Power supply device and power supply control method

Abstract

To provide a power supply device and a power supply control method, capable of continuing a stable supply of power by suppressing a modulation of an output voltage while preventing an instantaneous interruption even if a connection of a plurality of secondary batteries against a negative electrode is switched.SOLUTION: A power supply device comprises: a first battery and a second battery that perform charging and discharging; a first switch, one end of which is serially connected to an output part of the first battery; a second switch, one end of which is serially connected to an output part of the second battery; a parallel connection part to which the other end of the first switch and the other end of the second switch are connected; and a switch control part that controls opening and closing of the first and second switches. The switch control part changes the first switch from a closed state to an open state, and has an overlap period when both of the first and second switches become the closed state at the same time when the second switch is changed from the open state to the closed state.SELECTED DRAWING: Figure 1

Description

[Technical field]

[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. [Background technology]

[0002] Power supply devices have been proposed for enabling electrical equipment to be used outdoors or in emergencies. In such power supply devices, gasoline or other gas is generally used as fuel to drive an internal combustion engine, and the kinetic energy of the engine is converted into electrical energy. However, power supply devices using such internal combustion engines have the drawback that they cannot be used indoors or in enclosed spaces, since oxygen is consumed by the combustion of fuel. Therefore, power supply devices that supply power from secondary batteries that store electricity have become more common in recent years.

[0003] In such a power supply device using a secondary battery, the amount of power that can be supplied depends on the charge capacity of the secondary battery, so there is a problem that the secondary battery becomes large in size in order to continuously supply a large amount of power, which leads to an increase in weight and a high price. In order to avoid such problems, a power supply device has been proposed that is equipped with multiple detachable secondary batteries and switches between the power supply from the multiple secondary batteries (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP2006-296109A Summary of the Invention [Problem to be solved by the invention]

[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 switching batteries in a conventional power supply device.

[0006] The horizontal axis in Figure 10 indicates the passage of time, and the vertical axis indicates voltage. In Figure 10, the thick plots with small amplitude indicate the voltage at the input position of the DC-AC inverter. In Figure 10, the thin plots with large amplitude indicate the voltage at the output position 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. Near the center of Figure 10, the state in which the two secondary batteries are disconnected from the load is shown.

[0007] It can be seen that the voltage at the input of the DC-AC inverter changes before and after switching the connection of the secondary battery, and that there is a period of time at the moment of switching when no power is supplied from the secondary battery, 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 before and after switching the connection of the secondary battery when the output has stabilized, but a short-term voltage fluctuation occurs after the moment of switching.

[0008] As shown in Figure 10, when switching the connection of secondary batteries in conventional power supplies, momentary interruptions occur, making it difficult to continue supplying power to the load. In particular, in power supplies that convert the direct current supplied from secondary batteries to alternating current using a DC-AC inverter, the voltage fluctuations of the output alternating current become large, which can cause malfunctions of precision equipment and information equipment. In addition, in order to suppress the fluctuations in output voltage, a fast-response inverter power supply circuit is required, which causes problems such as an increase in the size and cost of the power supply.

[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 are capable of continuing to supply stable power by preventing momentary power interruptions and suppressing fluctuations in output voltage even when switching the connection of multiple secondary batteries to a load. [Means for solving the problem]

[0010] In order to solve the above problems, the power supply device of the present invention comprises 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 is characterized in that when the first switch is changed from a closed state to an open state and when the second switch is changed from an open state to a closed state, an overlap period is provided during which the first switch and the second switch are simultaneously in a closed state.

[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 interruptions and suppress fluctuations in the 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 parallel connection section is connected to a DC-AC inverter, and the overlap period is in the range of 0.5 to 5 periods of an output waveform from the DC-AC inverter.

[0014] In one aspect of the present invention, a peak fluctuation of the output waveform during the overlap period is 10% or less.

[0015] In one embodiment of the present invention, the output portion of the first battery is at a first potential, the output portion of the second battery is at a second potential, and during the overlap period, the potential of the parallel connection portion is at an intermediate potential between the first potential and the second potential.

[0016] In order to solve the above problems, the power supply control method of the present invention is a power supply control method that switches the connection between a first battery and a second battery that perform charging and discharging and a parallel connection section, and is characterized in that it has a first connection period in 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 in 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, and an overlap period is provided between the first connection period and the second connection period in which the output section of the first battery and the output section of the second battery are connected to the parallel connection section. Effect of the Invention

[0017] The present invention provides a power supply device and a power supply control method that can continue to supply stable power by preventing momentary power interruptions and suppressing fluctuations in output voltage even when switching the connection of multiple secondary batteries to a load. [Brief description of the drawings]

[0018] [Figure 1] 1 is a block diagram showing an example of the configuration of a power supply device 10 according to a first embodiment of the present invention. [Diagram 2] 2A shows a first connection period, FIG. 2B shows an overlap period, and FIG. 2C shows a second connection period, illustrating switching of connections in the power supply device 10. FIG. [Diagram 3]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. [Figure 4] 4A and 4B are graphs showing voltage fluctuations in Comparative Examples 1 and 2 in which no overlap period is provided, where FIG. 4A shows switching from a high voltage to a low voltage, and FIG. 4B shows switching from a low voltage to a high voltage. [Diagram 5] 13 is a graph showing an intermediate potential when an overlap period is provided. [Figure 6] 6A to 6D are graphs showing switching from a low voltage to a 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. [Figure 7] 7A and 7B are graphs showing switching from a high voltage to a 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. [Figure 8] 8A and 8B are graphs showing output fluctuations from a DC-AC inverter 13, where FIG. 8A shows Comparative Example 1 and Examples 5 and 6 when switching from a high voltage to a low voltage, FIG. 8B shows Comparative Example 2 and Examples 1 and 2 when switching from a low voltage to a high voltage, and FIG. 8C shows Examples 7 and 8. [Figure 9] 11 is a graph showing output fluctuations of a DC-AC inverter 13 in Comparative Examples 1 and 2 without an overlap period. [Figure 10] 1 is a graph showing voltage fluctuations during battery switching in a conventional power supply device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 are given the same reference numerals, and duplicated descriptions will be omitted as appropriate. FIG. 1 is a block diagram showing an example of the 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.

[0020] 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 control the first switch SW1 and the second switch SW2 by performing information processing according to a predetermined program. The switch control unit 11 may also monitor the state 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 state of each part and the predetermined program.

[0021] The first battery 12a and the second battery 12b are secondary batteries capable of charging and discharging power. As with known secondary batteries, the first battery 12a and the second battery 12b are provided with terminals used for charging and discharging, a BMS (Battery Management System) that controls charging and discharging, and the like. The output section of the first battery 12a is connected to one end of a first switch SW1, and the output section of the second battery 12b is connected to a second switch SW2. The voltage at the output section of the first battery 12a is VBA1, and the voltage at the output section of the second battery 12b is VBA2.

[0022] 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. 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. The reused battery cells may have different degrees of deterioration and may have different chargeable capacities and output voltages, but they can be used without problems in the power supply device 10 of this embodiment.

[0023] 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 an overlap period during a switching operation, which will be described later, and it may be difficult to ensure a sufficient overlap period.

[0024] The first switch SW1 and the second switch SW2 are parts that have one end connected to the output part of the first battery 12a and the second battery 12b, respectively, and 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 part. 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 part is DCAC_IN.

[0025] The specific configuration of the first switch SW1 and the second switch SW2 is not limited, and known semiconductor switches or mechanical switches can be used. As described later, the opening and closing operations of the first switch SW1 and the second switch SW2 are performed on the millisecond level, so it is preferable to use semiconductor switches such as field effect transistors (FETs) that are capable of high-speed switching operations.

[0026] The DC-AC inverter 13 is provided between the parallel connection unit and the load 14, and converts the direct current DCAC_IN input from the parallel connection unit into an alternating current AC_OUT and outputs it to the load 14. The specific circuit configuration of the DC-AC inverter 13 is not limited, 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. The AC_OUT output from the DC-AC inverter 13 is not limited, but it is preferable that it is in the voltage range of 100V to 220V and the frequency range of 50 to 60Hz, which are used as commercial power sources in various countries.

[0027] 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 a computer device, a network device, an electronic medical device, and an ultra-low temperature freezer. In the power supply device 10 of this embodiment, no momentary interruption occurs even when switching between multiple secondary batteries, and fluctuations in the output voltage can be suppressed, so that these loads 14 that require a stable power supply can be connected and used continuously.

[0028] 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.

[0029] Fig. 2 is a diagram showing 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 simplification, the switch control section 11 is omitted from Fig. 2, but the first switch SW1 and the second switch SW2 are controlled to open and close by a control signal sent from the switch control section 11. The arrows shown in the figure also show an example of the direction of current flow.

[0030] 2(a), the first switch SW1 is closed (ON) and the second switch SW2 is open (OFF). Therefore, a direct current is supplied from the first battery 12a to the first switch SW1 and the parallel connection unit, 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 an overlap period.

[0031] Here, examples of cases in which discharging from the first battery 12a is stopped include a case in which the remaining charge of the first battery 12a decreases and the battery is switched from being a battery to be discharged to being a battery to be charged. Another example is a case in which the first battery 12a is removed and a lock mechanism (not shown) is released. Another example is a case in which the user inputs an instruction to exclude the first battery 12a from being a battery to be discharged. Another example is a case in which the temperature of the first battery 12a rises and a protection instruction to stop discharging is sent by a control unit provided in the power supply device 10.

[0032] In the overlap period shown in FIG. 2(b), the first switch SW1 is closed (ON) and the second switch SW2 is closed (ON). In this overlap period, a direct current is supplied from the higher voltage of the first battery 12a and the second battery 12b to the parallel connection part, and 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 a current is supplied from the first battery 12a to the second battery 12b. When the second battery 12b has a higher voltage than the first battery 12a, the current flows in the opposite direction. After the overlap period set to a predetermined length has elapsed, the second connection period begins.

[0033] 2(c), the first switch SW1 is open (OFF) and the second switch SW2 is closed (ON). Therefore, a direct current is supplied from the second battery 12b to the second switch SW2 and the parallel connection unit, and is converted to AC_OUT by the DC-AC inverter 13 and supplied to the load 14. After that, the load 14 continues to operate using the power supplied from the second battery 12b.

[0034] 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 changes the second switch SW2 from an open state to a closed state, an overlap period is provided in 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.

[0035] During the overlap period, the first battery 12a, which has a higher voltage, discharges, and a current flows in the charging direction to the second battery 12b, which has a lower voltage. If the current in the charging direction of the second battery 12b is large during this overlap period, the protection circuit of the BMS provided in the second battery 12b will operate, 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 period so that an excessive current in the charging direction does not flow to the second battery 12b. The length of the overlap period will be described in detail later.

[0036] Fig. 3 is a timing chart showing the switching of connections in the power supply device 10, where Fig. 3(a) shows a signal of the first switch SW1, Fig. 3(b) shows a signal of the second switch SW2, Fig. 3(c) shows a voltage at the input position of the DC-AC inverter 13, and Fig. 3(d) shows a voltage at the output position of the DC-AC inverter 13. The horizontal axis in the figure indicates time t, and the vertical axis indicates voltage. Furthermore, up to time t1 indicates a first connection period, from time t1 to t2 indicates an overlap period, and from time t2 onwards indicates a second connection period.

[0037] As shown in Fig. 3(a), 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. Also, as shown in Fig. 3(b), 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.

[0038] 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 a 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 a 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.

[0039] 3(c) 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. 3(c) shows an example in which the intermediate potential is constant throughout the overlap period, the potential may change between VBA1 and VBA2.

[0040] As shown in Fig. 3(d), the voltage AC_OUT at the output position of the DC-AC inverter 13 is output as a sine wave AC. In Fig. 3(d), the waveform of AC_OUT after time t1 is marked with a circle, and each number indicates the order of a half cycle of the output waveform because the peak and bottom make up one cycle. In the first connection period, the peak voltage of AC_OUT is stable, but the overlap period begins at time t1, and the peak voltage fluctuates after DCAC_IN changes from VBA1 to the intermediate potential. Also, when the overlap period ends and the second connection period begins at time t2, the peak voltage fluctuates after DCAC_IN changes from the intermediate potential to VBA2.

[0041] The fluctuation in the peak voltage of AC_OUT becomes large at t1 when the overlap period begins and at t2 when the second connection period begins, and attenuates as the sine wave cycle progresses. This is because even if the input voltage to DC-AC inverter 13 changes, it is converted to the target output voltage value by the performance and time constant of DC-AC inverter 13. However, if the fluctuation in the peak voltage of output voltage AC_OUT is large and it takes a long time for it to attenuate and stabilize, there is a possibility that load 14 will not operate normally.

[0042] 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 is 10% or less.

[0043] (Comparative Example) FIG. 4 is a graph showing voltage fluctuations in Comparative Examples 1 and 2 in which no overlap period is provided, where 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, a thick plot with a small amplitude indicates the voltage DCAC_IN at the input position (parallel connection part) of the DC-AC inverter 13. In FIG. 4, a thin plot with a large amplitude indicates the voltage AC_OUT at the output position of the DC-AC inverter 13. In FIG. 4, a first connection period in which the first battery 12a is connected is shown, and the right half shows a second connection period in which the second battery 12b is connected. The output of the DC-AC inverter 13 is a sine wave of AC 100V, 50Hz, and the load 14 is 1kW. In addition, the output voltage VBA1 of the first battery 12a was 27V (high voltage side), and the output voltage VBA2 of the second battery 12b was 23V (low voltage side).

[0044] As shown in Fig. 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 Fig. 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.

[0045] (Example) In Examples 1 to 4, switching is performed from the second battery 12b on the low voltage side to the first battery 12a on the high voltage side, and the overlap period is set to 10 ms, 20 ms, 40 ms, and 60 ms, respectively. In Examples 5 to 8, switching is performed from the first battery 12a on the high voltage side to the second battery 12b on the low voltage side, and the overlap period is set to 10 ms, 20 ms, 40 ms, and 60 ms, respectively. In Examples 1 to 8, the output of the DC-AC inverter 13 is a sine wave of AC 100V and 50Hz, and the load 14 is 1kW, as in the comparative example. In addition, the output voltage VBA1 of the first battery 12a was 28.36V (high voltage side), and the output voltage VBA2 of the second battery 12b was 24.72V (low voltage side).

[0046] Fig. 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 setting of Example 8, thereby eliminating the influence of fluctuations in DCAC_IN caused by voltage conversion in the DC-AC inverter 13. It can be seen that in the overlap period between the first connection period and the second connection period, the voltage DCAC_IN of the parallel connection portion is 26.49V, which is an intermediate potential, and is between the output voltage 28.36V of the first battery 12a and the output voltage 24.72V of the second battery 12b.

[0047] Fig. 6 is a graph showing switching from a low voltage to a high voltage with an overlap period, 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. Fig. 7 is a graph showing switching from a high voltage to a low voltage with an overlap period, 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.

[0048] FIG. 8 shows a graph of 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 from the graphs shown in FIG. 6 and FIG. 7. 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 in switching from a high voltage to a low voltage, FIG. 8(b) shows Comparative Example 2 and Examples 1 and 2 in switching from a low voltage to a high voltage, and FIG. 8(c) shows Examples 7 and 8. The horizontal axis of FIG. 8 shows the peak order for each half cycle in the output waveform of AC_OUT after entering the overlap period at time t1. In both examples, the output of the DC-AC inverter 13 is 50 Hz, so the half cycle corresponds to 10 ms. The vertical axis of FIG. 8 shows the fluctuation amount of the peak voltage in the first connection period in the output waveform of the DC-AC inverter 13.

[0049] As shown in Figs. 8(a) and (b), in the plot of Comparative Example 1 (0 ms) where no overlap period is provided, the fluctuation amount of peaks 1 and 2 is larger than that of Examples 1 to 8. In particular, in Comparative Example 1 where switching is performed from the low voltage side to the high voltage side, the fluctuation amount of peaks 1 and 2 exceeds 10%, which may adversely affect the operation of load 14. In Comparative Example 2 where switching is performed from the high voltage side to the low voltage side, the fluctuation amount of peaks 1 and 2 is just under 9%. However, in power supply device 10, switching from the low voltage side to the high voltage side and switching from the high voltage side to the low voltage side occur frequently, so the peak fluctuation amount exceeds 10% during the usage period of load 14.

[0050] 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 Fig. 8(a), the amount of fluctuation of peaks 1 and 2 is smaller than that of Comparative Example 1, and is suppressed to 10% or less. In both Examples 5 and 6, the amount of fluctuation decreases after peaks 1 and 2, and converges to the output setting of the DC-AC inverter 13. In Examples 5 and 6, peaks 4 and 6 are plotted, respectively, and the convergence of the amount of fluctuation can be confirmed by plotting for a time longer than the overlap period.

[0051] In Example 1 (10 ms) and Example 2 (20 ms), which are switching from the high voltage side to the low voltage side shown in Fig. 8(b), 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.

[0052] 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 amount of peaks 1 and 2 is smaller than that of Comparative Example 1, and is suppressed to 10% or less. 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 it is possible to confirm the convergence tendency from the position of the second increase in peak fluctuation amount.

[0053] As shown in Fig. 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 extended. Therefore, it is preferable that the overlap period is in the range of 5 ms to 60 ms. Also, in Examples 7 and 8, a second increase in the peak fluctuation occurs at the stage when the overlap period ends and the second connection period begins, but a second increase in the peak fluctuation does not occur in Examples 5 and 6. Therefore, it is more preferable that the overlap period is in the range of 5 ms to 20 ms.

[0054] 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 figure, the solid line plot shows Comparative Example 1, the dashed line plot shows Comparative Example 2, and the dashed line shows the accumulation of the normalized fluctuation amount. As shown in FIG. 9, when no overlap period is provided in Comparative Examples 1 and 2, the peak fluctuation amount is almost converged by peaks 3 and 4, and the output waveform of AC_OUT is stabilized. Therefore, the response time of the DC-AC inverter 13 can be regarded as 30 to 40 ms. Furthermore, the accumulation of the fluctuation amount reaches 63% (-2 dB) by peak 2, and the time constant of the DC-AC inverter 13 is 20 ms.

[0055] By setting the overlap period within the response time of the DC-AC inverter 13, it is possible to suppress the second increase in the peak fluctuation amount by bringing the end time t2 of the overlap period 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.

[0056] Furthermore, by setting the overlap period within the time constant of the DC-AC inverter 13, it is possible to suppress the second increase in the peak fluctuation amount by making the end time t2 of the overlap period 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.

[0057] 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, an overlap period is provided during which the first switch SW1 and the second switch SW2 are simultaneously in a closed state. Therefore, even when switching the connection of multiple secondary batteries to the load 14, it is possible to continue to supply stable power by preventing momentary interruptions and suppressing fluctuations in the output voltage.

[0058] Second embodiment Next, a second embodiment of the present invention will be described. Descriptions of contents overlapping with the first embodiment will be omitted. In the first embodiment, a DC-AC inverter 13 is provided between the parallel connection part of the first switch SW1 and the second switch SW2 and the load 14 to convert a direct current into an 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 a direct current is used as the load 14.

[0059] 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 section, and the connection is switched in the order of the first connection period, the overlap period, and the second connection period. This prevents a momentary interruption in the voltage DCAC_IN input to the DC-DC converter, and keeps it at an intermediate potential during the overlap period.

[0060] In the power supply device 10 of this embodiment, when switching the connection from the first battery 12a to the second battery 12b, an overlap period is provided during which the first switch SW1 and the second switch SW2 are simultaneously in a closed state. Therefore, even when switching the connection of multiple secondary batteries to the load 14, it is possible to continue to supply stable power by preventing momentary interruptions and suppressing fluctuations in the output voltage.

[0061] 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. [Explanation of symbols]

[0062] 10…Power supply device 11...Switch control section 12a…1st battery 12b…Second battery 13…DC-AC inverter 14. Load SW1…First switch SW2: Second switch

Claims

1. a first battery and a second battery which are charged and discharged; A first switch having one end connected in series to an output portion of the first battery; A second switch, one end of which is connected in series to the output of the second battery; a parallel connection part to which the other end of the first switch and the other end of the second switch are connected; a switch control unit that controls opening and closing of the first switch and the second switch, a switch control unit that changes the first switch from a closed state to an open state and changes the second switch from an open state to a closed state, the switch control unit having an overlap period during which the first switch and the second switch are simultaneously in a closed state.

2. 2. The power supply device according to claim 1, A power supply device, wherein the overlap period is in the range of 5 ms to 60 ms.

3. 2. The power supply device according to claim 1, The parallel connection unit is connected to a DC-AC inverter, The power supply device according to claim 1, wherein the overlap period is in the range of 0.5 to 5 periods of the output waveform from the DC-AC inverter.

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

5. 2. The power supply device according to claim 1, an output of the first battery is at a first potential; the output of the second battery is at a second potential; a parallel connection part that has a potential at an intermediate potential between the first potential and the second potential during the overlap period;

6. A power supply control method for switching a connection between a first battery and a second battery which are charged and discharged and a parallel connection unit, the method comprising: a first connection period in which an output portion of the first battery is connected to the parallel connection portion and an output portion of the second battery is disconnected from the parallel connection portion; a second connection period in which an output portion of the first battery is disconnected from the parallel connection portion and an output portion of the second battery is connected to the parallel connection portion; a power supply control method comprising: a first connection period and a second connection period, the first connection period and the second connection period being connected to the parallel connection portion through an overlap period;

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