Power source device and power source control method

Abstract

Provided are a power source device and a power source control method with which, even when connections of a plurality of secondary batteries to a load are switched, it is possible to maintain a stable supply of power by suppressing fluctuations in output voltage while preventing instantaneous interruptions.　This power source device is provided with a plurality of batteries (12a to 12d) to be charged / discharged, and a charging / discharging control unit (11) that selects a battery to be discharged from among the plurality of batteries (12a to 12d) and connects the selected battery to a load, and selects a battery to be charged and connects the selected battery to a source of power. While excluding the battery to be charged from the plurality of batteries (12a to 12d), the charging / discharging control unit (11) selects a battery from a battery-to-be-discharged group included in a first potential range, as the battery to be discharged. If there is no battery included in the first potential range among the plurality of batteries (12a to 12d), the charging / discharging control unit (11) resets the first potential range and switches the battery to be discharged between a first battery and a second battery included in the battery-to-be-discharged group.

Description

Power supply device and power supply control method

[0001] The present invention relates to a power supply device and a power supply control method, and more particularly to a power supply device and a power supply control method for supplying power by switching between a plurality of secondary batteries.

[0002] In recent years, electric vehicles that operate their motors using power from charged secondary batteries have rapidly become popular. However, secondary batteries have a problem in that their charge / discharge performance deteriorates, shortening the driving range of the electric vehicle depending on the number of charge / discharge cycles. Even if a deteriorated secondary battery does not perform sufficiently for use in an electric vehicle, it may still have sufficient charge / discharge capacity for other purposes. Therefore, the present inventors have proposed using secondary batteries used in electric vehicles as power sources for other purposes (see Patent Document 1).

[0003] JP 2022-175980 A

[0004] However, in conventional power supply devices, when the remaining charge of a secondary battery connected to a load decreases or when the secondary battery is removed, the secondary battery is disconnected and then another secondary battery is selected and connected to the load. Therefore, when switching the connection of a secondary battery in conventional power supply devices, a momentary power interruption occurs, making it difficult to continuously supply power to the load. In particular, power supply devices that convert direct current (DC) supplied from a secondary battery to alternating current (AC) using a DC-AC inverter can experience large voltage fluctuations in the output AC current, potentially causing malfunctions in precision instruments and information devices. In particular, secondary batteries used in electric vehicles have lower impedance than those used in mobile phones and portable power supply devices, allowing them to supply larger currents, which creates the problem of large voltage fluctuations when switching between secondary batteries.

[0005] Therefore, the present invention has been made in consideration of the above-mentioned conventional problems, and aims to provide a power supply device and a power supply control method that can prevent momentary power interruptions and suppress fluctuations in output voltage, thereby continuing to supply stable power, even when switching the connection of multiple secondary batteries to a load.

[0006] In order to solve the above problem, the power supply device of the present invention comprises a plurality of batteries to be charged and discharged, and a charge / discharge control unit that selects a discharge target from the plurality of batteries and connects it to a load, and selects a charge target and connects it to a power source, and the charge / discharge control unit excludes the charge target from the plurality of batteries and selects one from a group of discharge targets included in a first potential range as the discharge target, and if there is no battery among the plurality of batteries that is included in the first potential range, resets the first potential range and switches the discharge target between a first battery and a second battery included in the group of discharge targets.

[0007] In such a power supply device of the present invention, the battery to be discharged is selected from the batteries included in the first potential range, so the potential difference between the first battery and the second battery is limited when switching the battery to be discharged, and the current flowing from the battery on the higher potential side to the battery on the lower potential side can be suppressed.Even when switching the connection of multiple secondary batteries connected to the load, it is possible to prevent momentary power interruptions and suppress fluctuations in output voltage, thereby continuing to supply stable power.

[0008] In one aspect of the present invention, the charge / discharge control unit excludes the discharge target from the plurality of batteries and selects one from a group of batteries to be charged that are included in a second potential range as the battery to be charged, and if there is no battery among the plurality of batteries that is included in the first potential range, resets the first potential range.

[0009] In one aspect of the present invention, the allowable current value is Imax, the impedance from the discharge target to the load is Rimp, and the first potential range is a range in which the upper and lower limit allowable potential difference Vper satisfies the relationship Vper≦Imax×Rimp.

[0010] In one aspect of the present invention, the permissible potential difference Vper is 3 V or less.

[0011] In one aspect of the present invention, when the discharge target is switched from the first battery to the second battery, an overlap period is provided in which the first battery and the second battery are simultaneously connected to the load.

[0012] In one aspect of the present invention, the overlap period is in the range of 100 msec or less.

[0013] In one aspect of the present invention, the discharge target is connected to the load via a DC-AC inverter, and the overlap period is within a range of five periods or less of an output waveform from the DC-AC inverter.

[0014] In one aspect of the present invention, the peak fluctuation of the output waveform during the overlap period is 5% or less.

[0015] In one aspect of the present invention, during the overlap period, the potential supplied to the DC-AC inverter is an intermediate potential between the potential of the first battery and the potential of the second battery.

[0016] In order to solve the above problem, the power supply control method of the present invention is a power supply control method that selects a discharge target from a plurality of batteries that are charged and discharged and connects it to a load, and selects a charge target and connects it to a power source, and is characterized in that the charge target is excluded from the plurality of batteries, and one battery is selected from a group of discharge targets included in a first potential range as the discharge target, and if there is no battery among the plurality of batteries that is included in the first potential range, the first potential range is reset, and the discharge target is switched between a first battery and a second battery included in the group of discharge targets.

[0017] The present invention provides a power supply device and a power supply control method that can prevent momentary power interruptions and suppress fluctuations in output voltage, even when switching the connection of multiple secondary batteries to a load, thereby continuing to supply stable power.

[0018] 3A is a block diagram illustrating an example of the configuration of a power supply device 10 according to a first embodiment of the present invention. It is a circuit diagram illustrating an example of output control from batteries 12a to 12d by a charge / discharge control unit 11. It is a timing chart illustrating switching of connections in the power supply device 10, where FIG. 3A shows a signal of switch SW1, FIG. 3B shows a signal of switch SW2, FIG. 3C shows a voltage at the input position of the DC-AC inverter 13, and FIG. 3D shows a voltage at the output position of the DC-AC inverter 13. It is a flowchart illustrating a power supply control method according to the first embodiment. It is a graph illustrating a case where output from batteries 12a to 12d to a load 14 continues. It is a graph illustrating a case where charging from solar panel 16 or power supply unit 17 continues for batteries 12a to 12d. It is a graph illustrating a case where charging from solar panel 16 or power supply unit 17 starts during output from batteries 12a to 12d to a load 14. It is a graph illustrating a case where battery 12d is not included in a discharge target group, and output from batteries 12a to 12c continues. 10 is a graph illustrating a case where battery 12d is not included in the group of batteries to be charged, and batteries 12a to 12c continue to be charged by solar panel 16 or power supply unit 17. Also, FIG. 10 is a graph illustrating a case where battery 12d is not included in the group of batteries to be discharged, and output from batteries 12a to 12c continues, and discharging progresses to a fully discharged state.

[0019] (First Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing will be assigned the same reference numerals, and redundant description will be omitted where appropriate. FIG. 1 is a block diagram showing an example configuration of a power supply device 10 according to this embodiment. As shown in FIG. 1, the power supply device 10 includes a charge / discharge control unit 11, batteries 12a to 12d, a DC-AC inverter 13, a load 14, an AC-DC converter 15, a solar panel 16, and a power supply unit 17.

[0020] The charge / discharge control unit 11 selects a discharge target from the batteries 12a to 12d and connects it to the load 14, and also selects a charge target from the batteries 12a to 12d and connects it to the solar panel 16 and power supply unit 17, which are power sources. The method by which the charge / discharge control unit 11 selects a discharge target and a charge target will be described in detail below. The specific configuration of the charge / discharge control unit 11 is not limited, but it includes a memory, an external storage device, a central processing unit (CPU), an information communication device, etc. (not shown), and performs information processing according to a predetermined program to switch between the connection and disconnection of the discharge target and the charge target. More specifically, the charge / discharge control unit 11 monitors the status of each component of the power supply device 10, and, based on the status of each component and the predetermined program, controls the opening and closing of switches (described below) connected to the batteries 12a to 12d to control the connection between the load 14, the AC-DC converter 15, the power supply unit 17, and the batteries 12a to 12d.

[0021] The batteries 12a to 12d are secondary batteries that can charge and discharge power. Like known secondary batteries, the batteries 12a to 12d each include terminals used for charging and discharging, a battery management system (BMS) that controls charging and discharging, and the like.

[0022] The specific configuration of the batteries 12a to 12d is not limited, and known lithium-ion batteries, nickel-metal hydride batteries, all-solid-state batteries, etc. may be used. Battery cells contained in secondary batteries used in electric vehicles, hybrid vehicles, etc. may be reused and used as the batteries 12a to 12d. The batteries 12a to 12d may have an internal impedance of 10 mΩ or less.

[0023] The DC-AC inverter 13 is provided between the batteries 12a to 12d and the load 14, and converts the direct current output from the batteries 12a to 12d into alternating current and outputs it to the load 14. There are no limitations on the specific circuit configuration of the DC-AC inverter 13, and a known configuration can be used, but it is preferable to output a sine wave in order to expand the range of objects that can be operated as the load 14. There are no limitations on the voltage and frequency of the alternating current output from the DC-AC inverter 13, but it is preferable that they be in the voltage range of 100 V to 220 V and the frequency range of 50 to 60 Hz, which are used as commercial power sources in various countries.

[0024] The load 14 is an electronic device connected to the output of the DC-AC inverter 13 and driven by the AC current output from the DC-AC inverter 13. The specific configuration of the load 14 is not limited, but examples include a computer device, a network device, a wireless communication repeater, and the like. Alternatively, the power supply device 10 may be placed in a structure such as a bench installed in a public place, and the output of the DC-AC inverter 13 may be used as an external power supply device, with the electronic device connected to the external power supply device serving as the load 14. The power supply device 10 of this embodiment does not experience momentary power interruptions when switching between multiple secondary batteries, and output voltage fluctuations are suppressed, allowing these loads 14 that require a stable power supply to be connected and used continuously.

[0025] The AC-DC converter 15 has an input connected to the power supply unit 17, converts AC to DC, and is connected to the charge / discharge control unit 11 to supply power to the batteries 12a to 12d. The specific configuration of the AC-DC converter 15 is not limited, but as an example, it converts, for example, 100 V AC supplied from a commercial power source into 30 V DC.

[0026] The solar panel 16 is a component in which solar cell elements are packaged to generate electromotive force when irradiated with light such as sunlight, and is the part that supplies power to the batteries 12a to 12d in accordance with the control of the charge / discharge control unit 11. There are no particular restrictions on the material of the solar cell elements that make up the solar panel 16, and multiple solar cell elements connected in series or parallel can be used as needed. The solar panel 16 supplies power to the batteries 12a to 12d to charge them in accordance with the control of the charge / discharge control unit 11, and therefore corresponds to the power source in the present invention.

[0027] The power supply unit 17 is a part that supplies alternating current to the AC-DC converter 15. The specific configuration of the power supply unit 17 is not limited, and a commercial power source, an AC power generator, or the like can be used. The power supply unit 17 supplies power to the batteries 12a to 12d to charge them in accordance with the control of the charge / discharge control unit 11, and therefore corresponds to the power source in the present invention.

[0028] 2 is a circuit diagram illustrating an example of output control from batteries 12a to 12d by charge / discharge control unit 11. In the example shown in FIG. 2, one end of switches SW1 to SW4 is connected in series to the output terminals of batteries 12a to 12d, respectively. Switches SW1 to SW4 are also connected in parallel with each other, with the other end connected to the input terminal of DC-AC inverter 13. A load 14 is connected to the output terminal of DC-AC inverter 13. Although charge / discharge control unit 11 and switches SW1 to SW4 are shown separately in FIG. 2, switches SW1 to SW4 and terminals and wiring connecting each unit may also be included in charge / discharge control unit 11.

[0029] The specific configuration of the switches SW1 to SW4 is not limited, and known semiconductor switches or mechanical switches can be used. As will be described later, the opening and closing operations of the switches SW1 to SW4 are performed on the order of milliseconds, so it is preferable to use semiconductor switches such as field effect transistors (FETs) that are capable of high-speed switching operations.

[0030] The charge / discharge control unit 11 monitors the status and voltage of each part of the power supply device 10 and controls the opening and closing operations of the switches SW1 to SW4 based on the status of each part and a predetermined program. The charge / discharge control unit 11 selects a battery to be discharged from among the batteries 12a to 12d, closes the switch SW1 to SW4 that corresponds to the battery to be discharged, and opens the others. As a result, only the battery to be discharged from among the batteries 12a to 12d is connected to the DC-AC inverter 13, and power is supplied to the load 14. The selection of the battery to be discharged and the switching timing of each switch SW1 to SW4 will be described in detail below.

[0031] 2, the output voltages of the batteries 12a to 12d are designated VBA1 to VBA4, the voltage on the input side (parallel connection portion) of the DC-AC inverter 13 is designated DCAC_IN, and the voltage on the output side of the DC-AC inverter 13 is designated DCAC_OUT. Although an example using four batteries 12a to 12d and four switches SW1 to SW4 is shown in FIGS. 1 and 2, the number is not limited, and three or five or more batteries may be connected in parallel.

[0032] Next, the control by the charge / discharge control unit 11 when switching the discharge target among the batteries 12a to 12d will be described with reference to FIG. 3. In FIG. 3, the case where the discharge target is switched from the battery 12a to the battery 12b will be described as an example, but similar switching control is performed for other combinations. FIG. 3 is a timing chart showing the switching of connections in the power supply device 10, where FIG. 3(a) shows the signal of the switch SW1, FIG. 3(b) shows the signal of the switch SW2, FIG. 3(c) shows the voltage at the input position of the DC-AC inverter 13, and FIG. 3(d) shows the voltage at the output position of the DC-AC inverter 13. The horizontal axis in the diagram represents time t, and the vertical axis represents voltage. Also, when the time t １ indicates the first connection period, and time t １ From t ２ indicates the overlap period, and time t ２ The following shows the second connection period.

[0033] 3(a) and 3(b), switch SW1 is closed (ON) and switch SW2 is open (OFF). Therefore, DC current is supplied from battery 12a to switch SW1 and the parallel connection section, converted to AC_OUT by DC-AC inverter 13, and supplied to load 14. When an instruction to switch the discharge target is issued in power supply device 10, discharge from battery 12a is stopped and an overlap period begins in which discharge is switched to discharge from battery 12b. The length of the overlap period is preferably 100 ms or less, and more preferably in the range of 10 ms to 100 ms.

[0034] Examples of cases where the battery 12a is switched as a target for discharging include when the remaining charge of the battery 12a becomes low and the battery 12a is removed from the list of targets for discharging, or when the battery 12a is switched as a target for charging. Another example is when the battery 12a is removed and a locking mechanism (not shown) is released. Another example is when the user inputs an instruction to remove the battery 12a from the list of targets for discharging. Another example is when the temperature of the battery 12a rises and a protection instruction to stop discharging is sent by the control unit of the power supply device 10.

[0035] 3(a) and 3(b), the switch SW1 is closed (ON) and the switch SW2 is closed (ON). During this overlap period, the battery 12a and the battery 12b are simultaneously connected to the load 14. Therefore, a direct current is supplied from the battery 12a or the battery 12b with the higher voltage to the parallel connection portion, and is converted to AC_OUT by the DC-AC inverter 13 and supplied to the load 14. After the overlap period set to a predetermined length has elapsed, the system transitions to the second connection period.

[0036] 3(a) and 3(b), the switch SW1 is in an open state (off) and the switch SW2 is in a closed state (on). Therefore, a direct current is supplied from the battery 12b to the switch SW2 and the parallel connection part, and is converted to AC_OUT by the DC-AC inverter 13 and supplied to the load 14. Thereafter, the load 14 continues to operate using the power supplied from the battery 12b.

[0037] As described above, in the power supply device 10 of this embodiment, when the charge / discharge control unit 11 changes the switch SW1 from a closed state to an open state and the switch SW2 from an open state to a closed state, an overlap period is provided in which the switches SW1 and SW2 are simultaneously in the closed state. Therefore, throughout the first connection period, the overlap period, and the second connection period, the battery 12a or the battery 12b is connected to the parallel connection unit, and no momentary interruption occurs during switching.

[0038] Furthermore, during the overlap period, the battery 12a, 12b with the higher voltage discharges, while the battery with the lower voltage flows with a current in the charging direction. If the current in the charging direction of the battery with the lower voltage is large during this overlap period, the protection circuit of the BMS will be activated, making subsequent charging and discharging operations impossible. Therefore, the length of the overlap period must be set to a short period so that an excessive current does not flow in the charging direction to the battery with the lower voltage of the battery 12a, 12b. The length of the overlap period will be described in detail below.

[0039] As shown in FIG. 3(c), the voltage at the input position (parallel connection portion) of the DC-AC inverter 13 is approximately equal to the output voltage VBA1 at the output portion of the battery 12a during the first connection period, and is approximately equal to the output voltage VBA2 at the output portion of the battery 12b during the second connection period. During the overlap period, the voltage at the input position (parallel connection portion) of the DC-AC inverter 13 is an intermediate potential between VBA1 and VBA2. While FIG. 3(c) illustrates an example in which the intermediate potential is near the average value of VBA1 and VBA2, it does not have to be the average value as long as it is between VBA1 and VBA2. Furthermore, while FIG. 3(c) illustrates an example in which the intermediate potential is constant throughout the overlap period, the potential may also vary between VBA1 and VBA2.

[0040] As shown in Fig. 3(d), the voltage AC_OUT at the output of the DC-AC inverter 13 is output as a sinusoidal AC voltage. １ In the first connection period, the peak voltage of AC_OUT is stable, but after time t １ The overlap period begins at time t, and the peak voltage fluctuates after DCAC_IN changes from VBA1 to the intermediate potential. ２ When the overlap period is followed by the second connection period, the peak voltage also fluctuates after DCAC_IN changes from the intermediate potential to VBA2.

[0041] The fluctuation of the peak voltage of AC_OUT is １ and entered the second connection period. ２ The voltage increases at a frequency of 1000 kHz and decays as the sine wave cycle elapses. This is because even if the input voltage to the DC-AC inverter 13 changes, it is converted to the target output voltage value depending on the performance and time constant of the DC-AC inverter 13. However, if the peak voltage of the voltage AC_OUT fluctuates greatly and it takes a long time for it to decay and stabilize, the load 14 may not operate normally.

[0042] Therefore, in the power supply device 10 of this embodiment, the overlap period is preferably set to a range of 100 ms or less, more preferably a range of 10 ms to 100 ms. Alternatively, the overlap period is preferably set to a range of 5 periods or less of the output waveform from the DC-AC inverter 13, more preferably a range of 0.5 periods to 5 periods, and even more preferably a range of 0.5 periods to 2 periods. Furthermore, it is preferable that the peak fluctuation of the output waveform from the DC-AC inverter 13 during the overlap period be 5% or less.

[0043] The control by the charge / discharge control unit 11 when switching the battery to be charged among the batteries 12a to 12d is not shown. One end of a charging switch (not shown) is connected to each of the batteries 12a to 12d, and the other end of each charging switch is connected to the output side of the AC-DC converter 15 or the solar panel 16. The charge / discharge control unit 11 selects the battery to be charged from among the batteries 12a to 12d, closes the charging switch corresponding to the battery to be discharged, and opens the others. As a result, only the battery to be charged among the batteries 12a to 12d is connected to the AC-DC converter 15 or the solar panel 16, and power for charging is supplied. When switching the battery to be charged, there is no need to provide an overlap period as there is when switching the battery to be discharged.

[0044] 4 is a flowchart illustrating the power supply control method according to this embodiment. In the power supply control method according to this embodiment, each step is repeatedly executed (looped) as shown in FIG. 4, and the selected group of charge targets, group of discharge targets, charge targets, and discharge targets are recorded in a memory or storage device and are continuously used in the next loop.

[0045] First, in a voltage measurement step of step S1, the charge / discharge control unit 11 measures the output voltages VBA1 to VBA4 of the batteries 12a to 12d. After the output voltages VBA1 to VBA4 have been acquired, the process proceeds to step S2.

[0046] Next, in step S2, a charging target group selection process, the charge / discharge control unit 11 selects candidates for charging targets as a charging target group based on the output voltages VBA1 to VBA4 of the batteries 12a to 12d. Here, one method for selecting the charging target group is to select the batteries so that the output voltages VBA1 to VBA4 are most often included in a predetermined potential range. Alternatively, the predetermined potential range may be set based on the largest output voltage among the output voltages VBA1 to VBA4. Furthermore, if a charging target group has already been determined for the batteries 12a to 12d, the charging target group is reselected. Furthermore, if a charging target group has already been determined but all of the batteries 12a to 12d included in the charging target group are outside the predetermined potential range, the predetermined potential range is reset and the charging target group is reselected. Once the selection of the charging target group is complete, the process proceeds to step S3.

[0047] Next, in step S3, a discharge target group selection process, the charge / discharge control unit 11 selects discharge target candidates as a discharge target group based on the output voltages VBA1 to VBA4 of the batteries 12a to 12d. Here, one method for selecting the discharge target group is to select the batteries so that the output voltages VBA1 to VBA4 are most often included in a predetermined potential range. Furthermore, if a discharge target group has already been determined among the batteries 12a to 12d, the batteries are reselected as the discharge target group. Furthermore, if a discharge target group has already been determined but all of the batteries 12a to 12d included in the discharge target group are outside the predetermined potential range, the predetermined potential range is reset and the discharge target group is reselected. Once the selection of the discharge target group is complete, the process proceeds to step S4.

[0048] Here, the predetermined potential range for selecting the group of batteries to be charged and the group of batteries to be discharged is a range in which the allowable potential difference Vper satisfies the relationship Vper≦Imax×Rimp, where Imax is the allowable current value allowed as an output to protect against short circuits inside power supply device 10 and Rimp is the impedance from the discharge target to load 14. In other words, the difference between the upper and lower limits of the predetermined potential range is equal to or less than the allowable potential difference Vper, and batteries 12a to 12d whose output voltages fall within this range are selected as the group of batteries to be charged or discharged.

[0049] As a specific example, if the allowable current value Imax is 88 A, the internal impedance of each of the batteries 12a to 12d is 2 mΩ, and the impedance Rimp of the power supply device 10 is 33.3 mΩ, then Vper = 88 × 0.033 = 2.9 V. In this case, the predetermined potential range for selecting the group of batteries to be charged and the group of batteries to be discharged must be 2.9 V or less, and as an example, 2.0 V can be set as the predetermined potential range.

[0050] Next, in step S4, a charging target determination step, it is determined whether the output voltage of one of the batteries 12a to 12d that has already been selected as a charging target is outside a predetermined potential range. If a charging target has not been selected or if the selected charging target is outside the predetermined potential range, the process proceeds to step S5, and if the selected charging target is within the predetermined potential range, the process proceeds to step S6.

[0051] In the charging target reselection step of step S5, one battery to be charged is selected from among the batteries 12a to 12d included in the group of batteries to be charged. Here, in selecting the charging target, batteries that are being discharged are excluded from the selection. Any of the batteries 12a to 12d included in the group of batteries to be charged may be selected as the charging target, but it is preferable to select the battery with the lowest potential among the batteries included in the group of batteries to be charged. Once the selection of the charging target is completed, the process proceeds to step S6.

[0052] Next, in step S6, a discharge target determination step is performed to determine whether the output voltage of one of the batteries 12a to 12d that has already been selected as a discharge target is outside a predetermined potential range. If a discharge target has not been selected or if a selected discharge target is outside the predetermined potential range, the process proceeds to step S7. If the selected discharge target is within the predetermined potential range, the process proceeds to step S8.

[0053] In the discharge target reselection step of step S7, one discharge target is selected from among the batteries 12a to 12d included in the discharge target group. Here, in selecting the discharge target, batteries that are being charged are excluded from the selection. Any of the batteries 12a to 12d included in the discharge target group may be selected as the discharge target, but it is preferable to select the battery with the highest potential among those included in the discharge target group. Once the discharge target selection is complete, the process proceeds to step S8.

[0054] Next, in the termination determination step of step S8, it is determined whether to terminate charging and discharging of the power supply device 10. If charging and discharging are to be terminated, the control loop is terminated, and if not, the process proceeds to step S1 and the control loop is repeated. Conditions for terminating charging and discharging include when an instruction to stop charging and discharging is input from outside, or when the power supply device 10 detects an abnormality.

[0055] Next, the selection of a group of batteries to be charged and a group of batteries to be discharged, and the continuation of charging and discharging of the power supply device 10 based on the selection of a group of batteries to be charged and a group of batteries to be discharged, will be described using FIGS. 5 to 10 . In each graph, the horizontal axis represents time, and the vertical axis represents voltage. The solid, dashed, single-dotted, and double-dotted lines in each graph represent the output voltages VBA1 to VBA4 of the batteries 12a to 12d. The ranges indicated by thin dashed lines in the graphs represent a predetermined potential range at a given point in time, and the width of the range is the allowable potential difference Vper. 34 V is shown as an example of a voltage when the batteries 12a to 12d are fully charged, with an SOC (State of Charge) of 100%, and 28 V is shown as an example of a voltage when the batteries are fully discharged, with an SOC of 0%.

[0056] FIG. 5 is a graph illustrating a case where output from the batteries 12a to 12d to the load 14 continues. In the example shown in FIG. 5, the output voltages VBA1 to VBA4 of the batteries 12a to 12d are 34 V, which is the same SOC of 100%, and the predetermined potential range is set to a value ranging from 34 V to the allowable potential difference Vper. In this case, because the batteries 12a to 12d are included within the range of the allowable potential difference Vper, all of the batteries 12a to 12d are selected as the group to be discharged. Of the batteries 12a to 12d selected as the group to be discharged, one that has not been selected as the battery to be charged is selected as the battery to be discharged. In the example shown in FIG. 5, the battery 12a is first selected as the battery to be discharged.

[0057] When the charge / discharge control unit 11 continues to output from the battery 12a to be discharged to the load 14, the output voltage VBA1 of the battery 12a gradually decreases and at some point falls outside the predetermined potential range. In this case, the charge / discharge control unit 11 reselects one of the batteries 12b to 12d included in the group of batteries to be discharged and switches the connection with the load 14. When switching from battery 12a to battery 12b, providing an overlap period as shown in FIG. 3 can suppress momentary interruptions during switching and fluctuations in the output voltage from the DC-AC inverter 13.

[0058] Similarly, the power supply device 10 continues to output power by sequentially switching among the batteries 12b-12d from the group to be discharged. At some point, all of the output voltages VBA1-VBA4 of the batteries 12a-12d fall outside the initially set predetermined potential range. In this case, the charge / discharge control unit 11 resets the predetermined potential range to include the output voltages VBA1-VBA4 of the batteries 12a-12d, and reselects the group to be discharged. In the example shown in FIG. 5 , the value of the output voltages VBA1-VBA4 at the time of resetting the predetermined potential range is set as the upper limit, and the width of the allowable potential difference Vper is set as a new predetermined potential range. Furthermore, the batteries 12a-12d included in the new predetermined potential range are reselected as the group to be discharged.

[0059] Thereafter, reselection of a discharge target from the discharge target group and reselection of a discharge target group are repeated, and power supply from power supply device 10 to load 14 continues until all output voltages VBA1 to VBA4 reach a fully discharged state. During this time, an overlap period is provided when switching the discharge target by charge / discharge control unit 11, thereby suppressing momentary interruptions and output voltage fluctuations in the output from power supply device 10. Furthermore, the output voltages VBA1 to VBA4 of batteries 12a to 12d included in the discharge target group always fall within the allowable potential difference Vper. As a result, even if the internal impedance of batteries 12a to 12d is small, at 10 mΩ or less, current flowing from the high-potential side to the low-potential side during the overlap period is suppressed, allowing output to continue without protective operation by the BMS.

[0060] FIG. 6 is a graph illustrating a case where batteries 12a to 12d are continuously charged from solar panel 16 or power supply unit 17. In the example shown in FIG. 6, the output voltages VBA1 to VBA4 of batteries 12a to 12d are 28 V, which is the same SOC of 0%, and the predetermined potential range is set to a value between 28 V and the allowable potential difference Vper. In this case, because batteries 12a to 12d are included within the range of the allowable potential difference Vper, all of batteries 12a to 12d are selected as the group to be charged. Of the batteries 12a to 12d selected as the group to be charged, one that has not been selected as the battery to be discharged is selected as the battery to be charged. In the example shown in FIG. 6, battery 12a is first selected as the battery to be discharged.

[0061] As the charge / discharge control unit 11 continues to charge the battery 12a to be charged, the output voltage VBA1 of the battery 12a gradually increases and at some point falls outside the predetermined potential range. In this case, the charge / discharge control unit 11 reselects one of the batteries 12b to 12d included in the group of batteries to be charged and switches the connection between the solar panel 16 and the power supply unit 17.

[0062] Similarly, the power supply device 10 continues charging by sequentially switching among the batteries 12b to 12d from the group to be charged. At some point, all of the output voltages VBA1 to VBA4 of the batteries 12a to 12d fall outside the initially set predetermined potential range. In this case, the charge / discharge control unit 11 resets the predetermined potential range to include the output voltages VBA1 to VBA4 of the batteries 12a to 12d, and reselects the group to be charged. In the example shown in FIG. 6 , the value of the output voltages VBA1 to VBA4 at the time the predetermined potential range is reset is set as the lower limit, and the width of the allowable potential difference Vper is set as a new predetermined potential range. Furthermore, the batteries 12a to 12d included in the new predetermined potential range are reselected as the group to be charged.

[0063] Thereafter, reselection of batteries to be charged from the group to be charged and reselection of the group to be charged are repeated, and charging of the power supply device 10 continues until all output voltages VBA1 to VBA4 reach a fully charged state. Here, the output voltages VBA1 to VBA4 of the batteries 12a to 12d included in the group to be charged always fall within the range of the allowable potential difference Vper. This makes it easy to include the batteries 12a to 12d within the range of Vper at the time of selecting the group to be discharged, even when the power supply device 10 switches from charging to discharging.

[0064] 7 is a graph illustrating a case where charging from the solar panel 16 or the power supply unit 17 is initiated during output from the batteries 12a to 12d to the load 14. First, similar to the discharging operation shown in FIG. 5, the batteries 12a to 12d are selected as a group to be discharged, and output from the power supply device 10 to the load 14 is continued by selecting and switching the batteries 12a to 12d to be discharged. At a certain point, when the supply of power from the solar panel 16 or the power supply unit 17 to the power supply device 10 is initiated, the charge / discharge control unit 11 performs a charging operation for the batteries 12a to 12d in parallel with the discharging operation from the batteries 12a to 12d, and switches to a charging / discharging operation.

[0065] 7, the group of batteries to be charged and the group of batteries to be discharged are reset when the power supply device 10 switches to charging / discharging operation. At this time, it is preferable to set a predetermined potential range so that all of the batteries 12a to 12d are included in the group of batteries to be charged and the group of batteries to be discharged. Specifically, the predetermined potential range for selecting the group of batteries to be charged and the group of batteries to be discharged is set to be the same, and the width of the allowable potential difference Vper is set so that all of the batteries 12a to 12d can be included in the group of batteries to be charged and the group of batteries to be discharged.

[0066] 7, the battery 12c, which was selected as the battery to be discharged before the operation was switched to charging / discharging, continues to be selected as the battery to be discharged. Furthermore, the batteries 12a, 12b, and 12d, excluding the battery 12c, are selected as a group of batteries to be charged, with the battery 12b being the first battery to be charged. At this time, the battery 12b selected as the battery to be charged is excluded from the group of batteries to be discharged.

[0067] As the charging and discharging operation of the power supply device 10 continues, the output voltage VBA3 of the battery 12c to be discharged gradually decreases and at some point falls outside the predetermined potential range. In this case, the charge / discharge control unit 11 reselects one of the batteries 12a and 12d included in the group of batteries to be discharged as the battery to be discharged, and switches the connection with the load 14. At this time, if the battery 12d is newly selected as the battery to be discharged, the battery 12d is excluded from the group of batteries to be charged, and the battery 12c is included in the group of batteries to be charged.

[0068] Furthermore, as the charging and discharging operation of the power supply device 10 continues, the output voltage VBA2 of the battery 12b to be charged gradually increases and at some point falls outside the predetermined potential range. In this case, the charge / discharge control unit 11 reselects one of the batteries 12a and 12c included in the group of batteries to be charged as the battery to be charged, and switches the connection to the solar panel 16 or the power supply unit 17. At this time, if the battery 12a is newly selected as the battery to be charged, the battery 12a is excluded from the group of batteries to be discharged, and the battery 12b is included in the group of batteries to be discharged.

[0069] Thereafter, in the charge / discharge operation of the power supply device 10, the reselection and switching of the discharge target and the charge target continues so that the output voltages VBA1 to VBA4 of the batteries 12a to 12d fall within the range of Vper. Furthermore, when the discharge target and the charge target are reselected, the charge target group and the discharge target group are also reselected as described above. While Figure 7 shows an example in which the power supply device 10 switches from a discharge operation to a charge / discharge operation in which charging and discharging are performed simultaneously, the switching from the charge operation to the charge / discharge operation shown in Figure 6 is similar.

[0070] 7 shows a case where the predetermined potential range for selecting a discharge target group and a charge target group does not change during charge / discharge operations, but the predetermined potential range may be changed over time. As an example, when the power output from the power supply device 10 to the load 14 is greater than the power supplied from the solar panel 16 or the power supply unit 17, the predetermined potential range may be decreased to a lower voltage over time. Conversely, when the power output from the power supply device 10 to the load 14 is less than the power supplied from the solar panel 16 or the power supply unit 17, the predetermined potential range may be increased to a higher voltage over time.

[0071] 7, the output voltages VBA1 to VBA4 of the batteries 12a to 12d included in the discharge target group and the charge target group always fall within the range of the allowable potential difference Vper. As a result, even when the internal impedance of the batteries 12a to 12d is small, at 10 mΩ or less, the current flowing from the high potential side to the low potential side during the overlap period is suppressed, and output can be continued without protective operation by the BMS.

[0072] 8 is a graph illustrating a case where the battery 12d is not included in the discharge target group and the batteries 12a to 12c continue to output power. The example shown in FIG. 8 assumes a case where the old battery 12d included in the power supply device 10 deteriorates and is replaced with a new battery 12d, and the SOC of the new battery 12d is lower than that of the other batteries 12a to 12c.

[0073] In the example shown in Figure 8, the output voltages VBA1 to VBA3 of batteries 12a to 12c are 34V, which is the same SOC of 100%, and the predetermined potential range is set to a value ranging from 34V to the allowable potential difference Vper. At this time, the output voltage VBA4 of battery 12d is not included within the range of the allowable potential difference Vper, so batteries 12a to 12c are selected as the group to be discharged, and battery 12d is excluded from the group to be discharged. Thereafter, similar to the example shown in Figure 5, the selection and connection of the batteries to be discharged are switched between batteries 12a to 12c included in the group to be discharged, and the predetermined potential range is also reset, while the discharging operation of power supply device 10 continues.

[0074] As the discharge operation of the power supply device 10 continues, at some point the output voltage VBA4 of battery 12d falls within the predetermined potential range for selecting a group of batteries to be discharged. After that, battery 12d is included in the group of batteries to be discharged and is also selected as a battery to be discharged. Therefore, as the discharge operation of the power supply device 10 continues, battery 12d, which was not initially included in the group of batteries to be discharged because its output voltage VBA4 was outside the predetermined potential range, is now included in the group of batteries to be discharged. Thereafter, the discharge operation can be continued with all batteries 12a to 12d falling within the range of the permissible potential difference Vper.

[0075] 9 is a graph illustrating a case where battery 12d is not included in the group to be charged, and batteries 12a to 12c continue to be charged by solar panel 16 or power supply unit 17. The example shown in Fig. 9 assumes a case where old battery 12d included in power supply device 10 deteriorates and is replaced with new battery 12d, and the SOC of new battery 12d is higher than the other batteries 12a to 12c.

[0076] In the example shown in Figure 9, the output voltages VBA1 to VBA3 of batteries 12a to 12c are 28V with a similar SOC of 0%, and the predetermined potential range is set to a value ranging from 28V to the allowable potential difference Vper. At this time, the output voltage VBA4 of battery 12d is not included within the range of the allowable potential difference Vper, so batteries 12a to 12c are selected as part of the group to be charged, and battery 12d is excluded from the group to be charged. Thereafter, as in the example shown in Figure 6, the selection and connection of the battery to be charged are switched between batteries 12a to 12c included in the group to be charged, and the charging operation of power supply device 10 continues while the predetermined potential range is also reset.

[0077] As the charging operation of the power supply device 10 continues, at some point the output voltage VBA4 of battery 12d falls within the predetermined potential range for selecting the group of batteries to be charged. After that, battery 12d is included in the group of batteries to be charged and is selected as a battery to be charged. Therefore, as the charging operation of the power supply device 10 continues, battery 12d, which was not initially included in the group of batteries to be charged because its output voltage VBA4 was outside the predetermined potential range, is now included in the group of batteries to be charged. Thereafter, charging can continue with all batteries 12a to 12d falling within the range of the permissible potential difference Vper.

[0078] 10 is a graph illustrating a case where battery 12d is not included in the discharge target group, and the discharge progresses to a fully discharged state as output from batteries 12a to 12c continues. The example shown in FIG. 10 assumes a case where old battery 12d provided in power supply device 10 deteriorates and is replaced with a new battery 12d, and the SOC of new battery 12d is higher than that of the other batteries 12a to 12c.

[0079] In the example shown in Figure 10, the output voltages VBA1 to VBA3 of batteries 12a to 12c have approximately the same SOC, and the predetermined potential range is set to the width of the allowable potential difference Vper. At this time, the output voltage VBA4 of battery 12d is not included within the range of the allowable potential difference Vper, so batteries 12a to 12c are selected as the group to be discharged, and battery 12d is excluded from the group to be discharged. Thereafter, as in the example shown in Figure 5, the selection and connection of the batteries to be discharged are switched among batteries 12a to 12c included in the group to be discharged, and the predetermined potential range is also reset, while the discharging operation of power supply device 10 continues.

[0080] Thereafter, reselection of a discharge target from the discharge target group and reselection of the discharge target group are repeated, and power supply from the power supply device 10 to the load 14 continues until the output voltages VBA1 to VBA3 of the batteries 12a to 12c reach a fully discharged state. At this stage, the charge / discharge control unit 11 resets the predetermined potential range to the allowable potential difference Vper so that the battery 12d, which is not in a fully discharged state, is included in the discharge target group.

[0081] The charge / discharge control unit 11 also selects battery 12d, which is included in the group of batteries to be discharged, as the battery to be discharged and performs a discharge operation from battery 12d. If the discharge operation causes the output voltage VBA4 of battery 12d to fall outside the predetermined potential range, none of batteries 12a to 12d is included in the group of batteries to be discharged, and the predetermined potential range is reset to include battery 12d in the group of batteries to be discharged. The discharge operation with battery 12d as the battery to be discharged continues until the output voltage VBA4 of battery 12d reaches an over-discharge state.

[0082] In the example shown in FIG. 10 , the discharge operation is switched from the initially set group of batteries 12a to 12c to battery 12d. At this time, the potential difference between the output voltage VBA2 of battery 12b and the output voltage VBA4 of battery 12d exceeds the allowable potential difference Vper. Therefore, in this discharge switching, no overlap period is provided when the charge / discharge control unit 11 switches from battery 12b to battery 12d. Because no overlap period is provided in this discharge switching, there is a possibility of momentary interruptions or fluctuations in the output voltage from the power supply device 10 to the load 14. However, this may be preferable to stopping the output from the power supply device 10 when battery 12d is not fully discharged.

[0083] 10, after the discharge switch, the discharge operation from battery 12d continues, and eventually the output voltage VBA4 of battery 12d reaches 28 V, which is the fully discharged state. At this time, batteries 12a to 12d are all in a fully discharged state, and the output voltages VBA1 to VBA4 of batteries 12a to 12d are within the permissible potential difference Vper. Therefore, when charging of power supply device 10 is started from solar panel 16 or power supply unit 17, all of batteries 12a to 12d are included in the group to be charged, and the charging operation can continue as shown in FIG.

[0084] 5 to 10, for simplicity, the case where the batteries 12a to 12d included in the charging group and the discharging group have the same SOC has been described, but the present invention can also be applied to cases where the output voltages VBA1 to VBA4 are different as long as they are within a predetermined potential range. Also, for simplicity, the case where the batteries 12a to 12d are initially in a fully charged state or a fully discharged state has been described, but the SOC in the initial state does not have to be 100% or 0%.

[0085] As described above, in the power supply device 10 and power supply control method of this embodiment, the discharge target is selected from the batteries 12a to 12d included in a predetermined potential range, so the potential difference between the batteries 12a and 12b when switching the discharge target is limited, and the current flowing from the higher potential battery 12a to the lower potential battery 12b can be suppressed. Even when switching the connection of multiple secondary batteries connected to the load 14, fluctuations in the output voltage can be suppressed while preventing momentary power interruptions, making it possible to continue supplying stable power.

[0086] Second Embodiment Next, a second embodiment of the present invention will be described. Description of content that overlaps with the first embodiment will be omitted. In the first embodiment, an example was shown in which a DC-AC inverter 13 was provided to convert direct current from batteries 12a to 12d into alternating current and output the alternating current to a load 14, but a DC-DC converter may be provided instead of the DC-AC inverter 13. When a DC-DC converter is used, an electronic device driven by direct current is used as the load 14.

[0087] Even when a DC-DC converter is used, the other ends of the switches SW1 and SW2 are connected to the parallel connection section, and the connection is switched in the order of the first connection period, the overlap period, and the second connection period. This prevents momentary interruptions in the voltage input to the DC-DC converter and keeps it at an intermediate potential during the overlap period.

[0088] Third Embodiment Next, a third embodiment of the present invention will be described. Description of content overlapping with the first embodiment will be omitted. In the first embodiment, an example was shown in which an overlap period was provided during which both batteries were connected to the load when the battery to be discharged was switched from the battery 12a to the battery 12b. However, an overlap period may not be provided. In this case, the timing for disconnecting the battery 12a to be discharged from the load 14 and the timing for connecting the battery 12b to the load 14 are set to be the same.

[0089] In the power supply device 10 and power supply control method of this embodiment, the discharge target is selected from batteries 12a to 12d included in a predetermined potential range, so the potential difference between battery 12a and battery 12b is limited when switching the discharge target, making it possible to suppress the current flowing from battery 12a on the higher potential side to battery 12b on the lower potential side.Even when switching the connection of multiple secondary batteries connected to load 14, it is possible to prevent momentary interruptions and suppress fluctuations in output voltage, thereby enabling a stable power supply to be continued.

[0090] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0091] 10... Power supply device, 11... Charge / discharge control section, 12a to 12d... Batteries, 13... DC-AC inverter, 14... Load, 15... AC-DC converter, 16... Solar panel, 17... Power supply section, VBA1 to VBA4... Output voltage, SW1 to SW4... Switches

Claims

1. A power supply device comprising: a plurality of batteries for charging and discharging; and a charge / discharge control unit that selects a discharge target from the plurality of batteries and connects it to a load, and selects a charge target and connects it to a power source, wherein the charge / discharge control unit excludes the charge target from the plurality of batteries and selects one from a group of discharge targets included in a first potential range as the discharge target; if there is no battery among the plurality of batteries that is included in the first potential range, resets the first potential range; and switches the discharge target between a first battery and a second battery included in the group of discharge targets.

2. A power supply device according to claim 1, wherein the charge / discharge control unit excludes the battery to be discharged from among the plurality of batteries and selects one battery from a group of batteries to be charged that are included in a second potential range as the battery to be charged, and if there is no battery among the plurality of batteries that is included in the first potential range, the power supply device is characterized in that the first potential range is reset.

3. A power supply device according to claim 1, wherein the allowable current value is Imax, the impedance from the discharge target to the load is Rimp, and the first potential range is a range in which the upper and lower limit allowable potential difference Vper satisfies the relationship Vper≦Imax×Rimp.

4. A power supply device according to claim 3, wherein the allowable potential difference Vper is 3V or less.

5. A power supply device according to claim 1, characterized in that, when the discharge target is switched from the first battery to the second battery, an overlap period is provided in which the first battery and the second battery are simultaneously connected to the load.

6. A power supply device according to claim 5, wherein the overlap period is in the range of 100 ms or less.

7. A power supply device according to claim 5, wherein the discharge target is connected to the load via a DC-AC inverter, and the overlap period is within a range of five periods or less of the output waveform from the DC-AC inverter.

8. A power supply device according to claim 7, wherein the peak fluctuation of said output waveform during said overlap period is 5% or less.

9. A power supply device according to claim 7, wherein during the overlap period, the potential supplied to the DC-AC inverter is an intermediate potential between the potential of the first battery and the potential of the second battery.

10. A power supply control method for selecting a discharge target from a plurality of batteries to be charged and discharged and connecting it to a load, and selecting a charge target and connecting it to a power source, the power supply control method comprising: excluding the charge target from the plurality of batteries, and selecting one from a group of discharge targets included in a first potential range as the discharge target; if there is no battery among the plurality of batteries included in the first potential range, resetting the first potential range; and switching the discharge target between a first battery and a second battery included in the group of discharge targets.

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