WO2024203195A1 - Vehicle power supply device - Google Patents

Abstract

[Problem] To protect a battery from overcharge. [Solution] A vehicle power supply device 1 comprising a battery 2, a vehicle power supply 3, a charge/discharge path 4, a switch unit 5, and a monitoring unit 91 of a control device 9. The switch unit 5 is provided with: a FET 51 and a FET 52 that are connected in series; a diode 53 of which an anode is disposed on the battery 2 side, the diode 53 being connected in parallel to the FET 51; and a diode 54 disposed in an orientation opposite from that of the diode 53, the diode 54 being connected in parallel to the FET 52. When protecting the battery 2 from overcharge, the monitoring unit 91 turns off the FET 51 and turns on the FET 52.

Description

Vehicle power supply device

The present invention relates to a power supply device for a vehicle.

A vehicle power supply device includes a battery, which is a secondary battery that supplies power to a vehicle load (see, for example, Patent Document 1). The vehicle power supply device may include, for example, multiple batteries. The multiple batteries may include, for example, a main battery that functions as the vehicle power supply, and a battery that functions as a backup power supply. These batteries are connected via a charge/discharge path, and can be charged and discharged from one another.

Patent No. 6944553

The voltage output by a vehicle power supply may exceed the normal range, depending on factors such as the usage conditions of the vehicle load. Since the voltage required for a backup battery is relatively low, a battery with a lower internal resistance than the battery that constitutes the vehicle power supply may be used. However, if a voltage higher than normal is applied from the vehicle power supply to the backup battery, this may result in the battery being overcharged.

In a vehicle power supply device in which multiple batteries are connected so that they can be charged and discharged, there is a need to protect the batteries from overcharging.

According to one aspect of the present invention, there is provided a vehicle power supply device comprising:
A first battery;
A second battery;
a charge/discharge path that connects the first battery and the second battery so as to be capable of charging and discharging each other;
A switch unit provided in the charge/discharge path;
a monitoring unit that monitors a state of the first battery and controls the switch unit;
The switch unit is
a first semiconductor switching element and a second semiconductor switching element connected in series;
a first diode having an anode disposed on the first battery side and connected in parallel to the first semiconductor switching element;
a second diode arranged in an opposite direction to the first diode and connected in parallel to the second semiconductor switching element;
When protecting the first battery from overcharging, the monitoring unit turns off the first semiconductor switching element and turns on the second semiconductor switching element.

　According to the present invention, the first battery can be protected from overcharging.

1 is a diagram showing an electrical configuration of a vehicle power supply device according to an embodiment of the present invention; FIG. 2 is a block diagram showing a functional configuration of a control device according to the embodiment. FIG. 13 is a diagram showing a state in which the FET 51 is turned off. FIG. 2 is a diagram illustrating discharging from a battery. 10 is a flowchart showing a process of a monitoring unit of the control device. FIG. 4 is a diagram showing an electrical configuration of a vehicle power supply device according to a first modified example. 13 is a flowchart showing a process of a monitoring unit according to Modification 2. FIG. 11 is a diagram showing an electrical configuration of a vehicle power supply device according to a third modified example. FIG. 13 is a diagram illustrating the setting of a threshold value TH1 in Modification 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle power supply device according to an embodiment of the present invention will now be described with reference to the drawings.
FIG. 1 is a diagram showing the electrical configuration of a vehicle power supply device 1 according to an embodiment.
FIG. 2 is a block diagram showing a functional configuration of the control device 9 according to the embodiment.
As shown in FIG. 1 , a vehicle power supply device 1 has a battery 2 (first battery), a vehicle power supply 3 (second battery), a charge/discharge path 4 , and a control device 9 .
The battery 2 is connected in parallel to a vehicle power supply 3 and a vehicle load 6 via a charge/discharge path 4 .
The battery 2 and the vehicle power supply 3 are capable of supplying electric power to a vehicle load 6 via a charge/discharge path 4. In addition, the battery 2 and the vehicle power supply 3 are capable of charging and discharging each other via the charge/discharge path 4.
In the vehicle power supply device 1, for example, the vehicle power supply 3 can be used as a power supply that mainly supplies power to the vehicle load 6, and the battery 2 can be used as a backup power supply for the vehicle power supply 3. Therefore, the battery 2 may be cheaper and have a smaller internal resistance than the battery that constitutes the vehicle power supply 3.

The vehicle loads 6 are various devices that are installed in the vehicle and require a power supply. Examples of the vehicle loads 6 include a driving control device, a DC/DC converter, an inverter, a headlight, an interior light, a turn signal, a power window, an audio system, an air conditioner, a car navigation system, etc.

The vehicle power supply 3 includes, for example, a secondary battery such as a lead storage battery. Although not shown, the vehicle power supply 3 is connected to a generator such as an alternator. The vehicle power supply 3 is charged by electricity generated by the alternator while the vehicle is running.

The battery 2 can be configured using a secondary battery such as a lithium ion battery. The battery 2 is a battery pack configured by connecting a plurality of cells in series. While Fig. 2 shows an example in which the battery 2 is configured by four cells C1 to C4, the number of cells that configure the battery 2 is not limited.
1, the positive terminal side (upper side in the figure) of the battery 2 is connected to a charge/discharge path 4, and the negative terminal side (lower side in the figure) is connected to a body ground. Although not shown, the battery 2 may include, in addition to a battery pack, a protection circuit such as a relay, a battery management system (BMS) that manages the charging and discharging of the battery 2, and the like.

The vehicle power supply device 1 includes a voltage sensor 72 (second voltage sensor) that measures the cell voltage _Vc of the battery 2. As shown in Fig. 2, the voltage sensor 72 is specifically composed of a group of voltage sensors that can measure the cell voltage _Vc of each of the cells C1 to C4 that make up the battery 2.

1, a switch unit 5 is provided in the charge/discharge path 4. The switch unit 5 switches between connection and disconnection of the battery 2 to and from the vehicle load 6 and the vehicle power supply 3.
The switch unit 5 includes a field effect transistor (FET) 51 which is a first semiconductor switching element, and a second semiconductor switching element FET 52. The FET 51 and the FET 52 are connected in series on the charge/discharge path 4.
The switch unit 5 further includes a diode 53 (first diode) connected in parallel to the FET 51 , and a diode 54 (second diode) connected in parallel to the FET 52 .
FIG. 1 shows a configuration in which the FET 51 is disposed on the vehicle power supply 3 side and the FET 52 is disposed on the battery 2 side, but the FET 51 may be disposed on the battery 2 side and the FET 52 may be disposed on the vehicle power supply 3 side.

The diodes 53 and 54 are components that allow current to flow in only one direction. The diode 53 connected to the FET 51 has an anode disposed on the battery 2 side and a cathode disposed on the vehicle power supply 3 side. In other words, the diode 53 is disposed so that current flows only in the direction from the battery 2 side to the vehicle power supply 3 side.
Diode 54 is disposed in the opposite direction to diode 53. That is, the cathode of diode 54 is disposed on the battery 2 side, and the anode is disposed on the vehicle power supply 3 side. That is, diode 54 is disposed so that current flows only in the direction from the vehicle power supply 3 side to the battery 2 side.

A fuse 41 is provided on the charge/discharge path 4 between the switch unit 5 and the vehicle power source 3. The fuse 41 cuts off the charge/discharge path 4 when an excessive current flows through the charge/discharge path 4.

The charge/discharge path 4 is provided with a voltage sensor 71 (first voltage sensor) whose terminals are connected to both ends of the FET 51. The voltage sensor 71 measures the potential difference PD between both ends of the FET 51. In addition, a voltage sensor 73 (third voltage sensor) is provided between the fuse 41 and the vehicle load 6 at the end of the charge/discharge path 4 on the vehicle load 6 side. The voltage sensor 73 measures the voltage applied from the vehicle power source 3 to the battery 2 (hereinafter referred to as "vehicle voltage").

The control device 9 can be configured, for example, as part of the functions of an ECU (Electronic Control Unit) that comprehensively controls charging and discharging of the battery 2 and the vehicle power supply 3 .
Although not shown, the control device 9 includes an arithmetic unit such as a CPU (Central Processing Unit), a storage device, a timer, an input/output port, etc. The storage device includes a ROM (Read Only Memory), a RAM (Random Access Memory), an EEPROM, etc. The CPU executes a program stored in the storage device to realize the functions of the control device 9. The storage device also stores data necessary for processing by the control device 9, and temporarily stores the processing results of the control device 9.
The control device 9 is connected to the voltage sensors 71, 72, and 73 and can acquire the measured values of each of them. Alternatively, the control device 9 may acquire the measured value of the voltage sensor 72 from a BMS (not shown) of the battery 2 via an in-vehicle LAN (Local Area Network) or the like constructed in the vehicle.

As shown in FIG. 2 , the control device 9 has a monitoring unit 91 and an estimation unit 92 as functional components for monitoring the state of the battery 2 and controlling the switch unit 5 .
The monitoring unit 91 controls the switch unit 5 to protect the battery 2 from overcharging.
When the vehicle is traveling, for example, if the electric power required by the vehicle load 6 increases, the voltage output by the vehicle power supply 3 may rise above the normal range. As described above, when the battery 2 is used as a backup power supply, a battery having an internal resistance smaller than that of the vehicle power supply 3 may be used as the battery 2. If a voltage higher than normal is applied from the vehicle power supply 3 to the battery 2 having a small internal resistance, this may result in overcharging of the battery 2.
Therefore, the monitoring unit 91 monitors the state of the battery 2 , and if there is a possibility of overcharging, controls the switch unit 5 to disconnect the battery 2 from the vehicle power supply 3 .

The estimation unit 92 estimates the state of charge (hereinafter referred to as “SOC”) of the battery 2 used for processing by the monitoring unit 91 .
The estimation unit 92 can estimate the SOC of the battery 2 by using a known method. As an example, the estimation unit 92 can estimate the SOC by a known method such as a Kalman filter or a current integration method using time series data of the cell voltage _Vc of the battery 2 measured by the voltage sensor 72. The estimation unit 92 periodically estimates the SOC while the vehicle is traveling. The SOC estimated by the estimation unit 92 is used in the processing of Modification 2 described below. Therefore, when the processing of Modification 2 is not performed in the control device 9, the estimation unit 92 may be omitted.

The monitoring unit 91 normally controls the FETs 51 and 52 of the switch unit 5 to be on, so that the battery 2 is connected to the vehicle power supply 3 and the vehicle load 6 via the charge/discharge path 4.
In Fig. 1, the current flow in the charge/discharge path 4 is indicated by a dotted line. When the vehicle is traveling, the alternator generates power to charge the vehicle power supply 3. When the vehicle power supply 3 discharges, power is supplied to the vehicle load 6 via the charge/discharge path 4, and the battery 2 is charged. That is, a current flows in the charge/discharge path 4 in a direction from the vehicle power supply 3 side to the battery 2 side (hereinafter referred to as the "charging direction").

When the monitoring unit 91 determines that the battery 2 is possibly overcharged while a current is flowing in the charging direction in the charge/discharge path 4, the monitoring unit 91 controls the switch unit 5 to cut off the current from the vehicle power supply 3, thereby protecting the battery 2 from overcharging. More specifically, the monitoring unit 91 controls the switch unit 5 to turn off the FET 51 and turn on the FET 52.
FIG. 3 is a diagram showing a state in which the FET 51 is turned off.
As shown in FIG. 3, when the FET 51 is turned off, the current conduction through the FET 51 is interrupted.
Here, diodes 53 and 54 are connected in parallel to FET 51 and FET 52. As described above, diode 53 connected in parallel to FET 51 allows current to flow only in the direction from battery 2 to vehicle power supply 3. In other words, diode 53 is arranged so that current flows in the discharging direction from battery 2 to vehicle power supply 3 but does not flow in the charging direction.
That is, when the FET 51 of the switch unit 5 is turned off, a current in the charging direction does not flow through either the FET 51 or the diode 53 connected in parallel to the FET 51. This blocks the current in the charging direction from the vehicle power supply 3 to the battery 2, and protects the battery 2 from overcharging.

In order to prevent the battery 2 from being overcharged, the monitoring unit 91 performs a determination process in accordance with the following two purposes.
Objective 1: To prevent the cell voltage _Vc of the battery 2 from exceeding the upper limit voltage _Vu of the battery 2.
Purpose 2: Prevent a large current that exceeds the allowable current of battery 2 from flowing.

1, when the FET 51 and the FET 52 are on, the vehicle voltage is applied to the battery 2, and the cell voltage _Vc of the battery 2 increases. As shown in Objective 1, if the cell voltage _Vc of the battery 2 exceeds the upper limit voltage _Vu of the battery 2, there is a possibility that the battery 2 may be overcharged.
As a determination process in accordance with Objective 1, the monitor 91 compares the voltage V ₂ of the battery 2 with a threshold TH 1 indicating the upper limit voltage of the entire battery 2 .
When the vehicle voltage exceeds the threshold TH1, the monitoring unit 91 switches the FET 51 from on to off. As described above, when the FETs 51 and 52 are on, the vehicle voltage is applied to the battery 2. Therefore, the monitoring unit 91 obtains each cell voltage _Vc from the voltage sensor 72, and calculates the voltage _V2 of the battery 2, which is the sum _ΣVc of each cell voltage _Vc . The monitoring unit 91 compares the voltage _V2 of the battery 2 with the threshold TH1.

The threshold value TH1 can be, for example, a value obtained by multiplying the upper limit voltage _Vu per unit cell constituting the battery 2 by the total number N of cells. The upper limit voltage _Vu per unit cell is a value that is set according to the specifications of the cell. For example, if the upper limit voltage per unit cell is 4.2 V and the total number of cells is 3, the threshold value TH1 is 4.2 V x 3 = 12.6 V. The threshold value TH1 can be calculated in advance and stored in a storage device.

As shown in Purpose 2, if a large current exceeding the allowable current flows through the charge/discharge path 4, it may cause effects such as overcharging the battery 2. A large current may flow when the difference between the vehicle voltage and the voltage of the battery 2 suddenly increases.
The current flowing through the charge/discharge path 4 can be calculated by the following formula (1).
Formula (1):
(Vehicle voltage - Battery 2 voltage V ₂ (= ΣV _c )) ÷ Resistance R of charging/discharging path 4 = Current I flowing through charging/discharging path 4

As shown in equation (1), the magnitude of the current flowing through the charge/discharge path 4 corresponds to the difference ΔV (vehicle voltage−voltage _V2 of battery 2) between the vehicle voltage and the voltage _V2 of the battery 2. When the current flowing through this charge/discharge path 4 exceeds the allowable current of the battery 2 and the charge/discharge path 4, the monitoring unit 91 needs to turn off the FET 51 to protect the battery 2 from the large current.

As a determination process in accordance with Purpose 2, the monitoring unit 91 calculates the difference ΔV between the vehicle voltage and the voltage _V2 of the battery 2, and compares it with a threshold value TH2. The threshold value TH2 indicates a voltage value (allowable voltage value) when a maximum allowable current flows through the battery 2 and the charge/discharge path 4. The threshold value TH2 is set in advance and stored in a storage device.

The monitoring unit 91 obtains the vehicle voltage measured by the voltage sensor 73, and can calculate the difference ΔV by subtracting the voltage V ₂ (=ΣV _c ) of the battery 2 from the vehicle voltage.

In this way, when the vehicle voltage is higher than the voltage of the battery 2 and a current in the charging direction is flowing through the charge/discharge path 4, the monitoring unit 91 controls to turn off the FET 51 to protect the battery 2 from overcharging.
After the FET 51 is turned off, for example, the vehicle voltage may become lower than the voltage of the battery 2. As an example, if power generation is not performed due to a malfunction of the alternator, the charging rate of the vehicle power supply 3 may decrease, causing the vehicle voltage to drop. In such a case, it is desirable for the battery 2 to discharge and charge the vehicle power supply 3 or supply power to the vehicle load 6.

FIG. 4 is a diagram for explaining discharging from the battery 2. As shown in FIG.
4, the FET 51 of the switch unit 5 is in an off state, but the diode 53 is connected in parallel to the FET 51. As described above, the anode of the diode 53 is disposed on the battery 2 side. Therefore, the diode 53 blocks a current in the charging direction but allows a current in the discharging direction to flow.

That is, in the vehicle power supply device 1 of this embodiment, when the vehicle voltage drops below the voltage of the battery 2 and the battery 2 is discharged, a current flows in the discharging direction through the charge/discharge path 4 via the FET 52 and the diode 53. This allows power to be supplied from the battery 2 to the vehicle power supply 3 and the vehicle load 6.
However, if discharge continues through the diode 53, there is a possibility that the heat generated by the diode 53 will increase. In particular, the diode tends to generate a large amount of heat in the forward direction (discharge direction). If a heat dissipation mechanism is provided to reduce the heat generated by the diode 53, the vehicle power supply device 1 will become larger, restricting the installation space in the vehicle and increasing the installation cost.
Therefore, when the control device 9 detects discharging of the battery 2, it controls the FET 51 to return from off to on. By turning on the FET 51, the current discharged from the battery 2 flows through the FET 51, so that heat generation in the diode 53 is reduced and a heat dissipation mechanism is not required.

The monitoring unit 91 detects the discharge of the battery 2 from the potential difference PD measured by the voltage sensor 71 connected to both ends of the FET 51 .
When the battery 2 is discharged with the FET 51 turned off, a current flows through the diode 53. That is, when the FET 51 is turned off, the voltage sensor 71 detects a potential difference PD across the two ends of the diode 53. When a current flows in the forward direction through the diode, even a small current of about 10 mA can detect a potential difference PD of about 0.6 V.
The monitoring unit 91 detects discharging of the battery 2 by comparing the potential difference PD measured by the voltage sensor 71 with a threshold value TH3. The threshold value TH3 is a potential difference indicating discharging of the battery 2, and can be set in advance and stored in the storage device. The control device 9 performs control to switch the FET 51 from off to on when the potential difference PD measured by the voltage sensor 71 exceeds the threshold value TH3.

Although a detailed description will be omitted, the monitoring unit 91 may turn on and off the FETs 51 and 52 for purposes other than protecting the battery 2 from overcharging as described above. For example, if the monitoring unit 91 determines that there is a malfunction in the battery 2, it may turn off both the FETs 51 and 52 and disconnect the battery 2 from the charge/discharge path 4.

The flow of processing by the control device 9 of the vehicle power supply device 1 in this embodiment will be described.
FIG. 5 is a flowchart showing the process of the monitoring unit 91 of the control device 9.
The monitoring unit 91 turns on the FET 51 and the FET 52 as an initial state.
The monitoring unit 91 acquires the cell voltage _Vc of the battery 2 from the voltage sensor 72, acquires the vehicle voltage from the voltage sensor 73, and calculates the sum _ΣVc of the cell voltages as the voltage _V2 of the battery 2 (step S01). The monitoring unit 91 compares the voltage _V2 of the battery 2 with a threshold value TH1 (step S02).
If the monitoring unit 91 determines that the voltage _V2 of the battery 2 exceeds the threshold TH1 (step S02: Yes), the control device 9 proceeds to step S05 and turns the FET 51 off.
When the voltage _V2 of the battery 2 is equal to or lower than the threshold value TH1 (step S02: No), the monitoring unit 91 calculates the difference ΔV between the vehicle voltage and the voltage _V2 of the battery 2 (step S03).
Specifically, the monitoring unit 91 acquires the vehicle voltage obtained by the voltage sensor 73, and calculates the difference ΔV by subtracting the voltage V ₂ (ΣV _c ) of the battery 2 calculated in step S01 from the vehicle voltage.
When the calculated difference ΔV exceeds the threshold value TH2 (step S04: Yes), the monitoring unit 91 proceeds to step S05 and turns off the FET 51.
If the difference ΔV is equal to or smaller than the threshold TH2 (step S04: No), the monitoring unit 91 leaves the FET 51 on and ends the process.

After turning off FET 51 in step S05, monitoring unit 91 obtains potential difference PD measured by voltage sensor 71 and compares it with threshold value TH3 (step S06). If potential difference PD exceeds threshold value TH3 (step S06: Yes), monitoring unit 91 detects discharge from battery 2 and turns on FET 51 (step S07).
After completing the process shown in Fig. 5, the monitoring unit 91 performs the process shown in Fig. 5 again from step S01. That is, the monitoring unit 91 repeatedly performs the process shown in Fig. 5 while the vehicle is running. This makes it possible to protect the battery 2 from overcharging.

As described above, the vehicle power supply device 1 of the present embodiment has the following configuration.
(1) Vehicle power supply device 1 includes:
A battery 2 (first battery); and
A vehicle power source 3 (a second battery);
a charge/discharge path 4 that connects the battery 2 and the vehicle power supply 3 so that they can be charged and discharged from each other;
A switch unit 5 provided in the charge/discharge path 4;
The control device 9 includes a monitoring unit 91 that monitors the state of the battery 2 and controls the switch unit 5 .
The switch unit 5 is
an FET 51 (a first semiconductor switching element) and an FET 52 (a second semiconductor switching element) connected in series;
A diode 53 (first diode) connected in parallel to the FET 51 with its anode located on the battery 2 side;
and a diode 54 (second diode) arranged in the opposite direction to the diode 53 and connected in parallel to the FET 52 .
When protecting the battery 2 from overcharging, the monitoring unit 91 turns the FET 51 off and turns the FET 52 on.

When the vehicle is traveling, power is supplied to the battery 2 from the vehicle power supply 3 via the charge/discharge path 4, and the battery 2 is charged. If the output voltage of the vehicle power supply 3 becomes higher than normal, the cell voltage _Vc of the battery 2 may exceed the upper limit voltage _Vu , and the battery 2 may be overcharged. Also, if the voltage difference ΔV between the battery 2 and the vehicle power supply 3 becomes large, a large current may flow through the charge/discharge path 4, and the battery 2 may be overcharged.
The vehicle power supply device 1 of this embodiment is provided with a switch unit 5 in the charge/discharge path 4. The monitoring unit 91 turns off the FET 51 of the switch unit 5 and turns on the FET 52, thereby cutting off the flow of power from the vehicle power supply 3 to the battery 2, thereby protecting the battery 2 from overcharging. Note that a diode 53 is connected in parallel to the FET 51, but since the battery 2 is disposed on the anode side of the diode 53, the flow of current in the charging direction is cut off.

On the other hand, when the SOC of the vehicle power supply 3 drops and the voltage of the vehicle power supply 3 becomes lower than the voltage of the battery 2, it is desirable to discharge the battery 2 and charge the vehicle power supply 3 or supply power to the vehicle load 6. Here, when the switch unit 5 is composed only of the FETs 51 and 52, turning off the FET 51 completely cuts off the charge/discharge path 4, and therefore the battery 2 cannot be discharged.
In this embodiment, a diode 53 is connected in parallel to the FET 51. The diode 53 has an anode disposed on the battery 2 side, and a current flows in the discharging direction from the battery 2 to the vehicle power supply 3.
That is, when the voltage of the vehicle power supply 3 drops, the current discharged from the battery 2 flows through the charge/discharge path 4 via the FET 52 in the on state and the diode 53 connected in parallel to the FET 51. This enables the battery 2 to discharge, and to charge the vehicle power supply 3 or to charge the vehicle load 6.

(2) After turning off FET 51 and turning on FET 52, if the monitoring unit 91 detects discharging of the battery 2, it turns on FET 51 and FET 52.

Continuing to discharge through the diode 53 increases heat generation in the diode 53. If a heat dissipation mechanism for dissipating heat from the diode 53 is provided, the vehicle power supply device 1 becomes larger and the installation costs increase.
In this embodiment, the monitoring unit 91 turns on the FET 51 when it detects discharging of the battery 2. This allows the current discharged from the battery 2 to pass through the FET 51, thereby reducing heat generation from the diode 53. This eliminates the need for a heat dissipation mechanism for the diode 53, making it possible to reduce the size of the vehicle power supply device 1 and the installation costs.

(3) The vehicle power supply device 1 includes a voltage sensor 71 (first voltage sensor) connected across the FET 51 .
The monitoring unit 91 detects the discharge from the battery 2 based on the potential difference PD measured by the voltage sensor 71 .

When FET 51 is off, current flows through diode 53, so voltage sensor 71 detects potential difference PD across both ends of diode 53. When current flows in the forward direction through diode 53, potential difference PD is easily detected even with a small current. In other words, when discharging of battery 2 begins, monitoring unit 91 can quickly detect the discharge and turn on FET 51, thereby reducing heat dissipation from diode 53.

(5) The vehicle power supply device 1 includes a voltage sensor 72 (second voltage sensor) that measures the voltage _Vc of each cell that constitutes the battery 2 .
The monitoring unit 91 calculates the sum ΣV _c of the voltages of the cells measured by the voltage sensor 72 while the FETs 51 and 52 are turned on, as the voltage V ₂ of the battery 2 .
When the calculated sum ΣV _c of the voltages of the cells exceeds a threshold TH 1 indicating the upper limit voltage of the battery 2 , the monitoring unit 91 turns off the FET 51 and turns on the FET 52 .

When the cell voltage _Vc of the battery 2 exceeds the upper limit voltage _Vu , there is a possibility that the battery 2 may be overcharged. In this embodiment, the monitoring unit 91 controls the FET 51 to be turned off using a threshold value TH1 set based on the upper limit voltage of the entire battery 2, thereby making it possible to appropriately protect the battery 2 from overcharging.

(6) The monitoring unit 91 uses a value obtained by multiplying the upper limit voltage _Vu per unit cell of the battery 2 by the total number N of cells constituting the battery 2 as the threshold value TH1.

The upper limit voltage of the entire battery 2 can be, for example, the upper limit voltage _Vu per unit cell multiplied by the total number of cells N. As a result, when the voltage applied to the battery 2 exceeds the upper limit voltage of the battery 2, the monitoring unit 91 turns off the FET 51, thereby protecting the battery 2 from overcharging. In addition, since a preset value can be used as the threshold value TH1, the calculation load of the monitoring unit 91 can be reduced.

(7) The vehicle power supply device 1 includes a voltage sensor 73 (third voltage sensor) that measures the vehicle voltage (the voltage applied from the second battery).
The monitoring unit 91 acquires a measurement value of the vehicle voltage from the voltage sensor 73. When the difference ΔV between the vehicle voltage and the voltage _V2 ( _ΣVc ) of the battery 2 exceeds a threshold TH2 (allowable voltage value), the monitoring unit 91 turns off the FET 51 and turns on the FET 52.

When the difference between the vehicle voltage and the voltage _V2 of the battery 2 becomes large, a large current exceeding the allowable current flows through the charge/discharge path 4, and there is a possibility that the battery 2 may be overcharged. Therefore, the monitoring unit 91 turns off the FET 51 when the difference ΔV between the vehicle voltage and the voltage of the battery 2 exceeds a threshold TH3 indicating the allowable voltage value. This makes it possible to protect the battery 2 from overcharging.

Modifications of the above-described embodiment will be described below. In the modification, the same components as those in the above-described embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.
<Modification 1>
FIG. 6 is a diagram showing the electrical configuration of a vehicle power supply device 1 according to the first modification.
In the above embodiment, an example in which the voltage sensor 71 (first voltage sensor) is connected to both ends of the FET 51 has been described, but the present invention is not limited to this.
6, in the first modification, terminals of a voltage sensor 71 are connected to both ends of a fuse 41 provided in a charge/discharge path 4. That is, the voltage sensor 71 measures a potential difference PD across the fuse 41.

In the first modification, the monitoring unit 91 detects the discharge of the battery 2 from the potential difference PD measured by the voltage sensor 71 connected across the fuse 41 .
As described above, when the battery 2 is discharged while the FET 51 is in the OFF state, a current flows through the charge/discharge path 4 via the diode 53. That is, since a current flows through the fuse 41 provided in the charge/discharge path 4, the monitoring unit 91 can detect the discharge of the battery from the measurement value of the voltage sensor 71 connected to both ends of the fuse 41. When the potential difference PD measured by the voltage sensor 71 exceeds the threshold TH3, the monitoring unit 91 can detect the discharge of the battery 2 and switch the FET 51 from OFF to ON.

As described above, the vehicle power supply device 1 according to the first modification has the following configuration, for example.
(4) The vehicle power supply device 1 includes a fuse 41 provided in the charge/discharge path 4,
and a voltage sensor 71 (first voltage sensor) connected to both ends of the fuse 41.
The monitoring unit 91 detects the discharge from the battery 2 based on the potential difference PD measured by the voltage sensor 71 .

The location where the voltage sensor 71 is provided is not limited to the examples shown in the embodiment and modified example 1. The voltage sensor 71 can be provided at a location where the potential difference PD can be easily detected. For example, although not shown, the voltage sensor 71 can be connected to both ends of a bus bar or a shunt resistor provided in the charge/discharge path 4.
Furthermore, in the embodiment and the first modified example, the monitoring unit 91 detects the discharge of the battery 2 based on the potential difference PD measured by the voltage sensor 71, but the present invention is not limited to this example. The monitoring unit 91 may detect the discharge of the battery 2 based on, for example, a measurement value of a current sensor provided in the charge/discharge path 4. The current sensor may be connected, for example, between the FET 51 of the switch unit 5 and the vehicle power source 3 in the charge/discharge path 4. The monitoring unit 91 can detect the discharge of the battery 2 when the current sensor measures a current flowing in the discharge direction.

<Modification 2>
As described above, the monitoring unit 91 protects the battery 2 by turning off the FET 51 when there is a possibility that the battery 2 may be overcharged.
Here, if the FET 51 continues to be turned off for a long period of time, the SOC of the battery 2 decreases, and when it becomes necessary to discharge the battery 2, there is a possibility that the required amount of discharge cannot be performed.
As shown in FIG. 2, the control device 9 includes an estimation unit 92 that periodically estimates the SOC while the vehicle is running.
In the second modification, when the SOC of the battery 2 estimated by the estimation unit 92 falls below a predetermined value PV _a after the monitoring unit 91 turns off the FET 51, the monitoring unit 91 charges the battery 2 by intermittently turning on the FET 51.
The predetermined value PV _a can be set based on the charging rate required for discharging the battery 2. The predetermined value PV _a can be set in advance and stored in a storage device.
Turning on the FET 51 intermittently means turning on the FET 51 for a short time, turning it off for a predetermined time, and then turning on the FET 51 for a short time again. Turning on the FET 51 for only a short time prevents overcharging of the battery 2. When the FET 51 is turned on, a current flows in the charging/discharging path 4 in the charging direction, so that the battery 2 is gradually charged.
When the battery 2 is gradually charged and the SOC exceeds a predetermined value PV _a , the monitoring unit 91 ends the control of intermittently turning on the FET 51. The predetermined value PV _a can be set in advance and stored in the storage device. The predetermined value PV _a can be, for example, a value higher than the predetermined value PV _a .

FIG. 7 is a flowchart showing the process of the monitoring unit 91 according to the second modification.
FIG. 7 shows the process of the monitoring unit 91 that is carried out after the FET 51 is turned off.
That is, the process of Fig. 7 is performed after the FET 51 is turned off in step S05 of Fig. 5. The process of Fig. 7 is performed in parallel with the process of detecting the discharge of the battery 2 shown in steps S06 to S07 of Fig. 5.

The monitoring unit 91 acquires the SOC of the battery 2 estimated by the estimation unit 92 (step S101).
The monitoring unit 91 compares the SOC of the battery 2 with a predetermined value PV _a (step S102).
If the SOC of the battery 2 is lower than a predetermined value PV _a (step S102: Yes), the monitoring unit 91 performs control to intermittently turn on the FET 51 (step S103). Only while the FET 51 is turned on for a short period of time, a current flows in the charging/discharging path 4 in the charging direction, and the battery 2 is gradually charged.
When the SOC of the battery 2 exceeds the predetermined value PV _a (step S104: Yes), the monitoring unit 91 ends the control of intermittently turning on the FET 51 (step S105).
The monitoring unit 91 repeats the process of Fig. 7 while the FET 51 is off. Furthermore, when the monitoring unit 91 detects discharge from the battery 2 and turns on the FET 51 in the parallel process of steps S06 to S07 of Fig. 5, the monitoring unit 91 ends the process of Fig. 7.

As described above, the vehicle power supply device 1 according to the second modification has, for example, the following configuration.
(9) The control device 9 of the vehicle power supply device 1 includes an estimation unit 92 that estimates the SOC (state of charge) of the battery 2 .
While the FET 51 is turned off and the FET 52 is turned on, if the SOC of the battery 2 estimated by the estimation unit 92 becomes lower than a predetermined value PV _a , the monitoring unit 91 intermittently turns on the FET 51 to charge the battery 2 from the vehicle power supply 3.

If the FET 51 is kept off for a long period of time, the battery 2 will not be charged, and the SOC of the battery 2 will drop, which may result in insufficient power being supplied during discharge. Therefore, when the SOC of the battery 2 falls below a predetermined value PV _a , the monitoring unit 91 performs control to intermittently turn on the FET 51, thereby making it possible to charge the battery 2 while preventing it from being overcharged.
The control device 9 may use the SOC estimated by the estimation unit 92 for processing other than that performed by the monitoring unit 91 .

<Modification 3>
FIG. 8 is a diagram showing the electrical configuration of a vehicle power supply device 1 according to the third modification.
In the third modification, as in the second modification, the SOC of the battery 2 is estimated after the FET 51 is turned off, and when the SOC of the battery 2 falls below a predetermined value PV _a , the battery 2 is charged.
As shown in FIG. 8 , the vehicle power supply device 1 according to the third modification includes a bypass path 8 provided separately from the charge/discharge path 4 .
The bypass path 8 connects the battery 2 and the vehicle power supply 3 so as to be capable of charging and discharging, and a DC/DC converter 81 (voltage regulator) is provided on the bypass path 8. A switch such as a relay is provided on the bypass path 8 between the DC/DC converter 81 and the vehicle power supply 3. By turning on the relay, charging and discharging between the battery 2 and the vehicle power supply 3 via the bypass path 8 becomes possible. The on and off of the relay is controlled by a monitoring unit 91.

As in the second modification shown in FIG. 7 , the estimation unit 92 periodically estimates the SOC of the battery 2 after the monitoring unit 91 performs control to turn off the FET 51 .
A monitoring unit 91 in the third modification performs a process of turning on a relay of the bypass path 8 instead of step S103 in Fig. 7 when the SOC of the battery 2 estimated by the estimation unit 92 falls below a predetermined value PV _a . The voltage of the current discharged from the vehicle power supply 3 is adjusted by a DC/DC converter 81 provided on the bypass path 8 and supplied to the battery 2. This makes it possible to charge the battery 2 while preventing the battery 2 from being over-discharged.
When the battery 2 is charged via the bypass path 8 and the SOC exceeds a predetermined value _PVb , the monitoring unit 91 turns off the relay to terminate the charging of the battery 2 .

As described above, the vehicle power supply device 1 according to the third modification has, for example, the following configuration.
(10) The vehicle power supply device 1 includes an estimation unit 92 of a control device 9 that estimates the SOC of the battery 2;
The battery 2 and the vehicle power supply 3 are connected to each other so as to be capable of being charged and discharged, and a bypass path 8 is provided with a DC/DC converter 81 (voltage regulator).
While the FET 51 is turned off and the FET 52 is turned on, if the SOC of the battery 2 becomes equal to or lower than a predetermined value PV _a , the monitoring unit 91 charges the battery 2 from the vehicle power supply 3 via the bypass path 8 .

If the FET 51 remains off for a long period of time, the battery 2 will not be charged, and the SOC of the battery 2 will drop, which may result in insufficient power being supplied during discharging. In the third modification, the vehicle power supply device 1 includes a bypass path 8 provided with a DC/DC converter 81. With this, when the monitoring unit 91 detects that the SOC of the battery 2 has fallen below a predetermined value PV _a , it is possible to charge the battery 2 from the vehicle power supply 3 via the bypass path 8 while preventing the battery 2 from being overcharged.
The voltage regulator is not limited to a DC/DC converter, and may be, for example, a diode provided in the bypass path 8 as a voltage regulator.

<Modification 4>
In the embodiment described above, the threshold value TH1 to be compared with the voltage _V2 of the battery 2 is set to a value obtained by multiplying the upper limit voltage _Vu per unit cell constituting the battery 2 by the total number N of cells, but the present invention is not limited to this embodiment.
In the fourth modification, an example will be described in which the monitoring unit 91 sequentially determines the threshold value TH1 using the cell voltage _Vc measured by the voltage sensor 72.

FIG. 9 is a diagram for explaining the setting of the threshold value TH1 in the fourth modification.
Fig. 9 shows an example of the cell voltage Vc measured by the voltage sensor 72, and as shown in Fig. 9, there is variation in the cell voltage _Vc . In the example of Fig. 9, among the four cells C1 to C4, the cell C4 shows the highest cell voltage (maximum cell voltage _Vcmax ). As shown in Fig. 9, the maximum cell voltage _Vcmax is the value closest to the upper limit voltage _Vu per unit cell. In other words, if a voltage (cross-hatched portion) at which this maximum cell voltage _Vcmax reaches the upper limit voltage _Vu is applied from the vehicle power source 3, there is a high possibility that the battery 2 will be overcharged.
Therefore, in the fourth modification, the monitoring unit 91 calculates the amount of voltage until the maximum cell voltage _Vcmax reaches the upper limit voltage _Vu , and sets the threshold value TH1 based on this amount of voltage.

Specifically, the monitoring unit 91 can calculate a threshold value TH1 indicating an upper limit voltage of the entire battery 2 by using the following equation (2).
Formula (2):
Threshold TH1=sum of all cell voltages ΣV _c +{(upper limit voltage per unit cell V _u −maximum cell voltage V _cmax )×total number of cells N}
That is, in equation (2), the upper limit voltage of the entire battery 2 which is a battery pack is calculated from the voltage amount until the maximum cell voltage V _cmax reaches the upper limit voltage V _u (upper limit voltage V _u per unit cell−maximum cell voltage V _cmax ).

Before comparing the voltage _V2 of the battery 2 with the threshold value TH1 in step S02 of FIG. 5, the monitoring unit 91 can calculate the threshold value TH1 using the formula (2).
5, the monitoring unit 91 selects the maximum cell voltage _Vcmax from the cell voltages _Vc acquired from the voltage sensor 72. The monitoring unit 91 can also use the sum _ΣVc of the cell voltages calculated as the voltage _V2 of the battery 2 in step S01 in the calculation of equation (2).
The upper limit voltage V _u per unit cell and the total number N of cells can be preset and stored in a storage device, similarly to the embodiment.

As described above, the vehicle power supply device 1 according to the fourth modification has the following configuration.
(8) The monitoring unit 91 calculates the threshold value TH1 by multiplying the difference between the upper limit voltage _Vu per unit cell of the battery 2 and the maximum cell voltage _Vcmax measured by the voltage sensor 72 by the total number of cells N, and adding the result to the sum _ΣVc of the voltages of each cell.

As in the embodiment described above, the threshold value TH1 can be set as the upper limit voltage _Vu per unit cell × the total number of cells N. However, if the upper limit voltage _Vu per unit cell is set high, and there is variation in the voltage _Vc of each cell, there is a possibility that the cell with the highest SOC will be overcharged before the threshold value TH1 is exceeded. The possibility of overcharging can be reduced by setting the upper limit voltage _Vu per unit cell low with a margin, but in this case, the charge that can be charged to the battery 2 will be reduced.
In the fourth modification, the threshold value TH1 is set in real time according to the maximum cell voltage _Vcmax measured by the voltage sensor 72. When the maximum cell voltage _Vcmax is high, the threshold value TH1 is set low, but when the maximum cell voltage _Vcmax is low, the threshold value TH1 is set high, and a surplus of charge is generated in the charge that can be charged to the battery 2.
That is, the vehicle power supply device 1 of the fourth modification can charge the battery 2 according to its state while protecting the battery 2 from overcharging.

<Other Modifications>
In the second and third modified examples, the battery 2 is charged when the SOC of the battery 2 decreases while the vehicle is traveling. However, the present invention is not limited to this.
For example, when the vehicle is stopped, the alternator does not generate power, so that the vehicle voltage is unlikely to be higher than normal and the battery 2 is unlikely to be overcharged. If the SOC of the battery 2 falls below a predetermined value PV _a after the monitoring unit 91 turns off the FET 51, the monitoring unit 91 can control the FET 51 to be turned on at the timing when the vehicle is stopped so that the battery 2 is charged. Note that the vehicle being stopped can include both a state in which the vehicle is parked and stopped from traveling, and a state in which the vehicle is temporarily stopped from traveling by braking or the like.

The above-mentioned modifications may be applied not only to the embodiment but also in combination with each other.

Note that, as an example of a judgment process using a threshold, when a judgment is made when the threshold comparison target is "above the threshold" or "below the threshold", it is not limited to this mode only. The comparison process can also include a mode in which a judgment is made when the threshold comparison target is "above the threshold" or "below the threshold". Conversely, when a judgment is made when the threshold comparison target is "above the threshold" or "below the threshold", it is not limited to this mode only, and the comparison process can also include a mode in which a judgment is made when the threshold comparison target is "above the threshold" or "below the threshold". In other words, the mode of judgment process using a threshold is not to be interpreted strictly as the example described above.

1 Vehicle power supply device 2 Battery (first battery)
3 Vehicle power supply (second battery)
4 Charging/discharging path 41 Fuse 5 Switch unit 51 FET (first semiconductor switching element)
52 FET (second semiconductor switching element)
53 Diode (first diode)
54 Diode (second diode)
71 Voltage sensor (first voltage sensor)
72 Voltage sensor (second voltage sensor)
73 Voltage sensor (third voltage sensor)
8 Bypass path 81 DC/DC converter (voltage regulator)
9 Control device 91 Monitoring unit 92 Estimation unit

Claims (10)

A first battery;
A second battery;
a charge/discharge path that connects the first battery and the second battery so as to be capable of charging and discharging each other;
A switch unit provided in the charge/discharge path;
a monitoring unit that monitors a state of the first battery and controls the switch unit;
The switch unit is
a first semiconductor switching element and a second semiconductor switching element connected in series;
a first diode having an anode disposed on the first battery side and connected in parallel to the first semiconductor switching element;
a second diode arranged in an opposite direction to the first diode and connected in parallel to the second semiconductor switching element;
The vehicle power supply device, wherein the monitoring unit turns off the first semiconductor switching element and turns on the second semiconductor switching element when protecting the first battery from overcharging. The vehicle power supply device according to claim 1, wherein the monitoring unit turns on the first semiconductor switching element and the second semiconductor switching element when it detects discharging of the first battery after turning off the first semiconductor switching element and turning on the second semiconductor switching element. a first voltage sensor connected to both ends of the first semiconductor switching element;
3. The vehicle power supply device according to claim 2, wherein the monitoring unit detects discharging from the first battery based on a potential difference measured by the first voltage sensor. A fuse provided in the charge/discharge path;
a first voltage sensor connected across the fuse;
3. The vehicle power supply device according to claim 2, wherein the monitoring unit detects discharging from the first battery based on a potential difference measured by the first voltage sensor. a second voltage sensor for measuring a voltage of each cell constituting the first battery;
the monitoring unit calculates a sum of the voltages of the cells as a voltage of the first battery while the first semiconductor switching element and the second semiconductor switching element are turned on;
2. The vehicle power supply device according to claim 1, wherein the monitoring unit turns off the first semiconductor switching element and turns on the second semiconductor switching element when a sum of the voltages of the cells exceeds a threshold value indicating an upper limit voltage of the first battery. The vehicle power supply device according to claim 5, wherein the monitoring unit uses a value obtained by multiplying the upper limit voltage per unit cell of the first battery by the total number of cells constituting the first battery as the threshold value. a third voltage sensor that measures a voltage applied from the second battery;
When a difference between a voltage applied from the second battery and a voltage of the first battery exceeds a tolerable voltage value,
7. The vehicle power supply device according to claim 5, wherein said first semiconductor switching element is turned off and said second semiconductor switching element is turned on. The vehicle power supply device according to claim 5, wherein the monitoring unit calculates the threshold by adding a value obtained by multiplying the difference between the upper limit voltage per unit cell of the first battery and the maximum cell voltage measured by the second voltage sensor by the total number of cells to the sum of the voltages of the cells. an estimation unit that estimates a charging rate of the first battery;
2. The vehicle power supply device according to claim 1, wherein, when the charging rate estimated by the estimator becomes lower than a predetermined value while the first semiconductor switching element is turned off and the second semiconductor switching element is turned on, the monitoring unit intermittently turns on the first semiconductor switching element to charge the first battery from the second battery. an estimation unit that estimates a charging rate of the first battery;
a bypass path that connects the first battery and the second battery so as to be capable of being charged and discharged and that is provided with a voltage regulator;
2. The vehicle power supply device according to claim 1, wherein the monitoring unit charges the first battery from the second battery via the bypass path when the charging rate estimated by the estimating unit becomes lower than a predetermined value while the first semiconductor switching element is turned off and the second semiconductor switching element is turned on.

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