Power supply device and power supply control method

Abstract

Provided are a power supply device and a power supply control method with which, even when a connection of a plurality of secondary batteries to a load is switched, it is possible to maintain a stable supply of power by suppressing fluctuations in an output voltage while preventing instantaneous interruption.　The power supply device comprises: a first battery and a second battery which perform charging and discharging; a first switch having one end connected in series to an output part of the first battery; a second switch having one end connected in series to an output part of the second battery; a parallel connection unit to which the other end of the first switch and the other end of the second switch are connected; and a switch control unit which controls opening and closing of the first switch and the second switch, wherein the switch control part has an overlap period during which the first switch and the second switch are simultaneously closed when changing the first switch from a closed state to an open state and changing the second switch from an open state to a closed state.

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] Power supply devices have been proposed for enabling electrical equipment to be used outdoors or in emergencies. These power supply devices typically use gasoline or other gas as fuel to drive an internal combustion engine, converting the engine's kinetic energy into electrical energy. However, power supply devices using internal combustion engines consume oxygen during fuel combustion, making them unsuitable for use indoors or in enclosed spaces. Therefore, power supply devices that supply power from secondary batteries that store electricity have become increasingly popular in recent years.

[0003] In power supply devices using such secondary batteries, the amount of power that can be supplied depends on the charge capacity of the secondary battery, and therefore, in order to continuously supply a large amount of power, the secondary battery must be large, resulting in increased weight and higher cost. To avoid this problem, power supply devices have been proposed that are equipped with multiple detachable secondary batteries and that switch between power supplies from the multiple secondary batteries (see, for example, Patent Document 1).

[0004] JP 2006-296109 A

[0005] 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. Figure 10 is a graph showing voltage fluctuations when batteries are switched in a conventional power supply device.

[0006] In Figure 10, the horizontal axis represents the passage of time, and the vertical axis represents voltage. In Figure 10, the thick plots with small amplitude represent the voltage at the input of the DC-AC inverter. In Figure 10, the thin plots with large amplitude represent the voltage at the output of the DC-AC inverter. Furthermore, in Figure 10, the left half shows a state in which a secondary battery with a low remaining charge and low output voltage is connected to a load, while the right half shows a state in which a secondary battery with a high remaining charge and high output voltage is connected to a load. The area near the center of Figure 10 shows a state in which the two secondary batteries are disconnected from the load.

[0007] It can be seen that the voltage at the input of the DC-AC inverter changes before and after switching the secondary battery connection, and that there is a period of time when no power is supplied from the secondary battery at the moment of switching, causing the voltage to drop suddenly. Also, it can be seen that the voltage at the output of the DC-AC inverter does not change once the output has stabilized before and after switching the secondary battery connection, but that a short-term voltage fluctuation occurs immediately after the moment of switching.

[0008] As shown in Figure 10, switching the connection of a secondary battery in a conventional power supply device can cause a momentary interruption in the supply of power, making it difficult to continuously supply power to a load. In particular, in power supply devices that convert direct current (DC) supplied from a secondary battery to alternating current (AC) using a DC-AC inverter, the voltage fluctuations of the output AC current can become large, potentially causing malfunctions in precision instruments and information devices. Furthermore, suppressing fluctuations in output voltage requires a fast-response inverter power supply circuit, which increases the size and cost of the power supply device.

[0009] 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.

[0010] In order to solve the above problem, the power supply device of the present invention includes a first battery and a second battery that are charged and discharged, a first switch having one end connected in series to an output section of the first battery, a second switch having one end connected in series to an output section of the second battery, a parallel connection section to which the other end of the first switch and the other end of the second switch are connected, and a switch control section that controls the opening and closing of the first switch and the second switch, wherein the switch control section has an overlap period during which the first switch and the second switch are simultaneously in the closed state when changing the first switch from a closed state to an open state and when changing the second switch from an open state to a closed state, the parallel connection section is connected to a DC-AC inverter, and the overlap period is in the range of 0.5 to 5 cycles of the output waveform from the DC-AC inverter. In addition, in order to solve the above-mentioned problems, a power supply device of the present invention includes a first battery and a second battery that are charged and discharged, a first switch having one end connected in series to an output terminal of the first battery, a second switch having one end connected in series to an output terminal of the second battery, a parallel connection portion to which the other end of the first switch and the other end of the second switch are connected, and a switch control portion that controls the opening and closing of the first switch and the second switch, wherein the switch control portion has an overlap period during which the first switch and the second switch are simultaneously in the closed state when changing the first switch from a closed state to an open state and when changing the second switch from an open state to a closed state, the output terminal of the first battery is at a first potential, the output terminal of the second battery is at a second potential, and during the overlap period, the potential of the parallel connection portion is an intermediate potential between the first potential and the second potential.

[0011] In such a power supply device of the present invention, when switching the connection from the first battery to the second battery, an overlap period is provided in which the first switch and the second switch are simultaneously closed. Therefore, even when switching the connection of multiple secondary batteries to the load, it is possible to prevent momentary power interruptions and suppress fluctuations in output voltage, thereby continuing to supply stable power.

[0012] In one aspect of the present invention, the overlap period is in the range of 5 ms to 60 ms.

[0013] In one aspect of the present invention, the peak fluctuation of the output waveform during the overlap period is 10% or less.

[0014] In order to solve the above problem, the power supply control method of the present invention is a power supply control method for switching the connection between a first battery and a second battery that are charged and discharged and a parallel connection unit, the power supply control method including a first connection period in which an output terminal of the first battery is connected to the parallel connection unit and an output terminal of the second battery is disconnected from the parallel connection unit, and a second connection period in which the output terminal of the first battery is disconnected from the parallel connection unit and the output terminal of the second battery is connected to the parallel connection unit, an overlap period is provided between the first connection period and the second connection period in which the output terminal of the first battery and the output terminal of the second battery are connected to the parallel connection unit, the parallel connection unit is connected to a DC-AC inverter, and the overlap period is in the range of 0.5 to 5 cycles of the output waveform from the DC-AC inverter. In addition, in order to solve the above-mentioned problems, a power supply control method of the present invention is a power supply control method for switching the connection between a first battery and a second battery that are charged and discharged and a parallel connection section, the power supply control method including: a first connection period in which an output terminal of the first battery is connected to the parallel connection section and an output terminal of the second battery is disconnected from the parallel connection section; and a second connection period in which the output terminal of the first battery is disconnected from the parallel connection section and the output terminal of the second battery is connected to the parallel connection section, and an overlap period in which the output terminal of the first battery and the output terminal of the second battery are connected to the parallel connection section is provided between the first connection period and the second connection period, the output terminal of the first battery is at a first potential, the output terminal of the second battery is at a second potential, and during the overlap period, the potential of the parallel connection section is an intermediate potential between the first potential and the second potential.

[0015] 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.

[0016] 3A and 3B are block diagrams illustrating an example configuration of a power supply device 10 according to a first embodiment of the present invention.

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[1010] [1 Graphs showing switching from low voltage to high voltage with an overlap period, where FIG. 6(a) shows Example 1, FIG. 6(b) shows Example 2, FIG. 6(c) shows Example 3, and FIG. 6(d) shows Example 4. Graphs showing switching from high voltage to low voltage with an overlap period, where FIG. 7(a) shows Example 5, FIG. 7(b) shows Example 6, FIG. 7(c) shows Example 7, and FIG. 7(d) shows Example 8. Graphs showing output fluctuations from the DC-AC inverter 13, where FIG. 8(a) shows Comparative Example 1 and Examples 5 and 6 when switching from high voltage to low voltage, FIG. 8(b) shows Comparative Example 2 and Examples 1 and 2 when switching from low voltage to high voltage, and FIG. 8(c) shows Examples 7 and 8. Graphs showing output fluctuations of the DC-AC inverter 13 in Comparative Examples 1 and 2 without an overlap period. Graphs showing voltage fluctuations when switching batteries in a conventional power supply device.

[0017] (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 duplicate descriptions 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 switch control unit 11, a first battery 12a, a second battery 12b, a first switch SW1, a second switch SW2, a DC-AC inverter 13, and a load 14.

[0018] The switch control unit 11 is a part that controls the opening and closing operations of the first switch SW1 and the second switch SW2. The specific configuration of the switch control unit 11 is not limited, but it may include a memory, an external storage device, a central processing unit (CPU), an information communication device, etc. (not shown), and may perform information processing according to a predetermined program to control the first switch SW1 and the second switch SW2. The switch control unit 11 may also monitor the status of each part of the power supply device 10 and control the opening and closing operations of the first switch SW1 and the second switch SW2 based on the status of each part and the predetermined program.

[0019] The first battery 12a and the second battery 12b are secondary batteries capable of charging and discharging power. Like known secondary batteries, the first battery 12a and the second battery 12b are equipped with terminals used for charging and discharging, a battery management system (BMS) that controls charging and discharging, and the like. The output of the first battery 12a is connected to one end of a first switch SW1, and the output of the second battery 12b is connected to a second switch SW2. The voltage at the output of the first battery 12a is VBA1, and the voltage at the output of the second battery 12b is VBA2.

[0020] The specific configuration of the first battery 12a and the second battery 12b is not limited, and known lithium-ion batteries, nickel-metal hydride batteries, all-solid-state batteries, etc. may be used. Furthermore, battery cells contained in secondary batteries used in electric vehicles, hybrid vehicles, etc. may be reused and used as the first battery 12a and the second battery 12b. It is assumed that the reused battery cells have different degrees of deterioration and may have different chargeable capacities and output voltages, but they can be used without any problems in the power supply device 10 of this embodiment.

[0021] The first battery 12a and the second battery 12b preferably have an internal impedance of 10 mΩ or more. If the internal impedance is less than 10 mΩ, an unintended charging operation may occur during the overlap period of the switching operation described below, making it difficult to ensure a sufficient overlap period.

[0022] The first switch SW1 and the second switch SW2 have one end connected to the output portion of the first battery 12a and the second battery 12b, respectively, and are components that connect and disconnect the first battery 12a and the second battery 12b and the load 14 by opening and closing operations. As shown in FIG. 1 , the other ends of the first switch SW1 and the second switch SW2 are connected to a parallel connection portion. As a result, the series connection of the first battery 12a and the first switch SW1 and the series connection of the second battery 12b and the second switch SW2 are connected in parallel to each other. The voltage of the parallel connection portion is DCAC_IN.

[0023] The specific configurations of the first switch SW1 and the second switch SW2 are not limited, and known semiconductor switches or mechanical switches can be used. As will be described later, the opening and closing operations of the first switch SW1 and the second switch SW2 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.

[0024] The DC-AC inverter 13 is provided between the parallel connection unit and the load 14, and converts DCAC_IN, a direct current input from the parallel connection unit, into AC_OUT 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 widen the range of targets that can be operated as the load 14. There are no limitations on the AC_OUT output from the DC-AC inverter 13, but it is preferable that it 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.

[0025] The load 14 is an electronic device that is connected to the output of the DC-AC inverter 13 and is driven by the AC current output from the DC-AC inverter 13. The load 14 is not limited, but examples include computers, network devices, electronic medical devices, and ultra-low temperature freezers. The power supply device 10 of this embodiment does not cause momentary power interruptions when switching between multiple secondary batteries and can suppress fluctuations in output voltage, so it can connect and continue to use these loads 14 that require a stable power supply.

[0026] 1 shows an example using two batteries and two switches, but the number of batteries and switches is not limited, and three or more batteries and switches may be used. Even when three or more batteries are selectively switched, the battery connected in the first connection period before the switching and the battery connected in the second connection period after the switching operate as a pair. Therefore, even when three or more batteries are provided in the power supply device 10, the operation and control of the connection switching are the same as when two batteries are used.

[0027] 2 is a diagram showing the switching of connections in the power supply device 10, with Fig. 2(a) showing a first connection period, Fig. 2(b) showing an overlap period, and Fig. 2(c) showing a second connection period. For simplicity, Fig. 2 does not show the switch control unit 11, but the first switch SW1 and the second switch SW2 are controlled to open and close by control signals sent from the switch control unit 11. The arrows shown in the figure schematically show an example of the direction of current.

[0028] 2A, the first switch SW1 is closed (ON) and the second switch SW2 is open (OFF). Therefore, DC current is supplied from the first battery 12a to the first switch SW1 and the parallel connection part, and is converted to AC_OUT by the DC-AC inverter 13 and supplied to the load 14. When an instruction is issued in the power supply device 10 to stop discharging from the first battery 12a and switch to discharging from the second battery 12b, the power supply device 10 transitions to the overlap period.

[0029] Examples of cases in which discharging from the first battery 12a is stopped include when the remaining charge of the first battery 12a decreases and the first battery 12a switches from being a battery to be discharged to being a battery to be charged, when the first battery 12a is removed and a locking mechanism (not shown) is released, when the user inputs a command to remove the first battery 12a from the list of batteries to be discharged, or when the temperature of the first battery 12a rises and a protection command to stop discharging is sent by the control unit of the power supply device 10.

[0030] During the overlap period shown in FIG. 2(b), the first switch SW1 is closed (ON) and the second switch SW2 is closed (ON). During this overlap period, DC current is supplied from the higher-voltage battery between the first battery 12a and the second battery 12b to the parallel connection, where it is converted to AC_OUT by the DC-AC inverter 13 and supplied to the load 14. In the example shown in FIG. 2(b), the first battery 12a has a higher voltage than the second battery 12b, and current is supplied from the first battery 12a to the second battery 12b. If the second battery 12b has a higher voltage than the first battery 12a, the current flows in the opposite direction. After a predetermined overlap period has elapsed, the system transitions to the second connection period.

[0031] 2(c), the first switch SW1 is in the open state (off) and the second switch SW2 is in the closed state (on). Therefore, direct current is supplied from the second battery 12b to the second 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 second battery 12b.

[0032] As described above, in the power supply device 10 of this embodiment, when the switch control unit 11 changes the first switch SW1 from a closed state to an open state and the second switch SW2 from an open state to a closed state, an overlap period is provided during which the first switch SW1 and the second switch SW2 are simultaneously in the closed state. Therefore, throughout the first connection period, the overlap period, and the second connection period, the first battery 12a or the second battery 12b is connected to the parallel connection unit, and no momentary interruption occurs during switching.

[0033] Furthermore, during the overlap period, the first battery 12a, which has the higher voltage, discharges, while a current flows in the charging direction to the second battery 12b, which has the lower voltage. If a large current flows in the charging direction to the second battery 12b during this overlap period, the protection circuit of the BMS provided in the second battery 12b will be activated, making it impossible to charge or discharge the second battery 12b. Therefore, the length of the overlap period needs to be set to a short length so as to prevent an excessive current from flowing in the charging direction to the second battery 12b. The length of the overlap period will be described in detail below.

[0034] 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 first switch SW1, FIG. 3(b) shows the signal of the second 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, time t １ indicates the first connection period, and time t １ From t ２indicates the overlap period, and time t ２ The following shows the second connection period.

[0035] As shown in Fig. 3A, an ON signal is applied to the first switch SW1 during the first connection period and the overlap period, and an OFF signal is applied to the first switch SW1 during the second connection period. As shown in Fig. 3B, an OFF signal is applied to the second switch SW2 during the first connection period, and an ON signal is applied to the second switch SW2 during the overlap period and the first connection period.

[0036] 3(c), the voltage at the input position (parallel connection portion) of the DC-AC inverter 13 is approximately equal to the voltage VBA1 (corresponding to the first potential) at the output portion of the first battery 12a during the first connection period, and is approximately equal to the voltage VBA2 (corresponding to the second potential) at the output portion of the second 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 at an intermediate potential between VBA1 and VBA2.

[0037] 3C shows an example in which the intermediate potential is close to the average value of VBA1 and VBA2, but it does not have to be the average value as long as it is between VBA1 and VBA2. Also, while FIG. 3C shows an example in which the intermediate potential is constant throughout the overlap period, the potential may vary between VBA1 and VBA2.

[0038] 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.

[0039] The fluctuation of the peak voltage of AC_OUT is １ and entered the second connection period. ２ 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 output voltage AC_OUT fluctuates greatly and it takes a long time for it to decay and stabilize, there is a possibility that the load 14 will not operate normally.

[0040] Therefore, in the power supply device 10 of this embodiment, the overlap period is preferably set in the range of 5 ms to 60 ms, more preferably in the range of 5 ms to 20 ms. Alternatively, the overlap period is preferably set in the range of 0.5 to 5 periods of the output waveform from the DC-AC inverter 13, more preferably in the range of 0.5 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 10% or less.

[0041] (Comparative Examples) FIG. 4 is a graph showing voltage fluctuations in Comparative Examples 1 and 2, which do not have an overlap period. FIG. 4(a) shows switching from a high voltage to a low voltage, and FIG. 4(b) shows switching from a low voltage to a high voltage. In FIG. 4, the thick plots with small amplitude indicate the voltage DCAC_IN at the input position (parallel connection) of the DC-AC inverter 13. In FIG. 4, the thin plots with large amplitude indicate the voltage AC_OUT at the output position of the DC-AC inverter 13. In FIG. 4, the first connection period in which the first battery 12a is connected is shown, and the right half indicates the second connection period in which the second battery 12b is connected. The output of the DC-AC inverter 13 is a 100 V AC, 50 Hz sine wave, and the load 14 is 1 kW. The output voltage VBA1 of the first battery 12a is 27 V (high voltage side), and the output voltage VBA2 of the second battery 12b is 23 V (low voltage side).

[0042] As shown in Figure 4(a), after switching from the first battery 12a on the high voltage side to the second battery 12b on the low voltage side, the peak fluctuation of AC_OUT was -8.7%. Also, as shown in Figure 4(b), after switching from the second battery 12b on the low voltage side to the first battery 12a on the high voltage side, the peak fluctuation of AC_OUT was +12.5%. Switching from low voltage to high voltage is referred to as Comparative Example 1, and switching from high voltage to low voltage is referred to as Comparative Example 2.

[0043] Examples: In Examples 1 to 4, switching was performed from the low-voltage second battery 12b to the high-voltage first battery 12a, with the overlap periods set to 10 ms, 20 ms, 40 ms, and 60 ms, respectively. In Examples 5 to 8, switching was performed from the high-voltage first battery 12a to the low-voltage second battery 12b, with the overlap periods set to 10 ms, 20 ms, 40 ms, and 60 ms, respectively. In Examples 1 to 8, as in the comparative example, the output of the DC-AC inverter 13 was a 100 V AC, 50 Hz sine wave, and the load 14 was 1 kW. The output voltage VBA1 of the first battery 12a was 28.36 V (high-voltage side), and the output voltage VBA2 of the second battery 12b was 24.72 V (low-voltage side).

[0044] 5 is a graph showing the intermediate potential when an overlap period is provided. In the example shown in FIG. 5, the load 14 is set to 0 kW in the settings of Example 8, thereby eliminating the influence of fluctuations in DCAC_IN due to voltage conversion in the DC-AC inverter 13. It can be seen that during the overlap period between the first connection period and the second connection period, the voltage DCAC_IN of the parallel connection section is 26.49 V, which is an intermediate potential, and is between the output voltage of the first battery 12a (28.36 V) and the output voltage of the second battery 12b (24.72 V).

[0045] 6A to 6D are graphs showing switching from a low voltage to a high voltage with an overlap period, where Fig. 6A shows Example 1, Fig. 6B shows Example 2, Fig. 6C shows Example 3, and Fig. 6D shows Example 4. Fig. 7A to 7D are graphs showing switching from a high voltage to a low voltage with an overlap period, where Fig. 7A shows Example 5, Fig. 7B shows Example 6, Fig. 7C shows Example 7, and Fig. 7D shows Example 8.

[0046] 6 and 7, a graph showing the results of measuring the peak fluctuation amount of AC_OUT for each half cycle for Comparative Examples 1 and 2 and Examples 1 to 8 is shown in FIG. 8. FIG. 8 is a graph showing the output fluctuation from the DC-AC inverter 13, where FIG. 8(a) shows Comparative Example 1 and Examples 5 and 6 when switching from a high voltage to a low voltage, FIG. 8(b) shows Comparative Example 2 and Examples 1 and 2 when switching from a low voltage to a high voltage, and FIG. 8(c) shows Examples 7 and 8. The horizontal axis of FIG. 8 is time t １ 8 shows the order of peaks for each half cycle in the output waveform of AC_OUT after the overlap period begins. In both examples, the output of the DC-AC inverter 13 is 50 Hz, so a half cycle corresponds to 10 ms. The vertical axis of FIG. 8 shows the amount of fluctuation in the peak voltage in the first connection period in the output waveform of the DC-AC inverter 13.

[0047] As shown in Figures 8(a) and (b), in the plot of Comparative Example 1 (0 ms) where no overlap period is provided, the fluctuations of Peaks 1 and 2 are larger than those of Examples 1-8. In particular, in Comparative Example 1, which involves switching from the low voltage side to the high voltage side, the fluctuations of Peaks 1 and 2 exceed 10%, which may adversely affect the operation of the load 14. In Comparative Example 2, which involves switching from the high voltage side to the low voltage side, the fluctuations of Peaks 1 and 2 are just under 9%. However, in the power supply device 10, switching from the low voltage side to the high voltage side and from the high voltage side to the low voltage side occurs frequently, so the peak fluctuations exceed 10% during the usage period of the load 14.

[0048] In Example 5 (10 ms) and Example 6 (20 ms), which are switching from the low voltage side to the high voltage side shown in Figure 8(a), the amount of fluctuation at Peaks 1 and 2 is smaller than in Comparative Example 1, being suppressed to 10% or less. Furthermore, in both Examples 5 and 6, the amount of fluctuation decreases after Peaks 1 and 2, converging to the output setting of the DC-AC inverter 13. In Examples 5 and 6, the plots are made up to Peaks 4 and 6, respectively, and the convergence of the amount of fluctuation can be confirmed by plotting for a time longer than the overlap period.

[0049] In Example 1 (10 ms) and Example 2 (20 ms) shown in Figure 8(b), which are switches from the high voltage side to the low voltage side, the maximum peak position is different from that of Comparative Example 2, but the maximum peak fluctuation amount is smaller than that of Comparative Example 2 and is suppressed to 8% or less. In both Examples 1 and 2, the fluctuation amount decreases after the maximum peak and converges to the output setting of the DC-AC inverter 13. In Examples 1 and 2, peaks 7 and 8 are plotted, respectively, and the convergence tendency from the position of the maximum peak fluctuation can be confirmed.

[0050] In Example 7 (40 ms) and Example 8 (60 ms), which are switching from the low voltage side to the high voltage side shown in Figure 8(c), the fluctuation amounts of Peaks 1 and 2 are smaller than in Comparative Example 1, being suppressed to 10% or less. Furthermore, in both Examples 7 and 8, after the fluctuation amount decreases after Peaks 1 and 2, there is a second increase in the peak fluctuation amount, but it does not exceed Peaks 1 and 2 and thereafter converges to the output setting of the DC-AC inverter 13. In Examples 7 and 8, the plots are up to Peaks 10 and 11, respectively, and a tendency for convergence from the position of the second increase in peak fluctuation amount can be confirmed.

[0051] As shown in Figure 8(c), in Example 8, the peak fluctuation continues until near Peak 11, and if the overlap period continues any longer, the time until convergence will be longer. Therefore, it is preferable to set the overlap period in the range of 5 ms to 60 ms. Furthermore, in Examples 7 and 8, a second increase in the peak fluctuation occurs when the overlap period ends and the second connection period begins, but in Examples 5 and 6, no second increase in the peak fluctuation occurs. Therefore, it is more preferable that the overlap period be in the range of 5 ms to 20 ms.

[0052] FIG. 9 is a graph showing the output fluctuation of the DC-AC inverter 13 in Comparative Examples 1 and 2 without an overlap period. In the graph, the solid line plot represents Comparative Example 1, the dashed line plot represents Comparative Example 2, and the dashed-dotted line represents the cumulative normalized fluctuation. As shown in FIG. 9 , when no overlap period is provided in Comparative Examples 1 and 2, the peak fluctuation substantially converges between peaks 3 and 4, and the AC_OUT output waveform stabilizes. Therefore, the response time of the DC-AC inverter 13 can be considered to be 30 to 40 ms. Furthermore, the cumulative fluctuation reaches 63% (-2 dB) by peak 2, and the time constant of the DC-AC inverter 13 is 20 ms.

[0053] By setting the overlap period within the response time of the DC-AC inverter 13, the end time t ２ This makes it possible to suppress the second increase in the peak fluctuation amount by keeping this within the response time of the DC-AC inverter 13. Therefore, it is preferable that the overlap period be in the range of 0.5 to 5 periods of the output waveform of AC_OUT from the DC-AC inverter 13.

[0054] In addition, by setting the overlap period within the time constant of the DC-AC inverter 13, the end time t ２ It is possible to suppress the second increase in the peak fluctuation amount by keeping this within the time constant of the DC-AC inverter 13. Therefore, it is more preferable that the overlap period be in the range of 0.5 to 2 periods of the output waveform of AC_OUT from the DC-AC inverter 13.

[0055] As described above, in the power supply device 10 of this embodiment, when switching the connection from the first battery 12a to the second battery 12b, there is an overlap period during which the first switch SW1 and the second switch SW2 are both closed. Therefore, even when switching the connection of multiple secondary batteries to the load 14, it is possible to prevent momentary power interruptions and suppress fluctuations in the output voltage, thereby continuing to supply stable power.

[0056] 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, a DC-AC inverter 13 is provided between the parallel connection portion of the first switch SW1 and the second switch SW2 and the load 14 to convert direct current into alternating current, 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.

[0057] Even when a DC-DC converter is used, the other ends of the first switch SW1 and the second switch SW2 are connected to the parallel connection part, and the connection is switched in the order of the first connection period, the overlap period, and the second connection period. As a result, no momentary interruption occurs in the voltage DCAC_IN input to the DC-DC converter, and it becomes an intermediate potential during the overlap period.

[0058] In the power supply device 10 of this embodiment, when switching the connection from the first battery 12a to the second battery 12b, there is an overlap period during which the first switch SW1 and the second switch SW2 are simultaneously in the closed state. Therefore, even when switching the connection of multiple secondary batteries to the load 14, it is possible to prevent momentary power interruptions and suppress fluctuations in the output voltage, thereby continuing to supply stable power.

[0059] 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.

[0060] REFERENCE SIGNS LIST 10... Power supply device 11... Switch control unit 12a... First battery 12b... Second battery 13... DC-AC inverter 14... Load SW1... First switch SW2... Second switch

Claims

1. A power supply device comprising: a first battery and a second battery for charging and discharging; a first switch having one end connected in series to an output section of the first battery; a second switch having one end connected in series to an output section of the second battery; a parallel connection section to which the other end of the first switch and the other end of the second switch are connected; and a switch control section for controlling the opening and closing of the first switch and the second switch, wherein the switch control section has an overlap period during which the first switch and the second switch are simultaneously in the closed state when the first switch is changed from a closed state to an open state and the second switch is changed from an open state to a closed state, the parallel connection section is connected to a DC-AC inverter, and the overlap period is in the range of 0.5 to 5 cycles of the output waveform from the DC-AC inverter.

2. A power supply device comprising: a first battery and a second battery for charging and discharging; a first switch having one end connected in series to an output section of the first battery; a second switch having one end connected in series to an output section of the second battery; a parallel connection section to which the other end of the first switch and the other end of the second switch are connected; and a switch control section for controlling the opening and closing of the first switch and the second switch, wherein the switch control section has an overlap period during which the first switch and the second switch are simultaneously in the closed state when changing the first switch from a closed state to an open state and when changing the second switch from an open state to a closed state, the output section of the first battery is at a first potential, and the output section of the second battery is at a second potential, and during the overlap period, the potential of the parallel connection section is an intermediate potential between the first potential and the second potential.

3. A power supply device according to claim 1, characterized in that the peak fluctuation of said output waveform during said overlap period is 10% or less.

4. A power supply device according to any one of claims 1 to 3, characterized in that the overlap period is in the range of 5 ms to 60 ms.

5. A power supply control method for switching the connection between a first battery and a second battery which are to be charged and discharged and a parallel connection section, comprising: a first connection period during which an output section of the first battery is connected to the parallel connection section and an output section of the second battery is disconnected from the parallel connection section; and a second connection period during which the output section of the first battery is disconnected from the parallel connection section and the output section of the second battery is connected to the parallel connection section; an overlap period is provided between the first connection period and the second connection period during which the output section of the first battery and the output section of the second battery are connected to the parallel connection section; the parallel connection section is connected to a DC-AC inverter; and the overlap period is within a range of 0.5 to 5 cycles of the output waveform from the DC-AC inverter.

6. A power supply control method for switching a connection between a first battery and a second battery which are to be charged and discharged and a parallel connection section, comprising: a first connection period during which an output part of the first battery is connected to the parallel connection section and an output part of the second battery is disconnected from the parallel connection section; and a second connection period during which the output part of the first battery is disconnected from the parallel connection section and the output part of the second battery is connected to the parallel connection section; an overlap period is provided between the first connection period and the second connection period during which the output part of the first battery and the output part of the second battery are connected to the parallel connection section; the output part of the first battery is at a first potential; the output part of the second battery is at a second potential; and during the overlap period, the potential of the parallel connection section is an intermediate potential between the first potential and the second potential.

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