Battery system

Abstract

To provide a battery system having a plurality of batteries and a relay that switches a connection relation of the batteries, and a technique for efficiently charging the plurality of batteries in consideration of losses of the relay.SOLUTION: A battery system includes a voltage converter, a series relay, and a parallel relay. The series relay and the parallel relay switch a connection relation of the plurality of batteries relative to the voltage converter. The controller compares series charge loss, which is a sum of losses of the voltage converter and the series relay when the series relay is closed to charge the plurality of batteries, with parallel charge loss, which is a sum of losses of the voltage converter and the parallel relay when the parallel relay is closed to charge the plurality of batteries. The controller charges the plurality of batteries in a mode of a smaller one of the series charge loss and the parallel charge loss.SELECTED DRAWING: Figure 2

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 series and parallel connections. Power loss also occurs in the relays, and the total loss varies depending on the number of relays closed. 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 herein includes multiple batteries, a voltage converter, a series relay, a parallel relay, 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 parallel relay connects the multiple batteries in parallel to the output terminal of the voltage converter. The controller compares a series charging loss, which is the sum of the losses in the voltage converter and the series relay when the series relay is closed to charge the multiple batteries, with a parallel charging loss, which is the sum of the losses in the voltage converter and the parallel relay when the parallel relay is closed to charge the multiple batteries. If the series charging loss is less than the parallel charging loss, the controller closes the series relay to charge the multiple batteries, and if the parallel charging loss is less than the series charging loss, the controller closes the parallel relay to charge the multiple batteries. The battery system disclosed herein can efficiently charge multiple batteries while taking relay loss into account.

[0006] Details and further improvements of the technology disclosed in this specification are described in the following "Description of Embodiments of the Invention." [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. 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 a parallel relay 22 (a first parallel relay 22a and a second parallel 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 parallel relay 22 (first parallel relay 22a and second parallel 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 parallel relay 22 includes a plurality of relays (a first parallel relay 22a and a second parallel relay 22b). The first parallel 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 parallel 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 parallel relays (first parallel relay 22a and second parallel relay 22b) corresponds to each of the multiple batteries (first battery 11 and second battery 12). The first parallel relay 22a corresponds to the first battery 11, and when the first parallel relay 22a is closed, the first battery 11 is connected between the output terminals 10c and 10d. The second parallel relay 22b corresponds to the second battery 12, and when the second parallel relay 22b is closed, the second battery 12 is connected between the output terminals 10c and 10d.

[0015] When the first parallel relay 22a and the second parallel 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 parallel relay 22a and the second parallel 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 parallel 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 parallel 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 shows a flowchart of the charging process executed by the controller 15. The process of the flowchart in FIG. 2 starts when the power source 30 is connected to the input terminals 10a and 10b of the voltage converter 10.

[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 parallel 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 parallel charging loss is the sum of the losses in the voltage converter 10 and the parallel relays 22a, 22b when multiple batteries (first battery 11 and second battery 12) are charged with the parallel relays 22a, 22b closed. Since the voltages of the first battery 11 and the second battery 12 are known, the target voltage ratio of the voltage converter 10 can be determined if the output voltage of the power source 30 is known, and the loss in the voltage converter 10 during charging is also determined. The target voltage ratio when the parallel relays 22a, 22b are closed is determined by (the higher of the voltage of the first battery 11 and the voltage of the second battery 12) / (the output voltage of the power source 30). Since the output current is known, the loss during charging in each of the parallel relays 22a, 22b can also be determined.

[0022] The controller 15 compares the series charging loss with the parallel charging loss (step S13). If the series charging loss is less than the parallel charging loss (step S13: YES), the controller 15 closes the series relay 21 and opens the parallel 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) described 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 parallel charging loss is less than the series charging loss (step S13: NO), the controller 15 closes the parallel relays 22a and 22b and opens the series relay 21 (step S18). At this time, the first battery 11 and the second battery 12 are connected in parallel between the output terminals 10c and 10d. The controller 15 starts 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 of the voltage converter 10 matches the target voltage ratio. The target voltage ratio in step S19 is determined by (the higher of the voltage of the first battery 11 and the voltage of the second battery 12) / (the output voltage of the power supply 30). 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).

[0024] 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 by connecting them in parallel (parallel charging). The controller 15 compares the loss during series charging (series charging loss) with the loss during parallel charging (parallel charging loss), and charges the batteries in the mode that results in less loss. The loss includes power loss in the relays. The battery system 2 can efficiently charge multiple batteries while also taking into account the loss in the relays that switch the battery connection circuits.

[0025] Generally, the higher the target voltage ratio, the lower the voltage conversion efficiency of the voltage converter 10. In other words, series charging generally results in greater losses in the voltage converter 10 than parallel charging. However, since the target voltage ratio is the ratio between the input and output voltages of the voltage converter 10, it depends on the output voltage of the power source 30. Meanwhile, the number of relays required to connect multiple batteries in series is smaller than the number of relays required to connect multiple batteries in parallel. The fewer the number of relays, the smaller the total loss of closed relays. Ultimately, the series charging loss and parallel charging loss depend on the output voltage of the power source 30, the target voltage ratio of the voltage converter 10, and the loss of closed relays, so the magnitude relationship between the series charging loss and parallel charging loss varies case by case.

[0026] The features of the battery system 2 are summarized below. The battery system 2 includes multiple batteries (a first battery 11 and a second battery 12), a voltage converter 10, a series relay 21, parallel 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 parallel relays 22a and 22b are closed, the multiple batteries are connected in parallel 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 multiple batteries are charged with the series relay 21 closed, and a parallel charging loss, which is the sum of the power losses in the voltage converter 10 and the parallel relays 22a and 22b when the multiple batteries are charged with the parallel relays 22a and 22b closed. When the series charging loss is less than the parallel charging loss, the controller 15 closes the series relay 21 and opens the parallel 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 body of multiple batteries) / (output voltage of the power source 30). When the parallel charging loss is less than the series charging loss, the controller 15 closes the parallel relays 22a and 22b and opens the series relay 21 to charge the multiple batteries. At this time, the controller 15 sets the target voltage ratio of the voltage converter 10 to (highest voltage of the multiple batteries) / (output voltage of the power source 30).

[0027] Some points to note regarding the technology described in the embodiments are described below. The battery system 2 of the embodiment takes into account relay losses (series relay losses and parallel relay losses). Here, "relay losses" include losses from a simple switch connecting two batteries in series or parallel, as well as losses from additional devices required to connect the two batteries. For example, if another voltage converter is connected to the path connecting two batteries in parallel (the path of parallel relays 22a and 22b in FIG. 1), the "relay losses" of the voltage converter may be included. In electric vehicles with inverters and motors, it is known that the inverter switching elements and the motor stator coil circuit also function as a voltage converter. When such a configuration is applied to the battery system of this specification, i.e., when a voltage converter using an inverter and a motor is included in the path of the parallel relay, the inverter and the auxiliary power consumption for inverter startup may also be included in the "parallel relay losses."

[0028] 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 is also applicable to a battery system including three or more batteries.

[0029] 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 parallel 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 parallel relay 22a and the second parallel 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.

[0030] 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]

[0031] 2: Battery system 10: Voltage converter 11: First battery 12: Second battery 15: Controller 21: Series relay 22, 22a, 22b: Parallel relay 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 parallel relay that connects the plurality of batteries to the output terminal in parallel; 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 a parallel charging loss, which is the sum of losses in the voltage converter and the parallel relay when the parallel relay is closed to charge the plurality of batteries, and closes the series relay to charge the plurality of batteries if the series charging loss is less than the parallel charging loss, and closes the parallel relay to charge the plurality of batteries if the parallel charging loss is less than the series charging loss; A battery system comprising:

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