in an electric vehicle that drives wheels by a motor. This electric vehicle includes at least one motor that drives the wheels, a battery pack that supplies power to the motor, and a power control unit that controls the supply power from the battery pack to the motor. The battery pack has at least one battery cell, a first boost converter that boosts the output power from the battery cell, and a first control device that controls the operation of the first boost converter. The power control unit has a second boost converter that boosts the output power from the battery pack, and a second control device that controls the operation of the second boost converter.

[0007] At least one of the first control device and the second control device is configured to execute a process of determining each boost width by the first boost converter and the second boost converter based on each loss predicted by the first boost converter and the second boost converter. However, in this process, when an index related to the temperature of the second boost converter exceeds a predetermined threshold value, a lower limit value is set for the boost width by the first boost converter. Thereby, suppressing the temperature rise of the second boost converter is prioritized over reducing the loss in each boost converter.

[0008] That is, according to the above-described configuration, normally, while monitoring each loss in the first boost converter and the second boost converter, each boost width by the two boost converters is determined respectively. Thereby, for the system voltage required for the motor, for example, the two boost converters can be made to share the boost so that the total loss in the two boost converters is minimized. On the other hand, when an index related to the temperature of the second boost converter (for example, the temperature of the boost element or the cooling water temperature) exceeds a predetermined threshold value, a lower limit value is set for the boost width by the first boost converter. By setting the lower limit value for the first boost converter, an upper limit value is also substantially set for the boost width distributed to the second boost converter, and the temperature rise of the second boost converter is suppressed. Thus, according to the present technology, it is possible to appropriately determine each boost width by the two boost converters while avoiding temperature abnormalities in the boost converters.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Referring to the drawings, the electric vehicle 2 of the embodiment will be described. Although it is an example, the electric vehicle 2 of this embodiment is a so-called plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle). Note that the configuration described in this embodiment is not limited to a plug-in hybrid electric vehicle, and can be similarly adopted for other types of electric vehicles. However, in a plug-in hybrid electric vehicle (or a hybrid electric vehicle), for example, compared with a battery electric vehicle, there is a situation where the mounting space of the battery pack 20 is limited. In such an electric vehicle, this technology can be preferably adopted.

[0011] As shown in FIG. 1, the electric vehicle 2 includes two motors 10, a battery pack 20, and a power control unit 30. Although not shown in the figure, the electric vehicle 2 further includes an engine connected to the two motors 10 via a power distribution mechanism (for example, a planetary gear mechanism).

[0012] The two motors 10 are devices that drive the wheels (not shown) of the electric vehicle 2 by the supply power from a plurality of battery cells 22. The two motors 10 are electrically connected to the plurality of battery cells 22 and mechanically connected to the wheels. Although not particularly limited, the two motors 10 are three-phase AC motors. The wheels driven by the two motors 10 may be front wheels or rear wheels. Although it is an example, in the electric vehicle 2 of this embodiment, the two motors 10 are connected to a pair of front wheels via a speed reducer and a differential device. Note that as another embodiment, the motor 10 may be a so-called in-wheel motor. In this case, the electric vehicle 2 can include a plurality of motors 10 according to the number of drive wheels.

[0013] The battery pack 20 includes a plurality of battery cells 22, a first boost converter 24, and a first control device 26.

[0014] The plurality of battery cells 22 are rechargeable secondary battery cells. Each battery cell 22 may be, for example, a lithium ion cell or an all-solid-state battery cell. The plurality of battery cells 22 are connected in series and in parallel, and the output voltage of the battery pack 20 is, for example, 100 volts or more. Note that the electric vehicle 2 in this embodiment is a plug-in hybrid electric vehicle, but in order to improve the cruising range during EV driving, the plurality of battery cells 22 mainly employ high-capacity types used in battery electric vehicles and the like.

[0015] The first boost converter 24 is electrically connected to the plurality of battery cells 22. The first boost converter 24 is configured to boost the output power from the plurality of battery cells 22. The specific configuration of the first boost converter 24 is not particularly limited. As an example, the first boost converter 24 in this embodiment is a non-insulated converter using switching elements and a coil.

[0016] The first control device 26 controls the operation of the first boost converter 24. The first control device 26 is connected to the first boost converter 24 via a signal line. The first control device 26 includes a processor and a memory, and controls the operation of the first boost converter 24 according to various programs stored in the memory.

[0017] The power control unit 30 includes a second boost converter 32, two inverters 36, and a second control device 34.

[0018] The second boost converter 32 is electrically connected between the first boost converter 24 of the battery pack 20 and the two inverters 36. The second boost converter 32 is configured to further boost the power boosted by the first boost converter 24. The specific configuration of the second boost converter 32 is not particularly limited. As an example, the first boost converter 24 in this embodiment is a non-insulated converter using switching elements and a coil, similar to the first boost converter 24.

[0019] The two inverters 36 are electrically connected between the second boost converter 32 and the two motors 10, respectively. The two inverters 36 are configured to convert the DC power boosted by the second boost converter 32 into three-phase AC power and supply it to the two motors 10, respectively. The specific configuration of the two inverters 36 is not particularly limited. As an example, the two inverters 36 in the present embodiment have a plurality of switching elements and freewheeling diodes connected in parallel to each switching element.

[0020] The second control device 34 controls the operations of the second boost converter 32 and the two inverters 36. The second control device 34 is connected to the second boost converter 32 and the two inverters 36 via signal lines. Similar to the first control device 26, the second control device 34 includes a processor and a memory, and controls the operations of the second boost converter 32 and the two inverters 36 according to various programs stored in the memory. Specifically described below, the second control device 34 monitors the temperature of the second boost converter 32 and is configured to limit the operation of the second boost converter 32 when the index indicates an excessive temperature rise of the second boost converter 32.

[0021] Referring to FIG. 2, the boost sharing control executed by the first control device 26 and the second control device 34 will be described. The first control device 26 and the second control device 34 repeatedly execute a series of processes shown in FIG. 2 when the electric vehicle 2 is running and accelerating from a stopped state. First, the second control device 34 acquires a torque request (S10). The torque request is information indicating the required torque requested for the two motors 10. Next, the second control device 34 calculates a minimum required voltage Vm based on the acquired required torque (S12). The minimum required voltage Vm is information indicating the minimum system voltage required to output the required torque and is also simply referred to as the required voltage. Next, the first control device 26 and the second control device 34 acquire the voltage value Vb of the plurality of battery cells 22 and determine whether the necessary minimum voltage (required voltage) Vm is equal to or higher than the voltage value Vb of the plurality of battery cells 22 (S14).

[0022] When the minimum required voltage Vm is equal to or higher than the voltage value Vb of the plurality of battery cells 22 (Vm≧Vb) (S14: Yes), the second control device 34 acquires the temperature Tp of the boosting element of the second boost converter 32 (S16). The boosting element mentioned here is, for example, a switching element or a coil of the second boost converter 32. On the other hand, when the minimum required voltage Vm is less than the voltage value Vb of the plurality of battery cells 22 (Vm<Vb) (S14: No), the first control device 26 and the second control device 34 do not issue a boosting request to the first boost converter 24 and the second boost converter 32 (S30). Then, the first control device 26 and the second control device 34 end the series of processes shown in FIG. 2 (end).

[0023] In the series of processes shown in FIG. 2, the second control device 34 determines whether or not the temperature Tp of the boosting element of the second boost converter 32 acquired in step S16 is equal to or higher than a preset threshold value Ta (S18). The threshold value Ta can be set to any value and can be appropriately changed according to the characteristics and types of the plurality of battery cells 22 and the second boost converter 32. When the temperature Tp of the boosting element of the second boost converter 32 is equal to or higher than the preset threshold value Ta (Tp≧Ta) (S18: Yes), the first control device 26 sets a preset lower limit value for the boosting width of the first boost converter 24 (S20). By setting the lower limit value for the boosting width of the first boost converter 24, an upper limit value is also substantially set for the boosting width distributed to the second boost converter 32. Thereby, the temperature rise of the second boost converter is suppressed. The lower limit value set here can be appropriately changed according to the characteristics and types of the plurality of battery cells 22, the first boost converter 24, and the second boost converter 32.

[0024] When the temperature Tp of the boosting element of the second boost converter 32 is not equal to or higher than a preset predetermined threshold Ta (Tp < Ta) (S18: No), the first control device 26 and the second control device 34 calculate the losses for each boosting width of the first boost converter 24 and the second boost converter 32 without setting a lower limit value for the boosting width of the first boost converter 24 (S22). The loss is the power loss that occurs when the first boost converter 24 and the second boost converter 32 boost power. Also, when a lower limit value is set for the boosting width of the first boost converter 24 in step S20, the first control device 26 and the second control device 34 calculate the losses for each boosting width of the first boost converter 24 and the second boost converter 32 within a range not less than the lower limit value of the boosting width of the first boost converter 24 (S22).

[0025] The first control device 26 and the second control device 34 determine the boosting widths at which the total losses of the first boost converter 24 and the second boost converter 32 are minimized among the losses for each boosting width calculated in step S22 (S24). The first control device 26 and the second control device 34 output a boosting request command to the first boost converter 24 and the second boost converter 32 according to the boosting widths determined in (S24) (S26). When the first control device 26 and the second control device 34 execute the processing up to step S26 or S30, they end the series of processing shown in FIG. 2 (end).

[0026] The first control device 26 and the second control device 34 repeatedly execute the series of processing shown in FIG. 2. As a result, when the boosting element of the second boost converter 32 is relatively hot, a lower limit value is set for the boosting width by the first boost converter 24, and as a result, the burden on the second boost converter 32 is reduced. That is, suppressing the temperature rise of the second boost converter 32 is prioritized over reducing the losses in each of the boost converters 24 and 32. As described above, in the power control unit 30, it is possible to avoid restricting the operation of the second boost converter 32.

[0027] The "temperature of the boosting element of the second boost converter 32" in this embodiment is an example of the "index related to the temperature of the second boost converter" in this technology. However, as another embodiment, the "index related to the temperature of the second boost converter" may be, for example, the temperature of the cooling water or other heat medium that cools the second boost converter 32.

[0028] As described above, the embodiments of the present technology have been described in detail, 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 utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Also, the technology illustrated in this specification or the drawings achieves a plurality of objectives simultaneously, and achieving one of those objectives itself has technical utility.

Explanation of Reference Numerals

[0029] 2: Electric vehicle, 10: Motor, 20: Battery pack, 22: Battery cell, 24: First boost converter, 26: First control device, 30: Power control unit, 32: Second boost converter, 34: Second control device, 36: Inverter

Claims

【Claim 1】 An electric vehicle comprising: at least one motor for driving wheels; a battery pack for supplying power to the motor; a power control unit for controlling the power supplied from the battery pack to the motor; wherein the battery pack includes at least one battery cell, a first boost converter for boosting the output power from the battery cell, and a first control device for controlling the operation of the first boost converter; the power control unit includes a second boost converter for boosting the output power from the battery pack, and a second control device for controlling the operation of the second boost converter; at least one of the first control device and the second control device is configured to execute a process of determining respective boost widths by the first boost converter and the second boost converter based on respective losses predicted by the first boost converter and the second boost converter; in the process, when an index related to the temperature of the second boost converter exceeds a predetermined threshold value, a lower limit value is set for the boost width by the first boost converter; an electric vehicle.

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