JP7505305B2 - Vehicle drive control device - Google Patents

Description

The present invention relates to a drive control device for a vehicle that drives a motor using battery power.

Conventionally, in hybrid vehicles and electric vehicles that run on a motor driven by battery power, a technique is known that calculates the power that the battery can output at any given time (upper battery power limit) and controls the motor so that the power actually output from the battery does not exceed the upper battery power limit. The upper battery power limit is calculated based on the remaining battery capacity (SOC) and battery temperature (see Patent Documents 1 and 2).

JP 2020-054026 A JP 2017-011940 A

When the electronic control device that manages the battery and the electronic control device that controls the motor are installed separately, the battery upper limit power is calculated by the former electronic control device, and the information is transmitted to the latter electronic control device. However, for example, due to a malfunction in the communication circuit, the information on the battery upper limit power may not reach the latter electronic control device. In this case, the motor may be driven without knowing the appropriate battery upper limit power, and the battery may be over-discharged. Similar issues may arise not only due to a malfunction in the communication circuit, but also when the former electronic control device malfunctions or sensors fail. Issues caused by sensor failures may also occur when the former electronic control device and the latter electronic control device are not installed separately.

One of the objectives of the present invention was devised in light of the above-mentioned problems, and is to provide a vehicle drive control device that can suppress over-discharge of the battery with a simple configuration. In addition to this objective, another objective of the present invention is to achieve effects that cannot be obtained with conventional technology, which are derived from the configurations shown in the "Mode for carrying out the invention" described below.

The disclosed drive control device for a vehicle includes a capacitor connected in parallel to a motor or an inverter mounted on a vehicle in a DC circuit connecting the motor or the inverter to a battery, a voltage sensor that detects a capacitor voltage that is the voltage of the capacitor, a control device that sets a battery upper limit power that is an upper limit value of the output of the battery based on the capacitor voltage and controls the motor or the inverter so that the actual output of the battery does not exceed the battery upper limit power, and a battery management device that calculates a maximum output of the battery . The control device has both a function of setting the battery upper limit power based on the maximum output and a function of setting the battery upper limit power based on the capacitor voltage when information on the maximum output cannot be obtained. The control device has a map that specifies a relationship between the capacitor voltage and the battery upper limit power. The map specifies a relationship in which the battery upper limit power is limited to a specified value when the capacitor voltage is equal to or higher than a first specified value, and the battery upper limit power decreases linearly as the capacitor voltage decreases when the capacitor voltage is lower than the first specified value. The control device stores the value of the maximum output, and when the value of the maximum output is less than the specified value and information about the maximum output cannot be obtained, sets the most recent value of the maximum output as the battery upper limit power.

The disclosed vehicle drive control device can suppress over-discharge of the battery with a simple configuration.

1 is a schematic diagram showing a configuration of a vehicle to which a drive control device according to an embodiment is applied; FIG. 2 is a circuit diagram showing a circuit for driving the motor shown in FIG. 1 . 3 is a graph showing characteristics stored in the vehicle ECU shown in FIG. 2 . 3 is a block diagram illustrating an example of calculation contents in the vehicle ECU shown in FIG. 2 . 3 is a flowchart illustrating a control procedure performed by the vehicle ECU shown in FIG. 2 . Graphs (A) to (E) are used to explain the control action of the vehicle ECU shown in FIG. 2. (A) shows the change over time in the state of communication with the BMU, (B) shows the change over time in the accelerator opening, (C) shows the change over time in the vehicle speed, (D) shows the change over time in the capacitor voltage, and (E) shows the change over time in the upper limit battery power. 3 is a flowchart illustrating a control procedure performed by the vehicle ECU shown in FIG. 2 . 3 is a flowchart illustrating a control procedure performed by the vehicle ECU shown in FIG. 2 .

[1. Configuration]
FIG. 1 is a schematic diagram showing the configuration of a vehicle 10 to which a drive control device according to an embodiment is applied. The vehicle 10 is a hybrid vehicle equipped with a motor 7 (electric motor) and an engine 8 (internal combustion engine) that function as drive sources. The motor 7 shown in FIG. 1 is a front motor that drives the front wheels. A similar motor 7 may also be provided on the rear wheel side. In addition, a battery 1 that stores electric power for driving the motor 7 is provided at an arbitrary position on the vehicle 10. The motor 7 is an AC motor generator that has both a function of running the vehicle 10 with the electric power of the battery 1 and a function of regenerating electric power by generating electric power using the inertia of the vehicle.

Battery 1 is a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride battery. This battery 1 can be charged by an external charging facility (external charging), by regenerative power from the motor 7, or by a generator (not shown) driven by the engine 8. Provided near (or inside) the battery 1 are a battery voltage sensor 2 that detects the voltage of the battery 1 (e.g., cell voltage or open voltage), a battery temperature sensor 3 that detects the temperature of the battery 1 (e.g., cell temperature or temperature inside the case), and a battery current sensor 30 that detects the current value related to the charging and discharging of the battery 1.

Figure 2 is a circuit diagram showing a DC circuit 9 for driving the motor 7 shown in Figure 1. The power of the battery 1 is input to the inverter 4 via the DC circuit 9, converted to AC power inside the inverter 4, and then supplied to the motor 7. The inverter 4 is a voltage-controlled power conversion device that converts the power of the DC circuit 9 (DC power) and the power of the AC circuit in which the motor 7 is installed (AC power) back and forth. The inverter 4 has a built-in three-phase bridge circuit including multiple switching elements. AC power for driving the motor 7 is generated by intermittently switching the connection state of each switching element. Semiconductor elements such as IGBTs and power MOSFETs are used as the switching elements.

Capacitor 5 is an electronic component for smoothing the power supplied to inverter 4. Capacitor 5 shown in FIG. 2 is connected in parallel to inverter 4 in DC circuit 9. If motor 7 is a DC motor, motor 7 will be placed at the position of inverter 4 in FIG. 2. Therefore, in this case, capacitor 5 is connected in parallel to motor 7. A voltage sensor 6 is provided near capacitor 5 to detect the voltage stored in capacitor 5 (capacitor voltage). The capacitor voltage when battery 1 is discharging is approximately equal to the open circuit voltage of battery 1.

As shown in FIG. 2, the battery voltage sensor 2, battery temperature sensor 3, and battery current sensor 30 are connected to a BMU 11 (Battery Management Unit). The inverter 4, voltage sensor 6, and motor 7 are connected to an MCU 12 (Motor Control Unit). Furthermore, the BMU 11 and MCU 12 are arranged to be able to communicate with a vehicle ECU 13 (control device) via an in-vehicle communication network. The vehicle ECU 13 is responsible for managing the BMU 11 and MCU 12.

Each of the BMU 11, MCU 12, and vehicle ECU 13 is an electronic control unit (ECU) mounted on the vehicle 10, and is an electronic device equipped with a processor and memory. The processor is, for example, a microprocessor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and the memory is, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), or a non-volatile memory. The contents of the control performed by each of the BMU 11, MCU 12, and vehicle ECU 13 are recorded and stored in the memory as firmware or an application program, and when a program is executed, the contents of the program are expanded in the memory space and executed by the processor.

The BMU 11 is an electronic control device responsible for monitoring the battery 1. Here, the maximum output [kW], which is the maximum power that the battery 1 can output at that time, is calculated based on the voltage, current, temperature, remaining capacity (SOC), and degree of deterioration of the battery 1. The information on the maximum output calculated here is transmitted to the vehicle ECU 13. The MCU 12 is an electronic control device that controls the operating state of the motor 7 and inverter 4. Here, information on the capacitor voltage detected by the voltage sensor 6 is acquired and transmitted to the vehicle ECU 13. In addition, based on information on the battery upper limit power calculated by the vehicle ECU 13, the operating state of the inverter 4 and motor 7 is controlled so that the actual output of the battery 1 does not exceed the battery upper limit power.

The vehicle ECU 13 has a function of setting the battery upper limit power, which is the upper limit value of the output of the battery 1, based on the capacitor voltage and transmitting the information to the MCU 12. The vehicle ECU 13 also stores a map 14 in which characteristics for setting the battery upper limit power are defined. The map 14 defines a relationship between the capacitor voltage and the battery upper limit power. FIG. 3 is a graph illustrating the relationship defined in the map 14. In the map 14, when the capacitor voltage is equal to or greater than a first predetermined value _V1 , the battery upper limit power is limited to a predetermined value _P1 . In addition, when the capacitor voltage is less than the first predetermined value _V1 , the battery upper limit power decreases linearly as the capacitor voltage becomes lower. When the capacitor voltage is less than a second predetermined value _V2 which is smaller than the first predetermined value _V1 , the battery upper limit power is limited to 0.

The vehicle ECU 13 of this embodiment does not always set the battery upper limit power by referring to the capacitor voltage, but sets the battery upper limit power based on the capacitor voltage only when at least one of the following conditions is met: If none of the following conditions is met, the vehicle ECU 13 sets the battery upper limit power based on the maximum output calculated by the BMU 11.
Condition 1: When information on the maximum output calculated by the BMU 11 cannot be obtained Condition 2: When communication with the BMU 11 is interrupted Condition 1 includes a state in which the calculation of the maximum output in the BMU 11 has stopped (malfunction of the BMU 11), a state in which the battery voltage sensor 2 has failed, a state in which the battery temperature sensor 3 has failed, etc. Condition 2 includes a state in which a malfunction of the in-vehicle network or a transmission failure of the BMU 11 has occurred, etc.

Figure 4 is a block diagram illustrating the calculation contents in the vehicle ECU 13. Information on the capacitor voltage detected by the voltage sensor 6 is input to the map 14 via the low-pass filter 15 (LPF). The low-pass filter 15 removes high-frequency components (noise) from the signal corresponding to the capacitor voltage and outputs the result to the map 14. The map 14 outputs a first battery upper limit power corresponding to the capacitor voltage. Information on the first battery upper limit power is input to the gradient limiter 16, and the change gradient (amount of change per unit time) is limited to a range in which it does not change suddenly, and then input to the minimum value selector 19.

The information on the maximum output calculated by the BMU 11 is input to the positive value side of the subtractor 21. On the other hand, a preset margin value (for example, a value of several [kW]) is input to the negative value side of the subtractor 21. The value obtained by subtracting the margin value from the maximum output is input to the second gradient limiter 22, where the gradient of change (amount of change per unit time) is limited to a range in which it does not change suddenly, and then input to the upper and lower limiter 23. The upper and lower limiter 23 limits the input value to a range from a predetermined upper limit value to a lower limit value, and transmits the value to the minimum value selector 19 and the selector 20. Here, the value output from the upper and lower limiter 23 is called the second battery upper limit power. The minimum value selector 19 selects the smaller value of the first battery upper limit power or the second battery upper limit power and outputs it to the selector 20.

"Limit judgment" in FIG. 4 is a flag for determining the selection result in selector 20, and has the characteristic of being ON when at least one of conditions 1 and 2 is met, and OFF when conditions 1 and 2 are not met. When limit judgment is ON, selector 20 selects the output of minimum value selector 19. In other words, if either condition 1 or 2 is met, the first battery upper limit power derived from the capacitor voltage becomes the final upper and lower battery power. Also, when limit judgment is OFF, that is, in a situation where conditions 1 and 2 are not met, the first battery upper limit power derived from the capacitor voltage is not selected, and the second battery upper limit power becomes the final upper and lower battery power. In this way, if conditions 1 and 2 are not met, the capacitor voltage is not referenced.

2. Flowchart
FIG. 5 is a flowchart illustrating a control procedure in the vehicle ECU 13. The control shown in this flowchart can also be applied to a vehicle ECU 13 that does not have the control configuration shown in FIG. 4. In step A1, various information is input to the vehicle ECU 13. In step A2, it is determined whether communication with the BMU 11 is interrupted. If this condition is met, the process proceeds to step A3, where the battery upper limit power is calculated based on the capacitor voltage. The value of the battery upper limit power is calculated based on the characteristics shown in FIG. 3, for example. In the subsequent step A4, the motor 7 and the inverter 4 are controlled based on the battery upper limit power. For example, the drive power of the motor 7 output from the inverter 4 is controlled so that the actual output of the battery 1 does not exceed the battery upper limit power.

If the condition in step A2 is not met, the process proceeds to step A5, where it is determined whether the vehicle ECU 13 has acquired maximum output information from the BMU 11. If this condition is not met, the process proceeds to step A3, where the same process as when communication is interrupted is carried out. On the other hand, if the upper limit in step A5 is met, the process proceeds to step A6, where the battery upper limit power is calculated based on the maximum output. In the subsequent step A4, the motor 7 and inverter 4 are controlled based on the battery upper limit power.

Fig. 7 is a modified example of the flowchart shown in Fig. 5. In this flow, step B1 for storing the value of maximum output transmitted from the BMU 11 in a memory or storage device is added between steps A1 and A2 in Fig. 5. At least the past value (previous value) of the maximum output is stored. In addition, after the YES route of step A2 and the NO route of step A5, step B2 is added in which it is determined whether the stored value of maximum output is equal to or greater than a predetermined value _P1 . If this condition is met, the process proceeds to step A3, and if not, the process proceeds to step A6.

Therefore, in step A6, while the maximum output information is being acquired, the battery upper limit power is calculated based on the most recent maximum output value. On the other hand, when the maximum output information cannot be acquired and the most recent maximum output value (retained value) is less than the predetermined value _P1 , the battery upper limit power is calculated based on the retained value, and for example, the most recent maximum output value is directly set as the battery upper limit power. Also, when the maximum output information cannot be acquired and the most recent maximum output value (retained value) is equal to or greater than the predetermined value _P1 , the battery upper limit power is calculated based on the capacitor voltage.

FIG. 8 is a modified example of the flowchart shown in FIG. 7. In this flow, like the flow shown in FIG. 5, step A3 is performed after the YES route of step A2 and the NO route of step A5, and then step C1 is performed. In step C1, it is determined whether the held value of the maximum output held in step B1 is equal to or greater than the battery upper limit power calculated in step A3. If the condition of step C1 is not satisfied, the process proceeds to step A6, where the battery upper limit power is calculated based on the held value. If the condition of step C1 is satisfied, the process proceeds to step A4, where the motor 7 and the inverter 4 are controlled based on the battery upper limit power calculated in step A3. Therefore, even if the held value is less than the predetermined value _P1 , when the battery upper limit power calculated from the capacitor voltage falls below the predetermined value _P1 , the motor 7 and the inverter 4 are controlled based on the battery upper limit power calculated from the capacitor voltage.

[3. Action]
6(A) to 6(E) are graphs for explaining the control action by the vehicle ECU 13. When communication with the BMU 11 is lost at time _t1 , the battery upper limit power is set based on the capacitor voltage at that time. As a result, as shown in FIG. 6(E), the value of the battery upper limit power decreases at time _t1 . Also, when the accelerator pedal is depressed at time _t2 , the motor 7 is driven and the vehicle 10 starts to run. Meanwhile, as shown in FIG. 6(D), the capacitor voltage gradually decreases from time _t3 , slightly after time _t2 .

After that, when the capacitor voltage falls below the first predetermined value _V1 at time _t4 , the battery upper limit power is further suppressed as shown in FIG. 6(E). This reduces the output of the motor 7, and the increase in vehicle speed (acceleration) becomes smaller. When the accelerator pedal is released at time _t5 , the motor 7 enters a coasting rotation state or regenerative power generation is performed. At this time, the capacitor voltage quickly recovers, and the battery upper limit power is set according to the capacitor voltage.

[4. Effects]
(1) In the above embodiment, the upper battery power limit is set based on the capacitor voltage, and the inverter 4 (and thus the motor 7) is controlled so that the actual output of the battery 1 does not exceed the upper battery power limit. In this way, by setting the upper battery power limit according to the voltage of the capacitor 5, it is possible to limit the actual output of the battery 1 even in a situation where the state of the battery 1 cannot be grasped. Therefore, over-discharging of the battery 1 can be suppressed with a simple configuration.

(2) The vehicle ECU 13 (control device) implements control to reduce the battery upper limit power as the capacitor voltage decreases. The capacitor voltage when the battery 1 is discharging is approximately equal to the open circuit voltage of the battery 1. Therefore, by reducing the battery upper limit power in response to a decrease in the capacitor voltage, the state of the voltage decrease of the battery 1 can be accurately reflected in the battery upper limit power, and over-discharge of the battery 1 can be appropriately prevented.

(3) In the above embodiment, a BMU 11 (battery management unit) is provided to calculate the maximum output of the battery 1. The vehicle ECU 13 (control unit) also has a function to set the upper battery power limit based on the maximum output, and a function to set the upper battery power limit based on the capacitor voltage when the maximum output information cannot be obtained. With this control configuration, the upper battery power limit can be set with high accuracy regardless of the quality of the communication state with the BMU 11, and over-discharge of the battery 1 can be appropriately prevented.

(4) In the above embodiment, an MCU 12 (motor control device) is provided separately from the BMU 11 (battery management device) and monitors the capacitor voltage detected by the voltage sensor 6. By monitoring the capacitor voltage with the MCU 12, which is separate from the BMU 11, the capacitor voltage can be accurately determined even when the BMU 11 is malfunctioning. Therefore, an appropriate battery upper limit power can be set, and over-discharging of the battery 1 can be prevented.

(5) The vehicle ECU 13 (control device) has a map 14 that defines the relationship between the capacitor voltage and the battery upper limit power. By using the map 14, the value of the battery upper limit power corresponding to the capacitor voltage can be quickly and easily set. This improves the controllability of the battery 1, the motor 7, and the inverter 4. In addition, by changing the relationship defined in the map 14, the strength of the limit on the battery upper limit power can be easily changed, making it easier to realize control that accurately responds to design changes and specification changes.

(6) In the map 14, as shown in FIG. 3, when the capacitor voltage is equal to or greater than the first predetermined value _V1 , the battery upper limit power is limited to a predetermined value _P1 . Also, when the capacitor voltage is less than the first predetermined value _V1 , a relationship is defined in which the lower the capacitor voltage, the more the battery upper limit power decreases linearly. In this way, when the capacitor voltage is less than the first predetermined value _V1 , the lower the capacitor voltage, the more the battery upper limit power is reduced, so that the state of the voltage drop of the battery 1 can be accurately reflected in the battery upper limit power, and over-discharge of the battery 1 can be appropriately prevented. On the other hand, when the capacitor voltage is equal to or greater than the first predetermined value _V1 , the battery upper limit power is fixed to the predetermined value _P1 , so that excessive limitation can be prevented, and the running performance of the vehicle 10 can be maintained.

(7) As shown in Fig. 3, the map 14 defines a relationship in which the battery upper limit power is limited to 0 when the capacitor voltage is less than a second predetermined value _V2 that is less than the first predetermined value _V1 . In this way, when the capacitor voltage is less than the second predetermined value _V2 , further discharging of the battery 1 can be stopped by setting the battery upper limit power to 0. Therefore, over-discharging of the battery 1 can be reliably prevented.

(8) As shown in Fig. 7, when the maximum output value is less than a predetermined value _P1 and the maximum output information cannot be obtained, the most recent maximum output value may be set as the battery upper limit power. With this control, the output of the battery 1 can be limited based on the most recent maximum output, even if the capacitor voltage has not dropped sufficiently at the time when the maximum output information cannot be obtained. Therefore, over-discharging of the battery 1 can be suppressed with a simple configuration.

(9) As shown in FIG. 8, if the most recent maximum output held value is less than the battery upper limit power calculated based on the capacitor voltage, the most recent maximum output may be set as the battery upper limit power. In other words, if the most recent maximum output held value is equal to or greater than the battery upper limit power calculated based on the capacitor voltage, the motor 7 and the inverter 4 may be controlled based on the battery upper limit power calculated based on the capacitor voltage without referring to the held value.

In other words, the battery upper limit power based on the capacitor voltage may be calculated while control based on the most recent maximum output is being performed, and the most recent maximum output value may be used until that value falls below the held value, after which the battery upper limit power based on the capacitor voltage may be used. In this case, the battery upper limit power finally obtained will be the smaller of the battery upper limit power calculated from the capacitor voltage and the held value. This type of control makes it possible to appropriately limit the output of battery 1, for example, in cases where the capacitor voltage is relatively high when maximum output information is no longer obtained, and the capacitor voltage subsequently drops. Therefore, over-discharge of battery 1 can be suppressed with a simple configuration.

5. Modifications
The above embodiment is merely an example, and there is no intention to exclude various modifications and application of techniques not specified in the present embodiment. Each configuration of the present embodiment can be modified in various ways without departing from the spirit of the embodiment. In addition, they can be selected or appropriately combined as needed. For example, in the above embodiment, a drive control device is described that controls an AC motor 7 using an inverter 4, but it is also possible to perform similar control using a DC motor 7. In this case, the DC motor 7 is interposed at the position of the inverter 4 in FIG. 2. By controlling the motor 7 so as not to exceed the battery upper limit power set based on the capacitor voltage, the same action and effect as the above embodiment can be obtained.

1 Battery 2 Battery voltage sensor 3 Battery temperature sensor 4 Inverter 5 Capacitor 6 Voltage sensor 7 Motor 8 Engine 9 DC circuit 10 Vehicle 11 BMU (Battery Management Unit)
12 MCU (controller, motor controller)
13 Vehicle ECU (control unit)
14: Map 15: Low-pass filter 16: Gradient limiter 19: Minimum value selector 20: Selector 21: Subtractor 22: Second gradient limiter 23: Upper and lower limiter 30: Battery current sensor

Claims (3)

a capacitor connected in parallel to a motor or an inverter mounted on a vehicle in a DC circuit connecting the motor or the inverter to a battery;
a voltage sensor for detecting a capacitor voltage, which is a voltage of the capacitor;
a control device that sets an upper limit battery power, which is an upper limit value of the output of the battery, based on the capacitor voltage and controls the motor or the inverter so that the actual output of the battery does not exceed the upper limit battery power;
A battery management device that calculates a maximum output of the battery,
the control device has a function of setting the battery upper limit power based on the maximum output, and a function of setting the battery upper limit power based on the capacitor voltage when information on the maximum output cannot be acquired;
the control device has a map that defines a relationship between the capacitor voltage and the battery upper limit power,
a relationship is defined in the map such that, when the capacitor voltage is equal to or greater than a first predetermined value, the battery upper limit power is limited to a predetermined value, and, when the capacitor voltage is less than the first predetermined value, the battery upper limit power linearly decreases as the capacitor voltage decreases;
The control device stores the value of the maximum output, and when the value of the maximum output is less than the predetermined value and information on the maximum output cannot be acquired, sets the most recent value of the maximum output as the upper limit power of the battery.
A drive control device for a vehicle. 2. The vehicle drive control device according to claim 1, wherein the map specifies a relationship in which the upper battery power limit is limited to 0 when the capacitor voltage is less than a second predetermined value that is smaller than the first predetermined value. 3. The vehicle drive control device according to claim 1, wherein the control device sets the most recent maximum output as the battery upper limit power when the most recent maximum output is less than the battery upper limit power calculated based on the capacitor voltage.

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