Power control device

Abstract

In a power control device, a control unit is configured to perform: discharge control, disconnecting a first switch and closing a second switch to release power from a backup power source to a backup load; first charge control, closing the first switch and disconnecting the second switch to charge the backup power source via a charging DC / DC converter; and second charge control, closing the first switch and closing the second switch to charge the backup power source via the second switch. When charging the backup power source, the second charge control is performed only when a current value of a charging current is equal to or greater than a first predetermined value and equal to or less than a second predetermined value, the second predetermined value being greater than the first predetermined value.

Description

Technical Field

[0001] The present disclosure relates to a power control device. Background Art

[0002] A vehicle power supply system is known, which includes a lead battery serving as a main power supply and a lithium-ion battery serving as a backup power supply (see, for example, Patent Document 1). In the vehicle power supply system disclosed in Patent Document 1, the lithium-ion battery is connected to the lead battery, an alternator, a load, and a backup load via a DC / DC converter. The DC / DC converter is a bidirectional DC / DC converter that converts the voltage on the lead battery side by switching operation and supplies the converted voltage to the lithium-ion battery side, or converts the voltage on the lithium-ion battery side and supplies the converted voltage to the lead battery side.

[0003] Patent Document 1: JP-A-2017-063543. Summary of the Invention

[0004] When the required output of the DC / DC converter increases due to an increase in the load to be driven, the cost of the DC / DC converter increases because, for example, the structure of the DC / DC converter needs to be significantly changed to improve the cooling performance of the DC / DC converter or the components need to be increased in size. Here, by providing a discharge path for releasing power from the backup power supply side to the backup load side without using a DC / DC converter, the cost of the DC / DC converter can be reduced.

[0005] The release of power from the backup power supply to the backup load is limited to, for example, the case where a power failure occurs on the main power supply side. In a normal state where no power failure occurs on the main power supply side, the backup power supply rarely releases power. Therefore, there is little opportunity to charge the backup power supply. Therefore, it is conceivable to reduce the cost by having a low-capacity DC / DC converter. However, in the case where an abnormal condition occurs, the backup power supply releases power, and the charge state of the backup power supply decreases, and it takes a long time to charge with a low-capacity DC / DC converter.

[0006] Therefore, it is conceivable to use the above discharge path when charging the backup power supply. However, depending on the voltage on the main power supply side or the open-circuit voltage of the backup power supply, the fluctuation range of the charging current may increase, and in this case, the charging current may exceed the allowable upper limit value.

[0007] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a power control device that can reduce the cost of the DC / DC converter and shorten the charging time while safely charging the backup power supply.

[0008] The present disclosure provides a power control device, which is in a power system. The power system includes a power supply unit, a main power supply, and a backup power supply. The power control device is connected to the power supply unit, the main power supply, and the backup power supply, and controls the charging and discharging of the backup power supply. The power control device includes: a power line to which the power supply unit, the main power supply, the backup power supply, and a backup load are connected; a first switch disposed on the power line and configured to connect and disconnect the power supply unit and the connection between the main power supply and the backup power supply; a second switch disposed on the power line and configured to connect and disconnect the connection between the backup power supply and the backup load; a charging DC / DC converter connected to the power line in parallel with the second switch and configured to convert the voltage supplied from the power supply unit side and supply the converted voltage to the backup power supply side; and a control unit configured to perform: a discharge control of disconnecting the first switch and connecting the second switch to release power from the backup power supply to the backup load; a first charging control of connecting the first switch and disconnecting the second switch to charge the backup power supply via the charging DC / DC converter; and a second charging control of connecting the first switch and connecting the second switch to charge the backup power supply via the second switch, wherein, when charging the backup power supply, the control unit is configured to perform the second charging control only when the current value of the charging current is equal to or greater than a first predetermined value and equal to or less than a second predetermined value, and the second predetermined value is greater than the first predetermined value.

[0009] In the present disclosure, when charging the backup power supply, the backup power supply is charged via the second switch only when the current value of the charging current is equal to or greater than a first predetermined value and equal to or less than a second predetermined value, and the second predetermined value is greater than the first predetermined value. In other cases, the backup power supply is charged via the charging DC / DC converter. Therefore, the cost of the DC / DC converter can be reduced by not providing a discharge DC / DC converter or by making the charging DC / DC converter have a low capacity, and the charging time can also be shortened while safely charging the backup power supply. Brief Description of the Drawings

[0010] Figure 1 is a diagram showing a vehicle-mounted power system including a control module according to an embodiment of the present disclosure.

[0011] Figure 2 is a diagram showing a vehicle-mounted power system including a control module according to an embodiment of the present disclosure.

[0012] Figure 3 is a diagram showing a vehicle-mounted power system including a control module according to an embodiment of the present disclosure.

[0013] Figure 4 is a diagram showing a vehicle-mounted power system including a control module according to an embodiment of the present disclosure.

[0014] Figure 5 It is a coordinate diagram showing the relationship between the voltage between the VB1 terminal and the internal part of the backup battery and the current value of the charging current in the case where the backup battery is charged using only the first charging path.

[0015] Figure 6 It is a coordinate diagram showing the relationship between the voltage between the VB1 terminal and the internal part of the backup battery and the current value of the charging current in the case where the backup battery is charged using the first charging path and the second charging path. Detailed implementation

[0016] Hereinafter, the present disclosure will be described according to preferred embodiments. The present disclosure is not limited to the embodiments to be described below, and appropriate changes can be made without departing from the scope of the present disclosure. Although some configurations are not shown or described in the embodiments to be described below, within the range where there is no contradiction in the following description, known or publicly known technologies are appropriately applied to the details of the technologies omitted.

[0017] Figures 1 to 4 It is a diagram showing an in-vehicle power supply system 1 including a control module 10 according to an embodiment of the present disclosure. As shown in these drawings, the in-vehicle power supply system 1, as an example of a power supply system, includes a main battery 2 as an example of a main power supply, a backup battery 3 as an example of a backup power supply, a high-voltage DC / DC converter 4 as an example of a power supply unit, and a control module 10 as an example of a power supply control device. In the in-vehicle power supply system 1 of the present embodiment, the main battery 2 is a conventional power supply that supplies power to a 12V main load 5, and the backup battery 3 is an emergency power supply that supplies power to a 12V backup load 6. In addition, the main battery 2 of the present embodiment is a 12V lead-acid battery. In contrast, the backup battery 3 of the present embodiment is a ternary lithium-ion secondary battery and has a higher rated voltage than the main battery 2.

[0018] The power supply unit includes, for example, a 48V or similar high-voltage power supply, a generator (such as an alternator), and the high-voltage DC / DC converter 4. The high-voltage DC / DC converter 4 reduces the high voltage output from the high-voltage power supply and the generator and outputs the reduced high voltage. The main battery 2, the main load 5, and the control module 10 are connected to a power line PL6, and the power line PL6 is connected to the output terminal of the high-voltage DC / DC converter 4. A VB1 terminal T1 is provided at one end of the power line PL1, a VB2 terminal T2 is provided at the other end of the power line PL1, and the power line PL1 is provided in the control module 10. The power line PL6 is connected to the VB1 terminal T1. The backup battery 3 is connected to the VB2 terminal T2 through a power line PL5. In addition, the backup load 6 is connected to the power line PL1.

[0019] As Figure 1As shown, in the normal state where no power failure occurs in the main power supply system, the power output from the high-voltage DC / DC converter 4 is supplied to the main load 5 and the main battery 2. When charging the backup battery 3, the power output from the high-voltage DC / DC converter 4 is supplied to the backup battery 3 via the control module 10.

[0020] On the other hand, as Figure 2 shown, when a power failure occurs in the main power supply system, power is supplied from the backup battery 3 to the backup load 6. That is, the charging and discharging of the backup battery 3 are controlled by the control module 10 such that: when, as Figure 1 shown, in the normal state where no power failure occurs in the main power supply system, the backup battery 3 is charged by the power output from the high-voltage DC / DC converter 4; when, as Figure 2 shown, a power failure occurs in the main power supply system, power is released from the backup battery 3 to the backup load 6.

[0021] The control module 10 includes a first switch 11, a second switch 12, a charging DC / DC converter 13, a discharge circuit 14, a central processing unit (CPU) 20 as an example of a control unit, and a power line PL1. The first switch 11 and the second switch 12 are provided on the power line PL1.

[0022] The first switch 11 is provided between the connection point P2 of the VB1 terminal T1 and the backup load 6. The first switch 11 is a transistor switch such as a metal oxide semiconductor field effect transistor (MOSFET). The first switch 11 is turned on in the normal state where no power failure occurs in the main power supply system to allow current to flow from the high-voltage DC / DC converter 4 side to the backup battery 3 side, as Figure 1 shown. On the other hand, when a power failure occurs in the main power supply system, the first switch 11 is turned off to cut off the current flowing from the backup battery 3 side to the high-voltage DC / DC converter 4 side, as Figure 2 shown.

[0023] The second switch 12 is provided on the power line PL1 between the connection point P2 of the backup load 6 and the VB2 terminal T2. The second switch 12 is a transistor switch such as a MOSFET. The second switch 12 is turned off when no power failure occurs in the main power supply system (when charging the backup battery 3) to cut off the current flowing from the high-voltage DC / DC converter 4 side to the backup power supply 3 side, as Figure 1 shown. On the other hand, when, as Figure 2 shown, a power failure occurs in the main power supply system (when the backup battery 3 releases power), the second switch 12 is turned on to allow current to flow from the backup battery 3 side to the backup load 6 side.

[0024] The charging DC / DC converter 13 is connected to the power line PL1 in parallel with the second switch 12. In other words, the charging DC / DC converter 13 is provided on a bypass line BL that bypasses the second switch 12. A shunt resistor Rsh1 for a current sensor is provided on the bypass line BL.

[0025] As Figure 1 shown, the charging DC / DC converter 13 converts the voltage output from the high-voltage DC / DC converter 4 and outputs the converted voltage to the backup battery 3. Here, the current flowing through the charging DC / DC converter 13 during charging of the backup battery 3 is a very small current of about 4 A, and the output capacity required by the charging DC / DC converter 13 is small. On the other hand, as Figure 2 shown, the current output from the backup battery 3 to the backup load 6 is a relatively large current of about 80 A.

[0026] As described above, the backup battery 3 releases power to the backup load 6 only in cases such as when a power failure occurs in the main power supply system. In a normal state where no power failure occurs in the main power supply system, the backup battery 3 rarely releases power. Therefore, there is almost no opportunity to charge the backup battery 3. Therefore, in the present embodiment, by having a low-capacity charging DC / DC converter 13, the cost of the DC / DC converter is reduced.

[0027] The discharge circuit 14 is connected to the power line PL4 via the power line PL3. The power line PL4 connects the power line PL1 and the Vout terminal T3. The Vout terminal T3 is the terminal to which the power line PL2 is connected, and the power line PL2 is connected to the backup load 6. The discharge circuit 14 includes a switch (not shown). When power is output from the high-voltage DC / DC converter 4 and the switch of the discharge circuit 14 is turned on, the first switch 11 is turned on and the second switch 12 is turned off, and current flows from the power line PL3 to the discharge circuit 14, as Figure 3 shown. A shunt resistor Rsh2 for a current sensor is provided on the power line PL4, between the connection point P2 and the connection point P3 of the power line PL3. In addition, a shunt resistor Rsh3 for a current sensor is provided on the power line PL3.

[0028] The CPU 20 controls the first switch 11, the second switch 12, the charging DC / DC converter 13, and the discharge circuit 14. For example, in the case of a power failure in the main power supply system, in a case where the output voltage of the main battery 2 decreases to a predetermined value or less, for example, the CPU 20 turns off the first switch 11 and turns on the second switch 12, as Figure 2 shown.

[0029] Here, when charging the backup battery 3, the CPU 20 switches between the first charging path and the second charging path according to the current values I1 and I2 of the charging current. The first charging path is the charging path passing through the charging DC / DC converter 13 as shown in Figure 1 , and the second charging path is the charging path passing through the second switch 12 as shown in Figure 4 . The current value I1 of the charging current is the current value of the charging current flowing through the first charging path as shown in Figure 1 , and the current value I2 of the charging current is the current value of the charging current flowing through the second charging path as shown in Figure 4 . As shown in Figure 1 , the CPU 20 turns on the first switch 11 and turns off the second switch 12, thereby supplying a charging current with a current value of I1 to the backup battery 3 via the charging DC / DC converter 13. On the other hand, as shown in Figure 4 , the CPU 20 turns on the first switch 11 and turns on the second switch 12, thereby supplying a charging current with a current value of I2 to the backup battery 3 via the second switch 12. In addition, when starting the vehicle (immediately after the ignition is turned on), the CPU 20 executes a process of estimating the current value I2 of the charging current in the case of charging the backup battery 3 using the second charging path.

[0030] Figure 5 is a coordinate diagram showing the relationship between the voltage (VB1 - OCV) between the VB1 terminal T1 and the internal part of the backup battery 3 and the current value I1 of the charging current in the case of charging the backup battery 3 using only the first charging path. Note that VB1 is the voltage output from the main battery 2 and input to the control module 10, and OCV is the open - circuit voltage of the backup battery 3. Figure 6 is a coordinate diagram showing the relationship between the voltage (VB1 - OCV) and the current value I2 of the charging current in the case of charging the backup battery 3 using the first charging path and the second charging path.

[0031] As shown in the coordinate diagram of Figure 5 , in the case of charging the backup battery 3 using only the first charging path, regardless of the voltage (VB1 - OCV), the current value I1 of the charging current is equal to or less than the maximum output current Ith1 (an example of the first predetermined value) of the charging DC / DC converter 13. That is, in the case of charging the backup battery 3 using only the first charging path, the current value I1 of the charging current decreases to be equal to or less than the maximum output current Ith1 of the charging DC / DC converter 13, and the charging DC / DC converter 13 has a lower capacity to reduce costs.

[0032] In contrast, as shown in Figure 6As shown in the coordinate diagram, when charging the backup battery 3 using not only the first charging path but also the second charging path, there is a situation where a charging current with a current value I2 equal to or greater than Ith1 is supplied to the backup battery 3 using the second charging path, so this charging current increases compared to the case of charging the backup battery 3 using only the first charging path.

[0033] Here, when supplying a charging current with a current value I2 equal to or greater than Ith1 to the backup battery 3 using the second charging path, it is necessary to suppress the current value I2 of the charging current to be equal to or less than the upper limit value allowed for the current flowing through the control module 10, and to be equal to or less than the upper limit value allowed for the charging current of the backup battery 3. Therefore, when starting the vehicle (immediately after the ignition is turned on), the CPU 20 executes a process of estimating the current value I2 of the charging current in the case of charging the backup battery 3 using the second charging path, and uses the second charging path to charge the backup battery 3 only when the current value I2 of the charging current estimated in the process satisfies Ith1 ≤ I2 ≤ Ith2. Here, Ith2 (an example of the first predetermined value) is the smaller of the upper limit value allowed for the current flowing through the control module 10 and the upper limit value allowed for the charging current of the backup battery 3. The estimation process for estimating the current value I2 of the charging current will be described below.

[0034] The current value I2 of the charging current in the case of charging the backup battery 3 using the second charging path is calculated using the following equation (1).

[0035] I2 = (VB1 - OCV) / R2…(1)

[0036] R2 is calculated using the following equation (2).

[0037] R2 = Rm1 + Rm2 + Rb…(2)

[0038] Rm1 and Rm2 are the internal resistances of the control module 10 (see Figures 1 to 4 ). Rm1 is the internal resistance between the first switch 11 and the second switch 12, and Rm2 is the internal resistance between the second switch 12 and the VB2 terminal T2. In addition, Rb is the internal resistance of the backup battery 3.

[0039] The internal resistance Rb of the backup battery 3 is calculated using the following equation (3).

[0040] Rb = α(VB2 - OCV) / I1…(3)

[0041] α is the conversion coefficient of the internal resistance Rb of the backup battery 3, which varies according to the discharge current and is obtained in advance by performing a battery characteristic evaluation test.

[0042] I1 is the current value of the charging current supplied to the backup battery 3 in the case of using the first charging path. To obtain the current value I1 of the charging current, the CPU 20 performs a process of causing the charging current to flow through the first charging path when starting the vehicle and measuring the current value I1 with a current sensor.

[0043] The internal resistance Rm1 is calculated using the following equation (4).

[0044] Rm1 = (VB1 - VBA) / Iout…(4)

[0045] VBA is the voltage between the first switch 11 and the second switch 12 (see Figures 1 to 4 ). Iout is the current value of the current output from the Vout terminal T3 to the backup load 6 (see Figure 2 and Figure 3 ). To obtain the current value Iout, the CPU 20 performs a process of causing the current to flow from the high-voltage DC / DC converter 4 to the backup load 6 via the power line PL4 when starting the vehicle and measuring the current value Iout with a current sensor.

[0046] The internal resistance Rm2 is calculated using the following equation (5).

[0047] Rm2 = (VB2 - VBA) / I3…(5)

[0048] I3 is the current value of the current flowing through the discharge circuit 14 (see Figure 3 ). To obtain the current value I3, the CPU 20 performs such a process that when starting the vehicle, by turning on the first switch 11 and turning off the second switch 12, the current flows from the high-voltage DC / DC converter 4 to the discharge circuit 14 via the power lines PL6, PL1, PL4, and PL3, and measures the current value I3.

[0049] When the current value I2 of the charging current estimated in the estimation process satisfies the relationship I2 < Ith1, I2 > Ith2, the CPU 20 charges the backup battery 3 using the first charging path. On the other hand, when the current value I2 of the charging current estimated in the estimation process satisfies the relationship Ith1 ≤ I2 ≤ Ith2, the CPU 20 charges the backup battery 3 using the second charging path.

[0050] As Figure 6As shown, as the difference (VB1 - OCV) between the voltage VB1 input to the control module 10 and the open circuit voltage OCV decreases, the internal resistance R2 decreases, and the rate of increase of the charging current increases. In this case, the time during which the backup battery 3 can be charged using the second charging path is shortened, the charging current decreases, and a longer charging time is required. Conversely, as the difference between the voltage VB1 input to the control module 10 and the open circuit voltage OCV increases, the internal resistance R2 increases, and the rate of increase of the charging current decreases. In this case, the time during which the backup battery 3 can be charged using the second charging path is extended, the charging current increases, and a shorter charging time is required.

[0051] That is, in the present embodiment, by estimating the internal resistance R2 between the voltage VB1 input to the control module 10 and the open circuit voltage OCV inside the backup battery 3, the current value I2 of the charging current can be estimated in the case of charging the backup battery 3 using the second charging path before starting to charge the backup battery 3. When the estimated current value I2 of the charging current is within the safety range based on the relationship between the allowable range of the current flowing through the control module 10 and the allowable range of the charging current of the backup battery 3, the backup battery 3 is charged using the second charging path. Therefore, compared with the case of charging the backup battery 3 using only the first charging path, the charging current can be increased, and the charging time can be shortened. In addition, although the current value I2 of the charging current flowing through the second charging path varies due to the voltage VB1 input from the main battery 2 to the control module 10, the open circuit voltage OCV of the backup battery 3, etc., it is possible to prevent the current value I2 from exceeding the allowable range of the current flowing through the control module 10 and the allowable range of the charging current of the backup battery 3. Therefore, by using a low-cost charging DC / DC converter 13, the cost of the control module 10 can be reduced, and the charging of the backup battery 3 can be safely performed and completed in a short time.

[0052] Although the present disclosure has been described based on embodiments, the present disclosure is not limited to the above-described embodiments. Without departing from the scope of the present disclosure, the present disclosure can be appropriately modified, or known or publicly known technologies can be appropriately combined.

[0053] For example, in the above embodiment, the discharge circuit 14 is provided, and power is released from the backup battery 3 to the discharge circuit 14, and the current value I2 of the charging current is calculated based on the current value I3 of the current flowing through the discharge circuit 14. Alternatively, other methods can be used to calculate the current value I2 of the charging current.

Claims

1. A power control device, the power control device being in a power supply system, the power supply system including a power supply unit, a main power supply, and a backup power supply, the power control device being connected to the power supply unit, the main power supply, and the backup power supply, and controlling charging and discharging of the backup power supply, the power control device including: A power line to which the power supply unit, the main power supply, the backup power supply, and a backup load are connected; A first switch provided on the power line and configured to connect and disconnect the connection between the power supply unit and the backup power supply and between the main power supply and the backup power supply; A second switch provided on the power line and configured to connect and disconnect the connection between the backup power supply and the backup load; A charging DC / DC converter connected to the power line in parallel with the second switch and configured to convert a voltage supplied from the power supply unit side and supply the converted voltage to the backup power supply side; And A control unit configured to perform: Discharge control, disconnecting the first switch and turning on the second switch to release power from the backup power supply to the backup load; First charging control, turning on the first switch and disconnecting the second switch to charge the backup power supply via the charging DC / DC converter; And Second charging control, turning on the first switch and turning on the second switch to charge the backup power supply via the second switch, wherein, when charging the backup power supply, the control unit is configured to perform the second charging control only when the current value of the charging current is equal to or greater than a first predetermined value and equal to or less than a second predetermined value, the second predetermined value being greater than the first predetermined value.

2. The power control device according to claim 1, further including: A discharge circuit provided between the second switch and the backup load, wherein the control unit is configured to perform a discharge process of turning on the first switch and disconnecting the second switch to release power from the power supply unit through the discharge circuit, and calculate the current value of the charging current based on the current value of the current flowing through the discharge circuit during the execution of the discharge process, the current value of the current output to the backup load, the current value of the current flowing through the backup power supply during the execution of the first charging control, the voltage and open-circuit voltage of the backup power supply, and the voltage between the first switch and the second switch.

3. The power control device according to claim 1 or 2, Among them, The first predetermined value is set to the maximum value of the output current of the charging DC / DC converter, and wherein, the second predetermined value is set to the smaller of the maximum value of the current flowing through the power control device and the maximum value of the charging current in the backup power supply.

4. The power control device according to claim 1 or 2, Among them, The control unit is configured to calculate the current value of the charging current based on the sum of the internal resistance of the backup power supply and the internal resistance from the first terminal to the second terminal, where the power supply unit and the main power supply are connected to the first terminal, and the backup power supply is connected to the second terminal.

5. The power supply control device according to claim 3, Among them, The control unit is configured to calculate the current value of the charging current based on the sum of the internal resistance of the backup power supply and the internal resistance from the first terminal to the second terminal, where the power supply unit and the main power supply are connected to the first terminal, and the backup power supply is connected to the second terminal.

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