Battery system

Abstract

To provide a technology related to a battery system including a plurality of batteries and a relay for switching a relation of connection of the plurality of batteries, for efficiently charging the plurality of batteries while considering a loss of the relay.SOLUTION: A battery system comprises a voltage converter, a serial relay, and an individual relay. The serial relay and the individual relay switches a relation of connection of a plurality of batteries to the voltage converter. A controller compares a serial charging loss, which is the sum of losses of the voltage converter and the serial relay when closing the serial relay and charging the plurality of batteries, with an individual charging loss, which is the sum of losses of the voltage converter and the individual relay when closing a plurality of individual relays in order and charging the respective batteries. The controller charges the plurality of batteries in a mode having a smaller one of the serial charging loss and the individual charging loss.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a battery system having a plurality of batteries. [Background technology]

[0002] Patent Document 1 discloses a battery system having multiple batteries. The battery system of Patent Document 1 allows selection between series charging, in which multiple batteries are connected in series and charged, and parallel charging, in which multiple batteries are connected in parallel and charged. The battery system is equipped with a voltage converter that converts the voltage of an external power source to a voltage suitable for charging. The target voltage ratio of the voltage converter differs between series charging and parallel charging. The different voltage ratios result in different conversion efficiencies (ratio of input power to output power) of the voltage converter. The controller of the battery system of Patent Document 1 compares the conversion efficiency of the voltage converter during series charging with that during parallel charging, and performs charging using the one with the better conversion efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6787271 Summary of the Invention [Problem to be solved by the invention]

[0004] Several relays are required to switch the connection state of multiple batteries between a series connection and a parallel connection. Power loss also occurs in the relays, and the total loss varies depending on the number of relays that are closed. In particular, in the case of a parallel connection, the number of relays that are closed increases, resulting in greater loss due to energizing multiple relays. This specification provides a battery system that can efficiently charge multiple batteries while taking relay loss into consideration. [Means for solving the problem]

[0005] The battery system disclosed in this specification includes multiple batteries, a voltage converter, a series relay, individual relays, and a controller. The voltage converter has an input terminal and an output terminal, and a power source is connected to the input terminal. The series relay connects the multiple batteries in series to the output terminal of the voltage converter. The multiple individual relays correspond to each of the multiple batteries and individually connect each battery to the output terminal. The controller compares a series charging loss, which is the sum of losses in the voltage converter and the series relay when the series relay is closed to charge the multiple batteries, with an individual charging loss, which is the sum of losses in the voltage converter and the individual relay when the multiple individual relays are closed sequentially to charge each battery. If the series charging loss is less than the individual charging loss, the controller closes the series relay to charge the multiple batteries, and if the individual charging loss is less than the series charging loss, the controller charges the multiple batteries while sequentially closing the individual relays. Charging the batteries individually reduces losses because fewer relays need to be closed compared to charging the multiple batteries connected in parallel simultaneously. The battery system disclosed in this specification is capable of efficiently charging multiple batteries while taking into consideration the loss of relays.

[0006] Note that "closing the individual relays sequentially" refers to a state in which only one of a plurality of individual relays is closed and the other individual relays are opened, and the individual relay to be closed is switched from time to time. If the battery system has two individual relays, "closing the individual relays sequentially" includes a mode in which the two individual relays are closed alternately. Details and further improvements of the technology disclosed in this specification will be described in the "Mode for Carrying Out the Invention" below. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram of a battery system according to an embodiment. [Figure 2] 4 is a flowchart of charging control executed by a controller. [Figure 3] 10 is a flowchart of the charging control executed by the controller (continuation of FIG. 2). [Figure 4] 4 is a time chart showing changes in the charge amounts of a first battery and a second battery. DETAILED DESCRIPTION OF THE INVENTION

[0008] A battery system 2 according to an embodiment will be described with reference to the drawings. Fig. 1 shows a block diagram of the battery system 2. The battery system 2 includes two batteries (a first battery 11 and a second battery 12). The battery system 2 is used as a power source that supplies power from the two batteries to an external electrical device.

[0009] The battery system 2 includes two batteries (a first battery 11 and a second battery 12), as well as a voltage converter 10, a controller 15, a series relay 21, and individual relays 22 (a first individual relay 22a and a second individual relay 22b).

[0010] The battery system 2 can charge two batteries (a first battery 11 and a second battery 12) using an external power supply 30. A voltage converter 10 converts the output voltage of the power supply 30 into a voltage suitable for charging the batteries. The power supply 30 for charging the batteries is connected to input terminals 10a and 10b of the voltage converter 10. Batteries are connected to output terminals 10c and 10d of the voltage converter 10. The positive terminal 10c of the output terminal is connected to the positive terminal of the first battery 11, and the negative terminal 10d of the output terminal is connected to the negative terminal of the second battery 12.

[0011] The series relay 21 and the individual relay 22 (first individual relay 22a and second individual relay 22b) are switches that determine the connection state of the battery to the output terminals 10c and 10d.

[0012] The series relay 21 is connected between the negative electrode of the first battery 11 and the positive electrode of the second battery 12. When the series relay 21 is closed, the first battery 11 and the second battery 12 are connected in series. The series relay 21 is a switch that connects the first battery 11 and the second battery 12 in series between the output terminals 10c and 10d of the voltage converter 10.

[0013] The individual relays 22 include a plurality of relays (first individual relay 22a and second individual relay 22b). The first individual relay 22a is connected between the negative electrode of the first battery 11 and the negative electrode 10d of the output terminal of the voltage converter 10. The second individual relay 22b is connected between the positive electrode of the second battery 12 and the positive electrode 10c of the output terminal of the voltage converter 10.

[0014] Each of the multiple individual relays (first individual relay 22a and second individual relay 22b) corresponds to each of the multiple batteries (first battery 11 and second battery 12). The first individual relay 22a corresponds to the first battery 11, and when the first individual relay 22a is closed, the first battery 11 is connected between the output terminals 10c and 10d. The second individual relay 22b corresponds to the second battery 12, and when the second individual relay 22b is closed, the second battery 12 is connected between the output terminals 10c and 10d.

[0015] When the first individual relay 22a and the second individual relay 22b are closed simultaneously, the first battery 11 and the second battery 12 are connected in parallel between the output terminals 10c and 10d. When one of the first individual relay 22a and the second individual relay 22b is closed and the other is opened, the battery corresponding to the closed relay is connected between the output terminals 10c and 10d.

[0016] Voltage converter 10 and relays (series relay 21 and individual relay 22) are controlled by controller 15. When charging power source 30 is connected to voltage converter 10, controller 15 closes one of series relay 21 and individual relay 22 to improve charging efficiency and starts charging. Note that "to improve charging efficiency" is equivalent to "to reduce power loss during charging."

[0017] 2 and 3 show flowcharts of the charging process executed by controller 15. The process of the flowcharts in Figures 2 and 3 starts when power supply 30 is connected to input terminals 10a and 10b of voltage converter 10. Note that the symbol "BT" in Figure 3 represents a battery, and the symbol "SOC" represents "State Of Charge," i.e., the amount of charge in the battery.

[0018] First, the controller 15 acquires the output voltage and output current of the power supply 30 (step S11). If communication with the power supply 30 is possible, the controller 15 acquires information about the output voltage and output current of the power supply 30 through communication. If communication with the power supply 30 is not possible, the controller 15 determines the output voltage of the power supply 30 based on measurement data from a voltage sensor (not shown) that measures the voltage between the input terminals 10a and 10b of the voltage converter 10. The controller 15 also operates the voltage converter 10 to allow a small amount of current to flow from the power supply 30, thereby measuring the output current of the power supply 30. The voltage converter 10 is also provided with a current sensor (not shown) that measures the output current of the power supply 30.

[0019] Next, controller 15 calculates the series charging loss and the individual charging loss (step S12). The series charging loss is the sum of the losses in voltage converter 10 and series relay 21 when multiple batteries (first battery 11 and second battery 12) are charged with series relay 21 closed. The voltage (series voltage) when first battery 11 and second battery 12 are connected in series is known. If the voltage of power source 30 can be obtained in step S11, the target voltage ratio of voltage converter 10 is determined (target voltage ratio = (total voltage when batteries are connected in series) / power supply voltage). The loss in voltage converter 10 during charging is determined from the target voltage ratio and the output current. The loss in series relay 21 when the output current flows through series relay 21 is also determined. The loss in series relay 21 is determined by the hardware characteristics of series relay 21 and can therefore be predicted in advance.

[0020] To be precise, the loss in the voltage converter 10 is determined by the following procedure. Once the target voltage ratio is determined, the voltage conversion efficiency of the voltage converter 10 is determined. The voltage conversion efficiency is determined by the hardware characteristics of the voltage converter 10 and depends on the voltage ratio. The loss in the voltage converter 10 is determined by the product of the voltage conversion efficiency and the power flowing through the voltage converter 10.

[0021] The individual charging loss is the sum of the losses in voltage converter 10 and individual relays 22a, 22b when individual relays 22a, 22b are closed sequentially to individually charge first battery 11 and second battery 12. Since the voltages of first battery 11 and second battery 12 are known, the target voltage ratio of voltage converter 10 can be determined if the output voltage of power source 30 is known, and the loss in voltage converter 10 during charging is also determined. Since the output current is known, the loss during charging in each of individual relays 22a, 22b can also be determined.

[0022] The controller 15 compares the series charging loss with the individual charging loss (step S13). If the series charging loss is less than the individual charging loss (step S13: YES), the controller 15 closes the series relay 21 and opens the individual relays 22a and 22b (step S14). The first battery 11 and the second battery 12 are connected in series between the output terminals 10c and 10d of the voltage converter 10. The controller 15 activates the voltage converter 10 (step S15). That is, the controller 15 starts charging. The controller 15 controls the voltage converter 10 so that the voltage ratio of the voltage converter 10 matches the target voltage ratio (the target voltage ratio when the batteries are connected in series) mentioned above. When charging of the first battery 11 and the second battery 12 is complete, the controller 15 stops the voltage converter 10 and ends the process (steps S16: YES, S17).

[0023] If it is determined in step S13 that the individual charging loss is less than the series charging loss (step S13: NO), the controller 15 closes the first individual relay 22a and opens the other relays (series relay 21 and second individual relay 22b) (step S18). At this time, only the first battery 11 is connected between the output terminals 10c and 10d. The controller 15 activates the voltage converter 10 (step S19). That is, the controller 15 starts charging. The controller 15 controls the voltage converter 10 so that the voltage ratio between the input terminal and the output terminal of the voltage converter 10 becomes (voltage of the first battery 11) / (output voltage of the power source 30).

[0024] The controller 15 continues charging the first battery 11 and the second battery 12 until they each reach a target state of charge (target SOC) (steps S21: NO, S24: NO). The controller 15 charges the first battery 11, and when the difference between the state of charge (SOC) of the first battery 11 and the state of charge (SOC) of the second battery 12 exceeds a threshold, the controller 15 switches the individual relays (steps S22: YES, S23). Here, "switching the individual relays" means opening a closed individual relay and closing an open individual relay. In step S18, the first individual relay 22a was closed and the second individual relay 22b was opened, so in step S23, the controller 15 opens the first individual relay 22a and closes the second individual relay 22b. As a result, only the second battery 12 is connected between the output terminals 10c and 10d. That is, the battery to be charged is switched from the first battery 11 to the second battery 12.

[0025] When the charge amount of the second battery 12 increases and the difference between the charge amount (SOC) of the second battery 12 and the charge amount (SOC) of the first battery 11 exceeds the threshold, the controller 15 switches the individual relay again (steps S22: YES, S23). Each time step S23 is repeated, the battery to be charged is switched. That is, the first battery 11 and the second battery 12 are gradually charged alternately. When both the first battery 11 and the second battery 12 reach the target charge amount (target SOC), the controller 15 stops the voltage converter 10 and ends the process (steps S21: YES, S24: YES, S25).

[0026] Fig. 4 shows an example of a time chart of changes in the charge amounts of the first battery 11 and the second battery 12. The solid line graph shows the charge amount of the first battery 11, and the dashed line graph shows the charge amount of the second battery 12. In Fig. 4, "BT" also means battery, and "SOC" means charge amount.

[0027] Charging begins at time T0. Initially, both the first battery 11 and the second battery 12 have low charge amounts. The first battery 11 is charged first. The charge amount of the first battery 11 increases, and at time T1, the difference in charge amount between the first battery 11 and the second battery reaches the threshold value dSth. The determination in step S22 becomes YES, and the controller 15 switches the individual relay (step S23). After time T1, the second battery 12 is charged. At time T2, the difference in charge amount between the first battery 11 and the second battery again reaches the threshold value dSth. At this time, the charge amount of the second battery 12 exceeds the charge amount of the first battery 11. The controller 15 again switches the individual relay (steps S22: YES, S23). After time T2, the first battery 11 is charged. At time T3, the charge amount of the first battery 11 reaches the target charge amount (target SOC), and the determination in step S21 becomes YES. Since the charge amount of the second battery 12 has not yet reached the target SOC, the determination in step S24 is NO, and the controller 15 switches the individual relay again (step S23). After time T3, the second battery 12 is charged. At time T4, the second battery 12 also reaches the target charge amount (target SOC), and the controller 15 ends the processing (steps S21: YES, S24: YES, S25). As shown in the graph in Figure 4, the first battery 11 and the second battery 12 are gradually charged alternately, and eventually both reach the target charge amount (target SOC).

[0028] As described above, the battery system 2 includes multiple batteries (first battery 11 and second battery 12) and can select either charging the batteries by connecting them in series (series charging) or charging them individually (individual charging). The controller 15 compares the loss during series charging (series charging loss) with the loss during individual charging (individual charging loss), and charges the batteries in the mode that results in less loss. The loss also includes power loss in relays. In particular, charging batteries individually results in less loss compared to charging multiple batteries connected in parallel because fewer relays are closed. The battery system 2 can efficiently charge multiple batteries while also taking into account the loss of the relays that switch the battery connection circuits.

[0029] The features of the battery system 2 are summarized below. The battery system 2 includes multiple batteries (first battery 11 and second battery 12), a voltage converter 10, a series relay 21, individual relays 22a and 22b, and a controller 15. The voltage converter 10 has input terminals 10a and 10b and output terminals 10c and 10d, and a power source 30 is connected to the input terminals 10a and 10b. When the series relay 21 is closed, the multiple batteries are connected in series to the output terminals 10c and 10d. When the individual relays 22a and 22b are closed, each of the multiple batteries is connected to the output terminals 10c and 10d. The controller 15 calculates a series charging loss, which is the sum of the power losses in the voltage converter 10 and the series relay 21 when the series relay 21 is closed to charge the multiple batteries. Furthermore, the controller 15 calculates the individual charging loss, which is the sum of the power losses in the voltage converter 10 and the individual relays 22a and 22b when the series relay 21 is opened and the individual relays 22a and 22b are closed sequentially to charge each of the multiple batteries sequentially. If the series charging loss is less than the individual charging loss, the controller 15 closes the series relay 21 and opens the individual relays 22a and 22b to charge the multiple batteries. At this time, the controller 15 sets the target voltage ratio of the voltage converter 10 to (total voltage of the series-connected multiple batteries) / (output voltage of the power source 30). If the individual charging loss is less than the series charging loss, the controller 15 opens the series relay 21 and closes the individual relays 22a and 22b sequentially to charge the multiple batteries individually. At this time, the controller 15 sets the target voltage ratio of the voltage converter 10 to (voltage of the battery to be charged) / (output voltage of the power source 30).

[0030] A note on the technology described in the embodiment will be described below. After starting charging, the controller 15 may return to step S12 at predetermined time intervals. That is, even after starting charging, the controller 15 may recalculate the series charging loss and the individual charging loss at predetermined time intervals and select the mode with the smaller loss (either series charging or individual charging).

[0031] The battery system 2 of the embodiment includes two batteries (a first battery 11 and a second battery 12). The technology disclosed in this specification can also be applied to a battery system including three or more batteries. In a battery system including three or more batteries, step S18 in FIG. 2 can be expressed as "close another individual relay and open all other individual relays."

[0032] The voltage converter 10 is a bidirectional converter that can adjust the voltage of the power applied to the output terminals 10c and 10d and output it from the input terminals 10a and 10b. When the battery system 2 is used as a power source, a device receiving power is connected to the output terminals 10c and 10d of the voltage converter 10. When the rated input voltage of the device is high, the controller 15 closes the series relay 21 and opens the individual relay 22. The total voltage of the first battery 11 and the second battery 12 connected in series is applied to the output terminals 10c and 10d of the voltage converter 10. When the rated input voltage of the device is low, the controller 15 opens the series relay 21 and closes one or both of the first individual relay 22a and the second individual relay 22b. The voltage of the first battery 11 or the second battery 12 is applied to the output terminals 10c and 10d of the voltage converter 10. After adjusting the opening and closing of the relay, the controller 15 controls the voltage converter 10 so that the voltage output from the input terminals 10a and 10b becomes the rated input voltage of the device.

[0033] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful. [Explanation of symbols]

[0034] 2: Battery system 10: Voltage converter 11: First battery 12: Second battery 15: Controller 21: Series relay 22, 22a, 22b: Individual relays 30: Power supply

Claims

[Claim 1] Multiple batteries and a voltage converter having an input terminal and an output terminal, the input terminal being connected to a power source; a series relay that connects the plurality of batteries in series to the output terminal; a plurality of individual relays corresponding to the plurality of batteries, each of which connects the battery to the output terminal; a controller that compares a series charging loss, which is the sum of losses in the voltage converter and the series relay when the series relay is closed to charge the plurality of batteries, with an individual charging loss, which is the sum of losses in the voltage converter and the individual relay when the individual relays are closed in sequence to charge each of the batteries, and closes the series relay to charge the plurality of batteries if the series charging loss is less than the individual charging loss, and opens the series relay and charges the plurality of batteries while closing the individual relays in sequence if the individual charging loss is less than the series charging loss; A battery system comprising:

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